WorldWideScience

Sample records for brown dwarf atmospheres

  1. Atmospheres of Brown Dwarfs

    CERN Document Server

    Helling, Christiane

    2014-01-01

    Brown Dwarfs are the coolest class of stellar objects known to date. Our present perception is that Brown Dwarfs follow the principles of star formation, and that Brown Dwarfs share many characteristics with planets. Being the darkest and lowest mass stars known makes Brown Dwarfs also the coolest stars known. This has profound implication for their spectral fingerprints. Brown Dwarfs cover a range of effective temperatures which cause brown dwarfs atmospheres to be a sequence that gradually changes from a M-dwarf-like spectrum into a planet-like spectrum. This further implies that below an effective temperature of < 2800K, clouds form already in atmospheres of objects marking the boundary between M-Dwarfs and brown dwarfs. Recent developments have sparked the interest in plasma processes in such very cool atmospheres: sporadic and quiescent radio emission has been observed in combination with decaying Xray-activity indicators across the fully convective boundary.

  2. Auroral Phenomena in Brown Dwarf Atmospheres

    Science.gov (United States)

    Pineda, J. Sebastian; Hallinan, Gregg

    2016-01-01

    Since the unexpected discovery of radio emission from brown dwarfs some 15 years ago, investigations into the nature of this emission have revealed that, despite their cool and neutral atmospheres, brown dwarfs harbor strong kG magnetic fields, but unlike the warmer stellar objects, they generate highly circularly polarized auroral radio emission, like the giant planets of the Solar System. Our recent results from Keck LRIS monitoring of the brown dwarf LSR1835+32 definitively confirm this picture by connecting the auroral radio emission to spectroscopic variability at optical wavelengths as coherent manifestations of strong large-scale magnetospheric auroral current systems. I present some of the results of my dissertation work to understand the nature brown dwarf auroral phenomena. My efforts include a survey of Late L dwarfs and T dwarfs, looking for auroral Hα emission and a concurrent survey looking for the auroral emission of H3+ from brown dwarfs with radio pulse detections. I discuss the potential connection of this auroral activity to brown dwarf weather phenomena and how brown dwarf aurorae may differ from the analogous emission of the magnetized giant planets in the Solar System.

  3. Non-equilibrium chemistry in the atmospheres of brown dwarfs

    CERN Document Server

    Saumon, D S; Freedman, R S; Lodders, K

    2002-01-01

    Carbon monoxide and ammonia have been detected in the spectrum of Gl 229B at abundances that differ substantially from those obtained from chemical equilibrium. Vertical mixing in the atmosphere is a mechanism that can drive slowly reacting species out of chemical equilibrium. We explore the effects of vertical mixing as a function of mixing efficiency and effective temperature on the chemical abundances in the atmospheres of brown dwarfs and on their spectra. The models compare favorably with the observational evidence and indicate that vertical mixing plays an important role in brown dwarf atmospheres.

  4. Atmospheric Circulation of Brown Dwarfs: Jets, Vortices, and Time Variability

    CERN Document Server

    Zhang, Xi

    2014-01-01

    A variety of observational evidence demonstrates that brown dwarfs exhibit active atmospheric circulations. In this study we use a shallow-water model to investigate the global atmospheric dynamics in the stratified layer overlying the convective zone on these rapidly rotating objects. We show that the existence and properties of the atmospheric circulation crucially depend on key parameters including the energy injection rate and radiative timescale. Under conditions of strong internal heat flux and weak radiative dissipation, a banded flow pattern comprising east-west jet streams spontaneously emerges from the interaction of atmospheric turbulence with the planetary rotation. In contrast, when the internal heat flux is weak and/or radiative dissipation is strong, turbulence injected into the atmosphere damps before it can self-organize into jets, leading to a flow dominated by isotropic turbulence and vortices instead. Based on the location of the transition, we suggest that many brown dwarfs may exhibit at...

  5. CLOUDS search for variability in brown dwarf atmospheres

    CERN Document Server

    Goldman, B; Marley, M S; Artigau, É; Baliyan, K S; Béjar, V J S; Caballero, J A; Chanover, N; Connelley, M; Doyon, R; Forveille, T; Ganesh, S; Gelino, C R; Hammel, H B; Holtzman, J; Joshi, S; Joshi, U C; Leggett, S K; Liu, M C; Martín, E L; Mohan, V; Nadeau, D; Sagar, R; Stephens, D

    2008-01-01

    Context: L-type ultra-cool dwarfs and brown dwarfs have cloudy atmospheres that could host weather-like phenomena. The detection of photometric or spectral variability would provide insight into unresolved atmospheric heterogeneities, such as holes in a global cloud deck. Aims: It has been proposed that growth of heterogeneities in the global cloud deck may account for the L- to T-type transition as brown dwarf photospheres evolve from cloudy to clear conditions. Such a mechanism is compatible with variability. We searched for variability in the spectra of five L6 to T6 brown dwarfs in order to test this hypothesis. Methods: We obtained spectroscopic time series using VLT/ISAAC, over 0.99-1.13um, and IRTF/SpeX for two of our targets, in J, H and K bands. We search for statistically variable lines and correlation between those. Results: High spectral-frequency variations are seen in some objects, but these detections are marginal and need to be confirmed. We find no evidence for large amplitude variations in s...

  6. Fingering convection and cloudless models for cool brown dwarf atmospheres

    CERN Document Server

    Tremblin, P; Mourier, P; Baraffe, I; Chabrier, G; Drummond, B; Homeier, D; Venot, O

    2015-01-01

    This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral type T and Y, whose modeling is a current challenge. Silicate and iron clouds are believed to disappear at the photosphere at the L/T transition, but cloudless models fail to reproduce correctly the spectra of T dwarfs, advocating for the addition of more physics, e.g. other types of clouds or internal energy transport mechanisms. We use a one-dimensional (1D) radiative/convective equilibrium code ATMO to investigate this issue. This code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the PT structure. Included opacity sources are H2-H2, H2-He, H2O, CO, CO2, CH4, NH3, K, Na, and TiO, VO if they are present in the atmosphere. We show that the spectra of Y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and NH3 quenching are taken into account. T dwarf spectra still have some reddening in e.g. J - H compared to cloudless mode...

  7. The Brown-dwarf Atmosphere Monitoring (BAM) Project II: Multi-epoch monitoring of extremely cool brown dwarfs

    CERN Document Server

    Rajan, A; Wilson, P A; Bulger, J; De Rosa, R J; Ward-Duong, K; Morley, C; Pont, F; Windhorst, R

    2015-01-01

    With the discovery of Y dwarfs by the WISE mission, the population of field brown dwarfs now extends to objects with temperatures comparable to those of Solar System planets. To investigate the atmospheres of these newly identified brown dwarfs, we have conducted a pilot study monitoring an initial sample of three late T-dwarfs (T6.5, T8 and T8.5) and one Y-dwarf (Y0) for infrared photometric variability at multiple epochs. With J-band imaging, each target was observed for a period of 1.0h to 4.5h per epoch, which covers a significant fraction of the expected rotational period. These measurements represent the first photometric monitoring for these targets. For three of the four targets (2M1047, Ross 458C and WISE0458), multi-epoch monitoring was performed, with the time span between epochs ranging from a few hours to ~2 years. During the first epoch, the T8.5 target WISE0458 exhibited variations with a remarkable min-to-max amplitude of 13%, while the second epoch light curve taken ~2 years later did not not...

  8. The Limiting Effects of Dust in Brown Dwarf Model Atmospheres

    CERN Document Server

    Allard, F; Alexander, D R; Tamanai, A; Schweitzer, A; Allard, France; Hauschildt, Peter H.; Alexander, David R.; Tamanai, Akemi; Schweitzer, Andreas

    2001-01-01

    We present opacity sampling model atmospheres, synthetic spectra and colors for brown dwarfs and very low mass stars in two limiting case of dust grain formation: 1) inefficient gravitational settling i.e. the dust is distributed according to the chemical equilibrium predictions, 2) efficient gravitational settling i.e. the dust forms and depletes refractory elements from the gas, but their opacity does not affect the thermal structure. The models include the formation of over 600 gas phase species, and 1000 liquids and crystals, and the opacities of 30 different types of grains including corundum (Al$_2$O$_3$), the magnesium aluminum spinel MgAl$_2$O$_4$, iron, enstatite (MgSiO$_3$), forsterite (Mg$_2$SiO$_4$), amorphous carbon, SiC, and a number of calcium silicates. The models extend from the beginning of the grain formation regime well into the condensation regime of water ice ($\\teff= 3000 - 100$ K) and encompasses the range of $\\log g= 2.5 - 6.0$ at solar metallicity. We find that silicate dust grains c...

  9. Irradiated brown dwarfs

    CERN Document Server

    Casewell, S L; Lawrie, K A; Maxted, P F L; Dobbie, P D; Napiwotzki, R

    2014-01-01

    We have observed the post common envelope binary WD0137-349 in the near infrared $J$, $H$ and $K$ bands and have determined that the photometry varies on the system period (116 min). The amplitude of the variability increases with increasing wavelength, indicating that the brown dwarf in the system is likely being irradiated by its 16500 K white dwarf companion. The effect of the (primarily) UV irradiation on the brown dwarf atmosphere is unknown, but it is possible that stratospheric hazes are formed. It is also possible that the brown dwarf (an L-T transition object) itself is variable due to patchy cloud cover. Both these scenarios are discussed, and suggestions for further study are made.

  10. Hunting for brown dwarf binaries and testing atmospheric models with X-Shooter

    CERN Document Server

    Manjavacas, E; Alcalá, J M; Zapatero-Osorio, M R; Béjar, V J S; Homeier, D; Bonnefoy, M; Smart, R L; Henning, T; Allard, F

    2015-01-01

    The determination of the brown dwarf binary fraction may contribute to the understanding of the substellar formation mechanisms. Unresolved brown dwarf binaries may be revealed through their peculiar spectra or the discrepancy between optical and near-infrared spectral type classification. We obtained medium-resolution spectra of 22 brown dwarfs with these characteristics using the X-Shooter spectrograph at the VLT. We aimed to identify brown dwarf binary candidates, and to test if the BT-Settl 2014 atmospheric models reproduce their observed spectra. To find binaries spanning the L-T boundary, we used spectral indices and compared the spectra of the selected candidates to single spectra and synthetic binary spectra. We used synthetic binary spectra with components of same spectral type to determine as well the sensitivity of the method to this class of binaries. We identified three candidates to be combination of L plus T brown dwarfs. We are not able to identify binaries with components of similar spectral ...

  11. Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets

    CERN Document Server

    Helling, Ch; Rodriguez-Barrera, I M; Wood, Kenneth; Robertson, G B; Stark, C R

    2016-01-01

    Brown dwarfs and giant gas extrasolar planets have cold atmospheres with a rich chemical compositions from which mineral cloud particles form. Their properties, like particle sizes and material composition, vary with height, and the mineral cloud particles are charged due to triboelectric processes in such dynamic atmospheres. The dynamics of the atmospheric gas is driven by the irradiating host star and/or by the rotation of the objects that changes during its lifetime. Thermal gas ionisation in these ultra-cool but dense atmospheres allows electrostatic interactions and magnetic coupling of a substantial atmosphere volume. Combined with a strong magnetic field $\\gg B_{\\rm Earth}$, a chromosphere and aurorae might form as suggested by radio and X-ray observations of brown dwarfs. Non-equilibrium processes like cosmic ray ionisation and discharge processes in clouds will increase the local pool of free electrons in the gas. Cosmic rays and lighting discharges also alter the composition of the local atmospheri...

  12. Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars II. Sulfur and Phosphorus

    CERN Document Server

    Visscher, C

    2005-01-01

    We use thermochemical equilibrium and kinetic calculations to model sulfur and phosphorus chemistry in the atmospheres of giant planets, brown dwarfs, low-mass stars, and extrasolar giant planets (EGPs). The chemical behavior of individual S- and P-bearing gases and condensates is determined as a function of pressure, temperature, and metallicity. Our results are independent of any particular model atmosphere and the behavior of different gases can be used to constrain atmospheric structure and metallicity. Hydrogen sulfide is the dominant sulfur gas in substellar atmospheres and approximately represents the atmospheric sulfur inventory. Depending on the prevailing S and C chemistry, the abundance of minor sulfur gases may constrain atmospheric temperatures or metallicity. Disequilibrium abundances of PH3 are expected in the observable atmospheres of substellar objects, and PH3 is representative of the total P abundance in giant planets and T dwarfs. A number of other phosphorus gases become relatively abunda...

  13. Hunting for brown dwarf binaries and testing atmospheric models with X-Shooter

    Science.gov (United States)

    Manjavacas, E.; Goldman, B.; Alcalá, J. M.; Zapatero-Osorio, M. R.; Béjar, V. J. S.; Homeier, D.; Bonnefoy, M.; Smart, R. L.; Henning, T.; Allard, F.

    2016-01-01

    The determination of the brown dwarf binary fraction may contribute to the understanding of the substellar formation mechanisms. Unresolved brown dwarf binaries may be revealed through their peculiar spectra or the discrepancy between optical and near-infrared spectral-type classification. We obtained medium-resolution spectra of 22 brown dwarfs with these characteristics using the X-Shooter spectrograph at the Very Large Telescope. We aimed to identify brown dwarf binary candidates, and to test if the BT-Settl 2014 atmospheric models reproduce their observed spectra. To find binaries spanning the L-T boundary, we used spectral indices and compared the spectra of the selected candidates to single spectra and synthetic binary spectra. We used synthetic binary spectra with components of same spectral type to determine as well the sensitivity of the method to this class of binaries. We identified three candidates to be combination of L plus T brown dwarfs. We are not able to identify binaries with components of similar spectral type. In our sample, we measured minimum binary fraction of 9.1^{+9.9}_{-3.0} per cent. From the best fit of the BT-Settl models 2014 to the observed spectra, we derived the atmospheric parameters for the single objects. The BT-Settl models were able to reproduce the majority of the spectral energy distributions from our objects, and the variation of the equivalent width of the Rb I (794.8 nm) and Cs I (852.0 nm) lines with the spectral type. None the less, these models did not reproduce the evolution of the equivalent widths of the Na I (818.3 and 819.5 nm) and K I (1253 nm) lines with the spectral type.

  14. Ionisation in atmospheres of Brown Dwarfs and extrasolar planets I The role of electron avalanche

    CERN Document Server

    Helling, Ch; Witte, S; Diver, D A

    2010-01-01

    Brown Dwarf and extrasolar planet atmospheres form clouds which strongly influence the local chemistry and physics. These clouds are globally neutral obeying dust-gas charge equilibrium which is, on short time scales, inconsistent with the observation of stochastic ionisation events of the solar system planets. We argue that a significant volume of the clouds in Brown Dwarfs and extrasolar planets is susceptible to local discharge events. These are electron avalanches triggered by charged dust grains. Such intra-cloud discharges occur on time scales shorter than the time needed to neutralise the dust grains by collisional processes. An ensemble of discharges is likely to produce enough free charges to suggest a partial and stochastic coupling of the atmosphere to a large-scale magnetic field.

  15. Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets

    Science.gov (United States)

    Helling, Ch; Rimmer, P. B.; Rodriguez-Barrera, I. M.; Wood, Kenneth; Robertson, G. B.; Stark, C. R.

    2016-07-01

    Brown dwarfs and giant gas extrasolar planets have cold atmospheres with rich chemical compositions from which mineral cloud particles form. Their properties, like particle sizes and material composition, vary with height, and the mineral cloud particles are charged due to triboelectric processes in such dynamic atmospheres. The dynamics of the atmospheric gas is driven by the irradiating host star and/or by the rotation of the objects that changes during its lifetime. Thermal gas ionisation in these ultra-cool but dense atmospheres allows electrostatic interactions and magnetic coupling of a substantial atmosphere volume. Combined with a strong magnetic field \\gg {{B}\\text{Earth}} , a chromosphere and aurorae might form as suggested by radio and x-ray observations of brown dwarfs. Non-equilibrium processes like cosmic ray ionisation and discharge processes in clouds will increase the local pool of free electrons in the gas. Cosmic rays and lighting discharges also alter the composition of the local atmospheric gas such that tracer molecules might be identified. Cosmic rays affect the atmosphere through air showers in a certain volume which was modelled with a 3D Monte Carlo radiative transfer code to be able to visualise their spacial extent. Given a certain degree of thermal ionisation of the atmospheric gas, we suggest that electron attachment to charge mineral cloud particles is too inefficient to cause an electrostatic disruption of the cloud particles. Cloud particles will therefore not be destroyed by Coulomb explosion for the local temperature in the collisional dominated brown dwarf and giant gas planet atmospheres. However, the cloud particles are destroyed electrostatically in regions with strong gas ionisation. The potential size of such cloud holes would, however, be too small and might occur too far inside the cloud to mimic the effect of, e.g. magnetic field induced star spots.

  16. The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs

    CERN Document Server

    Bailey, Jeremy

    2014-01-01

    The last few years has seen a dramatic increase in the number of exoplanets known and in the range of methods for characterising their atmospheric properties. At the same time, new discoveries of increasingly cooler brown dwarfs have pushed down their temperature range which now extends down to Y-dwarfs of <300 K. Modelling of these atmospheres has required the development of new techniques to deal with the molecular chemistry and clouds in these objects. The atmospheres of brown dwarfs are relatively well understood, but some problems remain, in particular the behavior of clouds at the L/T transition. Observational data for exoplanet atmosphere characterization is largely limited to giant exoplanets that are hot because they are near to their star (hot Jupiters) or because they are young and still cooling. For these planets there is good evidence for the presence of CO and H2O absorptions in the IR. Sodium absorption is observed in a number of objects. Reflected light measurements show that some giant exo...

  17. The cool atmospheres of the binary brown dwarf eps Indi B

    CERN Document Server

    Sterzik, M F; Hartung, M; Huélamo, N; Kaufer, A; Käufl, H U; Melo, C; Nürnberger, D; Siebenmorgen, R; Smette, A

    2005-01-01

    We have imaged $\\epsilon$ Indi B, the closest brown dwarf binary known, with VISIR at the VLT in three narrow-band mid-infrared bandpasses located around 8.6$\\mu$m, 10.5$\\mu$m and 11.3$\\mu$m. We are able to spatially resolve both components, and determine accurate mid-infrared photometry for both components independently. In particular, our VISIR observations allow to probe the NH$_3$ feature in the atmospheres of the cooler and warmer brown dwarfs. For the first time, we can disentangle the contributions of the two components, and find that % our photometry of $\\epsilon$ IndiBb is in good agreement with recent ``cloud-free'' atmosphere models having an effective temperature of $T_\\mathrm{eff}=800$ K. Component Ba agrees more with $T_\\mathrm{eff} \\approx 1100$ K rather than with $T_\\mathrm{eff}=1200$ K, as suggested by SPITZER spectroscopic observations of the combined $\\epsilon$ Indi B system (Roellig et al., 2004). Even higher effective temperatures appear inconsistent with our absolute photometry, as they ...

  18. IONIZATION IN ATMOSPHERES OF BROWN DWARFS AND EXTRASOLAR PLANETS. III. BREAKDOWN CONDITIONS FOR MINERAL CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Helling, Ch.; Jardine, M.; Stark, C. [SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS (United Kingdom); Diver, D., E-mail: ch@leap2010.eu [SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom)

    2013-04-20

    Electric discharges were detected directly in the cloudy atmospheres of Earth, Jupiter, and Saturn, are debatable for Venus, and indirectly inferred for Neptune and Uranus in our solar system. Sprites (and other types of transient luminous events) have been detected only on Earth, and are theoretically predicted for Jupiter, Saturn, and Venus. Cloud formation is a common phenomenon in ultra-cool atmospheres such as in brown dwarf and extrasolar planetary atmospheres. Cloud particles can be expected to carry considerable charges which may trigger discharge events via small-scale processes between individual cloud particles (intra-cloud discharges) or large-scale processes between clouds (inter-cloud discharges). We investigate electrostatic breakdown characteristics, like critical field strengths and critical charge densities per surface, to demonstrate under which conditions mineral clouds undergo electric discharge events which may trigger or be responsible for sporadic X-ray emission. We apply results from our kinetic dust cloud formation model that is part of the DRIFT-PHOENIX model atmosphere simulations. We present a first investigation of the dependence of the breakdown conditions in brown dwarf and giant gas exoplanets on the local gas-phase chemistry, the effective temperature, and primordial gas-phase metallicity. Our results suggest that different intra-cloud discharge processes dominate at different heights inside mineral clouds: local coronal (point discharges) and small-scale sparks at the bottom region of the cloud where the gas density is high, and flow discharges and large-scale sparks near, and maybe above, the cloud top. The comparison of the thermal degree of ionization and the number density of cloud particles allows us to suggest the efficiency with which discharges will occur in planetary atmospheres.

  19. IONIZATION IN ATMOSPHERES OF BROWN DWARFS AND EXTRASOLAR PLANETS. V. ALFVÉN IONIZATION

    International Nuclear Information System (INIS)

    Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbor localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfvén ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization (≥10–7) that they constitute plasmas. We outline the criteria required for Alfvén ionization and demonstrate its applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs, and M dwarfs with both solar and sub-solar metallicities. We find that Alfvén ionization is most efficient at mid to low atmospheric pressures where a seed plasma is easier to magnetize and the pressure gradients needed to drive the required neutral flows are the smallest. For the model atmospheres considered, our results show that degrees of ionization of 10–6-1 can be obtained as a result of Alfvén ionization. Observable consequences include continuum bremsstrahlung emission, superimposed with spectral lines from the plasma ion species (e.g., He, Mg, H2, or CO lines). Forbidden lines are also expected from the metastable population. The presence of an atmospheric plasma opens the door to a multitude of plasma and chemical processes not yet considered in current atmospheric models. The occurrence of Alfvén ionization may also be applicable to other astrophysical environments such as protoplanetary disks

  20. IONIZATION IN ATMOSPHERES OF BROWN DWARFS AND EXTRASOLAR PLANETS. V. ALFVÉN IONIZATION

    Energy Technology Data Exchange (ETDEWEB)

    Stark, C. R.; Helling, Ch.; Rimmer, P. B. [SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, KY16 9SS (United Kingdom); Diver, D. A., E-mail: craig.stark@st-andrews.ac.uk [SUPA, School of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow, G12 8QQ (United Kingdom)

    2013-10-10

    Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbor localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfvén ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization (≥10{sup –7}) that they constitute plasmas. We outline the criteria required for Alfvén ionization and demonstrate its applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs, and M dwarfs with both solar and sub-solar metallicities. We find that Alfvén ionization is most efficient at mid to low atmospheric pressures where a seed plasma is easier to magnetize and the pressure gradients needed to drive the required neutral flows are the smallest. For the model atmospheres considered, our results show that degrees of ionization of 10{sup –6}-1 can be obtained as a result of Alfvén ionization. Observable consequences include continuum bremsstrahlung emission, superimposed with spectral lines from the plasma ion species (e.g., He, Mg, H{sub 2}, or CO lines). Forbidden lines are also expected from the metastable population. The presence of an atmospheric plasma opens the door to a multitude of plasma and chemical processes not yet considered in current atmospheric models. The occurrence of Alfvén ionization may also be applicable to other astrophysical environments such as protoplanetary disks.

  1. Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres

    CERN Document Server

    Sharp, C M; Sharp, Christopher M.; Burrows, Adam

    2006-01-01

    We present a comprehensive description of the theory and practice of opacity calculations from the infrared to the ultraviolet needed to generate models of the atmospheres of brown dwarfs and extrasolar giant planets. Methods for using existing line lists and spectroscopic databases in disparate formats are presented and plots of the resulting absorptive opacities versus wavelength for the most important molecules and atoms at representative temperature/pressure points are provided. Electronic, ro-vibrational, bound-free, bound-bound, free-free, and collision-induced transitions and monochromatic opacities are derived, discussed, and analyzed. The species addressed include the alkali metals, iron, heavy metal oxides, metal hydrides, $H_2$, $H_2O$, $CH_4$, $CO$, $NH_3$, $H_2S$, $PH_3$, and representative grains. [Abridged

  2. Small hydrocarbon molecules in cloud-forming Brown Dwarf and giant gas planet atmospheres

    CERN Document Server

    Bilger, Camille; Helling, Christiane

    2013-01-01

    We study the abundances of complex carbon-bearing molecules in the oxygen-rich dust- forming atmospheres of Brown Dwarfs and giant gas planets. The inner atmospheric re- gions that form the inner boundary for thermochemical gas-phase models are investigated. Results from Drift-phoenix atmosphere simulations, which include the feedback of phase- non-equilibrium dust cloud formation on the atmospheric structure and the gas-phase abun- dances, are utilised. The resulting element depletion leads to a shift in the carbon-to-oxygen ratio such that several hydrocarbon molecules and cyanopolycyanopolyynene molecules can be present. An increase in surface gravity and/or a decrease in metallicity support the increase in the partial pressures of these species. CO, CO2, CH4, and HCN contain the largest fraction of carbon. In the upper atmosphere of low-metallicity objects, more carbon is contained in C4H than in CO, and also CH3 and C2H2 play an increasingly important role as carbon-sink. We determine chemical relaxation...

  3. Neptune's Dynamic Atmosphere from Kepler K2 Observations: Implications for Brown Dwarf Light Curve Analyses

    Science.gov (United States)

    Simon, Amy A.; Rowe, Jason F.; Gaulme, Patrick; Hammel, Heidi B.; Casewell, Sarah L.; Fortney, Jonathan J.; Gizis, John E.; Lissauer, Jack J.; Morales-Juberias, Raul; Orton, Glenn S.; Wong, Michael H.; Marley, Mark S.

    2016-02-01

    Observations of Neptune with the Kepler Space Telescope yield a 49 day light curve with 98% coverage at a 1 minute cadence. A significant signature in the light curve comes from discrete cloud features. We compare results extracted from the light curve data with contemporaneous disk-resolved imaging of Neptune from the Keck 10-m telescope at 1.65 microns and Hubble Space Telescope visible imaging acquired nine months later. This direct comparison validates the feature latitudes assigned to the K2 light curve periods based on Neptune's zonal wind profile, and confirms observed cloud feature variability. Although Neptune's clouds vary in location and intensity on short and long timescales, a single large discrete storm seen in Keck imaging dominates the K2 and Hubble light curves; smaller or fainter clouds likely contribute to short-term brightness variability. The K2 Neptune light curve, in conjunction with our imaging data, provides context for the interpretation of current and future brown dwarf and extrasolar planet variability measurements. In particular we suggest that the balance between large, relatively stable, atmospheric features and smaller, more transient, clouds controls the character of substellar atmospheric variability. Atmospheres dominated by a few large spots may show inherently greater light curve stability than those which exhibit a greater number of smaller features.

  4. Water Clouds in the Atmosphere of a Jupiter-Like Brown Dwarf

    Science.gov (United States)

    Kohler, Susanna

    2016-07-01

    Lying a mere 7.2 light-years away, WISE 0855 is the nearest known planetary-mass object. This brown dwarf, a failed star just slightly more massive than Jupiter, is also the coldest known compact body outside of our solar system and new observations have now provided us with a first look at its atmosphere.Temperaturepressure profiles of Jupiter, WISE 0855, and what was previously the coldest extrasolar object with a 5-m spectrum, Gl 570D. Thicker lines show the location of each objects 5-m photospheres. WISE 0855s and Jupiters photospheres are near the point where water starts to condense out into clouds (dashed line). [Skemer et al. 2016]Challenging ObservationsWith a chilly temperature of 250 K, the brown dwarf WISE 0855 is the closest thing weve been able to observe to a body resembling Jupiters ~130 K. WISE 0855 therefore presents an intriguing opportunity to directly study the atmosphere of an object whose physical characteristics are similar to our own gas giants.But studying the atmospheric characteristics of such a body is tricky. WISE 0855 is too cold and faint to be able to obtain traditional optical or near-infrared ( 2.5 m) spectroscopy of it. Luckily, like Jupiter, the opacity of its gas allows thermal emission from its deep atmosphere to escape through an atmospheric window around ~5 m.A team of scientists led by Andrew Skemer (UC Santa Cruz) set out to observe WISE 0855 in this window with the Gemini-North telescope and the Gemini Near-Infrared Spectrograph. Though WISE 0855 is five times fainter than the faintest object previously detected with ground-based 5-m spectroscopy, the dry air of Mauna Kea (and a lot of patience!) allowed the team to obtain unprecedented spectra of this object.WISE 0855s spectrum shows absorption features consistent with water vapor, and its best fit by a cloudy brown-dwarf model. [Skemer et al. 2016]Water Clouds FoundExoplanets and brown dwarfs cooler than ~350 K are expected to form water ice clouds in upper atmosphere

  5. New frontiers of high-resolution spectroscopy: Probing the atmospheres of brown dwarfs and reflected light from exoplanets

    Science.gov (United States)

    Birkby, Jayne; Alonso, Roi; Brogi, Matteo; Charbonneau, David; Fortney, Jonathan; Hoyer, Sergio; Johnson, John Asher; de Kok, Remco; Lopez-Morales, Mercedes; Montet, Ben; Snellen, Ignas

    2015-12-01

    High-resolution spectroscopy (R>25,000) is a robust and powerful tool in the near-infrared characterization of exoplanet atmospheres. It has unambiguously revealed the presence of carbon monoxide and water in several hot Jupiters, measured the rotation rate of beta Pic b, and suggested the presence of fast day-to-night winds in one atmosphere. The method is applicable to transiting, non-transiting, and directly-imaged planets. It works by resolving broad molecular bands in the planetary spectrum into a dense, unique forest of individual lines and tracing them directly by their Doppler shift, while the star and tellurics remain essentially stationary. I will focus on two ongoing efforts to expand this technique. First, I will present new results on 51 Peg b revealing its infrared atmospheric compositional properties, then I will discuss an ongoing optical HARPS-N/TNG campaign (due mid October 2015) to obtain a detailed albedo spectrum of 51 Peg b at 387-691 nm in bins of 50nm. This spectrum would provide strong constraints on the previously claimed high albedo and potentially cloudy nature of this planet. Second, I will discuss preliminary results from Keck/NIRSPAO observations (due late September 2015) of LHS 6343 C, a 1000 K transiting brown dwarf with an M-dwarf host star. The high-resolution method converts this system into an eclipsing, double-lined spectroscopic binary, thus allowing dynamical mass and radius estimates of the components, free from astrophysical assumptions. Alongside probing the atmospheric composition of the brown dwarf, these data would provide the first model-independent study of the bulk properties of an old brown dwarf, with masses accurate to <5%, placing a crucial constraint on brown dwarf evolution models.

  6. Assessing nucleation in cloud formation modelling for Brown Dwarf and Exoplanet atmospheres

    Science.gov (United States)

    Lee, Graham; Helling, Christiane; Giles, Helen; Bromley, Stefan

    2015-04-01

    Context. Substellar objects such as Brown Dwarfs and hot Jupiter exoplanets are cool enough that clouds can form in their atmospheres (Helling & Casewell 2014; A&ARv 22)). Unlike Earth, where cloud condensation nuclei are provided by the upward motion of sand or ash, in Brown Dwarf and hot Jupiters these condensation seeds form from the gas phase. This process proceeds in a stepwise chemical reaction of single monomer addition of a single nucleation species, referred to as homogeneous nucleation. The rate at which these seeds form is determined by the local thermodynamic conditions and the chemical composition of the local gas phase. Once the seed particles have formed, multiple materials are thermally stable and grow almost simultaneously by chemical surface reactions. This results in the growth of the condensation seeds to macroscopic particles of μm size. At the same time, the gas phase becomes depleted. Once temperatures become too high for thermal stability of the cloud particle, it evaporates until its constituents return to the gas phase. Convection from deeper atmospheric layers provides element replenishment to upper, cooler layers allowing the cloud formation process to reach a stationary state (Woitke & Helling 2003; A&A 399). Aims. The most efficient nucleation is a 'winner takes all' process as the losing molecules will condense on the surface of the faster nucleating seed particle. We apply new molecular (TiO2)N-cluster and SiO vapour data to our cloud formation model in order to re-asses the question of the primary nucleation species. Methods. We apply density functional theory (B3LYP, 6-311G(d)) using the computational chemistry package GAUSSIAN 09 to derive updated thermodynamical data for (TiO2)N-clusters as input for our TiO2 seed formation model. We test both TiO2 and SiO as primary nucleates assuming a homogeneous nucleation process and by solving a system of dust moment equations and element conservation for a pre-scribed Brown Dwarf

  7. Brown Dwarfs at the Exoplanet Mass Boundary

    Science.gov (United States)

    Faherty, J. K.; Cruz, K. L.; Rice, E. L.; Riedel, A.

    2014-10-01

    Young brown dwarfs and directly-imaged exoplanets have enticingly similar photometric and spectroscopic characteristics, indicating that their cool, low gravity atmospheres should be studied in concert. Similarities between the peculiar shaped H band, near and mid-IR photometry as well as location on color magnitude diagrams provide important clues about how to extract physical properties of planets from current brown dwarf observations. Our team has assigned >30 brown dwarfs to 10-150 Myr nearby moving groups. In so doing, we have discovered important diversity among this extremely low-mass (10 - 30 M_{Jup}) age-calibrated sample indicating that cloud properties play a critical role in their observables.

  8. Young Brown Dwarfs as Giant Exoplanet Analogs

    CERN Document Server

    Faherty, Jacqueline K; Rice, Emily L; Riedel, Adric

    2013-01-01

    Young brown dwarfs and directly-imaged exoplanets have enticingly similar photometric and spectroscopic characteristics, indicating that their cool, low gravity atmospheres should be studied in concert. Similarities between the peculiar shaped H band, near and mid-IR photometry as well as location on color magnitude diagrams provide important clues about how to extract physical properties of planets from current brown dwarf observations. In this proceeding we discuss systems newly assigned to 10-150 Myr nearby moving groups, highlight the diversity of this uniform age-calibrated brown dwarf sample, and reflect on their implication for understanding current and future planetary data.

  9. Ionisation in atmospheres of brown dwarfs and extrasolar planets VI: Properties of large-scale discharge events

    CERN Document Server

    Bailey, R L; Hodos, G; Bilger, C; Stark, C R

    2013-01-01

    Mineral clouds in substellar atmospheres play a special role as a catalyst for a variety of charge processes. If clouds are charged, the surrounding environment becomes electrically activated, and ensembles of charged grains are electrically discharging (e.g. by lightning), which significantly infuences the local chemistry creating conditions similar to those thought responsible for life in early planetary atmospheres. We note that such lightning discharges contribute also to the ionisation state of the atmosphere. We apply scaling laws for electrical discharge processes from laboratory measurements and numerical experiments to Drift-Phoenix model atmosphere results to model the discharge's propagation downwards (as lightning) and upwards (as sprites) through the atmospheric clouds. We evaluate the spatial extent and energetics of lightning discharges. The atmospheric volume affected (e.g. by increase of temperature or electron number) is larger in a brown dwarf atmosphere ($10^8 -~10^{10}$m$^3$) than in a gi...

  10. The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs

    CERN Document Server

    Wilson, P A; Patience, J

    2014-01-01

    Using SofI on the 3.5m New Technology Telescope, we have conducted an extensive near-infrared monitoring survey of an unbiased sample of 69 brown dwarfs spanning the L0 and T8 spectral range, with at least one example of each spectral type. Each target was observed for a 2-4 hour period in the Js-band, and the median photometric precision of the data is ~0.7%. A total of 14 brown dwarfs were identified as variables with min-to-max amplitudes ranging from 1.7% to 10.8% over the observed duration. All variables satisfy a statistical significance threshold with a p-value <5% based on comparison with the median reference star light curve. Approximately half of the variables show sinusoidal amplitude variations similar to 2M2139, and the remainder shows short timescale evolving light curves similar to SIMP0136. The L/T transition has been suggested to be a region of a higher degree of variability if patchy clouds are present and this survey was designed to test the patchy cloud model with photometric monitoring...

  11. Photometric brown-dwarf classification

    CERN Document Server

    Skrzypek, N

    2013-01-01

    We have developed a method "photo-type" to identify and accurately classify L and T dwarfs, onto the standard system, from photometry alone. We combine SDSS, UKIDSS and WISE data and classify point sources by comparing the izYJHKW1W2 colours against template colours for quasars, stars, and brown dwarfs. In a sample of $6.5\\times10^6$ bright point sources, J$<$17.5, from 3150 deg$^2$, we identify and type 898 L and T dwarfs, making this the largest homogeneously selected sample of brown dwarfs to date. The sample includes 713 (125) new (previously known) L dwarfs and 21 (39) T dwarfs. For the previously-known sources, the scatter in the plot of photo-type vs spectral type indicates that our photo-types are accurate to 1.5 (1.0) sub-types rms for L (T) dwarfs. Peculiar objects and candidate unresolved binaries are identified.

  12. The luminosities of the coldest brown dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Tinney, C. G. [School of Physics, UNSW Australia, NSW 2052 (Australia); Faherty, Jacqueline K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20005 (United States); Kirkpatrick, J. Davy [Infrared Processing and Analysis Center, MS100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Cushing, Mike [Department of Physics and Astronomy, The University of Toledo, OH 43606 (United States); Morley, Caroline V. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Wright, Edward L., E-mail: c.tinney@unsw.edu.au [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States)

    2014-11-20

    In recent years, brown dwarfs have been extended to a new Y-dwarf class with effective temperatures colder than 500 K and masses in the range of 5-30 Jupiter masses. They fill a crucial gap in observable atmospheric properties between the much colder gas-giant planets of our own solar system (at around 130 K) and both hotter T-type brown dwarfs and the hotter planets that can be imaged orbiting young nearby stars (both with effective temperatures in the range of 1500-1000 K). Distance measurements for these objects deliver absolute magnitudes that make critical tests of our understanding of very cool atmospheres. Here we report new distances for nine Y dwarfs and seven very late T dwarfs. These reveal that Y dwarfs do indeed represent a continuation of the T-dwarf sequence to both fainter luminosities and cooler temperatures. They also show that the coolest objects display a large range in absolute magnitude for a given photometric color. The latest atmospheric models show good agreement with the majority of these Y-dwarf absolute magnitudes. This is also the case for WISE0855-0714, the coldest and closest brown dwarf to the Sun, which shows evidence for water ice clouds. However, there are also some outstanding exceptions, which suggest either binarity or the presence of condensate clouds. The former is readily testable with current adaptive optics facilities. The latter would mean that the range of cloudiness in Y dwarfs is substantial with most hosting almost no clouds—while others have dense clouds, making them prime targets for future variability observations to study cloud dynamics.

  13. The Luminosities of the Coldest Brown Dwarfs

    CERN Document Server

    Tinney, C G; Kirkpatrick, J Davy; Cushing, Mike; Morley, Caroline V; Wright, Edward L

    2014-01-01

    In recent years brown dwarfs have been extended to a new Y-dwarf class with effective temperatures colder than 500K and masses in the range 5-30 Jupiter masses. They fill a crucial gap in observable atmospheric properties between the much colder gas-giant planets of our own Solar System (at around 130K) and both hotter T-type brown dwarfs and the hotter planets that can be imaged orbiting young nearby stars (both with effective temperatures of in the range 1500-1000K). Distance measurements for these objects deliver absolute magnitudes that make critical tests of our understanding of very cool atmospheres. Here we report new distances for nine Y dwarfs and seven very-late T dwarfs. These reveal that Y dwarfs do indeed represent a continuation of the T dwarf sequence to both fainter luminosities and cooler temperatures. They also show that the coolest objects display a large range in absolute magnitude for a given photometric colour. The latest atmospheric models show good agreement with the majority of these ...

  14. Ionization in atmospheres of brown dwarfs and extrasolar planets VI: Properties of large-scale discharge events

    International Nuclear Information System (INIS)

    Mineral clouds in substellar atmospheres play a special role as a catalyst for a variety of charge processes. If clouds are charged, the surrounding environment becomes electrically activated, and ensembles of charged grains are electrically discharging (e.g., by lightning), which significantly influences the local chemistry creating conditions similar to those thought responsible for life in early planetary atmospheres. We note that such lightning discharges contribute also to the ionization state of the atmosphere. We apply scaling laws for electrical discharge processes from laboratory measurements and numerical experiments to DRIFT-PHOENIX model atmosphere results to model the discharge's propagation downward (as lightning) and upward (as sprites) through the atmospheric clouds. We evaluate the spatial extent and energetics of lightning discharges. The atmospheric volume affected (e.g., by increase of temperature or electron number) is larger in a brown dwarf atmosphere (108-1010 m3) than in a giant gas planet (104-106 m3). Our results suggest that the total dissipated energy in one event is <1012 J for all models of initial solar metallicity. First attempts to show the influence of lightning on the local gas phase indicate an increase of small carbohydrate molecules like CH and CH2 at the expense of CO and CH4. Dust-forming molecules are destroyed and the cloud particle properties are frozen in unless enough time is available for complete evaporation. We summarize instruments potentially suitable to observe lightning on extrasolar objects.

  15. Race to the Top: Transiting Brown Dwarfs and Hot Jupiters

    Science.gov (United States)

    Beatty, Thomas G.

    2015-12-01

    There are currently twelve known transiting brown dwarfs, nine of which orbit single main-sequence stars. These systems give us one of the only ways in which we may directly measure the masses and radii brown dwarfs, which in turn provides strong constraints on theoretical models of brown dwarf interiors and atmospheres. In addition, the transiting brown dwarfs allow us to forge a link between our understanding of transiting hot Jupiters, and our understanding of the field brown dwarf population. Comparing the two gives us a unique avenue to explore the role and interaction of surface gravity and stellar irradiation in the atmospheres of sub-stellar objects. It also allows us to leverage the detailed spectroscopic information we have for field brown dwarfs to interpret the broadband colors of hot Jupiters. This provides us with insight into the L/T transition in brown dwarfs, and the atmospheric chemistry changes that occur in hot Jupiter atmospheres as they cool. I will discuss recent observational results, with a particular focus on the transiting brown dwarf KELT-1b, and suggest how more of these important systems may be discovered in the future.

  16. Neptune's Dynamic Atmosphere from Kepler K2 Observations: Implications for Brown Dwarf Light Curve Analyses

    CERN Document Server

    Simon, Amy A; Gaulme, Patrick; Hammel, Heidi B; Casewell, Sarah L; Fortney, Jonathan J; Gizis, John E; Lissauer, Jack J; Morales-Juberias, Raul; Orton, Glenn S; Wong, Michael H; Marley, Mark S

    2015-01-01

    Observations of Neptune with the Kepler Space Telescope yield a 49-day light curve with 98% coverage at a 1-minute cadence. A significant signature in the light curve comes from discrete cloud features. We compare results extracted from the light curve data with contemporaneous disk-resolved imaging of Neptune from the Keck 10-meter telescope at 1.65 microns and Hubble Space Telescope visible imaging acquired 9 months later. This direct comparison validates the feature latitudes assigned to the K2 light curve periods based on Neptune's zonal wind profile, and confirms observed cloud feature variability. Although Neptune's clouds vary in location and intensity on short and long time scales, a single large discrete storm seen in Keck imaging dominates the K2 and Hubble light curves; smaller or fainter clouds likely contribute to short-term brightness variability. The K2 Neptune light curve, in conjunction with our imaging data, provides context for the interpretation of current and future brown dwarf and extras...

  17. Quenching of Carbon Monoxide and Methane in the Atmospheres of Cool Brown Dwarfs and Hot Jupiters

    CERN Document Server

    Visscher, Channon

    2011-01-01

    We explore CO-CH4 quench kinetics in the atmospheres of substellar objects using updated time-scale arguments, as suggested by a thermochemical kinetics and diffusion model that transitions from the thermochemical-equilibrium regime in the deep atmosphere to a quench-chemical regime at higher altitudes. More specifically, we examine CO quench chemistry on the T dwarf Gliese 229B and CH4 quench chemistry on the hot-Jupiter HD 189733b. We describe a method for correctly calculating reverse rate coefficients for chemical reactions, discuss the predominant pathways for CO-CH4 interconversion as indicated by the model, and demonstrate that a simple time-scale approach can be used to accurately describe the behavior of quenched species when updated reaction kinetics and mixing-length-scale assumptions are used. Proper treatment of quench kinetics has important implications for estimates of molecular abundances and/or vertical mixing rates in the atmospheres of substellar objects. Our model results indicate signific...

  18. Benchmark Transiting Brown Dwarf LHS 6343 C: Spitzer Secondary Eclipse Observations Yield Brightness Temperature and Mid-T Spectral Class

    OpenAIRE

    Montet, Benjamin T.; Johnson, John Asher; Fortney, Jonathan J.; Desert, Jean-Michel

    2016-01-01

    There are no field brown dwarf analogs with measured masses, radii, and luminosities, precluding our ability to connect the population of transiting brown dwarfs with measurable masses and radii and field brown dwarfs with measurable luminosities and atmospheric properties. LHS 6343 C, a weakly irradiated brown dwarf transiting one member of an M+M binary in the Kepler field, provides the first opportunity to probe the atmosphere of a non-inflated brown dwarf with a measured mass and radius. ...

  19. Ionization in atmospheres of brown dwarfs and extrasolar planets VI: Properties of large-scale discharge events

    Energy Technology Data Exchange (ETDEWEB)

    Bailey, R. L.; Helling, Ch.; Hodosán, G.; Bilger, C.; Stark, C. R., E-mail: ch@leap2010.eu [SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS (United Kingdom)

    2014-03-20

    Mineral clouds in substellar atmospheres play a special role as a catalyst for a variety of charge processes. If clouds are charged, the surrounding environment becomes electrically activated, and ensembles of charged grains are electrically discharging (e.g., by lightning), which significantly influences the local chemistry creating conditions similar to those thought responsible for life in early planetary atmospheres. We note that such lightning discharges contribute also to the ionization state of the atmosphere. We apply scaling laws for electrical discharge processes from laboratory measurements and numerical experiments to DRIFT-PHOENIX model atmosphere results to model the discharge's propagation downward (as lightning) and upward (as sprites) through the atmospheric clouds. We evaluate the spatial extent and energetics of lightning discharges. The atmospheric volume affected (e.g., by increase of temperature or electron number) is larger in a brown dwarf atmosphere (10{sup 8}-10{sup 10} m{sup 3}) than in a giant gas planet (10{sup 4}-10{sup 6} m{sup 3}). Our results suggest that the total dissipated energy in one event is <10{sup 12} J for all models of initial solar metallicity. First attempts to show the influence of lightning on the local gas phase indicate an increase of small carbohydrate molecules like CH and CH{sub 2} at the expense of CO and CH{sub 4}. Dust-forming molecules are destroyed and the cloud particle properties are frozen in unless enough time is available for complete evaporation. We summarize instruments potentially suitable to observe lightning on extrasolar objects.

  20. Microlensing, Brown Dwarfs and GAIA

    CERN Document Server

    Evans, N W

    2014-01-01

    The GAIA satellite can precisely measure the masses of nearby brown dwarfs and lower main sequence stars by the microlensing effect. The scientific yield is maximised if the microlensing event is also followed with ground-based telescopes to provide densely sampled photometry. There are two possible strategies. First, ongoing events can be triggered by photometric or astrometric alerts by GAIA. Second, events can be predicted using known high proper motion stars as lenses. This is much easier, as the location and time of an event can be forecast. Using the GAIA source density, we estimate that the sample size of high proper motion ($>300$ mas yr$^{-1}$) brown dwarfs needed to provide predictable events during the 5 year mission lifetime is surprisingly small, only of the order of a hundred. This is comparable to the number of high proper motion brown dwarfs already known from the work of the UKIDSS Large Area Survey and the all-sky WISE satellite. Provided the relative parallax of the lens and the angular Ein...

  1. A Very Cool Pair of Brown Dwarfs

    Science.gov (United States)

    2011-03-01

    Observations with the European Southern Observatory's Very Large Telescope, along with two other telescopes, have shown that there is a new candidate for the coldest known star: a brown dwarf in a double system with about the same temperature as a freshly made cup of tea - hot in human terms, but extraordinarily cold for the surface of a star. This object is cool enough to begin crossing the blurred line dividing small cold stars from big hot planets. Brown dwarfs are essentially failed stars: they lack enough mass for gravity to trigger the nuclear reactions that make stars shine. The newly discovered brown dwarf, identified as CFBDSIR 1458+10B, is the dimmer member of a binary brown dwarf system located just 75 light-years from Earth [1]. The powerful X-shooter spectrograph on ESO's Very Large Telescope (VLT) was used to show that the composite object was very cool by brown dwarf standards. "We were very excited to see that this object had such a low temperature, but we couldn't have guessed that it would turn out to be a double system and have an even more interesting, even colder component," said Philippe Delorme of the Institut de planétologie et d'astrophysique de Grenoble (CNRS/Université Joseph Fourier), a co-author of the paper. CFBDSIR 1458+10 is the coolest brown dwarf binary found to date. The dimmer of the two dwarfs has now been found to have a temperature of about 100 degrees Celsius - the boiling point of water, and not much different from the temperature inside a sauna [2]. "At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets - it could even have water clouds in its atmosphere," said Michael Liu of the University of Hawaii's Institute for Astronomy, who is lead author of the paper describing this new work. "In fact, once we start taking images of gas-giant planets around Sun-like stars in the near future, I expect that many of them

  2. Correlated spectral variability in brown dwarfs

    CERN Document Server

    Bailer-Jones, C A L

    2007-01-01

    Models of brown dwarf atmospheres suggest they exhibit complex physical behaviour. Observations have shown that they are indeed dynamic, displaying small photometric variations over timescales of hours. Here I report results of infrared (0.95-1.64 micron) spectrophotometric monitoring of four field L and T dwarfs spanning timescales of 0.1-5.5 hrs, the goal being to learn more about the physical nature of this variability. Spectra are analysed differentially with respect to a simultaneously observed reference source in order to remove Earth-atmospheric variations. The variability amplitude detected is typically 2-10%, depending on the source and wavelength. I analyse the data for correlated variations between spectral indices. This approach is more robust than single band or chisq analyses, because it does not assume an amplitude for the (often uncertain) noise level (although the significance test still assumes a shape for the noise power spectrum). Three of the four targets show significant evidence for cor...

  3. Modeling the Cloudy Atmospheres of Cool Stars, Brown Dwarfs and Hot Exoplanets

    DEFF Research Database (Denmark)

    Juncher, Diana

    -consistent cloudy atmosphere models that can be used to properly determine the stellar parameters of cool stars. With this enhanced model atmosphere code I have created a grid of cool, dusty atmosphere models ranging in effective temperatures from Teff = 2000 − 3000 K. I have studied the formation and structure of...... properties of its host star, it is crucial that the stellar models linking the observations of a star to its properties are as precise as possible. The primary goal of this project is therefore to merge the model atmosphere code MARCS with the dust model code DRIFT, thus facilitating the computation of self...

  4. Microlensing Binaries with Candidate Brown Dwarf Companions

    DEFF Research Database (Denmark)

    Shin, I.-G; Han, C.; Gould, A.;

    2012-01-01

    Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation histories. In this paper, we present the candidate binaries with brown dwarf companions that are found by analyzing binary microlensing ...

  5. Cold Brown Dwarfs with WISE: Y Dwarfs and the Field Mass Function

    Science.gov (United States)

    Kirkpatrick, J. Davy

    2012-01-01

    Why study Brown Dwarf stars? They re the lowest mass byproducts of star formation.. They provide time capsules across the age of the Galaxy.. They show what low-T(sub eff) atmospheres look like.. They may be some of our closest neighbors in space..WISE is a 40cm Earth-orbiting telescope. There are 211 stars and only 33 brown dwarfs in this volume.. This means that stars outnumber brown dwarfs by a factor of 6:1 currently.. The number of brown dwarfs will continue to increase if:: (a) more nearby Y dwarf candidates are confirmed, or (b) our distances to known Y s are overestimated, or (c) there are colder BDs invisible to WISE..

  6. Brown dwarf disks with ALMA

    Energy Technology Data Exchange (ETDEWEB)

    Ricci, L.; Isella, A. [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Testi, L.; De Gregorio-Monsalvo, I. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Natta, A. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Scholz, A., E-mail: lricci@astro.caltech.edu [School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland)

    2014-08-10

    We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3-2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.

  7. Multiple scattering polarization – Application of Chandrasekhar’s formalisms to the atmosphere of brown dwarfs and extrasolar planets

    Indian Academy of Sciences (India)

    Sujan Sengupta; Mark S Marley

    2011-07-01

    Chandrasekhar’s formalisms for the transfer of polarized radiation are used to explain the observed dust scattering polarization of brown dwarfs in the optical band. Model polarization profiles for hot and young directly imaged extrasolar planets are presented with specific prediction of the degree of polarization in the infrared. The model invokes Chandrasekhar’s formalism for the rotation-induced oblateness of the objects that gives rise to the necessary asymmetry for yielding net non-zero disk integrated linear polarization. The observed optical polarization constrains the surface gravity and could be a tool to estimate the mass of extrasolar planets.

  8. Aeolus: A Markov--Chain Monte Carlo code for mapping ultracool atmospheres. An application on Jupiter and brown dwarf HST light curves

    CERN Document Server

    Karalidi, Theodora; Schneider, Glenn; Hanson, Jake R; Pasachoff, Jay M

    2015-01-01

    Deducing the cloud cover and its temporal evolution from the observed planetary spectra and phase curves can give us major insight into the atmospheric dynamics. In this paper, we present Aeolus, a Markov-Chain Monte Carlo code that maps the structure of brown dwarf and other ultracool atmospheres. We validated Aeolus on a set of unique Jupiter Hubble Space Telescope (HST) light curves. Aeolus accurately retrieves the properties of the major features of the jovian atmosphere such as the Great Red Spot and a major 5um hot spot. Aeolus is the first mapping code validated on actual observations of a giant planet over a full rotational period. For this study, we applied Aeolus to J and H-bands HST light curves of 2MASSJ21392676+0220226 and 2MASSJ0136565+093347. Aeolus retrieves three spots at the top-of-the-atmosphere (per observational wavelength) of these two brown dwarfs, with a surface coverage of 21+-3% and 20.3+-1.5% respectively. The Jupiter HST light curves will be publicly available via ADS/VIZIR.

  9. A USNO Search for Astrometric Companions to Brown Dwarfs IV

    Science.gov (United States)

    Bartlett, Jennifer L.; Vrba, F. J.; Munn, J. A.; Luginbuhl, C. B.; Tilleman, T.; Henden, A. A.

    2014-01-01

    Preliminary analyses of ten brown dwarfs observed by the U.S. Naval Observatory infrared parallax program show no clear indication of astrometric perturbations due to low mass companions. The data were collected using ASTROCAM on the 1.55-m (61-in) Kaj Strand Astrometric Reflector from 2000 September through 2006 June over periods from 2.0 to 5.3 years. After our standard solution for parallax and proper motion, the residuals were subjected to a time-series analysis using the Lomb-Scargle periodogram method. The multiplicity fraction for brown dwarfs constrains theories of brown dwarf formation and evolution. Binary systems, especially those that straddle the transition between L and T spectral types, are also significant tests of atmospheric models. In addition, the identification of companions would have enabled the eventual measurement of the associated masses. This search for astrometric companions is an extension of the initial infrared parallax program. When finalized, the trigonometric parallaxes for these brown dwarfs will provide accurate distances for use in determining their luminosities and temperatures. The brown dwarfs in this subsample have spectral types that range from late M through mid-T. None of them are known binaries. Distance estimates place six of these objects within the 25-pc limit of the Solar Neighborhood, and preliminary parallaxes place another three between 25 and 35 pc. These substellar objects are located north of -15° Dec. The brown dwarfs evaluated are 2MASS J00325937+1410371, 2MASS J01514155+1244300 (BF Ari) 2MASS J02074284+0000564, 2MASS J03095345-0753156, SDSS J083717.21-000018.0, 2MASS J11101001+0116130, 2MASS J13262981-0038314 (2MUCD 11143), 2MASS J17502385+4222373, 2MASS J23391025+1352284, and 2MASS J23565477-1553111. Analyses of another 30 brown dwarfs were presented earlier and the analyses of 19 more brown dwarfs are planned.

  10. A USNO Search for Astrometric Companions to Brown Dwarfs III

    Science.gov (United States)

    Bartlett, Jennifer L.; Vrba, F. J.; Munn, J. A.; Luginbuhl, C. B.; Tillman, T.; Henden, A. A.

    2013-01-01

    Preliminary analyses of ten brown dwarfs observed by the U.S. Naval Observatory infrared parallax program show no clear indication of astrometric perturbations due to low mass companions. The data were collected using ASTROCAM on the 1.55-m Strand Astrometric Reflector from 2000 October through 2006 June over periods from 1.3 to 5.4 years. After our standard solution for parallax and proper motion, the residuals were subjected to a time-series analysis using the Lomb-Scargle periodogram method. The multiplicity fraction for brown dwarfs constrains theories of brown dwarf formation and evolution. Binary systems, especially those that straddle the transition between L and T spectral types, are also significant tests of atmospheric models. In addition, the identification of companions would have enabled the eventual measurement of the associated masses. This search for astrometric companions is an extension of the initial infrared parallax program. When finalized, the trigonometric parallaxes for these brown dwarfs will provide accurate distances for use in determining their luminosities and temperatures. The brown dwarfs in this subsample have spectral types that range from early L through mid-T. None are known binaries. Distance estimates place all but two within the 25-pc limit of the Solar Neighborhood; one outlier has a distance of approximately 62 pc based on its preliminary parallax. These substellar objects are located north of -25° Dec. and lie between 13h and 23h in R.A. The brown dwarfs evaluated are 2MASS J13464634-0031501, SDSS J144600.60+002452.0, 2MASS J16241436+0029158, 2MASS J17580545+4633099, 2MASS J19010601+4718136, 2MASS J21241387+0059599, 2MASS J22425317+2542573, 2MASS J22443167+2043433, 2MASS J22541892+3123498, and 2MASS J22552907-0034336. Analyses of another 20 brown dwarfs were presented earlier and the analyses of 19 more brown dwarfs are planned.

  11. Temperature Fluctuations as a Source of Brown Dwarf Variability

    CERN Document Server

    Robinson, Tyler D

    2014-01-01

    A number of brown dwarfs are now known to be variable with observed amplitudes as large as 10-30% at some wavelengths. While spatial inhomogeneities in cloud coverage and thickness are likely responsible for much of the observed variability, it is possible that some of the variations arise from atmospheric temperature fluctuations instead of, or in addition to, clouds. To better understand the role that thermal variability might play we present a case study of brown dwarf variability using a newly-developed one-dimensional, time-stepping model of atmospheric thermal structure. We focus on the effects of thermal perturbations, intentionally simplifying the problem through omission of clouds and atmospheric circulation. Model results demonstrate that thermal perturbations occurring deep in the atmosphere (at pressures greater than 10 bar) of a model T-dwarf can be communicated to the upper atmosphere through radiative heating via the windows in near-infrared water opacity. The response time depends on where in ...

  12. A global cloud map of the nearest known brown dwarf

    CERN Document Server

    Crossfield, I J M; Schlieder, J E; Deacon, N R; Bonnefoy, M; Homeier, D; Allard, F; Buenzli, E; Henning, Th; Brandner, W; Goldman, B; Kopytova, T

    2014-01-01

    Brown dwarfs -- substellar bodies more massive than planets but not massive enough to initiate the sustained hydrogen fusion that powers self-luminous stars -- are born hot and slowly cool as they age. As they cool below about 2,300 K, liquid or crystalline particles composed of calcium aluminates, silicates and iron condense into atmospheric 'dust', which disappears at still cooler temperatures (around 1,300 K). Models to explain this dust dispersal include both an abrupt sinking of the entire cloud deck into the deep, unob- servable atmosphere and breakup of the cloud into scattered patches (as seen on Jupiter and Saturn). Thus far, observations of brown dwarfs have been limited to globally integrated measurements, which can reveal surface inhomogeneities but cannot unambiguously resolve surface features. Here we report a two-dimensional map of a brown dwarf's surface that allows identification of large-scale bright and dark features, indicative of patchy clouds.

  13. Atom Resonance Lines for Modeling Atmosphere: Studies of Pressure-Broadening of Alkali Atom Resonance Lines for Modeling Atmospheres of Extrasolar Giant Planets and Brown Dwarfs

    Science.gov (United States)

    Hasan, Hashima (Technical Monitor); Kirby, K.; Babb, J.; Yoshino, K.

    2005-01-01

    We report on progress made in a joint program of theoretical and experimental research to study the line-broadening of alkali atom resonance lines due to collisions with species such as helium and molecular hydrogen. Accurate knowledge of the line profiles of Na and K as a function of temperature and pressure will allow such lines to serve as valuable diagnostics of the atmospheres of brown dwarfs and extra-solar giant planets. A new experimental apparatus has been designed, built and tested over the past year, and we are poised to begin collecting data on the first system of interest, the potassium resonance lines perturbed by collisions with helium. On the theoretical front, calculations of line-broadening due to sodium collisions with helium are nearly complete, using accurate molecular potential energy curves and transition moments just recently computed for this system. In addition we have completed calculations of the three relevant potential energy curves and associated transition moments for K - He, using the MOLPRO quantum chemistry codes. Currently, calculations of the potential surfaces describing K-H2 are in progress.

  14. Chandra Captures Flare From Brown Dwarf

    Science.gov (United States)

    2000-07-01

    The first flare ever seen from a brown dwarf, or failed star, was detected by NASA's Chandra X-ray Observatory. The bright X-ray flare has implications for understanding the explosive activity and origin of magnetic fields of extremely low mass stars. Chandra detected no X-rays at all from LP 944-20 for the first nine hours of a twelve hour observation, then the source flared dramatically before it faded away over the next two hours. "We were shocked," said Dr. Robert Rutledge of the California Institute of Technology in Pasadena, the lead author on the discovery paper to appear in the July 20 issue of Astrophysical Journal Letters. "We didn't expect to see flaring from such a lightweight object. This is really the 'mouse that roared.'" Chandra LP 944-20 X-ray Image Press Image and Caption The energy emitted in the brown dwarf flare was comparable to a small solar flare, and was a billion times greater than observed X-ray flares from Jupiter. The flaring energy is believed to come from a twisted magnetic field. "This is the strongest evidence yet that brown dwarfs and possibly young giant planets have magnetic fields, and that a large amount of energy can be released in a flare," said Dr. Eduardo Martin, also of Caltech and a member of the team. Professor Gibor Basri of the University of California, Berkeley, the principal investigator for this observation, speculated that the flare "could have its origin in the turbulent magnetized hot material beneath the surface of the brown dwarf. A sub-surface flare could heat the atmosphere, allowing currents to flow and give rise to the X-ray flare -- like a stroke of lightning." LP 944-20 is about 500 million years old and has a mass that is about 60 times that of Jupiter, or 6 percent that of the Sun. Its diameter is about one-tenth that of the Sun and it has a rotation period of less than five hours. Located in the constellation Fornax in the southern skies, LP 944-20 is one of the best studied brown dwarfs because it is

  15. Adaptive Optics Observations of Exoplanets, Brown Dwarfs, & Binary Stars

    CERN Document Server

    Hinkley, Sasha

    2011-01-01

    The current direct observations of brown dwarfs and exoplanets have been obtained using instruments not specifically designed for overcoming the large contrast ratio between the host star and any wide-separation faint companions. However, we are about to witness the birth of several new dedicated observing platforms specifically geared towards high contrast imaging of these objects. The Gemini Planet Imager, VLT-SPHERE, Subaru HiCIAO, and Project 1640 at the Palomar 5m telescope will return images of numerous exoplanets and brown dwarfs over hundreds of observing nights in the next five years. Along with diffraction-limited coronagraphs and high-order adaptive optics, these instruments also will return spectral and polarimetric information on any discovered targets, giving clues to their atmospheric compositions and characteristics. Such spectral characterization will be key to forming a detailed theory of comparative exoplanetary science which will be widely applicable to both exoplanets and brown dwarfs. Fu...

  16. Using Clustering Algorithms to Identify Brown Dwarf Characteristics

    Science.gov (United States)

    Choban, Caleb

    2016-06-01

    Brown dwarfs are stars that are not massive enough to sustain core hydrogen fusion, and thus fade and cool over time. The molecular composition of brown dwarf atmospheres can be determined by observing absorption features in their infrared spectrum, which can be quantified using spectral indices. Comparing these indices to one another, we can determine what kind of brown dwarf it is, and if it is young or metal-poor. We explored a new method for identifying these subgroups through the expectation-maximization machine learning clustering algorithm, which provides a quantitative and statistical way of identifying index pairs which separate rare populations. We specifically quantified two statistics, completeness and concentration, to identify the best index pairs. Starting with a training set, we defined selection regions for young, metal-poor and binary brown dwarfs, and tested these on a large sample of L dwarfs. We present the results of this analysis, and demonstrate that new objects in these classes can be found through these methods.

  17. Discovery of Nearest Known Brown Dwarf

    Science.gov (United States)

    2003-01-01

    near-infrared (0.9-2.5 µm) spectrum of Epsilon Indi B, obtained on November 16-17, 2002, with the SOFI multi-mode instrument on the ESO 3.5-m New Technology Telescope (NTT) at the La Silla Observatory (Chile) The total integration time is 360 sec. Regions of strong absorption in the Earth's atmosphere have been removed for clarity. The locations of prominent molecular absorption bands from water (H2O), methane (CH4) and carbon monoxide (CO) in the atmosphere of Epsilon Indi B are indicated. Also labelled are some spectral lines from potassium (KI, at 1.25 and 1.52 µm) and sodium (NaI, at 2.33 µm) atoms. From these data, the spectral type of Epsilon Indi B is determined as T2.5V, corresponding to an effective temperature of 'just' 1000 ± 60 °C. Within days of its discovery in the database, the astronomers managed to secure an infrared spectrum of Epsilon Indi B using the SOFI instrument on the ESO 3.5-m New Technology Telescope (NTT) at the La Silla Observatory (Chile). The spectrum showed the broad absorption features due to methane and water steam in its upper atmosphere, indicating a temperature of 'only' 1000 °C. Ordinary stars are never this cool - Epsilon Indi B was confirmed as a brown dwarf. Brown dwarfs are thought to form in much the same way as stars, by the gravitational collapse of clumps of cold gas and dust in dense molecular clouds. However, for reasons not yet entirely clear, some clumps end up with masses less than about 7.5% of that of our Sun, or 75 times the mass of planet Jupiter. Below that boundary, there is not enough pressure in the core to initiate nuclear hydrogen fusion, the long-lasting and stable source of power for ordinary stars like the Sun. Except for a brief early phase where some deuterium is burned, these low-mass objects simply continue to cool and fade slowly away while releasing the heat left-over from their birth. Theoretical discussions of such objects began some 40 years ago. They were first named 'black dwarfs' and

  18. Testing Model Atmospheres for Young Very Low Mass Stars and Brown Dwarfs in the Infrared: Evidence for Significantly Underestimated Dust Opacities

    CERN Document Server

    Tottle, Jonathan

    2014-01-01

    We test state-of-the-art model atmospheres for young very low-mass stars and brown dwarfs in the infrared, by comparing the predicted synthetic photometry over 1.2-24 {\\mu}m to the observed photometry of M-type spectral templates in star-forming regions. We find that (1) in both early and late young M types, the model atmospheres imply effective temperatures (Teff) several hundred Kelvin lower than predicted by the standard Pre-Main Sequence spectral type-Teff conversion scale (where the latter is based on theoretical evolutionary models). It is only in the mid-M types that the two temperature estimates agree. (2) The Teff discrepancy in the early M types (corresponding to stellar masses above 0.6 Msol at a few Myr) probably arises from remaining uncertainties in the treatment of atmospheric convection. The agreement in the mid-M types implies a reasonably good atmospheric modeling of H2O opacities, which dominate in the infrared at these spectral types. Conversely, the Teff discrepancy in the late M types is...

  19. Flash ionisation signature in coherent cyclotron emission from Brown Dwarfs

    CERN Document Server

    Vorgul, Irena

    2016-01-01

    Brown dwarfs form mineral clouds in their atmospheres, where charged particles can produce large-scale discharges in form of lightning resulting in a substantial sudden increase of local ionisation. Brown dwarfs are observed to emit cyclotron radio emission. We show that signatures of strong transient atmospheric ionisation events (flash ionisation) can be imprinted on a pre-existing radiation. Detection of such flash ionisation events will open investigations into the ionisation state and atmospheric dynamics. Such ionisation events can also result from explosion shock waves, bursts or eruptions. We present an analytical model that describes the modulation of a pre-existing electromagnetic radiation by a time-dependent (flash) conductivity that is characteristic for flash ionisation events like lightning. Our conductivity model reproduces the conductivity function derived from observations of Terrestrial Gamma Ray Flashes, and is applicable to astrophysical objects with strong temporal variations in the loca...

  20. DISCOVERY OF AN UNUSUALLY RED L-TYPE BROWN DWARF

    International Nuclear Information System (INIS)

    We report the discovery of an unusually red brown dwarf found in a search for high proper motion objects using WISE and 2MASS data. WISEP J004701.06+680352.1 is moving at 0.''44 yr–1 and lies relatively close to the Galactic plane (b = 5.02). Near-infrared photometry and spectroscopy reveals that this is one of the reddest (2MASS J – Ks 2.55 ± 0.08 mag) field L dwarfs yet detected, making this object an important member of the class of unusually red L dwarfs. We discuss evidence for thick condensate clouds and speculate on the age of the object. Although models by different research groups agree that thick clouds can explain the red spectrum, they predict dramatically different effective temperatures, ranging from 1100 K to 1600 K. This brown dwarf is well suited for additional studies of extremely dusty substellar atmospheres because it is relatively bright (Ks = 13.05 ± 0.03 mag), which should also contribute to an improved understanding of young gas-giant planets and the transition between L and T brown dwarfs.

  1. The First Spectrum of the Coldest Brown Dwarf

    CERN Document Server

    Skemer, Andrew; Allers, Katelyn; Geballe, Thomas; Marley, Mark; Fortney, Jonathan; Faherty, Jacqueline; Bjoraker, Gordon; Lupu, Roxana

    2016-01-01

    The recently discovered brown dwarf WISE 0855 presents our first opportunity to directly study an object outside the Solar System that is nearly as cold as our own gas giant planets. However the traditional methodology for characterizing brown dwarfs---near infrared spectroscopy---is not currently feasible as WISE 0855 is too cold and faint. To characterize this frozen extrasolar world we obtained a 4.5-5.2 $\\mu$m spectrum, the same bandpass long used to study Jupiter's deep thermal emission. Our spectrum reveals the presence of atmospheric water vapor and clouds, with an absorption profile that is strikingly similar to Jupiter. The spectrum is high enough quality to allow the investigation of dynamical and chemical processes that have long been studied in Jupiter's atmosphere, but now on an extrasolar world.

  2. A search for rocky planets transiting brown dwarfs

    CERN Document Server

    Triaud, Amaury H M J; Selsis, Franck; Winn, Joshua N; Demory, Brice-Olivier; Artigau, Etienne; Laughlin, Gregory P; Seager, Sara; Helling, Christiane; Mayor, Michel; Albert, Loic; Anderson, Richard I; Bolmont, Emeline; Doyon, Rene; Forveille, Thierry; Hagelberg, Janis; Leconte, Jeremy; Lendl, Monika; Littlefair, Stuart; Raymond, Sean; Sahlmann, Johannes

    2013-01-01

    Exoplanetary science has reached a historic moment. The James Webb Space Telescope will be capable of probing the atmospheres of rocky planets, and perhaps even search for biologically produced gases. However this is contingent on identifying suitable targets before the end of the mission. A race therefore, is on, to find transiting planets with the most favorable properties, in time for the launch. Here, we describe a realistic opportunity to discover extremely favorable targets - rocky planets transiting nearby brown dwarfs - using the Spitzer Space Telescope as a survey instrument. Harnessing the continuous time coverage and the exquisite precision of Spitzer in a 5,400 hour campaign monitoring nearby brown dwarfs, we will detect a handful of planetary systems with planets as small as Mars. The survey we envision is a logical extension of the immense progress that has been realized in the field of exoplanets and a natural outcome of the exploration of the solar neighborhood to map where the nearest habitab...

  3. Polarimetric Detection of Exoplanets Transiting T- and L- Brown Dwarfs

    CERN Document Server

    Sengupta, Sujan

    2016-01-01

    While scattering of light by atoms and molecules yields large amount of polarization at the B-band of both T- and L-dwarfs, scattering by dust grains in cloudy atmosphere of L-dwarfs gives rise to significant polarization at the far-optical and infra-red wavelengths where these objects are much brighter. However, the observable disk averaged polarization should be zero if the clouds are uniformly distributed and the object is spherically symmetric. Therefore, in order to explain the observed large polarization of several L-dwarfs, rotation-induced oblateness or horizontally inhomogeneous cloud distribution in the atmosphere is invoked. On the other hand, when an extra-solar planet of Earth-size or larger transits the brown dwarf along the line of sight, the asymmetry induced during the transit gives rise to a net non-zero, time dependent polarization. Employing atmospheric models for a range of effective temperature and surface gravity appropriate for T- and L-dwarfs, I derive the time dependent polarization ...

  4. Eclipse Observations of a Temperate Transiting Brown Dwarf

    Science.gov (United States)

    Beatty, Thomas; Curtis, Jason; Montet, Benjamin; Vanderberg, Andrew

    2016-08-01

    We wish to use 15.7 hours of Spitzer time to observe two eclipses, one each at 3.6 um and 4.5 um of a newly discovered transiting brown dwarf, which we refer to as R147-BD. R147-BD is a 36 MJ object on a 5.3 day orbit about a K=10.666, 5800K solar analog. Uniquely, R147-BD and its host star are both members of the 3.0 Gyr old open cluster Ruprecht 147. R147-BD is thus one of the only transiting brown dwarfs for which we have a robust isochronal age that is not dependent upon brown dwarf evolutionary models. These models predict that a field object with the mass and age of R147-BD should have an effective temperature of about 800K due to internal heat. The zero-albedo blackbody equilibrium temperature for R147-BD, based only on its host star's insolation, is 1125K. This makes R147-BD the first observationally accessible sub-stellar object for which the internal and external energy fluxes are approximately equal, and it can serve as a unique laboratory to test the effect of stellar irradiation on the vertical pressure-temperature structure and clouds of giant planets. Specifically, we wish to investigate three different questions with these observations. First, how does the measured mass, radius, age and emission of R147-BD compare to brown dwarf evolution models, and how have these been altered by stellar irradiation? Second, does R147-BD's dayside atmosphere resemble its isolated field equivalent, or is it closer to hot Jupiters at similar temperatures? Third, can we constrain the cloud properties of R147-BD's dayside? Besides these particular science questions, observations of R147-BD allow us to scout-out future JWST observations of temperate giant planets, which also will have roughly equal amounts of stellar irradiation and internal heat.

  5. The First Spectrum of the Coldest Brown Dwarf

    Science.gov (United States)

    Skemer, Andrew J.; Morley, Caroline V.; Allers, Katelyn N.; Geballe, Thomas R.; Marley, Mark S.; Fortney, Jonathan J.; Faherty, Jacqueline K.; Bjoraker, Gordon L.; Lupu, Roxana

    2016-08-01

    The recently discovered brown dwarf WISE 0855 presents the first opportunity to directly study an object outside the solar system that is nearly as cold as our own gas giant planets. However, the traditional methodology for characterizing brown dwarfs—near-infrared spectroscopy—is not currently feasible, as WISE 0855 is too cold and faint. To characterize this frozen extrasolar world we obtained a 4.5–5.2 μm spectrum, the same bandpass long used to study Jupiter’s deep thermal emission. Our spectrum reveals the presence of atmospheric water vapor and clouds, with an absorption profile that is strikingly similar to Jupiter’s. The spectrum quality is high enough to allow for the investigation of dynamical and chemical processes that have long been studied in Jupiter’s atmosphere, but now on an extrasolar world.

  6. a Faint and Lonely Brown Dwarf in the Solar Vicinity

    Science.gov (United States)

    1997-04-01

    identical to other known Brown Dwarfs, its measured characteristics indicate that it must be located at a distance of only 10 parsecs, that is about 33 light-years, from the solar system. Its temperature is obviously below 1700 degrees C (where TiO and VO condense as dust grains [3] so that the spectral lines of these molecules are no longer seen). Its mass can be no more than 75 times that of Jupiter, or 6 percent of that of the Sun. During recent years, several Brown Dwarf candidates have been de-masked as low-mass stars and only recently a few Brown Dwarfs were identified in the Pleiades star cluster. Those Brown Dwarfs are quite young and therefore comparatively hotter and brighter. Contrarily, KELU-1 is most probably somewhat older and its unique location so close to us greatly facilitates future investigations. Moreover, it is not at all `disturbed' by the presence of other objects in its immediate surroundings, as this is the case for all other known objects of this type. It will now be important to obtain accurate measurements of KELU-1's parallax , that is, the small annual change of its position in the sky that is caused by the Earth's motion around the Sun and thus the viewing angle of an Earth-based observer. This should be possible within the next year. Moreover, high resolution spectral investigations with large telescope facilities, soon to include the ESO Very Large Telescope at the Paranal observatory in northern Chile, will now for the first time enable us to investigate the processes that take place in the relatively cold upper layers of Brown Dwarfs. For instance, the observed presence of lithium shows that its atmosphere must be different from that of low-mass stars. KELU-1 and the `Dark Matter' From the fact that KELU-1 is so faint that it was barely detectable on the ESO Schmidt plates, it is possible to estimate that the total volume so far surveyed for this type of objects by this research programme is rather small, only about 23 cubic parsecs (800

  7. An irradiated brown-dwarf companion to an accreting white dwarf

    Science.gov (United States)

    Hernández Santisteban, Juan V.; Knigge, Christian; Littlefair, Stuart P.; Breton, Rene P.; Dhillon, Vikram S.; Gänsicke, Boris T.; Marsh, Thomas R.; Pretorius, Magaretha L.; Southworth, John; Hauschildt, Peter H.

    2016-05-01

    Interacting compact binary systems provide a natural laboratory in which to study irradiated substellar objects. As the mass-losing secondary (donor) in these systems makes a transition from the stellar to the substellar regime, it is also irradiated by the primary (compact accretor). The internal and external energy fluxes are both expected to be comparable in these objects, providing access to an unexplored irradiation regime. The atmospheric properties of donors are largely unknown, but could be modified by the irradiation. To constrain models of donor atmospheres, it is necessary to obtain accurate observational estimates of their physical properties (masses, radii, temperatures and albedos). Here we report the spectroscopic detection and characterization of an irradiated substellar donor in an accreting white-dwarf binary system. Our near-infrared observations allow us to determine a model-independent mass estimate for the donor of 0.055 ± 0.008 solar masses and an average spectral type of L1 ± 1, supporting both theoretical predictions and model-dependent observational constraints that suggest that the donor is a brown dwarf. Our time-resolved data also allow us to estimate the average irradiation-induced temperature difference between the dayside and nightside of the substellar donor (57 kelvin) and the maximum difference between the hottest and coolest parts of its surface (200 kelvin). The observations are well described by a simple geometric reprocessing model with a bolometric (Bond) albedo of less than 0.54 at the 2σ confidence level, consistent with high reprocessing efficiency, but poor lateral heat redistribution in the atmosphere of the brown-dwarf donor. These results add to our knowledge of binary evolution, in that the donor has survived the transition from the stellar to the substellar regime, and of substellar atmospheres, in that we have been able to test a regime in which the irradiation and the internal energy of a brown dwarf are

  8. HST Spectral Mapping of L/T Transition Brown Dwarfs Reveals Cloud Thickness Variations

    CERN Document Server

    Apai, Daniel; Buenzli, Esther; Burrows, Adam; Reid, Iain N; Jayawardhana, Ray

    2013-01-01

    Most directly imaged giant exoplanets are fainter than brown dwarfs with similar spectra. To explain their relative underluminosity unusually cloudy atmospheres have been proposed. However, with multiple parameters varying between any two objects, it remained difficult to observationally test this idea. We present a new method, sensitive time-resolved Hubble Space Telescope near-infrared spectroscopy, to study two rotating L/T transition brown dwarfs (2M2139 and SIMP0136). The observations provide spatially and spectrally resolved mapping of the cloud decks of the brown dwarfs. The data allow the study of cloud structure variations while other parameters are unchanged. We find that both brown dwarfs display variations of identical nature: J- and H-band brightness variations with minimal color and spectral changes. Our light curve models show that even the simplest surface brightness distributions require at least three elliptical spots. We show that for each source the spectral changes can be reproduced with ...

  9. Extending the Canada-France Brown Dwarf Survey to the near infrared

    Directory of Open Access Journals (Sweden)

    Bertin E.

    2011-07-01

    Full Text Available We present the first results of the Canada-France Brown Dwarfs Survey-InfraRed, hereafter CFBDSIR, our near infrared extension to the optical wide field survey CFBDS. Our final objectives are to constrain ultracool atmosphere physics by finding a statistically significant sample of objects cooler than 600K and to explore the ultracool brown dwarf mass function building on a well defined sample of such objects. We identify candidates in CFHT/Wircam J and CFHT/MegaCam z′ images using optimized psf-fitting within Source Extractor, and follow them up with pointed near infrared imaging with SOFI at NTT. We have so far analysed and followed up all candidates on the first 66 square degrees of the 280 square degrees survey. We identified 64 T dwarfs candidates with z′− J > 3.5 and have confirmed 3 of them as ultracool brown dwarfs (later than T7 dwarfs and Y dwarfs candidates, and 14 of them as early and mid-T dwarfs based on their far red and NIR colours. We also present here the NIR spectra of one of these ultracool dwarfs, CFBDSIR1458 which confirms it as one of the coldest brown dwarf known, in the 500–600 K temperature range.

  10. INDICATIONS OF WATER CLOUDS IN THE COLDEST KNOWN BROWN DWARF

    Energy Technology Data Exchange (ETDEWEB)

    Faherty, Jacqueline K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 (United States); Tinney, C. G. [School of Physics, UNSW Australia, Sydney, NSW 2052 (Australia); Skemer, Andrew [Steward Observatory, Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States); Monson, Andrew J., E-mail: jfaherty@ciw.edu [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States)

    2014-09-20

    We present a deep near-infrared image of the newly discovered brown dwarf WISE J085510.83-071442.5 (W0855) using the FourStar imager at Las Campanas Observatory. Our detection of J3 = 24.8{sub −0.35}{sup +0.53} (J {sub MKO} = 25.0{sub −0.35}{sup +0.53}) at 2.6σ—or equivalently an upper limit of J3 > 23.8 (J {sub MKO} > 24.0) at 5σ makes W0855 the reddest brown dwarf ever categorized (J {sub MKO} – W2 = 10.984{sub −0.35}{sup +0.53} at 2.6σ—or equivalently an upper limit of J {sub MKO} – W2 > 9.984 at 5σ) and refines its position on color-magnitude diagrams. Comparing the new photometry with chemical equilibrium model atmosphere predictions, we demonstrate that W0855 is 2.7σ from models using a cloudless atmosphere and well reproduced by partly cloudy models (50%) containing sulfide and water ice clouds. Non-equilibrium chemistry or non-solar metallicity may change predictions, however using currently available model approaches, this is the first candidate outside our own solar system to have direct evidence for water clouds.

  11. An irradiated brown-dwarf companion to an accreting white dwarf

    CERN Document Server

    Santisteban, Juan V Hernández; Littlefair, Stuart P; Breton, Rene P; Dhillon, Vikram S; Gänsicke, Boris T; Marsh, Thomas R; Pretorius, Magaretha L; Southworth, John; Hauschildt, Peter H

    2016-01-01

    Brown dwarfs and giant planets orbiting close to a host star are subjected to significant irradiation that can modify the properties of their atmospheres. In order to test the atmospheric models that are used to describe these systems, it is necessary to obtain accurate observational estimates of their physical properties (masses, radii, temperatures, albedos). Interacting compact binary systems provide a natural laboratory for studying strongly irradiated sub-stellar objects. As the mass-losing secondary in these systems makes a critical, but poorly understood transition from the stellar to the sub-stellar regime, it is also strongly irradiated by the compact accretor. In fact, the internal and external energy fluxes are both expected to be comparable in these objects, providing access to an unexplored irradiation regime. However, the atmospheric properties of such donors have so far remained largely unknown. Here, we report the direct spectroscopic detection and characterisation of an irradiated sub-stellar...

  12. Forming isolated brown dwarfs by turbulent fragmentation

    CERN Document Server

    Lomax, O; Hubber, D A

    2016-01-01

    We use Smoothed Particle Hydrodynamics to explore the circumstances under which an isolated very-low-mass prestellar core can be formed by colliding turbulent flows and collapse to form a brown-dwarf. Our simulations suggest that the flows need not be very fast, but do need to be very strongly convergent, i.e. the gas must flow in at comparable speeds from all sides, which seems rather unlikely. We therefore revisit the object Oph-B11, which Andre, Ward-Thompson and Greaves (2012) have identified as a prestellar core with mass between $\\sim 0.020\\,\\mathrm{M_\\odot}$ and $\\sim 0.030\\,\\mathrm{M_\\odot}$. We reanalyse the observations using a Markov-chain Monte Carlo method that allows us (i) to include the uncertainties on the distance, temperature and dust mass opacity, and (ii) to consider different Bayesian prior distributions of the mass. We estimate that the posterior probability that Oph-B11 has a mass below the hydrogen burning limit at $\\sim 0.075\\,\\mathrm{M_\\odot}$, is between 0.66 and 0.86. We conclude ...

  13. Relation between Brown Dwarfs and Exoplanets

    CERN Document Server

    Torres, Lauren Melissa Flor; Schröeder, Klauss-Peter; Caretta, César A; Jack, Dennis

    2016-01-01

    One of the most debated subjects in Astronomy since the discovery of exoplanets is how can we distinguish the most massive of such objects from very-low mass stars like Brown Dwarfs (BDs)? We have been looking for evidences of a difference in physical characteristics that could be related to different formation processes. Using a new diagnostic diagram that compares the baryonic gravitational potential (BGP) with the distances from their host stars, we have classified a sample of 355 well-studied exoplanets according to their possible structures. We have then compared the exoplanets to a sample of 87 confirmed BDs, identifying a range in BGP that could be common to both objects. By analyzing the mass-radius relations (MRR) of the exoplanets and BDs in those different BGP ranges, we were able to distinguish different characteristic behaviors. By comparing with models in the literature, our results suggest that BDs and massive exoplanets might have similar structures dominated by liquid metallic hydrogen (LMH).

  14. WASP-30b: a 61 Mjup brown dwarf transiting a V=12, F8 star

    CERN Document Server

    Anderson, D R; Hellier, C; Lendl, M; Maxted, P F L; Pollacco, D; Queloz, D; Smalley, B; Smith, A M S; Todd, I; Triaud, A H M J; West, R G; Barros, S C C; Enoch, B; Gillon, M; Lister, T A; Pepe, F; Ségransan, D; Street, R A; Udry, S

    2010-01-01

    We report the discovery of a 61-Jupiter-mass brown dwarf, which transits its F8V, rotationally-synchronised host star, WASP-30, every 4.16 days. From a range of age indicators, we estimate the system age to be 1-2 Gyr. We derive a radius (0.89 \\pm 0.02 RJup) for the companion that is consistent with that predicted (0.914 RJup) by a model of a 1-Gyr-old, non-irradiated brown dwarf with a dusty atmosphere.

  15. The BASS survey for brown dwarfs in young moving groups

    Science.gov (United States)

    Gagne, Jonathan; Lafreniere, David; Doyon, Rene; Malo, Lison; Faherty, Jacqueline K.; Artigau, Etienne; Cruz, Kelle L.; Burgasser, Adam J.; Filippazzo, Joe; Naud, Marie-Eve; Albert, Loic; Bouchard, Sandie; Gizis, John; Robert, Jasmin; Nadeau, Daniel; Bowsher, Emily C.; Nicholls, Christine

    2016-01-01

    I will present in this dissertation talk the construction and follow-up of the BANYAN All-Sky Survey (BASS) that we led to identify dozens of new isolated young brown dwarfs in the Solar neighborhood, several of which have physical properties such as mass, age and temperature that make them similar to exoplanets that were recently discovered using the method of direct imaging.Such isolated analogs of the giant, gaseous exoplanets are precious benchmarks that will allow a deep characterization of their atmospheres using high-resolution and high signal-to-noise spectroscopy, which is made possible due to the absence of a nearby and bright host star.I will end by describing BASS-Ultracool, an extension of BASS that focuses on the identification of extremely cool isolated exoplanet analogs that display methane in their atmospheres. This survey has already uncovered the first bonafide T dwarf member of a moving group, the ~150 Myr AB Doradus T5, SDSS1110+0116.

  16. Can brown dwarfs survive on close orbits around convective stars?

    CERN Document Server

    Damiani, Cilia

    2016-01-01

    Brown dwarfs straddle the mass range transition from planetary to stellar objects. There is a relative paucity of brown dwarfs companions around FGKM stars compared to exoplanets for orbital periods less than a few years, but most of the short-period brown dwarf companions fully characterised by transits and radial velocities are found around F-type stars. We examine the hypothesis that brown dwarf companions could not survive on close orbit around stars with important convective envelopes because the tides and angular momentum loss through magnetic breaking should lead to a rapid orbital decay and quick engulfment of the companion. We use a classical Skumanich-type braking law, and constant time-lag tidal theory to assess the characteristic timescale for orbital decay for the brown dwarf mass range as a function of the host properties. We find that F-type stars may host massive companions for a significantly longer time than G-type stars for a given orbital period, which may explain the paucity of G-type hos...

  17. Herschel survey of brown dwarf disks in Rho Ophiuchi

    CERN Document Server

    de Oliveira, C Alves; Marton, G; Pinte, C; Kiss, Cs; Kun, M; Kóspál, Á; André, Ph; Könyves, V

    2013-01-01

    Recent observations of the Rho Ophiuchi cluster with the Herschel Space Observatory allow us to probe the spectral energy distribution (SED) of the brown dwarf population in the far-IR, where the disk emission peaks. We performed aperture photometry at 70, 100, and 160 micron, and constructed SEDs for all previously known brown dwarfs detected. These were complemented with ancillary photometry at shorter wavelengths. We compared the observed SEDs to a grid of synthetic disks produced with the radiative transfer code MCFOST, and used the relative figure of merit estimated from the Bayesian inference of each disk parameter to analyse the structural properties. We detected 12 Class II brown dwarfs with Herschel, which corresponds to one-third of all currently known brown dwarf members of Rho Ophiuchi. We do not detect any of the known Class III brown dwarfs. Comparison to models reveals that the disks are best described by an inner radius between 0.01 and 0.07 AU, and a flared disk geometry with a flaring index ...

  18. Pulsating Helium Atmosphere White Dwarfs

    Science.gov (United States)

    Provencal, Judith; Montgomery, Michael H.; Bischoff-Kim, Agnes; Shipman, Harry; Nitta, Atsuko; Whole Earth Telescope Collaboration

    2015-08-01

    The overwhelming majority of all stars currently on the main sequence as well as those from earlier generations will or have ended their stellar lives as white dwarf stars. White dwarfs are rich forensic laboratories linking the history and future evolution of our Galaxy. Their structure and atmospheric composition provide evidence of how the progenitors lived, how they evolved, and how they died. This information reveals details of processes governing the behavior of contemporary main sequence stars. Combined with their distribution in luminosity/temperature, white dwarfs strongly constrain models of galactic and cosmological evolution.GD358 is among the brightest (mv =13.7) and best studied of the pulsating white dwarfs. This helium atmoshere pulsator (DBV) has an extensive photometric database spanning 30 years, including nine multisite Whole Earth Telescope campaigns. GD358 exhibits a range of behaviors, from drastic changes in excited pulsation modes to variable multiplet splittings. We use GD358 as a template for an examination of the DBV class, combining photometric results with recent COS spectroscopy. The results present new questions concerning DB formation and evolution.

  19. Can brown dwarfs survive on close orbits around convective stars?

    Science.gov (United States)

    Damiani, C.; Díaz, R. F.

    2016-04-01

    Context. The mass range of brown dwarfs extends across the planetary domain to stellar objects. There is a relative paucity of brown dwarfs companions around FGKM-type stars compared to exoplanets for orbital periods of less than a few years, but most of the short-period brown dwarf companions that are fully characterised by transits and radial velocities are found around F-type stars. Aims: We examine the hypothesis that brown dwarf companions could not survive on close orbit around stars with important convective envelopes because the tides and angular momentum loss, the result of magnetic braking, would lead to a rapid orbital decay with the companion being quickly engulfed. Methods: We use a classical Skumanich-type braking law and constant time-lag tidal theory to assess the characteristic timescale for orbital decay for the brown dwarf mass range as a function of the host properties. Results: We find that F-type stars may host massive companions for a significantly longer time than G-type stars for a given orbital period, which may explain the paucity of G-type hosts for brown dwarfs with an orbital period less than five days. On the other hand, we show that the small radius of early M-type stars contributes to orbital decay timescales that are only half those of F-type stars, despite their more efficient tidal dissipation and magnetic braking. For fully convective later type M-dwarfs, orbital decay timescales could be orders of magnitude greater than for F-type stars. Moreover, we find that, for a wide range of values of tidal dissipation efficiency and magnetic braking, it is safe to assume that orbital decay for massive companions can be neglected for orbital periods greater than ten days. Conclusions: For orbital periods greater than ten days, brown dwarf occurrence should largely be unaffected by tidal decay, whatever the mass of the host. On closer orbital periods, the rapid engulfment of massive companions could explain the lack of G and K-type hosts

  20. On the properties of discs around accreting brown dwarfs

    CERN Document Server

    Mayne, Nathan

    2010-01-01

    We present a grid of models of accreting brown dwarf systems with circumstellar discs. The calculations involve a self-consistent solution of both vertical hydrostatic and radiative equilibrium along with a sophisticated treatment of dust sublimation. We have simulated observations of the spectral energy distributions and several broadband photometric systems. Analysis of the disc structures and simulated observations reveal a natural dichotomy in accretion rates, with \\logmdot $>-$9 and $\\leq -$9 classed as extreme and typical accretors respectively. Derivation of ages and masses from our simulated photometry using isochrones is demonstrated to be unreliable even for typical accretors. Although current brown dwarf disc candidate selection criteria have been shown to be largely reliable when applied to our model grid we suggest improved selection criteria in several colour indices. We show that as accretion rates increase brown dwarf disc systems are less likely to be correctly identified. This suggests that,...

  1. Halo dark clusters of brown dwarfs and molecular clouds

    CERN Document Server

    De Paolis, F; Jetzer, Ph; Roncadelli, M; 10.1086/305692

    2009-01-01

    The discovery of Massive Astrophysical Compact Halo Objects (MACHOs) in microlensing experiments makes it compelling to understand their physical nature, as well as their formation mechanism. Within the present uncertainties, brown dwarfs are a viable candidate for MACHOs, and the present paper deals with this option. According to a recently proposed scenario, brown dwarfs are clumped along with cold molecular clouds into dark clusters -- in several respects similar to globular clusters -- which form in the outer part of the galactic halo. Here, we analyze the dynamics of these dark clusters and we address the possibility that a sizable fraction of MACHOs can be binary brown dwarfs. Moreover, we point out that Ly-$\\alpha$ absorption systems naturally fit within the present picture.

  2. HST SPECTRAL MAPPING OF L/T TRANSITION BROWN DWARFS REVEALS CLOUD THICKNESS VARIATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Apai, Daniel [Department of Astronomy, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Radigan, Jacqueline; Jayawardhana, Ray [Department of Astronomy, University of Toronto, 50 St. George Street, Toronto M5S 3H4 (Canada); Buenzli, Esther [Department of Astronomy and Steward Observatory, 933 N. Cherry Avenue, University of Arizona, Tucson, AZ 85721 (United States); Burrows, Adam [Department of Astrophysical Sciences, 105 Peyton Hall, Princeton University, Princeton, NJ 08544 (United States); Reid, Iain Neill, E-mail: apai@as.arizona.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21212 (United States)

    2013-05-10

    Most directly imaged giant exoplanets are fainter than brown dwarfs with similar spectra. To explain their relative underluminosity, unusually cloudy atmospheres have been proposed. However, with multiple parameters varying between any two objects, it remained difficult to observationally test this idea. We present a new method, sensitive time-resolved Hubble Space Telescope near-infrared spectroscopy, to study two rotating L/T transition brown dwarfs (2M2139 and SIMP0136). The observations provide spatially and spectrally resolved mapping of the cloud decks of the brown dwarfs. The data allow the study of cloud structure variations while other parameters are unchanged. We find that both brown dwarfs display variations of identical nature: J- and H-band brightness variations with minimal color and spectral changes. Our light curve models show that even the simplest surface brightness distributions require at least three elliptical spots. We show that for each source the spectral changes can be reproduced with a linear combination of only two different spectra, i.e., the entire surface is covered by two distinct types of regions. Modeling the color changes and spectral variations together reveal patchy cloud covers consisting of a spatially heterogeneous mix of low-brightness, low-temperature thick clouds and brighter, thin, and warm clouds. We show that the same thick cloud patches seen in our varying brown dwarf targets, if extended to the entire photosphere, predict near-infrared colors/magnitudes matching the range occupied by the directly imaged exoplanets that are cooler and less luminous than brown dwarfs with similar spectral types. This supports the models in which thick clouds are responsible for the near-infrared properties of these ''underluminous'' exoplanets.

  3. Benchmark Transiting Brown Dwarf LHS 6343 C: Spitzer Secondary Eclipse Observations Yield Brightness Temperature and mid-T Spectral Class

    CERN Document Server

    Montet, Benjamin T; Fortney, Jonathan J; Desert, Jean-Michel

    2016-01-01

    There are no field brown dwarf analogs with measured masses, radii, and luminosities, precluding our ability to connect the population of transiting brown dwarfs with measurable masses and radii and field brown dwarfs with measurable luminosities and atmospheric properties. LHS 6343 C, a weakly-irradiated brown dwarf transiting one member of an M+M binary in the Kepler field, provides the first opportunity to probe the atmosphere of a non-inflated brown dwarf with a measured mass and radius. Here, we analyze four Spitzer observations of secondary eclipses of LHS 6343 C behind LHS 6343 A. Jointly fitting the eclipses with a Gaussian process noise model of the instrumental systematics, we measure eclipse depths of 1.06 \\pm 0.21 ppt at 3.6 microns and 2.09 \\pm 0.08 ppt at 4.5 microns, corresponding to brightness temperatures of 1026 \\pm 57 K and 1249 \\pm 36 K, respectively. We then apply brown dwarf evolutionary models to infer a bolometric luminosity log(L_star / L_sun) = -5.16 \\pm 0.04. Given the known physica...

  4. Brown dwarf photospheres are patchy: A Hubble space telescope near-infrared spectroscopic survey finds frequent low-level variability

    International Nuclear Information System (INIS)

    Condensate clouds strongly impact the spectra of brown dwarfs and exoplanets. Recent discoveries of variable L/T transition dwarfs argued for patchy clouds in at least some ultracool atmospheres. This study aims to measure the frequency and level of spectral variability in brown dwarfs and to search for correlations with spectral type. We used Hubble Space Telescope/Wide Field Camera 3 to obtain spectroscopic time series for 22 brown dwarfs of spectral types ranging from L5 to T6 at 1.1-1.7 μm for ≈40 minutes per object. Using Bayesian analysis, we find six brown dwarfs with confident (p > 95%) variability in the relative flux in at least one wavelength region at sub-percent precision, and five brown dwarfs with tentative (p > 68%) variability. We derive a minimum variability fraction fmin=27−7+11% over all covered spectral types. The fraction of variables is equal within errors for mid-L, late-L, and mid-T spectral types; for early-T dwarfs we do not find any confident variable but the sample is too small to derive meaningful limits. For some objects, the variability occurs primarily in the flux peak in the J or H band, others are variable throughout the spectrum or only in specific absorption regions. Four sources may have broadband peak-to-peak amplitudes exceeding 1%. Our measurements are not sensitive to very long periods, inclinations near pole-on and rotationally symmetric heterogeneity. The detection statistics are consistent with most brown dwarf photospheres being patchy. While multiple-percent near-infrared variability may be rare and confined to the L/T transition, low-level heterogeneities are a frequent characteristic of brown dwarf atmospheres.

  5. Brown dwarf photospheres are patchy: A Hubble space telescope near-infrared spectroscopic survey finds frequent low-level variability

    Energy Technology Data Exchange (ETDEWEB)

    Buenzli, Esther; Apai, Dániel [Department of Astronomy and Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Radigan, Jacqueline; Reid, I. Neill [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Flateau, Davin, E-mail: ebuenzli@email.arizona.edu [Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)

    2014-02-20

    Condensate clouds strongly impact the spectra of brown dwarfs and exoplanets. Recent discoveries of variable L/T transition dwarfs argued for patchy clouds in at least some ultracool atmospheres. This study aims to measure the frequency and level of spectral variability in brown dwarfs and to search for correlations with spectral type. We used Hubble Space Telescope/Wide Field Camera 3 to obtain spectroscopic time series for 22 brown dwarfs of spectral types ranging from L5 to T6 at 1.1-1.7 μm for ≈40 minutes per object. Using Bayesian analysis, we find six brown dwarfs with confident (p > 95%) variability in the relative flux in at least one wavelength region at sub-percent precision, and five brown dwarfs with tentative (p > 68%) variability. We derive a minimum variability fraction f{sub min}=27{sub −7}{sup +11}% over all covered spectral types. The fraction of variables is equal within errors for mid-L, late-L, and mid-T spectral types; for early-T dwarfs we do not find any confident variable but the sample is too small to derive meaningful limits. For some objects, the variability occurs primarily in the flux peak in the J or H band, others are variable throughout the spectrum or only in specific absorption regions. Four sources may have broadband peak-to-peak amplitudes exceeding 1%. Our measurements are not sensitive to very long periods, inclinations near pole-on and rotationally symmetric heterogeneity. The detection statistics are consistent with most brown dwarf photospheres being patchy. While multiple-percent near-infrared variability may be rare and confined to the L/T transition, low-level heterogeneities are a frequent characteristic of brown dwarf atmospheres.

  6. Variability of Two Young L/T Transition Brown Dwarfs

    Science.gov (United States)

    Allers, Katelyn; Biller, Beth; Gallimore, Jack; Crossfield, Ian

    2015-10-01

    We propose for photometric monitoring observations of WISEP J004701.06+680352 (hereinafter W0047) and 2MASSWJ2244316+204343 (hereinafter 2M2244) using Spitzer/IRAC. Both objects are kinematically confirmed L7 members of the 150 Myr old AB Doradus moving group and show remarkable spectral similarity in both the near-IR and optical. The WoW survey found that L/T transition brown dwarfs having detected mid-IR variability are redder than the typical J - K color for their spectral type. A Cycle 11 exploration program (P.I. Metchev) is investigating the geometrical dependence of color and variability by expanding the original WoW sample. If inclination and J - K color are correlated (as predicted by Metchev et al.), then the spectral and photometric diversity seen across the L/T transition could be explained by geometry rather than diversity in atmospheric chemistry and dynamics. This would have wide ranging implications for the way we model cloud dissipation for brown dwarfs and extrasolar planets. Our proposed observations will provide an important test of the Metchev et al. prediction complementary to their Cycle 11 program. W0047 and 2M2244 are the same age, and have remarkably similar colors (J - K = 2.55 and 2.46 mags, respectively) and underlying spectra. Thus, if Metchev's prediction about the correlation of inclination and spectral morphology holds true, we would expect that W0047 and 2M2244 should have similar inclinations. However, the measured v sin(i) values for W0047 and 2M2244 are quite different. This difference in v sin(i) could be due to spin-axis inclination (with W0047 having a smaller i) or orbital period (with W0047 having a longer period), both of which we will determine from our proposed observations. This test is a unique opportunity, as there are no other free-floating L/T transition dwarfs known to be both coeval and spectrally similar. Our proposed observations will also extend the spectral type range for young objects surveyed for variability

  7. Fundmental Parameters of Low-Mass Stars, Brown Dwarfs, and Planets

    Science.gov (United States)

    Montet, Benjamin; Johnson, John A.; Bowler, Brendan; Shkolnik, Evgenya

    2016-01-01

    Despite advances in evolutionary models of low-mass stars and brown dwarfs, these models remain poorly constrained by observations. In order to test these predictions directly, masses of individual stars must be measured and combined with broadband photometry and medium-resolution spectroscopy to probe stellar atmospheres. I will present results from an astrometric and spectroscopic survey of low-mass pre-main sequence binary stars to measure individual dynamical masses and compare to model predictions. This is the first systematic test of a large number of stellar systems of intermediate age between young star-forming regions and old field stars. Stars in our sample are members of the Tuc-Hor, AB Doradus, and beta Pictoris moving groups, the last of which includes GJ 3305 AB, the wide binary companion to the imaged exoplanet host 51 Eri. I will also present results of Spitzer observations of secondary eclipses of LHS 6343 C, a T dwarf transiting one member of an M+M binary in the Kepler field. By combining these data with Kepler photometry and radial velocity observations, we can measure the luminosity, mass, and radius of the brown dwarf. This is the first non-inflated brown dwarf for which all three of these parameters have been measured, providing the first benchmark to test model predictions of the masses and radii of field T dwarfs. I will discuss these results in the context of K2 and TESS, which will find additional benchmark transiting brown dwarfs over the course of their missions, including a description of the first planet catalog developed from K2 data and a program to search for transiting planets around mid-M dwarfs.

  8. Flash ionization signature in coherent cyclotron emission from brown dwarfs

    Science.gov (United States)

    Vorgul, I.; Helling, Ch.

    2016-05-01

    Brown dwarfs (BDs) form mineral clouds in their atmospheres, where charged particles can produce large-scale discharges in the form of lightning resulting in substantial sudden increase of local ionization. BDs are observed to emit cyclotron radio emission. We show that signatures of strong transient atmospheric ionization events (flash ionization) can be imprinted on a pre-existing radiation. Detection of such flash ionization events will open investigations into the ionization state and atmospheric dynamics. Such events can also result from explosion shock waves, material outbursts or (volcanic) eruptions. We present an analytical model that describes the modulation of a pre-existing electromagnetic radiation by a time-dependent (flash) conductivity that is characteristic for flash ionization events like lightning. Our conductivity model reproduces the conductivity function derived from observations of terrestrial gamma-ray flashes, and is applicable to astrophysical objects with strong temporal variations in the local ionization, as in planetary atmospheres and protoplanetary discs. We show that the field responds with a characteristic flash-shaped pulse to a conductivity flash of intermediate intensity. More powerful ionization events result in smaller variations of the initial radiation, or in its damping. We show that the characteristic damping of the response field for high-power initial radiation carries information about the ionization flash magnitude and duration. The duration of the pulse amplification or the damping is consistently shorter for larger conductivity variations and can be used to evaluate the intensity of the flash ionization. Our work suggests that cyclotron emission could be probe signals for electrification processes inside BD atmosphere.

  9. Brown Dwarf Photospheres are Patchy: A Hubble Space Telescope Near-infrared Spectroscopic Survey Finds Frequent Low-level Variability

    CERN Document Server

    Buenzli, Esther; Radigan, Jacqueline; Reid, I Neill; Flateau, Davin

    2013-01-01

    Condensate clouds strongly impact the spectra of brown dwarfs and exoplanets. Recent discoveries of variable L/T transition dwarfs argued for patchy clouds in at least some ultracool atmospheres. This study aims to measure the frequency and level of spectral variability in brown dwarfs and to search for correlations with spectral type. We used HST/WFC3 to obtain spectroscopic time series for 22 brown dwarfs of spectral types ranging from L5 to T6 at 1.1-1.7 $\\mu$m for $\\approx$40 min per object. Using Bayesian analysis, we find 6 brown dwarfs with confident $(p>95\\%)$ variability in the relative flux in at least one wavelength region at sub-percent precision, and 5 brown dwarfs with tentative $(p>68\\%)$ variability. We derive a minimum variability fraction $f_{min}=27^{+11}_{-7}\\%$ over all covered spectral types. The fraction of variables is equal within errors for mid L, late L and mid T spectral types; for early T dwarfs we do not find any confident variable but the sample is too small to derive meaningful...

  10. The First Ultra-Cool Brown Dwarf Discovered by the Wide-field Infrared Survey Explorer

    CERN Document Server

    Mainzer, A; Skrutskie, M; Gelino, C R; Kirkpatrick, J Davy; Jarrett, T; Masci, F; Marley, M; Saumon, D; Wright, E; Beaton, R; Dietrich, M; Eisenhardt, P; Garnavich, P; Kuhn, O; Leisawitz, D; Marsh, K; McLean, I; Padgett, D; Rueff, K

    2010-01-01

    We report the discovery of the first new ultra-cool brown dwarf found with the Wide-field Infrared Survey Explorer (WISE). The object's preliminary designation is WISEPC J045853.90+643451.9. Follow-up spectroscopy with the LUCIFER instrument on the Large Binocular Telescope indicates that it is a very late-type T dwarf with a spectral type approximately equal to T9. Fits to an IRTF/SpeX 0.8-2.5 micron spectrum to the model atmospheres of Marley and Saumon indicate an effective temperature of approximately 600 K as well as the presence of vertical mixing in its atmosphere. The new brown dwarf is easily detected by WISE, with a signal-to-noise ratio of ~36 at 4.6 microns. Current estimates place it at a distance of 6 to 10 pc. This object represents the first in what will likely be hundreds of nearby brown dwarfs found by WISE that will be suitable for follow up observations, including those with the James Webb Space Telescope. One of the two primary scientific goals of the WISE mission is to find the coolest, ...

  11. Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets

    CERN Document Server

    Zahnle, Kevin J

    2014-01-01

    We address disequilibrum abundances of some simple molecules in the atmospheres of solar composition brown dwarfs and self-luminous extrasolar giant planets using a kinetics-based 1D atmospheric chemistry model. We employ cloudless atmospheres of approximately solar metallicity. Our approach is to use the complete model to survey the parameter space with effective temperatures between 500 K and 1100 K. In all of these worlds equilibrium chemistry favors CH4 over CO in the parts of the atmosphere that can be seen from Earth. Small surface gravity of planets strongly discriminates against CH4 when compared to an otherwise comparable brown dwarf. If vertical mixing is comparable to Jupiter's, methane becomes more abundant than CO in Jupiter-mass planets cooler than 500 K. Sluggish vertical mixing can raise this threshold to 600 K; but clouds or more vigorous vertical mixing could lower this threshold to 400 K. The comparable threshold in brown dwarfs is 1100 K. Ammonia is also sensitive to gravity, but unlike CH...

  12. Lightning climatology of exoplanets and brown dwarfs guided by Solar System data

    CERN Document Server

    Hodosán, Gabriella; Asensio-Torres, Rubén; Vorgul, Irena; Rimmer, Paul B

    2016-01-01

    Clouds form on extrasolar planets and brown dwarfs where lightning could occur. Lightning is a tracer of atmospheric convection, cloud formation and ionization processes as known from the Solar System, and may be significant for the formation of prebiotic molecules. We study lightning climatology for the different atmospheric environments of Earth, Venus, Jupiter and Saturn. We present lightning distribution maps for Earth, Jupiter and Saturn, and flash densities for these planets and Venus, based on optical and/or radio measurements from the WWLLN and STARNET radio networks, the LIS/OTD satellite instruments, the Galileo, Cassini, New Horizons and Venus Express spacecraft. We also present flash densities calculated for several phases of two volcano eruptions, Eyjafjallaj\\"okull's (2010) and Mt Redoubt's (2009). We estimate lightning rates for sample, transiting and directly imaged extrasolar planets and brown dwarfs. Based on the large variety of exoplanets, six categories are suggested for which we use the ...

  13. Using Narrow Band Photometry to Classify Stars and Brown Dwarfs

    CERN Document Server

    Mainzer, A K; Sievers, J L; Young, E T; Lean, Ian S. Mc

    2004-01-01

    We present a new system of narrow band filters in the near infrared that can be used to classify stars and brown dwarfs. This set of four filters, spanning the H band, can be used to identify molecular features unique to brown dwarfs, such as H2O and CH4. The four filters are centered at 1.495 um (H2O), 1.595 um (continuum), 1.66 um (CH4), and 1.75 um (H2O). Using two H2O filters allows us to solve for individual objects' reddenings. This can be accomplished by constructing a color-color-color cube and rotating it until the reddening vector disappears. We created a model of predicted color-color-color values for different spectral types by integrating filter bandpass data with spectra of known stars and brown dwarfs. We validated this model by making photometric measurements of seven known L and T dwarfs, ranging from L1 - T7.5. The photometric measurements agree with the model to within +/-0.1 mag, allowing us to create spectral indices for different spectral types. We can classify A through early M stars to...

  14. A non-uniform distribution of the nearest brown dwarfs

    CERN Document Server

    Bihain, G

    2016-01-01

    The census of solar neighbours is still complemented by new discoveries, mainly of very low-mass, faint dwarfs, close to or within the substellar domain. These discoveries contribute to a better understanding of the field population; its origin in terms of Galactic dynamics and (sub)stellar formation and evolution. Also, the nearest stars and brown dwarfs at any given age allow the most precise direct characterization, including the search for planetary companions. We aim to further assess the substellar census on the Galactic plane. We projected the 136 stars and 26 brown dwarfs known at <6.5 pc on the Galactic plane and evaluated their distributions. Stars present a uniform- and brown dwarfs a non-uniform distribution, with 21 objects behind the Sun and only five ahead relative to the direction of rotation of the Galaxy. This substellar configuration has a probability of 0.098$^{+10.878}_{-0.098}$% relative to uniformity. The helio- and geocentric nature of the distribution suggests it might result in pa...

  15. The atomic and molecular content of disks around very low-mass stars and brown dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Pascucci, I. [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Herczeg, G. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Carr, J. S. [Naval Research Laboratory, Code 7211, Washington, DC 20375 (United States); Bruderer, S., E-mail: pascucci@lpl.arizona.edu [Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, D-85748 Garching (Germany)

    2013-12-20

    There is growing observational evidence that disk evolution is stellar-mass-dependent. Here, we show that these dependencies extend to the atomic and molecular content of disk atmospheres. We analyze a unique dataset of high-resolution Spitzer/IRS spectra from eight very low mass star and brown dwarf disks. We report the first detections of Ne{sup +}, H{sub 2}, CO{sub 2}, and tentative detections of H{sub 2}O toward these faint and low-mass disks. Two of our [Ne II] 12.81 μm emission lines likely trace the hot (≥5000 K) disk surface irradiated by X-ray photons from the central stellar/sub-stellar object. The H{sub 2} S(2) and S(1) fluxes are consistent with arising below the fully or partially ionized surface traced by the [Ne II] emission in gas at ∼600 K. We confirm the higher C{sub 2}H{sub 2}/HCN flux and column density ratio in brown dwarf disks previously noted from low-resolution IRS spectra. Our high-resolution spectra also show that the HCN/H{sub 2}O fluxes of brown dwarf disks are on average higher than those of T Tauri disks. Our LTE modeling hints that this difference extends to column density ratios if H{sub 2}O lines trace warm ≥600 K disk gas. These trends suggest that the inner regions of brown dwarf disks have a lower O/C ratio than those of T Tauri disks, which may result from a more efficient formation of non-migrating icy planetesimals. An O/C = 1, as inferred from our analysis, would have profound implications on the bulk composition of rocky planets that can form around very low mass stars and brown dwarfs.

  16. Methane, carbon monoxide, and ammonia in brown dwarfs and self-luminous giant planets

    International Nuclear Information System (INIS)

    We address disequilibrium abundances of some simple molecules in the atmospheres of solar composition brown dwarfs and self-luminous extrasolar giant planets using a kinetics-based one-dimensional atmospheric chemistry model. Our approach is to use the full kinetics model to survey the parameter space with effective temperatures between 500 K and 1100 K. In all of these worlds, equilibrium chemistry favors CH4 over CO in the parts of the atmosphere that can be seen from Earth, but in most disequilibrium favors CO. The small surface gravity of a planet strongly discriminates against CH4 when compared to an otherwise comparable brown dwarf. If vertical mixing is like Jupiter's, the transition from methane to CO occurs at 500 K in a planet. Sluggish vertical mixing can raise this to 600 K, but clouds or more vigorous vertical mixing could lower this to 400 K. The comparable thresholds in brown dwarfs are 1100 ± 100 K. Ammonia is also sensitive to gravity, but, unlike CH4/CO, the NH3/N2 ratio is insensitive to mixing, which makes NH3 a potential proxy for gravity. HCN may become interesting in high-gravity brown dwarfs with very strong vertical mixing. Detailed analysis of the CO-CH4 reaction network reveals that the bottleneck to CO hydrogenation goes through methanol, in partial agreement with previous work. Simple, easy to use quenching relations are derived by fitting to the complete chemistry of the full ensemble of models. These relations are valid for determining CO, CH4, NH3, HCN, and CO2 abundances in the range of self-luminous worlds we have studied, but may not apply if atmospheres are strongly heated at high altitudes by processes not considered here (e.g., wave breaking).

  17. Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets

    Science.gov (United States)

    Zahnle, Kevin J.; Marley, Mark S.

    2014-12-01

    We address disequilibrium abundances of some simple molecules in the atmospheres of solar composition brown dwarfs and self-luminous extrasolar giant planets using a kinetics-based one-dimensional atmospheric chemistry model. Our approach is to use the full kinetics model to survey the parameter space with effective temperatures between 500 K and 1100 K. In all of these worlds, equilibrium chemistry favors CH4 over CO in the parts of the atmosphere that can be seen from Earth, but in most disequilibrium favors CO. The small surface gravity of a planet strongly discriminates against CH4 when compared to an otherwise comparable brown dwarf. If vertical mixing is like Jupiter's, the transition from methane to CO occurs at 500 K in a planet. Sluggish vertical mixing can raise this to 600 K, but clouds or more vigorous vertical mixing could lower this to 400 K. The comparable thresholds in brown dwarfs are 1100 ± 100 K. Ammonia is also sensitive to gravity, but, unlike CH4/CO, the NH3/N2 ratio is insensitive to mixing, which makes NH3 a potential proxy for gravity. HCN may become interesting in high-gravity brown dwarfs with very strong vertical mixing. Detailed analysis of the CO-CH4 reaction network reveals that the bottleneck to CO hydrogenation goes through methanol, in partial agreement with previous work. Simple, easy to use quenching relations are derived by fitting to the complete chemistry of the full ensemble of models. These relations are valid for determining CO, CH4, NH3, HCN, and CO2 abundances in the range of self-luminous worlds we have studied, but may not apply if atmospheres are strongly heated at high altitudes by processes not considered here (e.g., wave breaking).

  18. Exploration of the brown dwarf regime around solar-like stars by CoRoT

    CERN Document Server

    Csizmadia, Szilárd

    2016-01-01

    Aims. A summary of the CoRoT brown dwarf investigations are presented. Methods. Transiting brown dwarfs around solar like stars were studied by using the photometric time-series of CoRoT, and ground based radial velocity measurements. Results. CoRoT detected three transiting brown dwarfs around F and G dwarf stars. The occurence rate of brown dwarfs was found to be 0.20 +/- 0.15% around solar-like stars which is compatible with the value obtained by Kepler-data.

  19. A KECK LGS AO SEARCH FOR BROWN DWARF AND PLANETARY MASS COMPANIONS TO UPPER SCORPIUS BROWN DWARFS

    International Nuclear Information System (INIS)

    We searched for binary companions to 20 young brown dwarfs in the Upper Scorpius association (145 pc, 5 Myr, nearest OB association) with the Laser Guide Star adaptive optics system and the facility infrared camera NIRC2 on the 10 m Keck II telescope. We discovered a 0.''14 companion (20.9 ± 0.4 AU) to the sun object SCH J16091837-20073523. From spectral deconvolution of integrated-light near-IR spectroscopy of SCH1609 using the SpeX spectrograph (Rayner et al. 2003), we estimate primary and secondary spectral types of M6 ± 0.5 and M7 ± 1.0, corresponding to masses of 79 ± 17 MJup and 55 ± 25 MJup at an age of 5 Myr and masses of 84 ± 15 MJup and 60 ± 25 MJup at an age of 10 Myr. For our survey objects with spectral types later than M8, we find an upper limit on the binary fraction of Jup) brown dwarfs in Upper Sco is similar to that for T dwarfs in the field; for higher mass brown dwarfs and very low mass stars, there is an excess of medium-separation (10-50 AU projected separation) young binaries with respect to the field. These medium-separation binaries will likely survive to late ages.

  20. A white dwarf with an oxygen atmosphere.

    Science.gov (United States)

    Kepler, S O; Koester, Detlev; Ourique, Gustavo

    2016-04-01

    Stars born with masses below around 10 solar masses end their lives as white dwarf stars. Their atmospheres are dominated by the lightest elements because gravitational diffusion brings the lightest element to the surface. We report the discovery of a white dwarf with an atmosphere completely dominated by oxygen, SDSS J124043.01+671034.68. After oxygen, the next most abundant elements in its atmosphere are neon and magnesium, but these are lower by a factor of ≥25 by number. The fact that no hydrogen or helium are observed is surprising. Oxygen, neon, and magnesium are the products of carbon burning, which occurs in stars at the high-mass end of pre-white dwarf formation. This star, a possible oxygen-neon white dwarf, will provide a rare observational test of the evolutionary paths toward white dwarfs. PMID:27034367

  1. A white dwarf with an oxygen atmosphere

    Science.gov (United States)

    Kepler, S. O.; Koester, Detlev; Ourique, Gustavo

    2016-04-01

    Stars born with masses below around 10 solar masses end their lives as white dwarf stars. Their atmospheres are dominated by the lightest elements because gravitational diffusion brings the lightest element to the surface. We report the discovery of a white dwarf with an atmosphere completely dominated by oxygen, SDSS J124043.01+671034.68. After oxygen, the next most abundant elements in its atmosphere are neon and magnesium, but these are lower by a factor of ≥25 by number. The fact that no hydrogen or helium are observed is surprising. Oxygen, neon, and magnesium are the products of carbon burning, which occurs in stars at the high-mass end of pre-white dwarf formation. This star, a possible oxygen-neon white dwarf, will provide a rare observational test of the evolutionary paths toward white dwarfs.

  2. OGLE-2014-BLG-0257L: A Microlensing Brown Dwarf Orbiting a Low-mass M Dwarf

    CERN Document Server

    Han, C; Udalski, A; Gould, A; Bozza, V; Szymański, M K; Soszyński, I; Poleski, R; Kozłowski, S; Pietrukowicz, P; Skowron, J; Ulaczyk, K; Wyrzykowski, Ł

    2016-01-01

    In this paper, we report the discovery of a binary composed of a brown dwarf and a low-mass M dwarf from the observation of the microlensing event OGLE-2014-BLG-0257. Resolution of the very short-lasting caustic crossing combined with the detection of subtle continuous deviation in the lensing light curve induced by the Earth's orbital motion enable us to precisely measure both the Einstein radius \\theta_E and the lens parallax pi_E, which are the two quantities needed to unambiguously determine the mass and distance to the lens. It is found that the companion is a substellar brown dwarf with a mass 0.036 +/- 0.005 Msun (37.7 +/- 5.2\\ M_J) and it is orbiting an M dwarf with a mass 0.19 +/- 0.02 Msun. The binary is located at a distance 1.25 +/- 0.13 kpc toward the Galactic bulge and the projected separation between the binary components is 0.61 +/- 0.07 AU. The separation scaled by the mass of the host is 3.2 AU/Msun. Under the assumption that separations scale with masses, then, the discovered brown dwarf is...

  3. How Dry is the Brown Dwarf Desert?: Quantifying the Relative Number of Planets, Brown Dwarfs and Stellar Companions around Nearby Sun-like Stars

    CERN Document Server

    Grether, D; Grether, Daniel; Lineweaver, Charles H.

    2004-01-01

    Sun-like stars have stellar, brown dwarf and planetary companions. To help constrain their formation and migration scenarios, we analyse the close companions (orbital period 2 M_Solar respectively. However, we find no evidence that companion mass scales with host mass in general. Approximately 16% of Sun-like stars have close (P < 5 years) companions more massive than Jupiter: 11% are stellar, 1% are brown dwarf and 4% are giant planets. The companion mass function in the brown dwarf and stellar mass range, has a different shape than the initial mass function of individual stars and free-floating brown dwarfs. This suggests either a different spectrum of gravitational fragmentation in the formation environment or post-formation migratory processes disinclined to leave brown dwarfs in close orbits.

  4. DISCOVERY OF A WIDE BINARY BROWN DWARF BORN IN ISOLATION

    International Nuclear Information System (INIS)

    During a survey for stars with disks in the Taurus star-forming region using the Spitzer Space Telescope, we have discovered a pair of young brown dwarfs, FU Tau A and B, in the Barnard 215 dark cloud. They have a projected angular separation of 5.''7, corresponding to 800 AU at the distance of Taurus. To assess the nature of these two objects, we have obtained spectra of them and constructed spectral energy distributions. Both sources are young (∼1 Myr) according to their Hα emission, gravity-sensitive spectral features, and mid-infrared excess emission. The proper motion of FU Tau A provides additional evidence of its membership in Taurus. We measure spectral types of M7.25 and M9.25 for FU Tau A and B, respectively, which correspond to masses of ∼0.05 and ∼0.015 Msun according to the evolutionary models of Chabrier and Baraffe. FU Tau A is significantly overluminous relative to an isochrone passing through FU Tau B and relative to other members of Taurus near its spectral type, which may indicate that it is an unresolved binary. FU Tau A and B are likely to be components of a binary system based on the low probability (∼3 x 10-4) that Taurus would produce two unrelated brown dwarfs with a projected separation of a ≤ 6''. Barnard 215 contains only one other young star and is in a remote area of Taurus, making FU Tau A and B the first spectroscopically confirmed brown dwarfs discovered forming in isolation rather than in a stellar cluster or aggregate. Because they were born in isolation and comprise a weakly bound binary, dynamical interactions with stars could not have played a role in their formation, and thus are not essential for the birth of brown dwarfs.

  5. Planetesimals to brown dwarfs: What is a planet?

    OpenAIRE

    Basri, Gibor; Brown, Michael E.

    2006-01-01

    The past 15 years have brought about a revolution in our understanding of our Solar System and other planetary systems. During this time, discoveries include the first Kuiper Belt Objects, the first brown dwarfs, and the first extra-solar planets. Although discoveries continue apace, they have called into question our previous perspectives on planets, both here and elsewhere. The result has been a debate about the meaning of the word ''planet'' itself. It became clear that scientists do not h...

  6. The disk around the brown dwarf KPNO Tau 3

    Energy Technology Data Exchange (ETDEWEB)

    Broekhoven-Fiene, Hannah; Matthews, Brenda; Di Francesco, James [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P6 (Canada); Duchêne, Gaspard [Department of Astronomy, University of California at Berkeley, Hearst Field Annex, B-20, Berkeley, CA 94720-3411 (United States); Scholz, Aleks [School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS (United Kingdom); Chrysostomou, Antonio [Joint Astronomy Centre, 660 North Aóhoku Place, University Park, Hilo, HI 96720 (United States); Jayawardhana, Ray [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada)

    2014-07-10

    We present submillimeter observations of the young brown dwarfs KPNO Tau 1, KPNO Tau 3, and KPNO Tau 6 at 450 μm and 850 μm taken with the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. KPNO Tau 3 and KPNO Tau 6 have been previously identified as Class II objects hosting accretion disks, whereas KPNO Tau 1 has been identified as a Class III object and shows no evidence of circumsubstellar material. Our 3σ detection of cold dust around KPNO Tau 3 implies a total disk mass of (4.0 ± 1.1) × 10{sup –4} M{sub ☉} (assuming a gas to dust ratio of 100:1). We place tight constraints on any disks around KPNO Tau 1 or KPNO Tau 6 of <2.1 × 10{sup –4} M{sub ☉} and <2.7 × 10{sup –4} M{sub ☉}, respectively. Modeling the spectral energy distribution of KPNO Tau 3 and its disk suggests the disk properties (geometry, dust mass, and grain size distribution) are consistent with observations of other brown dwarf disks and low-mass T-Tauri stars. In particular, the disk-to-host mass ratio for KPNO Tau 3 is congruent with the scenario that at least some brown dwarfs form via the same mechanism as low-mass stars.

  7. Epsilon Indi Ba/Bb: the nearest binary brown dwarf

    CERN Document Server

    McCaughrean, M J; Scholz, R D; Lenzen, R; Biller, B; Brandner, W; Hartung, M; Lodieu, N

    2004-01-01

    We have carried out high angular resolution near-infrared imaging and low-resolution (R~1000) spectroscopy of the nearest known brown dwarf, Eps Indi B, using the ESO VLT NAOS/CONICA adaptive optics system. We find it to be a close binary with an angular separation of 0.732 arcsec, corresponding to 2.65AU at the 3.626pc distance of the Eps Indi system, as also noted by Volk et al. (2003). In our discovery paper (Scholz et al. 2003), we concluded that Eps Indi B was a ~50Mjup T2.5 dwarf: our revised finding is that the two system components (Eps Indi Ba and Eps Indi Bb) have spectral types of T1 and T6, respectively, and estimated masses of 44 and 28Mjup, respectively, assuming an age of 1.3Gyr. Errors in the masses are +/-10 and +/-7Mjup, respectively, dominated by the uncertainty in the age determination (0.8-2Gyr range). This uniquely well-characterised T dwarf binary system should prove important in the study of low-mass, cool brown dwarfs. The two components are bright and relatively well-resolved: it is ...

  8. A Signature of Chromospheric Activity in Brown Dwarfs Revealed by 2.5-5.0 Micron AKARI Spectra

    CERN Document Server

    Sorahana, Satoko; Yamamura, Issei

    2014-01-01

    We propose that the 2.7 micron H_2O, 3.3 micron CH_4 and 4.6 micron CO absorption bands can be good tracers of chromospheric activity in brown dwarfs. In our previous study, we found that there are difficulties in explaining entire spectra between 1.0 and 5.0 microns with the Unified Cloudy Model (UCM), a brown dwarf atmosphere model. Based on simple radiative equilibrium, temperature in a model atmosphere usually decreases monotonically with height. However, if a brown dwarf has a chromosphere, as inferred by some observations, the temperature in the upper atmosphere is higher. We construct a simple model that takes into account heating due to chromospheric activity by setting a temperature floor in an upper atmosphere, and find that the model spectra of 3 brown dwarfs with moderate H-alpha emission, an indicator of chromospheric activity, are considerably improved to match the AKARI spectra. Because of the higher temperatures in the upper atmospheres, the amount of CH_4 molecules is reduced and the absorpti...

  9. Spitzer and z' secondary eclipse observations of the highly irradiated transiting brown dwarf KELT-1b

    Energy Technology Data Exchange (ETDEWEB)

    Beatty, Thomas G.; Gaudi, B. Scott [Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States); Collins, Karen A.; Kielkopf, John F. [Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292 (United States); Fortney, Jonathan [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Knutson, Heather [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Bruns, Jacob M. [Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States); Showman, Adam P. [Lunar and Planetary Laboratory, 1629 E. University Blvd., University of Arizona, Tucson, AZ (United States); Eastman, Jason [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Santa Barbara, CA 93117 (United States); Pepper, Joshua [Department of Physics, Lehigh University, Bethlehem, PA 18015 (United States); Siverd, Robert J.; Stassun, Keivan G., E-mail: tbeatty@astronomy.ohio-state.edu [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States)

    2014-03-10

    We present secondary eclipse observations of the highly irradiated transiting brown dwarf KELT-1b. These observations represent the first constraints on the atmospheric dynamics of a highly irradiated brown dwarf, the atmospheres of irradiated giant planets at high surface gravity, and the atmospheres of brown dwarfs that are dominated by external, rather than internal, energy. Using the Spitzer Space Telescope, we measure secondary eclipse depths of 0.195% ± 0.010% at 3.6 μm and 0.200% ± 0.012% at 4.5 μm. We also find tentative evidence for the secondary eclipse in the z' band with a depth of 0.049% ± 0.023%. These measured eclipse depths are most consistent with an atmosphere model in which there is a strong substellar hotspot, implying that heat redistribution in the atmosphere of KELT-1b is low. While models with a more mild hotspot or even with dayside heat redistribution are only marginally disfavored, models with complete heat redistribution are strongly ruled out. The eclipse depths also prefer an atmosphere with no TiO inversion layer, although a model with TiO inversion is permitted in the dayside heat redistribution case, and we consider the possibility of a day-night TiO cold trap in this object. For the first time, we compare the IRAC colors of brown dwarfs and hot Jupiters as a function of effective temperature. Importantly, our measurements reveal that KELT-1b has a [3.6] – [4.5] color of 0.07 ± 0.11, identical to that of isolated brown dwarfs of similarly high temperature. In contrast, hot Jupiters generally show redder [3.6] – [4.5] colors of ∼0.4, with a very large range from ∼0 to ∼1. Evidently, despite being more similar to hot Jupiters than to isolated brown dwarfs in terms of external forcing of the atmosphere by stellar insolation, KELT-1b appears to have an atmosphere most like that of other brown dwarfs. This suggests that surface gravity is very important in controlling the atmospheric systems of substellar mass bodies.

  10. A Brown Dwarf Joins the Jet-Set

    Science.gov (United States)

    2007-05-01

    Jets of matter have been discovered around a very low mass 'failed star', mimicking a process seen in young stars. This suggests that these 'brown dwarfs' form in a similar manner to normal stars but also that outflows are driven out by objects as massive as hundreds of millions of solar masses down to Jupiter-sized objects. The brown dwarf with the name 2MASS1207-3932 is full of surprises [1]. Its companion, a 5 Jupiter-mass giant, was the first confirmed exoplanet for which astronomers could obtain an image (see ESO 23/04 and 12/05), thereby opening a new field of research - the direct detection of alien worlds. It was then later found (see ESO 19/06) that the brown dwarf has a disc surrounding it, not unlike very young stars. ESO PR Photo 24/07 ESO PR Photo 24/07 Jets from a Brown Dwarf (Artist's Impression) Now, astronomers using ESO's Very Large Telescope (VLT) have found that the young brown dwarf is also spewing jets, a behaviour again quite similar to young stars. The mass of the brown dwarf is only 24 Jupiter-masses. Hence, it is by far the smallest object known to drive an outflow. "This leads us to the tantalizing prospect that young giant planets could also be associated with outflows," says Emma Whelan, the lead-author of the paper reporting the results. The outflows were discovered using an amazing technique known as spectro-astrometry, based on high resolution spectra taken with UVES on the VLT. Such a technique was required due to the difficulty of the task. While in normal young stars - known as T-Tauri stars for the prototype of their class - the jets are large and bright enough to be seen directly, this is not the case around brown dwarfs: the length scale of the jets, recovered with spectro-astrometry is only about 0.1 arcsecond long, that is, the size of a two Euro coin seen from 40 km away. The jets stretch about 1 billion kilometres and the material is rushing away from the brown dwarf with a speed of a few kilometres per second. The

  11. A Brown Dwarf Census from the SIMP Survey

    CERN Document Server

    Robert, Jasmin; Artigau, Étienne; Lafrenière, David; Nadeau, Daniel; Doyon, René; Malo, Lison; Albert, Loïc; Simard, Corinne; Gagliuffi, Daniella C Bardalez; Burgasser, Adam J

    2016-01-01

    We have conducted a near-infrared (NIR) proper motion survey, the Sondage Infrarouge de Mouvement Propre (SIMP), in order to discover field ultracool dwarfs (UCD) in the solar neighborhood. The survey was conducted by imaging $\\sim28\\%$ of the sky with the Camera PAnoramique Proche-InfraRouge (CPAPIR) both in the southern hemisphere at the Cerro Tololo Inter-American Observatory (CTIO) 1.5-m telescope, and in the northern hemisphere at the Observatoire du Mont-M\\'egantic (OMM) 1.6-m telescope and comparing the source positions from these observations with the Two Micron All-Sky Survey Point Source Catalog (2MASS PSC). Additional color criteria were used to further discriminate unwanted astrophysical sources. We present the results of a NIR spectroscopic follow-up of 169 M, L and T dwarfs. Among the sources discovered are two young field brown dwarfs, six unusually red M and L dwarfs, twenty-five unusually blue M and L dwarfs, two candidate unresolved L+T binaries and twenty-four peculiar UCDs. Additionally, w...

  12. Statistical Properties of Brown Dwarf Companions: Implications for Different Formation Mechanisms

    CERN Document Server

    Ma, Bo

    2013-01-01

    The mass domain where massive extrasolar planets and brown dwarfs overlap is still poorly understood due to the paucity of brown dwarfs orbiting close to solar-type stars, the so-called brown dwarf desert. In this paper we collect all of available data about close brown dwarfs around solar type stars and their host stars from literature and study the demographics of the brown dwarf desert. The data clearly show a short period and a medium mass gap in the brown dwarf period-mass distribution diagram ($ 35brown dwarf desert. Observation biases are highly unlikely to cause this gap due to its short period and medium mass, of which brown dwarfs can be easily detected by previous RV surveys. Brown dwarfs above and below this gap have significantly different eccentricity distribution, which not only confirms that this gap is real, but also implies that they may have different origins. Our further statistical study indicates t...

  13. The Spectral Energy Distribution of the Coldest Known Brown Dwarf

    CERN Document Server

    Luhman, K L

    2016-01-01

    WISE J085510.83-071442.5 (hereafter WISE 0855-0714) is the coldest known brown dwarf (~250 K) and the fourth closest known system to the Sun (2.2 pc). It has been previously detected only in the J band and two mid-IR bands. To better measure its spectral energy distribution (SED), we have performed deep imaging of WISE 0855-0714 in six optical and near-IR bands with Gemini Observatory, the Very Large Telescope, and the Hubble Space Telescope. Five of the bands show detections, although one detection is marginal (S/N~3). We also have obtained two epochs of images with the Spitzer Space Telescope for use in refining the parallax of the brown dwarf. By combining astrometry from this work and previous studies, we have derived a parallax of 0.449+/-0.008" (2.23+/-0.04 pc). We have compared our photometry for WISE 0855-0714 to data for known Y dwarfs and to the predictions of three suites of models by Saumon et al. (2012) and Morley et al. (2012, 2014) that are defined by the presence or absence of clouds and non-e...

  14. Epsilon Indi Ba, Bb: a spectroscopic study of the nearest known brown dwarfs

    CERN Document Server

    King, Robert R; Homeier, Derek; Allard, France; Scholz, Ralf-Dieter; Lodieu, Nicolas

    2008-01-01

    The discovery of Epsilon Indi Ba and Bb, a nearby binary brown dwarf system with a main-sequence companion, allows a concerted campaign to characterise the physical parameters of two T dwarfs providing benchmarks against which atmospheric and evolutionary models can be tested. Some recent observations suggest the models at low mass and intermediate age may not reflect reality with, however, few conclusive tests. We are carrying out a comprehensive characterisation of these, the nearest known brown dwarfs, to allow constraints to be placed upon models of cool field dwarfs. We present broadband photometry from the V- to M-band and the individual spectrum of both components from 0.6-5.1 microns at a resolution of up to R=5000. A custom analytic profile fitting routine was implemented to extract the blended spectra and photometry of both components separated by 0.7 arcsec. We confirm the spectral types to be T1 and T6, and notably, we do not detect lithium at 6708A in the more massive object which may be indicati...

  15. CONFIRMATION OF ONE OF THE COLDEST KNOWN BROWN DWARFS

    International Nuclear Information System (INIS)

    Using two epochs of 4.5 μm images from the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope, we recently identified a common proper motion companion to the white dwarf WD 0806-661 that is a candidate for the coldest known brown dwarf. To verify its cool nature, we have obtained images of this object at 3.6 μm with IRAC, at J with the High Acuity Wide-field K-band Imager (HAWK-I) on the Very Large Telescope, and in a filter covering the red half of J with FourStar on Magellan. WD 0806-661 B is detected by IRAC but not HAWK-I or FourStar. From these data we measure colors of [3.6] – [4.5] = 2.77 ± 0.16 and J – [4.5] > 7.0 (S/N eff = 300-345 K.

  16. Akari Observations of Brown Dwarfs. II CO2 as Probe of Carbon and Oxygen Abundances in Brown Dwarfs

    CERN Document Server

    Tsuji, Takashi; Sorahana, Satoko

    2011-01-01

    Recent observations with the infrared astronomical satellite AKARI have shown that the CO2 bands at 4.2 micron in three brown dwarfs are much stronger than expected from the unified cloudy model (UCM) based on recent solar C & O abundances. This result has been a puzzle, but we now find that this is simply an abundance effect: We show that these strong CO2 bands can be explained with the UCMs based on the classical C & O abundances (log Ac and log Ao), which are about 0.2 dex larger compared to the recent values. Since three other brown dwarfs could be well interpreted with the recent solar C & O abundances, we require at least two model sequences based on the different chemical compositions to interpret all the AKARI spectra. The reason for this is that the CO2 band is especially sensitive to C & O abundances, since the CO2 abundance depends approximately on AcAo^2 --- the cube of C & O abundances. For this reason, even low resolution spectra of very cool dwarfs, especially of CO2 cannot ...

  17. K-H2 line shapes for the spectra of cool brown dwarfs

    Science.gov (United States)

    Allard, N. F.; Spiegelman, F.; Kielkopf, J. F.

    2016-04-01

    Observations of cooler and cooler brown dwarfs show that the contribution from broadening at many bars pressure is becoming important. The opacity in the red optical to near-IR region under these conditions is dominated by the extremely pressure-broadened wings of the alkali resonance lines, in particular, the K I resonance doublet at 0.77 μm. Collisions with H2 are preponderant in brown dwarf atmospheres at an effective temperature of about 1000 K; the H2 perturber densities reach several 1019 even in Jupiter-mass planets and exceed 1020 for super-Jupiters and older Y dwarfs. As a consequence, it appears that when the far wing absorption due to alkali atoms in a dense H2 atmosphere is significant, accurate pressure broadened profiles that are valid at high densities of H2 should be incorporated into spectral models. The opacity tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A21

  18. Exploring the Role of Sub-micron Sized Dust Grains in the Atmospheres of Red L0 - L6 Dwarfs

    CERN Document Server

    Hiranaka, Kay; Douglas, Stephanie T; Marley, Mark S; Baldassare, Vivienne F

    2016-01-01

    We examine the hypothesis that the red near-infrared colors of some L dwarfs could be explained by a "dust haze" of small particles in their upper atmospheres. This dust haze would exist in conjunction with the clouds found in dwarfs with more typical colors. We developed a model which uses Mie theory and the Hansen particle size distributions to reproduce the extinction due to the proposed dust haze. We apply our method to 23 young L dwarfs and 23 red field L dwarfs. We constrain the properties of the dust haze including particle size distribution and column density using Markov-Chain Monte Carlo methods. We find that sub-micron range silicate grains reproduce the observed reddening. Current brown dwarf atmosphere models include large grain (1--100~$\\mu m$) dust clouds but not submicron dust grains. Our results provide a strong proof of concept and motivate a combination of large and small dust grains in brown dwarf atmosphere models.

  19. Polarimetric Detection of Exoplanets Transiting T- and L- Brown Dwarfs

    OpenAIRE

    Sengupta, Sujan

    2016-01-01

    While scattering of light by atoms and molecules yields large amount of polarization at the B-band of both T- and L-dwarfs, scattering by dust grains in cloudy atmosphere of L-dwarfs gives rise to significant polarization at the far-optical and infra-red wavelengths where these objects are much brighter. However, the observable disk averaged polarization should be zero if the clouds are uniformly distributed and the object is spherically symmetric. Therefore, in order to explain the observed ...

  20. White dwarf stars with carbon atmospheres.

    Science.gov (United States)

    Dufour, P; Liebert, J; Fontaine, G; Behara, N

    2007-11-22

    White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for approximately 80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4-7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch. PMID:18033290

  1. HD 91669B: A NEW BROWN DWARF CANDIDATE FROM THE MCDONALD OBSERVATORY PLANET SEARCH

    International Nuclear Information System (INIS)

    We report the detection of a brown dwarf candidate orbiting the metal-rich K dwarf HD 91669, based on radial-velocity data from the McDonald Observatory Planet Search. HD 91669b is a substellar object in an eccentric orbit (e = 0.45) at a separation of 1.2 AU. The minimum mass of 30.6M Jup places this object firmly within the brown dwarf desert for inclinations i ∼> 230. This is the second rare close-in brown dwarf candidate discovered by the McDonald planet search program.

  2. The Brown Dwarf Kinematics Project (BDKP). III. Parallaxes for 70 Ultracool Dwarfs

    Science.gov (United States)

    Faherty, Jacqueline K.; Burgasser, Adam J.; Walter, Frederick M.; Van der Bliek, Nicole; Shara, Michael M.; Cruz, Kelle L.; West, Andrew A.; Vrba, Frederick J.; Anglada-Escudé, Guillem

    2012-06-01

    We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical-mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color-color diagrams. We report new polynomial relations between spectral type and MJHK . Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a "bright" (unresolved binary) and a "faint" (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in MJ where there is a [1.2-1.4] mag difference. A similar yet dampened brightening of [0.3-0.5] mag happens at MH and a plateau or dimming of [-0.2 to -0.3] mag is seen in MK . Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color-magnitude diagrams. However we find that a near constant temperature of 1200 ±100 K along a narrow spectral subtype of T0-T4 is required to account for the brightening and color-magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially "ultra-cloudy" compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least [0.2-1.0] mag underluminous in MJH and/or MK compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new spectral-type/absolute magnitude polynomial for analysis.

  3. THE BROWN DWARF KINEMATICS PROJECT (BDKP). III. PARALLAXES FOR 70 ULTRACOOL DWARFS

    International Nuclear Information System (INIS)

    We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical-mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color-color diagrams. We report new polynomial relations between spectral type and MJHK. Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a 'bright' (unresolved binary) and a 'faint' (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in MJ where there is a [1.2-1.4] mag difference. A similar yet dampened brightening of [0.3-0.5] mag happens at MH and a plateau or dimming of [–0.2 to –0.3] mag is seen in MK . Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color-magnitude diagrams. However we find that a near constant temperature of 1200 ±100 K along a narrow spectral subtype of T0-T4 is required to account for the brightening and color-magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially 'ultra-cloudy' compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least [0.2-1.0] mag underluminous in MJH and/or MK compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new spectral-type/absolute magnitude polynomial for analysis.

  4. THE BROWN DWARF KINEMATICS PROJECT (BDKP). III. PARALLAXES FOR 70 ULTRACOOL DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Faherty, Jacqueline K.; Shara, Michael M.; Cruz, Kelle L. [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10034 (United States); Burgasser, Adam J. [Center of Astrophysics and Space Sciences, Department of Physics, University of California, San Diego, CA 92093 (United States); Walter, Frederick M. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States); Van der Bliek, Nicole [CTIO/National Optical Astronomy Observatory (Chile); West, Andrew A. [Department of Astronomy, Boston University, 725 Commonwealth Ave Boston, MA 02215 (United States); Vrba, Frederick J. [US Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff, AZ 86002 (United States); Anglada-Escude, Guillem, E-mail: jfaherty@amnh.org [Department of Terrestrial Magnetism, Carnegie Institution of Washington 5241 Broad Branch Road, NW, Washington, DC 20015 (United States)

    2012-06-10

    We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical-mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color-color diagrams. We report new polynomial relations between spectral type and M{sub JHK}. Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a 'bright' (unresolved binary) and a 'faint' (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in M{sub J} where there is a [1.2-1.4] mag difference. A similar yet dampened brightening of [0.3-0.5] mag happens at M{sub H} and a plateau or dimming of [-0.2 to -0.3] mag is seen in M{sub K} . Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color-magnitude diagrams. However we find that a near constant temperature of 1200 {+-}100 K along a narrow spectral subtype of T0-T4 is required to account for the brightening and color-magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially 'ultra-cloudy' compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least [0.2-1.0] mag underluminous in M{sub JH} and/or M{sub K} compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new

  5. AKARI OBSERVATIONS OF BROWN DWARFS. III. CO, CO2, AND CH4 FUNDAMENTAL BANDS AND PHYSICAL PARAMETERS

    International Nuclear Information System (INIS)

    We investigate variations in the strengths of three molecular bands, CH4 at 3.3 μm, CO at 4.6 μm, and CO2 at 4.2 μm, in 16 brown dwarf spectra obtained by AKARI. Spectral features are examined along the sequence of source classes from L1 to T8. We find that the CH4 3.3 μm band is present in the spectra of brown dwarfs later than L5, and the CO 4.6 μm band appears in all spectral types. The CO2 absorption band at 4.2 μm is detected in late-L and T-type dwarfs. To better understand brown dwarf atmospheres, we analyze the observed spectra using the Unified Cloudy Model. The physical parameters of the AKARI sample, i.e., atmospheric effective temperature T eff, surface gravity log g, and critical temperature T cr, are derived. We also model IRTF/SpeX and UKIRT/CGS4 spectra in addition to the AKARI data in order to derive the most probable physical parameters. Correlations between the spectral type and the modeled parameters are examined. We confirm that the spectral-type sequence of late-L dwarfs is not related to T eff, but instead originates as a result of the effect of dust.

  6. Analytic Models of Brown Dwarfs and The Substellar Mass Limit

    CERN Document Server

    Auddy, Sayantan; Valluri, S R

    2016-01-01

    We present the current status of the analytic theory of brown dwarf evolution and the lower mass limit of the hydrogen burning main sequence stars. In the spirit of a simplified analytic theory we also introduce some modifications to the existing models. We give an exact expression for the pressure of an ideal non-relativistic Fermi gas at a finite temperature, therefore allowing for non-zero values of the degeneracy parameter ($\\psi = \\frac{kT}{\\mu_{F}}$, where $\\mu_{F}$ is the Fermi energy). We review the derivation of surface luminosity using an entropy matching condition and the first-order phase transition between the molecular hydrogen in the outer envelope and the partially-ionized hydrogen in the inner region. We also discuss the results of modern simulations of the plasma phase transition, which illustrate the uncertainties in determining its critical temperature. Based on the existing models and with some simple modification we find the maximum mass for a brown dwarf to be in the range $0.064M_\\odot...

  7. MOA-2007-BLG-197: Exploring the brown dwarf desert

    CERN Document Server

    Ranc, C; Albrow, M D; Kubas, D; Bond, I A; Batista, V; Beaulieu, J -P; Bennett, D P; Dominik, M; Dong, Subo; Fouqué, P; Gould, A; Greenhill, J; Jørgensen, U G; Kains, N; Menzies, J; Sumi, T; Bachelet, E; Coutures, C; Dieters, S; Prester, D Dominis; Donatowicz, J; Gaudi, B S; Han, C; Hundertmark, M; Horne, K; Kane, S R; Lee, C -U; Marquette, J -B; Park, B -G; Pollard, K R; Sahu, K C; Street, R; Tsapras, Y; Wambsganss, J; Williams, A; Zub, M; Abe, F; Fukui, A; Itow, Y; Masuda, K; Matsubara, Y; Muraki, Y; Ohnishi, K; Rattenbury, N; Saito, To; Sullivan, D J; Sweatman, W L; Tristram, P J; Yock, P C M; Yonehara, A

    2015-01-01

    We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by a network of telescopes from the PLANET, MOA, and uFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve, we derived the binary lens separation in Einstein radius units (s~1.13) and a mass ratio of (4.732+/-0.020)x10^{-2}. Annual parallax, lens orbital motion and finite source effects were included in the models. To recover the lens system's physical parameters, we combined the resulting light curve best-fit parameters with (J,H,Ks) magnitudes obtained with VLT NaCo and calibrated using IRSF and 2MASS data. We derived a lens total mass of 0.86+/-0.04 Msun and a lens distance of 4.2+/-0.3 kpc. We find that the companion of MOA-2007-BLG-197L is a brown dwarf of 41+/-2 Mjup observed at a projected separation of 4.3+/-0.1 A...

  8. Spitzer Observations of two TW Hydrae Association Brown Dwarfs

    CERN Document Server

    Riaz, B; Hmiel, A; Riaz, Basmah; Gizis, John E.; Hmiel, Abraham

    2006-01-01

    We present Spitzer Space Telescope observations of two TW Hydrae Association brown dwarfs, 2MASSW J1207334-393254 and 2MASSW J1139511-315921, in the IRAC and MIPS 24 micron bands. Based on their IRAC colors, we have classified them as Classical and Weak-line T Tauri stars, respectively. For 2MASSW J1207334-393254, we have found that a flat disk model fits the data very well. This brown dwarf shows the presence of warm (T > 100 K) circumstellar dust close (R < 0.2 AU) to it, and does not display any signs of cleansing of dust within several AU of the star. In comparison with other TWA members that show excess in IR, we suggest that there exists a different disk evolution/dust processing mechanism for stellar and sub-stellar objects. 2MASSW J1139511-315921 does not show any significant excess in any of the IRAC bands, but a small one at 24 micron, which is not significant enough to suggest the presence of warm dust around this star. It shows signs of dust cleansing in the inner several AU, similar to most of...

  9. New Brown Dwarf Disks in the TW Hydrae Association

    CERN Document Server

    Riaz, B

    2008-01-01

    In our analysis of {\\it Spitzer}/IRS archival data on the stellar and sub-stellar members of the TW Hydrae Association (TWA), we have discovered two new brown dwarf disks: a flat optically thick disk around SSSPM J1102-3431 (SSSPM 1102), and a transition disk around 2MASS J1139511-315921 (2M1139). The disk structure for SSSPM 1102 is found to be very similar to the known brown dwarf disk 2MASSW J1207334-393254 (2M1207), with excess emission observed at wavelengths as short as 5 $\\micron$. 2M1139 shows no excess emission shortward of $\\sim$20 $\\micron$, but flares up at longer wavelengths, and is the first transition disk detected among the sub-stellar members of TWA. We also report on the {\\it Spitzer}/70 $\\micron$ observations, and the presence of a weak {\\it absorption} 10 $\\micron$ silicate feature for 2M1207. The absorption can be attributed to a close to edge-on disk at a 75$\\degr$ inclination. The 10 $\\micron$ spectrum for 2M1207 shows crystalline forsterite features, with a peak in absorption near 11.3...

  10. Search for exoplanets and brown dwarfs with VLBI.

    Science.gov (United States)

    Katarzyński, K.; Gawroński, M.; Goździewski, K.

    2016-06-01

    The main aim of this work is to estimate possible radio GHz emission of extrasolar planets and brown dwarfs and to check if such radiation can be detected by Very Large Baseline Interferometers (VLBI). In the estimation we assume that the emission may originate in processes similar to those observed in the Jupiter system. The frequency of the radio emission that is produced in this system depends mostly on the magnetic field strength. Jupiter's magnetic field (˜9 G on average) allows for radiation from kHz frequencies up to 40 MHz. This is is well below the frequency range of VLBI. However, it was demonstrated that the magnetic field strength in massive and young object may be up to two orders of magnitude higher than for Jupiter, which is especially relevant for planets around short-lived A type stars. This should extend the range of the emission up to GHz frequencies. We calculated expected flux densities of radio emission for a variety of hypothetical young planetary systems. We analysed two different emission scenarios, and found that the radiation induced by moons (process similar to Jupiter-Io interactions) appears to be less efficient than the emission generated by a stellar wind on a planetary magnetosphere. We also estimated hypothetical emission of planets and brown dwarfs located around relatively young and massive main sequence A-type stars. Our results show that the emission produced by stellar winds could be detected by currently operating VLBI networks.

  11. Search for exoplanets and brown dwarfs with VLBI

    Science.gov (United States)

    Katarzyński, K.; Gawroński, M.; Goździewski, K.

    2016-09-01

    The main aim of this work is to estimate possible radio GHz emission of extrasolar planets and brown dwarfs and to check if such radiation can be detected by Very Large Baseline Interferometers (VLBI). In the estimation we assume that the emission may originate in processes similar to those observed in the Jupiter system. The frequency of the radio emission that is produced in this system depends mostly on the magnetic field strength. Jupiter's magnetic field (˜9 G on average) allows for radiation from kHz frequencies up to 40 MHz. This is well below the frequency range of VLBI. However, it was demonstrated that the magnetic field strength in massive and young object may be up to two orders of magnitude higher than for Jupiter, which is especially relevant for planets around short-lived A type stars. This should extend the range of the emission up to GHz frequencies. We calculated expected flux densities of radio emission for a variety of hypothetical young planetary systems. We analysed two different emission scenarios, and found that the radiation induced by moons (process similar to Jupiter-Io interactions) appears to be less efficient than the emission generated by a stellar wind on a planetary magnetosphere. We also estimated hypothetical emission of planets and brown dwarfs located around relatively young and massive main-sequence A-type stars. Our results show that the emission produced by stellar winds could be detected by currently operating VLBI networks.

  12. The disk around the brown dwarf KPNO Tau 3

    CERN Document Server

    Broekhoven-Fiene, Hannah; Duchene, Gaspard; Di Francesco, James; Scholz, Aleks; Chrysostomou, Antonio; Jayawardhana, Ray

    2014-01-01

    We present submillimeter observations of the young brown dwarfs KPNO Tau 1, KPNO Tau 3, and KPNO Tau 6 at 450 micron and 850 micron taken with the Submillimeter Common-User Bolometer Array on the James Clerke Maxwell Telescope. KPNO Tau 3 and KPNO Tau 6 have been previously identified as Class II objects hosting accretion disks, whereas KPNO Tau 1 has been identified as a Class III object and shows no evidence of circumsubstellar material. Our 3 sigma detection of cold dust around KPNO Tau 3 implies a total disk mass of (4.0 +/- 1.1) x 10^{-4} Msolar (assuming a gas to dust ratio of 100:1). We place tight constraints on any disks around KPNO Tau 1 or KPNO Tau 6 of <2.1 x 10^{-4} Msolar and <2.7 x 10^{-4} Msolar, respectively. Modeling the spectral energy distribution of KPNO Tau 3 and its disk suggests the disk properties (geometry, dust mass, and grain size distribution) are consistent with observations of other brown dwarf disks and low-mass T-Tauri stars. In particular, the disk-to-host mass ratio fo...

  13. The Coolest Isolated Brown Dwarf Candidate Member of TWA

    CERN Document Server

    Gagné, Jonathan; Cruz, Kelle; Lafrenière, David; Doyon, René; Malo, Lison; Artigau, Étienne

    2014-01-01

    We present two new late-type brown dwarf candidate members of the TW Hydrae association (TWA) : 2MASS J12074836-3900043 and 2MASS J12474428-3816464, which were found as part of the BANYAN all-sky survey (BASS) for brown dwarf members to nearby young associations. We obtained near-infrared (NIR) spectroscopy for both objects (NIR spectral types are respectively L1 and M9), as well as optical spectroscopy for J1207-3900 (optical spectral type is L0{\\gamma}), and show that both display clear signs of low-gravity, and thus youth. We use the BANYAN II Bayesian inference tool to show that both objects are candidate members to TWA with a very low probability of being field contaminants, although the kinematics of J1247-3816 seem slightly at odds with that of other TWA members. J1207-3900 is currently the latest-type and the only isolated L-type candidate member of TWA. Measuring the distance and radial velocity of both objects is still required to claim them as bona fide members. Such late-type objects are predicted...

  14. Epsilon Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

    CERN Document Server

    King, Robert R; Homeier, Derek; Allard, France; Scholz, Ralf-Dieter; Lodieu, Nicolas

    2009-01-01

    The discovery of epsilon Indi Ba, Bb, a binary brown dwarf system very close to the Sun, makes possible a concerted campaign to characterise the physical parameters of two T dwarfs. Recent observations suggest substellar atmospheric and evolutionary models may be inconsistent with observations, but there have been few conclusive tests to date. We therefore aim to characterise these benchmark brown dwarfs to place constraints on such models. We have obtained high angular resolution optical, near-infrared, and thermal-infrared imaging and medium-resolution (up to R~5000) spectroscopy of epsilon Indi Ba, Bb with the ESO VLT and present VRIzJHKL'M' broad-band photometry and 0.63--5.1 micron spectroscopy of the individual components. Furthermore, we use deep AO-imaging to place upper limits on the (model-dependent) mass of any further system members. We derive luminosities of log L/L_sun = -4.699+/-0.017 and -5.232+/-0.020 for epsilon Indi Ba, Bb, respectively, and using the dynamical system mass and COND03 evolut...

  15. White dwarf atmospheres and circumstellar environments

    CERN Document Server

    Hoard, Donald W

    2012-01-01

    Written by selected astronomers at the forefront of their fields, this timely and novel book compiles the latest results from research on white dwarf stars, complementing existing literature by focusing on fascinating new developments in our understanding of the atmospheric and circumstellar environments of these stellar remnants. Complete with a thorough refresher on the observational characteristics and physical basis for white dwarf classification, this is a must-have resource for researchers interested in the late stages of stellar evolution, circumstellar dust and nebulae, and the future

  16. Bok Prize Lecture (shared) The Brown Dwarf Radial Velocity Survey

    Science.gov (United States)

    Charbonneau, Dave

    2004-03-01

    The swarm of nearby brown dwarfs and very low mass stars is an attractive sample for radial velocity monitoring. Such work is best conducted with an echelle spectrograph operating at infrared wavelengths where these objects(i) are most luminous, (ii) have a forest of molecular features, providing an excellent velocity metric, and {iii) are superimposed on the telluric spectrum, which yields the requisite wavelength calibration. I will present first results from such a survey, with a precision sufficient to detect Jupiter-mass planets with orbital periods of less than a year. Should such systems be uncovered, the planets would be amenable to direct study, due to system proximity, and the favorable contrast ratio between the planet and parent object.

  17. Planetesimals To Brown Dwarfs: What is a Planet?

    CERN Document Server

    Basri, G; Basri, Gibor; Brown, Michael E.

    2006-01-01

    The past 15 years have brought about a revolution in our understanding of our Solar System and other planetary systems. During this time, discoveries include the first Kuiper Belt Objects, the first brown dwarfs, and the first extra-solar planets. Although discoveries continue apace, they have called into question our previous perspectives on planets, both here and elsewhere. The result has been a debate about the meaning of the word ''planet'' itself. It became clear that scientists do not have a widely accepted or clear definition of what a planet is, and both scientists and the public are confused (and sometimes annoyed) by its use in various contexts. Because ''planet'' is a very widely used term, it seems worth the attempt to resolve this problem. In this essay, we try to cover all the issues that have come to the fore, and bring clarity (if not resolution) to the debate.

  18. NEW H2 COLLISION-INDUCED ABSORPTION AND NH3 OPACITY AND THE SPECTRA OF THE COOLEST BROWN DWARFS

    International Nuclear Information System (INIS)

    We present new cloudy and cloudless model atmospheres for brown dwarfs using recent ab initio calculations of the line list of ammonia (NH3) and of the collision-induced absorption of molecular hydrogen (H2). We compare the new synthetic spectra with models based on an earlier description of the H2 and NH3 opacities. We find a significant improvement in fitting the nearly complete spectral energy distribution of the T7p dwarf Gliese 570D and in near-infrared color-magnitude diagrams of field brown dwarfs. We apply these new models to the identification of NH3 absorption in the H-band peak of very late T dwarfs and the new Y dwarfs and discuss the observed trend in the NH3-H spectral index. The new NH3 line list also allows a detailed study of the medium-resolution spectrum of the T9/T10 dwarf UGPS J072227.51–054031.2 where we identify several specific features caused by NH3.

  19. The formation of brown dwarfs in discs: Physics, numerics, and observations

    CERN Document Server

    Stamatellos, Dimitris

    2010-01-01

    A large fraction of brown dwarfs and low-mass stars may form by gravitational fragmentation of relatively massive (a few 0.1 Msun), extended (a few hundred AU) discs around Sun-like stars. We present an ensemble of radiative hydrodynamic simulations that examine the conditions for disc fragmentation. We demonstrate that this model can explain the low-mass IMF, the brown dwarf desert, and the binary properties of low-mass stars and brown dwarfs. Observing discs that are undergoing fragmentation is possible but very improbable, as the process of disc fragmentation is short lived (discs fragment within a few thousand years).

  20. Chemistry Of Atmospheric Brown Carbon

    Energy Technology Data Exchange (ETDEWEB)

    Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey

    2015-05-27

    Organic carbon (OC) accounts for a large fraction of atmospheric aerosol and has profound effects on air quality, atmospheric chemistry and climate forcing. Molecular composition of the OC and its evolution during common processes of atmospheric aging have been a subject of extensive research over the last decade (see reviews of Ervens et al.,1 Hallquist et al.,2 Herckes et al.,3 Carlton et al.,4 Kroll and Seinfeld,5 Rudich et al.,6 and Kanakidou et al.7). Even though many fundamental advances have been reported in these studies, our understanding of the climate-related properties of atmospheric OC is still incomplete and the specific ways in which OC impacts atmospheric environment and climate forcing are just beginning to be understood. This review covers one topic of particular interest in this area –environmental chemistry of light-absorbing aerosol OC and its impact on radiative forcing.

  1. THE SEARCH FOR PLANETARY MASS COMPANIONS TO FIELD BROWN DWARFS WITH HST/NICMOS

    International Nuclear Information System (INIS)

    We present the results of a high-resolution spectral differential imaging survey of 12 nearby, relatively young field L dwarfs (≤1 Gyr) carried out with the Hubble Space Telescope/NICMOS to search for planetary mass companions at small physical separations from their host. The survey resolved two brown dwarf binaries: the L dwarf system Kelu-1 AB and the newly discovered L/T transition system 2MASS 031059+164815 AB. For both systems, common proper motion has already been confirmed in follow-up observations which have been published elsewhere. The derived separations of the binaries are smaller than 6 AU and consistent with previous brown dwarf binary statistics. Their mass ratios of q ≥ 0.8 confirm the preference for equal-mass systems similar to a large number of other surveys. Furthermore, we found tentative evidence for a companion to the L4 dwarf 2MASSW 033703-175807, straddling the brown dwarf/planetary mass boundary and revealing an uncommonly low-mass ratio system (q ∼ 0.2) compared to the vast majority of previously found brown dwarf binaries. With a derived minimum mass of 10-15 MJup a planetary nature of the secondary cannot be ruled out yet. However, it seems more likely to be a very low mass brown dwarf secondary at the border of the spectral T/Y transition regime, primarily due to its similarities to recently found very cool T dwarfs. This would make it one of the closest resolved brown dwarf binaries (0.''087 ± 0.''015, corresponding to 2.52 ± 0.44 AU at a distance of 29 pc) with the coolest (Teff ∼ 600-630 K) and least massive companion to any L or T dwarf.

  2. Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B

    CERN Document Server

    Line, Michael R; Burningham, Ben; Fortney, Jonathan; Marley, Mark

    2015-01-01

    Interpreting the spectra of brown dwarfs is key to determining the fundamental physical and chemical processes occurring in their atmospheres. Powerful Bayesian atmospheric retrieval tools have recently been applied to both exoplanet and brown dwarf spectra to tease out the thermal structures and molecular abundances to understand those processes. In this manuscript we develop a significantly upgraded retrieval method and apply it to the SpeX spectral library data of two benchmark late T-dwarfs, Gl570D and HD3651B, to establish the validity of our upgraded forward model parameterization and Bayesian estimator. Our retrieved metallicities, gravities, and effective temperature are consistent with the metallicity and presumed ages of the systems. We add the carbon-to-oxygen ratio as a new dimension to benchmark systems and find good agreement between carbon-to-oxygens ratio derived in the brown dwarfs and the host stars. Furthermore, we have for the first time unambiguously determined the presence of ammonia in ...

  3. NLTT 41135: A FIELD M DWARF + BROWN DWARF ECLIPSING BINARY IN A TRIPLE SYSTEM, DISCOVERED BY THE MEARTH OBSERVATORY

    International Nuclear Information System (INIS)

    We report the discovery of an eclipsing companion to NLTT 41135, a nearby M5 dwarf that was already known to have a wider, slightly more massive common proper motion companion, NLTT 41136, at 2.''4 separation. Analysis of combined-light and RV curves of the system indicates that NLTT 41135B is a (31-34) ± 3MJup brown dwarf (where the range depends on the unknown metallicity of the host star) on a circular orbit. The visual M dwarf pair appears to be physically bound, so the system forms a hierarchical triple, with masses approximately in the ratio 8:6:1. The eclipses are grazing, preventing an unambiguous measurement of the secondary radius, but follow-up observations of the secondary eclipse (e.g., with the James Webb Space Telescope) could permit measurements of the surface brightness ratio between the two objects, and thus place constraints on models of brown dwarfs.

  4. Brown dwarf disks with ALMA: evidence for truncated dust disks in Ophiuchus

    CERN Document Server

    Testi, L; Scholz, A; Tazzari, M; Ricci, L; Monsalvo, I de Gregorio

    2016-01-01

    The study of the properties of disks around young brown dwarfs can provide important clues on the formation of these very low mass objects and on the possibility of forming planetary systems around them. The presence of warm dusty disks around brown dwarfs is well known, based on near- and mid-infrared studies. High angular resolution observations of the cold outer disk are limited, we used ALMA to attempt a first survey of young brown dwarfs in the rho-Ophiuchi star forming region with ALMA. All 17 young brown dwarfs in our sample were observed at 890 um in the continuum at ~0.5" angular resolution. The sensitivity of our observations was chosen to detect ~0.5 MEarth of dust. We detect continuum emission in 11 disks (65% of the total), the estimated mass of dust in the detected disks ranges from ~0.5 to ~6 MEarth. These disk masses imply that planet formation around brown dwarfs may be relatively rare and that the supra-Jupiter mass companions found around some brown dwarfs are probably the result of a binar...

  5. Atmospheric studies of C2 white dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Swanson, S.R.

    1989-01-01

    Model atmosphere and line formation calculations for the delta nu = + 1 Swan bands of the C2 molecule are presented for seven white dwarfs and are compared to high resolution optical spectra. Limits on the C-12 to C-13 ratio are computed for highly pressure broadened lines and are used to analyze the observed spectra for any sign of absorption by the (C-12)(C-13) molecule. The metal abundances in cool white dwarf atmospheres and the usefulness of the determination of the C-12 to C-13 ratio are discussed. The line center shift and the pressure broadening are used to determine a value for the van der Waals interaction constant, C6. This is done using a detailed line modelling program which explicitly includes approximately 2000 rotational transition lines within the vibrational bands, in conjunction with atmospheric models calculated by the LUCIFER atmosphere modelling program. The isotopic shift of the vibrational and rotational lines is also included in the model to compare the detectability of various C-12 to C-13 ratios. The line models fit the observed spectra with varying degrees of accuracy. One star, WD0548-001, shows an unusually small pressure shift and broadening for the high pressures that the atmospheric model predicts. The results show that only in the hottest stars with the least pressure broadened lines in this study can the isotopic effect be seen. With the data available, the best limit on the C-12 to C-13 ratio is a minimum of 40 for WD0856 + 331. The models show that even for very high signal to noise data, the isotopic shift in the Swan bands in very cool white dwarfs would be difficult to separate from the pressure broadening effects. It is shown that the isotopic ratio is high enough to rule out the possibility that the carbon is a relic from previous CNO burning.

  6. Atmospheric studies of C2 white dwarfs

    International Nuclear Information System (INIS)

    Model atmosphere and line formation calculations for the delta nu = + 1 Swan bands of the C2 molecule are presented for seven white dwarfs and are compared to high resolution optical spectra. Limits on the C-12 to C-13 ratio are computed for highly pressure broadened lines and are used to analyze the observed spectra for any sign of absorption by the (C-12)(C-13) molecule. The metal abundances in cool white dwarf atmospheres and the usefulness of the determination of the C-12 to C-13 ratio are discussed. The line center shift and the pressure broadening are used to determine a value for the van der Waals interaction constant, C6. This is done using a detailed line modelling program which explicitly includes approximately 2000 rotational transition lines within the vibrational bands, in conjunction with atmospheric models calculated by the LUCIFER atmosphere modelling program. The isotopic shift of the vibrational and rotational lines is also included in the model to compare the detectability of various C-12 to C-13 ratios. The line models fit the observed spectra with varying degrees of accuracy. One star, WD0548-001, shows an unusually small pressure shift and broadening for the high pressures that the atmospheric model predicts. The results show that only in the hottest stars with the least pressure broadened lines in this study can the isotopic effect be seen. With the data available, the best limit on the C-12 to C-13 ratio is a minimum of 40 for WD0856 + 331. The models show that even for very high signal to noise data, the isotopic shift in the Swan bands in very cool white dwarfs would be difficult to separate from the pressure broadening effects. It is shown that the isotopic ratio is high enough to rule out the possibility that the carbon is a relic from previous CNO burning

  7. Mapping the shores of the brown dwarf desert. IV. Ophiuchus

    CERN Document Server

    Cheetham, Anthony C; Ireland, Michael J; Cieza, Lucas; Rizzuto, Aaron C; Tuthill, Peter G

    2015-01-01

    We conduct a multiplicity survey of members of the rho Ophiuchus cloud complex with high resolution imaging to characterize the multiple star population of this nearby star forming region and investigate the relation between stellar multiplicity and star and planet formation. Our aperture masking survey reveals the presence of 5 new stellar companions beyond the reach of previous studies, but does not result in the detection of any new substellar companions. We find that 43+/-6% of the 114 stars in our survey have stellar mass companions between 1.3-780AU, while 7 (+8 -5)% host brown dwarf companions in the same interval. By combining this information with knowledge of disk-hosting stars, we show that the presence of a close binary companion (separation < 40 AU) significantly influences the lifetime of protoplanetary disks, a phenomenon previously seen in older star forming regions. At the ~1-2Myr age of our Ophiuchus members ~2/3 of close binary systems have lost their disks, compared to only ~30% of sing...

  8. HABITABLE PLANETS ECLIPSING BROWN DWARFS: STRATEGIES FOR DETECTION AND CHARACTERIZATION

    Energy Technology Data Exchange (ETDEWEB)

    Belu, Adrian R.; Selsis, Franck; Raymond, Sean N.; Bolmont, Emeline [Universite de Bordeaux, LAB, UMR 5804, F-33270, Floirac (France); Palle, Enric [Instituto de Astrofisica de Canarias, E-38205 La Laguna (Spain); Street, Rachel [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Goleta, CA 93117 (United States); Sahu, D. K.; Anupama, G. C. [Indian Institute of Astrophysics, Koramangala, Bangalore 560034 (India); Von Braun, Kaspar [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Figueira, Pedro [Centro de Astrofisica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Ribas, Ignasi, E-mail: belu@obs.u-bordeaux1.fr [Institut de Ciencies de l' Espai (CSIC-IEEC), Campus UAB, Facultat de Ciencies, Torre C5, parell, 2a pl., E-08193 Bellaterra (Spain)

    2013-05-10

    Given the very close proximity of their habitable zones, brown dwarfs (BDs) represent high-value targets in the search for nearby transiting habitable planets that may be suitable for follow-up occultation spectroscopy. In this paper, we develop search strategies to find habitable planets transiting BDs depending on their maximum habitable orbital period (P{sub HZ{sub out}}). Habitable planets with P{sub HZ{sub out}} shorter than the useful duration of a night (e.g., 8-10 hr) can be screened with 100% completeness from a single location and in a single night (near-IR). More luminous BDs require continuous monitoring for longer duration, e.g., from space or from a longitude-distributed network (one test scheduling achieved three telescopes, 13.5 contiguous hours). Using a simulated survey of the 21 closest known BDs (within 7 pc) we find that the probability of detecting at least one transiting habitable planet is between 4.5{sup +5.6}{sub -1.4}% and 56{sup +31}{sub -13}%, depending on our assumptions. We calculate that BDs within 5-10 pc are characterizable for potential biosignatures with a 6.5 m space telescope using {approx}1% of a five-year mission's lifetime spread over a contiguous segment only one-fifth to one-tenth of this duration.

  9. Search for exoplanets and brown dwarfs with VLBI

    CERN Document Server

    Katarzynski, K; Gozdziewski, K

    2016-01-01

    The main aim of this work is to estimate possible radio GHz emission of extrasolar planets and brown dwarfs and to check if such radiation can be detected by Very Large Baseline Interferometers (VLBI). In the estimation we assume that the emission may originate in processes similar to those observed in the Jupiter system. The frequency of the radio emission that is produced in this system depends mostly on the magnetic field strength. Jupiter's magnetic field ($\\sim 9$ G on average) allows for radiation from kHz frequencies up to 40 MHz. This is well below the frequency range of VLBI. However, it was demonstrated that the magnetic field strength in massive and young object may be up to two orders of magnitude higher than for Jupiter, which is especially relevant for planets around short-lived A type stars. This should extend the range of the emission up to GHz frequencies. We calculated expected flux densities of radio emission for a variety of hypothetical young planetary systems. We analysed two different e...

  10. New light on dark stars red dwarfs, low-mass stars, brown dwarfs

    CERN Document Server

    Reid, I Neill

    2000-01-01

    Perhaps the most common question that a child asks when he or she sees the night sky from a dark site for the first time is: 'How many stars are there?' This happens to be a question which has exercised the intellectual skills of many astronomers over the course of most of the last century, including, for the last two decades, one of the authors of this text. Until recently, the most accurate answer was 'We are not certain, but there is a good chance that almost all of them are M dwarfs. ' Within the last three years, results from new sky-surveys - particularly the first deep surveys at near­ infrared wavelengths - have provided a breakthrough in this subject, solidifying our census of the lowest-mass stars and identifying large numbers of the hitherto almost mythical substellar-mass brown dwarfs. These extremely low-luminosity objects are the central subjects of this book, and the subtitle should be interpreted accordingly. The expression 'low-mass stars' carries a wide range of meanings in the astronomical...

  11. The TRENDS High-Contrast Imaging Survey. VI. Discovery of a Mass, Age, and Metallicity Benchmark Brown Dwarf

    OpenAIRE

    Crepp, Justin R.; Gonzales, Erica J.; Bechter, Eric B.; Montet, Benjamin T.; Johnson, John Asher; Piskorz, Danielle; Howard, Andrew W.; Isaacson, Howard

    2016-01-01

    The mass and age of substellar objects are degenerate parameters leaving the evolutionary state of brown dwarfs ambiguous without additional information. Theoretical models are normally used to help distinguish between old, massive brown dwarfs and young, low mass brown dwarfs but these models have yet to be properly calibrated. We have carried out an infrared high-contrast imaging program with the goal of detecting substellar objects as companions to nearby stars to help break degeneracies i...

  12. THE FIRST ULTRA-COOL BROWN DWARF DISCOVERED BY THE WIDE-FIELD INFRARED SURVEY EXPLORER

    International Nuclear Information System (INIS)

    We report the discovery of the first new ultra-cool brown dwarf (BDs) found with the Wide-field Infrared Survey Explorer (WISE). The object's preliminary designation is WISEPC J045853.90+643451.9. Follow-up spectroscopy with the LUCIFER instrument on the Large Binocular Telescope indicates that it is a very late-type T dwarf with a spectral type approximately equal to T9. Fits to an IRTF/SpeX 0.8-2.5 μm spectrum to the model atmospheres of Marley and Saumon indicate an effective temperature of approximately 600 K as well as the presence of vertical mixing in its atmosphere. The new BD is easily detected by WISE, with a signal-to-noise ratio of ∼36 at 4.6 μm. Current estimates place it at a distance of 6-10 pc. This object represents the first in what will likely be hundreds of nearby BDs found by WISE that will be suitable for follow-up observations, including those with the James Webb Space Telescope. One of the two primary scientific goals of the WISE mission is to find the coolest, closest stars to our Sun; the discovery of this new BD proves that WISE is capable of fulfilling this objective.

  13. The First Ultra-cool Brown Dwarf Discovered by the Wide-field Infrared Survey Explorer

    Science.gov (United States)

    Mainzer, A.; Cushing, Michael C.; Skrutskie, M.; Gelino, C. R.; Kirkpatrick, J. Davy; Jarrett, T.; Masci, F.; Marley, Mark S.; Saumon, D.; Wright, E.; Beaton, R.; Dietrich, M.; Eisenhardt, P.; Garnavich, P.; Kuhn, O.; Leisawitz, D.; Marsh, K.; McLean, I.; Padgett, D.; Rueff, K.

    2011-01-01

    We report the discovery of the first new ultra-cool brown dwarf (BDs) found with the Wide-field Infrared Survey Explorer (WISE). The object's preliminary designation is WISEPC J045853.90+643451.9. Follow-up spectroscopy with the LUCIFER instrument on the Large Binocular Telescope indicates that it is a very late-type T dwarf with a spectral type approximately equal to T9. Fits to an IRTF/SpeX 0.8-2.5 μm spectrum to the model atmospheres of Marley and Saumon indicate an effective temperature of approximately 600 K as well as the presence of vertical mixing in its atmosphere. The new BD is easily detected by WISE, with a signal-to-noise ratio of ~36 at 4.6 μm. Current estimates place it at a distance of 6-10 pc. This object represents the first in what will likely be hundreds of nearby BDs found by WISE that will be suitable for follow-up observations, including those with the James Webb Space Telescope. One of the two primary scientific goals of the WISE mission is to find the coolest, closest stars to our Sun; the discovery of this new BD proves that WISE is capable of fulfilling this objective.

  14. Deriving the true mass of an unresolved Brown Dwarf companion to an M-Dwarf with AO aided astrometry*

    Directory of Open Access Journals (Sweden)

    Kürster M.

    2011-07-01

    Full Text Available From radial velocity (RV detections alone one does not get all orbital parameters needed to derive the true mass of a non-transiting, unresolved substellar companion to a star. Additional astrometric measurements are needed to calculate the inclination and the longitude of the ascending node. Until today only few true substellar companion masses have been determined by this method with the HST fine guidance sensor [1, 2]. We aim to derive the true mass of a brown dwarf candidate companion to an early M 2.5V dwarf with groundbased high-resolution astrometry aided by adaptive optics. We found this unique brown dwarf desert object, whose distance to the host star is only 0.42 AU, in our UVES precision RV survey of M dwarfs, inferring a minimum companion mass of 27 Jupiter masses [3]. Combining the data with HIPPARCOS astrometry, we found a probability of only 2.9% that the companion is stellar. We therefore observed the host star together with a reference star within a monitoring program with VLT/NACO to derive the true mass of the companion and establish its nature (brown dwarf vs. star. Simultaneous observations of a reference field in a globular cluster are performed to determine the stability of the adaptive optics (AO plus detector system and check its suitability for such high-precision astrometric measurements over several epochs which are needed to find and analyse extrasolar planet systems.

  15. Studies of the Coldest Brown Dwarfs with the James Webb Space Telescope

    Science.gov (United States)

    Roellig, Thomas L.

    2016-01-01

    The coolest T and Y-class Brown Dwarf objects are very faint and are therefore very poorly understood, since they are barely detectable with the current astronomical instrumentation. The upcoming James Webb Space Telescope now in development for a launch in the Fall of 2018 will have vastly increased sensitivity in the near and mid-infrared compared to any current facilities and will not be affected by telluric absorption over its entire wavelength range of operations. As a result it will be an ideal tool to obtain information about the composition and temperature-pressure structure in these objects' atmospheres. This presentation will outline the JWST guaranteed time observing plans for these studies.

  16. New Ideas in the Theory of Extrasolar Giant Planets and Brown Dwarfs

    CERN Document Server

    Burrows, A; Lunine, J I; Marley, M S; Saumon, D S; Burrows, Adam

    1998-01-01

    We summarize and extend recent work on the theory of extrasolar giant planets (EGPs) and brown dwarfs, paying particular attention to Gliese 229 B, the albedos of EGPs, the compositions of substellar atmospheres, the connections with the giant planets in the solar system, cloud physics, and non-gray spectral synthesis. The role of condensates in altering the optical spectrum of Gliese 229 B is explored, as are the systematics of the reflection spectra from extrasolar giant planets near their primaries. In addition, we discuss the role of convection and disequilibrium chemistry in explaining the anomalous detection of CO in Gliese 229 B. Throughout, we highlight the distinctive chemistry that defines this new class of objects and set goals for future study.

  17. WASP-30b: A 61 MJup BROWN DWARF TRANSITING A V = 12, F8 STAR

    International Nuclear Information System (INIS)

    We report the discovery of a 61-Jupiter-mass brown dwarf (BD), which transits its F8V host star, WASP-30, every 4.16 days. From a range of age indicators we estimate the system age to be 1-2 Gyr. We derive a radius (0.89 ± 0.02 RJup) for the companion that is consistent with that predicted (0.914 RJup) by a model of a 1 Gyr old, non-irradiated BD with a dusty atmosphere. The location of WASP-30b in the minimum of the mass-radius relation is consistent with the quantitative prediction of Chabrier and Baraffe, thus confirming the theory.

  18. Rotation periods and astrometric motions of the Luhman 16AB brown dwarfs by high-resolution lucky-imaging monitoring

    CERN Document Server

    Mancini, L; Littlefair, S P; Southworth, J; Bozza, V; Damasso, M; Dominik, M; Hundertmark, M; Jorgensen, U G; Juncher, D; Popovas, A; Rabus, M; Rahvar, S; Schmidt, R W; Skottfelt, J; Snodgrass, C; Sozzetti, A; Alsubai, K; Bramich, D M; Novati, S Calchi; Ciceri, S; D'Ago, G; Jaimes, R Figuera; Galianni, P; Gu, S -H; Harpsoe, K; Haugbolle, T; Henning, Th; Hinse, T C; Kains, N; Korhonen, H; Scarpetta, G; Starkey, D; Surdej, J; Wang, X -B; Wertz, O

    2015-01-01

    Context. Photometric monitoring of the variability of brown dwarfs can provide useful information about the structure of clouds in their cold atmospheres. The brown-dwarf binary system Luhman 16AB is an interesting target for such a study, as its components stand at the L/T transition and show high levels of variability. Luhman 16AB is also the third closest system to the Solar system, allowing precise astrometric investigations with ground-based facilities. Aims. The aim of the work is to estimate the rotation period and study the astrometric motion of both components. Methods. We have monitored Luhman 16AB over a period of two years with the lucky-imaging camera mounted on the Danish 1.54m telescope at La Silla, through a special i+z long-pass filter, which allowed us to clearly resolve the two brown dwarfs into single objects. An intense monitoring of the target was also performed over 16 nights, in which we observed a peak-to-peak variability of 0.20 \\pm 0.02 mag and 0.34 \\pm 0.02 mag for Luhman 16A and 1...

  19. Probing Cloud-Driven Variability on Two of the Youngest, Lowest-Mass Brown Dwarfs in the Solar Neighborhood

    Science.gov (United States)

    Schneider, Adam; Cushing, Michael; Kirkpatrick, J. Davy

    2016-08-01

    Young, late-type brown dwarfs share many properties with directly imaged giant extrasolar planets. They therefore provide unique testbeds for investigating the physical conditions present in this critical temperature and mass regime. WISEA 1147-2040 and 2MASS 1119-1137, two recently discovered late-type (~L7) brown dwarfs, have both been determined to be members of the ~10 Myr old TW Hya Association (Kellogg et al. 2016, Schneider et al. 2016). Each has an estimated mass of 5-6 MJup, making them two of the youngest and lowest-mass free floating objects yet found in the solar neighborhood. As such, these two planetary mass objects provide unparalleled laboratories for investigating giant planet-like atmospheres far from the contaminating starlight of a host sun. Condensate clouds play a critical role in shaping the emergent spectra of both brown dwarfs and gas giant planets, and can cause photometric variability via their non-uniform spatial distribution. We propose to photometrically monitor WISEA 1147-2040 and 2MASS 1119-1137 in order to search for the presence of cloud-driven variability to 1) investigate the potential trend of low surface gravity with high-amplitude variability in a previously unexplored mass regime and 2) explore the angular momentum evolution of isolated planetary mass objects.

  20. SMA and CARMA observations of young brown dwarfs in ρ Ophiuchi and Taurus

    Directory of Open Access Journals (Sweden)

    Lee C.-F.

    2011-07-01

    Full Text Available Molecular outflows provide vital information about the earliest stages in the birth of stars, studying the molecular outflow properties is therefore crucial for understanding how stars form. Brown dwarfs with masses between that of stars and planets are not massive enough to maintain stable hydrogen-burning fusion reactions during most of their lifetime. Their origins are subject to much debate in recent literature because their masses are far below the typical mass where core collapse is expected to occur. Based on Submillimeter Array (SMA and Combined Array for Research in Millimeter-wave Astronomy (CARMA observations, we present the first detections of bipolar molecular outflows from young brown dwarfs in ρ Ophiuchi and Taurus. Our results demonstrate that the bipolar molecular outflow operates down to brown dwarf masses, occurring in brown dwarfs as a scaled-down version of the universal process seen in young low-mass stars. This demonstrates that brown dwarfs and low-mass stars likely share the same formation mechanism.

  1. On the mass segregation of stars and brown dwarfs in Taurus

    CERN Document Server

    Parker, Richard J; Goodwin, Simon P; Moraux, Estelle; Allison, Richard J; Guieu, Sylvain; Guedel, Manuel

    2010-01-01

    We use the new minimum spanning tree (MST) method to look for mass segregation in the Taurus association. The method computes the ratio of MST lengths of any chosen subset of objects, including the most massive stars and brown dwarfs, to the MST lengths of random sets of stars and brown dwarfs in the cluster. This mass segregation ratio (Lambda_MSR) enables a quantitative measure of the spatial distribution of high-mass and low-mass stars, and brown dwarfs to be made in Taurus. We find that the most massive stars in Taurus are inversely mass segregated, with Lambda_MSR = 0.70 +/- 0.10 (Lambda_MSR = 1 corresponds to no mass segregation), which differs from the strong mass segregation signatures found in more dense and massive clusters such as Orion. The brown dwarfs in Taurus are not mass segregated, although we find evidence that some low-mass stars are, with an Lambda_MSR = 1.25 +/- 0.15. Finally, we compare our results to previous measures of the spatial distribution of stars and brown dwarfs in Taurus, and...

  2. Atmospheric Brown Clouds- from science towards policy

    Science.gov (United States)

    Sherestha, S.; Iyngararasan, M.

    2010-12-01

    Atmospheric Brown Clouds (ABCs) and its interaction with climate change is an emerging environmental issue. Studies demonstrate that ABCs and its interaction with build-up of greenhouse gases significantly affect the regional climate, glacial melting, hydrological cycle, agriculture and public health. For the next decades, the regional aerosol effects will continue to play a major role in environmental management as long as current strong sources of air pollution remain. An integrated multi-pollutant multi-sectoral approach for addressing atmospheric issues will result in optimum environmental and socioeconomic benefits. Regional intergovernmental networks have been established to address air pollution issues in different parts of the globe. These intergovernmental networks could be empowered to promote integrated approach for addressing the atmospheric environmental issues.

  3. Cloud Atlas: Discovery of Patchy Clouds and High-amplitude Rotational Modulations In a Young, Extremely Red L-type Brown Dwarf

    CERN Document Server

    Lew, Ben W P; Zhou, Yifan; Schneider, Glenn; Burgasser, Adam J; Karalidi, Theodora; Yang, Hao; Marley, Mark S; Cowan, N B; Bedin,; R., L; Metchev, Stanimir A; Radigan, Jacqueline; Lowrance, Patrick J

    2016-01-01

    Condensate clouds fundamentally impact the atmospheric structure and spectra of exoplanets and brown dwarfs but the connections between surface gravity, cloud structure, dust in the upper atmosphere, and the red colors of some brown dwarfs remain poorly understood. Rotational modulations enable the study of different clouds in the same atmosphere, thereby providing a method to isolate the effects of clouds. Here we present the discovery of high peak-to-peak amplitude (8%) rotational modulations in a low-gravity, extremely red (J-Ks=2.55) L6 dwarf WISEP J004701.06+680352.1 (W0047). Using the Hubble Space Telescope (HST) time-resolved grism spectroscopy we find a best-fit rotational period (13.20$\\pm$0.14 hours) with a larger amplitude at 1.1 micron than at 1.7 micron. This is the third largest near-infrared variability amplitude measured in a brown dwarf, demonstrating that large-amplitude variations are not limited to the L/T transition but are present in some extremely red L-type dwarfs. We report a tentativ...

  4. Diagnostics of models and observations in the contexts of exoplanets, brown dwarfs, and very low-mass stars.

    Science.gov (United States)

    Kopytova, Taisiya

    2016-01-01

    When studying isolated brown dwarfs and directly imaged exoplanets with insignificant orbital motion,we have to rely on theoretical models to determine basic parameters such as mass, age, effective temperature, and surface gravity.While stellar and atmospheric models are rapidly evolving, we need a powerful tool to test and calibrate them.In my thesis, I focussed on comparing interior and atmospheric models with observational data, in the effort of taking into account various systematic effects that can significantly influence the data analysis.As a first step, about 460 candidate member os the Hyades were screened for companions using diffraction limited imaging observation (both our own data and archival data). As a result I could establish the single star sequence for the Hyades comprising about 250 stars (Kopytova et al. 2015, accepted to A&A). Open clusters contain many coeval objects of the same chemical composition and age, and spanning a range of masses. We compare the obtained sequence with a set of theoretical isochrones identifying systematic offsets and revealing probable issues in the models.However, there are many cases when it is impossible to test models before comparing them with observations.As a second step, we apply atmospheric models for constraining parameters of WISE 0855-07, the coolest known Y dwarf(Kopytova et al. 2014, ApJ 797, 3). We demonstrate the limits of constraining effective temperature and the presence/absence of water clouds.As a third step, we introduce a novel method to take into account the above-mentioned systematics. We construct a "systematics vector" that allows us to reveal problematic wavelength ranges when fitting atmospheric models to observed near-infrared spectraof brown dwarfs and exoplanets (Kopytova et al., in prep.). This approach plays a crucial role when retrieving abundances for these objects, in particularly, a C/O ratio. The latter parameter is an important key to formation scenarios of brown dwarf and

  5. CFBDSIR J1458+1013B: A Very Cold (>T10) Brown Dwarf in a Binary System

    CERN Document Server

    Liu, Michael C; Dupuy, Trent J; Bowler, Brendan P; Albert, Loic; Artigau, Etienne; Reyle, Celine; Forveille, Thierry; Delfosse, Xavier

    2011-01-01

    (Abridged) We have identified CFBDSIR J1458+10 as a 0.11" binary using Keck laser guide star AO imaging. We measure a parallactic distance of 23.1+/-2.4 pc to the system based on CFHT near-IR astrometry. We assign a spectral type of T9.5 to the integrated-light near-IR spectrum, and model atmospheres suggest a slightly higher temperature and surface gravity than the T10 dwarf UGPS J0722-05. Thus, CFBDSIR J1458+10AB is the coolest brown dwarf binary to date. Its secondary component has an absolute H-band magnitude that is 1.9+/-0.3 mag fainter than UGPS J0722-05, giving an inferred spectral type of >T10. The secondary's bolometric luminosity of ~2 x 10^{-7} L_sun makes it the least luminous known brown dwarf by a factor of 4-5. By comparing to models and known T9-T10 objects, we estimate a temperature of 370+/-40 K and a mass of 6-15 Mjup for CFBDSIR J1458+10B. At such extremes, atmospheric models predict the onset of novel photospheric processes, namely the appearance of water clouds and the removal of strong...

  6. Spectral energy distribution simulations of a possible ring structure around the young, red brown dwarf G196-3B

    CERN Document Server

    Zakhozhay, Olga V; Béjar, Víctor J S; Boehler, Yann

    2016-01-01

    The origin of the very red optical and infrared colours of intermediate-age ($\\sim$10 - 500 Myr) L-type dwarfs remains unknown. It has been suggested that low-gravity atmospheres containing large amounts of dust may account for the observed reddish nature. We explored an alternative scenario by simulating protoplanetary and debris discs around G196-3B, which is an L3 young brown dwarf with a mass of $\\sim 15$ $M_{\\rm Jup}$ and an age in the interval 20 - 300 Myr. The best-fit solution to G196-3B's photometric spectral energy distribution from optical wavelengths through 24 $\\mu$m corresponds to the combination of an unreddened L3 atmosphere ($T_{\\rm eff} \\approx 1870$~K) and a warm ($\\approx$ 1280 K), narrow ($\\approx$ 0.07 - 0.11 R$_{\\odot}$) debris disc located at very close distances ($\\approx$ 0.12 - 0.20 R$_{\\odot}$) from the central brown dwarf. This putative, optically thick, dusty belt, whose presence is compatible with the relatively young system age, would have a mass $\\ge 7\\times 10^{-10}$ M$_{\\opl...

  7. The BANYAN All-Sky Survey for Brown Dwarf Members of Young Moving Groups

    Science.gov (United States)

    Gagné, Jonathan; Lafrenière, David; Doyon, René; Faherty, Jacqueline K.; Malo, Lison; Cruz, Kelle L.; Artigau, Étienne; Burgasser, Adam J.; Naud, Marie-Eve; Bouchard, Sandie; Gizis, John E.; Albert, Loïc

    2016-01-01

    We describe in this work the BASS survey for brown dwarfs in young moving groups of the solar neighborhood, and summarize the results that it generated. These include the discovery of the 2MASS J01033563-5515561 (AB)b and 2MASS J02192210-3925225 B young companions near the deuterium-burning limit as well as 44 new low-mass stars and 69 new brown dwarfs with a spectroscopically confirmed low gravity. Among those, ~20 have estimated masses within the planetary regime, one is a new L4 γ bona fide member of AB Doradus, three are TW Hydrae candidates with later spectral types (L1-L4) than all of its previously known members and six are among the first contenders for low-gravity >= L5 β/γ brown dwarfs, reminiscent of WISEP J004701.06+680352.1, PSO J318.5338-22.8603 and VHS J125601.92-125723.9 b. Finally, we describe a future version of this survey, BASS-Ultracool, that will specifically target >= L5 candidate members of young moving groups. First experimentations in designing the survey have already led to the discovery of a new T dwarf bona fide member of AB Doradus, as well as the serendipitous discoveries of an L9 subdwarf and an L5 + T5 brown dwarf binary.

  8. Photochemical processing of aqueous atmospheric brown carbon

    Science.gov (United States)

    Zhao, R.; Lee, A. K. Y.; Huang, L.; Li, X.; Yang, F.; Abbatt, J. P. D.

    2015-06-01

    Atmospheric brown carbon (BrC) is a collective term for light absorbing organic compounds in the atmosphere. While the identification of BrC and its formation mechanisms is currently a central effort in the community, little is known about the atmospheric removal processes of aerosol BrC. As a result, we report on a series of laboratory studies of photochemical processing of BrC in the aqueous phase, by direct photolysis and OH oxidation. Solutions of ammonium sulfate mixed with glyoxal (GLYAS) or methylglyoxal (MGAS) are used as surrogates for a class of secondary BrC mediated by imine intermediates. Three nitrophenol species, namely 4-nitrophenol, 5-nitroguaiacol and 4-nitrocatechol, were investigated as a class of water-soluble BrC originating from biomass burning. Photochemical processing induced significant changes in the absorptive properties of BrC. The imine-mediated BrC solutions exhibited rapid photo-bleaching with both direct photolysis and OH oxidation, with atmospheric half-lives of minutes to a few hours. The nitrophenol species exhibited photo-enhancement in the visible range during direct photolysis and the onset of OH oxidation, but rapid photo-bleaching was induced by further OH exposure on an atmospheric timescale of an hour or less. To illustrate the atmospheric relevance of this work, we also performed direct photolysis experiments on water-soluble organic carbon extracted from biofuel combustion samples and observed rapid changes in the optical properties of these samples as well. Overall, these experiments indicate that atmospheric models need to incorporate representations of atmospheric processing of BrC species to accurately model their radiative impacts.

  9. Combing the Brown Dwarf Desert with the APOGEE Catalog of Stellar and Substellar Companion Candidates

    Science.gov (United States)

    Troup, Nicholas William; De Lee, Nathan M.; Carlberg, Joleen K.; Nidever, David L.; Majewski, Steven R.; Stassun, Keivan; Covey, Kevin R.; Skrutskie, Michael F.; Allende-Prieto, Carlos; Hearty, Fred R.; APOGEE Substellar Companions Working Group

    2016-01-01

    While both exoplanets and stellar-mass companions have been found in extremely short-period orbits, there has been a paucity of brown dwarf (BD) companions orbiting Sun-like stars, a phenomenon known as the "Brown Dwarf Desert." However, more recent work has shown that this Desert might be limited in extent, only existing for small separation (a test this hypothesis by constraining the formation mechanisms of BD companions, and exploring their orbital evolution as their host evolves off the main sequence.

  10. Stability of CO_2 Atmospheres on Desiccated M Dwarf Exoplanets

    OpenAIRE

    Gao, Peter; Hu, Renyu; Robinson, Tyler D.; Li, Cheng; Yung, Yuk L.

    2015-01-01

    We investigate the chemical stability of CO2-dominated atmospheres of desiccated M dwarf terrestrial exoplanets using a 1-dimensional photochemical model. Around Sun-like stars, CO2 photolysis by Far-UV (FUV) radiation is balanced by recombination reactions that depend on water abundance. Planets orbiting M dwarf stars experience more FUV radiation, and could be depleted in water due to M dwarfs' prolonged, high-luminosity pre-main sequences (Luger & Barnes 2015). We show that, for water-depl...

  11. The Rotation of Young Low-Mass Stars and Brown Dwarfs

    CERN Document Server

    Herbst, W; Mundt, R; Scholz, A

    2006-01-01

    We review the current state of our knowledge concerning the rotation and angular momentum evolution of young stellar objects and brown dwarfs from a primarily observational view point. Periods are typically accurate to 1% and available for about 1700 stars and 30 brown dwarfs in young clusters. Discussion of angular momentum evolution also requires knowledge of stellar radii, which are poorly known for pre-main sequence stars. It is clear that rotation rates at a given age depend strongly on mass; higher mass stars (0.4-1.2 M$_\\odot$) have longer periods than lower mass stars and brown dwarfs. On the other hand, specific angular momentum is approximately independent of mass for low mass pre-main sequence stars and young brown dwarfs. A spread of about a factor of 30 is seen at any given mass and age. The evolution of rotation of solar-like stars during the first 100 Myr is discussed. A broad, bimodal distribution exists at the earliest observable phases ($\\sim$1 Myr) for stars more massive than 0.4 M$_\\odot$....

  12. Evolution of Young Brown Dwarf Disks in the Mid-Infrared

    CERN Document Server

    Sterzik, M F; Apai, D; Van der Bliek, N; Dullemond, C P; Sterzik, Michael F.; Pascucci, Ilaria; Apai, Daniel; Bliek, Nicole van der; Dullemond, Cornelis P.

    2004-01-01

    We have imaged two bona-fide brown dwarfs with TReCS/GEMINI-S and find mid-infrared excess emission that can be explained by optically thick dust disk models. In the case of the young ($\\approx$2Myr) Cha H$\\alpha$1 we measure fluxes at 10.4$\\mu$m and 12.3$\\mu$m that are fully consistent with a standard flared disk model and prominent silicate emission. For the $\\approx$ 10Myr old brown dwarf 2MASS1207-3932 located in the TW Hydrae association we find photospheric excess emission at 8.7$\\mu$m and 10.4$\\mu$m, and confirm disk accretion as likely cause of its strong activity. Disks around brown dwarfs likely last at least as long as their low-mass stellar counterparts in the T-Tauri phase. Grain growth, dust settling, and evolution of the geometry of brown dwarfs disks may appear on a timescale of 10Myr and can be witnessed by observations in the mid-infrared.

  13. A magnetic field evolution scenario for brown dwarfs and giant planets

    CERN Document Server

    Reiners, Ansgar

    2010-01-01

    Very little is known about magnetic fields of extrasolar planets and brown dwarfs. We use the energy flux scaling law presented by Christensen et al. (2009) to calculate the evolution of average magnetic fields in extrasolar planets and brown dwarfs under the assumption of fast rotation, which is probably the case for most of them. We find that massive brown dwarfs of about 70 M_Jup can have fields of a few kilo-Gauss during the first few hundred Million years. These fields can grow by a factor of two before they weaken after deuterium burning has stopped. Brown dwarfs with weak deuterium burning and extrasolar giant planets start with magnetic fields between ~100G and ~1kG at the age of a few Myr, depending on their mass. Their magnetic field weakens steadily until after 10Gyr it has shrunk by about a factor of 10. We use observed X-ray luminosities to estimate the age of the known extrasolar giant planets that are more massive than 0.3M_Jup and closer than 20pc. Taking into account the age estimate, and ass...

  14. PROTOPLANETARY DISK MASSES FROM STARS TO BROWN DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Mohanty, Subhanjoy; Mortlock, Daniel [Imperial College London, 1010 Blackett Lab, Prince Consort Rd., London SW7 2AZ (United Kingdom); Greaves, Jane [SUPA, Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS (United Kingdom); Pascucci, Ilaria; Apai, Daniel [Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, Tucson AZ 85721 (United States); Scholz, Aleks [School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland); Thompson, Mark [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Lodato, Giuseppe [Dipartimento di Fisica, Universita Degli Studi di Milano, Via Celoria 16, I-20133 Milano (Italy); Looper, Dagny, E-mail: s.mohanty@imperial.ac.uk [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822 (United States)

    2013-08-20

    We present SCUBA-2 850 {mu}m observations of seven very low mass stars (VLMS) and brown dwarfs (BDs). Three are in Taurus and four in the TW Hydrae Association (TWA), and all are classical T Tauri (cTT) analogs. We detect two of the three Taurus disks (one only marginally), but none of the TWA ones. For standard grains in cTT disks, our 3{sigma} limits correspond to a dust mass of 1.2 M{sub Circled-Plus} in Taurus and a mere 0.2 M{sub Circled-Plus} in the TWA (3-10 Multiplication-Sign deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, {rho} Oph, and the TWA to investigate the trends in disk mass and grain growth during the cTT phase. Assuming a gas-to-dust mass ratio of 100:1 and fiducial surface density and temperature profiles guided by current data, we find the following. (1) The minimum disk outer radius required to explain the upper envelope of sub-mm/mm fluxes is {approx}100 AU for intermediate-mass stars, solar types, and VLMS, and {approx}20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M{sub *} from BDs to VLMS to solar-type stars, no such increase is observed from solar-type to intermediate-mass stars. We propose this is due to enhanced photoevaporation around intermediate stellar masses. (3) Many of the disks around Taurus and {rho} Oph intermediate-mass and solar-type stars evince an opacity index of {beta} {approx} 0-1, indicating significant grain growth. Of the only four VLMS/BDs in these regions with multi-wavelength measurements, three are consistent with considerable grain growth, though optically thick disks are not ruled out. (4) For the TWA VLMS (TWA 30A and B), combining our 850 {mu}m fluxes with the known accretion rates and ages suggests substantial grain growth by 10 Myr, comparable to that in the previously studied TWA cTTs Hen 3-600A and TW Hya. The degree of grain growth in the TWA BDs (2M1207A and SSPM1102) remains largely unknown. (5) A

  15. Temperature constraints on the coldest brown dwarf known WISE 0855-0714

    CERN Document Server

    Beamín, J C; Bayo, A; Mužić, K; Boffin, H M J; Allard, F; Homeier, D; Minniti, D; Gromadzki, M; Kurtev, R; Lodieu, N; Martin, E L; Mendez, R A

    2014-01-01

    Context. Nearby isolated planetary mass objects are beginning to be discovered, but their individual properties are poorly constrained because their low surface temperatures and strong molecular self-absorption make them extremely faint. Aims. We aimed to detect the near infrared emission of the coldest brown dwarf (BD) found so far WISE0855$-$0714, located $\\sim$2.2 pc away, and to improve its temperature estimate (T$_{\\rm eff}$= 225-260 K) from a comparison with state of the art models of BD atmospheres. Methods. We observed the field containing WISE0855-0714 with HAWK-I at the VLT in the $Y$ band. For BDs with T$_{\\rm eff}24.4 mag at 3-$\\sigma$ level, leading to Y-[4.5]>10.5. Combining this limit with previous detections and upper limits at other wavelengths, WISE0855-0714 is confirmed as the reddest BD detected. We applied spectral energy distribution fitting with collections of models from two independent groups for extremely cool BD atmospheres leading to an effective temperature of T$_{\\rm eff}<$250...

  16. Spitzer and z' Secondary Eclipse Observations of the Highly Irradiated Transiting Brown Dwarf KELT-1b

    CERN Document Server

    Beatty, Thomas G; Fortney, Jonathan; Knutson, Heather; Gaudi, B Scott; Bruns, Jacob M; Showman, Adam P; Eastman, Jason; Pepper, Joshua; Siverd, Robert; Stassun, Keivan G; Kielkopf, John F

    2013-01-01

    We present secondary eclipse observations of the highly irradiated transiting brown dwarf KELT-1b. Using the Spitzer Space Telescope, we measure secondary eclipse depths of 0.195+/-0.010% at 3.6um and 0.200+/-0.012% at 4.5um, corresponding to a fairly grey color of [3.6]-[4.5]=0.07+/-0.11. Using four separate ground-based light curves, we find tentative evidence for the secondary eclipse in the z' band with a depth of 0.049+/-0.023%. These observations suggest that the amount of heat redistribution in the atmosphere to the night side is very low, and prefer a model in which there is no TiO inversion and a strong substellar hotspot. However, models with no TiO and a more mild hotspot, or with TiO absorption and complete dayside redistribution, are only marginally disfavored. The eclipse timings and durations indicate that the orbital eccentricity of KELT-1b is consistent with circular to better than a percent. These observations represent the first constraints on the atmospheric dynamics of a highly irradiated...

  17. Rare White dwarf stars with carbon atmospheres

    OpenAIRE

    Dufour, P.; Liebert, James; Fontaine, G.; Behara, N.

    2007-01-01

    White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 msun and 8-10 msun, where msun is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for ~80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs...

  18. Pure hydrogen atmosphere for very cool white dwarfs

    CERN Document Server

    Saumon, D S

    1999-01-01

    Microlensing events observed in the line of sight toward the LMC indicate that a significant fraction of the mass of the dark halo of the Galaxy is probably composed of white dwarfs. In addition, white dwarf sequences have now be observed in the HR diagrams of several globular clusters. Because of the unavailability of white dwarf atmospheres for Teff < 4000K, cooling time scales for white dwarfs older than ~ 10 Gyr are very uncertain. Moreover, the identification of a MACHO white dwarf population by direct observation depends on a knowledge of the colors and bolometric corrections of very-cool white dwarfs. In this paper we present the first detailed model atmospheres and spectra of very cool hydrogen white dwarfs for Teff < 4000K. We include the latest description of the opacities of hydrogen and significantly, we introduce a non-ideal equation of state in the atmosphere calculation. We find that due to strong absorption from H_2 in the infrared, very old white dwarfs are brightest in the V, R, and I ...

  19. Mid-infrared followup of cold brown dwarfs: diversity in age, mass and metallicity

    Energy Technology Data Exchange (ETDEWEB)

    Saumon, Didier [Los Alamos National Laboratory; Leggett, Sandy K [GEMINI OBSERVATORY; Burningham, Ben [HERTFORDSHITE UNIV; Marley, Mark S [NASA AMES; Waren, S J [IMPERIAL COLLEGE LONDON; Jones, H R A [HERTFORDSHIRE U; Pinfield, D J [HERTFORDSHIRE U; Smart, R L [ASTRONOMICAL OBS

    2009-01-01

    We present new Spitzer IRAC [3.6], [4.5], [5.8] and [8.0] photometry of nine very late-type T dwarfs. Combining this with previously published photometry, we investigate trends with type and color that are useful for both the planning and interpretation of infrared surveys designed to discover the coldest T or Y dwarfs. Brown dwarfs with effective temperature (T{sub eff}) below 700 K emit more than half their flux at wavelengths longer than 3 {micro}m, and the ratio of the mid-infrared flux to the near-infrared flux becomes very sensitive to T{sub eff} at these low temperatures. We confirm that the color H (1.6 {micro}m) - [4.5] is a good indicator of T{sub eff} with a relatively weak dependence on metallicity and gravity. Conversely, the colors H - K (2.2 {micro}m) and [4.5] - [5.8] are sensitive to metallicity and gravity. Thus near- and mid-infrared photometry provide useful indicators of the fundamental properties of brown dwarfs, and if temperature and gravity are known, then mass and age can be reliably determined from evolutionary models. There are twelve dwarfs currently known with H - [4.5] > 3.0, and {approx} 500 < T{sub eff} K {approx}< 800, which we examine in detail. The ages of the dwarfs in the sample range from very young (0.1 - 1.0 Gyr) to relatively old (3 - 12 Gyr). The mass range is possibly as low as 5 Jupiter masses to up to 70 Jupiter masses, i.e. near the hydrogen burning limit. The metallicities also span a large range, from [m/H]= -0.3 to [m/H]= +0.2. The small number of T8 - T9 dwarfs found in the UKIRT Infrared Deep Sky Survey to date appear to be predominantly young low-mass dwarfs. Accurate mid-infrared photometry of cold brown dwarfs is essentially impossible from the ground, and extensions to the mid-infrared space missions warm-Spitzer and WISE are desirable in order to obtain the vital mid-infrared data for cold brown dwarfs, and to discover more of these rare objects.

  20. CHARACTERIZING THE BROWN DWARF FORMATION CHANNELS FROM THE INITIAL MASS FUNCTION AND BINARY-STAR DYNAMICS

    International Nuclear Information System (INIS)

    The stellar initial mass function (IMF) is a key property of stellar populations. There is growing evidence that the classical star-formation mechanism by the direct cloud fragmentation process has difficulties reproducing the observed abundance and binary properties of brown dwarfs and very-low-mass stars. In particular, recent analytical derivations of the stellar IMF exhibit a deficit of brown dwarfs compared to observational data. Here we derive the residual mass function of brown dwarfs as an empirical measure of the brown dwarf deficiency in recent star-formation models with respect to observations and show that it is compatible with the substellar part of the Thies-Kroupa IMF and the mass function obtained by numerical simulations. We conclude that the existing models may be further improved by including a substellar correction term that accounts for additional formation channels like disk or filament fragmentation. The term ''peripheral fragmentation'' is introduced here for such additional formation channels. In addition, we present an updated analytical model of stellar and substellar binarity. The resulting binary fraction and the dynamically evolved companion mass-ratio distribution are in good agreement with observational data on stellar and very-low-mass binaries in the Galactic field, in clusters, and in dynamically unprocessed groups of stars if all stars form as binaries with stellar companions. Cautionary notes are given on the proper analysis of mass functions and the companion mass-ratio distribution and the interpretation of the results. The existence of accretion disks around young brown dwarfs does not imply that these form just like stars in direct fragmentation

  1. CHARACTERIZING THE BROWN DWARF FORMATION CHANNELS FROM THE INITIAL MASS FUNCTION AND BINARY-STAR DYNAMICS

    Energy Technology Data Exchange (ETDEWEB)

    Thies, Ingo; Pflamm-Altenburg, Jan; Kroupa, Pavel; Marks, Michael [Helmholtz-Institut für Strahlen- und Kernphysik (HISKP), Universität Bonn, Nussallee 14-16, D-53115 Bonn (Germany)

    2015-02-10

    The stellar initial mass function (IMF) is a key property of stellar populations. There is growing evidence that the classical star-formation mechanism by the direct cloud fragmentation process has difficulties reproducing the observed abundance and binary properties of brown dwarfs and very-low-mass stars. In particular, recent analytical derivations of the stellar IMF exhibit a deficit of brown dwarfs compared to observational data. Here we derive the residual mass function of brown dwarfs as an empirical measure of the brown dwarf deficiency in recent star-formation models with respect to observations and show that it is compatible with the substellar part of the Thies-Kroupa IMF and the mass function obtained by numerical simulations. We conclude that the existing models may be further improved by including a substellar correction term that accounts for additional formation channels like disk or filament fragmentation. The term ''peripheral fragmentation'' is introduced here for such additional formation channels. In addition, we present an updated analytical model of stellar and substellar binarity. The resulting binary fraction and the dynamically evolved companion mass-ratio distribution are in good agreement with observational data on stellar and very-low-mass binaries in the Galactic field, in clusters, and in dynamically unprocessed groups of stars if all stars form as binaries with stellar companions. Cautionary notes are given on the proper analysis of mass functions and the companion mass-ratio distribution and the interpretation of the results. The existence of accretion disks around young brown dwarfs does not imply that these form just like stars in direct fragmentation.

  2. A submillimetre search for pre- and proto-brown dwarfs in Chamaeleon II

    Science.gov (United States)

    de Gregorio-Monsalvo, I.; Barrado, D.; Bouy, H.; Bayo, A.; Palau, A.; Morales-Calderón, M.; Huélamo, N.; Morata, O.; Merín, B.; Eiroa, C.

    2016-05-01

    Context. The Chamaeleon II molecular cloud is an active star-forming region that offers an excellent opportunity to study the formation of brown dwarfs in the southern hemisphere. Aims: Our aims are to identify a population of pre- and proto-brown dwarfs (5σ mass limit threshold of ~0.015 M⊙) and provide information on the formation mechanisms of substellar objects. Methods: We performed high sensitivity observations at 870 μm using the LABOCA bolometer at the APEX telescope towards an active star-forming region in Chamaeleon II. The data are complemented by an extensive multiwavelength catalogue of sources, which covers the optical to the far-infrared, to study the nature of the LABOCA detections. Results: We detect 15 cores at 870 μm, and 11 of them show masses in the substellar regime. The most intense objects in the surveyed field correspond to the submillimetre counterparts of the well-known young stellar objects DK Cha and IRAS 12500-7658. We identify a possible proto-brown dwarf candidate (ChaII-APEX-L) with IRAC emission at 3.6 and 4.5 μm. Conclusions: Our analysis indicates that most of the spatially resolved cores are transient, and that the point-like starless cores in the substellar regime (with masses between 0.016 M⊙ and 0.066 M⊙) could be pre-brown dwarfs cores that are gravitationally unstable if they have radii less than 220 AU to 907 AU (1.2'' to 5'' at 178 pc), respectively, for different masses. ALMA observations will be key to revealing the energetic state of these pre-brown dwarfs candidates.

  3. $Extrasolar~Storms$: Pressure-dependent Changes In Light Curve Phase In Brown Dwarfs From Simultaneous $Hubble$ and $Spitzer$ Observations

    CERN Document Server

    Yang, Hao; Marley, Mark S; Karalidi, Theodora; Flateau, Davin; Showman, Adam P; Metchev, Stanimir; Buenzli, Esther; Radigan, Jacqueline; Artigau, Étienne; Lowrance, Patrick J; Burgasser, Adam J

    2016-01-01

    We present $Spitzer$/IRAC Ch1 and Ch2 monitoring of six brown dwarfs during 8 different epochs over the course of 20 months. For four brown dwarfs, we also obtained simulataneous $HST$/WFC3 G141 Grism spectra during two epochs and derived light curves in five narrow-band filters. Probing different pressure levels in the atmospheres, the multi-wavelength light curves of our six targets all exhibit variations, and the shape of the light curves evolves over the timescale of a rotation period, ranging from 1.4 h to 13 h. We compare the shapes of the light curves and estimate the phase shifts between the light curves observed at different wavelengths by comparing the phase of the primary Fourier components. We use state-of-the-art atmosphere models to determine the flux contribution of different pressure layers to the observed flux in each filter. We find that the light curves that probe higher pressures are similar and in phase, but are offset and often different from the light curves that probe lower pressures. ...

  4. Population Properties of Brown Dwarf Analogs to Exoplanets

    CERN Document Server

    Faherty, Jacqueline K; Cruz, Kelle L; Gagne, Jonathan; Filippazzo, Joseph C; Lambrides, Erini; Fica, Haley; Weinberger, Alycia; Thorstensen, John R; Tinney, C G; Baldassare, Vivienne; Lemonier, Emily; Rice, Emily L

    2016-01-01

    We present a kinematic analysis of 152 low surface gravity M7-L8 dwarfs by adding 8 parallaxes, 38 radial velocities, and 19 proper motions. We find 39 objects to be high-likelihood or bona fide members of nearby moving groups, 92 objects to be ambiguous members and 21 objects that are non-members. We find that gravity classification and photometric color separate 5-150 Myr sources from > 3 Gyr field objects, but they do not correlate one-to-one with the narrower 5 -150 Myr age range. The absolute magnitudes of low-gravity sources from J band through W3 show a flux redistribution when compared to equivalent field sources that is correlated with spectral subtype. Clouds, which are a far more dominant opacity source for L dwarfs, are the likely cause. On CMDs, the latest-type low-gravity L dwarfs drive the elbow of the L/T transition up to 1 mag redder and 1 mag fainter than field dwarfs at M_J but are consistent with or brighter than the elbow at M_W1 and M_W2. Furthermore, there is an indication on CMD's (suc...

  5. The Surface Densities of Disk Brown Dwarfs in JWST Surveys

    Science.gov (United States)

    Ryan, R. E., Jr.; Reid, I. N.

    2016-04-01

    We present predictions for the surface density of ultracool dwarfs (with spectral types M8-T8) for a host of deep fields that are likely to be observed with the James Webb Space Telescope. Based on simple thin and thick/thin disk (exponential) models, we show that the typical distance modulus is μ ≈ 9.8 mag, which at high Galactic latitude is 5{log}(2 {z}{scl})-5. Since this is a property of the density distribution of an exponential disk, it is independent of spectral type or stellar sample. Using the published estimates of the ultracool dwarf luminosity function, we show that their number counts typically peak around J˜ 24 mag with a total surface density of {{Σ }}˜ 0.3 arcmin-2, but with a strong dependence on galactic coordinate and spectral type. Owing to the exponential shape of the disk, the ultracool dwarfs are very rare at faint magnitudes (J≥slant 27 mag), with typical densities of {{Σ }}˜ 0.005 arcmin-2 (or ˜ 20% of the total contribution within the field). Therefore, in very narrow and deep fields, we predict there are only a few ultracool dwarfs, and hence these stars are likely not a severe contaminant in searches for high-redshift galaxies. Furthermore, the ultracool dwarfs are expected to be considerably brighter than the high-redshift galaxies, so samples near the faint end of the high-redshift galaxy population will be the purest. We present the star-count formalism in a simplified way so that observers may easily predict the number of stars for their conditions (field, depth, wavelength, etc.).

  6. Go Long! Identifying Distant Brown Dwarfs in HST/WFC3 Parallel Field

    Science.gov (United States)

    Aganze, Christian; Burgasser, Adam J.; Malkan, Matthew Arnold; Masters, Daniel C.; Mercado, Gretel; Suarez, Adrian; Tamiya, Tomoki

    2016-01-01

    The spatial distribution of brown dwarfs beyond the local Solar Neighborhood is crucial for understanding their Galactic formation, dynamical and evolutionary history. Wide-field red optical and infrared surveys (e.g., 2MASS, SDSS, WISE) have enabled measures of the local density of brown dwarfs, but probe a relatively shallow (˜100 parsecs) volume; few constraints exist for the scale height or radial distributions of these low mass and low luminosity objects. We have searched ~1400 square arcminutes of WFC3 Infrared Spectroscopic Parallel Survey (WISPS) data to identify distant brown dwarfs (d > 300 pc) with near-infrared grism spectra from the the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3). Using spectral indices to identify candidates, measure spectral types and estimate distances, and comparing the WFC3 spectra to spectral templates in the SpeX Prism Library, we report our first results from this work, the discovery of ~50 late-M, L and T dwarfs with distances of 30 - 1000+ pc. We compare the distance and spectral type distribution to population simulations, and discuss current selection biases.The material presented here is based on work supported by the National Aeronautics and Space Administration under Grant No. NNX15AI75G

  7. Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Lumninous Infrared Galaxy Candidates

    Science.gov (United States)

    Griffith, Roger L.; Kirkpatrick, J. Davy; Eisenhardt, Peter R. M.; Gelino, Christopher R.; Cushing, Michael C.; Benford, Dominic; Blain, Andrew; Bridge, Carrie R.; Cohen, Martin; Cutri, Roc M.; Donoso, Emilio; Jarrett, Thomas H.; Lonsdale, Carol; Mace, Gregory; Mainzer, A.; Marsh, Ken; Padgett, Deborah; Petty, Sara; Ressler, Michael E.; Skrutskie, Michael F.; Stanford, Spencer A.; Stern, Daniel; Tsai, Chao-Wei; Wright, Edward L.; Wu, Jingwen

    2012-01-01

    We present Spitzer 3.6 and 4.5 micrometer photometry and positions for a sample of 1510 brown dwarf candidates identified by the Wide-field Infrared Survey Explorer (WISE) all-sky survey. Of these, 166 have been spectroscopically classified as objects with spectral types M(1), L(7), T(146), and Y(12). Sixteen other objects are non-(sub)stellar in nature. The remainder are most likely distant L and T dwarfs lacking spectroscopic verification, other Y dwarf candidates still awaiting follow-up, and assorted other objects whose Spitzer photometry reveals them to be background sources. We present a catalog of Spitzer photometry for all astrophysical sources identified in these fields and use this catalog to identify seven fainter (4.5 m to approximately 17.0 mag) brown dwarf candidates, which are possibly wide-field companions to the original WISE sources. To test this hypothesis, we use a sample of 919 Spitzer observations around WISE-selected high-redshift hyper-luminous infrared galaxy candidates. For this control sample, we find another six brown dwarf candidates, suggesting that the seven companion candidates are not physically associated. In fact, only one of these seven Spitzer brown dwarf candidates has a photometric distance estimate consistent with being a companion to the WISE brown dwarf candidate. Other than this, there is no evidence for any widely separated (greater than 20 AU) ultra-cool binaries. As an adjunct to this paper, we make available a source catalog of 7.33 x 10(exp 5) objects detected in all of these Spitzer follow-up fields for use by the astronomical community. The complete catalog includes the Spitzer 3.6 and 4.5 m photometry, along with positionally matched B and R photometry from USNO-B; J, H, and Ks photometry from Two Micron All-Sky Survey; and W1, W2, W3, and W4 photometry from the WISE all-sky catalog.

  8. The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs

    CERN Document Server

    McLean, I S; McGovern, M R; Burgasser, A J; Kirkpatrick, J D; Rice, E L; Kim, S S; Lean, Ian S. Mc; Govern, Mark R. Mc; Burgasser, Adam J.; Rice, Emily L.; Kim, Sungsoo S.

    2006-01-01

    We present a sequence of high resolution (R~20,000 or 15 km/s) infrared spectra of stars and brown dwarfs spanning spectral types M2.5 to T6. Observations of 16 objects were obtained using eight echelle orders to cover part of the J-band from 1.165-1.323 micron with NIRSPEC on the Keck II telescope. By comparing opacity plots and line lists, over 200 weak features in the J-band are identified with either FeH or H2O transitions. Absorption by FeH attains maximum strength in the mid-L dwarfs, while H2O absorption becomes systematically stronger towards later spectral types. Narrow resolved features broaden markedly after the M to L transition. Our high resolution spectra also reveal that the disappearance of neutral Al lines at the boundary between M and L dwarfs is remarkably abrupt, presumably because of the formation of grains. Neutral Fe lines can be traced to mid-L dwarfs before Fe is removed by condensation. The neutral potassium (K I) doublets that dominate the J-band have pressure broadened wings that c...

  9. The Surface Densities of Disk Brown Dwarfs in JWST Surveys

    CERN Document Server

    Ryan, R E

    2015-01-01

    We present predictions for the surface density of ultracool dwarfs (with spectral types M8-T8) for a host of deep fields that are likely to be observed with the James Webb Space Telescope. Based on simple thin and thick/thin disk (exponential) models, we show the typical distance modulus is mu~9.8 mag, which at high Galactic latitude is 5log(2 z_scl)-5. Since this is a property of the density distribution of an exponential disk, it is independent of spectral type or stellar sample. Using the published estimates of the ultracool dwarf luminosity function, we show that their number counts typically peak around J~24 mag with a total surface density of Sigma ~ 0.3 arcmin^-2, but with a strong dependence on galactic coordinate and spectral type. Owing to the exponential shape of the disk, the ultracool dwarfs are very rare at faint magnitudes (J>~27 mag), with typical densities of Sigma~0.005 arcmin^-2 (or ~20% of the total contribution within the field). Therefore in the very narrow and deep fields, we predict th...

  10. UKIDSS detections of cool brown dwarfs - proper motions of 14 known $>$T5 dwarfs and discovery of three new T5.5-T6 dwarfs

    CERN Document Server

    Scholz, Ralf-Dieter; Schnurr, Olivier; Storm, Jesper

    2012-01-01

    AIMS: We contribute to improving the census of cool brown dwarfs (late-T and Y dwarfs) in the immediate solar neighbourhood. METHODS: By combining near-infrared (NIR) data of UKIDSS with mid-infrared WISE and other available NIR (2MASS) and red optical (SDSS $z$-band) multi-epoch data we detect high proper motion (HPM) objects with colours typical of late spectral types ($>$T5). We use NIR low-resolution spectroscopy for the classification of new candidates. RESULTS: We determined new proper motions for 14 known T5.5-Y0 dwarfs, many of them being significantly ($>$2-10 times) more accurate than previous ones. We detected three new candidates, ULAS J0954+0623, ULAS J1152+0359, and ULAS J1204-0150, by their HPMs and colours. Using previously published and new UKIDSS positions of the known nearby T8 dwarf WISE J0254+0223 we improved its trigonometric parallax to 165$\\pm$20 mas. For the three new objects we obtained NIR spectroscopic follow-up with LBT/LUCIFER classifying them as T5.5 and T6 dwarfs. With their es...

  11. ALMA and CARMA observations of Brown Dwarfs disks: testing the models of dust evolution

    CERN Document Server

    Ricci, L; Natta, A; Scholz, A; de Gregorio-Monsalvo, I; Isella, A; Carpenter, J M

    2013-01-01

    The first steps toward planet formation involve the coagulation of small microscopic grains into larger and larger pebbles and rocks in gas-rich disks around young stars and brown dwarfs. Observations in the sub-millimeter can trace mm/cm-sized pebbles in the outer disks, and investigate the mechanisms of coagulation/fragmentation and radial migration of these solids. These represent key, yet not fully understood ingredients for our understanding of the formation of planetesimals, the building blocks of planets. Here we present the first results from an observational program using the ALMA and CARMA sub-mm/mm interferometers aimed at characterizing the dust properties and disk structure of young disks around brown dwarfs and very low mass stars. Given the physical conditions expected for these disks, they represent critical test beds for the models of the early stages of planet formation in proto-planetary disks.

  12. Exoplanets versus brown dwarfs: the CoRoT view and the future

    CERN Document Server

    Schneider, Jean

    2016-01-01

    CoRoT has detected by transit several tens of objects whose radii run from 1.67 Earth radius. Their mass run from less than 5.7 Earth mass (CoRoT-24 b, Alonso et al. 2014) to 63 Jupiter mass (CoRoT-15 b, Bouchy et al. 2011). One could be tempted to think that more massive the object is, the larger it is in size and that there is some limit in mass and/or radius beyond which objects are not planets but very low mass stars below the 80 Jupiter mass limit to trigger nuclear fusion (namely "brown dwarfs" ). CoRoT findings contribute to the planet versus brown dwarf debate since there is no clear mass-radius relation.

  13. Characterization of a Brown Rot Fungus Isolated from Dwarf Flowering Almond in Korea

    OpenAIRE

    Shim, Myoung Yong; Jeon, Young Jae; Kim, Seong Hwan

    2007-01-01

    The fruits showing brown rot symptom on dwarf flowering almond were found in Gongju, Chungchungnam-Do in Korea in July 2005. Small water-soaked lesions on the fruits were initiated, and gradually developed to soft rot covered with gray conidia. Then the diseased fruits were shrunk and became grayish-black mummies. A fungus was isolated from the diseased fruit and its morphological, cultural and molecular genetic characteristics were investigated. Typical blastospores of Monilinia spp. were ob...

  14. A search for brown dwarf like secondaries in cataclysmic variables

    Science.gov (United States)

    Mennickent, R. E.; Diaz, M. P.

    2002-11-01

    We present VTL/ISAAC infrared spectroscopy of a sample of short-orbital-period cataclysmic variables that are candidates for harbouring substellar companions. We have detected the K I and Na I absorption lines of the companion star in VY Aqr. The overall spectral distribution in this system is best fitted with an M9.5 type dwarf spectrum, implying a distance of 100 +/- 10 pc. VY Aqr seems to fall far from the theoretical distribution of secondary star temperatures around the orbital period minimum. Fitting of the IR spectral energy distribution (SED) was performed by comparing the observed spectrum with late-type templates. The application of such a spectral fitting procedure suggests that the continuum shape in the 1.1-2.5 μm spectral region in short-orbital-period cataclysmic variables may be a useful indicator of the companion's spectral type. SED fitting for RZ Leo and CU Vel suggests M5-type dwarf companions, and distances of 340 +/- 110 and 150 +/- 50 pc, respectively. These systems may be placed in the upper evolution branch for short-period cataclysmic variables.

  15. Accretion-ejection connection in the young brown dwarf candidate ISO-Cha1 217

    CERN Document Server

    Whelan, E T; Bacciotti, F; Nisini, B; Bonito, R; Antoniucci, S; Stelzer, B; Biazzo, K; D'Elia, V; Ray, T P

    2014-01-01

    As the number of observed brown dwarf outflows is growing it is important to investigate how these outflows compare to the well studied jets from young stellar objects. A key point of comparison is the relationship between outflow and accretion activity and in particular the ratio between the mass outflow and accretion rates ($\\dot{M}_{out}$/$\\dot{M}_{acc}$). The brown dwarf candidate ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric study of brown dwarfs, to be driving an asymmetric outflow with the blue-shifted lobe having a position angle of $\\sim$ 20$^{\\circ}$. The aim here is to further investigate the properties of ISO-ChaI 217, the morphology and kinematics of its outflow, and to better constrain ($\\dot{M}_{out}$/$\\dot{M}_{acc}$). The outflow is spatially resolved in the $[SII]\\lambda \\lambda 6716,6731$ lines and is detected out to $\\sim$ 1\\farcs6 in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry between the two lobes is confirmed although the velocity as...

  16. Young, Low-Mass Brown Dwarfs with Mid-Infrared Excesses

    CERN Document Server

    Allers, K N; Jaffe, D T; Kessler-Silacci, J E

    2006-01-01

    We have combined new I, J, H, and Ks imaging of portions of the Chamaeleon II, Lupus I, and Ophiuchus star-forming clouds with 3.6 to 24 micron imaging from the Spitzer Legacy Program, "From Molecular Clouds to Planet Forming Disks", to identify a sample of 19 young stars, brown dwarfs and sub-brown dwarfs showing mid-infrared excess emission. The resulting sample includes sources with luminosities of 0.5>log(L/Lsun)>-3.1. Six of the more luminous sources in our sample have been previously identified by other surveys for young stars and brown dwarfs. Five of the sources in our sample have nominal masses at or below the deuterium burning limit (~12 M_J). Over three decades in luminosity, our sources have an approximately constant ratio of excess to stellar luminosity. We compare our observed SEDs to theoretical models of a central source with a passive irradiated circumstellar disk and test the effects of disk inclination, disk flaring, and the size of the inner disk hole on the strength/shape of the excess. T...

  17. The BANYAN All-Sky Survey for Brown Dwarf Members of Young Moving Groups

    CERN Document Server

    Gagné, Jonathan; Doyon, René; Faherty, Jacqueline K; Malo, Lison; Cruz, Kelle L; Artigau, Étienne; Burgasser, Adam J; Naud, Marie-Eve; Bouchard, Sandie; Gizis, John E; Albert, Loïc

    2015-01-01

    We describe in this work the BASS survey for brown dwarfs in young moving groups of the solar neighborhood, and summarize the results that it generated. These include the discovery of the 2MASS J01033563-5515561 (AB)b and 2MASS J02192210-3925225 B young companions near the deuterium-burning limit as well as 44 new low-mass stars and 69 new brown dwarfs with a spectroscopically confirmed low gravity. Among those, ~20 have estimated masses within the planetary regime, one is a new L4 $\\gamma$ bona fide member of AB Doradus, three are TW Hydrae candidates with later spectral types (L1-L4) than all of its previously known members and six are among the first contenders to low-gravity $\\geq$ L5 $\\beta$/$\\gamma$ brown dwarfs, reminiscent of WISEP J004701.06+680352.1, PSO J318.5338-22.8603 and VHS J125601.92-125723.9 b. Finally, we describe a future version of this survey, BASS-Ultracool, that will specifically target $\\geq$ L5 candidate members of young moving groups. First experimentations in designing the survey h...

  18. Rotation Periods of Young Brown Dwarfs: K2 Survey in Upper Scorpius

    CERN Document Server

    Scholz, Aleks; Jayawardhana, Ray; Muzic, Koraljka

    2015-01-01

    We report rotational periods for 16 young brown dwarfs in the nearby Upper Scorpius association, based on 72 days of high-cadence, high-precision photometry from the Kepler space telescope's K2 mission. The periods range from a few hours to two days (plus one outlier at 5 days), with a median just above one day, confirming that brown dwarfs, except at the very youngest ages, are fast rotators. Interestingly, four of the slowest rotators in our sample exhibit mid-infrared excess emission from disks; at least two also show signs of disk eclipses and accretion in the lightcurves. Comparing these new periods with those for two other young clusters and simple angular momentum evolution tracks, we find little or no rotational braking in brown dwarfs between 1-10 Myr, in contrast to low-mass stars. Our findings show that disk braking, while still at work, is inefficient in the substellar regime, thus provide an important constraint on the mass dependence of the braking mechanism.

  19. Mid-Infrared Selection of Brown Dwarfs and High-Redshift Quasars

    CERN Document Server

    Stern, D; Allen, L; Bian, C; Blain, A; Brand, K; Brodwin, M; Brown, M J I; Cool, R; Desai, V; Dey, A; Eisenhardt, P; González, A; Jannuzi, B T; Menendez-Delmestre, K; Smith, H A; Soifer, B T; Tiede, G P; Wright, E

    2006-01-01

    We discuss color selection of rare objects in a wide-field, multiband survey spanning from the optical to the mid-infrared. Simple color criteria simultaneously identify and distinguish two of the most sought after astrophysical sources: the coolest brown dwarfs and the most distant quasars. We present spectroscopically-confirmed examples of each class identified in the IRAC Shallow Survey of the Bootes field of the NOAO Deep Wide-Field Survey. ISS J142950.9+333012 is a T4.5 brown dwarf at a distance of approximately 42 pc, and ISS J142738.5+331242 is a radio-loud quasar at redshift z=6.12. Our selection criteria identify a total of four candidates over 8 square degrees of the Bootes field. The other two candidates are both confirmed 5.5brown dwarfs and higher redshift quasars.

  20. EPIC201702477b: A Long Period Transiting Brown Dwarf from K2

    CERN Document Server

    Bayliss, D; Santerne, A; Dragomir, D; Zhou, G; Shporer, A; Colón, K D; Almenara, J; Armstrong, D J; Barrado, D; Barros, S C C; Bento, J; Boisse, I; Bouchy, F; Brown, D J A; Brown, T; Cameron, A; Cochran, W D; Demangeon, O; Deleuil, M; Díaz, R F; Fulton, B; Horne, K; Hébrard, G; Lillo-Box, J; Lovis, C; Mawet, D; Ngo, H; Osborn, H; Palle, E; Petigura, E; Pollacco, D; Santos, N; Sefako, R; Siverd, R; Sousa, S G; Tsantaki, M

    2016-01-01

    We report the discovery of EPIC201702477b, a transiting brown dwarf in a long period (40.73691 +/- 0.00037 day) and eccentric (e=0.2281 +/- 0.0026) orbit. This system was initially reported as a planetary candidate based on two transit events seen in K2 Campaign 1 photometry and later validated as an exoplanet. We confirm the transit and refine the ephemeris with two subsequent ground-based detections of the transit using the LCOGT 1m telescope network. We rule out any transit timing variations above the level of 30s. Using high precision radial velocity measurements from HARPS and SOPHIE we identify the transiting companion as a brown dwarf with a mass, radius, and bulk density of 66.9 +/- 1.7 M$_J$, 0.757 +/- 0.065 R$_J$, and 191+/-51 g.cm$^{-3}$ respectively. EPIC201702477b is the smallest radius brown dwarf yet discovered, with a mass just below the H-burning limit. It has the highest density of any planet, substellar mass object or main-sequence star discovered so far. We find evidence in the set of know...

  1. X-ray emission from young brown dwarfs in the Orion Nebula Cluster

    CERN Document Server

    Preibisch, T; Grosso, N; Feigelson, E D; Flaccomio, E; Getman, K; Hillenbrand, L A; Meeus, G; Micela, G; Sciortino, S; Stelzer, B; Preibisch, Thomas; Caughrean, Mark J. Mc; Grosso, Nicolas; Feigelson, Eric D.; Flaccomio, Ettore; Getman, Konstantin; Hillenbrand, Lynne A.; Meeus, Gwendolyn; Micela, Giusi; Sciortino, Salvatore; Stelzer, Beate

    2005-01-01

    We use the sensitive X-ray data from the Chandra Orion Ultradeep Project (COUP) to study the X-ray properties of 34 spectroscopically-identified brown dwarfs with near-infrared spectral types between M6 and M9 in the core of the Orion Nebula Cluster. Nine of the 34 objects are clearly detected as X-ray sources. The apparently low detection rate is in many cases related to the substantial extinction of these brown dwarfs; considering only the BDs with $A_V \\leq 5$ mag, nearly half of the objects (7 out of 16) are detected in X-rays. Our 10-day long X-ray lightcurves of these objects exhibit strong variability, including numerous flares. While one of the objects was only detected during a short flare, a statistical analysis of the lightcurves provides evidence for continuous (`quiescent') emission in addition to flares for all other objects. Of these, the $\\sim$ M9 brown dwarf COUP 1255 = HC 212 is one of the coolest known objects with a clear detection of quiescent X-ray emission. The X-ray properties (spectra...

  2. The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data

    CERN Document Server

    Tsvetanov, Z I

    2000-01-01

    We report the discovery of a second field methane brown dwarf from the commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS J134646.45-003150.4 (SDSS 1346-00), was selected because of its very red color and stellar appearance. Its spectrum between 0.8-2.5 mic is dominated by strong absorption bands of H_2O and CH_4 and closely mimics those of Gliese 229B and SDSS 162414.37+002915.6 (SDSS 1624+00), two other known methane brown dwarfs. SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that it lies about 11 pc from the sun. The ratio of flux at 2.1 mic to that at 1.27 mic is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which suggests that SDSS 1346-00 has a slightly higher effective temperature than the others. Based on a search area of 130 sq. deg. and a detection limit of z* = 19.8, we estimate a space density of 0.05 pc^-3 for methane brown dwarfs with T_eff ~ 1000 K in the 40 pc^3 volume of our search. This estimate is based on small-sample s...

  3. The SOPHIE search for northern extrasolar planets IX. Populating the brown dwarf desert

    CERN Document Server

    Wilson, P A; Santos, N C; Sahlmann, J; Montagnier, G; Astudillo-Defru, N; Boisse, I; Bouchy, F; Rey, J; Arnold, L; Bonfils, X; Bourrier, V; Courcol, B; Deleuil, M; Delfosse, X; Díaz, R F; Ehrenreich, D; Forveille, T; Moutou, C; Pepe, F; Santerne, A; Ségransan, D; Udry, S

    2016-01-01

    Radial velocity planet search surveys of nearby Solar-type stars have shown a strong deficit of brown dwarf companions within $\\sim5\\,\\mathrm{AU}$. There is presently no comprehensive explanation of this lack of brown dwarf companions, therefore, increasing the sample of such objects is crucial to understand their formation and evolution. Based on precise radial velocities obtained using the SOPHIE spectrograph at Observatoire de Haute-Provence we characterise the orbital parameters of $15$ companions to solar-type stars and constrain their true mass using astrometric data from the Hipparcos space mission. The nine companions not shown to be stellar in nature have minimum masses ranging from ~$13$ to $70\\,\\mathrm{M}_{\\mathrm{Jup}}$, and are well distributed across the planet/brown dwarf mass regime, making them an important contribution to the known population of massive companions around solar-type stars. We characterise six companions as stellar in nature with masses ranging from a minimum mass of $76 \\pm 4...

  4. The SOPHIE search for northern extrasolar planets. IX. Populating the brown dwarf desert

    Science.gov (United States)

    Wilson, P. A.; Hébrard, G.; Santos, N. C.; Sahlmann, J.; Montagnier, G.; Astudillo-Defru, N.; Boisse, I.; Bouchy, F.; Rey, J.; Arnold, L.; Bonfils, X.; Bourrier, V.; Courcol, B.; Deleuil, M.; Delfosse, X.; Díaz, , R. F.; Ehrenreich, D.; Forveille, T.; Moutou, C.; Pepe, F.; Santerne, A.; Ségransan, D.; Udry, S.

    2016-04-01

    Radial velocity planet search surveys of nearby solar-type stars have shown a strong scarcity of brown dwarf companions within ~5 AU. There is presently no comprehensive explanation for this lack of brown dwarf companions; therefore, increasing the sample of such objects is crucial to understand their formation and evolution. Based on precise radial velocities obtained using the SOPHIE spectrograph at Observatoire de Haute-Provence we characterise the orbital parameters of 15 companions to solar-type stars and constrain their true mass using astrometric data from the Hipparcos space mission. The nine companions not shown to be stellar in nature have minimum masses ranging from ~13 to 70 MJup, and are well distributed across the planet/brown dwarf mass regime, making them an important contribution to the known population of massive companions around solar-type stars. We characterise six companions as stellar in nature with masses ranging from a minimum mass of 76 ± 4 MJup to a mass of 0.35 ± 0.03 M⊙. The orbital parameters of two previously known substellar candidates are improved. Based on observations collected with the SOPHIE spectrograph on the 1.93 m telescope at Observatoire de Haute-Provence (CNRS), France, by the SOPHIE Consortium.The radial velocity measurements are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A144

  5. A submillimeter search for pre- and proto-brown dwarfs in Chamaeleon II

    CERN Document Server

    de Gregorio-Monsalvo, I; Bouy, H; Bayo, A; Palau, Aina; Morales-Calderon, M; Huelamo, N; Morata, O; Merin, B; Eiroa, C

    2015-01-01

    Context. Chamaeleon II molecular cloud is an active star forming region that offers an excellent opportunity for studying the formation of brown dwarfs in the southern hemisphere. Aims. Our aims are to identify a population of pre- and proto- brown dwarfs (5 sigma mass limit threshold of ~0.015 Msun) and provide information on the formation mechanisms of substellar objects. Methods. We performed high sensitivity observations at 870 microns using the LABOCA bolometer at the APEX telescope towards an active star forming region in Chamaeleon II. The data are complemented with an extensive multiwavelength catalogue of sources from the optical to the far-infrared to study the nature of the LABOCA detections. Results. We detect fifteen cores at 870 microns, and eleven of them show masses in the substellar regime. The most intense objects in the surveyed field correspond to the submillimeter counterparts of the well known young stellar objects DK Cha and IRAS 12500-7658. We identify a possible proto-brown dwarf cand...

  6. Towards Precise Ages and Masses of Free Floating Planetary Mass Brown Dwarfs

    CERN Document Server

    Canty, James; Roche, Patrick; Pinfield, David

    2013-01-01

    Measurement of the substellar initial mass function (IMF) in very young clusters is hampered by the possibility of the age spread of cluster members. This is particularly serious for candidate planetary mass objects (PMOs), which have a very similar location to older and more massive brown dwarfs on the Hertzsprung-Russell Diagram (HRD). This degeneracy can be lifted by the measurement of gravity-sensitive spectral features. To this end we have obtained medium resolution (R~5000) Near-infrared Integral Field Spectrometer (NIFS) K band spectra of a sample of late M- / early L-type dwarfs. The sample comprises old field dwarfs and very young brown dwarfs in the Taurus association and in the Sigma Orionis cluster. We demonstrate a positive correlation between the strengths of the 2.21micron NaI doublet and the objects' ages. We demonstrate a further correlation between these objects' ages and the shape of their K band spectra. We have quantified this correlation in the form of a new index, the H2(K) index. This ...

  7. The atmospheric parameters of nearby white dwarfs revisited

    Science.gov (United States)

    Giammichele, N.; Bergeron, P.; Dufour, P.

    2010-11-01

    We present improved atmospheric parameters of nearby white dwarfs lying within 20 pc of the Sun. The aim of the current study is to obtain the best statistical model of the least-biased sample of the white dwarf population. A homogeneous analysis of the local population is performed combining detailed spectroscopic and photometric analyses based on improved model atmosphere calculations for various spectral types including DA, DQ, and DZ stars. The spectroscopic technique is applied to all stars in our sample for which optical spectra are available. Photometric energy distributions, when available, are also combined to trigonometric parallax measurements to derive effective temperatures, stellar radii, as well as atmospheric compositions. A revised catalog of white dwarfs in the solar neighborhood is completed. Effective temperature, mass distributions, and luminosity function are also discussed.

  8. Cloudless Atmospheres for L/T Dwarfs and Extrasolar Giant Planets

    Science.gov (United States)

    Tremblin, P.; Amundsen, D. S.; Chabrier, G.; Baraffe, I.; Drummond, B.; Hinkley, S.; Mourier, P.; Venot, O.

    2016-01-01

    The admitted, conventional scenario to explain the complex spectral evolution of brown dwarfs (BDs) since their first detection 20 years ago has always been the key role played by micron-size condensates, called "dust" or "clouds," in their atmosphere. This scenario, however, faces major problems, in particular the J-band brightening and the resurgence of FeH absorption at the L to T transition, and a physical first-principle understanding of this transition is lacking. In this Letter, we propose a new, completely different explanation for BD and extrasolar giant planet (EGP) spectral evolution, without the need to invoke clouds. We show that, due to the slowness of the CO/ CH4 and N2/NH3 chemical reactions, brown dwarf (L and T, respectively) and EGP atmospheres are subject to a thermo-chemical instability similar in nature to the fingering or chemical convective instability present in Earth oceans and at the Earth core/mantle boundary. The induced small-scale turbulent energy transport reduces the temperature gradient in the atmosphere, explaining the observed increase in near-infrared J-H and J-K colors of L dwarfs and hot EGPs, while a warming up of the deep atmosphere along the L to T transition, as the CO/CH4 instability vanishes, naturally solves the two aforementioned puzzles, and provides a physical explanation of the L to T transition. This new picture leads to a drastic revision of our understanding of BD and EGP atmospheres and their evolution.

  9. The Brown Dwarf Kinematics Project (BDKP). III. Parallaxes for 70 Ultracool Dwarfs

    OpenAIRE

    Faherty, Jacqueline K.; Burgasser, Adam J.; Walter, Frederick M.; van der Bliek, Nicole; Shara, Michael M.; Cruz, Kelle L.; West, Andrew A.; Vrba, Frederick J.; Anglada-Escud, Guillem

    2012-01-01

    We report parallax measurements for 70 ultracool dwarfs (UCDs). Using both literature values and our sample, we report new polynomial relations between spectral type and M$_{JHK}$. Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a "bright" (unresolved binary) and "faint" (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in M$_{J}$ where there is a [1.2 - 1...

  10. Search For Oxygen in Cool DQ White Dwarf Atmospheres

    OpenAIRE

    Kilic, M.; Winget, D. E.; von Hippel, T.; Lester, D. F.; Saumon, D

    2002-01-01

    We report new infrared spectroscopic observations of cool DQ white dwarfs by using Coolspec on the 2.7m Harlan-Smith Telescope. DQs have helium-rich atmospheres with traces of molecular carbon thought to be the result of convective dredge-up from their C/O interiors. Recent model calculations predict that oxygen should also be present in DQ atmospheres in detectable amounts. Our synthetic spectra calculations for He-rich white dwarfs with traces of C and O indicate that CO should be easily de...

  11. Molecular Abundances in the Atmosphere of the T Dwarf Gl 229B

    CERN Document Server

    Saumon, D S; Leggett, S K; Marley, M S; Freedman, R S; Lodders, K; Fegley, B; Sen-Gupta, S K

    2000-01-01

    We present new, high resolution, infrared spectra of the T dwarf Gliese 229B in the J, H, and K bandpasses. We analyze each of these as well as previously published spectra to determine its metallicity and the abundances of NH3 and CO in terms of the surface gravity of Gl 229B, which remains poorly constrained. The metallicity increases with increasing gravity and is below the solar value unless Gl 229B is a high-gravity brown dwarf with log g(cgs) ~ 5.5. The NH3 abundance is determined from both the H and the K band spectra which probe two different levels in the atmosphere. We find that the abundance from the K band data is well below that expected from chemical equilibrium, which we interpret as strong evidence for dynamical transport of NH3 in the atmosphere. This is consistent with the previous detection of CO and provides additional constraints on the dynamics of the atmosphere of this T dwarf.

  12. The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)

    Science.gov (United States)

    Kirkpatrick, J. Davy; Cushing, Michael C.; Gelino, Christopher R.; Griffith, Roger L.; Skrutskie, Michael F.; Marsh, Kenneth A.; Wright, Edward L.; Mainzer, A.; Eisenhardt, Peter R.; McLean, Ian S.; Thompson, Maggie A.; Bauer, James M.; Benford, Dominic J.; Bridge, Carrie R.; Lake, Sean E.; Petty, Sara M.; Stanford, S. A.; Tsai, Chao-Wei; Bailey, Vanessa; Beichman, Charles A.; Bloom, Joshua S.; Bochanski, John J.; Burgasser, Adam J.; Capak, Peter L.; Cruz, Kelle L.; Hinz, Philip M.; Kartaltepe, Jeyhan S.; Knox, Russell P.; Manohar, Swarnima; Masters, Daniel; Morales-Calderón, Maria; Prato, Lisa A.; Rodigas, Timothy J.; Salvato, Mara; Schurr, Steven D.; Scoville, Nicholas Z.; Simcoe, Robert A.; Stapelfeldt, Karl R.; Stern, Daniel; Stock, Nathan D.; Vacca, William D.

    2011-12-01

    We present ground-based spectroscopic verification of 6 Y dwarfs (see also Cushing et al.), 89 T dwarfs, 8 L dwarfs, and 1 M dwarf identified by the Wide-field Infrared Survey Explorer (WISE). Eighty of these are cold brown dwarfs with spectral types >=T6, six of which have been announced earlier by Mainzer et al. and Burgasser et al. We present color-color and color-type diagrams showing the locus of M, L, T, and Y dwarfs in WISE color space. Near-infrared and, in a few cases, optical spectra are presented for these discoveries. Near-infrared classifications as late as early Y are presented and objects with peculiar spectra are discussed. Using these new discoveries, we are also able to extend the optical T dwarf classification scheme from T8 to T9. After deriving an absolute WISE 4.6 μm (W2) magnitude versus spectral type relation, we estimate spectrophotometric distances to our discoveries. We also use available astrometric measurements to provide preliminary trigonometric parallaxes to four of our discoveries, which have types of L9 pec (red), T8, T9, and Y0; all of these lie within 10 pc of the Sun. The Y0 dwarf, WISE 1541-2250, is the closest at 2.8+1.3 -0.6 pc if this 2.8 pc value persists after continued monitoring, WISE 1541-2250 will become the seventh closest stellar system to the Sun. Another 10 objects, with types between T6 and >Y0, have spectrophotometric distance estimates also placing them within 10 pc. The closest of these, the T6 dwarf WISE 1506+7027, is believed to fall at a distance of ~4.9 pc. WISE multi-epoch positions supplemented with positional info primarily from the Spitzer/Infrared Array Camera allow us to calculate proper motions and tangential velocities for roughly one-half of the new discoveries. This work represents the first step by WISE to complete a full-sky, volume-limited census of late-T and Y dwarfs. Using early results from this census, we present preliminary, lower limits to the space density of these objects and discuss

  13. UKIDSS detections of cool brown dwarfs. Proper motions of 14 known >T5 dwarfs and discovery of three new T5.5-T6 dwarfs

    Science.gov (United States)

    Scholz, R.-D.; Bihain, G.; Schnurr, O.; Storm, J.

    2012-05-01

    Aims: We contribute to improving the census of cool brown dwarfs (late-T and Y dwarfs) in the immediate solar neighbourhood. Methods: By combining near-infrared (NIR) data of UKIDSS with mid-infrared WISE and other available NIR (2MASS) and red optical (SDSS z-band) multi-epoch data we detected high proper motion (HPM) objects with colours typical of late spectral types (>T5). We used NIR low-resolution spectroscopy for the classification of new candidates. Results: We determined new proper motions for 14 known T5.5-Y0 dwarfs, many of which are significantly (>2-10 times) more accurate than previous ones. We detected three new candidates, ULAS J0954+0623, ULAS J1152+0359, and ULAS J1204-0150, by their HPMs and colours. Using previously published and new UKIDSS positions of the known nearby T8 dwarf WISE J0254+0223 we improved its trigonometric parallax to 165 ± 20 mas. For the three new objects we obtained NIR spectroscopic follow-up with LBT/LUCIFER classifying them as T5.5 and T6 dwarfs. With their estimated spectroscopic distances of about 25-30 pc, their proper motions of about 430-650 mas/yr lead to tangential velocities of about 50-80 km s-1, typical of the Galactic thin-disk population. Based on observations with the Large Binocular Telescope (LBT)Tables 1-5 are available in electronic form at http://www.aanda.org

  14. Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs

    CERN Document Server

    Faherty, Jacqueline K; Burgasser, Adam J; Tinney, Chris; Osip, David J; Filippazzo, Joseph C; Simcoe, Robert A

    2014-01-01

    We present medium resolution optical and NIR spectral data for components of the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf binary. The optical spectra reveal strong 6708 A Li I absorption in both Luhman 16A (8.0+/-0.4 A) and Luhman 16B (3.8+/-0.4 A). Interestingly, this is the first detection of Li I absorption in a T dwarf. Combined with the lack of surface gravity features, the Li I detection constrains the system age to 0.1 - 3 Gyr. In the NIR data, we find strong KI absorption at 1.168, 1.177, 1.243, and 1.254 {\\mu}m in both components. Compared to the strength of KI line absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker while Luhman 16B is stronger. Analyzing the spectral region around each doublet in distance scaled flux units and comparing the two sources, we confirm the J band flux reversal and find that Luhman 16B has a brighter continuum in the 1.17 {\\mu}m and 1.25 {\\mu}m regions than Luhman 16A. Converting flux units to a brightness temperature...

  15. The First Science Results from SPHERE: Disproving the Predicted Brown Dwarf around V471 Tau

    CERN Document Server

    Hardy, A; Parsons, S G; Caceres, C; Retamales, G; Wahhaj, Z; Mawet, D; Canovas, H; Cieza, L; Marsh, T R; Bours, M C P; Dhillon, V S; Bayo, A

    2015-01-01

    Variations of eclipse arrival times have recently been detected in several post common envelope binaries consisting of a white dwarf and a main sequence companion star. The generally favoured explanation for these timing variations is the gravitational pull of one or more circumbinary substellar objects periodically moving the center of mass of the host binary. Using the new extreme-AO instrument SPHERE, we image the prototype eclipsing post-common envelope binary V471 Tau in search of the brown dwarf that is believed to be responsible for variations in its eclipse arrival times. We report that an unprecedented contrast of 12.1 magnitudes in the H band at a separation of 260 mas was achieved, but resulted in a non-detection. This implies that there is no brown dwarf present in the system unless it is three magnitudes fainter than predicted by evolutionary track models, and provides damaging evidence against the circumbinary interpretation of eclipse timing variations. In the case of V471 Tau, a more consisten...

  16. Habitable Planets Around White and Brown Dwarfs: The Perils of a Cooling Primary

    CERN Document Server

    Barnes, Rory

    2012-01-01

    White and brown dwarfs are astrophysical objects that are bright enough to support an insolation habitable zone (IHZ). Unlike hydrogen-burning stars, they cool and become less luminous with time, and hence their IHZ moves in with time. The inner edge of the IHZ is defined as the orbital radius at which a planet may enter a moist or runaway greenhouse, phenomena that can remove a planet's surface water forever. Thus, as the IHZ moves in, planets that enter it may no longer have any water, and are still uninhabitable. Additionally, the close proximity of the IHZ to the primary leads to concern that tidal heating may also be strong enough to trigger a runaway greenhouse, even for orbital eccentricities as small as 10^-6. Water loss occurs due to photolyzation by UV photons in the planetary stratosphere, followed by hydrogen escape. Young white dwarfs emit a large amount of these photons as their surface temperatures are over 10^4 K. The situation is less clear for brown dwarfs, as observational data do not const...

  17. A Search for Substellar Companions to the Two Nearest Brown Dwarf Systems

    CERN Document Server

    Melso, N D; Luhman, K L

    2015-01-01

    WISE J104915.57-531906.1 A+B and WISE J085510.83-071442.5 were recently discovered as the third and fourth closest known systems to the Sun, respectively (2.0 and 2.3 pc). The former consists of a L8+T0.5 binary and the latter is a probable Y dwarf and is the coldest known brown dwarf (~250 K). We present a search for common proper motion companions to these brown dwarfs using multi-epoch mid-infrared images from the Spitzer Space Telescope. We have also obtained near-infrared adaptive optics images of WISE J104915.57-531906.1 A+B with the Very Large Telescope to search for companions at smaller separations than reached by Spitzer. No new companions are detected in either system. At projected separations of 25-420" (50-840 AU) for WISE J104915.57-531906.1 A+B and 4-420" (9-970 AU) for WISE J085510.83-071442.5, the Spitzer images are sensitive to companions with M_4.5=1 M_Jup for ages of >=1 Gyr and temperatures of >=150 K. The detection limit in the adaptive optics images of WISE J104915.57-531906.1 A+B is dH...

  18. Characterizing the atmospheres of transiting rocky planets around late type dwarfs

    CERN Document Server

    Pallé, E; Muñoz, A García

    2011-01-01

    Visible and near-infrared spectra of transiting hot Jupiter planets have recently been observed, revealing some of the atmospheric constituents of their atmospheres. In the near future, it is probable that primary and secondary eclipse observations of Earth-like rocky planets will also be achieved. The characterization of the Earth's transmission spectrum has shown that both major and trace atmospheric constituents may present strong absorption features, including important bio-markers such as water, oxygen and methane. Our simulations using a recently published empirical Earth's transmission spectrum, and the stellar spectra for a variety of stellar types, indicate that the new generation of extremely large telescopes, such as the proposed 42-meter European Extremely Large Telescope(E-ELT), could be capable of retrieving the transmission spectrum of an Earth-like planet around very cool stars and brown dwarfs (Teff < 3100 K). For a twin of Earth around a star with Teff around 3100 K (M4), for example, the...

  19. Cloudless atmospheres for L/T dwarfs and extra-solar giant planets

    CERN Document Server

    Tremblin, P; Chabrier, G; Baraffe, I; Drummond, B; Hinkley, S; Mourier, P; Venot, O

    2016-01-01

    The admitted, conventional scenario to explain the complex spectral evolution of brown dwarfs (BD) since their first detections twenty years ago, has always been the key role played by micron-size condensates, called "dust" or "clouds", in their atmosphere. This scenario, however, faces major problems, in particular the J-band brightening and the resurgence of FeH absorption at the L to T transition, and a physical first-principle understanding of this transition is lacking. In this paper, we propose a new, completely different explanation for BD and extrasolar giant planet (EGP) spectral evolution, without the need to invoke clouds. We show that, due to the slowness of the CO/CH4 and N2/NH3 chemical reactions, brown dwarf (L and T, respectively) and EGP atmospheres are subject to a thermo-chemical instability similar in nature to the fingering or chemical convective instability present in Earth oceans and at the Earth core/mantle boundary. The induced small-scale turbulent energy transport reduces the temper...

  20. WD0837+185:the formation and evolution of an extreme mass ratio white dwarf-brown dwarf binary in Praesepe

    CERN Document Server

    Casewell, S L; Wynn, G A; Alexander, R D; Napiwotzki, R; Lawrie, K A; Dobbie, P D; Jameson, R F; Hodgkin, S T

    2012-01-01

    There is a striking and unexplained dearth of brown dwarf companions in close orbits (< 3AU) around stars more massive than the Sun, in stark contrast to the frequency of stellar and planetary companions. Although rare and relatively short-lived, these systems leave detectable evolutionary end points in the form of white dwarf - brown dwarf binaries and these remnants can offer unique insights into the births and deaths of their parent systems. We present the discovery of a close (orbital separation ~ 0.006 AU) substellar companion to a massive white dwarf member of the Praesepe star cluster. Using the cluster age and the mass of the white dwarf we constrain the mass of the white dwarf progenitor star to lie in the range 3.5 - 3.7 Msun (B9). The high mass of the white dwarf means the substellar companion must have been engulfed by the B star's envelope while it was on the late asymptotic giant branch (AGB). Hence, the initial separation of the system was ~2 AU, with common envelope evolution reducing the s...

  1. Atmospheric parameters and carbon abundance for hot DB white dwarfs

    CERN Document Server

    Koester, Detlev; Gänsicke, Boris T

    2014-01-01

    Atmospheric parameters for hot DB (helium atmosphere) white dwarfs near effective temperatures of 25000K are extremely difficult to determine from optical spectroscopy. This is particularly unfortunate, because this is the range of variable DBV or V777 Her stars. Accurate atmospheric parameters are needed to help or confirm the asteroseismic analysis of these objects. Another important aspect is the new class of white dwarfs - the hot DQ - detected by Dufour et al. (2007), with spectra dominated by carbon lines. The analysis shows that their atmospheres are pure carbon. The origin of these stars is not yet understood, but they may have an evolutionary link with the hotter DBs as studied here. Our aim is to determine accurate atmospheric parameters and element abundances and study the implications for the evolution white dwarfs of spectral classes DB and hot DQ. High resolution UV spectra of five DBs are studied with model atmospheres. We determine stellar parameters and abundances or upper limits of C and Si....

  2. Rotation periods and astrometric motions of the Luhman 16AB brown dwarfs by high-resolution lucky-imaging monitoring

    Science.gov (United States)

    Mancini, L.; Giacobbe, P.; Littlefair, S. P.; Southworth, J.; Bozza, V.; Damasso, M.; Dominik, M.; Hundertmark, M.; Jørgensen, U. G.; Juncher, D.; Popovas, A.; Rabus, M.; Rahvar, S.; Schmidt, R. W.; Skottfelt, J.; Snodgrass, C.; Sozzetti, A.; Alsubai, K.; Bramich, D. M.; Calchi Novati, S.; Ciceri, S.; D'Ago, G.; Figuera Jaimes, R.; Galianni, P.; Gu, S.-H.; Harpsøe, K.; Haugbølle, T.; Henning, Th.; Hinse, T. C.; Kains, N.; Korhonen, H.; Scarpetta, G.; Starkey, D.; Surdej, J.; Wang, X.-B.; Wertz, O.

    2015-12-01

    Context. Photometric monitoring of the variability of brown dwarfs can provide useful information about the structure of clouds in their cold atmospheres.The brown-dwarf binary system Luhman 16AB is an interesting target for such a study, because its components stand at the L/T transition and show high levels of variability. Luhman 16AB is also the third closest system to the solar system, which allows precise astrometric investigations with ground-based facilities. Aims: The aim of the work is to estimate the rotation period and study the astrometric motion of both components. Methods: We have monitored Luhman 16AB over a period of two years with the lucky-imaging camera mounted on the Danish 1.54 m telescope at La Silla, through a special i + z long-pass filter, which allowed us to clearly resolve the two brown dwarfs into single objects. An intense monitoring of the target was also performed over 16 nights, in which we observed a peak-to-peak variability of 0.20 ± 0.02 mag and 0.34 ± 0.02 mag for Luhman 16A and 16B, respectively. Results: We used the 16-night time-series data to estimate the rotation period of the two components. We found that Luhman 16B rotates with a period of 5.1 ± 0.1 h, in very good agreement with previous measurements. For Luhman 16A, we report that it rotates more slowly than its companion, and even though we were not able to get a robust determination, our data indicate a rotation period of roughly 8 h. This implies that the rotation axes of the two components are well aligned and suggests a scenario in which the two objects underwent the same accretion process. The 2-year complete data set was used to study the astrometric motion of Luhman 16AB. We predict a motion of the system that is not consistent with a previous estimate based on two months of monitoring, but cannot confirm or refute the presence of additional planetary-mass bodies in the system. Based on data collected by MiNDSTEp with the Danish 1.54 m telescope at the ESO La

  3. Adaptive Optics imaging of VHS 1256-1257: A Low Mass Companion to a Brown Dwarf Binary System

    CERN Document Server

    Stone, Jordan M; Kratter, Kaitlin M; Dupuy, Trent J; Close, Laird M; Eisner, Josh A; Fortney, Jonathan J; Hinz, Philip M; Males, Jared R; Morley, Caroline V; Morzinski, Katie M; Ward-Duong, Kimberly

    2016-01-01

    Recently, Gauza et al. (2015) reported the discovery of a companion to the late M-dwarf, VHS J125601.92-125723.9 (VHS 1256-1257). The companion's absolute photometry suggests its mass and atmosphere are similar to the HR 8799 planets. However, as a wide companion to a late-type star, it is more accessible to spectroscopic characterization. We discovered that the primary of this system is an equal-magnitude binary. For an age $\\sim300$ Myr the A and B components each have a mass of $64.6^{+0.8}_{-2.0}~M_{\\mathrm{Jup}}$, and the b component has a mass of $11.2^{+9.7}_{-1.8}$, making VHS 1256-1257 only the third brown dwarf triple system. There exists some tension between the spectrophotometric distance of $17.2\\pm2.6$ pc and the parallax distance of $12.7\\pm1.0$ pc. At 12.7 pc VHS1256-1257 A and B would be the faintest known M7.5 objects, and are even faint outliers among M8 types. If the larger spectrophotmetric distance is more accurate than the parallax, then the mass of each component increases. In particul...

  4. Multi-fibre optical spectroscopy of low-mass stars and brown dwarfs in Upper Sco

    CERN Document Server

    Lodieu, N; Hambly, N C

    2011-01-01

    We have obtained multi-fibre intermediate-resolution optical spectroscopy of 94 photometric and proper motion selected low-mass star and brown dwarf candidates in Upper Sco with AAT/AAOmega. We have estimated the spectral types and measured the equivalent widths of youth and gravity diagnostic features to confirm the spectroscopic membership of about 95% of the candidates extracted from 6.5 square degrees in Upper Sco. We also detect lithium in the spectra with the highest signal-to-noise, consolidating our conclusions about their youth. Furthermore, we derive an estimate of our selections using spectroscopic data obtained for a large number of stars falling into the instrument's field-of-view. We have estimated the effective temperatures and masses for each new spectroscopic member using the latest evolutionary models available for low-mass stars and brown dwarfs. Combining the current optical spectroscopy presented here with near-infrared spectroscopy obtained for the faintest photometric candidates, we con...

  5. The First Brown Dwarf/Planetary-Mass Object in the 32 Orionis Group

    CERN Document Server

    Burgasser, Adam J; Mamajek, Eric E; Gagne, Jonathan; Faherty, Jacqueline K; Tallis, Melisa; Choban, Caleb; Escala, Ivanna; Aganze, Christian

    2016-01-01

    The 32 Orionis group is a co-moving group of roughly 20 young (24 Myr) M3-B5 stars 100 pc from the Sun. Here we report the discovery of its first substellar member, WISE J052857.69+090104.2. This source was previously reported to be an M giant star based on its unusual near-infrared spectrum and lack of measurable proper motion. We re-analyze previous data and new moderate-resolution spectroscopy from Magellan/FIRE to demonstrate that this source is a young near-infrared L1 brown dwarf with very low surface gravity features. Spectral model fits indicate T$_{eff}$ = 1880$^{+150}_{-70}$ K and $\\log{g}$ = 3.8$^{+0.2}_{-0.2}$ (cgs), consistent with a 15-22 Myr object with a mass near the deuterium-burning limit. Its sky position, estimated distance, kinematics (both proper motion and radial velocity), and spectral characteristics are all consistent with membership in 32 Orionis, and its temperature and age imply a mass (M = 14$^{+4}_{-3}$ M$_{Jup}$) that straddles the brown dwarf/planetary-mass object boundary. T...

  6. The radius anomaly in the planet/brown dwarf overlapping mass regime

    Directory of Open Access Journals (Sweden)

    Baraffe I.

    2011-02-01

    Full Text Available The recent detection of the transit of very massive substellar companions (Deleuil et al. 2008; Bouchy et al. 2010; Anderson et al. 2010; Bakos et al. 2010 provides a strong constraint to planet and brown dwarf formation and migration mechanisms. Whether these objects are brown dwarfs originating from the gravitational collapse of a dense molecular cloud that, at the same time, gave birth to the more massive stellar companion, or whether they are planets that formed through core accretion of solids in the protoplanetary disk can not always be determined unambiguously and the mechanisms responsible for their short orbital distances are not yet fully understood. In this contribution, we examine the possibility to constrain the nature of a massive substellar object from the various observables provided by the combination of Radial Velocity and Photometry measurements (e.g. Mp , Rp , M⋆, Age, a, e.... In a second part, developments in the modeling of tidal evolution at high eccentricity and inclination - as measured for HD 80 606 with e = 0.9337 (Naef et al. 2001 , XO-3 with a stellar obliquity ε⋆  > 37.3 ± 3.7 deg (Hébrard et al. 2008; Winn et al. 2009 and several other exoplanets - are discussed along with their implication in the understanding of the radius anomaly problem of extrasolar giant planets.

  7. A Venus-mass Planet Orbiting a Brown Dwarf: A Missing Link between Planets and Moons

    Science.gov (United States)

    Udalski, A.; Jung, Y. K.; Han, C.; Gould, A.; Kozłowski, S.; Skowron, J.; Poleski, R.; Soszyński, I.; Pietrukowicz, P.; Mróz, P.; Szymański, M. K.; Wyrzykowski, Ł.; Ulaczyk, K.; Pietrzyński, G.; Shvartzvald, Y.; Maoz, D.; Kaspi, S.; Gaudi, B. S.; Hwang, K.-H.; Choi, J.-Y.; Shin, I.-G.; Park, H.; Bozza, V.

    2015-10-01

    The co-planarity of solar system planets led Kant to suggest that they formed from an accretion disk, and the discovery of hundreds of such disks around young stars as well as hundreds of co-planar planetary systems by the Kepler satellite demonstrate that this formation mechanism is extremely widespread. Many moons in the solar system, such as the Galilean moons of Jupiter, also formed out of the accretion disks that coalesced into the giant planets. Here we report the discovery of an intermediate system, OGLE-2013-BLG-0723LB/Bb, composed of a Venus-mass planet orbiting a brown dwarf, which may be viewed either as a scaled-down version of a planet plus a star or as a scaled-up version of a moon plus a planet orbiting a star. The latter analogy can be further extended since they orbit in the potential of a larger, stellar body. For ice-rock companions formed in the outer parts of accretion disks, like Uranus and Callisto, the scaled masses and separations of the three types of systems are similar, leading us to suggest that the formation processes of companions within accretion disks around stars, brown dwarfs, and planets are similar.

  8. DISCOVERY OF A ∼250 K BROWN DWARF AT 2 pc FROM THE SUN

    International Nuclear Information System (INIS)

    Through a previous analysis of multi-epoch astrometry from the Wide-field Infrared Survey Explorer (WISE), I identified WISE J085510.83–071442.5 as a new high proper motion object. By combining astrometry from WISE and the Spitzer Space Telescope, I have measured a proper motion of 8.1 ± 0.1'' yr–1 and a parallax of 0.454 ± 0.045'' (2.20−0.20+0.24 pc) for WISE J085510.83–071442.5, giving it the third highest proper motion and the fourth largest parallax of any known star or brown dwarf. It is also the coldest known brown dwarf based on its absolute magnitude at 4.5 μm and its color in [3.6]-[4.5]. By comparing M 4.5 with the values predicted by theoretical evolutionary models, I estimate an effective temperature of 225-260 K and a mass of 3-10 M Jup for the age range of 1-10 Gyr that encompasses most nearby stars

  9. Dynamical masses for the nearest brown dwarf binary: Epsilon Indi Ba, Bb

    CERN Document Server

    Cardoso, C V; King, R R; Close, L M; Scholz, R -D; Lenzen, R; Brandner, W; Lodieu, N; Zinnecker, H

    2008-01-01

    We present preliminary astrometric results for the closest known brown dwarf binary to the Sun: Epsilon Indi Ba, Bb at a distance of 3.626 pc. Via ongoing monitoring of the relative separation of the two brown dwarfs (spectral types T1 and T6) with the VLT NACO near-IR adaptive optics system since June 2004, we obtain a model-independent dynamical total mass for the system of 121 MJup, some 60% larger than the one obtained by McCaughrean et al. (2004), implying that the system may be as old as 5 Gyr. We have also been monitoring the absolute astrometric motions of the system using the VLT FORS2 optical imager since August 2005 to determine the individual masses. We predict a periastron passage in early 2010, by which time the system mass will be constrained to < 1 MJup and we will be able to determine the individual masses accurately in a dynamical, model-independent manner.

  10. VLT X-shooter spectroscopy of the nearest brown dwarf binary

    CERN Document Server

    Lodieu, N; Rebolo, R; Bejar, V J S; Pavlenko, Y; Perez-Garrido, A

    2015-01-01

    The aim of the project is to characterise both components of the nearest brown dwarf sytem to the Sun, WISE J104915.57-531906.1 (=Luhman16AB) at optical and near-infrared wavelengths. We obtained high signal-to-noise intermediate-resolution (R~6000-11000) optical (600-1000 nm) and near-infrared (1000-2480nm) spectra of each component of Luhman16AB, the closest brown dwarf binary to the Sun, with the X-Shooter instrument on the Very Large Telescope. We classify the primary and secondary of the Luhman16 system as L6-L7.5 and T0+/-1, respectively, in agreement with previous measurements published in the literature. We present measurements of the lithium pseudo-equivalent widths, which appears of similar strength on both components (8.2+/-1.0 Angstroms and 8.4+/-1.5 Angstroms for the L and T components, respectively). The presence of lithium (Lithium 7) in both components imply masses below 0.06 Msun while comparison with models suggests lower limits of 0.04 Msun. The detection of lithium in the T component is th...

  11. Spitzer IRS Observations of Disks around Brown Dwarfs in the TW Hydra Association

    CERN Document Server

    Morrow, A L; Espaillat, C; D'Alessio, P; Adame, L; Calvet, N; Forrest, W J; Sargent, B; Hartmann, L; Watson, D M; Bohac, C J

    2008-01-01

    Using SpeX at the NASA Infrared Telescope Facility and the Spitzer Infrared Spectrograph, we have obtained infrared spectra from 0.7 to 30um for three young brown dwarfs in the TW Hydra Association (~10 Myr), 2M J1207-3932, 2M J1139-3159, and SS J1102-3431. The spectral energy distribution for 2M J1139-3159 is consistent with a stellar photosphere for the entire wavelength range of our data while the other two objects exhibit significant excess emission at >5um. We are able to reproduce the excess emission from each brown dwarf using our models of irradiated accretion disks. According to our model fits, both disks have experienced a high degree of dust settling. We also find that silicate emission at 10 and 20um is absent from the spectra of these disks, indicating that grains in the upper disk layers have grown to sizes larger than ~5um. Both of these characteristics are consistent with previous observations of decreasing silicate emission with lower stellar masses and older ages. These trends suggest that e...

  12. Brown dwarf disks with Herschel: Linking far-infrared and (sub)-mm fluxes

    CERN Document Server

    Daemgen, Sebastian; Scholz, Alexander; Testi, Leonardo; Jayawardhana, Ray; Greaves, Jane; Eastwood, Daniel

    2016-01-01

    Brown dwarf disks are excellent laboratories to test our understanding of disk physics in an extreme parameter regime. In this paper we investigate a sample of 29 well-characterized brown dwarfs and very low mass stars, for which Herschel far-infrared fluxes as well as (sub)-mm fluxes are available. We have measured new Herschel PACS fluxes for 11 objects and complement these with (sub)-mm data and Herschel fluxes from the literature. We analyze their spectral energy distributions in comparison with results from radiative transfer modeling. Fluxes in the far-infrared are strongly affected by the shape and temperature of the disk (and hence stellar luminosity), whereas the (sub)-mm fluxes mostly depend on disk mass. Nevertheless, there is a clear correlation between far-infrared and (sub)-mm fluxes. We argue that the link results from the combination of the stellar mass-luminosity relation and a scaling between disk mass and stellar mass. We find strong evidence of dust settling to the disk midplane. The spect...

  13. Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun

    CERN Document Server

    Luhman, K L

    2014-01-01

    Through a previous analysis of multi-epoch astrometry from the Wide-field Infrared Survey Explorer (WISE), I identified WISE J085510.83-071442.5 as a new high proper motion object. By combining astrometry from WISE and the Spitzer Space Telescope, I have measured a proper motion of 8.1+/-0.1"/yr and a parallax of 0.454+/-0.045" (2.20+0.24/-0.20 pc) for WISE J085510.83-071442.5, giving it the third highest proper motion and the fourth largest parallax of any known star or brown dwarf. It is also the coldest known brown dwarf based on its absolute magnitude at 4.5um and its color in [3.6]-[4.5]. By comparing M4.5 with the values predicted by theoretical evolutionary models, I estimate an effective temperature of 225-260 K and a mass of 3-10 Mjup for the age range of 1-10 Gyr that encompasses most nearby stars.

  14. HST ROTATIONAL SPECTRAL MAPPING OF TWO L-TYPE BROWN DWARFS: VARIABILITY IN AND OUT OF WATER BANDS INDICATES HIGH-ALTITUDE HAZE LAYERS

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Hao; Apai, Dániel; Karalidi, Theodora [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Marley, Mark S. [NASA Ames Research Center, Naval Air Station, Moffett Field, Mountain View, CA 94035 (United States); Saumon, Didier [Los Alamos National Lab, Los Alamos, NM 87545 (United States); Morley, Caroline V. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Buenzli, Esther [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Artigau, Étienne [Département de Physique, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 (Canada); Radigan, Jacqueline [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Metchev, Stanimir [Department of Physics and Astronomy, Western University, 1151 Richmond Street, London, ON N6A 3K7 (Canada); Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Mohanty, Subhanjoy [Imperial College London, 1010 Blackett Lab, Prince Consort Road, London SW7 2AZ (United Kingdom); Lowrance, Patrick J. [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Showman, Adam P.; Flateau, Davin [Department of Planetary Sciences, University of Arizona, 1629 East University Boulevard, Tucson, AZ 85721 (United States); Heinze, Aren N., E-mail: haoyang@email.arizona.edu [Department of Physics and Astronomy, State University of New York, Stony Brook, NY 11794-3800 (United States)

    2015-01-01

    We present time-resolved near-infrared spectroscopy of two L5 dwarfs, 2MASS J18212815+1414010 and 2MASS J15074759–1627386, observed with the Wide Field Camera 3 instrument on the Hubble Space Telescope (HST). We study the wavelength dependence of rotation-modulated flux variations between 1.1 μm and 1.7 μm. We find that the water absorption bands of the two L5 dwarfs at 1.15 μm and 1.4 μm vary at similar amplitudes as the adjacent continuum. This differs from the results of previous HST observations of L/T transition dwarfs, in which the water absorption at 1.4 μm displays variations of about half of the amplitude at other wavelengths. We find that the relative amplitude of flux variability out of the water band with respect to that in the water band shows a increasing trend from the L5 dwarfs toward the early T dwarfs. We utilize the models of Saumon and Marley and find that the observed variability of the L5 dwarfs can be explained by the presence of spatially varying high-altitude haze layers above the condensate clouds. Therefore, our observations show that the heterogeneity of haze layers—the driver of the variability—must be located at very low pressures, where even the water opacity is negligible. In the near future, the rotational spectral mapping technique could be utilized for other atomic and molecular species to probe different pressure levels in the atmospheres of brown dwarfs and exoplanets and uncover both horizontal and vertical cloud structures.

  15. HST ROTATIONAL SPECTRAL MAPPING OF TWO L-TYPE BROWN DWARFS: VARIABILITY IN AND OUT OF WATER BANDS INDICATES HIGH-ALTITUDE HAZE LAYERS

    International Nuclear Information System (INIS)

    We present time-resolved near-infrared spectroscopy of two L5 dwarfs, 2MASS J18212815+1414010 and 2MASS J15074759–1627386, observed with the Wide Field Camera 3 instrument on the Hubble Space Telescope (HST). We study the wavelength dependence of rotation-modulated flux variations between 1.1 μm and 1.7 μm. We find that the water absorption bands of the two L5 dwarfs at 1.15 μm and 1.4 μm vary at similar amplitudes as the adjacent continuum. This differs from the results of previous HST observations of L/T transition dwarfs, in which the water absorption at 1.4 μm displays variations of about half of the amplitude at other wavelengths. We find that the relative amplitude of flux variability out of the water band with respect to that in the water band shows a increasing trend from the L5 dwarfs toward the early T dwarfs. We utilize the models of Saumon and Marley and find that the observed variability of the L5 dwarfs can be explained by the presence of spatially varying high-altitude haze layers above the condensate clouds. Therefore, our observations show that the heterogeneity of haze layers—the driver of the variability—must be located at very low pressures, where even the water opacity is negligible. In the near future, the rotational spectral mapping technique could be utilized for other atomic and molecular species to probe different pressure levels in the atmospheres of brown dwarfs and exoplanets and uncover both horizontal and vertical cloud structures

  16. Brown Dwarfs in Young Moving Groups from Pan-STARRS1. I. AB Doradus

    CERN Document Server

    Aller, Kimberly M; Magnier, Eugene A; Best, William M J; Kotson, Michael C; Burgett, William S; Chambers, Kenneth C; Hodapp, Klaus W; Flewelling, Heather; Kaiser, Nick; Metcalf, Nigel; Tonry, John L; Wainscoat, Richard J; Waters, Christopher

    2016-01-01

    Substellar members of young ($\\lesssim$150 Myr) moving groups are valuable benchmarks to empirically define brown dwarf evolution with age and to study the low-mass end of the initial mass function. We have combined Pan-STARRS1 (PS1) proper motions with optical$-$IR photometry from PS1, 2MASS and $\\textit{WISE}$ to search for substellar members of the AB Dor Moving Group within $\\approx$50 pc and with spectral types of late-M to early-L, corresponding to masses down to $\\approx$30 M$_{Jup}$ at the age of the group ($\\approx$125 Myr). Including both photometry and proper motions allows us to better select candidates by excluding field dwarfs whose colors are similar to young AB~Dor Moving Group members. Our near-IR spectroscopy has identified six ultracool dwarfs (M6$-$L4; $\\approx$30$-$100 M$_{Jup}$) with intermediate surface gravities (INT-G) as candidate members of the AB Dor Moving Group. We find another two candidate members with spectra showing hints of youth but consistent with field gravities. We also ...

  17. DE0823-49 is a juvenile binary brown dwarf at 20.7 pc

    Science.gov (United States)

    Sahlmann, J.; Burgasser, A. J.; Martín, E. L.; Lazorenko, P. F.; Bardalez Gagliuffi, D. C.; Mayor, M.; Ségransan, D.; Queloz, D.; Udry, S.

    2015-07-01

    Astrometric monitoring of the nearby early-L dwarf DE0823-49 has revealed a low-mass companion in a 248-day orbit that was announced in an earlier work. Here, we present new astrometric and spectroscopic observations that allow us to characterise the system in detail. The optical spectrum shows Li i-absorption indicative of a young age and/or substellar mass for the primary component. The near-infrared spectrum is best reproduced by a binary system of brown dwarfs with spectral types of L1.5 + L5.5 and effective temperatures of 2150 ± 100 K and 1670 ± 140 K. To conform with the photocentric orbit size measured with astrometry and the current understanding of substellar evolution, the system must have an age in the 80-500 Myr range. Evolutionary models predict component masses in the ranges of M1 ≃ 0.028-0.063 M⊙ and M2 ≃ 0.018-0.045 M⊙ with a mass ratio of q ≃ 0.64-0.74. Multi-epoch radial velocity measurements unambiguously establish the three-dimensional orbit of the system and allow us to investigate its kinematic properties. DE0823-49 emerges as a rare example of a nearby brown dwarf binary with orbit, component properties, and age that are characterised well. It is a juvenile resident of the solar neighbourhood, but does not appear to belong to a known young association or moving group. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme IDs 086.C-0680, 088.C-0679, 090.C-0786, and 092.C-0202.

  18. The First Brown Dwarf/Planetary-mass Object in the 32 Orionis Group

    Science.gov (United States)

    Burgasser, Adam J.; Lopez, Mike A.; Mamajek, Eric E.; Gagné, Jonathan; Faherty, Jacqueline K.; Tallis, Melisa; Choban, Caleb; Tamiya, Tomoki; Escala, Ivanna; Aganze, Christian

    2016-03-01

    The 32 Orionis group is a co-moving group of roughly 20 young (24 Myr) M3-B5 stars 100 pc from the Sun. Here we report the discovery of its first substellar member, WISE J052857.69+090104.2. This source was previously reported to be an M giant star based on its unusual near-infrared spectrum and lack of measureable proper motion. We re-analyze previous data and new moderate-resolution spectroscopy from Magellan/Folded-port InfraRed Echellette to demonstrate that this source is a young near-infrared L1 brown dwarf with very low surface gravity features. Spectral model fits indicate Teff = 1880{}-70+150 K and {log}g = 3.8{}-0.2+0.2, consistent with a 15-22 Myr object with a mass near the deuterium-burning limit. Its sky position, estimated distance, kinematics (both proper motion and radial velocity), and spectral characteristics are all consistent with membership in 32 Orionis, and its temperature and age imply a mass (M = {14}-3+4 MJ) that straddles the brown dwarf/planetary-mass object boundary. The source has a somewhat red J-W2 color compared to other L1 dwarfs, but this is likely a low-gravity-related temperature offset; we find no evidence of significant excess reddening from a disk or cool companion in the 3-5 μm waveband. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  19. Atmospheric activity in red dwarf stars

    International Nuclear Information System (INIS)

    Active and inactive stars of similar mass and luminosity have similar physical conditions in their photospheres, outside of magnetically disturbed regions. Such field structures give rise to stellar activity, which manifests itself at all heights of the atmosphere. Observations of uneven distributions of flux across the stellar disc have led to the disovery of photospheric starspots, chromospheric plage areas, and coronal holes. Localized transient behavior has been identified in both thermal and non-thermal sources, such as flares, shock waves and particle acceleration. The common element to all active regions is the presence of strong magnetic field structures connecting the violently turbulent deep layers in the convection zones of stars with the tenuous outer atmospheres. Transport and dissipation of energy into the chromospheric and coronal regions are still much debated topics

  20. The TRENDS High-Contrast Imaging Survey. VI. Discovery of a Mass, Age, and Metallicity Benchmark Brown Dwarf

    CERN Document Server

    Crepp, Justin R; Bechter, Eric B; Montet, Benjamin T; Johnson, John Asher; Piskorz, Danielle; Howard, Andrew W; Isaacson, Howard

    2016-01-01

    The mass and age of substellar objects are degenerate parameters leaving the evolutionary state of brown dwarfs ambiguous without additional information. Theoretical models are normally used to help distinguish between old, massive brown dwarfs and young, low mass brown dwarfs but these models have yet to be properly calibrated. We have carried out an infrared high-contrast imaging program with the goal of detecting substellar objects as companions to nearby stars to help break degeneracies in inferred physical properties such as mass, age, and composition. Rather than using imaging observations alone, our targets are pre-selected based on the existence of dynamical accelerations informed from years of stellar radial velocity (RV) measurements. In this paper, we present the discovery of a rare benchmark brown dwarf orbiting the nearby ($d=18.69\\pm0.19$ pc), solar-type (G9V) star HD 4747 ([Fe/H]=$-0.22\\pm0.04$) with a projected separation of only $\\rho=11.3\\pm0.2$ AU ($\\theta \\approx$ 0.6''). Precise Doppler m...

  1. ALMA OBSERVATIONS OF {rho}-Oph 102: GRAIN GROWTH AND MOLECULAR GAS IN THE DISK AROUND A YOUNG BROWN DWARF

    Energy Technology Data Exchange (ETDEWEB)

    Ricci, L. [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Testi, L. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Natta, A. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Scholz, A. [School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland); De Gregorio-Monsalvo, I., E-mail: lricci@astro.caltech.edu [Joint ALMA Observatory (JAO)/ESO, Alonso de Cordova 3107, Vitacura 763 0335, Santiago de Chile (Chile)

    2012-12-20

    We present ALMA continuum and spectral line observations of the young brown dwarf {rho}-Oph 102 at about 0.89 mm and 3.2 mm. We detect dust emission from the disk at these wavelengths and derive an upper limit on the radius of the dusty disk of {approx}40 AU. The derived variation of the dust opacity with frequency in the millimeter (mm) provides evidence for the presence of mm-sized grains in the disk's outer regions. This result demonstrates that mm-sized grains are found even in the low-density environments of brown dwarf disks and challenges our current understanding of dust evolution in disks. The CO map at 345 GHz clearly reveals molecular gas emission at the location of the brown dwarf, indicating a gas-rich disk as typically found for disks surrounding young pre-main-sequence stars. We derive a disk mass of {approx}0.3%-1% of the mass of the central brown dwarf, similar to the typical values found for disks around more massive young stars.

  2. Atmospheric Properties of T Dwarfs Inferred from Model Fits at Low Spectral Resolution

    Science.gov (United States)

    Godfrey, Paige A.; Rice, Emily L.; Filippazzo, Joe; Douglas, Stephanie; BDNYC

    2016-01-01

    Brown dwarfs are substellar objects that cool over time because they are not massive enough to sustain hydrogen fusion at their cores. While spectral types (M, L, T, Y) generally correlate with decreasing temperature, spectral subclasses (T0, T1, T2, etc.) do not, suggesting that secondary parameters (gravity, metallicity, dust) play a role in the spectral type-temperature relationship. We investigate this relationship for T dwarfs, which make up the coolest fully-populated spectral class of substellar objects. Our sample consists of 154 T dwarfs with low resolution (R~75-100) near-infrared (~0.8-2.5 micron) spectra from the SpeX Prism Library and the literature. We compare each observed spectrum to synthetic spectra from four model grids using a Markov-Chain Monte Carlo analysis to determine robust best-fit parameters and uncertainties. We evaluate the best fit parameters from each model grid per object to constrain how spectral type relates to decreasing temperature and increasing surface gravity and to compare the consistency of each model grid. To test for discrepant results when fitting to relatively narrow wavelength ranges, this analysis is performed on the full spectrum of the Y, J, H, and K bands and on each band separately. New detections of cooler objects extending into the Y dwarf and exoplanet regimes motivate our model comparisons and search for trends with spectral type and other observational properties across the decreasing temperatures in order to better understand the atmospheres of substellar objects, including cool gas giant exoplanets.

  3. MOA-2013-BLG-220Lb: Planetary Companion to a Possible Brown Dwarf Host

    CERN Document Server

    Yee, J C; Gould, A; Skowron, J; Bond, I A; Udalski, A; Hundertmark, M; Monard, L A G; Porritt, I; Nelson, P; Bozza, V; Albrow, M D; Choi, J -Y; Christie, G W; DePoy, D L; Gaudi, B S; Hwang, K -H; Jung, Y K; Lee, C -U; McCormick, J; Natusch, T; Ngan, H; Park, H; Pogge, R W; Shin, I -G; Tan, T -G; Abe, F; Bennett, D P; Bond, I A; Botzler, C S; Freeman, M; Fukui, A; Fukunaga, D; Itow, Y; Koshimoto, N; Larsen, P; Ling, C H; Masuda, K; Matsubara, Y; Muraki, Y; Namba, S; Ohnishi, K; Philpott, L; Rattenbury, N J; Saito, To; Sullivan, D J; Sumi, T; Sweatman, W L; Suzuki, D; Tristram, P J; Tsurumi, N; Wada, K; Yamai, N; Yock, P C M; Yonehara, A; Szymański, M K; Ulaczyk, K; Kozłowski, S; Poleski, R; Wyrzykowski, Ł; Kubiak, M; Pietrukowicz, P; Pietrzyński, G; Soszyński, I; Bramich, D M; Browne, P; Horne, K; Ipatov, S; Kains, N; Snodgrass, C; Steele, I A; Street, R; Tsapras, Y

    2014-01-01

    Based on its high proper motion $\\mu=12.5\\pm 1\\,\\masyr$, MOA-2013-BLG-220Lb is the best candidate to date for a microlensing planet with a verifiable brown dwarf host. This candidacy can be partially tested immediately and more fully tested by $\\sim 2021$, when the source and lens will have separated sufficiently to be resolved in high-resolution images even if the lens is at the bottom of the main sequence, and so extremely faint, $H\\sim 24$. The planet-star mass ratio is $q=3.01\\pm 0.02\\times 10^{-3}$. The planet could have been detected and characterized purely with follow-up data. The potential to completely characterize planetary events from followup data has far-reaching implications for microlensing surveys, both current and into the LSST era.

  4. MICROLENSING DISCOVERY OF A POPULATION OF VERY TIGHT, VERY LOW MASS BINARY BROWN DWARFS

    International Nuclear Information System (INIS)

    Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs (BDs) are poorly understood. The multiplicity properties and minimum mass of the BD mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low mass, very tight binary systems. These binaries have directly and precisely measured total system masses of 0.025 M☉ and 0.034 M☉, and projected separations of 0.31 AU and 0.19 AU, making them the lowest-mass and tightest field BD binaries known. The discovery of a population of such binaries indicates that BD binaries can robustly form at least down to masses of ∼0.02 M☉. Future microlensing surveys will measure a mass-selected sample of BD binary systems, which can then be directly compared to similar samples of stellar binaries.

  5. A search for mass segregation of stars and brown dwarfs in \\rho\\ Ophiuchi

    CERN Document Server

    Parker, Richard J; de Oliveira, Catarina Alves

    2012-01-01

    We apply two different algorithms to search for mass segregation to a recent observational census of the rho Ophiuchi star forming region. Firstly, we apply the Lambda_MSR method, which compares the minimum spanning tree (MST) of a chosen subset of stars to MSTs of random subsets of stars in the cluster, and determine the mass segregation ratio, Lambda_MSR. Secondly, we apply the m-Sigma method, which calculates the local stellar surface density around each star and determines the statistical significance of the average surface density for a chosen mass bin, compared to the average surface density in the whole cluster. Using both methods, we find no indication of mass segregation (normal or inverse) in the spatial distribution of stars and brown dwarfs in rho Ophiuchi. Although rho Ophiuchi suffers from high visual extinction, we show that a significant mass segregation signature would be detectable, albeit slightly diluted, despite dust obscuration of centrally located massive stars.

  6. A LOFAR mini-survey for low-frequency radio emission from the nearest brown dwarfs

    CERN Document Server

    Burningham, Ben; Nichols, J D; Casewell, S L; Littlefair, S P; Stark, C; Burleigh, M R; Metchev, S; Tannock, M E; van Weeren, R J; Williams, W L; Wynn, G A

    2016-01-01

    We have conducted a mini-survey for low-frequency radio emission from some of the closest brown dwarfs to the Sun with rapid rotation rates: SIMP J013656.5+093347, WISEPC J150649.97+702736.0, and WISEPA J174124.26+255319.5. We have placed robust 3-sigma upper limits on the flux density in the 111 - 169 MHz frequency range for these targets: WISE 1506: < 0.72 mJy; WISE 1741: < 0.87 mJy; SIMP 0136: < 0.66 mJy. At 8 hours of integration per target to achieve these limits, we find that systematic and detailed study of this class of object at LOFAR frequencies will require a substantial dedication of resources.

  7. A Chandra Observation of the TW Hydrae Association Brown Dwarf 2MASSW J1139511-315921

    CERN Document Server

    Castro, Philip J; Gagné, Marc

    2011-01-01

    We report on a sequence of Chandra X-ray Observatory observations of the TW Hydrae brown dwarf (BD) 2MASSW J1139511-315921 (2M1139). In the combined 31 ks ACIS-S exposure, 2M1139 is detected at the 3-sigma confidence level. We find an X-ray luminosity of L_X = 1.4^(+2.7)_(-1.0) x 10^26 ergs s^-1 or log(L_X/L_bol) = -4.8 +/- 0.3. This object is similar to another TW Hydrae BD member, CD-33 7795B (TWA 5B): both have H-alpha emission, both show no signatures of accretion, and both have comparable ages and spectral types. TWA 5B was previously detected in X-rays with a luminosity of L_X = 4 x 10^27 ergs s^-1 or log(L_X/L_bol) = -3.4, an order of magnitude more luminous in X-rays than 2M1139. We find that the discrepancy between the X-ray luminosity of 2M1139 and TWA 5B is consistent with the spread in X-ray luminosity in the Orion Nebula Cluster (ONC) for BDs of similar spectral types. Though rotation may play a role in the X-ray activity of ultracool dwarfs like 2M1139 and TWA 5B, the discrepancy cannot be expla...

  8. DE0823$-$49 is a juvenile binary brown dwarf at 20.7 pc

    CERN Document Server

    Sahlmann, J; Martín, E L; Lazorenko, P F; Gagliuffi, D C Bardalez; Mayor, M; Ségransan, D; Queloz, D; Udry, S

    2015-01-01

    Astrometric monitoring of the nearby early-L dwarf DE0823$-$49 has revealed a low-mass companion in a 248-day orbit that was announced in an earlier work. Here, we present new astrometric and spectroscopic observations that allow us to characterise the system in detail. The optical spectrum shows LiI-absorption indicative of a young age and/or substellar mass for the primary component. The near-infrared spectrum is best reproduced by a binary system of brown dwarfs with spectral types of L1.5 $+$ L5.5 and effective temperatures of $2150\\pm100$ K and $1670\\pm140$ K. To conform with the photocentric orbit size measured with astrometry and the current understanding of substellar evolution, the system must have an age in the 80--500 Myr range. Evolutionary models predict component masses in the ranges of $M_1\\simeq0.028-0.063\\,M_\\odot$ and $M_2\\simeq0.018-0.045\\,M_\\odot$ with a mass ratio of $q\\simeq0.64-0.74$. Multi-epoch radial velocity measurements unambiguously establish the three-dimensional orbit of the sys...

  9. The Properties of the 500 K Dwarf UGPS J072227.51-054031.2, and a Study of the Far-Red Flux of Cold Brown Dwarfs

    CERN Document Server

    Leggett, S K; Marley, M S; Lodders, K; Canty, J; Lucas, P; Smart, R L; Tinney, C G; Homeier, D; Allard, F; Burningham, Ben; Day-Jones, A; Fegley, B; Ishii, Miki; Jones, H R A; Marocco, F; Pinfield, D J; Tamura, M

    2012-01-01

    We present i and z photometry for 25 T dwarfs and one L dwarf. Combined with published photometry, the data show that the i - z, z - Y and z - J colors of T dwarfs are very red, and continue to increase through to the late-type T dwarfs, with a hint of a saturation for the latest types with T_eff ~ 600 K. We present new 0.7-1.0 um and 2.8-4.2 um spectra for the very late-type T dwarf UGPS J072227.51-054031.2, as well as improved astrometry for this dwarf. Examination of the spectral energy distribution using the new and published data, with Saumon & Marley models, shows that the dwarf has T_eff = 505 +/- 10 K, a mass of 3-11 M_Jupiter and an age between 60 Myr and 1 Gyr. This young age is consistent with the thin disk kinematics of the dwarf. The mass range overlaps with that usually considered to be planetary, despite this being an unbound object discovered in the field near the Sun. This apparently young rapid rotator is also undergoing vigorous atmospheric mixing, as determined by the IRAC and WISE-2 4...

  10. Three new cool brown dwarfs discovered with the wide-field infrared survey explorer (WISE) and an improved spectrum of the Y0 dwarf wise J041022.71+150248.4

    International Nuclear Information System (INIS)

    As part of a larger search of Wide-field Infrared Survey Explorer (WISE) data for cool brown dwarfs with effective temperatures less than 1000 K, we present the discovery of three new cool brown dwarfs with spectral types later than T7. Using low-resolution, near-infrared spectra obtained with the NASA Infrared Telescope Facility and the Hubble Space Telescope, we derive spectral types of T9.5 for WISE J094305.98+360723.5, T8 for WISE J200050.19+362950.1, and Y0: for WISE J220905.73+271143.9. The identification of WISE J220905.73+271143.9 as a Y dwarf brings the total number of spectroscopically confirmed Y dwarfs to 17. In addition, we present an improved spectrum (i.e., higher signal-to-noise ratio) of the Y0 dwarf WISE J041022.71+150248.4 that confirms the Cushing et al. classification of Y0. Spectrophotometric distance estimates place all three new brown dwarfs at distances less than 12 pc, with WISE J200050.19+362950.1 lying at a distance of only 3.9-8.0 pc. Finally, we note that brown dwarfs like WISE J200050.19+362950.1 that lie in or near the Galactic plane offer an exciting opportunity to directly measure the mass of a brown dwarf via astrometric microlensing.

  11. 2MASS J035523.37+113343.7: A YOUNG, DUSTY, NEARBY, ISOLATED BROWN DWARF RESEMBLING A GIANT EXOPLANET

    Energy Technology Data Exchange (ETDEWEB)

    Faherty, Jacqueline K. [Department of Astronomy, Universidad de Chile Cerro Calan, Las Condes (Chile); Rice, Emily L.; Cruz, Kelle L.; Nunez, Alejandro [Department of Astrophysics , American Museum of Natural History, Central Park West at 79th Street, New York, NY 10034 (United States); Mamajek, Eric E., E-mail: jfaherty17@gmail.com, E-mail: jfaherty@amnh.org [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)

    2013-01-01

    We present parallax and proper motion measurements, near-infrared spectra, and Wide-field Infrared Survey Explorer photometry for the low surface gravity L5{gamma} dwarf 2MASS J035523.37+113343.7 (2M0355). We use these data to evaluate photometric, spectral, and kinematic signatures of youth as 2M0355 is the reddest isolated L dwarf yet classified. We confirm its low-gravity spectral morphology and find a strong resemblance to the sharp triangular shaped H-band spectrum of the {approx}10 Myr planetary-mass object 2M1207b. We find that 2M0355 is underluminous compared to a normal field L5 dwarf in the optical and Mauna Kea Observatory J, H, and K bands and transitions to being overluminous from 3 to 12 {mu}m, indicating that enhanced photospheric dust shifts flux to longer wavelengths for young, low-gravity objects, creating a red spectral energy distribution. Investigating the near-infrared color-magnitude diagram for brown dwarfs confirms that 2M0355 is redder and underluminous compared to the known brown dwarf population, similar to the peculiarities of directly imaged exoplanets 2M1207b and HR8799bcd. We calculate UVW space velocities and find that the motion of 2M0355 is consistent with young disk objects (<2-3 Gyr) and it shows a high likelihood of membership in the AB Doradus association.

  12. 2MASS J035523.37+113343.7: A YOUNG, DUSTY, NEARBY, ISOLATED BROWN DWARF RESEMBLING A GIANT EXOPLANET

    International Nuclear Information System (INIS)

    We present parallax and proper motion measurements, near-infrared spectra, and Wide-field Infrared Survey Explorer photometry for the low surface gravity L5γ dwarf 2MASS J035523.37+113343.7 (2M0355). We use these data to evaluate photometric, spectral, and kinematic signatures of youth as 2M0355 is the reddest isolated L dwarf yet classified. We confirm its low-gravity spectral morphology and find a strong resemblance to the sharp triangular shaped H-band spectrum of the ∼10 Myr planetary-mass object 2M1207b. We find that 2M0355 is underluminous compared to a normal field L5 dwarf in the optical and Mauna Kea Observatory J, H, and K bands and transitions to being overluminous from 3 to 12 μm, indicating that enhanced photospheric dust shifts flux to longer wavelengths for young, low-gravity objects, creating a red spectral energy distribution. Investigating the near-infrared color-magnitude diagram for brown dwarfs confirms that 2M0355 is redder and underluminous compared to the known brown dwarf population, similar to the peculiarities of directly imaged exoplanets 2M1207b and HR8799bcd. We calculate UVW space velocities and find that the motion of 2M0355 is consistent with young disk objects (<2-3 Gyr) and it shows a high likelihood of membership in the AB Doradus association.

  13. The spectroscopic study of M8.5-M9.5 stars and brown dwarfs

    Directory of Open Access Journals (Sweden)

    Pavlenko Y.V.

    2013-04-01

    Full Text Available We present high-resolution spectra analysis of the three late-M dwarfs LP944-20, SIPS J2045-6332 and DENIS-P J0021.0-4244. The stellar spectra were observed with Very Large Telescope/Ultraviolet–Visual Echelle Spectrograph (VLT/UVES in optical and near-infrared regions. The effective temperatures Teff and log g was defined by comparing observed and theoretical energy distributions for the investigated objects. Synthetic spectra were calculated for PHOENIX atmosphere models – COND and DUSTY, as well as for Semi-empirical atmosphere model. We discuss the influence of the effects associated with dust in stellar atmosphere on the energy distribution in the stellar spectra.

  14. The Brown Dwarf Kinematics Project (BDKP). IV. Radial Velocities of 85 Late-M and L dwarfs with MagE

    CERN Document Server

    Burgasser, Adam J; Gagne, Jonathan; Bochanski, John J; Faherty, Jaqueline K; West, Andrew A; Mamajek, Eric E; Schmidt, Sarah J; Cruz, Kelle L

    2015-01-01

    Radial velocity measurements are presented for 85 late M- and L-type very low mass stars and brown dwarfs obtained with the Magellan Echellette (MagE) spectrograph. Targets primarily have distances within 20 pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2--3 km/s, and combined these with astrometric and spectrophotometric data to calculate $UVW$ velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2$\\pm$0.2 Gyr for sources within 20 pc. We find significantly different kinematic ages between late-M dwarfs (4.0$\\pm$0.2 Gyr) and L dwarfs (6.5$\\pm$0.4 Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric $U$ velocity distribution w...

  15. CLOUD STRUCTURE OF THE NEAREST BROWN DWARFS: SPECTROSCOPIC VARIABILITY OF LUHMAN 16AB FROM THE HUBBLE SPACE TELESCOPE

    International Nuclear Information System (INIS)

    The binary brown dwarf WISE J104915.57–531906.1 (also Luhman 16AB), composed of a late-L and early-T dwarf, is a prototypical L/T transition flux reversal binary located at a distance of only 2 pc. Luhman 16B is a known variable whose light curves evolve rapidly. We present a spatially resolved spectroscopic time-series of Luhman 16A and B covering 6.5 hr using the Hubble Space Telescope/WFC3 at 1.1-1.66 μm. The small, count-dependent variability of Luhman 16A at the beginning of the observations likely stems from instrumental systematics; Luhman 16A appears non-variable above ≈0.4%. Its spectrum is well fit by a single cloud layer with intermediate cloud thickness (f sed = 2, T eff = 1200 K). Luhman 16B varies at all wavelengths with peak-to-valley amplitudes of 7%-11%. The amplitude and light curve shape changes over only one rotation period. The lowest relative amplitude is found in the deep water absorption band at 1.4 μm, otherwise it mostly decreases gradually from the blue to the red edge of the spectrum. This is very similar to the other two known highly variable early-T dwarfs. A two-component cloud model accounts for most of the variability, although small deviations are seen in the water absorption band. We fit the mean spectrum and relative amplitudes with a linear combination of two models of a warm, thinner cloud (T eff = 1300 K, f sed = 3) and a cooler, thicker cloud (T eff = 1000-1100 K, f sed = 1), assuming out-of-equilibrium atmospheric chemistry. A model with parameters as for Luhman 16A except for the addition of cloud holes cannot reproduce the variability of Luhman 16B, indicating more complex cloud evolution through the L/T transition. The projected separation of the binary has decreased by ≈0.''3 in eight months

  16. Database Cross-Correlation at Scale: A Complete Census of Cool and Peculiar Brown Dwarfs in the 2MASS/SDSS Overlap

    Science.gov (United States)

    Metchev, Stanimir

    Cross-correlation of surveys at different wavelengths is an effective way to leverage existing data for the generation of new science. We propose to perform a cross-match of the complete 2MASS and SDSS surveys as a demonstration of database cross-correlation at scale. The specific science case focuses on identifying cool brown dwarfs. Hundreds of L and T dwarfs have been discovered in the solar neighborhood, ~90% of which from 2MASS or SDSS. These have offered an unprecedented empirical context for the creation of sophisticated substellar phenomenology. A few dozen peculiar L and T dwarfs have also emerged from the larger sample. Their unusual spectral energy distributions have been particularly informative about the ranges of temperature, surface gravity, and dust content in ultra-cool atmospheres. Nevertheless, fundamental aspects of our knowledge of substellar astrophysics remain fragmented. The local space density of T dwarfs is hardly known to better than a factor of several. In fact, some of the nearest cool brown dwarfs may have escaped detection. Dust and cloud dynamics in ultra-cool atmospheres, and their dependence on temperature, gravity, and metallicity remain poorly understood. And in all likelihood, the few known examples of peculiar L and T dwarfs represent merely the extremes of a broad range of existing atmospheric conditions that have yet to be revealed. A combined search on 2MASS and SDSS is an effective way to generate a large, complete sample of L and T dwarfs to address these shortcomings. Cross-correlation of the two surveys can probe deeper, to cooler effective temperatures, and to a higher completeness level than searches on either survey alone. We validated this approach through a test cross-match of the 2099 sq.deg overlap area between 2MASS and SDSS Data Release 1. The demonstration project resulted not only in the first unbiased estimate of the space density and luminosity function of T0-T8 dwarfs, but also in doubling of the then known

  17. A CHANDRA OBSERVATION OF THE TW HYDRAE ASSOCIATION BROWN DWARF 2MASSW J1139511-315921

    International Nuclear Information System (INIS)

    We report on a sequence of Chandra X-Ray Observatory observations of the TW Hydrae brown dwarf (BD) 2MASSW J1139511-315921 (2M1139). In the combined 31 ks ACIS-S exposure, 2M1139 is detected at the 3σ confidence level. We find an X-ray luminosity of LX = 1.4+2.7-1.0 x 1026 erg s-1 or log LX/Lbol = -4.8 ± 0.3. This object is similar to another TW Hydrae BD member, CD-33 7795B (TWA 5B): both have Hα emission, both show no signatures of accretion, and both have comparable ages and spectral types. TWA 5B was previously detected in X-rays with a luminosity of LX = 4 x 1027 erg s-1 or log LX/Lbol = -3.4, an order of magnitude more luminous in X-rays than 2M1139. We find that the discrepancy between the X-ray luminosity of 2M1139 and TWA 5B is consistent with the spread in X-ray luminosity in the Orion Nebula Cluster for BDs of similar spectral types. Though rotation may play a role in the X-ray activity of ultracool dwarfs like 2M1139 and TWA 5B, the discrepancy cannot be explained by rotation alone. We also examine two X-ray bright objects in the field of view of our Chandra observations and find one to be of spectral type K0IV and identify it as a possible RS Canum Venaticorum, and another X-ray bright object whose light curve clearly shows the decay phase of an X-ray flare.

  18. CHARACTERIZING THE ATMOSPHERES OF TRANSITING ROCKY PLANETS AROUND LATE-TYPE DWARFS

    International Nuclear Information System (INIS)

    Visible and near-infrared spectra of transiting hot Jupiter planets have recently been observed, revealing some of the atmospheric constituents of their atmospheres. In the near future, it is probable that primary and secondary eclipse observations of Earth-like rocky planets will also be achieved. The characterization of Earth's transmission spectrum has shown that both major and trace atmospheric constituents may present strong absorption features, including important bio-markers such as water, oxygen, and methane. Our simulations using a recently published empirical Earth's transmission spectrum, and the stellar spectra for a variety of stellar types, indicate that the new generation of extremely large telescopes, such as the proposed 42 m European Extremely Large Telescope, could be capable of retrieving the transmission spectrum of an Earth-like planet around very cool stars and brown dwarfs (Teff ≤ ∼3100 K). For a twin of Earth around a star with Teff ∼ 3100 K (M4), for example, the spectral features of H2O, CH4, CO2, and O2 in the wavelength range between 0.9 and 2.4 μm can simultaneously be detected within 100 hr of observing time, or even less for a late-M star. Such detection would constitute proof for the existence of life in that planet. The detection time can be reduced to a few hours for a super-Earth type of planet with twice Earth's radius.

  19. Structural and compositional properties of brown dwarf disks: the case of 2MASS J04442713+2512164

    CERN Document Server

    Bouy, H; Pinte, C; Olofsson, J; Navascues, D Barrado y; Martín, E L; Pantin, E; Monin, J -L; Basri, G; Augereau, J -C; Ménard, F; Duvert, G; Duchêne, G; Marchis, F; Bayo, A; Bottinelli, S; Lefort, B; Guieu, S

    2008-01-01

    In order to improve our understanding of substellar formation, we have performed a compositional and structural study of a brown dwarf disk. We present the result of photometric, spectroscopic and imaging observations of 2MASS J04442713+2512164, a young brown dwarf (M7.25) member of the Taurus association. Our dataset, combined with results from the literature, provides a complete coverage of the spectral energy distribution from the optical to the millimeter including the first photometric measurement of a brown dwarf disk at 3.7mm, and allows us to perform a detailed analysis of the disk properties. The target was known to have a disk. High resolution optical spectroscopy shows that it is intensely accreting, and powers a jet and an outflow. The disk structure is similar to that observed for more massive TTauri stars. Spectral decomposition models of Spitzer/IRS spectra suggest that the mid-infrared emission from the optically thin disk layers is dominated by grains with intermediate sizes (1.5micron). Crys...

  20. 2MASSJ035523.51+113337.4: A Young, Dusty, Nearby, Isolated Brown Dwarf Resembling A Giant Exoplanet

    CERN Document Server

    Faherty, Jacqueline K; Cruz, Kelle L; Mamajek, Eric E; Núñez, Alejandro

    2012-01-01

    We present parallax and proper motion measurements, near-infrared spectra, and WISE photometry for the low surface gravity L5gamma dwarf 2MASSJ035523.51+113337.4 (2M0355). We use these data to evaluate photometric, spectral, and kinematic signatures of youth. We confirm low-gravity spectral morphology and find a strong resemblance to the sharp triangular shaped H-band spectrum of the ~10 Myr planetary-mass object 2MASSJ1207b. We find that 2M0355 is underluminous compared to a normal field L5 dwarf in the optical and MKO J,H, and K bands and transitions to being overluminous from 3-12 microns indicating that enhanced photospheric dust shifts flux to longer wavelengths for young, low-gravity objects, creating a red spectral energy distribution. Investigating the near-infrared color magnitude diagram for brown dwarfs confirms that 2M0355 is redder and underluminous compared to the known brown dwarf population, similar to the peculiarities of directly imaged exoplanets 2MASSJ1207b and HR8799bcd. We calculate UVW ...

  1. WISEP J004701.06+680352.1: An intermediate surface gravity, dusty brown dwarf in the AB Dor Moving Group

    CERN Document Server

    Gizis, John E; Liu, Michael C; Harris, Hugh C; Faherty, Jacqueline K; Burgasser, Adam J; Kirkpatrick, J Davy

    2014-01-01

    We present spectroscopy, astrometry, and photometry of the brown dwarf WISEP J004701.06+680352.1 (W0047+68), an unusually red field L dwarf at a distance of $12.2 \\pm 0.4$ parsecs. The three-dimensional space motion identifies it as a member of the AB Dor Moving Group, an identification supported by our classification of W0047+68 as intermediate surface gravity (INT-G) using the Allers \\& Liu (2013) near-infrared classification system. This moving group membership implies near-solar metallicity, age $\\sim 100-125$ Myr, $M \\approx 0.018~M_\\odot$, and $\\log g \\approx 4.5$; the thick condensate clouds needed to explain the infrared spectrum are therefore a result of the lower surface gravity than ordinary field brown dwarfs. From the observed luminosity and evolutionary model radius, we find $T_{eff} \\approx 1300 $K, a temperature normally associated with early T dwarfs. Thick clouds are also used to explain the spectral properties of directly imaged giant planets, and we discuss the successes and challenges...

  2. The Solar Neighborhood XXVIII: The Multiplicity Fraction of Nearby Stars from 5 to 70 AU and the Brown Dwarf Desert Around M Dwarfs

    CERN Document Server

    Dieterich, Sergio B; Golimowski, David A; Krist, John E; Tanner, Angelle M

    2012-01-01

    We report on our analysis of HST/NICMOS snapshot high resolution images of 255 stars in 201 systems within ~10 parsecs of the Sun. Photometry was obtained through filters F110W, F180M, F207M, and F222M using NICMOS Camera 2. These filters were selected to permit clear identification of cool brown dwarfs through methane contrast imaging. With a plate scale of 76 mas/pixel, NICMOS can easily resolve binaries with sub-arcsecond separations in the 19".5x19".5 field of view. We previously reported five companions to nearby M and L dwarfs from this search. No new companions were discovered during the second phase of data analysis presented here, confirming that stellar/substellar binaries are rare. We establish magnitude and separation limits for which companions can be ruled out for each star in the sample, and then perform a comprehensive sensitivity and completeness analysis for the subsample of 138 M dwarfs in 126 systems. We calculate a multiplicity fraction of 0.0{-0.0}^{+3.5}% for L companions to M dwarfs in...

  3. SEISMOLOGY OF A MASSIVE PULSATING HYDROGEN ATMOSPHERE WHITE DWARF

    International Nuclear Information System (INIS)

    We report our observations of the new pulsating hydrogen atmosphere white dwarf SDSS J132350.28+010304.22. We discovered periodic photometric variations in frequency and amplitude that are commensurate with nonradial g-mode pulsations in ZZ Ceti stars. This, along with estimates for the star's temperature and gravity, establishes it as a massive ZZ Ceti star. We used time-series photometric observations with the 4.1 m SOAR Telescope, complemented by contemporary McDonald Observatory 2.1 m data, to discover the photometric variability. The light curve of SDSS J132350.28+010304.22 shows at least nine detectable frequencies. We used these frequencies to make an asteroseismic determination of the total mass and effective temperature of the star: M* = 0.88 ± 0.02 M☉ and Teff = 12, 100 ± 140 K. These values are consistent with those derived from the optical spectra and photometric colors.

  4. Detection of brown dwarf-like objects in the core of NGC3603

    CERN Document Server

    Spezzi, Loredana; De Marchi, Guido; Young, Erick T; Paresce, Francesco; Dopita, Michael A; Andersen, Morten; Panagia, Nino; Balick, Bruce; Bond, Howard E; Calzetti, Daniela; Carollo, C Marcella; Disney, Michael J; Frogel, Jay A; Hall, Donald N B; Holtzman, Jon A; Kimble, Randy A; McCarthy, Patrick J; O'Connell, Robert W; Saha, Abhijit; Silk, Joseph I; Trauger, John T; Walker, Alistair R; Whitmore, Bradley C; Windhorst, Rogier A

    2011-01-01

    We use near-infrared data obtained with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope to identify objects having the colors of brown dwarfs (BDs) in the field of the massive galactic cluster NGC 3603. These are identified through use of a combination of narrow and medium band filters spanning the J and H bands, and which are particularly sensitive to the presence of the 1.3-1.5{\\mu}m H2O molecular band - unique to BDs. We provide a calibration of the relationship between effective temperature and color for both field stars and for BDs. This photometric method provides effective temperatures for BDs to an accuracy of {\\pm}350K relative to spectroscopic techniques. This accuracy is shown to be not significantly affected by either stellar surface gravity or uncertainties in the interstellar extinction. We identify nine objects having effective temperature between 1700 and 2200 K, typical of BDs, observed J-band magnitudes in the range 19.5-21.5, and that are strongly clustered towards the luminous...

  5. A molecular outflow driven by the brown dwarf binary FU Tau

    CERN Document Server

    Monin, J -L; Lefloch, B; Dougados, C; de Oliveira, C Alves

    2013-01-01

    We report the detection of a molecular outflow driven by the brown dwarf binary FU Tau. Using the IRAM 30 m telescope we observed the $^{12}$CO(2-1) (CO) emission in the vicinity of FU Tau and detected a bipolar outflow by examining the wings of the CO(2-1) line as we moved away from the source position. An integrated map of the wing emission between 3 kms$^{-1}$ and 5 kms$^{-1}$ reveals a blue-shifted lobe at a position of $\\sim$ 20 \\arcsec\\ from the FU Tau system and at a position angle of $\\sim$ 20$^{\\circ}$. The beam size of the observations is $11\\arcsec$\\ hence it is not possible to distinguish between the two components of the FU Tau binary. However as optical forbidden emission, a strong tracer of the shocks caused by outflow activity, has been detected in the spectrum of FU Tau A we assume this component to be the driving source of the molecular outflow. We estimate the mass and mass outflow rate of the outflow at 4 $\\times$ 10$^{-6}$ \\Msun\\ and 6 $\\times$ 10$^{-10}$ \\Msun/yr respectively. These resu...

  6. Not Alone: Tracing the Origins of Very Low Mass Stars and Brown Dwarfs Through Multiplicity Studies

    CERN Document Server

    Burgasser, A J; Siegler, N; Close, L; Allen, P; Lowrance, P J; Gizis, J; Burgasser, Adam J.; Siegler, Nick; Close, Laird; Allen, Peter; Lowrance, Patrick; Gizis, John

    2006-01-01

    The properties of multiple stellar systems have long provided important empirical constraints for star formation theories, enabling (along with several other lines of evidence) a concrete, qualitative picture of the birth and early evolution of normal stars. At very low masses (VLM; M = 0.8) occurring infrequently (perhaps 10-30%). Both the frequency and maximum separation of stellar and brown dwarf binaries steadily decrease for lower system masses, suggesting that VLM binary formation and/or evolution may be a mass-dependent process. There is evidence for a fairly rapid decline in the number of loosely-bound systems below ~0.3 M_sun, corresponding to a factor of 10-20 increase in the minimum binding energy of VLM binaries as compared to more massive stellar binaries. This wide-separation ``desert'' is present among both field (~1-5 Gyr) and older (> 100 Myr) cluster systems, while the youngest (<~10 Myr) VLM binaries, particularly those in nearby, low-density star forming regions, appear to have somewhat...

  7. The SONYC survey: Towards a complete census of brown dwarfs in star forming regions

    CERN Document Server

    Muzic, K; Geers, V C; Jayawardhana, R; Tamura, M; Dawson, P; Ray, T P

    2013-01-01

    SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey program to provide a census of the substellar population in nearby star forming regions. We have conducted deep optical and near-infrared photometry in five young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3), combined with proper motions, and followed by extensive spectroscopic campaigns with Subaru and VLT, in which we have obtained more than 700 spectra of candidate low-mass objects. We have identified and characterized more than 60 new substellar objects, among them a handful of objects with masses close to, or below the Deuterium burning limit. Through SONYC and surveys by other groups, the substellar IMF is now well characterized down to ~ 5 - 10 MJup, and we find that the ratio of the number of stars with respect to brown dwarfs lies between 2 and 6. A comprehensive survey of NGC 1333 reveals that, down to ~5MJup, free-floating objects with planetary masses are 20-50 times less numerous than stars, i.e. ...

  8. New Low-Mass Stars and Brown Dwarfs with Disks in Lupus

    CERN Document Server

    Allen, P R; Myers, P C; Megeath, S T; Allen, L E; Hartmann, L; Fazio, G G

    2007-01-01

    Using the Infrared Array Camera and the Multiband Imaging Photometer aboard the {\\it Spitzer Space Telescope}, we have obtained images of the Lupus 3 star-forming cloud at 3.6, 4.5, 5.8, 8.0, and 24 \\micron. We present photometry in these bands for the 41 previously known members that are within our images. In addition, we have identified 19 possible new members of the cloud based on red 3.6-8.0 \\micron colors that are indicative of circumstellar disks. We have performed optical spectroscopy on 6 of these candidates, all of which are confirmed as young low-mass members of Lupus 3. The spectral types of these new members range from M4.75 to M8, corresponding to masses of 0.2-0.03 $M_\\odot$ for ages of $\\sim1$ Myr according to theoretical evolutionary models. We also present optical spectroscopy of a candidate disk-bearing object in the vicinity of the Lupus 1 cloud, 2M 1541-3345, which Jayawardhana & Ivanov recently classified as a young brown dwarf ($M\\sim0.03$ $M_\\odot$) with a spectral type of M8. In co...

  9. The properties of discs around planets and brown dwarfs as evidence for disc fragmentation

    CERN Document Server

    Stamatellos, Dimitris

    2015-01-01

    Direct imaging searches have revealed many very low-mass objects, including a small number of planetary mass objects, as wide-orbit companions to young stars. The formation mechanism of these objects remains uncertain. In this paper we present the predictions of the disc fragmentation model regarding the properties of the discs around such low-mass objects. We find that the discs around objects that have formed by fragmentation in discs hosted by Sun-like stars (referred to as 'parent' discs and 'parent' stars) are more massive than expected from the ${M}_{\\rm disc}-M_*$ relation (which is derived for stars with masses $M_*>0.2 {\\rm M}_{\\odot}$). Accordingly, the accretion rates onto these objects are also higher than expected from the $\\dot{M}_*-M_*$ relation. Moreover there is no significant correlation between the mass of the brown dwarf or planet with the mass of its disc nor with the accretion rate from the disc onto it. The discs around objects that form by disc fragmentation have larger than expected m...

  10. Evolution of brown dwarf disks: A Spitzer survey in Upper Scorpius

    CERN Document Server

    Scholz, A; Wood, K; Meeus, G; Stelzer, B; Walker, C; O'Sullivan, M; Scholz, Alexander; Jayawardhana, Ray; Wood, Kenneth; Meeus, Gwendolyn; Stelzer, Beate; Walker, Christina; Sullivan, Mark O'

    2007-01-01

    We have carried out a Spitzer survey for brown dwarf (BD) disks in the ~5 Myr old Upper Scorpius (UpSco) star forming region, using IRS spectroscopy from 8 to 12\\mu m and MIPS photometry at 24\\mu m. Our sample consists of 35 confirmed very low mass members of UpSco. Thirteen objects in this sample show clear excess flux at 24\\mu m, explained by dust emission from a circum-sub-stellar disk. Objects without excess emission either have no disks at all or disks with inner opacity holes of at least ~5 AU radii. Our disk frequency of 37\\pm 9% is higher than what has been derived previously for K0-M5 stars in the same region (on a 1.8 sigma confidence level), suggesting a mass-dependent disk lifetime in UpSco. The clear distinction between objects with and without disks as well as the lack of transition objects shows that disk dissipation inside 5 AU occurs rapidly, probably on timescales of <~10^5 years. For the objects with disks, most SEDs are uniformly flat with flux levels of a few mJy, well modeled as emiss...

  11. Characterizing the disk around the TW Hydrae Association brown dwarf 2MASSW J1207334-393254

    CERN Document Server

    Gizis, B R J E

    2007-01-01

    We present detailed modeling of the disk around the TW Hydrae Association (TWA) brown dwarf 2MASSW J1207334-393254 (2M1207), using {\\it Spitzer} observations from 3.6 to 24 $\\micron$. The spectral energy distribution (SED) does not show a high amount of flaring. We have obtained a good fit using a flat disk of mass between $10^{-4}$ and $10^{-6}$ $M_{\\sun}$, $\\dot{M}$ $\\la10^{-11} M_{\\sun}$/yr and a large inclination angle between 60$\\degr$ and 70$\\degr$. We have used three different grain models to fit the 10 $\\micron$ Si emission feature, and have found the results to be consistent with ISM-like dust. In comparison with other TWA members, this suggests lesser dust processing for 2M1207 which could be explained by mechanisms such as aggregate fragmentation and/or turbulent mixing. We have found a good fit using an inner disk radius equal to the dust sublimation radius, which indicates the absence of an inner hole in the disk. This suggests the presence of a small K-$L^{\\prime}$ excess, similar to the observe...

  12. New brown dwarfs in Upper Sco using UKIDSS Galactic Cluster Survey science verification data

    CERN Document Server

    Lodieu, N; Jameson, R F; Hodgkin, S T; Carraro, G; Kendall, T R

    2006-01-01

    We present first results from a deep (J = 18.7), wide-field (6.5 square degrees) infrared (ZYJHK) survey in the Upper Sco association conducted within the science verification phase of the UKIRT Infrared Deep Sky Survey Galactic Cluster Survey (GCS). Cluster members define a sequence well separated from field stars in the (Z-J,Z) colour-magnitude diagram. We have selected a total of 164 candidates with J = 10.5-18.7 mag from the (Z-J,Z) and (Y-J,Y) diagrams. We further investigated the location of those candidates in the other colour-magnitude and colour-colour diagrams to weed out contaminants. The cross-correlation of the GCS catalogue with the 2MASS database confirms the membership of 116 photometric candidates down to 20 Jupiter masses as they lie within a 2 sigma circle centred on the association mean motion. The final list of cluster members contains 129 sources with masses between 0.3 and 0.007 Msun. We extracted a dozen new low-mass brown dwarfs below 20 Mjup, the limit of previous surveys in the regi...

  13. New Brown Dwarfs and an Updated Initial Mass Function in Taurus

    CERN Document Server

    Luhman, K L

    2004-01-01

    I have performed a search for young low-mass stars and brown dwarfs (BDs) in 2 regions encompassing a total area of 4 deg^2 in the Taurus star-forming region, discovering 15 new members of Taurus. In addition, I present 7 new members outside of these areas from the initial stage of a survey of all of Taurus. These 22 objects exhibit spectral types of M4.5-M9.25 and masses of 0.3-0.015 M_sun according to the theoretical evolutionary models of Baraffe and Chabrier, 7 of which are likely to be BDs. Emission in H(alpha), He I, Ca II, [O I], and [S II] and excess emission in optical and near-IR bands among some of these objects suggest the presence of accretion, outflows, and circumstellar disks. The results from the 4 deg^2 survey have been combined with previous studies of Taurus to arrive at an IMF for a total area of 12.4 deg^2. As in the previous IMFs for Taurus, the updated IMF peaks at a higher mass (0.8 M_sun) than the mass functions in IC 348 and Orion (0.1-0.2 M_sun). Meanwhile, the deficit of BDs in Tau...

  14. BANYAN. VIII. New Low-Mass Stars and Brown Dwarfs with Candidate Circumstellar Disks

    CERN Document Server

    Boucher, Anne; Gagné, Jonathan; Malo, Lison; Faherty, Jacqueline K; Doyon, René; Chen, Christine H

    2016-01-01

    We present the results of a search for new circumstellar disks around low-mass stars and brown dwarfs with spectral types >K5 that are confirmed or candidate members of nearby young moving groups. Our search input sample was drawn from the BANYAN surveys of Malo et al. and Gagn\\'e et al. Two-Micron All-Sky Survey and Wide-field Infrared Survey Explorer data were used to detect near- to mid-infrared excesses that would reveal the presence of circumstellar disks. A total of 13 targets with convincing excesses were identified: four are new and nine were already known in the literature. The new candidates are 2MASS J05010082$-$4337102 (M4.5), J08561384$-$1342242 (M8$\\,\\gamma$), J12474428$-$3816464 (M9$\\,\\gamma$) and J02265658$-$5327032 (L0$\\,\\delta$), and are candidate members of the TW Hya ($\\sim10\\pm 3\\,$Myr), Columba ($\\sim 42^{+6}_{-4}\\,$Myr) and Tucana-Horologium ($\\sim 45\\pm 4\\,$Myr) associations, with masses of $120$ and $13-18\\,M_{\\mathrm{Jup}}$. The M8$-$L0 objects in Columba and Tucana-Horologium are po...

  15. A Venus-Mass Planet Orbiting a Brown Dwarf: Missing Link between Planets and Moons

    CERN Document Server

    Udalski, A; Han, C; Gould, A; Kozlowski, S; Skowron, J; Poleski, R; Soszyński, I; Pietrukowicz, P; Mróz, P; Szymański, M K; Wyrzykowski, Ł; Ulaczyk, K; Pietrzyński, G; Shvartzvald, Y; Maoz, D; Kaspi, S; Gaudi, B S; Hwang, K -H; Choi, J -Y; Shin, I -G; Park, H; Bozza, V

    2015-01-01

    The co-planarity of solar-system planets led Kant to suggest that they formed from an accretion disk, and the discovery of hundreds of such disks around young stars as well as hundreds of co-planar planetary systems by the {\\it Kepler} satellite demonstrate that this formation mechanism is extremely widespread. Many moons in the solar system, such as the Galilean moons of Jupiter, also formed out of the accretion disks that coalesced into the giant planets. We report here the discovery of an intermediate system OGLE-2013-BLG-0723LB/Bb composed of a Venus-mass planet orbiting a brown dwarf, which may be viewed either as a scaled down version of a planet plus star or as a scaled up version of a moon plus planet orbiting a star. The latter analogy can be further extended since they orbit in the potential of a larger, stellar body. For ice-rock companions formed in the outer parts of accretion disks, like Uranus and Callisto, the scaled masses and separations of the three types of systems are similar, leading us ...

  16. ON THE SURVIVAL OF BROWN DWARFS AND PLANETS ENGULFED BY THEIR GIANT HOST STAR

    Energy Technology Data Exchange (ETDEWEB)

    Passy, Jean-Claude; Mac Low, Mordecai-Mark [Department of Astrophysics, American Museum of Natural History, New York, NY (United States); De Marco, Orsola [Department of Physics and Astronomy, Macquarie University, Sydney, NSW (Australia)

    2012-11-10

    The recent discovery of two Earth-mass planets in close orbits around an evolved star has raised questions as to whether substellar companions can survive encounters with their host stars. We consider whether these companions could have been stripped of significant amounts of mass during the phase when they orbited through the dense inner envelopes of the giant. We apply the criterion derived by Murray et al. for disruption of gravitationally bound objects by ram pressure to determine whether mass loss may have played a role in the histories of these and other recently discovered low-mass companions to evolved stars. We find that the brown dwarf and Jovian-mass objects circling WD 0137-349, SDSS J08205+0008, and HIP 13044 are most unlikely to have lost significant mass during the common envelope phase. However, the Earth-mass planets found around KIC 05807616 could well be the remnants of one or two Jovian-mass planets that lost extensive mass during the common envelope phase.

  17. A Search for Companions to Brown Dwarfs in the Taurus and Chamaeleon Star Forming Regions

    CERN Document Server

    Todorov, K O; Konopacky, Q M; McLeod, K K; Apai, D; Ghez, A M; Pascucci, I; Robberto, M

    2014-01-01

    We present the results of a search for companions to young brown dwarfs in the Taurus and Chamaeleon I star forming regions (1/2-3 Myr). We have used WFPC2 on board HST to obtain F791W and F850LP images of 47 members of these regions that have spectral types of M6-L0 (0.01-0.1 Msun). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. We have applied PSF subtraction to the primaries and have searched the resulting images for objects that have colors and magnitudes that are indicative of young low-mass objects. Through this process, we have identified promising candidate companions to 2MASS J04414489+2301513 (rho=0.105"/15 AU), 2MASS J04221332+1934392 (rho=0.05"/7 AU), and ISO 217 (rho=0.03"/5 AU). We reported the discovery of the first candidate in a previous study, showing that it has a similar proper motion as the primary through a comparison of astrometry measured with WFPC2 and Gemini adaptive optics. We have collected an additional e...

  18. Self-consistent evolution of accreting low-mass stars and brown dwarfs

    CERN Document Server

    Baraffe, I; Vorobyov, E I; Chabrier, G

    2016-01-01

    We present self-consistent calculations coupling numerical hydrodynamics simulations of collapsing pre-stellar cores and stellar evolution models of accreting objects. We analyse the main impact of consistent accretion history on the evolution and lithium depletion of young low-mass stars and brown dwarfs. These consistent models confirm the generation of a luminosity spread in Herzsprung-Russell diagrams at ages $\\sim$ 1-10 Myr. They also confirm that early accretion can produce objects with abnormal Li depletion, as found in a previous study that was based on arbitrary accretion rates. The results strengthen that objects with anomalously high level of Li depletion in young clusters should be extremely rare. We also find that early phases of burst accretion can produce coeval models of similar mass with a range of different Li surface abundances, and in particular with Li-excess compared to the predictions of non-accreting counterparts. This result is due to a subtle competition between the effect of burst a...

  19. Extended Transiting Disks and Rings Around Planets and Brown Dwarfs: Theoretical Constraints

    CERN Document Server

    Zanazzi, J J

    2016-01-01

    Newly formed planets (or brown dwarfs) may possess disks or rings that occupy an appreciable fraction of the planet's Hill sphere and extend beyond the Laplace radius, where the tidal torque from the host star dominates over the torque from the oblate planet. Such a disk/ring can exhibit unique, detectable transit signatures, provided that the disk/ring is significantly misaligned with the orbital plane of the planet. There exists tentative evidence for an extended ring system around the young K5 star 1 SWASP J140747-354542. We present a general theoretical study of the inclination (warp) profile of circumplanetary disks under the combined influences of the tidal torque from the central star, the torque from the oblate planet and the self-gravity of the disk. We calculate the steady-state warp profile ("generalized Laplace Surface") and investigate the condition for coherent precession of the disk. We find that to maintain non-negligible misalignment between the extended outer disk and the planet's orbital pl...

  20. Atmospheric aerosol brown carbon in the high Himalayas

    Science.gov (United States)

    Kirillova, Elena; Decesari, Stefano; Marinoni, Angela; Bonasoni, Paolo; Vuillermoz, Elisa; Facchini, M. Cristina; Fuzzi, Sandro

    2016-04-01

    Anthropogenic light-absorbing atmospheric aerosol can reach very high concentrations in the planetary boundary layer in South-East Asia ("brown clouds"), affecting atmospheric transparency and generating spatial gradients of temperature over land with a possible impact on atmospheric dynamics and monsoon circulation. Besides black carbon (BC), an important light-absorbing component of anthropogenic aerosols is the organic carbon component known as 'brown carbon' (BrC). In this research, we provided first measurements of atmospheric aerosol BrC in the high Himalayas during different seasons. Aerosol sampling was conducted at the GAW-WMO Global station "Nepal Climate Observatory-Pyramid" (NCO-P) located in the high Khumbu valley at 5079 m a.s.l. in the foothills of Mt. Everest. PM10 aerosol samples were collected from July 2013 to November 2014. The sampling strategy was set up in order to discriminate the daytime valley breeze bringing polluted air masses up to the observatory and free tropospheric air during nighttime. Water-soluble BrC (WS-BrC) and methanol-soluble BrC (MeS-BrC) were extracted and analyzed using a UV/VIS spectrophotometer equipped with a 50 cm liquid waveguide capillary cell. In the polluted air masses, the highest levels of the BrC light absorption coefficient at 365 nm (babs365) were observed during the pre-monsoon season (1.83±1.46 Mm‑1 for WS-BrC and 2.86±2.49 Mm‑1 for MeS-BrC) and the lowest during the monsoon season (0.21±0.22 Mm‑1 for WS-BrC and 0.32±0.29 Mm‑1 for MeS-BrC). The pre-monsoon season is the most frequently influenced by a strong atmospheric brown cloud (ABC) transport to NCO-P due to increased convection and mixing layer height over South Asia combined with the highest up-valley wind speed and the increase of the emissions from open fires due to the agricultural practice along the Himalayas foothills and the Indo-Gangetic Plain. In contrast, the monsoon season is characterized by a weakened valley wind regime and an

  1. WISEP J004701.06+680352.1: AN INTERMEDIATE SURFACE GRAVITY, DUSTY BROWN DWARF IN THE AB DOR MOVING GROUP

    Energy Technology Data Exchange (ETDEWEB)

    Gizis, John E. [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Allers, Katelyn N. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Liu, Michael C. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu HI 96822 (United States); Harris, Hugh C. [US Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86001 (United States); Faherty, Jacqueline K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington 5241 Broad Branch Road NW, Washington, DC 20015 (United States); Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Kirkpatrick, J. Davy [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States)

    2015-02-01

    We present spectroscopy, astrometry, and photometry of the brown dwarf WISEP J004701.06+680352.1 (W0047+68), an unusually red field L dwarf at a distance of 12.2 ± 0.4 pc. The three-dimensional space motion identifies it as a member of the AB Dor Moving Group, an identification supported by our classification of W0047+68 as intermediate surface gravity (INT-G) using the Allers and Liu near-infrared classification system. This moving group membership implies near-solar metallicity, age ∼100-125 Myr, M ≈ 0.018 M {sub ☉}, and log g ≈ 4.5; the thick condensate clouds needed to explain the infrared spectrum are, therefore, a result of surface gravity that is lower than that of ordinary field brown dwarfs. From the observed luminosity and evolutionary model radius, we find T {sub eff} ≈ 1300 K, a temperature normally associated with early T dwarfs. Thick clouds are also used to explain the spectral properties of directly imaged giant planets, and we discuss the successes and challenges for such substellar models in matching the observed optical and infrared spectra. W0047+68 shows that cloud thickness is more sensitive to intermediate surface gravity than in most models. We also present a trigonometric parallax of the dusty L6 dwarf 2MASS J21481628+4003593. It lies at 8.060 ± 0.036 parsecs; its astrometry is consistent with the view that it is older and metal-rich.

  2. WISEP J004701.06+680352.1: AN INTERMEDIATE SURFACE GRAVITY, DUSTY BROWN DWARF IN THE AB DOR MOVING GROUP

    International Nuclear Information System (INIS)

    We present spectroscopy, astrometry, and photometry of the brown dwarf WISEP J004701.06+680352.1 (W0047+68), an unusually red field L dwarf at a distance of 12.2 ± 0.4 pc. The three-dimensional space motion identifies it as a member of the AB Dor Moving Group, an identification supported by our classification of W0047+68 as intermediate surface gravity (INT-G) using the Allers and Liu near-infrared classification system. This moving group membership implies near-solar metallicity, age ∼100-125 Myr, M ≈ 0.018 M ☉, and log g ≈ 4.5; the thick condensate clouds needed to explain the infrared spectrum are, therefore, a result of surface gravity that is lower than that of ordinary field brown dwarfs. From the observed luminosity and evolutionary model radius, we find T eff ≈ 1300 K, a temperature normally associated with early T dwarfs. Thick clouds are also used to explain the spectral properties of directly imaged giant planets, and we discuss the successes and challenges for such substellar models in matching the observed optical and infrared spectra. W0047+68 shows that cloud thickness is more sensitive to intermediate surface gravity than in most models. We also present a trigonometric parallax of the dusty L6 dwarf 2MASS J21481628+4003593. It lies at 8.060 ± 0.036 parsecs; its astrometry is consistent with the view that it is older and metal-rich

  3. Deep Near-IR Observations of the Globular Cluster M4: Hunting for Brown Dwarfs

    Science.gov (United States)

    Dieball, A.; Bedin, L. R.; Knigge, C.; Rich, R. M.; Allard, F.; Dotter, A.; Richer, H.; Zurek, D.

    2016-01-01

    We present an analysis of deep Hubble Space Telescope (HST)/Wide Field Camera 3 near-IR (NIR) imaging data of the globular cluster (GC) M4. The best-photometry NIR color-magnitude diagram (CMD) clearly shows the main sequence extending toward the expected end of the hydrogen-burning limit and going beyond this point toward fainter sources. The white dwarf (WD) sequence can be identified. As such, this is the deepest NIR CMD of a GC to date. Archival HST optical data were used for proper-motion cleaning of the CMD and for distinguishing the WDs from brown dwarf (BD) candidates. Detection limits in the NIR are around F110W ≈ 26.5 mag and F160W ≈ 27 mag, and in the optical around F775W ≈ 28 mag. Comparing our observed CMDs with theoretical models, we conclude that we have reached beyond the H-burning limit in our NIR CMD and are probably just above or around this limit in our optical-NIR CMDs. Thus, any faint NIR sources that have no optical counterpart are potential BD candidates, since the optical data are not deep enough to detect them. We visually inspected the positions of NIR sources that are fainter than the H-burning limit in F110W and for which the optical photometry did not return a counterpart. We found in total five sources for which we did not get an optical measurement. For four of these five sources, a faint optical counterpart could be visually identified, and an upper optical magnitude was estimated. Based on these upper optical magnitude limits, we conclude that one source is likely a WD, one source could be either a WD or BD candidate, and the remaining two sources agree with being BD candidates. No optical counterpart could be detected for just one source, which makes this source a good BD candidate. We conclude that we found in total four good BD candidates.

  4. A HERSCHEL SURVEY OF COLD DUST IN DISKS AROUND BROWN DWARFS AND LOW-MASS STARS

    International Nuclear Information System (INIS)

    We report the complete photometric results from our Herschel study which is the first comprehensive program to search for far-infrared emission from cold dust around young brown dwarfs (BDs). We surveyed 50 fields containing 51 known or suspected BDs and very low mass stars that have evidence of circumstellar disks based on Spitzer photometry and/or spectroscopy. The objects with known spectral types range from M3 to M9.5. Four of the candidates were subsequently identified as extragalactic objects. Of the remaining 47 we have successfully detected 36 at 70 μm and 14 at 160 μm with signal-to-noise ratio (S/N) greater than 3, as well as several additional possible detections with low S/N. The objects exhibit a range of [24]-[70] μm colors suggesting a range in mass and/or structure of the outer disk. We present modeling of the spectral energy distributions of the sample and discuss trends visible in the data. Using two Monte Carlo radiative transfer codes we investigate disk masses and geometry. We find a very wide range in modeled total disk masses from less than 10–6 M☉ up to 10–3 M☉ with a median disk mass of the order of 3 × 10–5 M☉, suggesting that the median ratio of disk mass to central object mass may be lower than for T Tauri stars. The disk scale heights and flaring angles, however, cover a range consistent with those seen around T Tauri stars. The host clouds in which the young BDs and low-mass stars are located span a range in estimated age from ∼1-3 Myr to ∼10 Myr and represent a variety of star-forming environments. No obvious dependence on cloud location or age is seen in the disk properties, though the statistical significance of this conclusion is not strong.

  5. DETECTION OF BROWN DWARF LIKE OBJECTS IN THE CORE OF NGC 3603

    International Nuclear Information System (INIS)

    We used near-infrared data obtained with the Wide Field Camera 3 on the Hubble Space Telescope to identify objects having the colors of brown dwarfs (BDs) in the field of the massive galactic cluster NGC 3603. These are identified through a combination of narrow- and medium-band filters which span the J and H bands and are particularly sensitive to the presence of the 1.3-1.5 μm H2O molecular band unique to BDs. We provide a calibration of the relationship between effective temperature and color for both field stars and BDs. This photometric method provides effective temperatures for BDs to an accuracy of ±350 K relative to spectroscopic techniques. This accuracy is shown to be not significantly affected by either stellar surface gravity or uncertainties in the interstellar extinction. We identify nine objects having effective temperatures between 1700 and 2200 K, typical of BDs, observed J-band magnitudes in the range 19.5-21.5, and that are strongly clustered toward the luminous core of NGC 3603. However, if these are located at the distance of the cluster, they are far too luminous to be normal BDs. We argue that it is unlikely that these objects are either artifacts of our data set, normal field BDs/M-type giants, or extragalactic contaminants and, therefore, might represent a new class of stars having the effective temperatures of BDs but with luminosities of more massive stars. We explore the interesting scenario in which these objects would be normal stars that have recently tidally ingested a hot Jupiter, the remnants of which are providing a short-lived extended photosphere to the central star. In this case, we would expect them to show the signature of fast rotation.

  6. MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS-AURIGA

    International Nuclear Information System (INIS)

    We have conducted a high-resolution imaging study of the Taurus-Auriga star-forming region in order to characterize the primordial outcome of multiple star formation and the extent of the brown dwarf desert. Our survey identified 16 new binary companions to primary stars with masses of 0.25-2.5 Msun, raising the total number of binary pairs (including components of high-order multiples) with separations of 3-5000 AU to 90. We find that ∼2/3-3/4 of all Taurus members are multiple systems of two or more stars, while the other ∼1/4-1/3 appear to have formed as single stars; the distribution of high-order multiplicity suggests that fragmentation into a wide binary has no impact on the subsequent probability that either component will fragment again. The separation distribution for solar-type stars (0.7-2.5 Msun) is nearly log-flat over separations of 3-5000 AU, but lower-mass stars (0.25-0.7 Msun) show a paucity of binary companions with separations of ∼>200 AU. Across this full mass range, companion masses are well described with a linear-flat function; all system mass ratios (q = MB /MA ) are equally probable, apparently including substellar companions. Our results are broadly consistent with the two expected modes of binary formation (free-fall fragmentation on large scales and disk fragmentation on small scales), but the distributions provide some clues as to the epochs at which the companions are likely to form.

  7. WISEP J060738.65+242953.4: A Nearby. Pole-On L8 Brown Dwarf with Radio Emission

    CERN Document Server

    Gizis, John E; Burgasser, Adam J; Libralato, Mattia; Nardiello, Domenico; Piotto, Giampaolo; Bedin, Luigi R; Berger, Edo; Paudel, Rishi

    2016-01-01

    We present a simultaneous, multi-wavelength campaign targeting the nearby (7.2 pc) L8/L9 (optical/near-infrared) dwarf WISEP J060738.65+242953.4 in the mid-infrared, radio, and optical. Spitzer Space Telescope observations show no variability at the 0.2% level over 10 hours each in the 3.6 and 4.5 micron bands. Kepler K2 monitoring over 36 days in Campaign 0 rules out stable periodic signals in the optical with amplitudes great than 1.5% and periods between 1.5 hours and 2 days. Non-simultaneous Gemini optical spectroscopy detects lithium, constraining this L dwarf to be less than ~2 Gyr old, but no Balmer emission is observed. The low measured projected rotation velocity (v sin i < 6 km/s) and lack of variability are very unusual compared to other brown dwarfs, and we argue that this substellar object is likely viewed pole-on. We detect quiescent (non-bursting) radio emission with the VLA. Amongst radio detected L and T dwarfs, it has the lowest observed L_nu and the lowest v sin i. We discuss the implica...

  8. A statistical analysis of seeds and other high-contrast exoplanet surveys: massive planets or low-mass brown dwarfs?

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, Timothy D.; Spiegel, David S. [Institute for Advanced Study, Princeton, NJ (United States); McElwain, Michael W.; Grady, C. A. [Exoplanets and Stellar Astrophysics Laboratory, Goddard Space Flight Center, Greenbelt, MD (United States); Turner, Edwin L. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States); Mede, Kyle; Kuzuhara, Masayuki [University of Tokyo, Tokyo (Japan); Schlieder, Joshua E.; Brandner, W.; Feldt, M. [Max Planck Institute for Astronomy, Heidelberg (Germany); Wisniewski, John P. [HL Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK (United States); Abe, L. [Laboratoire Hippolyte Fizeau, Nice (France); Biller, B. [University of Edinburgh, Edinburgh, Scotland (United Kingdom); Carson, J. [College of Charleston, Charleston, SC (United States); Currie, T. [Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON (Canada); Egner, S.; Golota, T.; Guyon, O. [Subaru Telescope, Hilo, Hawai' i (United States); Goto, M. [Universitäts-Sternwarte München, Munich (Germany); Hashimoto, J. [National Astronomical Observatory of Japan, Tokyo (Japan); and others

    2014-10-20

    We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections (κ And b, two ∼60 M {sub J} brown dwarf companions in the Pleiades, PZ Tel B, and CD–35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of ∼30-100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at ∼5 M {sub J}, with a single power-law distribution. We find that p(M, a)∝M {sup –0.65} {sup ±} {sup 0.60} a {sup –0.85} {sup ±} {sup 0.39} (1σ errors) provides an adequate fit to our data, with 1.0%-3.1% (68% confidence) of stars hosting 5-70 M {sub J} companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs.

  9. A statistical analysis of seeds and other high-contrast exoplanet surveys: massive planets or low-mass brown dwarfs?

    International Nuclear Information System (INIS)

    We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections (κ And b, two ∼60 M J brown dwarf companions in the Pleiades, PZ Tel B, and CD–35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of ∼30-100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at ∼5 M J, with a single power-law distribution. We find that p(M, a)∝M –0.65 ± 0.60 a –0.85 ± 0.39 (1σ errors) provides an adequate fit to our data, with 1.0%-3.1% (68% confidence) of stars hosting 5-70 M J companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs.

  10. Brown carbon: a significant atmospheric absorber of solar radiation?

    Directory of Open Access Journals (Sweden)

    Y. Feng

    2013-01-01

    Full Text Available Several recent observational studies have shown organic carbon aerosols to be a significant source of absorption of solar radiation. The absorbing part of organic aerosols is referred to as brown carbon. Comparisons with observations indicate that model-simulated aerosol absorption is under-estimated in global models, one of the reasons being the neglect of brown carbon. Using a global chemical transport model coupled with a radiative transfer model, we estimate for the first time the enhanced absorption of solar radiation due to "brown" carbon (BrC in a global model. When BrC is included, the simulated wavelength dependence of aerosol absorption, as measured by the Angstrom exponent increases from 0.9 to 1.2 and thus agrees better with AERONET spectral observations at 440–870 nm. The resulting absorbing aerosol optical depth increases by 3–18% at 550 nm and up to 56% at 350 nm. The global simulations suggest that BrC contributes up to +0.25 W m−2 or 19% of the absorption by anthropogenic aerosols, of which 72% is attributed to black carbon, and 9% is due to sulfate and non-absorbing organic aerosols coated on black carbon. Like black carbon, the overall forcing of BrC at the top of the atmosphere (TOA is a warming effect (+0.11 W m−2, while the effect at the surface is a reduction or dimming (−0.14 W m−2. Because of the inclusion of BrC in our model, the direct radiative effect of organic carbonaceous aerosols changes from cooling (−0.08 W m−2 to warming (+0.025 W m−2 at the TOA, on a global mean basis. Over source regions and above clouds, the absorption of BrC is more significant and thus can play an important role in photochemistry and the hydrologic cycle.

  11. SEISMOLOGY OF A MASSIVE PULSATING HYDROGEN ATMOSPHERE WHITE DWARF

    Energy Technology Data Exchange (ETDEWEB)

    Kepler, S. O.; Pelisoli, Ingrid; Pecanha, Viviane; Costa, J. E. S. [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS (Brazil); Fraga, Luciano [Southern Observatory for Astrophysical Research, Casilla 603, La Serena (Chile); Hermes, J. J.; Winget, D. E.; Castanheira, Barbara [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712-1083 (United States); Corsico, A. H.; Romero, A. D.; Althaus, Leandro [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata (Argentina); Kleinman, S. J.; Nitta, A. [Gemini Observatory, Northern Operations Center, 670 North A' ohoku Place, Hilo, HI 96720 (United States); Koester, D. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Kiel, D-24098 Kiel (Germany); Kuelebi, Baybars [Institut de Ciencies de L' Espai, Universitat Autonoma de Barcelon and Institute for Space Studies of Catalonia, c/Gran Capita 2-4, Edif. Nexus 104, E-08034 Barcelona (Spain); Jordan, Stefan [Astronomisches Rechen-Institut, ZAH, Moenchhofstr. 12-14, D-69120 Heidelberg (Germany); Kanaan, Antonio, E-mail: kepler@if.ufrgs.br [Departamento de Fisica, Universidade Federal de Santa Catarina, Florianopolis, SC (Brazil)

    2012-10-01

    We report our observations of the new pulsating hydrogen atmosphere white dwarf SDSS J132350.28+010304.22. We discovered periodic photometric variations in frequency and amplitude that are commensurate with nonradial g-mode pulsations in ZZ Ceti stars. This, along with estimates for the star's temperature and gravity, establishes it as a massive ZZ Ceti star. We used time-series photometric observations with the 4.1 m SOAR Telescope, complemented by contemporary McDonald Observatory 2.1 m data, to discover the photometric variability. The light curve of SDSS J132350.28+010304.22 shows at least nine detectable frequencies. We used these frequencies to make an asteroseismic determination of the total mass and effective temperature of the star: M{sub *} = 0.88 {+-} 0.02 M{sub Sun} and T{sub eff} = 12, 100 {+-} 140 K. These values are consistent with those derived from the optical spectra and photometric colors.

  12. Hubble Space Telescope Observations of Binary Very-Low-Mass Stars and Brown Dwarfs

    OpenAIRE

    Gizis, J. E.; Reid, I N; Knapp, G. R.; Liebert, J.; Kirkpatrick, J. D.; Koerner, D. W.; Burgasser, A. J.

    2003-01-01

    We present analysis of Hubble Space Telescope images of 82 nearby field late-M and L dwarfs. We resolve 13 of these systems into double M/L dwarf systems and identify an additional possible binary. Combined with previous observations of 20 L dwarfs, we derive an observed binary fraction for ultracool dwarfs of 17+4-3%, where the statistics included systems with separations in the range 1.6-16 A.U. We argue that accounting for biases and incompleteness leads to an estimated binary fraction 15+...

  13. Herschel/PACS view of disks around low-mass stars and brown dwarfs in the TW Hya association

    CERN Document Server

    Liu, Yao; Gong, Munan; Allers, Katelyn N; Brown, Joanna M; Kraus, Adam L; Liu, Michael C; Shkolnik, Evgenya L; van Dishoeck, Ewine F

    2014-01-01

    We conducted Herschel/PACS observations of five very low-mass stars or brown dwarfs located in the TW Hya association with the goal of characterizing the properties of disks in the low stellar mass regime. We detected all five targets at $70\\,\\mu{\\rm{m}}$ and $100\\,\\mu{\\rm{m}}$ and three targets at $160\\,\\mu{\\rm{m}}$. Our observations, combined with previous photometry from 2MASS, WISE, and SCUBA-2, enabled us to construct SEDs with extended wavelength coverage. Using sophisticated radiative transfer models, we analyzed the observed SEDs of the five detected objects with a hybrid fitting strategy that combines the model grids and the simulated annealing algorithm and evaluated the constraints on the disk properties via the Bayesian inference method. The modelling suggests that disks around low-mass stars and brown dwarfs are generally flatter than their higher mass counterparts, but the range of disk mass extends to well below the value found in T Tauri stars, and the disk scale heights are comparable in both...

  14. A Cautionary Tale: MARVELS Brown Dwarf Candidate Reveals Itself To Be A Very Long Period, Highly Eccentric Spectroscopic Stellar Binary

    CERN Document Server

    Mack, Claude E; Deshpande, Rohit; Wisniewski, John P; Stassun, Keivan G; Gaudi, B Scott; Fleming, Scott W; Mahadevan, Suvrath; De Lee, Nathan; Eastman, Jason; Ghezzi, Luan; Hernandez, Jonay I Gonzalez; Femenia, Bruno; Ferreira, Leticia; de Mello, Gustavo Porto; Crepp, Justin R; Sanchez, Daniel Mata; Agol, Eric; Beatty, Thomas G; Bizyaev, Dmitry; Brewington, Howard; Cargile, Phillip A; da Costa, Luiz N; Esposito, Massimiliano; Ebelke, Garret; Hebb, Leslie; Jiang, Peng; Kane, Stephen R; Lee, Brian; Maia, Marcio A G; Malanushenko, Elena; Malanushenko, Victor; Oravetz, Daniel; Paegert, Martin; Pan, Kaike; Prieto, Carlos Allende; Peper, Joshua; Rebolo, Rafael; Roy, Arpita; Santiago, Basilio X; Schneider, Donald P; Simmons, Audrey; Siverd, Robert J; Snedden, Stephanie; Tofflemire, Benjamin M

    2013-01-01

    We report the discovery of a highly eccentric, double-lined spectroscopic binary star system (TYC 3010-1494-1), comprising two solar-type stars that we had initially identified as a single star with a brown dwarf companion. At the moderate resolving power of the MARVELS spectrograph and the spectrographs used for subsequent radial-velocity (RV) measurements (R ~ <30,000), this particular stellar binary mimics a single-lined binary with an RV signal that would be induced by a brown dwarf companion (Msin(i)~50 M_Jup) to a solar-type primary. At least three properties of this system allow it to masquerade as a single star with a very low-mass companion: its large eccentricity (e~0.8), its relatively long period (P~238 days), and the approximately perpendicular orientation of the semi-major axis with respect to the line of sight (omega~189 degrees). As a result of these properties, for ~95% of the orbit the two sets of stellar spectral lines are completely blended, and the RV measurements based on centroiding ...

  15. Variable and polarized radio emission from the T6 brown dwarf WISEP J112254.73+255021.5

    CERN Document Server

    Williams, P K G; Berger, E

    2016-01-01

    Route & Wolszczan (2016) recently detected five radio bursts from the T6 dwarf WISEP J112254.73+255021.5 and used the timing of these events to propose that this object rotates with an ultra-short period of ~17.3 minutes. We conducted follow-up observations with the Very Large Array and Gemini-North but found no evidence for this periodicity. We do, however, observe variable, highly circularly polarized radio emission possibly with a period of 116 minutes, although our observation lasted only 162 minutes and so more data are needed to confirm it. Our proposed periodicity is typical of other radio-active ultracool dwarfs. The handedness of the circular polarization alternates with time and there is no evidence for any unpolarized emission component, the first time such a phenomenology has been observed in radio studies of very low-mass stars and brown dwarfs. We suggest that the object's magnetic dipole axis may be highly misaligned relative to its rotation axis.

  16. New evidence for a substellar luminosity problem: Dynamical mass for the brown dwarf binary Gl 417BC

    Energy Technology Data Exchange (ETDEWEB)

    Dupuy, Trent J. [The University of Texas at Austin, Department of Astronomy, 2515 Speedway C1400, Austin, TX 78712 (United States); Liu, Michael C. [Institute for Astronomy, University of Hawai' i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Ireland, Michael J. [Department of Physics and Astronomy, Macquarie University, NSW 2109 (Australia)

    2014-08-01

    We present new evidence for a problem with cooling rates predicted by substellar evolutionary models that implies that model-derived masses in the literature for brown dwarfs and directly imaged planets may be too high. Based on our dynamical mass for Gl 417BC (L4.5+L6) and a gyrochronology system age from its young, solar-type host star, commonly used models predict luminosities 0.2-0.4 dex lower than we observe. This corroborates a similar luminosity-age discrepancy identified in our previous work on the L4+L4 binary HD 130948BC, which coincidentally has nearly identical component masses (≈50-55 M{sub Jup}) and age (≈800 Myr) as Gl 417BC. Such a luminosity offset would cause systematic errors of 15%-25% in model-derived masses at this age. After comparing different models, including cloudless models that should not be appropriate for mid-L dwarfs like Gl 417BC and HD 130948BC but actually match their luminosities better, we speculate the observed overluminosity could be caused by opacity holes (i.e., patchy clouds) in these objects. Moreover, from hybrid substellar evolutionary models that account for cloud disappearance, we infer the corresponding phase of overluminosity may extend from a few hundred million years up to a few gigayears and cause masses to be overestimated by up to 25%, even well after clouds disappear from view entirely. Thus, the range of ages and spectral types affected by this potential systematic shift in luminosity evolution would encompass most known directly imaged gas-giants and field brown dwarfs.

  17. Membership, binarity and accretion among very low-mass stars and brown dwarfs of the σ Orionis cluster

    Science.gov (United States)

    Kenyon, M. J.; Jeffries, R. D.; Naylor, Tim; Oliveira, J. M.; Maxted, P. F. L.

    2005-01-01

    Intermediate-resolution (R~ 7000) spectroscopy is presented for 76 photometrically selected very low-mass (0.04 consistent with the cluster mean. Photometric selection alone therefore appears to be very effective in identifying cluster members in this mass range. Only six objects appear to be certain non-members; however, a substantial subset of 13 candidates have ambiguous or contradictory indications of membership and lack Li absorption. Together with an observed spread in the equivalent width of the Li absorption feature in the cooler stars of our sample, this indicates that there may be deficiencies in our understanding of the formation of this line in cool, low-gravity objects. Four candidate binary cluster members are identified. Consideration of sampling and radial velocity measurement precision leads us to conclude that either the fraction of very low-mass stars and brown dwarfs in small separation (a < 1 au) binary systems is larger than in field M-dwarfs, or the distribution of separations is much less skewed towards large separations. This conclusion hinges critically on the correct identification of the small number of binary candidates, although it remains significant even when only the candidate members displaying Li absorption are considered. Broadened Hα emission, indicative of circum(sub)stellar accretion discs is found in five or six of the candidate cluster members, three of which probably have substellar masses. The fraction of accretors (10 +/- 5 per cent) is similar to that found in stars of higher mass in the σ Ori cluster using Hα emission as a diagnostic, but much lower than found for very low-mass stars and brown dwarfs of younger clusters. The time-scale for accretion rates to drop to <~10-11 Msolar yr-1 is hence less than the age of the σ Ori cluster (3-7 Myr) for most low-mass objects.

  18. New evidence for a substellar luminosity problem: Dynamical mass for the brown dwarf binary Gl 417BC

    International Nuclear Information System (INIS)

    We present new evidence for a problem with cooling rates predicted by substellar evolutionary models that implies that model-derived masses in the literature for brown dwarfs and directly imaged planets may be too high. Based on our dynamical mass for Gl 417BC (L4.5+L6) and a gyrochronology system age from its young, solar-type host star, commonly used models predict luminosities 0.2-0.4 dex lower than we observe. This corroborates a similar luminosity-age discrepancy identified in our previous work on the L4+L4 binary HD 130948BC, which coincidentally has nearly identical component masses (≈50-55 MJup) and age (≈800 Myr) as Gl 417BC. Such a luminosity offset would cause systematic errors of 15%-25% in model-derived masses at this age. After comparing different models, including cloudless models that should not be appropriate for mid-L dwarfs like Gl 417BC and HD 130948BC but actually match their luminosities better, we speculate the observed overluminosity could be caused by opacity holes (i.e., patchy clouds) in these objects. Moreover, from hybrid substellar evolutionary models that account for cloud disappearance, we infer the corresponding phase of overluminosity may extend from a few hundred million years up to a few gigayears and cause masses to be overestimated by up to 25%, even well after clouds disappear from view entirely. Thus, the range of ages and spectral types affected by this potential systematic shift in luminosity evolution would encompass most known directly imaged gas-giants and field brown dwarfs.

  19. Albedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation

    OpenAIRE

    Ortiz, J. L.; Sicardy, B.; Braga-Ribas, F.; Alvarez-Candal, A; Lellouch, E.; Duffard, R.; Pinilla-Alonso, N.; Ivanov, V. D.; Littlefair, S. P.; Camargo, J. I. B.; Assafin, M.; Unda-Sanzana, E.; Jehin, Emmanuel; Morales, N.; G. Tancredi

    2012-01-01

    Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos. Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto, and is currently at a distance to the Sun intermediate between the two. Although Makemake's ...

  20. The SOPHIE search for northern extrasolar planets VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions

    CERN Document Server

    Bouchy, F; Díaz, R F; Forveille, T; Boisse, I; Arnold, L; Astudillo-Defru, N; Beuzit, J -L; Bonfils, X; Borgniet, S; Bourrier, V; Courcol, B; Delfosse, X; Demangeon, O; Delorme, P; Ehrenreich, D; Hébrard, G; Lagrange, A -M; Mayor, M; Montagnier, G; Moutou, C; Naef, D; Pepe, F; Perrier, C; Queloz, D; Rey, J; Sahlmann, J; Santerne, A; Santos, N C; Sivan, J -P; Udry, S; Wilson, P A

    2015-01-01

    Long-period brown dwarf companions detected in radial velocity surveys are important targets for direct imaging and astrometry to calibrate the mass-luminosity relation of substellar objects. Through a 20-year radial velocity monitoring of solar-type stars that began with ELODIE and was extended with SOPHIE spectrographs, giant exoplanets and brown dwarfs with orbital periods longer than ten years are discovered. We report the detection of five new potential brown dwarfs with minimum masses between 32 and 83 Jupiter mass orbiting solar-type stars with periods longer than ten years. An upper mass limit of these companions is provided using astrometric Hipparcos data, high-angular resolution imaging made with PUEO, and a deep analysis of the cross-correlation function of the main stellar spectra to search for blend effects or faint secondary components. These objects double the number of known brown dwarf companions with orbital periods longer than ten years and reinforce the conclusion that the occurrence of s...

  1. BANYAN. V. A SYSTEMATIC ALL-SKY SURVEY FOR NEW VERY LATE-TYPE LOW-MASS STARS AND BROWN DWARFS IN NEARBY YOUNG MOVING GROUPS

    Energy Technology Data Exchange (ETDEWEB)

    Gagné, Jonathan; Lafrenière, David; Doyon, René; Malo, Lison; Artigau, Étienne [Département de Physique, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 (Canada)

    2015-01-10

    We present the BANYAN All-Sky Survey (BASS) catalog, consisting of 228 new late-type (M4-L6) candidate members of nearby young moving groups (YMGs) with an expected false-positive rate of ∼13%. This sample includes 79 new candidate young brown dwarfs and 22 planetary-mass objects. These candidates were identified through the first systematic all-sky survey for late-type low-mass stars and brown dwarfs in YMGs. We cross-matched the Two Micron All Sky Survey and AllWISE catalogs outside of the galactic plane to build a sample of 98,970 potential ≥M5 dwarfs in the solar neighborhood and calculated their proper motions with typical precisions of 5-15 mas yr{sup –1}. We selected highly probable candidate members of several YMGs from this sample using the Bayesian Analysis for Nearby Young AssociatioNs II tool (BANYAN II). We used the most probable statistical distances inferred from BANYAN II to estimate the spectral type and mass of these candidate YMG members. We used this unique sample to show tentative signs of mass segregation in the AB Doradus moving group and the Tucana-Horologium and Columba associations. The BASS sample has already been successful in identifying several new young brown dwarfs in earlier publications, and will be of great interest in studying the initial mass function of YMGs and for the search of exoplanets by direct imaging; the input sample of potential close-by ≥M5 dwarfs will be useful to study the kinematics of low-mass stars and brown dwarfs and search for new proper motion pairs.

  2. The SOPHIE search for northern extrasolar planets. VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions

    Science.gov (United States)

    Bouchy, F.; Ségransan, D.; Díaz, R. F.; Forveille, T.; Boisse, I.; Arnold, L.; Astudillo-Defru, N.; Beuzit, J.-L.; Bonfils, X.; Borgniet, S.; Bourrier, V.; Courcol, B.; Delfosse, X.; Demangeon, O.; Delorme, P.; Ehrenreich, D.; Hébrard, G.; Lagrange, A.-M.; Mayor, M.; Montagnier, G.; Moutou, C.; Naef, D.; Pepe, F.; Perrier, C.; Queloz, D.; Rey, J.; Sahlmann, J.; Santerne, A.; Santos, N. C.; Sivan, J.-P.; Udry, S.; Wilson, P. A.

    2016-01-01

    Long-period brown dwarf companions detected in radial velocity surveys are important targets for direct imaging and astrometry to calibrate the mass-luminosity relation of substellar objects. Through a 20-yr radial velocity monitoring of solar-type stars that began with ELODIE and was extended with SOPHIE spectrographs, giant exoplanets and brown dwarfs with orbital periods longer than ten years are discovered. We report the detection of five new potential brown dwarfs with minimum masses between 32 and 83 MJup orbiting solar-type stars with periods longer than ten years. An upper mass limit of these companions is provided using astrometric Hipparcos data, high-angular resolution imaging made with PUEO, and a deep analysis of the cross-correlation function of the main stellar spectra to search for blend effects or faint secondary components. These objects double the number of known brown dwarf companions with orbital periods longer than ten years and reinforce the conclusion that the occurrence of such objects increases with orbital separation. With a projected separation larger than 100 mas, all these brown dwarf candidates are appropriate targets for high-contrast and high angular resolution imaging. Based on observations made with ELODIE and SOPHIE spectrographs on the 1.93-m telescope at Observatoire de Haute-Provence (CNRS/AMU), France.Tables 5-9 (RV data) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A46

  3. Brown carbon: a significant atmospheric absorber of solar radiation?

    Directory of Open Access Journals (Sweden)

    Y. Feng

    2013-09-01

    Full Text Available Several recent observational studies have shown organic carbon aerosols to be a significant source of absorption of solar radiation. The absorbing part of organic aerosols is referred to as "brown" carbon (BrC. Using a global chemical transport model and a radiative transfer model, we estimate for the first time the enhanced absorption of solar radiation due to BrC in a global model. The simulated wavelength dependence of aerosol absorption, as measured by the absorption Ångström exponent (AAE, increases from 0.9 for non-absorbing organic carbon to 1.2 (1.0 for strongly (moderately absorbing BrC. The calculated AAE for the strongly absorbing BrC agrees with AERONET spectral observations at 440–870 nm over most regions but overpredicts for the biomass burning-dominated South America and southern Africa, in which the inclusion of moderately absorbing BrC has better agreement. The resulting aerosol absorption optical depth increases by 18% (3% at 550 nm and 56% (38% at 380 nm for strongly (moderately absorbing BrC. The global simulations suggest that the strongly absorbing BrC contributes up to +0.25 W m−2 or 19% of the absorption by anthropogenic aerosols, while 72% is attributed to black carbon, and 9% is due to sulfate and non-absorbing organic aerosols coated on black carbon. Like black carbon, the absorption of BrC (moderately to strongly inserts a warming effect at the top of the atmosphere (TOA (0.04 to 0.11 W m−2, while the effect at the surface is a reduction (−0.06 to −0.14 W m−2. Inclusion of the strongly absorption of BrC in our model causes the direct radiative forcing (global mean of organic carbon aerosols at the TOA to change from cooling (−0.08 W m−2 to warming (+0.025 W m−2. Over source regions and above clouds, the absorption of BrC is higher and thus can play an important role in photochemistry and the hydrologic cycle.

  4. Tidal evolution of CoRoT massive planets and brown dwarfs and of their host stars

    CERN Document Server

    Ferraz-Mello, Sylvio

    2016-01-01

    Aims: Revisit and improvement of the main results obtained in the study of the tidal evolution of several massive CoRoT planets and brown dwarfs and of the rotation of their host stars. Methods: Simulations of the past and future evolution of the orbital and rotational elements of the systems under the joint action of the tidal torques and the braking due to the stellar wind. Results: Presentation of several paradigms and significant examples of tidal evolution in extrasolar planetary systems. It is shown that the high quality of the photometric and spectrographic observations of the CoRoT objects allow for a precise study of their past and future evolution and to estimate the tidal parameters ruling the dissipation in the systems.

  5. Structure and evolution of the first CoRoT exoplanets: Probing the Brown Dwarf/Planet overlapping mass regime

    CERN Document Server

    Leconte, J; Chabrier, G; Barman, T; Levrard, B

    2009-01-01

    We present detailed structure and evolution calculations for the first transiting extrasolar planets discovered by the space-based CoRoT mission. Comparisons between theoretical and observed radii provide information on the internal composition of the CoRoT objects. We distinguish three different categories of planets emerging from these discoveries and from previous ground-based surveys: (i) planets explained by standard planetary models including irradiation, (ii) abnormally bloated planets and (iii) massive objects belonging to the overlapping mass regime between planets and brown dwarfs. For the second category, we show that tidal heating can explain the relevant CoRoT objects, providing non-zero eccentricities. We stress that the usual assumption of a quick circularization of the orbit by tides, as usually done in transit light curve analysis, is not justified a priori, as suggested recently by Levrard et al. (2009), and that eccentricity analysis should be carefully redone for some observations. Finally...

  6. Discovery of a companion at the brown dwarf limit to the solar-type star Gliese 29

    Science.gov (United States)

    Chini, R.; Fuhrmann, K.; Pozo Nuñez, F.; Ramolla, M.; Kaderhandt, L.; Niedworok, N.; Hodapp, K.-W.

    2016-07-01

    Gliese 29 is a 7 to 8 Gyr old, southern Population I turnoff star with a large proper motion of 1 arcsec/yr. Using recent direct imaging observations with the 0.8 m Infrared Imaging System (IRIS) of the Universitätssternwarte Bochum near Cerro Armazones in Chile, we demonstrate that the faint source 2MASS J00402651-5927168 at a projected angular separation ρ=6.35 arcsec is a common-proper-motion companion to Gl 29. Provided this source is not part of a further subsystem, the IRIS J- and K_s-band photometry either implies a spectral type of about L2, based on its absolute magnitude, or an approximate mass M_B ≃ 0.077 M⊙, suggesting that it may even be a brown dwarf. Assuming a face-on circular orbit this faint companion orbits Gl 29 in 1880 years.

  7. A CAUTIONARY TALE: MARVELS BROWN DWARF CANDIDATE REVEALS ITSELF TO BE A VERY LONG PERIOD, HIGHLY ECCENTRIC SPECTROSCOPIC STELLAR BINARY

    International Nuclear Information System (INIS)

    We report the discovery of a highly eccentric, double-lined spectroscopic binary star system (TYC 3010-1494-1), comprising two solar-type stars that we had initially identified as a single star with a brown dwarf companion. At the moderate resolving power of the MARVELS spectrograph and the spectrographs used for subsequent radial-velocity (RV) measurements (R ∼Jup) to a solar-type primary. At least three properties of this system allow it to masquerade as a single star with a very-low-mass companion: its large eccentricity (e ∼ 0.8), its relatively long period (P ∼ 238 days), and the approximately perpendicular orientation of the semi-major axis with respect to the line of sight (ω ∼ 189°). As a result of these properties, for ∼95% of the orbit the two sets of stellar spectral lines are completely blended, and the RV measurements based on centroiding on the apparently single-lined spectrum is very well fit by an orbit solution indicative of a brown dwarf companion on a more circular orbit (e ∼ 0.3). Only during the ∼5% of the orbit near periastron passage does the true, double-lined nature and large RV amplitude of ∼15 km s–1 reveal itself. The discovery of this binary system is an important lesson for RV surveys searching for substellar companions; at a given resolution and observing cadence, a survey will be susceptible to these kinds of astrophysical false positives for a range of orbital parameters. Finally, for surveys like MARVELS that lack the resolution for a useful line bisector analysis, it is imperative to monitor the peak of the cross-correlation function for suspicious changes in width or shape, so that such false positives can be flagged during the candidate vetting process.

  8. First simultaneous microlensing observations by two space telescopes: $Spitzer$ & $Swift$ reveal a brown dwarf in event OGLE-2015-BLG-1319

    CERN Document Server

    Shvartzvald, Y; Udalski, A; Gould, A; Sumi, T; Street, R A; Novati, S Calchi; Hundertmark, M; Bozza, V; Beichman, C; Bryden, G; Carey, S; Drummond, J; Fausnaugh, M; Gaudi, B S; Henderson, C B; Tan, T G; Wibking, B; Pogge, R W; Yee, J C; Zhu, W; Tsapras, Y; Bachelet, E; Dominik, M; Bramich, D M; Cassan, A; Jaimes, R Figuera; Horne, K; Ranc, C; Schmidt, R; Snodgrass, C; Wambsganss, J; Steele, I A; Menzies, J; Mao, S; Poleski, R; Pawlak, M; Szymański, M K; Skowron, J; Mróz, P; Kozłowski, S; Wyrzykowski, Ł; Pietrukowicz, P; Soszyński, I; Ulaczyk, K; Abe, F; Asakura, Y; Barry, R K; Bennett, D P; Bhattacharya, A; Bond, I A; Freeman, M; Hirao, Y; Itow, Y; Koshimoto, N; Li, M C A; Ling, C H; Masuda, K; Fukui, A; Matsubara, Y; Muraki, Y; Nagakane, M; Nishioka, T; Ohnishi, K; Oyokawa, H; Rattenbury, N J; Saito, To; Sharan, A; Sullivan, D J; Suzuki, D; Tristram, P J; Yonehara, A; Jørgensen, U G; Burgdorf, M J; Ciceri, S; D'Ago, G; Evans, D F; Hinse, T C; Kains, N; Kerins, E; Korhonen, H; Mancini, L; Popovas, A; Rabus, M; Rahvar, S; Scarpetta, G; Skottfelt, J; Southworth, J; Peixinho, N; Verma, P; Sbarufatti, B; Kennea, J A; Gehrels, N

    2016-01-01

    Simultaneous observations of microlensing events from multiple locations allow for the breaking of degeneracies between the physical properties of the lensing system, specifically by exploring different regions of the lens plane and by directly measuring the "microlens parallax". We report the discovery of a 30-55$M_J$ brown dwarf orbiting a K dwarf in microlensing event OGLE-2015-BLG-1319. The system is located at a distance of $\\sim$5 kpc toward the Galactic bulge. The event was observed by several ground-based groups as well as by $Spitzer$ and $Swift$, allowing the measurement of the physical properties. However, the event is still subject to an 8-fold degeneracy, in particular the well-known close-wide degeneracy, and thus the projected separation between the two lens components is either $\\sim$0.25 AU or $\\sim$45 AU. This is the first microlensing event observed by $Swift$, with the UVOT camera. We study the region of microlensing parameter space to which $Swift$ is sensitive, finding that while for thi...

  9. The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation

    CERN Document Server

    Stamatellos, Dimitris

    2008-01-01

    We suggest that a high proportion of brown dwarfs are formed by gravitational fragmentation of massive extended discs around Sun-like stars. Such discs should arise frequently, but should be observed infrequently, precisely because they fragment rapidly. By performing an ensemble of radiation-hydrodynamic simulations, we show that such discs fragment within a few thousand years, and produce mainlybrown dwarf (BDs) stars, but also planetary mass (PM) stars and very low-mass hydrogen-burning (HB) stars. Most of the the PM stars and BDs are ejected by mutual interactions. We analyse the statistical properties of these stars, and compare them with observations. After a few hundred thousand years the Sun-like primary is typically left with a close low-mass HB companion, and two much wider companions: a low-mass HB star and a BD star, or a BD-BD binary. There is a BD desert extending out to at least ~100 AU; this is because BDs tend to be formed further out than low-mass HB stars, and then they tend to be scattered...

  10. Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope

    CERN Document Server

    Buenzli, Esther; Marley, Mark S; Apai, Daniel; Radigan, Jacqueline; Bedin, Luigi R; Reid, I Neill; Morley, Caroline V

    2014-01-01

    The binary brown dwarf WISE J104915.57$-$531906.1 (also Luhman 16AB), composed of a late L and early T dwarf, is a prototypical L/T transition flux reversal binary located at only 2 pc distance. Luhman 16B is a known variable whose light curves evolve rapidly. We present spatially resolved spectroscopic time-series of Luhman 16A and B covering 6.5 h using HST/WFC3 at 1.1 to 1.66 $\\mu$m. The small, count-dependent variability of Luhman 16A at the beginning of the observations likely stems from instrumental systematics; Luhman 16A appears non-variable above $\\approx$0.4%. Its spectrum is well fit by a single cloud layer with intermediate cloud thickness (f_sed=2, Teff=1200 K). Luhman 16B varies at all wavelengths with peak-to-valley amplitudes of 7-11%. The amplitude and light curve shape changes over only one rotation period. The lowest relative amplitude is found in the deep water absorption band at 1.4 $\\mu$m, otherwise it mostly decreases gradually from the blue to the red edge of the spectrum. This is very...

  11. Two very nearby (d ~ 5 pc) ultracool brown dwarfs detected by their large proper motions from WISE, 2MASS, and SDSS data

    CERN Document Server

    Scholz, R -D; Schnurr, O; Storm, J

    2011-01-01

    Aims: WISE provides an infrared all-sky survey which aims at completing our knowledge on the possibly dramatically increasing number of brown dwarfs with lower temperatures. We search for the nearest representatives of the coolest brown dwarfs, which will be very interesting for detailed follow-up observations, once they haven been discovered. Methods: We have used the preliminary data release from WISE, selected bright candidates with colours typical of late-T dwarfs, tried to match them with faint 2MASS and SDSS objects, to determine their proper motions, and to follow-up them spectroscopically. Results: We have identified two new ultracool brown dwarfs, WISE J0254+0223 and WISE J1741+2553, with large proper motions of about 2.5 and 1.5 arcsec/yr, respectively. With their w1-w2~3.0 and J-w2~4.0 colour indices we expect them both to have a spectral type of ~T9-T10 and absolute magnitude of M_{w2}~14. For WISE J1741+2553 we confirm a spectral type of T10 from near-infrared spectroscopy with LBT/LUCIFER1. From...

  12. The Size and Shape of the Milky Way Disk and Halo from M-type Brown Dwarfs in the BoRG Survey

    CERN Document Server

    van Vledder, Isabel; Holwerda, B W; Kenworthy, M A; Bouwens, R J; Trenti, M

    2016-01-01

    We have identified 274 M-type Brown Dwarfs in the Hubble Space Telescope's Wide Field Camera 3 (WFC3) pure parallel fields from the Brightest of Reionizing Galaxies (BoRG) survey for high redshift galaxies. These are near-infrared observations with multiple lines-of-sight out of our Milky Way. Using these observed M-type Brown Dwarfs we fitted a Galactic disk and halo model with a Markov chain Monte Carlo (MCMC) analysis. This model worked best with the scale length of the disk fixed at $h$ = 2.6 kpc. For the scale height of the disk, we found $z_0 = 0.29^{+0.02}_{-0.019}$ kpc and for the central number density $\\rho_0 = 0.29^{+0.20}_{-0.13}$ \\#/pc$^3$. For the halo we derived a flattening parameter $\\kappa$ = 0.45$\\pm{0.04}$ and a power-law index $p$ = 2.4$\\pm{0.07}$. We found the fraction of M-type brown dwarfs in the local density that belong to the halo to be $f_{h}$ = 0.0075$^{+0.0025}_{-0.0019}$. We found no correlation between subtype of M-dwarf and any model parameters. The total number of M-type Brow...

  13. The Brown Dwarf Kinematics Project. II. Details on Nine Wide Common Proper Motion Very Low Mass Companions to Nearby Stars

    Science.gov (United States)

    Faherty, Jacqueline K.; Burgasser, Adam J.; West, Andrew A.; Bochanski, John J.; Cruz, Kelle L.; Shara, Michael M.; Walter, Frederick M.

    2010-01-01

    We report on nine wide common proper motion systems containing late-type M, L, or T companions. We confirm six previously reported companions, and identify three new systems. The ages of these systems are determined using diagnostics for both stellar primaries and low-mass secondaries and masses for the secondaries are inferred using evolutionary models. Of our three new discoveries, the M3+T6.5 pair G 204-39 and SDSS J1758+4633 has an age constrained to 0.5-1.5 Gyr making the secondary a potentially useful brown dwarf benchmark. The G5+L4 pair G 200-28 and SDSS J1416+5006 has a projected separation of ~25,000 AU making it one of the widest and lowest binding energy systems known to date. The system containing NLTT 2274 and SDSS J0041+1341 is an older M4+L0 (>4.5 Gyr) pair which shows Hα activity in the secondary but not the primary making it a useful tracer of age/mass/activity trends. Two of the nine systems have discrepant component ages that emerge from stellar or ultracool diagnostics indicating possible shortcomings in our understanding of the age diagnostics of stars and brown dwarfs. We find a resolved binary frequency for widely separated (>100 AU) low-mass companions (i.e., at least a triple system) which is at least twice the frequency found for the field ultracool dwarf population. The ratio of triples to binaries and quadruples to binaries is also high for this sample: 3:5 and 1:4, respectively, compared to 8 pc sample values of 1:4 and 1:26. The additional components in these wide companion systems indicates a formation mechanism that requires a third or fourth component to maintain gravitational stability or facilitate the exchange of angular momentum. The binding energies for the nine multiples discussed in this text are among the lowest known for wide low-mass systems, suggesting that weakly bound, low-to-intermediate mass (0.2 M sun meter Magellan Telescopes located at Las Campanas Observatory, Chile. This paper makes use of data obtained with

  14. THE BROWN DWARF KINEMATICS PROJECT. II. DETAILS ON NINE WIDE COMMON PROPER MOTION VERY LOW MASS COMPANIONS TO NEARBY STARS ,

    International Nuclear Information System (INIS)

    We report on nine wide common proper motion systems containing late-type M, L, or T companions. We confirm six previously reported companions, and identify three new systems. The ages of these systems are determined using diagnostics for both stellar primaries and low-mass secondaries and masses for the secondaries are inferred using evolutionary models. Of our three new discoveries, the M3+T6.5 pair G 204-39 and SDSS J1758+4633 has an age constrained to 0.5-1.5 Gyr making the secondary a potentially useful brown dwarf benchmark. The G5+L4 pair G 200-28 and SDSS J1416+5006 has a projected separation of ∼25,000 AU making it one of the widest and lowest binding energy systems known to date. The system containing NLTT 2274 and SDSS J0041+1341 is an older M4+L0 (>4.5 Gyr) pair which shows Hα activity in the secondary but not the primary making it a useful tracer of age/mass/activity trends. Two of the nine systems have discrepant component ages that emerge from stellar or ultracool diagnostics indicating possible shortcomings in our understanding of the age diagnostics of stars and brown dwarfs. We find a resolved binary frequency for widely separated (>100 AU) low-mass companions (i.e., at least a triple system) which is at least twice the frequency found for the field ultracool dwarf population. The ratio of triples to binaries and quadruples to binaries is also high for this sample: 3:5 and 1:4, respectively, compared to 8 pc sample values of 1:4 and 1:26. The additional components in these wide companion systems indicates a formation mechanism that requires a third or fourth component to maintain gravitational stability or facilitate the exchange of angular momentum. The binding energies for the nine multiples discussed in this text are among the lowest known for wide low-mass systems, suggesting that weakly bound, low-to-intermediate mass (0.2 M sun totsun) multiples can form and survive to exist in the field (1-8 Gyr).

  15. THE PROPERTIES OF THE 500 K DWARF UGPS J072227.51–054031.2 AND A STUDY OF THE FAR-RED FLUX OF COLD BROWN DWARFS

    International Nuclear Information System (INIS)

    We present i and z photometry for 25 T dwarfs and 1 L dwarf. Combined with published photometry, the data show that the i – z, z – Y, and z – J colors of T dwarfs are very red, and continue to increase through to the late-type T dwarfs, with a hint of a saturation for the latest types with Teff ≈ 600 K. We present new 0.7-1.0 μm and 2.8-4.2 μm spectra for the very late type T dwarf UGPS J072227.51–054031.2, as well as improved astrometry for this dwarf. Examination of the spectral energy distribution using new and published data, with Saumon and Marley models, shows that the dwarf has Teff = 505 ± 10 K, a mass of 3-11 MJupiter, and an age between 60 Myr and 1 Gyr. This young age is consistent with the thin disk kinematics of the dwarf. The mass range overlaps with that usually considered to be planetary, despite this being an unbound object discovered in the field near the Sun. This apparently young rapid rotator is also undergoing vigorous atmospheric mixing, as determined by the IRAC and WISE 4.5 μm photometry and the Saumon and Marley models. The optical spectrum for this 500 K object shows clearly detected lines of the neutral alkalis Cs and Rb, which are emitted from deep atmospheric layers with temperatures of 900-1200 K.

  16. Stabilization of CO2 Atmospheres on Exoplanets around M Dwarf Stars

    CERN Document Server

    Gao, Peter; Robinson, Tyler D; Li, Cheng; Yung, Yuk L

    2015-01-01

    We investigate the chemical stability of CO2-dominated atmospheres of M dwarf terrestrial exoplanets using a 1-dimensional photochemical model. On planets orbiting Sun-like stars, the photolysis of CO2 by Far-UV (FUV) radiation is balanced by the reaction between CO and OH, the rate of which depends on H2O abundance. By comparison, planets orbiting M dwarf stars experience higher FUV radiation compared to planets orbiting Sun-like stars, and they are also likely to have low H2O abundance due to M dwarfs having a prolonged, high-luminosity pre-main sequence (Luger & Barnes 2015). We show that, for H2O-depleted planets around M dwarfs, a CO2-dominated atmosphere is stable to conversion to CO and O2 by relying on a catalytic cycle involving H2O2 photolysis. However, this cycle breaks down for planets with atmospheric hydrogen mixing ratios below ~1 ppm, resulting in ~40% of the atmospheric CO2 being converted to CO and O2 on a time scale of 1 Myr. The increased abundance of O2 also results in high O3 concent...

  17. Four Numerical Approaches for Solving the Radiative Transfer Equation in Magnetized White-Dwarf Atmospheres

    OpenAIRE

    Jordan, Stefan; Schmidt, Holger

    2003-01-01

    We compare four different methods to calculate radiative transfer through a magnetized stellar atmosphere, and apply them to the case of magnetic white dwarfs. All methods are numerically stable enough to allow determination of the magnetic field structure, but distinctions between faster, simplifying, methods, and elaborate, but more CPU-time consuming, methods, can be made.

  18. The polluted atmospheres of cool white dwarfs and the magnetic field connection

    Czech Academy of Sciences Publication Activity Database

    Kawka, Adela; Vennes, Stephane

    2014-01-01

    Roč. 439, č. 1 (2014), L90-L94. ISSN 0035-8711 R&D Projects: GA ČR GAP209/12/0217; GA ČR GA13-14581S Institutional support: RVO:67985815 Keywords : white dwarfs * stars: abundances * stars: atmospheres Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.107, year: 2014

  19. First Light LBT AO Images of HR 8799 bcde at 1.65 and 3.3 Microns: New Discrepancies between Young Planets and Old Brown Dwarfs

    CERN Document Server

    Skemer, Andrew J; Esposito, Simone; Burrows, Adam; Leisenring, Jarron; Skrutskie, Michael; Desidera, Silvano; Mesa, Dino; Arcidiacono, Carmelo; Mannucci, Filippo; Rodigas, Timothy J; Close, Laird; McCarthy, Don; Kulesa, Craig; Agapito, Guido; Apai, Daniel; Argomedo, Javier; Bailey, Vanessa; Boutsia, Konstantina; Briguglio, Runa; Brusa, Guido; Busoni, Lorenzo; Claudi, Riccardo; Eisner, Joshua; Fini, Luca; Follette, Katherine B; Garnavich, Peter; Gratton, Raffaele; Guerra, Juan Carlos; Hill, John M; Hoffmann, William F; Jones, Terry; Krejny, Megan; Males, Jared; Masciadri, Elena; Meyer, Michael R; Miller, Douglas L; Morzinski, Katie; Nelson, Matthew; Pinna, Enrico; Puglisi, Alfio; Quanz, Sascha P; Quiros-Pacheco, Fernando; Riccardi, Armando; Stefanini, Paolo; Vaitheeswaran, Vidhya; Wilson, John C; Xompero, Marco

    2012-01-01

    As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3$ micron photometry of the innermost planet (for the first time) and put strong upper-limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 microns compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find that removing CH4 to fit the 3.3 micron photometry increases the predicted L' (3.8 microns) flux enough that it is inconsistent with observations. In an effort to fit the ...

  20. The parsec program: a large sample of brown dwarf trigonometric parallaxes

    Science.gov (United States)

    Andrei, Alexandre H.; Smart, Richard L.; Bucciarelli, Beatrice; Penna, Jucira L.; Marocco, Federico; Lattanzi, Mario G.; Crosta, Mariateresa; Teixeira, Ramakrishna

    2013-02-01

    We report on the parsec program, which observed 140 L and T dwarfs on a regular basis from 2007 to 2011, using the WIFI camera on the ESO/2.2 m telescope. Trigonometric parallaxes at 5 mas precision are derived for 49 objects, and mas yr-1-level proper motions are derived for approximately 200,000 objects in the same fields. We discuss image cleaning, object centroiding, and astrometric methods, in particular three different approaches for trigonometric parallax determination.

  1. Three new massive companions in the planet-brown dwarf boundary detected with SOPHIE

    Directory of Open Access Journals (Sweden)

    Santerne A.

    2011-02-01

    Full Text Available We report the detection of three new massive companions to mainsequence stars based on precise radial velocities obtained with the SOPHIE spectrograph, as part of an ongoing programme to search for extrasolar planets. The minimum masses of the detected companions range from around 16 Mjup to around 60 Mjup, and therefore lie at both sides of the boundary between massive extrasolar planets and brown dwarves.

  2. J-Band Infrared Spectroscopy of a Sample of Brown Dwarfs Using NIRSPEC on Keck II.

    Science.gov (United States)

    McLean; Wilcox; Becklin; Figer; Gilbert; Graham; Larkin; Levenson; Teplitz; Kirkpatrick

    2000-04-10

    Near-infrared spectroscopic observations of a sample of very cool, low-mass objects are presented with higher spectral resolution than in any previous studies. Six of the objects are L dwarfs, ranging in spectral class from L2 to L8/9, and the seventh is a methane or T dwarf. These new observations were obtained during commissioning of the near-infrared spectrometer (NIRSPEC), the first high-resolution near-infrared cryogenic spectrograph for the Keck II 10 m telescope on Mauna Kea, Hawaii. Spectra with a resolving power of R approximately 2500 from 1.135 to 1.360 µm (approximately J band) are presented for each source. At this resolution, a rich spectral structure is revealed, much of which is due to blending of unresolved molecular transitions. Strong lines due to neutral potassium (K i) and bands due to iron hydride (FeH) and steam (H2O) change significantly throughout the L sequence. Iron hydride disappears between L5 and L8, the steam bands deepen, and the K i lines gradually become weaker but wider because of pressure broadening. An unidentified feature occurs at 1.22 µm that has a temperature dependence like FeH but has no counterpart in the available FeH opacity data. Because these objects are 3-6 mag brighter in the near-infrared compared with the I band, spectral classification is efficient. One of the objects studied (2MASSW J1523+3014) is the coolest L dwarf discovered so far by the 2 Micron All-Sky Survey (2MASS), but its spectrum is still significantly different from the methane-dominated objects such as Gl 229B or SDSS 1624+0029. PMID:10727388

  3. Investigating the long-lived clouds of early L dwarfs with Spitzer and K2.

    Science.gov (United States)

    Gizis, John; Lowrance, Patrick; Paudel, Rishi

    2016-08-01

    We propose to monitor two bright L0 dwarfs with Spitzer. Unlike cooler brown dwarfs whose clouds evolve on timescales of hours and days, the best studied L1 dwarf star has a cloud feature that lasted for over two years. This discovery was enabled by Kepler optical photometry combined with Spitzer mid-infrared photometry. The upcoming K2 Campaign 10 happens to include two bright L0 dwarfs, and they will repeated in K2 Campaign 17, providing two uniquely accurate optical light curves that sample timescales from minutes to years. By probing higher altitudes in the L dwarf atmospheres, the Spitzer IRAC photometry would enable us to test whether the optical variability in these two objects also come from long-lived clouds. This would establish whether the Kepler field L1 dwarf is a fluke or whether the weather and cloud lifetimes in warm (~2300K) atmospheres are qualititatively different than in cooler brown dwarfs.

  4. A search for brown-dwarf like secondaries in cataclysmic variables

    CERN Document Server

    Mennickent, R E

    2002-01-01

    We present VTL/ISAAC infrared spectroscopy of a sample of short orbital period cataclysmic variables which are candidates for harboring substellar companions. We have detected the KI and NaI absorption lines of the companion star in VY Aqr. The overall spectral distribution in this system is best fit with a M9.5 type dwarf spectra, implying a distance of $100 \\pm 10$ pc. VY Aqr seems to fall far from the theoretical distribution of secondary star temperatures around the orbital period minimum. Fitting of the IR spectral energy distribution (SED) was performed by comparing the observed spectrum with late-type templates. The application of such a spectral fitting procedure suggests that the continuum shape in the 1.1-2.5 $\\mu$m spectral region in short orbital period cataclysmic variables may be an useful indicator of the companion spectral type. The SED fitting for RZ Leo and CU Vel suggests M5 type dwarf companions, and distances of 340 $\\pm$ 110 and 150 $\\pm$ 50 pc, respectively. These systems may be placed ...

  5. Extrasolar planets and brown dwarfs around AF-type stars. IX. The HARPS southern sample

    CERN Document Server

    Borgniet, Simon; Meunier, Nadège; Galland, Franck

    2016-01-01

    Massive, Main-Sequence AF-type stars have so far remained unexplored in past radial velocity surveys, due to their small number of spectral lines and their high rotational velocities that prevent the classic RV computation method. Our aim was to search for giant planets around AF MS stars, to get first statistical information on their occurrence rate and to compare the results with evolved stars and lower-mass MS stars. We used the HARPS spectrograph located on the 3.6m telescope at ESO La Silla Observatory to observe 108 AF MS stars with B-V in the -0.04 to 0.58 range and masses in the range 1.1-3.6 Msun. We used our SAFIR software specifically developed to compute the radial velocities of these early-type stars. We report the new detection of a mpsini = 4.51 Mjup companion with a ~826-day period to the F6V dwarf HD111998. We present new data on the 2-planet system around the F6IV-V dwarf HD60532. We also report the detection of 14 binaries with long-term RV trends. 70% of our targets show detection limits b...

  6. J-Band Infrared Spectroscopy of a Sample of Brown Dwarfs Using Nirspec on Keck II

    CERN Document Server

    McLean, I S; Becklin, E E; Figer, D F; Gilbert, A M; Graham, J R; Larkin, J E; Levenson, N A; Teplitz, H I; Kirkpatrick, J D; Lean, Ian S. Mc; Wilcox, Mavourneen K.; Figer, Donald F.; Gilbert, Andrea M.; Graham, James R.; Larkin, James E.; Teplitz, Harry I.

    2000-01-01

    Near-infrared spectroscopic observations of a sample of very cool, low-massobjects are presented with higher spectral resolution than in any previousstudies. Six of the objects are L-dwarfs, ranging in spectral class from L2 toL8/9, and the seventh is a methane or T-dwarf. These new observations wereobtained during commissioning of NIRSPEC, the first high-resolutionnear-infrared cryogenic spectrograph for the Keck II 10-meter telescope onMauna Kea, Hawaii. Spectra with a resolving power of R=2500 from 1.135 to 1.360microns (approximately J-band) are presented for each source. At thisresolution, a rich spectral structure is revealed, much of which is due toblending of unresolved molecular transitions. Strong lines due to neutralpotassium (K I), and bands due to iron hydride (FeH) and steam (H2O) changesignificantly throughout the L sequence. Iron hydride disappears between L5 andL8, the steam bands deepen and the K I lines gradually become weaker but widerdue to pressure broadening. An unidentified feature occ...

  7. A brown dwarf companion to the intermediate-mass star HR6037

    CERN Document Server

    Huelamo, N; Ivanov, V D; Chauvin, G; Carraro, G; Sterzik, M F; Melo, C H F; Bonnefoy, M; Hartung, M; Haubois, X; Foellmi, C

    2010-01-01

    In the course of an imaging survey we have detected a visual companion to the intermediate-mass star HR 6037. In this letter, we present two epoch observations of the binary with NACO/VLT, and near-IR spectroscopy of the secondary with ISAAC/VLT. The NACO observations allow us to confirm HR 6037B as a co-moving companion. Its J and H band ISAAC spectra suggest the object has an spectral type of M9+-1, with a surface gravity intermediate between that of 10 Myr dwarfs and field dwarfs with identical spectral type. The comparison of its Ks-band photometry with evolutionary tracks allows us to derive a mass, effective temperature, and surface gravity of 62+-20 MJup, Teff = 2330+-200 K, and log g = 5.1+-0.2, respectively. The small mass ratio of the binary, -0.03, and its long orbital period, -5000 yr, makes HR 6037 a rare and uncommon binary system.

  8. WEATHER ON THE NEAREST BROWN DWARFS: RESOLVED SIMULTANEOUS MULTI-WAVELENGTH VARIABILITY MONITORING OF WISE J104915.57–531906.1AB

    Energy Technology Data Exchange (ETDEWEB)

    Biller, Beth A.; Crossfield, Ian J. M.; Mancini, Luigi; Ciceri, Simona; Kopytova, Taisiya G.; Bonnefoy, Mickaël; Deacon, Niall R.; Schlieder, Joshua E.; Buenzli, Esther; Brandner, Wolfgang; Bailer-Jones, Coryn A. L.; Henning, Thomas; Goldman, Bertrand [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Southworth, John [Astrophysics Group, Keele University, Staffordshire, ST5 5BG (United Kingdom); Allard, France; Homeier, Derek; Freytag, Bernd [Centre de Recherche Astrophysique de Lyon, Ecole Normale Supérieure de Lyon, 46 allée d' Italie, F-69364 Lyon cedex 07 (France); Greiner, Jochen [Max-Planck Institute for extraterrestrische Physik, D-85748 Garching, Giessenbachstr (Germany)

    2013-11-20

    We present two epochs of MPG/ESO 2.2 m GROND simultaneous six-band (r'i'z' JHK) photometric monitoring of the closest known L/T transition brown dwarf binary WISE J104915.57–531906.1AB. We report here the first resolved variability monitoring of both the T0.5 and L7.5 components. We obtained 4 hr of focused observations on the night of 2013 April 22 (UT), as well as 4 hr of defocused (unresolved) observations on the night of 2013 April 16 (UT). We note a number of robust trends in our light curves. The r' and i' light curves appear to be anti-correlated with z' and H for the T0.5 component and in the unresolved light curve. In the defocused dataset, J appears correlated with z' and H and anti-correlated with r' and i', while in the focused dataset we measure no variability for J at the level of our photometric precision, likely due to evolving weather phenomena. In our focused T0.5 component light curve, the K band light curve displays a significant phase offset relative to both H and z'. We argue that the measured phase offsets are correlated with atmospheric pressure probed at each band, as estimated from one-dimensional atmospheric models. We also report low-amplitude variability in i' and z' intrinsic to the L7.5 component.

  9. WEATHER ON THE NEAREST BROWN DWARFS: RESOLVED SIMULTANEOUS MULTI-WAVELENGTH VARIABILITY MONITORING OF WISE J104915.57–531906.1AB

    International Nuclear Information System (INIS)

    We present two epochs of MPG/ESO 2.2 m GROND simultaneous six-band (r'i'z' JHK) photometric monitoring of the closest known L/T transition brown dwarf binary WISE J104915.57–531906.1AB. We report here the first resolved variability monitoring of both the T0.5 and L7.5 components. We obtained 4 hr of focused observations on the night of 2013 April 22 (UT), as well as 4 hr of defocused (unresolved) observations on the night of 2013 April 16 (UT). We note a number of robust trends in our light curves. The r' and i' light curves appear to be anti-correlated with z' and H for the T0.5 component and in the unresolved light curve. In the defocused dataset, J appears correlated with z' and H and anti-correlated with r' and i', while in the focused dataset we measure no variability for J at the level of our photometric precision, likely due to evolving weather phenomena. In our focused T0.5 component light curve, the K band light curve displays a significant phase offset relative to both H and z'. We argue that the measured phase offsets are correlated with atmospheric pressure probed at each band, as estimated from one-dimensional atmospheric models. We also report low-amplitude variability in i' and z' intrinsic to the L7.5 component

  10. The kinematics of very low mass dwarfs: splinter session summary

    CERN Document Server

    Burgasser, Adam J; Schmidt, Sarah; West, Andrew A; Osorio, Maria Rosa Zapatero; Pineda, J Sebastian; Burningham, Ben; Nicholls, C; Sanderson, Robyn; Shkolnik, Evgenya; Rodriguez, David; Riedel, Adric; Joergens, Viki

    2013-01-01

    Kinematic investigations are being increasingly deployed in studies of the lowest mass stars and brown dwarfs to investigate their origins, characterize their atmospheres, and examine the evolution of their physical parameters. This article summarizes the contributions made at the Kinematics of Very Low Mass Dwarfs Splinter Session. Results discussed include analysis of kinematic distributions of M, L and T dwarfs; theoretical tools for interpreting these distributions; identifications of very low mass halo dwarfs and wide companions to nearby stars; radial velocity variability among young and very cool brown dwarfs; and the search and identification of M dwarfs in young moving groups. A summary of discussion points at the conclusion of the Splinter is also presented.

  11. Exoplanets versus brown dwarfs: the CoRoT view and the future

    OpenAIRE

    Schneider, Jean

    2016-01-01

    CoRoT has detected by transit several tens of objects whose radii run from 1.67 Earth radius. Their mass run from less than 5.7 Earth mass (CoRoT-24 b, Alonso et al. 2014) to 63 Jupiter mass (CoRoT-15 b, Bouchy et al. 2011). One could be tempted to think that more massive the object is, the larger it is in size and that there is some limit in mass and/or radius beyond which objects are not planets but very low mass stars below the 80 Jupiter mass limit to trigger nuclear fusion (namely "brown...

  12. The composition and structure of white dwarf atmospheres revealed by extreme ultraviolet spectroscopy

    Science.gov (United States)

    Barstow, Martin A.; Hubeny, Ivan; Lanz, Thierry; Holberg, Jay B.; Sion, Edward M.

    1995-01-01

    The ROentgen SATellite (ROSAT) and Extreme UltraViolet Explorer (EUVE) all-sky surveys have resulted in an important change in our understanding of the general composition of hydrogen-rich DA white dwarf atmospheres, with the photospheric opacity dominated by heavy elements rather than helium in the hottest stars (T > 40, 000 K). Most stars cooler than 40,000 K have more or less pure H atmospheres. However, one question, which has not been resolved, concerned the specific nature of the heavy elements and the role of helium in the hottest white dwarfs. One view of white dwarf evolution requires that H-rich DA stars form by gravitational settling of He from either DAO or He-rich central stars of planetary nebulae. In this case, the youngest (hottest) DA white dwarfs may still contain visible traces of He. Spectroscopic observations now available with EUVE provide a crucial test of these ideas. Analysis of data from the EUVE Guest Observer programme and EUVE public archive allows quantitative consideration of the sources of EUV opacity and places limits on the abundance of He which may be present.

  13. Precise atmospheric parameters for the shortest-period binary white dwarfs: gravitational waves, metals, and pulsations

    International Nuclear Information System (INIS)

    We present a detailed spectroscopic analysis of 61 low-mass white dwarfs and provide precise atmospheric parameters, masses, and updated binary system parameters based on our new model atmosphere grids and the most recent evolutionary model calculations. For the first time, we measure systematic abundances of He, Ca, and Mg for metal-rich, extremely low mass white dwarfs and examine the distribution of these abundances as a function of effective temperature and mass. Based on our preliminary results, we discuss the possibility that shell flashes may be responsible for the presence of the observed He and metals. We compare stellar radii derived from our spectroscopic analysis to model-independent measurements and find good agreement except for white dwarfs with T eff ≲ 10,000 K. We also calculate the expected gravitational wave strain for each system and discuss their significance to the eLISA space-borne gravitational wave observatory. Finally, we provide an update on the instability strip of extremely low mass white dwarf pulsators.

  14. Panchromatic Calibration of Astronomical Observations with State-of-the-Art White Dwarf Model Atmospheres

    Science.gov (United States)

    Rauch, T.

    2016-05-01

    Theoretical spectral energy distributions (SEDs) of white dwarfs provide a powerful tool for cross-calibration and sensitivity control of instruments from the far infrared to the X-ray energy range. Such SEDs can be calculated from fully metal-line blanketed NLTE model-atmospheres that are e.g. computed by the Tübingen NLTE Model-Atmosphere Package (TMAP) that has arrived at a high level of sophistication. TMAP was successfully employed for the reliable spectral analysis of many hot, compact post-AGB stars. High-quality stellar spectra obtained over a wide energy range establish a data base with a large number of spectral lines of many successive ions of different species. Their analysis allows to determine effective temperatures, surface gravities, and element abundances of individual (pre-)white dwarfs with very small error ranges. We present applications of TMAP SEDs for spectral analyses of hot, compact stars in the parameter range from (pre-) white dwarfs to neutron stars and demonstrate the improvement of flux calibration using white-dwarf SEDs that are e.g. available via registered services in the Virtual Observatory.

  15. The Reanalysis of the ROSAT Data of GQ Mus (1983) Using White Dwarf Atmosphere Emission Models

    CERN Document Server

    Balman, S

    2001-01-01

    The analyses of X-ray emission from classical novae during the outburst stage have shown that the soft X-ray emission below 1 keV, which is thought to originate from the photosphere of the white dwarf, is inconsistent with the simple blackbody model of emission. Thus, $ROSAT$ Position Sensitive Proportional Counter (PSPC) archival data of the classical novae GQ Mus 1983 (GQ Mus) have been reanalyzed in order to understand the spectral development in the X-ray wavelengths during the outburst stage. The X-ray spectra are fitted with the hot white dwarf atmosphere emission models developed for the remnants of classical novae near the Eddington luminosity. The post-outburst X-ray spectra of the remnant white dwarf is examined in the context of evolution on the Hertzsprung-Russell diagram using C-O enhanced atmosphere models. The data obtained in 1991 August (during the ROSAT All Sky Survey) indicate that the effective temperature is kT_e<54 eV (<6.2x10^5 K). The 1992 February data show that the white dwarf ...

  16. The basic structure of hot white dwarfs atmospheres as a function of composition

    International Nuclear Information System (INIS)

    Non-gray model atmospheres and continuum surface flux distributions for hot white dwarfs have been calculated using 7 different chemical compositions. These include typical DA, non-DA, 'HZ 21', and 'HZ 34' mixtures and (for comparison purposes) normal population I abundances. The models cover the range 3 104 K 4 K and have been calculated using our own model atmosphere and absorption coefficient program. The results are used to obtain a better qualitative and intuitive understanding of the properties of hot white dwarf atmospheres and their dependence on chemical composition. We discuss specifically the dependence of the surface cooling and backwarming effects as well as the atmospheric density on Tsub(eff) and on element abundances. Furthermore, we investigate the fundamental differences between the surface fluxes (especially in the UV) of DA, non-DA and 'normal composition' stars. The importance of the electron scattering contribution to the source function in determining the EUV surface flux of DA stars is strongly emphasized. Finally, we discuss the basic qualitative differences between the energy distribution of the surface flux from hot white dwarf photospheres and the predicted coronal radiation from non-DA stars. (orig.)

  17. An Analysis of the SEEDS High-Contrast Exoplanet Survey: Massive Planets or Low-Mass Brown Dwarfs?

    CERN Document Server

    Brandt, Timothy D; Turner, Edwin L; Mede, Kyle; Spiegel, David S; Kuzuhara, Masayuki; Schlieder, Joshua E; Wisniewski, John P; Abe, L; Brandner, W; Carson, J; Currie, T; Egner, S; Feldt, M; Golota, T; Goto, M; Grady, C A; Guyon, O; Hashimoto, J; Hayano, Y; Hayashi, M; Hayashi, S; Henning, T; Hodapp, K W; Inutsuka, S; Ishii, M; Iye, M; Janson, M; Kandori, R; Knapp, G R; Kudo, T; Kusakabe, N; Kwon, J; Matsuo, T; Miyama, S; Morino, J -I; Moro-Martín, A; Nishimura, T; Pyo, T -S; Serabyn, E; Suto, H; Suzuki, R; Takami, M; Takato, N; Terada, H; Thalmann, C; Tomono, D; Watanabe, M; Yamada, T; Takami, H; Usuda, T; Tamura, M

    2014-01-01

    We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars observed by HiCIAO on the Subaru Telescope, NIRI on Gemini North, and NICI on Gemini South. The stars cover a wide range of ages and spectral types, and include five detections (kap And b, two ~60 M_J brown dwarf companions in the Pleiades, PZ Tel B, and CD-35 2722 B). We conduct a uniform, Bayesian analysis of the ages of our entire sample, using both membership in a kinematic moving group and activity/rotation age indicators, to obtain posterior age distributions. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis beyond which the distribution function for radial-velocity planets cannot extend, finding model-dependent values of ~30--100 AU. Finally, we treat our entire subst...

  18. VizieR Online Data Catalog: The ELM survey. VII. 15 new ELM white dwarf cand. (Brown+, 2016)

    Science.gov (United States)

    Brown, W. R.; Gianninas, A.; Kilic, M.; Kenyon, S. J.; Allende Prieto, C.

    2016-05-01

    We present observations of 15 new extremely low-mass white dwarf (ELM WD) candidates. Ten objects are selected by color for our targeted spectroscopic ELM Survey program as described in Brown et al. (2012ApJ...744..142B). Five objects come from follow-up spectroscopy of the completed Hypervelocity Star survey. We acquire spectra for the 15 ELM WD candidates using the Blue Channel spectrograph on the 6.5m MMT telescope. We configured the Blue Channel spectrograph to obtain 3650-4500Å spectral coverage with 1.0Å spectral resolution. We acquire additional spectra for 5 objects using the KOSMOS spectrograph on the Kitt Peak National Observatory 4m Mayall telescope on program numbers 2014B-0119 and 2015A-0082. We configured the KOSMOS spectrograph to obtain 3500-6200Å spectral coverage with 2.0Å spectral resolution. We also acquire spectra for objects with g<17mag using the FAST spectrograph on the Fred Lawrence Whipple Observatory 1.5m Tillinghast telescope. We configured the FAST spectrograph to obtain 3500-5500Å spectral coverage with 1.7Å spectral resolution. (3 data files).

  19. The number fraction of discs around brown dwarfs in Orion OB1a and the 25 Orionis group

    CERN Document Server

    Downes, Juan José; Ballesteros-Paredes, Javier; Mateu, Cecilia; Briceño, César; Hernández, Jesús; Petr-Gotzens, Monika G; Calvet, Nuria; Hartmann, Lee; Mauco, Karina

    2015-01-01

    We present a study of 15 new brown dwarfs belonging to the $\\sim7$ Myr old 25 Orionis group and Orion OB1a sub-association with spectral types between M6 and M9 and estimated masses between $\\sim0.07$M$_\\odot$ and $\\sim0.01$ M$_\\odot$. By comparing them through a Bayesian method with low mass stars ($0.8\\lesssim$ M/M$_\\odot\\lesssim0.1$) from previous works in the 25 Orionis group, we found statistically significant differences in the number fraction of classical T Tauri stars, weak T Tauri stars, class II, evolved discs and purely photospheric emitters at both sides of the sub-stellar mass limit. Particularly we found a fraction of $3.9^{+2.4}_{-1.6}~\\%$ low mass stars classified as CTTS and class II or evolved discs, against a fraction of $33.3^{+10.8}_{-9.8}~\\%$ in the sub-stellar mass domain. Our results support the suggested scenario in which the dissipation of discs is less efficient for decreasing mass of the central object.

  20. Detection of a tertiary brown dwarf companion in the sdB-typ e eclipsing binary HS 0705+6700

    CERN Document Server

    Qian, S; Zola, S; Liao, W; Liu, L; Li, L; Winiarski, M; Kuligowska, E; Kreiner, J

    2009-01-01

    HS 0705+6700 is a short-period (P=2.3 hours), close binary containing a hot sdB-type primary and a fully convective secondary. We have monitored this eclipsing binary for more than 2 years and as a result, 32 times of light minimum were obtained. Based on our new eclipse times together with these compiled from the literature, it is discovered that the O-C curve of HS 0705+6700 shows a cyclic variation with a period of 7.15 years and a semiamplitude of 92.4 s. The periodic change was analyzed for the light-travel time effect that may be due to the presence of a tertiary companion. The mass of the third body is determined to be M3 sin i = 0.0377 (+/-0.0043) M when a total mass of 0.617 M for HS 0705+6700 is adopted. For orbital inclinations i >= 32.8, the mass of the tertiary component would be below the stable hydrogen-burning limit of M3~0.072 M, and thus it would be a brown dwarf. The third body is orbiting the sdB-type binary at a distance shorter than 3.6 astronomical units (AU). HS 0705+6700 was formed th...

  1. HST NICMOS Imaging of the Planetary-mass Companion to the Young Brown Dwarf 2MASS J1207334-393254

    CERN Document Server

    Song, I; Zuckerman, B; Farihi, J; Becklin, E E; Bessell, M S; Lowrance, P J; MacIntosh, B A; Song, Inseok

    2006-01-01

    Multi-band (0.9 to 1.6 um) images of the TW Hydrae Association (TWA) brown dwarf, 2MASS J1207334-393254 (also known as 2M1207), and its candidate planetary mass companion (2M1207b) were obtained on 2004 Aug 28 and 2005 Apr 26 with HST/NICMOS. The images from these two epochs unequivocally confirm the two objects as a common proper motion pair (16.0 sigma confidence). A new measurement of the proper motion of 2M1207 implies a distance to the system of 59+-7 pc and a projected separation of 46+-5 AU. The NICMOS and previously published VLT photometry of 2M1207b, extending overall from 0.9 to 3.8 um, are fully consistent with an object of a few Jupiter masses at the canonical age of a TWA member (~8 Myr) based on evolutionary models of young giant planets. These observations provide information on the physical nature of 2M1207b and unambiguously establish that the first direct image of a planetary mass companion in orbit around a self-luminous body, other than our Sun, has been secured.

  2. Emission Line Variability of the Accreting Young Brown Dwarf 2MASSW J1207334-393254: From Hours to Years

    CERN Document Server

    Stelzer, Beate; Jayawardhana, Ray

    2007-01-01

    We have obtained a series of high-resolution optical spectra for the brown dwarf 2MASSW J1207334-393254 (2M1207) using the ESO Very Large Telescope with the UVES spectrograph during two consecutive observing nights (time resolution of ~12 min) and the Magellan Clay telescope with the MIKE spectrograph. Combined with previously published results, these data allow us to investigate changes in the emission line spectrum of 2M1207 on timescales of hours to years. Most of the emission line profiles of 2M1207 are broad, in particular that of Halpha, indicating that the dominant fraction of the emission must be attributed to disk accretion rather than to magnetic activity. From the Halpha 10% width we deduce a relatively stable accretion rate between 10^(-10.1...-9.8) Msun/yr for two nights of consecutive observations. Therefore, either the accretion stream is nearly homogeneous over (sub-)stellar longitude or the system is seen face-on. Small but significant variations are evident throughout our near-continuous obs...

  3. IRAS 16253-2429: the First Proto-Brown Dwarf Binary Candidate Identified through Dynamics of Jets

    CERN Document Server

    Hsieh, Tien-Hao; Belloche, Arnaud; Wyrowski, Friedrich

    2016-01-01

    The formation mechanism of brown dwarfs (BDs) is one of the long-standing problems in star formation because the typical Jeans mass in molecular clouds is too large to form these substellar objects. To answer this question, it is crucial to study a BD at the embedded phase. IRAS 16253-2429 is classified as a very low luminosity object (VeLLO) with internal luminosity 0.1 Lsun. VeLLOs are believed to be very low-mass protostars or even proto-BDs. We observed the jet/outflow driven by IRAS 16253-2429 in CO (2-1), (6-5), and (7-6) using the IRAM 30 m and APEX telescopes and the SMA in order to study its dynamical features and physical properties. Our SMA map reveals two protostellar jets, indicating the existence of a proto-binary system as implied by the precessing jet detected in H2 emission. We detect a wiggling pattern in the position-velocity diagrams along the jet axes, which is likely due to the binary orbital motion. Based on this, we derive the current mass of the binary as ~0.032 Msun. Given the low en...

  4. Deuterium Burning in Massive Giant Planets and Low-Mass Brown Dwarfs formed by Core-Nucleated Accretion

    CERN Document Server

    Bodenheimer, Peter; Lissauer, Jack J; Fortney, Jonathan J; Saumon, Didier

    2013-01-01

    Formation of bodies near the deuterium-burning limit is considered by detailed numerical simulations according to the core-nucleated giant planet accretion scenario. The objects, with heavy-element cores in the range 5-30 Mearth, are assumed to accrete gas up to final masses of 10-15 Jupiter masses (Mjup). After the formation process, which lasts 1-5 Myr and which ends with a 'cold-start', low-entropy configuration, the bodies evolve at constant mass up to an age of several Gyr. Deuterium burning via proton capture is included in the calculation, and we determined the mass, M50, above which more than 50% of the initial deuterium is burned. This often-quoted borderline between giant planets and brown dwarfs is found to depend only slightly on parameters, such as core mass, stellar mass, formation location, solid surface density in the protoplanetary disk, disk viscosity, and dust opacity. The values for M50 fall in the range 11.6-13.6 Mjup, in agreement with previous determinations that do not take the formati...

  5. Photoevaporation of Earth and Super-Earth Atmospheres in the Habitable Zones of M Dwarfs

    Science.gov (United States)

    Mohanty, Subhanjoy

    2015-08-01

    Kepler data show that multiple terrestrial-sized planets (i.e., Earths / super-Earths), packed in very close to the central star, are the norm in exoplanetary systems around low-mass stars. Around M dwarfs, a significant fraction of these planets reside within the Habitable Zone (HZ). This has kindled intense excitement about the possibility of finding habitable planets around these cool red stars. However, M dwarfs also remain extremely magnetically active for much longer than solar-type stars: e.g., an M3 dwarf evinces saturated levels of coronal and chromospheric activity over Gyr timescales, compared to ~100 Myr for solar-mass stars. Thus, basal levels of coronal/chromospheric X-ray/EUV emission from M dwarfs, integrated over their saturated activity lifetimes, may severely photoevaporate the atmospheres of terrestrial planets in M dwarf HZs; this would only be exacerbated by flares (which are correspondingly more intense in active M dwarfs). Here we present detailed hydrodynamic calculations of such photoevaporation for planets spanning a range of Earth/super-Earth sizes, residing in the HZ of M dwarfs of various spectral sub-types, over Gyr evolutionary timescales. Our calculations include the effects of: (1) simultaneous X-ray and EUV heating, using state-of-the-art stellar XUV SED models; (2) the change in the stellar XUV SED over evolutionary timescales; (3) realistic radiative losses (which can both dominate and vary in time); (4) thermal evolution of the planetary core; and (5) a range of initial planetary entropies (i.e.,`hot' or `cold' start) and core compositions. The analysis yields the location and extent of the HZ as a function of planetary mass, core composition, initial conditions and M sub-type. We will focus on H/He dominated (i.e., solar abundance) atmospheres; however, we will also discuss qualtitative trends for CO2 / H2O dominated atmospheres, which we are beginning to explore by coupling a detailed photochemical code with our hydrodynamic

  6. A search for brown dwarf like secondaries in cataclysmic variables - II

    Science.gov (United States)

    Mennickent, R. E.; Diaz, M. P.; Tappert, C.

    2004-02-01

    We have examined VTL/ISAAC 1-2.5 μm spectroscopy of a sample of short-orbital-period cataclysmic variables which are candidates for harbouring substellar companions. We provide descriptions of the infrared spectra of EI Psc, V834 Cen, WX Cet, VW Hyi, TY PsA and BW Scl. Fitting of the infrared (IR) spectral energy distribution (SED) was performed by comparing the observed spectrum with late-type templates. Absorption features of the secondary star were detected in EI Psc and V834 Cen, consistent with dwarf secondaries of spectral type K 5 +/- 1 and M 8 +/- 0.5, respectively. In addition, we report the first detection of the secondary star in VW Hyi. The SED in this case is well matched by an L 0 +/- 2 type secondary contributing 23 per cent to the overall flux at λ= 1.15 μm. This is a surprising result for a system with a relatively high mass transfer rate. We discuss the implication of our findings on the current scenarios for cataclysmic variable star evolution.

  7. Search for brown-dwarf like secondaries in cataclysmic variables II

    CERN Document Server

    Mennickent, R E; Tappert, C

    2004-01-01

    We have examined VTL/ISAAC 1-2.5 $\\umu$m spectroscopy of a sample of short orbital period cataclysmic variables which are candidates for harboring substellar companions. We provide descriptions of the infrared spectrum of \\hbox{EI Psc}, \\hbox{V834 Cen}, \\hbox{WX Cet}, \\hbox{VW Hyi}, \\hbox{TY PsA} and \\hbox{BW Scl}. Fitting of the IR spectral energy distribution (SED) was performed by comparing the observed spectrum with late-type templates. Absorption features of the secondary star were detected in \\hbox{EI Psc} and \\hbox{V834 Cen}, consistent with dwarf secondaries of spectral type K 5 $\\pm$ 1 and M 8 $\\pm$ 0.5, respectively. In addition, we report the first detection of the secondary star in \\hbox{VW Hyi}. The SED in this case is well matched by an L 0 $\\pm$ 2 type secondary contributing 23 per cent to the overall flux at $\\lambda$ = 1.15 $\\umu$m. This is a surprising result for a system with a relatively high mass transfer rate. We discuss the implication of our findings on the current scenarios for catacl...

  8. DANCING IN THE DARK: NEW BROWN DWARF BINARIES FROM KERNEL PHASE INTERFEROMETRY

    International Nuclear Information System (INIS)

    This paper revisits a sample of ultracool dwarfs in the solar neighborhood previously observed with the Hubble Space Telescope's NICMOS NIC1 instrument. We have applied a novel high angular resolution data analysis technique based on the extraction and fitting of kernel phases to archival data. This was found to deliver a dramatic improvement over earlier analysis methods, permitting a search for companions down to projected separations of ∼1 AU on NIC1 snapshot images. We reveal five new close binary candidates and present revised astrometry on previously known binaries, all of which were recovered with the technique. The new candidate binaries have sufficiently close separation to determine dynamical masses in a short-term observing campaign. We also present four marginal detections of objects which may be very close binaries or high-contrast companions. Including only confident detections within 19 pc, we report a binary fraction of at least ϵb = 17.2−3.7+5.7%. The results reported here provide new insights into the population of nearby ultracool binaries, while also offering an incisive case study of the benefits conferred by the kernel phase approach in the recovery of companions within a few resolution elements of the point-spread function core.

  9. DANCING IN THE DARK: NEW BROWN DWARF BINARIES FROM KERNEL PHASE INTERFEROMETRY

    Energy Technology Data Exchange (ETDEWEB)

    Pope, Benjamin; Tuthill, Peter [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2226 (Australia); Martinache, Frantz, E-mail: bjsp@physics.usyd.edu.au, E-mail: p.tuthill@physics.usyd.edu.au, E-mail: frantz@naoj.org [National Astronomical Observatory of Japan, Subaru Telescope, Hilo, HI 96720 (United States)

    2013-04-20

    This paper revisits a sample of ultracool dwarfs in the solar neighborhood previously observed with the Hubble Space Telescope's NICMOS NIC1 instrument. We have applied a novel high angular resolution data analysis technique based on the extraction and fitting of kernel phases to archival data. This was found to deliver a dramatic improvement over earlier analysis methods, permitting a search for companions down to projected separations of {approx}1 AU on NIC1 snapshot images. We reveal five new close binary candidates and present revised astrometry on previously known binaries, all of which were recovered with the technique. The new candidate binaries have sufficiently close separation to determine dynamical masses in a short-term observing campaign. We also present four marginal detections of objects which may be very close binaries or high-contrast companions. Including only confident detections within 19 pc, we report a binary fraction of at least #Greek Lunate Epsilon Symbol#{sub b} = 17.2{sub -3.7}{sup +5.7}%. The results reported here provide new insights into the population of nearby ultracool binaries, while also offering an incisive case study of the benefits conferred by the kernel phase approach in the recovery of companions within a few resolution elements of the point-spread function core.

  10. Stars and brown dwarfs in the sigma Orionis cluster. II. A proper motion study

    CERN Document Server

    Caballero, Jose A

    2010-01-01

    AIMS. I seek to fully know the stellar and substellar populations in the young sigma Orionis open cluster, which is a benchmark for star-forming studies. Because of the very low proper motion of the cluster, late-type dwarfs with appreciable proper motion in the foreground of sigma Orionis can be easily discarded for expensive spectroscopic follow-up. METHODS. I use the Aladin sky atlas, USNO-B1, public astrometric catalogues, and photographic plate digitisations to identify stars with proper motions inconsistent with cluster membership in a circular area of radius 30 arcmin centred on the early-type multiple system sigma Ori. Mostly due to the long time baseline, of more than half a century, the errors in the measured proper motions are lower than 2 mas/a. RESULTS. Of the 42 stars selected for astrometric follow-up, 37 of them are proper-motion cluster interlopers. Some USNO-B1 measurements were affected by partially resolved (visual) multiplicity and target faintness. Because of their late spectral types an...

  11. Dancing in the Dark: New Brown Dwarf Binaries from Kernel Phase Interferometry

    CERN Document Server

    Pope, Benjamin; Tuthill, Peter

    2013-01-01

    This paper revisits a sample of ultracool dwarfs in the Solar neighborhood previously observed with the Hubble Space Telescope's NICMOS NIC1 instrument. We have applied a novel high angular resolution data analysis technique based on the extraction and fitting of kernel phases to archival data. This was found to deliver a dramatic improvement over earlier analysis methods, permitting a search for companions down to projected separations of $\\sim$1 AU on NIC1 snapshot images. We reveal five new close binary candidates and present revised astrometry on previously-known binaries, all of which were recovered with the technique. The new candidate binaries have sufficiently close separation to determine dynamical masses in a short-term observing campaign. We also present four marginal detections of objects which may be very close binaries or high contrast companions. Including only confident detections within 19 parsecs, we report a binary fraction of at least $\\epsilon_b = 17.2^{+5.7}_{-3.7}%$. The results reporte...

  12. A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres

    CERN Document Server

    Helling, Ch; Allard, F; Dehn, M; Hauschild, P; Homeier, D; Lodders, K; Marley, M; Rietmeijer, F; Tsuji, T; Woitke, P

    2008-01-01

    The atmospheres of substellar objects contain clouds of oxides, iron, silicates, and other refractory condensates. Water clouds are expected in the coolest objects. The opacity of these `dust' clouds strongly affects both the atmospheric temperature-pressure profile and the emergent flux. Thus any attempt to model the spectra of these atmospheres must incorporate a cloud model. However the diversity of cloud models in atmospheric simulations is large and it is not always clear how the underlying physics of the various models compare. Likewise the observational consequences of different modeling approaches can be masked by other model differences, making objective comparisons challenging. In order to clarify the current state of the modeling approaches, this paper compares five different cloud models in two sets of tests. Test case 1 tests the dust cloud models for a prescribed L, L--T, and T-dwarf atmospheric (temperature T, pressure p, convective velocity vconv)-structures. Test case 2 compares complete mode...

  13. Opportunities for Laboratory Opacity Chemistry Studies to Facilitate Characterization of Young Giant Planets and Brown Dwarfs

    Science.gov (United States)

    Marley, Mark; Freedman, Richard S.

    2015-01-01

    The thermal emission spectra of young giant planets is shaped by the opacity of atoms and molecules residing in their atmospheres. While great strides have been made in improving the opacities of important molecules, particularly NH3 and CH4, at high temperatures, much more work is needed to understand the opacity and chemistry of atomic Na and K. The highly pressure broadened fundamental band of Na and K in the optical stretches into the near-infrared, strongly influencing the shape of the Y and K spectral bands. Since young giant planets are bright in these bands it is important to understand the influences on the spectral shape. Discerning gravity and atmospheric composition is difficult, if not impossible, without both good atomic opacities as well as an excellent understanding of the relevant atmospheric chemistry. Since Na and K condense at temperatures near 500 to 600 K, the chemistry of the condensation process must be well understood as well, particularly any disequilibrium chemical pathways. Comparisons of the current generation of sophisticated atmospheric models and available data, however, reveal important shortcomings in the models. We will review the current state of observations and theory of young giant planets and will discuss these and other specific examples where improved laboratory measurements for alkali compounds have the potential of substantially improving our understanding of these atmospheres.

  14. FIRST LIGHT LBT AO IMAGES OF HR 8799 bcde AT 1.6 AND 3.3 μm: NEW DISCREPANCIES BETWEEN YOUNG PLANETS AND OLD BROWN DWARFS

    International Nuclear Information System (INIS)

    As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H band and 3.3 μm with the new Large Binocular Telescope adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3 μm photometry of the innermost planet (for the first time) and put strong upper limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 μm compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 μm due to CH4 opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres but find that removing CH4 to fit the 3.3 μm photometry increases the predicted L' (3.8 μm) flux enough that it is inconsistent with observations. In an effort to fit the spectral energy distribution of the HR 8799 planets, we construct mixtures of cloudy atmospheres, which are intended to represent planets covered by clouds of varying opacity. In this scenario, regions with low opacity look hot and bright, while regions with high opacity look faint, similar to the patchy cloud structures on Jupiter and L/T transition brown dwarfs. Our mixed-cloud models reproduce all of the available data, but self-consistent models are still necessary to demonstrate their viability.

  15. Atmospheres and Oceans of Rocky Planets In and Beyond the Habitable Zones of M dwarfs

    Science.gov (United States)

    Tian, Feng

    2015-12-01

    he evolution of M dwarfs during their pre-main-sequence phase causes rocky planets in and beyond the habitable zones these stars to be in the runaway and moist greenhouse states. This scenario has been studied by three groups of researchers recently (Ramirez and Kaltenegger 2014, Tian and Ida 2015, Luger and Barnes 2015), and their consensus is that massive amount of water could have been lost during this time -- early evolution of M dwarfs could have changed the water contents of rocky planets around them, which could strongly influence the habitability of rocky planets around low mass stars. It has been proposed that dense oxygen dominant atmospheres (up to 2000 bars, Luger and Barnes 2015) because of rapid water loss. Is this true? If so, what's the condition for such atmospheres to exist and can they be maintained? On the other hand, what's the likelihood for sub-Neptunes to shrink into habitable planets under such environment? In general how is the habitability of planets around M dwarfs different from those around Sun-type stars? These are the questions we will attempt to address in this work.

  16. A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey

    CERN Document Server

    Kilic, Mukremin; Tremblay, P -E; von Hippel, Ted; Bergeron, P; Harris, Hugh C; Munn, Jeffrey A; Williams, Kurtis A; Gates, Evalyn; Farihi, J

    2010-01-01

    We present optical spectroscopy and near-infrared photometry of 126 cool white dwarfs in the Sloan Digital Sky Survey (SDSS). Our sample includes high proper motion targets selected using the SDSS and USNO-B astrometry and a dozen previously known ultracool white dwarf candidates. Our optical spectroscopic observations demonstrate that a clean selection of large samples of cool white dwarfs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic Survey Telescope datasets) is possible using a reduced proper motion diagram and a tangential velocity cut-off (depending on the proper motion accuracy) of 30 km/s. Our near-infrared observations reveal eight new stars with significant absorption. We use the optical and near-infrared photometry to perform a detailed model atmosphere analysis. More than 80% of the stars in our sample are consistent with either pure hydrogen or pure helium atmospheres. However, the eight stars with significant infrared absorption and the majority of the previously known ultra...

  17. The impact of M-dwarf atmosphere modelling on planet detection

    CERN Document Server

    Bozhinova, I; Stark, C

    2013-01-01

    Being able to accurately estimate stellar parameters based on spectral observations is important not only for understanding the stars themselves but it is also vital for the determination of exoplanet parameters. M dwarfs are discussed as targets for planet detection as these stars are less massive, less luminous and have smaller radii making it possible to detect smaller and lighter planets. Therefore M-dwarfs could prove to be a valuable source for examining the lower mass end of planet distribution, but in order to do that, one must first take care to understand the characteristics of the host stars well enough. Up to date, there are several families of stellar model atmospheres. We focus on the ATLAS9, MARCS and Drift-Phoenix families in the M-dwarf parameter space. We examine the di?erences in the (Tgas, pgas) structures, synthetic photometric fluxes and related colour indices.We find discrepancies in the hotter regions of the stellar atmosphere between the ATLAS and MARCS models. The MARCS and Drift-Pho...

  18. Whole-genome expression analysis of Rice black-streaked dwarf virus in different plant hosts and small brown planthopper.

    Science.gov (United States)

    Xu, Qiufang; Ni, Haiping; Zhang, Jinfeng; Lan, Ying; Ren, Chunmei; Zhou, Yijun

    2015-11-10

    Rice black-streaked dwarf virus (RBSDV) can infect a number of gramineous plants and cause severe crop yield losses in southeast Asian countries. The virus is transmitted by small brown planthopper (SBPH) in a persistent circulative manner. The interactions between RBSDV and its different hosts remain unknown. Besides, how the virus adjusts itself to infect different hosts is unclear. In the present study, the relative RNA levels of the thirteen RBSDV genes in rice, maize, wheat, and SBPH were measured by real-time quantitative PCR. P7-1 and P10 genes were predominantly expressed whereas P8 and P7-2 genes were expressed at low levels in plant hosts. Similar to the expression in rice, P7-1 was the most abundantly expressed gene and P8 was expressed at the lowest level in SBPH, indicating that RBSDV adopts the same strategy to infect distinct hosts. The high expression levels of the P7-1 gene in both plants and insect suggest that it can be used as the target gene for disease diagnostics. However, the expression levels of some genes varied from host to host. P5-1, P6 and P9-1, the components of the RBSDV viroplasm, are differentially expressed in different hosts. Moreover, western blot analysis showed that the quantity of the P9-1 protein was more abundant in SBPH than in plant hosts. These data indicate that the virus may adjust its own gene expression to replicate in different hosts. Analysis of time course of gene expression revealed that P7-1 stands out as the only gene highly expressed at the earliest time point and its expression precedes all others throughout infection from 8 to 24days post-inoculation. The high expression levels of the P7-1 gene suggest that it plays a significant role in RBSDV-host interactions. PMID:26149652

  19. DEUTERIUM BURNING IN MASSIVE GIANT PLANETS AND LOW-MASS BROWN DWARFS FORMED BY CORE-NUCLEATED ACCRETION

    Energy Technology Data Exchange (ETDEWEB)

    Bodenheimer, Peter [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); D' Angelo, Gennaro; Lissauer, Jack J. [Space Science and Astrobiology Division, NASA-Ames Research Center, Moffett Field, CA 94035 (United States); Fortney, Jonathan J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Saumon, Didier, E-mail: peter@ucolick.org, E-mail: gennaro.dangelo@nasa.gov, E-mail: Jack.J.Lissauer@nasa.gov, E-mail: jfortney@ucolick.org, E-mail: dsaumon@lanl.gov [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545 (United States)

    2013-06-20

    Using detailed numerical simulations, we study the formation of bodies near the deuterium-burning limit according to the core-nucleated giant planet accretion scenario. The objects, with heavy-element cores in the range 5-30 M{sub Circled-Plus }, are assumed to accrete gas up to final masses of 10-15 Jupiter masses (M{sub Jup}). After the formation process, which lasts 1-5 Myr and which ends with a ''cold-start'', low-entropy configuration, the bodies evolve at constant mass up to an age of several Gyr. Deuterium burning via proton capture is included in the calculation, and we determined the mass, M{sub 50}, above which more than 50% of the initial deuterium is burned. This often-quoted borderline between giant planets and brown dwarfs is found to depend only slightly on parameters, such as core mass, stellar mass, formation location, solid surface density in the protoplanetary disk, disk viscosity, and dust opacity. The values for M{sub 50} fall in the range 11.6-13.6 M{sub Jup}, in agreement with previous determinations that do not take the formation process into account. For a given opacity law during the formation process, objects with higher core masses form more quickly. The result is higher entropy in the envelope at the completion of accretion, yielding lower values of M{sub 50}. For masses above M{sub 50}, during the deuterium-burning phase, objects expand and increase in luminosity by one to three orders of magnitude. Evolutionary tracks in the luminosity versus time diagram are compared with the observed position of the companion to Beta Pictoris.

  20. DETECTION OF A TERTIARY BROWN DWARF COMPANION IN THE sdB-TYPE ECLIPSING BINARY HS 0705+6700

    International Nuclear Information System (INIS)

    HS 0705+6700 is a short-period (P = 2.3 hr), close binary containing a hot sdB-type primary and a fully convective secondary. We have monitored this eclipsing binary for more than two years and as a result, 32 times of light minimum were obtained. Based on our new eclipse times together with these compiled from the literature, it is discovered that the observed-calculated curve of HS 0705+6700 shows a cyclic variation with a period of 7.15 years and a semiamplitude of 92.4 s. The periodic change was analyzed for the light-travel time effect that may be due to the presence of a tertiary companion. The mass of the third body is determined to be M 3sin i' = 0.0377(±0.0043) M sun when a total mass of 0.617 M sun for HS 0705+6700 is adopted. For orbital inclinations i' ≥ 32.08, the mass of the tertiary component would be below the stable hydrogen-burning limit of M 3 ∼ 0.072 M sun, and thus it would be a brown dwarf. The third body is orbiting the sdB-type binary at a distance shorter than 3.6 AU. HS 0705+6700 was formed through the evolution of a common envelope after the primary becomes a red giant. The detection of a substellar companion in HS 0705+6700 system at this distance from the binary could give some constraints on stellar evolution in such systems and the interactions between red giants and their companions.

  1. DEUTERIUM BURNING IN MASSIVE GIANT PLANETS AND LOW-MASS BROWN DWARFS FORMED BY CORE-NUCLEATED ACCRETION

    International Nuclear Information System (INIS)

    Using detailed numerical simulations, we study the formation of bodies near the deuterium-burning limit according to the core-nucleated giant planet accretion scenario. The objects, with heavy-element cores in the range 5-30 M⊕, are assumed to accrete gas up to final masses of 10-15 Jupiter masses (MJup). After the formation process, which lasts 1-5 Myr and which ends with a ''cold-start'', low-entropy configuration, the bodies evolve at constant mass up to an age of several Gyr. Deuterium burning via proton capture is included in the calculation, and we determined the mass, M50, above which more than 50% of the initial deuterium is burned. This often-quoted borderline between giant planets and brown dwarfs is found to depend only slightly on parameters, such as core mass, stellar mass, formation location, solid surface density in the protoplanetary disk, disk viscosity, and dust opacity. The values for M50 fall in the range 11.6-13.6 MJup, in agreement with previous determinations that do not take the formation process into account. For a given opacity law during the formation process, objects with higher core masses form more quickly. The result is higher entropy in the envelope at the completion of accretion, yielding lower values of M50. For masses above M50, during the deuterium-burning phase, objects expand and increase in luminosity by one to three orders of magnitude. Evolutionary tracks in the luminosity versus time diagram are compared with the observed position of the companion to Beta Pictoris.

  2. SPATIALLY RESOLVED OBSERVATIONS OF THE BIPOLAR OPTICAL OUTFLOW FROM THE BROWN DWARF 2MASS J12073347-3932540

    Energy Technology Data Exchange (ETDEWEB)

    Whelan, E. T.; Ray, T. P. [Dublin Institute for Advanced Studies, School of Cosmic Physics, 31 Fitzwilliam Place, Dublin 2 (Ireland); Comeron, F. [ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Bacciotti, F. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Kavanagh, P. J. [Institut fuer Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Eberhard Karls Universitaet, D-72076 Tuebingen (Germany)

    2012-12-20

    Studies of brown dwarf (BD) outflows provide information pertinent to questions on BD formation, as well as allowing outflow mechanisms to be investigated at the lowest masses. Here new observations of the bipolar outflow from the 24 M{sub JUP} BD 2MASS J12073347-3932540 are presented. The outflow was originally identified through the spectro-astrometric analysis of the [O I]{lambda}6300 emission line. Follow-up observations consisting of spectra and [S II], R-band and I-band images were obtained. The new spectra confirm the original results and are used to constrain the outflow position angle (P.A.) at {approx}65 Degree-Sign . The [O I]{lambda}6300 emission line region is spatially resolved and the outflow is detected in the [S II] images. The detection is firstly in the form of an elongation of the point-spread function (PSF) along the direction of the outflow P.A. Four faint knot-like features (labeled A-D) are also observed to the southwest of 2MASS J12073347-3932540 along the same P.A. suggested by the spectra and the elongation in the PSF. Interestingly, D, the feature furthest from the source, is bow shaped with the apex pointing away from 2MASS J12073347-3932540. A color-color analysis allows us to conclude that at least feature D is part of the outflow under investigation while A is likely a star or galaxy. Follow-up observations are needed to confirm the origin of B and C. This is a first for a BD, as BD optical outflows have to date only been detected using spectro-astrometry. This result also demonstrates for the first time that BD outflows can be collimated and episodic.

  3. Water Clouds in Y Dwarfs and Exoplanets

    CERN Document Server

    Morley, Caroline V; Fortney, Jonathan J; Lupu, Roxana; Saumon, Didier; Greene, Tom; Lodders, Katharina

    2014-01-01

    The formation of clouds affects brown dwarf and planetary atmospheres of nearly all effective temperatures. Iron and silicate condense in L dwarf atmospheres and dissipate at the L/T transition. Minor species such as sulfides and salts condense in mid-late T dwarfs. For brown dwarfs below Teff=450 K, water condenses in the upper atmosphere to form ice clouds. Currently over a dozen objects in this temperature range have been discovered, and few previous theoretical studies have addressed the effect of water clouds on brown dwarf or exoplanetary spectra. Here we present a new grid of models that include the effect of water cloud opacity. We find that they become optically thick in objects below Teff=350-375 K. Unlike refractory cloud materials, water ice particles are significantly non-gray absorbers; they predominantly scatter at optical wavelengths through J band and absorb in the infrared with prominent features, the strongest of which is at 2.8 microns. H2O, NH3, CH4, and H2 CIA are dominant opacity source...

  4. Quantification of browning kinetics and colour change for quince (Cydonia oblonga Mill.) exposed to atmospheric conditions

    OpenAIRE

    Guiné, Raquel; Barroca, Maria João

    2014-01-01

    Because quince is a fruit that shows a very strong tendency for developing an intense browning when exposed to air, even though for short periods of time, the aim of this work was to evaluate the kinetics of colour change for quince exposed to atmospheric air at ambient temperature over a period of 2 hours. The quince was cut into slices that were left exposed to air, and colour measurements were done right after cutting and every 5 min, usi...

  5. SPLAT: Using Spectral Indices to Identify and Characterize Ultracool Stars, Brown Dwarfs and Exoplanets in Deep Surveys and as Companions to Nearby Stars

    Science.gov (United States)

    Aganze, Christian; Burgasser, Adam J.; Martin, Eduardo; Konopacky, Quinn; Masters, Daniel C.

    2016-06-01

    The majority of ultracool dwarf stars and brown dwarfs currently known were identified in wide-field red optical and infrared surveys, enabling measures of the local, typically isolated, population in a relatively shallow (based on templates and tools developed as part of the SpeX Prism Library Analysis Toolkit. In particular, we define and characterize specifically-tuned sets spectral indices that optimize selection of cool dwarfs and distinguish rare populations (subdwarfs, young planetary-mass objects) based on low-resolution, limited-wavelength-coverage spectral data; and present a template-matching classification method for these instruments. We apply these techniques to HST/WFC3 parallel fields data in the WISPS and HST-3D programs, where our spectral index set allows high completeness and low contamination for searches of late M, L and T dwarfs to distances out to ~3 kpc.The material presented here is based on work supported by the National Aeronautics and Space Administration under Grant No. NNX15AI75G.

  6. OGLE‐2008‐BLG‐510: first automated real‐time detection of a weak microlensing anomaly – brown dwarf or stellar binary?★

    DEFF Research Database (Denmark)

    Bozza, V.; Dominik, M.; Rattenbury, N. J.;

    2012-01-01

    ‐lens and binary‐source models, including the possibility that the lens system consists of an M dwarf orbited by a brown dwarf. The detection of this microlensing anomaly and our analysis demonstrate that: (1) automated real‐time detection of weak microlensing anomalies with immediate feedback is feasible......The microlensing event OGLE‐2008‐BLG‐510 is characterized by an evident asymmetric shape of the peak, promptly detected by the Automated Robotic Terrestrial Exoplanet Microlensing Search (ARTEMiS) system in real time. The skewness of the light curve appears to be compatible both with binary......, efficient and sensitive, (2) rather common weak features intrinsically come with ambiguities that are not easily resolved from photometric light curves, (3) a modelling approach that finds all features of parameter space rather than just the ‘favourite model’ is required and (4) the data quality is most...

  7. EARLY STAR-FORMING PROCESSES IN DENSE MOLECULAR CLOUD L328; IDENTIFICATION OF L328-IRS AS A PROTO-BROWN DWARF

    International Nuclear Information System (INIS)

    This paper presents the results of millimeter to sub-millimeter observations of CO, HCN, N2H+, and HCO+ lines in the dense molecular cloud L328, which harbors L328-IRS, a Very Low Luminosity Object (VeLLO). Our analysis of the line width finds that 13CO and N2H+ lines are broadened right over the smallest sub-core S2 where L328-IRS is located, while they are significantly narrower in other regions of L328. Thus, L328-IRS has a direct association with the sub-core. CO observations show a bipolar outflow from this VeLLO with an extent of ∼0.08 pc. The outflow momentum flux and efficiency are much less than those of low-mass protostars. The most likely mass accretion rate (∼3.6 × 10–7 M☉ yr–1) inferred from the analysis of the CO outflow is an order of magnitude smaller than the canonical value for a protostar. If the main accretion lasts during the typical Class 0 period of a protostar, L328-IRS will accrete the mass of a brown dwarf, but not that of a star. Given that its envelope mass is small (∼0.09 M☉) and 100% star formation rate is unlikely, we suggest that L328-IRS is likely a proto-brown dwarf. Inward motions are found in global scale in the L328 cloud and its sub-cores with a typical infall speed found in starless cores. L328 is found to be fairly well isolated from other nearby clouds and seems to be forming three sub-cores simultaneously through a gravitational fragmentation process. Altogether, these all leave L328-IRS as the best example supporting the idea that a brown dwarf forms like a normal star

  8. Automatic parameterization and analysis of stellar atmospheres: a study of the DA white dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    McMahan, R.K. Jr.

    1986-01-01

    A method for automatically calculating atmospheric parameters of hydrogen-rich degenerate stars from low resolution spectra is advanced and then applied to the spectra of 53 DA white dwarfs. All data were taken using the Mark II spectrograph on the McGraw-Hill 1.3 m telescope and cover the spectral range lambdalambda4100-7000 at a resolution of eight Angstroms. The model grid was generated at Dartmouth using the atmosphere code LUCIFER; it contained over 275 synthetic spectra extending from 6000 to 100,000 K in effective temperature and 7.4-9.3 in log g. A new value for the width of the DA mass distribution was achieved using the techniques presented here. Accuracies in the atmospheric parameters greater than twice those previously published were obtained. These results place strict constraints on the magnitude of mass loss in stars in the red giant phase, as well as in the mechanisms responsible for the loss.

  9. The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits . III. The frequency of brown dwarfs and giant planets as companions to solar-type stars

    Science.gov (United States)

    Reggiani, M.; Meyer, M. R.; Chauvin, G.; Vigan, A.; Quanz, S. P.; Biller, B.; Bonavita, M.; Desidera, S.; Delorme, P.; Hagelberg, J.; Maire, A.-L.; Boccaletti, A.; Beuzit, J.-L.; Buenzli, E.; Carson, J.; Covino, E.; Feldt, M.; Girard, J.; Gratton, R.; Henning, T.; Kasper, M.; Lagrange, A.-M.; Mesa, D.; Messina, S.; Montagnier, G.; Mordasini, C.; Mouillet, D.; Schlieder, J. E.; Segransan, D.; Thalmann, C.; Zurlo, A.

    2016-02-01

    Context. In recent years there have been many attempts to characterize the occurrence and distribution of stellar, brown dwarf (BD), and planetary-mass companions to solar-type stars with the aim of constraining formation mechanisms. From radial velocity observations a dearth of companions with masses between 10-40 MJupiter has been noticed at close separations, suggesting the possibility of a distinct formation mechanism for objects above and below this range. Aims: We present a model for the substellar companion mass function (CMF). This model consists of the superposition of the planet and BD companion mass distributions, assuming that we can extrapolate the radial velocity measured CMF for planets to larger separations and the stellar companion mass-ratio distribution over all separations into the BD mass regime. By using both the results of the VLT/NaCo large program (NaCo-LP) and the complementary archive datasets, which probe the occurrence of planets and BDs on wide orbits around solar-type stars, we place some constraints on the planet and BD distributions. Methods: We developed a Monte Carlo simulation tool to predict the outcome of a given survey, depending on the shape of the orbital parameter distributions (mass, semimajor axis, eccentricity, and inclination). Comparing the predictions with the results of the observations, we calculate the likelihood of different models and which models can be ruled out. Results: Current observations are consistent with the proposed model for the CMF, as long as a sufficiently small outer truncation radius (≲100 AU) is introduced for the planet separation distribution. Some regions of parameter space can be excluded by the observations. Conclusions: We conclude that the results of the direct imaging surveys searching for substellar companions around Sun-like stars are consistent with a combined substellar mass spectrum of planets and BDs. This mass distribution has a minimum between 10 and 50 MJupiter, in agreement

  10. Tidal Downsizing Model. III. Planets from sub-Earths to Brown Dwarfs: structure and metallicity preferences

    CERN Document Server

    Nayakshin, Sergei

    2015-01-01

    We present improved population synthesis calculations in the context of the Tidal Downsizing (TD) hypothesis for planet formation. Our models provide natural explanations and/or quantitative match to exoplanet observations in the following categories: (i) most abundant planets being super-Earths; (ii) cores more massive than $\\sim 5-15 M_\\oplus$ are enveloped by massive metal-rich atmospheres; (iii) the frequency of occurrence of close-in gas giant planets correlates strongly with metallicity of the host star; (iv) no such correlation is found for sub-Neptune planets; (v) presence of massive cores in giant planets; (vi) the composition of gas giant planets is over-abundant in metals compared to their host stars; (vii) this over-abundance decreases with planet's mass, as observed; (viii) a deep valley in the planet mass function between masses of $\\sim 10-20 M_\\oplus$ and $\\sim 100 M_\\oplus$. We provide a number of observational predictions distinguishing the model from Core Accretion: (a) composition of the m...

  11. Exploring Links Between Orbital Dynamics and Atmospheres in Kepler M Dwarf Planetary Systems

    Science.gov (United States)

    Ballard, Sarah

    2015-12-01

    The Solar System furnishes the most familiar planetary architecture: many planets, orbiting nearly coplanar to one another. However, the most common planetary systems in the Milky Way orbit much smaller M dwarf stars, and these may present a very different blueprint. The Kepler data set has furnished more than 100 exoplanets orbiting stars half the mass of the sun and smaller. Half of these planets reside in systems with at least one additional planet. The data much prefer a model with two distinct modes of planet formation around M dwarfs, which occur in roughly equal measure. One mode is one very similar to the Solar System in terms of multiplicity and coplanarity, and the other is very dissimilar. Given this so-called "Kepler Dichotomy," we examine the broadband transmission spectra (with data from Kepler and hundreds of hours of Spitzer observations) of dozens of M dwarf planets: half of which reside in one type of planetary system, and half in the other. Although the data set is too small and the observational uncertainty too large to characterize any one system alone, we examine ensemble trends between planetary dynamics and atmospheric content.

  12. Variability in Hot Carbon-Dominated Atmosphere (hot DQ) White Dwarfs: Rapid Rotation?

    CERN Document Server

    Williams, Kurtis A; Winget, D E; Falcon, Ross E; Bierwagon, Michael

    2015-01-01

    Hot white dwarfs with carbon-dominated atmospheres (hot DQs) are a cryptic class of white dwarfs. In addition to their deficiency of hydrogen and helium, most of these stars are highly magnetic, and a large fraction vary in luminosity. This variability has been ascribed to nonradial pulsations, but increasing data call this explanation into question. We present studies of short-term variability in seven hot DQ white dwarfs. Three (SDSS J1426+5752, SDSS J2200-0741, and SDSS J2348-0942) were known to be variable. Their photometric modulations are coherent over at least two years, and we find no evidence for variability at frequencies that are not harmonics. We present the first time-series photometry for three additional hot DQs (SDSS J0236-0734, SDSS J1402+3818, and SDSS J1615+4543); none are observed to vary, but the signal-to-noise is low. Finally, we present high speed photometry for SDSS J0005-1002, known to exhibit a 2.1 d photometric variation; we do not observe any short-term variability. Monoperiodicit...

  13. Ab initio Stellar Astrophysics: Reliable Modeling of Cool White Dwarf Atmospheres

    CERN Document Server

    Kowalski, Piotr M

    2010-01-01

    Over the last decade {\\it ab initio} modeling of material properties has become widespread in diverse fields of research. It has proved to be a powerful tool for predicting various properties of matter under extreme conditions. We apply modern computational chemistry and materials science methods, including density functional theory (DFT), to solve lingering problems in the modeling of the dense atmospheres of cool white dwarfs ($T_{\\rm eff}\\rm <7000 \\, K$). Our work on the revision and improvements of the absorption mechanisms in the hydrogen and helium dominated atmospheres resulted in a new set of atmosphere models. By inclusion of the Ly-$\\rm \\alpha$ red wing opacity we successfully fitted the entire spectral energy distributions of known cool DA stars. In the subsequent work we fitted the majority of the coolest stars with hydrogen-rich models. This finding challenges our understanding of the spectral evolution of cool white dwarfs. We discuss a few examples, including the cool companion to the pulsar...

  14. Atmospheric effects of stellar cosmic rays on Earth-like exoplanets orbiting M-dwarfs

    CERN Document Server

    Tabataba-Vakili, F; Grießmeier, J -M; Rauer, H

    2016-01-01

    M-dwarf stars are generally considered favourable for rocky planet detection. However, such planets may be subject to extreme conditions due to possible high stellar activity. The goal of this work is to determine the potential effect of stellar cosmic rays on key atmospheric species of Earth-like planets orbiting in the habitable zone of M-dwarf stars and show corresponding changes in the planetary spectra. We build upon the cosmic rays model scheme of Grenfell et al. (2012), who considered cosmic ray induced NOx production, by adding further cosmic ray induced production mechanisms (e.g. for HOx) and introducing primary protons of a wider energy range (16 MeV - 0.5 TeV). Previous studies suggested that planets in the habitable zone that are subject to strong flaring conditions have high atmospheric methane concentrations, while their ozone biosignature is completely destroyed. Our current study shows, however, that adding cosmic ray induced HOx production can cause a decrease in atmospheric methane abundanc...

  15. Characterization of the Nearby L/T Binary Brown Dwarf WISE J104915.57-531906.1 at 2 Parsecs from the Sun

    CERN Document Server

    Kniazev, A Y; Muzic, K; Mehner, A; Boffin, H M J; Kurtev, R; Melo, C; Ivanov, V D; Girard, J; Mawet, D; Schmidtobreick, L; Huelamo, N; Borissova, J; Minniti, D; Ishibashi, K; Potter, S B; Beletsky, Y; Buckley, D A H; Crawford, S; Gulbis, A A S; Kotze, P; Miszalski, B; Pickering, T E; Colmenero, E Romero; Williams, T B

    2013-01-01

    WISE J104915.57-531906.1 is a candidate L/T brown dwarf binary located 2pc from the Sun. The pair contains the closest known brown dwarfs and is the third closest known system, stellar or sub-stellar. Here we report the first comprehensive follow-up observations of this newly uncovered system. We have determined the spectral types of both components (L8+/-1, T1+/-2) and their radial velocities (V_rad~23.1, 19.5 km/s) using the Southern African Large Telescope (SALT) and other facilities located at the South African Astronomical Observatory (SAAO). The relative radial velocity of the two components is smaller than the range of orbital velocities for theoretically predicted masses, implying that they form a gravitationally bound system. We report resolved near-infrared $JHK_S$ photometry from the IRSF telescope at the SAAO which yields colors consistent with the spectroscopically derived spectral types. Our apparent magnitudes predict a distance of ~2.25pc, similar to the previous measurement. The available kin...

  16. Dust masses of disks around 8 Brown Dwarfs and Very Low-Mass Stars in Upper Sco OB1 and Ophiuchus

    CERN Document Server

    van der Plas, G; Ward-Duong, K; Bulger, J; Harvey, P M; Pinte, C; Patience, J; Hales, A; Casassus, S

    2016-01-01

    We present the results of ALMA band 7 observations of dust and CO gas in the disks around 7 objects with spectral types ranging between M5.5 and M7.5 in Upper Scorpius OB1, and one M3 star in Ophiuchus. We detect unresolved continuum emission in all but one source, and the $^{12}$CO J=3-2 line in two sources. We constrain the dust and gas content of these systems using a grid of models calculated with the radiative transfer code MCFOST, and find disk dust masses between 0.1 and 1 M$_\\oplus$, suggesting that the stellar mass / disk mass correlation can be extrapolated for brown dwarfs with masses as low as 0.05 M$_\\odot$. The one disk in Upper Sco in which we detect CO emission, 2MASS J15555600, is also the disk with warmest inner disk as traced by its H - [4.5] photometric color. Using our radiative transfer grid, we extend the correlation between stellar luminosity and mass-averaged disk dust temperature originally derived for stellar mass objects to the brown dwarf regime to $\\langle T_{dust} \\rangle \\appro...

  17. Water clouds in Y dwarfs and exoplanets

    Energy Technology Data Exchange (ETDEWEB)

    Morley, Caroline V.; Fortney, Jonathan J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Marley, Mark S.; Lupu, Roxana; Greene, Tom [NASA Ames Research Center, Naval Air Station, Moffett Field, Mountain View, CA 94035 (United States); Saumon, Didier [Los Alamos National Lab, Los Alamos, NM 87545 (United States); Lodders, Katharina, E-mail: cmorley@ucolick.org [Washington University in St Louis, 1 Brookings Drive, St Louis, MO 63130 (United States)

    2014-05-20

    The formation of clouds affects brown dwarf and planetary atmospheres of nearly all effective temperatures. Iron and silicate condense in L dwarf atmospheres and dissipate at the L/T transition. Minor species such as sulfides and salts condense in mid- to late T dwarfs. For brown dwarfs below T {sub eff} ∼ 450 K, water condenses in the upper atmosphere to form ice clouds. Currently, over a dozen objects in this temperature range have been discovered, and few previous theoretical studies have addressed the effect of water clouds on brown dwarf or exoplanetary spectra. Here we present a new grid of models that include the effect of water cloud opacity. We find that they become optically thick in objects below T {sub eff} ∼ 350-375 K. Unlike refractory cloud materials, water-ice particles are significantly nongray absorbers; they predominantly scatter at optical wavelengths through the J band and absorb in the infrared with prominent features, the strongest of which is at 2.8 μm. H{sub 2}O, NH{sub 3}, CH{sub 4}, and H{sub 2} CIA are dominant opacity sources; less abundant species may also be detectable, including the alkalis, H{sub 2}S, and PH{sub 3}. PH{sub 3}, which has been detected in Jupiter, is expected to have a strong signature in the mid-infrared at 4.3 μm in Y dwarfs around T {sub eff} = 450 K; if disequilibrium chemistry increases the abundance of PH{sub 3}, it may be detectable over a wider effective temperature range than models predict. We show results incorporating disequilibrium nitrogen and carbon chemistry and predict signatures of low gravity in planetary mass objects. Finally, we make predictions for the observability of Y dwarfs and planets with existing and future instruments, including the James Webb Space Telescope and Gemini Planet Imager.

  18. Photometric brown-dwarf classification. II. A homogeneous sample of 1361 L and T dwarfs brighter than J = 17.5 with accurate spectral types

    Science.gov (United States)

    Skrzypek, N.; Warren, S. J.; Faherty, J. K.

    2016-04-01

    We present a homogeneous sample of 1361 L and T dwarfs brighter than J = 17.5 (of which 998 are new), from an effective area of 3070 deg2, classified by the photo-type method to an accuracy of one spectral sub-type using izYJHKW1W2 photometry from SDSS+UKIDSS+WISE. Other than a small bias in the early L types, the sample is shown to be effectively complete to the magnitude limit, for all spectral types L0 to T8. The nature of the bias is an incompleteness estimated at 3% because peculiar blue L dwarfs of type L4 and earlier are classified late M. There is a corresponding overcompleteness because peculiar red (likely young) late M dwarfs are classified early L. Contamination of the sample is confirmed to be small: so far spectroscopy has been obtained for 19 sources in the catalogue and all are confirmed to be ultracool dwarfs. We provide coordinates and izYJHKW1W2 photometry of all sources. We identify an apparent discontinuity, Δm ~ 0.4 mag, in the Y - K colour between spectral types L7 and L8. We present near-infrared spectra of nine sources identified by photo-type as peculiar, including a new low-gravity source ULAS J005505.68+013436.0, with spectroscopic classification L2γ. We provide revised izYJHKW1W2 template colours for late M dwarfs, types M7 to M9. The catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A49

  19. Atmospheric effects of stellar cosmic rays on Earth-like exoplanets orbiting M-dwarfs

    Science.gov (United States)

    Tabataba-Vakili, F.; Grenfell, J. L.; Grießmeier, J.-M.; Rauer, H.

    2016-01-01

    M-dwarf stars are generally considered favourable for rocky planet detection. However, such planets may be subject to extreme conditions due to possible high stellar activity. The goal of this work is to determine the potential effect of stellar cosmic rays on key atmospheric species of Earth-like planets orbiting in the habitable zone of M-dwarf stars and show corresponding changes in the planetary spectra. We build upon the cosmic rays model scheme of previous works, who considered cosmic ray induced NOx production, by adding further cosmic ray induced production mechanisms (e.g. for HOx) and introducing primary protons of a wider energy range (16 MeV-0.5 TeV). Previous studies suggested that planets in the habitable zone that are subject to strong flaring conditions have high atmospheric methane concentrations, while their ozone biosignature is completely destroyed. Our current study shows, however, that adding cosmic ray induced HOx production can cause a decrease in atmospheric methane abundance of up to 80%. Furthermore, the cosmic ray induced HOx molecules react with NOx to produce HNO3, which produces strong HNO3 signals in the theoretical spectra and reduces NOx-induced catalytic destruction of ozone so that more than 25% of the ozone column remains. Hence, an ozone signal remains visible in the theoretical spectrum (albeit with a weaker intensity) when incorporating the new cosmic ray induced NOx and HOx schemes, even for a constantly flaring M-star case. We also find that HNO3 levels may be high enough to be potentially detectable. Since ozone concentrations, which act as the key shield against harmful UV radiation, are affected by cosmic rays via NOx-induced catalytic destruction of ozone, the impact of stellar cosmic rays on surface UV fluxes is also studied.

  20. Discovery of Three Pulsating, Mixed Atmosphere, Extremely Low-Mass White Dwarf Precursors

    CERN Document Server

    Gianninas, A; Fontaine, G; Browm, Warren R; Kilic, Mukremin

    2016-01-01

    We report the discovery of pulsations in three mixed atmosphere, extremely low-mass white dwarf (ELM WD, M $<$ 0.3 M$_{\\odot}$) precursors. Following the recent discoveries of pulsations in both ELM and pre-ELM WDs, we targeted pre-ELM WDs with mixed H/He atmospheres with high-speed photometry. We find significant optical variability in all three observed targets with periods in the range 320--590 s, consistent in time-scale with theoretical predictions of p-mode pulsations in mixed-atmosphere $\\approx$ 0.18 M$_{\\odot}$ He-core pre-ELM WDs. This represents the first empirical evidence that pulsations in pre-ELM WDs can only occur if a significant amount of He is present in the atmosphere. Future, more extensive, time-series photometry of the brightest of the three new pulsators offers an excellent opportunity to constrain the thickness of the surface H layer which regulates the cooling timescales for ELM WDs.

  1. The polluted atmosphere of the white dwarf NLTT 25792 and the diversity of circumstellar environments

    CERN Document Server

    Vennes, S

    2013-01-01

    We present an analysis of X-Shooter spectra of the polluted, hydrogen-rich white dwarf NLTT 25792. The spectra show strong lines of calcium (Ca H&K, near-infrared calcium triplet, and Ca I 4226 and numerous lines of iron along with magnesium and aluminum lines from which we draw the abundance pattern. Moreover, the photospheric Ca H&K lines are possibly blended with a circumstellar component shifted by -20 km/s relative to the photosphere. A comparison with a sample of four white dwarfs with similar parameters show considerable variations in their abundance patterns, particularly in the calcium to magnesium abundance ratio that varies by a factor of five within this sample. The observed variations, even after accounting for diffusion effects, imply similar variations in the putative accretion source. Also, we find that silicon and sodium are significantly underabundant in the atmosphere of NLTT 25792, a fact that may offer some clues on the nature of the accretion source.

  2. Extreme abundance ratios in the polluted atmosphere of the cool white dwarf NLTT 19868

    Science.gov (United States)

    Kawka, Adela; Vennes, Stéphane

    2016-05-01

    We present an analysis of intermediate-dispersion spectra and photometric data of the newly identified cool, polluted white dwarf NLTT 19868. The spectra obtained with X-shooter on the Very Large Telescope-Melipal show strong lines of calcium, and several lines of magnesium, aluminium and iron. We use these spectra and the optical-to-near-infrared spectral energy distribution to constrain the atmospheric parameters of NLTT 19868. Our analysis shows that NLTT 19868 is iron poor with respect to aluminium and calcium. A comparison with other cool, polluted white dwarfs shows that the Fe to Ca abundance ratio (Fe/Ca) varies by up to approximately two orders of magnitudes over a narrow temperature range with NLTT 19868 at one extremum in the Fe/Ca ratio and, in contrast, NLTT 888 at the other extremum. The sample shows evidence of extreme diversity in the composition of the accreted material: in the case of NLTT 888, the inferred composition of the accreted matter is akin to iron-rich planetary core composition, while in the case of NLTT 19868 it is close to mantle composition depleted by subsequent chemical separation at the bottom of the convection zone.

  3. Extreme abundance ratios in the polluted atmosphere of the cool white dwarf NLTT19868

    CERN Document Server

    Kawka, Adela

    2016-01-01

    We present an analysis of intermediate-dispersion spectra and photometric data of the newly identified cool, polluted white dwarf NLTT19868. The spectra obtained with X-shooter on the Very Large Telescope (VLT)-Melipal show strong lines of calcium, and several lines of magnesium, aluminium and iron. We use these spectra and the optical-to-near infrared spectral energy distribution to constrain the atmospheric parameters of NLTT19868. Our analysis shows that NLTT19868 is iron poor with respect to aluminium and calcium. A comparison with other cool, polluted white dwarfs shows that the Fe to Ca abundance ratio (Fe/Ca) varies by up to approximately two orders of magnitudes over a narrow temperature range with NLTT19868 at one extremum in the Fe/Ca ratio and, in contrast, NLTT888 at the other extremum. The sample shows evidence of extreme diversity in the composition of the accreted material: In the case of NLTT888, the inferred composition of the accreted matter is akin to iron-rich planetary core composition, w...

  4. Automatic parameterization and analysis of stellar atmospheres: a study of the DA white dwarfs

    International Nuclear Information System (INIS)

    A method for automatically calculating atmospheric parameters of hydrogen-rich degenerate stars from low resolution spectra is advanced and then applied to the spectra of 53 DA white dwarfs. All data were taken using the Mark II spectrograph on the McGraw-Hill 1.3 m telescope and cover the spectral range λλ4100-7000 at a resolution of eight Angstroms. The model grid was generated at Dartmouth using the atmosphere code LUCIFER; it contained over 275 synthetic spectra extending from 6000 to 100,000 K in effective temperature and 7.4-9.3 in log g. A new value for the width of the DA mass distribution was achieved using the techniques presented here. Accuracies in the atmospheric parameters greater than twice those previously published were obtained. These results place strict constraints on the magnitude of mass loss in stars in the red giant phase, as well as in the mechanisms responsible for the loss

  5. Discovery of an M9.5 Candidate Brown Dwarf in the TW Hydrae Association - DENIS J124514.1-442907

    CERN Document Server

    Looper, Dagny L; Kirkpatrick, J Davy; Swift, Brandon J

    2007-01-01

    We report the discovery of a fifth candidate substellar system in the ~5-10 Myr TW Hydrae Association - DENIS J124514.1-442907. This object has a NIR spectrum remarkably similar to that of 2MASS J1139511-315921, a known TW Hydrae brown dwarf, with low surface gravity features such as a triangular-shaped H-band, deep H2O absorption, weak alkali lines, and weak hydride bands. We find an optical spectral type of M9.5 and estimate a mass of <24 M_Jup, assuming an age of ~5-10 Myr. While the measured proper motion for DENIS J124514.1-442907 is inconclusive as a test for membership, its position in the sky is coincident with the TW Hydrae Association. A more accurate proper motion measurement, higher resolution spectroscopy for radial velocity, and a parallax measurement are needed to derive the true space motion and to confirm its membership.

  6. CHARACTERIZATION OF THE NEARBY L/T BINARY BROWN DWARF WISE J104915.57–531906.1 AT 2 pc FROM THE SUN

    International Nuclear Information System (INIS)

    WISE J104915.57–531906.1 is a L/T brown dwarf binary located 2 pc from the Sun. The pair contains the closest known brown dwarfs and is the third closest known system, stellar or sub-stellar. We report comprehensive follow-up observations of this newly uncovered system. We have determined the spectral types of both components (L8 ± 1, for the primary, agreeing with the discovery paper; T1.5 ± 2 for the secondary, which was lacking spectroscopic type determination in the discovery paper) and, for the first time, their radial velocities (Vrad ∼ 23.1, 19.5 km s–1) using optical spectra obtained at the Southern African Large Telescope and other facilities located at the South African Astronomical Observatory (SAAO). The relative radial velocity of the two components is smaller than the range of orbital velocities for theoretically predicted masses, implying that they form a gravitationally bound system. We report resolved near-infrared JHKS photometry from the Infrared Survey Facility telescope at the SAAO which yields colors consistent with the spectroscopically derived spectral types. The available kinematic and photometric information excludes the possibility that the object belongs to any of the known nearby young moving groups or associations. Simultaneous optical polarimetry observations taken at the SAAO 1.9 m give a non-detection with an upper limit of 0.07%. For the given spectral types and absolute magnitudes, 1 Gyr theoretical models predict masses of 0.04-0.05 M☉ for the primary, and 0.03-0.05 M☉ for the secondary.

  7. Magnetospheric structure and atmospheric Joule heating of habitable planets orbiting M-dwarf stars

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, O.; Drake, J. J.; Garraffo, C.; Poppenhaeger, K. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Glocer, A. [NASA/GSFC, Code 673, Greenbelt, MD 20771 (United States); Bell, J. M. [Center for Planetary Atmospheres and Flight Sciences, National Institute of Aerospace, Hampton, VA 23666 (United States); Ridley, A. J.; Gombosi, T. I. [Center for Space Environment Modeling, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States)

    2014-07-20

    We study the magnetospheric structure and the ionospheric Joule Heating of planets orbiting M-dwarf stars in the habitable zone using a set of magnetohydrodynamic models. The stellar wind solution is used to drive a model for the planetary magnetosphere, which is coupled with a model for the planetary ionosphere. Our simulations reveal that the space environment around close-in habitable planets is extreme, and the stellar wind plasma conditions change from sub- to super-Alfvénic along the planetary orbit. As a result, the magnetospheric structure changes dramatically with a bow shock forming in the super-Alfvénic sectors, while no bow shock forms in the sub-Alfvénic sectors. The planets reside most of the time in the sub-Alfvénic sectors with poor atmospheric protection. A significant amount of Joule Heating is provided at the top of the atmosphere as a result of the intense stellar wind. For the steady-state solution, the heating is about 0.1%-3% of the total incoming stellar irradiation, and it is enhanced by 50% for the time-dependent case. The significant Joule Heating obtained here should be considered in models for the atmospheres of habitable planets in terms of the thickness of the atmosphere, the top-side temperature and density, the boundary conditions for the atmospheric pressure, and particle radiation and transport. Here we assume constant ionospheric Pedersen conductance similar to that of the Earth. The conductance could be greater due to the intense EUV radiation leading to smaller heating rates. We plan to quantify the ionospheric conductance in future study.

  8. Astrometric planet search around southern ultracool dwarfs III. Discovery of a brown dwarf in a 3-year orbit around DE0630-18

    CERN Document Server

    Sahlmann, J; Segransan, D; Martin, E L; Mayor, M; Queloz, D; Udry, S

    2015-01-01

    Using astrometric measurements obtained with the FORS2/VLT camera, we are searching for low-mass companions around 20 nearby ultracool dwarfs. With a single-measurement precision of 0.1 milli-arcseconds, our survey is sensitive to a wide range of companion masses from planetary companions to binary systems. Here, we report the discovery and orbit characterisation of a new ultracool binary at a distance of 19.5 pc from Earth that is composed of the M8.5-dwarf primary DE0630-18 and a substellar companion. The nearly edge-on orbit is moderately eccentric (e=0.23) with an orbital period of 1120 d, which corresponds to a relative separation in semimajor axis of approximately 1.1 AU. We obtained a high-resolution optical spectrum with UVES/VLT and measured the system's heliocentric radial velocity. The spectrum does not exhibit lithium absorption at 670.8 nm, indicating that the system is not extremely young. A preliminary estimate of the binary's physical parameters tells us that it is composed of a primary at the...

  9. Observed Variability at 1um and 4um in the Y0 Brown Dwarf WISEP J173835.52+273258.9

    CERN Document Server

    Leggett, S K; Hardegree-Ullman, Kevin K; Trucks, Jesica L; Marley, M S; Morley, Caroline V; Saumon, D; Carey, S J; Fortney, J J; Gelino, C R; Gizis, J E; Kirkpatrick, J D; Mace, G N

    2016-01-01

    We have monitored photometrically the Y0 brown dwarf WISEP J173835.52+273258.9 (W1738) at both near- and mid-infrared wavelengths. This ~1 Gyr-old 400K dwarf is at a distance of 8pc and has a mass around 5 M_Jupiter. We observed W1738 using two near-infrared filters at lambda~1um, Y and J, on Gemini observatory, and two mid-infrared filters at lambda~4um, [3.6] and [4.5], on the Spitzer observatory. Twenty-four hours were spent on the source by Spitzer on each of June 30 and October 30 2013 UT. Between these observations, around 5 hours were spent on the source by Gemini on each of July 17 and August 23 2013 UT. The mid-infrared light curves show significant evolution between the two observations separated by four months. We find that a double sinusoid can be fit to the [4.5] data, where one sinusoid has a period of 6.0 +/- 0.1 hours and the other a period of 3.0 +/- 0.1 hours. The near-infrared observations suggest variability with a ~3.0 hour period, although only at a <~2 sigma confidence level. We inte...

  10. The Collapse of the Wien Tail in the Coldest Brown Dwarf? Hubble Space Telescope Near-Infrared Photometry of WISE J085510.83-071442.5

    CERN Document Server

    Schneider, Adam C; Kirkpatrick, J Davy; Gelino, Chris R

    2016-01-01

    We present Hubble Space Telescope (HST) near-infrared photometry of the coldest known brown dwarf, WISE J085510.83$-$071442.5 (WISE 0855$-$0714). WISE 0855$-$0714 was observed with the Wide Field Camera 3 (WFC3) aboard HST using the F105W, F125W, and F160W filters, which approximate the $Y$, $J$, and $H$ near-infrared bands. WISE 0855$-$0714 is undetected at F105W with a corresponding 2$\\sigma$ magnitude limit of $\\sim$26.9. We marginally detect WISE 0855$-$0714 in the F125W images (S/N $\\sim$4), with a measured magnitude of 26.41 $\\pm$ 0.27, more than a magnitude fainter than the $J-$band magnitude reported by Faherty and coworkers. WISE J0855$-$0714 is clearly detected in the F160W band, with a magnitude of 23.90 $\\pm$ 0.02, the first secure detection of WISE 0855$-$0714 in the near-infrared. Based on these data, we find that WISE 0855$-$0714 has extremely red F105W$-$F125W and F125W$-$F160W colors relative to other known Y dwarfs. We find that when compared to the models of Saumon et al. and Morley et al.,...

  11. Dust cloud lightning in extraterrestrial atmospheres

    CERN Document Server

    Helling, Christiane; Diver, Declan; Witte, Soeren

    2012-01-01

    Lightning is present in all solar system planets which form clouds in their atmospheres. Cloud formation outside our solar system is possible in objects with much higher temperatures than on Earth or on Jupiter: Brown dwarfs and giant extrasolar gas planets form clouds made of mixed materials and a large spectrum of grain sizes. These clouds are globally neutral obeying dust-gas charge equilibrium which is, on short timescales, inconsistent with the observation of stochastic ionization events of the solar system planets. We argue that a significant volume of the clouds in brown dwarfs and extrasolar planets is susceptible to local discharge events and that the upper cloud layers are most suitable for powerful lightning-like discharge events. We discuss various sources of atmospheric ionisation, including thermal ionisation and a first estimate of ionisation by cosmic rays, and argue that we should expect thunderstorms also in the atmospheres of brown dwarfs and giant gas planets which contain mineral clouds.

  12. Analysis of two eclipsing hot subdwarf binaries with a low mass stellar and a brown dwarf companion

    OpenAIRE

    Schaffenroth, Veronika; Geier, Stephan; Heber, Ulrich; Drechsel, Horst; O̸stensen, Roy H.; Maxted, Pierre F. L.; Kupfer, Thomas; Barlow, Brad N.

    2010-01-01

    The formation of hot subdwarf stars (sdBs), which are core helium‐burning stars located on the extended horizontal branch, is still not understood. Many of the known hot subdwarf stars reside in close binary systems with short orbital periods between a few hours and a few days with either M star or white dwarf companions. Common envelope ejection is the most probable formation channel. Among these, eclipsing systems are of special importance because it is possible to constrain the parameters ...

  13. DISCOVERY OF TWO VERY WIDE BINARIES WITH ULTRACOOL COMPANIONS AND A NEW BROWN DWARF AT THE L/T TRANSITION

    International Nuclear Information System (INIS)

    We present the discovery and spectroscopic follow-up of a nearby late-type L dwarf (2M0614+3950), and two extremely wide very low mass binary systems (2M0525-7425AB and 2M1348-1344AB), resulting from our search for common proper motion pairs containing ultracool components in the Two Micron All Sky Survey and the Wide-field Infrared Survey Explorer catalogs. The near-infrared spectrum of 2M0614+3950 indicates a spectral type L9 ± 1 object residing at a distance of 26.0 ± 1.8 pc. The optical spectrum of 2M0525-7425A reveals an M3.0 ± 0.5 dwarf primary, accompanied by a secondary previously classified as L2. The system has an angular separation of ∼44'', equivalent to ∼2000 AU at a distance of 46.0 ± 3.0 pc. Using optical and infrared spectra, respectively, we classify the components of 2M1348-1344AB as M4.5 ± 0.5 and T5.5 ± 1. The angular separation of ∼68'' is equivalent to ∼1400 AU at a distance of 20.7 ± 1.4 pc. 2M1348-1344AB is one of only six very wide (separation >1000 AU) systems containing late T dwarfs known to date.

  14. Response of Atmospheric Biomarkers to NOx-induced Photochemistry Generated by Stellar Cosmic Rays for Earth-like Planets in the Habitable Zone of M-Dwarf Stars

    OpenAIRE

    Grenfell, John Lee; Grriessmeier, Jean-Mathias; von Paris, Philip; Patzer, Beate; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2015-01-01

    Understanding whether M-dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M-dwarfs ranging from quiet up to strong flaring conditions and investiga...

  15. The constitution of the atmospheric layers and the extreme ultraviolet spectrum of hot hydrogen-rich white dwarfs

    Science.gov (United States)

    Vennes, Stephane

    1992-01-01

    An analysis is presented of the atmospheric properties of hot, H-rich, DA white dwarfs that is based on optical, UV, and X-ray observations aimed at predicting detailed spectral properties of these stars in the range 80-800 A. The divergences between observations from a sample of 15 hot DA white dwarfs emitting in the EUV/soft X-ray range and pure H synthetic spectra calculated from a grid of model atmospheres characterized by Teff and g are examined. Seven out of 15 DA stars are found to consistently exhibit pure hydrogen atmospheres, the remaining seven stars showing inconsistency between FUV and EUV/soft X-ray data that can be explained by the presence of trace EUV/soft X-ray absorbers. Synthetic data are computed assuming two other possible chemical structures: photospheric traces of radiatively levitated heavy elements and a stratified hydrogen/helium distribution. Predictions about forthcoming medium-resolution observations of the EUV spectrum of selected hot H-rich white dwarfs are made.

  16. Time series photometry of the helium atmosphere pulsating white dwarf EC 04207-474

    CERN Document Server

    Chote, P; Montgomery, M H; Provencal, J L

    2014-01-01

    We present the analysis of 71 hours of high quality time-series CCD photometry of the helium atmosphere pulsating white dwarf (DBV) EC 04207-4748 obtained using the facilities at Mt John University Observatory in New Zealand. The photometric data set consists of four week-long observing sessions covering the period March to November 2011. A Fourier analysis of the lightcurves yielded clear evidence of four independent eigenmodes in the star with the dominant mode having a period of 447 s. The lightcurve variations exhibit distinct nonsinusoidal shapes, which results in significant harmonics of the dominant frequency appearing in the Fourier transforms. These observed variations are interpreted in terms of nonlinear contributions from the energy flux transmission through the subsurface convection zone in the star. Our modelling of this mechanism, using the methods first introduced by Montgomery (2005), yields a time-averaged convective response time of tau_0 ~ 150 s for the star, and this is shown to be broadl...

  17. Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058-5234

    CERN Document Server

    Sullivan, D J; O'Donoghue, D; Winget, D E; Kilkenny, D; Van Wyk, F; Kanaan, A; Kepler, S O; Nitta, A; Kawaler, S D; Montgomery, M H; Nather, R E; O'Brien, M S; Bischoff-Kim, A; Wood, M; Jiang, X J; Leibowitz, E M; Ibbetson, P; Zola, S; Krzesínski, J; Pajdosz, G; Vauclair, G; Dolez, N; Chevreton, M

    2008-01-01

    We present the analysis of a total of 177h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058-5234. The bulk of the observations (135h) were obtained during a WET campaign (XCOV15) in July 1997 that featured coordinated observing from 4 southern observatory sites over an 8-day period. The remaining data (42h) were obtained in June 2004 at Mt John Observatory in NZ over a one-week observing period. This work significantly extends the discovery observations of this low-amplitude (few percent) pulsator by increasing the number of detected frequencies from 8 to 18, and employs a simulation procedure to confirm the reality of these frequencies to a high level of significance (1 in 1000). The nature of the observed pulsation spectrum precludes identification of unique pulsation mode properties using any clearly discernable trends. However, we have used a global modelling procedure employing genetic algorithm techniques to identify the n, l values of 8 pulsat...

  18. A STUDY OF THE DIVERSE T DWARF POPULATION REVEALED BY WISE

    International Nuclear Information System (INIS)

    We report the discovery of 87 new T dwarfs uncovered with the Wide-field Infrared Survey Explorer (WISE) and 3 brown dwarfs with extremely red near-infrared colors that exhibit characteristics of both L and T dwarfs. Two of the new T dwarfs are likely binaries with L7 ± 1 primaries and mid-type T secondaries. In addition, our follow-up program has confirmed 10 previously identified T dwarfs and 4 photometrically selected L and T dwarf candidates in the literature. This sample, along with the previous WISE discoveries, triples the number of known brown dwarfs with spectral types later than T5. Using the WISE All-Sky Source Catalog we present updated color-color and color-type diagrams for all the WISE-discovered T and Y dwarfs. Near-infrared spectra of the new discoveries are presented along with spectral classifications. To accommodate later T dwarfs we have modified the integrated flux method of determining spectral indices to instead use the median flux. Furthermore, a newly defined J-narrow index differentiates the early-type Y dwarfs from late-type T dwarfs based on the J-band continuum slope. The K/J indices for this expanded sample show that 32% of late-type T dwarfs have suppressed K-band flux and are blue relative to the spectral standards, while only 11% are redder than the standards. Comparison of the Y/J and K/J index to models suggests diverse atmospheric conditions and supports the possible re-emergence of clouds after the L/T transition. We also discuss peculiar brown dwarfs and candidates that were found not to be substellar, including two young stellar objects and two active galactic nuclei. The substantial increase in the number of known late-type T dwarfs provides a population that will be used to test models of cold atmospheres and star formation. The coolest WISE-discovered brown dwarfs are the closest of their type and will remain the only sample of their kind for many years to come.

  19. Radio Emission and Orbital Motion from the Close-Encounter Star-Brown Dwarf Binary WISE J072003.20-084651.2

    CERN Document Server

    Burgasser, Adam J; Todd, Jacob; Gelino, Christopher R; Hallinan, Gregg; Gagliuffi, Daniella Bardalez

    2015-01-01

    We report the detection of radio emission and orbital motion from the nearby star-brown dwarf binary WISE J072003.20-084651.2AB. Radio observations across the 4.5-6.5 GHz band with the Very Large Array identify at the position of the system quiescent emission with a flux density of 15$\\pm$3 $\\mu$Jy, and a highly-polarized radio source that underwent a 2-3 min burst with peak flux density 300$\\pm$90 $\\mu$Jy. The latter emission is likely a low-level magnetic flare similar to optical flares previously observed for this source. No outbursts were detected in separate narrow-band H$\\alpha$ monitoring observations. We report new high-resolution imaging and spectroscopic observations that confirm the presence of a co-moving T5.5 secondary and provide the first indications of three-dimensional orbital motion. We used these data to revise our estimates for the orbital period (4.1$^{+2.7}_{-1.3}$ yr) and tightly constrain the orbital inclination to be nearly edge-on (93.6\\deg$^{+1.6\\deg}_{-1.4\\deg}$), although robust m...

  20. Discovery of a 0.15" Binary Brown Dwarf 2MASSJ 1426316+155701 With Gemini/Hokupa'a Adaptive Optics

    CERN Document Server

    Close, L M; Brandner, W; Lloyd-Hart, M; Liebert, J; Burrows, A; Siegler, N

    2002-01-01

    Use of the highly sensitive Hokupa'a curvature wavefront sensor has allowed for the first time direct adaptive optics (AO) guiding on brown dwarfs and VLM stars (SpT=M7-L2). An initial survey of 9 such objects discovered one 0.15" binary (2MASSJ 1426316+155701). The companion is about half as bright as the primary (Delta K = 0.61+/-0.05$, Delta H = 0.70+/-0.05) and has even redder colors H-K=0.59+/-0.14 than the primary. The blended spectrum of the binary has been previously determined to be M9.0. We modeled a blend of an M8.5 template and a L1-L3 template reproducing a M9.0 spectrum in the case of Delta K = 0.61+/-0.05,Delta H = 0.70\\pm0.05$. These spectral types also match the observed H-K colors of each star. Based the previously observed low space motion and $H_{\\alpha}$ activity we assign an age of $0.8^{+6.7}_{-0.3} Gyr$. Utilizing this age range and the latest DUSTY models of the Lyon group we assign a photometric distance of $18.8^{+1.44}_{-1.02} pc$ and masses of $M_{A}=0.074^{+0.005}_{-0.011} M_\\odo...

  1. AB INITIO EQUATIONS OF STATE FOR HYDROGEN (H-REOS.3) AND HELIUM (He-REOS.3) AND THEIR IMPLICATIONS FOR THE INTERIOR OF BROWN DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Andreas; Lorenzen, Winfried; Schöttler, Manuel; Redmer, Ronald [Institut für Physik, Universität Rostock, D-18051 Rostock (Germany); Fortney, Jonathan J.; Nettelmann, Nadine [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2015-01-01

    We present new equations of state (EOSs) for hydrogen and helium covering a wide range of temperatures from 60 K to 10{sup 7} K and densities from 10{sup –10} g cm{sup –3} to 10{sup 3} g cm{sup –3}. They include an extended set of ab initio EOS data for the strongly correlated quantum regime with an accurate connection to data derived from other approaches for the neighboring regions. We compare linear mixing isotherms based on our EOS tables with available real mixture data. A first important astrophysical application of this new EOS data is the calculation of interior models for Jupiter and comparison with recent results. Second, mass-radius relations are calculated for Brown Dwarfs (BDs) which we compare with predictions derived from the widely used EOS of Saumon, Chabrier, and van Horn. Furthermore, we calculate interior models for typical BDs with different masses, namely, Corot-3b, Gliese-229b, and Corot-15b, and the giant planet KOI-889b. The predictions for the central pressures and densities differ by up to 10% dependent on the EOS used. Our EOS tables are made available in the supplemental material of this paper.

  2. New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System

    CERN Document Server

    Wu, Ya-Lin; Males, Jared R; Barman, Travis S; Morzinski, Katie M; Follette, Katherine B; Bailey, Vanessa; Rodigas, Timothy J; Hinz, Philip; Puglisi, Alfio; Xompero, Marco; Briguglio, Runa

    2015-01-01

    We used the Magellan adaptive optics (MagAO) system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths. We detect it at r', i', z', and Ys. With our new photometry and Teff~2500 K derived from the shape its K-band spectrum, we find that CT Cha B has Av = 3.4+/-1.1 mag, and a mass of 14-24 Mj according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates that the companion has significant Halpha emission and a mass accretion rate ~6*10^-10 Msun/yr, similar to some substellar companions. Proper motion analysis shows that another point source within 2" of CT Cha A is not physical. This paper demonstrates how visible wavelength AO photometry (r', i', z', Ys) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions.

  3. Weather on the Nearest Brown Dwarfs: Resolved Simultaneous Multi-Wavelength Variability Monitoring of WISE J104915.57-531906.1AB

    CERN Document Server

    Biller, Beth A; Mancini, Luigi; Ciceri, Simona; Southworth, John; Kopytova, Taisiya G; Bonnefoy, Mickaël; Deacon, Niall R; Schlieder, Joshua E; Buenzli, Esther; Brandner, Wolfgang; Allard, France; Homeier, Derek; Freytag, Bernd; Bailer-Jones, Coryn A L; Greiner, Jochen; Henning, Thomas; Goldman, Bertrand

    2013-01-01

    We present two epochs of MPG/ESO 2.2m GROND simultaneous 6-band ($r'i'z'JHK$) photometric monitoring of the closest known L/T transition brown dwarf binary WISE J104915.57-531906.1AB. We report here the first resolved variability monitoring of both the T0.5 and L7.5 components. We obtained 4 hours of focused observations on the night of UT 2013-04-22, as well as 4 hours of defocused (unresolved) observations on the night of UT 2013-04-16. We note a number of robust trends in our light curves. The $r'$ and $i'$ light curves appear to be anticorrelated with $z'$ and $H$ for the T0.5 component and in the unresolved lightcurve. In the defocused dataset, $J$ appears correlated with $z'$ and $H$ and anticorrelated with $r'$ and $i'$, while in the focused dataset we measure no variability for $J$ at the level of our photometric precision, likely due to evolving weather phenomena. In our focused T0.5 component lightcurve, the $K$ band lightcurve displays a significant phase offset relative to both $H$ and $z'$. We ar...

  4. The Brown Dwarf Kinematics Project (BDKP). II. Details on Nine Wide Common Proper Motion Very Low-Mass Companions to Nearby Stars

    CERN Document Server

    Faherty, Jacqueline K; West, Andrew A; Bochanski, John J; Cruz, Kelle L; Shara, Michael M; Walter, Frederick M

    2009-01-01

    We report on nine wide common proper motion systems containing late-type M, L, or T companions. We confirm six previously reported companions, and identify three new systems. The ages of these systems are determined using diagnostics for both stellar primaries and low--mass secondaries and masses for the secondaries are inferred using evolutionary models. Of our three new discoveries, the M3+T6.5 pair G 204-39 and SDSS J1758+4633 has an age constrained to 0.5-1.5 Gyr making the secondary a potentially useful brown dwarf benchmark. The G5+L4 pair G 200-28 and SDSS J1416+5006 has a projected separation of ~25,000 AU making it one of the widest and lowest binding energy systems known to date. The system containing NLTT 2274 and SDSS J0041+1341 is an older M4+L0 (>4.5 Gyr) pair which shows Halpha activity in the secondary but not the primary making it a useful tracer of age/mass/activity trends. We find a resolved binary frequency for widely-separated (> 100 AU) low--mass companions (i.e. at least a triple system...

  5. AB INITIO EQUATIONS OF STATE FOR HYDROGEN (H-REOS.3) AND HELIUM (He-REOS.3) AND THEIR IMPLICATIONS FOR THE INTERIOR OF BROWN DWARFS

    International Nuclear Information System (INIS)

    We present new equations of state (EOSs) for hydrogen and helium covering a wide range of temperatures from 60 K to 107 K and densities from 10–10 g cm–3 to 103 g cm–3. They include an extended set of ab initio EOS data for the strongly correlated quantum regime with an accurate connection to data derived from other approaches for the neighboring regions. We compare linear mixing isotherms based on our EOS tables with available real mixture data. A first important astrophysical application of this new EOS data is the calculation of interior models for Jupiter and comparison with recent results. Second, mass-radius relations are calculated for Brown Dwarfs (BDs) which we compare with predictions derived from the widely used EOS of Saumon, Chabrier, and van Horn. Furthermore, we calculate interior models for typical BDs with different masses, namely, Corot-3b, Gliese-229b, and Corot-15b, and the giant planet KOI-889b. The predictions for the central pressures and densities differ by up to 10% dependent on the EOS used. Our EOS tables are made available in the supplemental material of this paper

  6. Stochastic accretion of planetesimals onto white dwarfs: constraints on the mass distribution of accreted material from atmospheric pollution

    CERN Document Server

    Wyatt, M C; Pringle, J E; Bonsor, A

    2014-01-01

    This paper explores how the stochastic accretion of planetesimals onto white dwarfs would be manifested in observations of their atmospheric pollution. Archival observations of pollution levels for unbiased samples of DA and non-DA white dwarfs are used to derive the distribution of accretion rates, confirming that rates become systematically lower as sinking time is decreased, with no discernable dependence on cooling age. The accretion rates expected from planetesimals that are all the same mass (ie, a mono-mass distribution) are explored both analytically and using a Monte Carlo model, quantifying how measured accretion rates inevitably depend on sinking time, since different sinking times probe different times since the last accretion event. However, that dependence is so dramatic that a mono-mass distribution can be excluded. Consideration of accretion from a broad distribution of planetesimal masses uncovers an important conceptual difference: accretion is continuous (rather than stochastic) for planete...

  7. The polluted atmospheres of cool white dwarfs and the magnetic field connection

    CERN Document Server

    Kawka, A

    2014-01-01

    We present an analysis of X-Shooter spectra of the polluted hydrogen-rich white dwarfs (DAZ) NLTT 888 and NLTT 53908. The spectra of NLTT 53908 show strong, Zeeman-split calcium lines (CaII H&K and Ca I $\\lambda 4226$) and the star appears to be a close relative of the polluted magnetic white dwarf (DAZH) NLTT 10480, while the spectra of NLTT 888 show narrow lines of calcium and iron. A comparison of the DAZ NLTT 888 and the DAZH NLTT 53908 with other class members illustrates the diversity of environment and formation circumstances surrounding these objects. In particular, we find that the incidence of magnetism in old, polluted white dwarfs significantly exceeds that found in the general white dwarf population which suggests an hypothetical link between a crowded planetary system and magnetic field generation.

  8. GASEOUS MEAN OPACITIES FOR GIANT PLANET AND ULTRACOOL DWARF ATMOSPHERES OVER A RANGE OF METALLICITIES AND TEMPERATURES

    International Nuclear Information System (INIS)

    We present new calculations of Rosseland and Planck gaseous mean opacities relevant to the atmospheres of giant planets and ultracool dwarfs. Such calculations are used in modeling the atmospheres, interiors, formation, and evolution of these objects. Our calculations are an expansion of those presented in Freedman et al. to include lower pressures, finer temperature resolution, and also the higher metallicities most relevant for giant planet atmospheres. Calculations span 1 μbar to 300 bar, and 75-4000 K, in a nearly square grid. Opacities at metallicities from solar to 50 times solar abundances are calculated. We also provide an analytic fit to the Rosseland mean opacities over the grid in pressure, temperature, and metallicity. In addition to computing mean opacities at these local temperatures, we also calculate them with weighting functions up to 7000 K, to simulate the mean opacities for incident stellar intensities, rather than locally thermally emitted intensities. The chemical equilibrium calculations account for the settling of condensates in a gravitational field and are applicable to cloud-free giant planet and ultracool dwarf atmospheres, but not circumstellar disks. We provide our extensive opacity tables for public use

  9. GASEOUS MEAN OPACITIES FOR GIANT PLANET AND ULTRACOOL DWARF ATMOSPHERES OVER A RANGE OF METALLICITIES AND TEMPERATURES

    Energy Technology Data Exchange (ETDEWEB)

    Freedman, Richard S. [SETI Institute, Mountain View, CA (United States); Lustig-Yaeger, Jacob [Department of Physics, University of California, Santa Cruz, CA 95064 (United States); Fortney, Jonathan J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Lupu, Roxana E.; Marley, Mark S. [Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA (United States); Lodders, Katharina, E-mail: Richard.S.Freedman@nasa.gov [Planetary Chemistry Laboratory, Washington University, St. Louis, MO (United States)

    2014-10-01

    We present new calculations of Rosseland and Planck gaseous mean opacities relevant to the atmospheres of giant planets and ultracool dwarfs. Such calculations are used in modeling the atmospheres, interiors, formation, and evolution of these objects. Our calculations are an expansion of those presented in Freedman et al. to include lower pressures, finer temperature resolution, and also the higher metallicities most relevant for giant planet atmospheres. Calculations span 1 μbar to 300 bar, and 75-4000 K, in a nearly square grid. Opacities at metallicities from solar to 50 times solar abundances are calculated. We also provide an analytic fit to the Rosseland mean opacities over the grid in pressure, temperature, and metallicity. In addition to computing mean opacities at these local temperatures, we also calculate them with weighting functions up to 7000 K, to simulate the mean opacities for incident stellar intensities, rather than locally thermally emitted intensities. The chemical equilibrium calculations account for the settling of condensates in a gravitational field and are applicable to cloud-free giant planet and ultracool dwarf atmospheres, but not circumstellar disks. We provide our extensive opacity tables for public use.

  10. Potential biosignatures in super-Earth atmospheres. I. Spectral appearance of super-Earths around M dwarfs

    Science.gov (United States)

    Rauer, H.; Gebauer, S.; Paris, P. V.; Cabrera, J.; Godolt, M.; Grenfell, J. L.; Belu, A.; Selsis, F.; Hedelt, P.; Schreier, F.

    2011-05-01

    Atmospheric temperature and mixing ratio profiles of terrestrial planets vary with the spectral energy flux distribution for different types of M-dwarf stars and the planetary gravity. We investigate the resulting effects on the spectral appearance of molecular absorption bands, which are relevant as indicators for potential planetary habitability during primary and secondary eclipse for transiting terrestrial planets with Earth-like biomass emissions. Atmospheric profiles are computed using a plane-parallel, 1D climate model coupled with a chemistry model. We then calculate simulated spectra using a line-by-line radiative transfer model. We find that emission spectra during secondary eclipse show increasing absorption of methane, water, and ozone for planets orbiting quiet M0-M3 dwarfs and the active M-type star AD Leo compared with solar-type central stars. However, for planets orbiting very cool and quiet M dwarfs (M4 to M7), increasing temperatures in the mid-atmosphere lead to reduced absorption signals, which impedes the detection of molecules in these scenarios. Transmission spectra during primary eclipse show strong absorption features of CH4, N2O and H2O for planets orbiting quiet M0-M7 stars and AD Leo. The N2O absorption of an Earth-sized planet orbiting a quiet M7 star can even be as strong as the CO2 signal. However, ozone absorption decreases for planets orbiting these cool central stars owing to chemical effects in the atmosphere. To investigate the effect on the spectroscopic detection of absorption bands with potential future satellite missions, we compute signal-to-noise-ratios (SNR) for a James Webb Space Telescope (JWST)-like aperture telescope.

  11. A Near-Infrared Spectroscopic Study of Young Field Ultracool Dwarfs: Additional Analysis

    CERN Document Server

    Allers, K N

    2013-01-01

    We present additional analysis of the classification system presented in Allers & Liu (2013). We refer the reader to Allers & Liu (2013) for a detailed discussion of our near-IR spectral type and gravity classification system. Here, we address questions and comments from participants of the Brown Dwarfs Come of Age meeting. In particular, we examine the effects of binarity and metallicity on our classification system. We also present our classification of Pleiades brown dwarfs using published spectra. Lastly, we determine SpTs and calculate gravity-sensitive indices for the BT-Settl atmospheric models and compare them to observations.

  12. Atmospheric brown clouds reach the Tibetan Plateau by crossing the Himalayas

    Directory of Open Access Journals (Sweden)

    Z. L. Lüthi

    2015-06-01

    Full Text Available The Himalayas and the Tibetan Plateau region (HTP, despite being a remote and sparsely populated area, is regularly exposed to polluted air masses with significant amounts of aerosols including black carbon. These dark, light-absorbing particles are known to exert a great melting potential on mountain cryospheric reservoirs through albedo reduction and radiative forcing. This study combines ground-based and satellite remote sensing data to identify a severe aerosol pollution episode observed simultaneously in central Tibet and on the southern side of the Himalayas during 13–19 March 2009 (pre-monsoon. Trajectory calculations based on the high-resolution numerical weather prediction model COSMO are used to locate the source regions and study the mechanisms of pollution transport in the complex topography of the HTP. We detail how polluted air masses from an atmospheric brown cloud (ABC over South Asia reach the Tibetan Plateau within a few days. Lifting and advection of polluted air masses over the great mountain range is enabled by a combination of synoptic-scale and local meteorological processes. During the days prior to the event, winds over the Indo-Gangetic Plain (IGP are generally weak at lower levels, allowing for accumulation of pollutants and thus the formation of ABCs. The subsequent passing of synoptic-scale troughs leads to southwesterly flow in the middle troposphere over northern and central India, carrying the polluted air masses across the Himalayas. As the IGP is known to be a hotspot of ABCs, the cross-Himalayan transport of polluted air masses may have serious implications for the cryosphere in the HTP and impact climate on regional to global scales. Since the current study focuses on one particularly strong pollution episode, quantifying the frequency and magnitude of similar events in a climatological study is required to assess the total impact.

  13. Radiocarbon (14C) source apportionment of carbonaceous aerosol components in the Asian Atmospheric Brown Cloud

    International Nuclear Information System (INIS)

    Full text: Light-absorbing carbonaceous matter constitutes one of the largest uncertainties in climate modeling. The high concentrations of black carbon - soot - in the Asian Brown Cloud lead to strong atmospheric heating and large surface cooling that is as important to regional climate forcing as greenhouse gases, yet the sources of these aerosols are not well understood. Emission inventory models suggest that biofuel/biomass burning accounts for 60 - 90 % of the sources of these aerosol components whereas measurements of the elemental composition of ambient aerosols compared with source signatures point to combustion of fossil fuel as the primary culprit. However, both approaches acknowledge large uncertainties in source apportionment of the elusively defined black carbon. This study approached the sourcing challenge by applying microscale radiocarbon measurements to aerosol particles collected during the winter monsoon both over the Indian Ocean and in central India. The radiocarbon approach is ideally suited to this task as fossil sources are void of 14C whereas biomass combustion products hold a contemporary 14C signal. High-volume air samples of total carbonaceous aerosols revealed 14C signals that were similar for N. Indian source and Indian Ocean receptor regions, consistent with the absence of any significant formation of secondary organic aerosols, with a 60 - 70 % contribution from biomass combustion and biogenic sources. Isolates of elemental or soot carbon fractions varied between 40 - 70 %, depending on isolation method. These novel radiocarbon constraints on the sources of light-absorbing carbonaceous matter aid prioritizing of what combustion processes to target for emission mitigations of these health-afflicting and climate-forcing aerosols in the South Asian region. (author)

  14. Identification of the pathogen causing brown rot of Chinese Dwarf Cherry( Cerasus humilis%欧李褐腐病病原菌鉴定

    Institute of Scientific and Technical Information of China (English)

    徐成楠; 周宗山; 吴玉星; 迟福梅; 张红军

    2011-01-01

    欧李[ Cerasus humilis( Bge.) Sok.]为蔷薇科樱桃属果树,别名钙果,原产中国,分布于我国的黑龙江、辽宁、内蒙古、河北、山东、山西等省区.多生长在向阳山坡或沙丘边缘,资源相当丰富.欧李株高0.3~1.5m,多为0.5~0.7m左右,是目前世界上最矮小的木本果树.果实可鲜食或加工,含糖、蛋白质、维生素C,特别是矿质元素铁和钙的含量很高,每100果肉干分别含有58和360 mg种仁可作药用,中药称之为"郁李仁"可消毒化肿.%One serious disease happened on the fruit of Chinese Dwarf Cherry in Liaoning Province recently. The typical symptom was brown spot formed on the fruit surface. The spot spread quickly through the whole fruits, then the fruits were rotten. There were tomentum round shaped mildew formed on the surface of symptomatic fruits. The pathogen was isolated from infected fruits. After pathogenicity tests in lab and field and re-isolation, the isolate HI was determined to be responsible for the disease. HI colony on PDA was 70 -75 mm in diameter, with concentric rings in grayish or light brown color after 7 days incubation at 221 with illumination of 12 h near-UV/12 h dark. The conidia were one-celled, hyaline, lemon-shaped, (10-27) jun x (7-17) jun on PDA, produced in branched monilioid chains. The rDNA ITS sequence of islolates HI and Gl had 100% similarity with those of Monilinia fructicola in GenBank. The amplification results with three Monilinia specific primer pairs showed that only primer pair ITSlMfcl and ITS4Mfcl could amplify a 356 bp fragment. Based on the morphological characteristics and rDNA molecular analysis, the pathogen was finally identified as M. Fructicola.

  15. Radio Emission and Orbital Motion from the Close-encounter Star-Brown Dwarf Binary WISE J072003.20-084651.2

    Science.gov (United States)

    Burgasser, Adam J.; Melis, Carl; Todd, Jacob; Gelino, Christopher R.; Hallinan, Gregg; Bardalez Gagliuffi, Daniella

    2015-12-01

    We report the detection of radio emission and orbital motion from the nearby star-brown dwarf binary WISE J072003.20-084651.2AB. Radio observations across the 4.5-6.5 GHz band with the Very Large Array identify at the position of the system quiescent emission with a flux density of 15 ± 3 μJy, and a highly polarized radio source that underwent a 2-3 minute burst with peak flux density 300 ± 90 μJy. The latter emission is likely a low-level magnetic flare similar to optical flares previously observed for this source. No outbursts were detected in separate narrow-band Hα monitoring observations. We report new high-resolution imaging and spectroscopic observations that confirm the presence of a co-moving T5.5 secondary and provide the first indications of three-dimensional orbital motion. We used these data to revise our estimates for the orbital period (4.1{}-1.3+2.7 year) and tightly constrain the orbital inclination to be nearly edge-on (93.°6+1.°6-1.°4), although robust measures of the component and system masses will require further monitoring. The inferred orbital motion does not change the high likelihood that this radio-emitting very low-mass binary made a close pass to the Sun in the past 100 kyr. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  16. A THERMAL INFRARED IMAGING STUDY OF VERY LOW MASS, WIDE-SEPARATION BROWN DWARF COMPANIONS TO UPPER SCORPIUS STARS: CONSTRAINING CIRCUMSTELLAR ENVIRONMENTS

    International Nuclear Information System (INIS)

    We present a 3-5 μm LBT/MMT adaptive optics imaging study of three Upper Scorpius stars with brown dwarf (BD) companions with very low masses/mass ratios (MBD Jup; MBD/M* ≈ 1%-2%) and wide separations (300-700 AU): GSC 06214, 1RXS 1609, and HIP 78530. We combine these new thermal IR data with existing 1-4 μm and 24 μm photometry to constrain the properties of the BDs and identify evidence for circumprimary/circumsecondary disks in these unusual systems. We confirm that GSC 06214B is surrounded by a disk, further showing that this disk produces a broadband IR excess due to small dust near the dust sublimation radius. An unresolved 24 μm excess in the system may be explained by the contribution from this disk. 1RXS 1609B exhibits no 3-4 μm excess, nor does its primary; however, the system as a whole has a modest 24 μm excess, which may come from warm dust around the primary and/or BD. Neither object in the HIP 78530 system exhibits near- to mid-IR excesses. We additionally find that the 1-4 μm colors of HIP 78530B match a spectral type of M3 ± 2, inconsistent with the M8 spectral type assigned based on its near-IR spectrum, indicating that it may be a low-mass star rather than a BD. We present new upper limits on additional low-mass companions in the system (Jup beyond 175 AU). Finally, we examine the utility of circumsecondary disks as probes of the formation histories of wide BD companions, finding that the presence of a disk may disfavor BD formation near the primary with subsequent outward scattering.

  17. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. IV. A CANDIDATE BROWN DWARF OR LOW-MASS STELLAR COMPANION TO HIP 67526

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Peng; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Ma Bo; Wang, Ji [Astronomy Department, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611 (United States); Cargile, Phillip; Hebb, Leslie; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Porto de Mello, Gustavo F.; Ferreira, Leticia D. [Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira do Pedro Antonio, 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I. [Instituto de Astrofisica de Canarias, C/Via Lactea S/N, E-38200 La Laguna (Spain); Gaudi, B. Scott [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Laboratorio Interinstitucional de e-Astronomia (LIneA), Rio de Janeiro, RJ 20921-400 (Brazil); Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Agol, Eric, E-mail: jpaty@mail.ustc.edu.cn [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); and others

    2013-09-15

    We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695{sup +0.0188}{sub -0.0187} days, an eccentricity of 0.4375 {+-} 0.0040, and a semi-amplitude of 2948.14{sup +16.65}{sub -16.55} m s{sup -1}. Using additional high-resolution spectroscopy, we find the host star has an effective temperature T{sub eff} = 6004 {+-} 34 K, a surface gravity log g (cgs) =4.55 {+-} 0.17, and a metallicity [Fe/H] =+0.04 {+-} 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 {+-} 0.09 M{sub Sun} and 0.92 {+-} 0.19 R{sub Sun }. The minimum mass of MARVELS-5b is 65.0 {+-} 2.9M{sub Jup}, indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 {+-} 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M{sub Sun} at a separation larger than 40 AU.

  18. A THERMAL INFRARED IMAGING STUDY OF VERY LOW MASS, WIDE-SEPARATION BROWN DWARF COMPANIONS TO UPPER SCORPIUS STARS: CONSTRAINING CIRCUMSTELLAR ENVIRONMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Bailey, Vanessa; Hinz, Philip M.; Su, Kate Y. L.; Hoffmann, William F.; Rieke, George; Rodigas, Timothy; Skemer, Andrew; Vaitheeswaran, Vidhya [Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Currie, Thayne [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Esposito, Simone; Pinna, Enrico; Puglisi, Alfio [Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy); Hill, John M. [Large Binocular Telescope Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Jones, Terry [School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States); Kim, Jihun [College of Optical Sciences, University of Arizona, 1630 E. University Blvd., Tucson, AZ 85721 (United States); Leisenring, Jarron; Meyer, Michael [Institut fuer Angewandte Physik, Eidgenoessische Technische Hochschule-Zuerich, CH-8093 (Switzerland); Murray-Clay, Ruth; Skrutskie, Michael F. [Harvard-Smithsonian Center for Astrophysics, Harvard University, 60 Garden St., Cambridge, MA 02138 (United States); Nelson, Matthew J., E-mail: vbailey@as.arizona.edu [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); and others

    2013-04-10

    We present a 3-5 {mu}m LBT/MMT adaptive optics imaging study of three Upper Scorpius stars with brown dwarf (BD) companions with very low masses/mass ratios (M{sub BD} <25 M{sub Jup}; M{sub BD}/M{sub *} Almost-Equal-To 1%-2%) and wide separations (300-700 AU): GSC 06214, 1RXS 1609, and HIP 78530. We combine these new thermal IR data with existing 1-4 {mu}m and 24 {mu}m photometry to constrain the properties of the BDs and identify evidence for circumprimary/circumsecondary disks in these unusual systems. We confirm that GSC 06214B is surrounded by a disk, further showing that this disk produces a broadband IR excess due to small dust near the dust sublimation radius. An unresolved 24 {mu}m excess in the system may be explained by the contribution from this disk. 1RXS 1609B exhibits no 3-4 {mu}m excess, nor does its primary; however, the system as a whole has a modest 24 {mu}m excess, which may come from warm dust around the primary and/or BD. Neither object in the HIP 78530 system exhibits near- to mid-IR excesses. We additionally find that the 1-4 {mu}m colors of HIP 78530B match a spectral type of M3 {+-} 2, inconsistent with the M8 spectral type assigned based on its near-IR spectrum, indicating that it may be a low-mass star rather than a BD. We present new upper limits on additional low-mass companions in the system (<5 M{sub Jup} beyond 175 AU). Finally, we examine the utility of circumsecondary disks as probes of the formation histories of wide BD companions, finding that the presence of a disk may disfavor BD formation near the primary with subsequent outward scattering.

  19. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. IV. A CANDIDATE BROWN DWARF OR LOW-MASS STELLAR COMPANION TO HIP 67526

    International Nuclear Information System (INIS)

    We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695+0.0188-0.0187 days, an eccentricity of 0.4375 ± 0.0040, and a semi-amplitude of 2948.14+16.65-16.55 m s–1. Using additional high-resolution spectroscopy, we find the host star has an effective temperature Teff = 6004 ± 34 K, a surface gravity log g (cgs) =4.55 ± 0.17, and a metallicity [Fe/H] =+0.04 ± 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 ± 0.09 M☉ and 0.92 ± 0.19 R☉. The minimum mass of MARVELS-5b is 65.0 ± 2.9MJup, indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 ± 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M☉ at a separation larger than 40 AU

  20. Clouds and Hazes in Exoplanet Atmospheres

    CERN Document Server

    Marley, Mark S; Cuzzi, Jeffrey N; Kitzmann, Daniel

    2013-01-01

    Clouds and hazes are commonplace in the atmospheres of solar system planets and are likely ubiquitous in the atmospheres of extrasolar planets as well. Clouds affect every aspect of a planetary atmosphere, from the transport of radiation, to atmospheric chemistry, to dynamics and they influence - if not control - aspects such as surface temperature and habitability. In this review we aim to provide an introduction to the role and properties of clouds in exoplanetary atmospheres. We consider the role clouds play in influencing the spectra of planets as well as their habitability and detectability. We briefly summarize how clouds are treated in terrestrial climate models and consider the far simpler approaches that have been taken so far to model exoplanet clouds, the evidence for which we also review. Since clouds play a major role in the atmospheres of certain classes of brown dwarfs we briefly discuss brown dwarf cloud modeling as well. We also review how the scattering and extinction efficiencies of cloud p...

  1. Empirical Near Infrared colors for low-mass stars and brown dwarfs in the Orion Nebula Cluster

    CERN Document Server

    Scandariato, Gaetano; Robberto, Massimo; Pagano, Isabella; Stassun, Keivan

    2012-01-01

    Atmospheric and evolutionary models for low-mass stars rely on approximate assumptions on the physics of the stellar structure and the atmospheric radiative transfer. This leads to biased theoretical predictions on the photospheric Spectral Energy Distributions of Pre-Main Sequence (PMS) stars, and affects the derivation of stellar parameters from photometric data. Our goal is to correct the biases present in the theoretical predictions for the near-IR photometry of low-mass PMS stars. Using empirical intrinsic IR colors, we assess the accuracy of current synthetic spectral libraries and evolutionary models. We consider a sample of ~300 PMS stars in the Orion Nebula Cluster (age 1 Myr) with measured luminosities, temperatures and photospheric JHKs photometry. By analyzing the photospheric colors of our sample of stars, we find that the synthetic JHKs photometry provided by theoretical spectral templates for late spectral types (>K6) are accurate at the level of ~0.2 mag, while colors are accurate at ~0.1 mag....

  2. Response of Atmospheric Biomarkers to NOx-induced Photochemistry Generated by Stellar Cosmic Rays for Earth-like Planets in the Habitable Zone of M-Dwarf Stars

    CERN Document Server

    Grenfell, John Lee; von Paris, Philip; Patzer, Beate; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2015-01-01

    Understanding whether M-dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M-dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N2), which leads to production of nitrogen oxides in the planetary atmosphere, hence affecting biomarkers such as ozone. We apply a stationary model, that is, without a time-dependence, hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by t...

  3. Effect of controlled atmosphere storage on pericarp browning, bioactive compounds and antioxidant enzymes of litchi fruits.

    Science.gov (United States)

    Ali, Sajid; Khan, Ahmad Sattar; Malik, Aman Ullah; Shahid, Muhammad

    2016-09-01

    'Gola' litchi fruits were stored under ten different CA-combinations at 5±1°C to investigate its effects on pericarp browning, biochemical quality and antioxidative activities. Control fruit turned completely brown after 28days of storage and were excluded from the study. Fruit-stored under CA7-combination (1% O2+5% CO2) showed reduced weight loss, pericarp browning, membrane leakage and malondialdehyde contents. Soluble solid contents, titratable acidity and ascorbic acid contents were higher in CA7-stored fruit. Activities of catalase and superoxide dismutase enzymes, levels of total anthocyanins, DPPH radical-scavenging-activity and phenolic contents were significantly higher in CA7-stored litchi fruit. In contrast, activities of polyphenol oxidase and peroxidase enzymes were substantially lower in fruit kept under CA7-combination. Fruit subjected to CA7-conditions also maintained higher organoleptic quality. In conclusion, 1% O2+5% CO2 CA-conditions delayed pericarp browning, maintained antioxidative activities and biochemical characteristics along with better organoleptic quality of litchi fruit for 35days. PMID:27041293

  4. NLTE model atmospheres for the hottest white dwarfs: Spectral analysis of the compact component in nova V4743 Sgr

    CERN Document Server

    Rauch, T; Gonzales-Riestra, R; Nelson, T; Still, M; Werner, K; Wilms, J; 10.1088/0004-637X/717/1/363

    2010-01-01

    Half a year after its outburst in September 2002, nova V4743 Sgr evolved into the brightest supersoft X-ray source in the sky with a flux maximum around 30A. We calculated grids of synthetic energy distributions (SEDs) based on NLTE model atmospheres for the analysis of the hottest white dwarfs and present the result of fits to Chandra and XMM-Newton grating X-ray spectra of V4743 Sgr of outstanding quality, exhibiting prominent resonance lines of C V, C VI, N VI, N VII, and O VII in absorption. The nova reached its highest effective temperature (Teff = 740 +/- 70kK) around April 2003 and remained at that temperature at least until September 2003. We conclude that the white dwarf is massive, about 1.1 - 1.2 Msun. The nuclear-burning phase lasted for 2 to 2.5 years after the outburst, probably the average duration for a classical nova. The photosphere of V4743 Sgr was strongly carbon deficient (about times solar) and enriched in nitrogen and oxygen (> 5 times solar). Especially the very low C/N ratio indicates...

  5. Very Low-Mass Stellar and Substellar Companions to Solar-like Stars From MARVELS VI: A Giant Planet and a Brown Dwarf Candidate in a Close Binary System HD 87646

    CERN Document Server

    Ma, Bo; Wolszczan, Alex; Muterspaugh, Matthew W; Lee, Brian; Henry, Gregory W; Schneider, Donald P; Martin, Eduardo L; Niedzielski, Andrzej; Xie, Jiwei; Fleming, Scott W; Thomas, Neil; Williamson, Michael; Zhu, Zhaohuan; Agol, Eric; Bizyaev, Dmitry; da Costa, Luiz Nicolaci; Jiang, Peng; Fiorenzano, A F Martinez; Hernandez, Jonay I Gonzalez; Guo, Pengcheng; Grieves, Nolan; Li, Rui; Liu, Jane; Mahadevan, Suvrath; Mazeh, Tsevi; Nguyen, Duy Cuong; Paegert, Martin; Sithajan, Sirinrat; Stassun, Keivan; Thirupathi, Sivarani; van Eyken, Julian C; Wan, Xiaoke; Wang, Ji; Wisniewski, John P; Zhao, Bo; Zucker, Shay

    2016-01-01

    We report the detections of a giant planet (MARVELS-7b) and a brown dwarf candidate (MARVELS-7c) around the primary star in the close binary system, HD 87646. It is the first close binary system with more than one substellar circum-primary companion discovered to the best of our knowledge. The detection of this giant planet was accomplished using the first multi-object Doppler instrument (KeckET) at the Sloan Digital Sky Survey (SDSS) telescope. Subsequent radial velocity observations using ET at Kitt Peak National Observatory, HRS at HET, the "Classic" spectrograph at the Automatic Spectroscopic Telescope at Fairborn Observatory, and MARVELS from SDSS-III confirmed this giant planet discovery and revealed the existence of a long-period brown dwarf in this binary. HD 87646 is a close binary with a separation of $\\sim22$ AU between the two stars, estimated using the Hipparcos catalogue and our newly acquired AO image from PALAO on the 200-inch Hale Telescope at Palomar. The primary star in the binary, HD 87646...

  6. K2 Discovery of Young Eclipsing Binaries in Upper Scorpius: Direct Mass and Radius Determinations for the Lowest Mass Stars and Initial Characterization of an Eclipsing Brown Dwarf Binary

    CERN Document Server

    David, Trevor J; Cody, Ann Marie; Carpenter, John M; Howard, Andrew W

    2015-01-01

    We report the discovery of three low-mass double-lined eclipsing binaries in the pre-main sequence Upper Scorpius association, revealed by $K2$ photometric monitoring of the region over $\\sim$ 78 days. The orbital periods of all three systems are $<$5 days. We use the $K2$ photometry plus multiple Keck/HIRES radial velocities and spectroscopic flux ratios to determine fundamental stellar parameters for both the primary and secondary components of each system, along with the orbital parameters. We present tentative evidence that EPIC 203868608 is a hierarchical triple system comprised of an eclipsing pair of $\\sim$25 $M_\\mathrm{Jup}$ brown dwarfs with a wide M-type companion. If confirmed, it would constitute only the second double-lined eclipsing brown dwarf binary system discovered to date. The double-lined system EPIC 203710387 is composed of nearly identical M4.5-M5 stars with fundamentally determined masses and radii measured to better than 3% precision ($M_1=0.1169\\pm0.0031 M_\\odot$, $M_2=0.1065\\pm0.0...

  7. The EBLM Project I-Physical and orbital parameters, including spin-orbit angles, of two low-mass eclipsing binaries on opposite sides of the Brown Dwarf limit

    CERN Document Server

    Triaud, Amaury H M J; Anderson, David R; Cargile, Phill; Cameron, Andrew Collier; Doyle, Amanda P; Faedi, Francesca; Gillon, Michaël; Chew, Yilen Gomez Maqueo; Hellier, Coel; Jehin, Emmanuel; Maxted, Pierre; Naef, Dominique; Pepe, Francesco; Pollacco, Don; Queloz, Didier; Ségransan, Damien; Smalley, Barry; Stassun, Keivan; Udry, Stéphane; West, Richard G

    2012-01-01

    This paper introduces a series of papers aiming to study the dozens of low mass eclipsing binaries (EBLM), with F, G, K primaries, that have been discovered in the course of the WASP survey. Our objects are mostly single-line binaries whose eclipses have been detected by WASP and were initially followed up as potential planetary transit candidates. These have bright primaries, which facilitates spectroscopic observations during transit and allows the study of the spin-orbit distribution of F, G, K+M eclipsing binaries through the Rossiter-McLaughlin effect. Here we report on the spin-orbit angle of WASP-30b, a transiting brown dwarf, and improve its orbital parameters. We also present the mass, radius, spin-orbit angle and orbital parameters of a new eclipsing binary, J1219-39b (1SWAPJ121921.03-395125.6, TYC 7760-484-1), which, with a mass of 95 +/- 2 Mjup, is close to the limit between brown dwarfs and stars. We find that both objects orbit in planes that appear aligned with their primaries' equatorial plane...

  8. The heavily polluted atmosphere of the DAZ white dwarf GALEX J193156.8+011745

    Czech Academy of Sciences Publication Activity Database

    Vennes, Stephane; Kawka, Adela; Németh, Péter

    2010-01-01

    Roč. 404, č. 1 (2010), L40-L44. ISSN 0035-8711 R&D Projects: GA AV ČR(CZ) IAA300030908; GA ČR GAP209/10/0967; GA MŠk(CZ) LC06014 Grant ostatní: GA AV ČR(CZ) IAA301630901 Institutional research plan: CEZ:AV0Z10030501 Keywords : GALEX J193156.8+011745 * white dwarfs Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.888, year: 2010

  9. Radiative Levitation of Silicon in the Atmospheres of Two Hyades DA White Dwarfs

    OpenAIRE

    Chayer, P.

    2013-01-01

    The presence of silicon at the surface of the two Hyades DA white dwarfs WD 0421+162 and WD 0431+126 requires mechanisms that counteract the effects of the downward diffusion. Radiative levitation calculations indicate that the silicon abundance observed in WD 0431+126 corresponds to the abundance supported by radiative levitation. Detailed time-dependent diffusion calculations that take into account radiative levitation and accretion indicate that accretion with rates of dM/dt(Si) < 1.00E4 g...

  10. Effect of inert atmosphere on the postharvest browning of manzanilla olives and optimization by response surface methodology of the aqueous treatments.

    Science.gov (United States)

    Segovia-Bravo, Kharla A; García-García, Pedro; López-López, Antonio; Garrido-Fernández, Antonio

    2012-05-01

    Subjecting bruised olives to a nitrogen atmosphere during the postharvest period prevented the oxidation of phenols and subsequent browning. However, a rapid phenol oxidation and browning occurred when fruits were re-exposed to air. Based on models deduced from the effects of aqueous antioxidant solutions on changes in different color parameters in the fermented product, the treatments to prevent browning were optimized. The recommended procedure consists of placing the harvested olives in a cold (4 to 8 °C) solution of 3% sodium metabisulfite with the pH adjusted to 3.0 (by adding food grade HCl) and applying the lye treatment before 8 h from picking. The use of these conditions led to mechanically harvested Spanish style olives with hardly any visible browning. PMID:22489596

  11. HST Rotational Spectral Mapping of Two L-Type Brown Dwarfs: Variability In and Out of Water Bands Indicates High-Altitude Haze Layers

    CERN Document Server

    Yang, Hao; Marley, Mark S; Saumon, Didier; Morley, Caroline V; Buenzli, Esther; Artigau, Etienne; Radigan, Jacqueline; Metchev, Stanimir; Burgasser, Adam J; Mohanty, Subhanjoy; Lowrance, Patrick L; Showman, Adam P; Karalidi, Theodora; Flateau, Davin; Heinze, Aren N

    2014-01-01

    We present time-resolved near-infrared spectroscopy of two L5 dwarfs, 2MASS J18212815+1414010 and 2MASS J15074759-1627386, observed with the Wide Field Camera 3 instrument on the Hubble Space Telescope (HST). We study the wavelength dependence of rotation-modulated flux variations between 1.1 $\\mu$m and 1.7 $\\mu$m. We find that the water absorption bands of the two L5 dwarfs at 1.15 $\\mu$m and 1.4 $\\mu$m vary at similar amplitudes as the adjacent continuum. This differs from the results of previous HST observations of L/T transition dwarfs, in which the water absorption at 1.4 $\\mu$m displays variations of about half of the amplitude at other wavelengths. We find that the relative amplitude of flux variability out of the water band with respect to that in the water band shows a increasing trend from the L5 dwarfs toward the early T dwarfs. We utilize the models of Saumon & Marley (2008) and find that the observed variability of the L5 dwarfs can be explained by the presence of spatially varying high-altit...

  12. Juvenile Ultracool Dwarfs

    CERN Document Server

    Rice, Emily L; Cruz, Kelle; Barman, Travis; Looper, Dagny; Malo, Lison; Mamajek, Eric E; Metchev, Stanimir; Shkolnik, Evgenya L

    2011-01-01

    Juvenile ultracool dwarfs are late spectral type objects (later than ~M6) with ages between 10 Myr and several 100 Myr. Their age-related properties lie intermediate between very low mass objects in nearby star-forming regions (ages 1-5 Myr) and field stars and brown dwarfs that are members of the disk population (ages 1-5 Gyr). Kinematic associations of nearby young stars with ages from ~10-100 Myr provide sources for juvenile ultracool dwarfs. The lowest mass confirmed members of these groups are late-M dwarfs. Several apparently young L dwarfs and a few T dwarfs are known, but they have not been kinematically associated with any groups. Normalizing the field IMF to the high mass population of these groups suggests that more low mass (mainly late-M and possibly L dwarf) members have yet to be found. The lowest mass members of these groups, along with low mass companions to known young stars, provide benchmark objects with which spectroscopic age indicators for juvenile ultracool dwarfs can be calibrated and...

  13. Secondary brown carbon - Formation of light-absorbing compounds in atmospheric particulates from selected dicarbonyls and amines

    Science.gov (United States)

    Kampf, Christopher; Filippi, Alexander; Hoffmann, Thorsten

    2015-04-01

    One of the main open questions regarding organic compounds in atmospheric chemistry today is related to the formation of optically-active compounds and the occurrence of so called brown carbon (Andreae and Gelencsér, 2006). While organic compounds in ambient fine particles for decades have been assumed to not absorb solar radiation, thus resulting in a net cooling effect on climate (IPCC, 2007), it is now generally accepted that a continuum of light-absorbing carbonaceous species is present in fine aerosols (Pöschl, 2003). In this study, light-absorbing compounds from reactions between dicarbonyl compounds, i.e., glyoxal, methylglyoxal, acetylacetone, 2,3-butanedione, 2,5-hexanedione, and glutaraldehyde, and amine species, i.e., ammonia and glycine, were investigated at atmospherically relevant concentrations in bulk solution experiments mimicking atmospheric particulates. Product analyses were performed using UV/Vis spectrophotometry and (ultra) high performance liquid chromatography coupled to diode array detection and ion trap mass spectrometry (HPLC-DAD-ESI-MS/MS), as well as ultra-high resolution (Orbitrap) mass spectrometry (UHPLC-ESI-HRMS/MS). We demonstrate that light-absorbing compounds are formed from a variety of atmospherically relevant dicarbonyls via particle phase reactions with amine nucleophiles. Single dicarbonyl and mixed dicarbonyl experiments were performed and products were analyzed. The reaction products are suggested to be cyclic nitrogen containing compounds such as imidazoles or dihydropyridines as well as open chain compounds resulting from aldol condensation reactions. Further, the reactive turnover was found to be higher at increasing pH values. The aforementioned processes may be of higher relevance in regions with high aerosol pH, e.g., resulting from high ammonia emissions as for example in northern India (Clarisse et al., 2009). References Andreae, M.O., and Gelencsér, A. (2006): Black carbon or brown carbon? The nature of light

  14. Two Extraordinary Substellar Binaries at the T/Y Transition and the Y-Band Fluxes of the Coolest Brown Dwarfs

    CERN Document Server

    Liu, Michael C; Bowler, Brendan P; Leggett, S K; Best, William M J

    2012-01-01

    Using Keck laser guide star adaptive optics imaging, we have found that the T9 dwarf WISE J1217+1626 and T8 dwarf WISE J1711+3500 are exceptional binaries, with unusually wide separations (~0.8 arcsec, 8-15 AU), large near-IR flux ratios (~2-3 mags), and small mass ratios (~0.5). Keck/NIRSPEC H-band spectra give a spectral type of Y0 for WISE J1217+1626B, and photometric estimates suggest T9.5 for WISE J1711+3500B. The WISE J1217+1626AB system is very similar to the T9+Y0 binary CFBDSIR J1458+1013AB; these two systems are the coldest known substellar multiples, having secondary components of ~400 K and being planetary-mass binaries if their ages are <~1 Gyr. Both WISE J1217+1626B and CFBDSIR J1458+1013B have strikingly blue Y-J colors compared to previously known T dwarfs, including their T9 primaries. Combining all available data, we find that Y-J color drops precipitously between the very latest T dwarfs and the Y dwarfs. The fact that this is seen in (coeval, mono-metallicity) binaries demonstrates that...

  15. The Polluted Atmosphere of the White Dwarf NLTT 25792 and the Diversity of Circumstellar Environments

    Czech Academy of Sciences Publication Activity Database

    Vennes, Stephane; Kawka, Adela

    2013-01-01

    Roč. 779, č. 1 (2013), 70/1-70/10. ISSN 0004-637X R&D Projects: GA ČR GA13-14581S; GA ČR GAP209/12/0217 Institutional support: RVO:67985815 Keywords : stars * abundances * atmospheres Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 6.280, year: 2013

  16. A PATCHY CLOUD MODEL FOR THE L TO T DWARF TRANSITION

    International Nuclear Information System (INIS)

    One mechanism suggested for the L to T dwarf spectral type transition is the appearance of relatively cloud-free regions across the disk of brown dwarfs as they cool. The existence of partly cloudy regions has been supported by evidence for variability in dwarfs in the late L to early T spectral range, but no self-consistent atmosphere models of such partly cloudy objects have yet been constructed. Here, we present a new approach for consistently modeling partly cloudy brown dwarfs and giant planets. We find that even a small fraction of cloud holes dramatically alter the atmospheric thermal profile, spectra, and photometric colors of a given object. With decreasing cloudiness objects briskly become bluer in J - K and brighten in J band, as is observed at the L/T transition. Model spectra of partly cloudy objects are similar to our models with globally homogenous, but thinner, clouds. Hence, spectra alone may not be sufficient to distinguish partial cloudiness although variability and polarization measurements are potential observational signatures. Finally, we note that partial cloud cover may be an alternative explanation for the blue L dwarfs.

  17. Pressure shifts and abundance gradients in the atmosphere of the DAZ white dwarf GALEX J193156.8+011745

    CERN Document Server

    Vennes, S; Nemeth, P

    2011-01-01

    We present a detailed model atmosphere analysis of high-dispersion and high signal-to-noise ratio spectra of the heavily polluted DAZ white dwarf GALEX J1931+0117. The spectra obtained with the VLT-Kueyen/UV-Visual Echelle Spectrograph show several well-resolved Si II spectral lines enabling a study of pressure effects on line profiles. We observed large Stark shifts in silicon lines in agreement with theoretical predictions and laboratory measurements. Taking into account Stark shifts in the calculation of synthetic spectra we reduced the scatter in individual line radial velocity measurements from ~ 3 to < 1 km/s. We present revised abundances of O, Mg, Si, Ca, and Fe based on a critical review of line broadening parameters and oscillator strengths. The new measurements are generally in agreement with our previous analysis with the exception of magnesium with a revised abundance a factor of two lower than previously estimated. The magnesium, silicon and iron abundances exceed solar abundances, but the ox...

  18. Atmospheres and surfaces of small bodies and dwarf planets in the Kuiper Belt

    Directory of Open Access Journals (Sweden)

    Schaller E.L.

    2010-12-01

    Full Text Available Kuiper Belt Objects (KBOs are icy relics orbiting the sun beyond Neptune left over from the planetary accretion disk. These bodies act as unique tracers of the chemical, thermal, and dynamical history of our solar system. Over 1000 Kuiper Belt Objects (KBOs and centaurs (objects with perihelia between the giant planets have been discovered over the past two decades. While the vast majority of these objects are small ( 6-meter telescopes, have allowed for the first detailed studies of their surfaces and atmospheres. Visible and near-infrared spectroscopy of KBOs and centaurs has revealed a great diversity of surface compositions. Only the largest and coldest objects are capable of retaining volatile ices and atmospheres. Knowledge of the dynamics, physical properties, and collisional history of objects in the Kuiper belt is important for understanding solar system formation and evolution.

  19. Wave energy in white dwarf atmospheres. I - Magnetohydrodynamic energy spectra for homogeneous DB and layered DA stars

    Science.gov (United States)

    Musielak, Zdzislaw E.

    1987-01-01

    The radiative damping of acoustic and MHD waves that propagate through white dwarf photospheric layers is studied, and other damping processes that may be important for the propagation of the MHD waves are calculated. The amount of energy remaining after the damping processes have occurred in different types of waves is estimated. The results show that lower acoustic fluxes should be expected in layered DA and homogeneous DB white dwarfs than had previously been estimated. Acoustic emission manifests itself in an enhancement of the quadrupole term, but this term may become comparable to or even lower than the dipole term for cool white dwarfs. Energy carried by the acoustic waves is significantly dissipated in deep photospheric layers, mainly because of radiative damping. Acoustically heated corona cannot exist around DA and DB white dwarfs in a range T(eff) = 10,000-30,000 K and for log g = 7 and 8. However, relatively hot and massive white dwarfs could be exceptions.

  20. Accuracy of atmospheric parameters of FGK dwarfs determined by spectrum fitting

    CERN Document Server

    Ryabchikova, T; Pakhomov, Yu; Tsymbal, V; Titarenko, A; Sitnova, T; Alexeeva, S; Fossati, L; Mashonkina, L

    2015-01-01

    We performed extensive tests of the accuracy of atmospheric parameter determination for FGK stars based on the spectrum fitting procedure Spectroscopy Made Easy (SME). Our stellar sample consists of 13 objects, including the Sun, in the temperature range 5000--6600~K and metallicity range -1.4 -- +0.4. The analysed stars have the advantage of having parameters derived by interferometry. For each star we use spectra obtained with different spectrographs and different signal-to-noise ratios (S/N). For the fitting we adopted three different sets of constraints and test how the derived parameters depend upon the spectral regions (masks) used in SME. We developed and implemented in SME a new method for estimating uncertainties in the resulting parameters based on fitting residuals, partial derivatives, and data uncertainties. For stars in the 5700--6600 K range the best agreement with the effective temperatures derived by interferometry is achieved when spectrum fitting includes the H$\\alpha$ and H$\\beta$ lines, w...

  1. K2 Discovery of Young Eclipsing Binaries in Upper Scorpius: Direct Mass and Radius Determinations for the Lowest Mass Stars and Initial Characterization of an Eclipsing Brown Dwarf Binary

    Science.gov (United States)

    David, Trevor J.; Hillenbrand, Lynne A.; Cody, Ann Marie; Carpenter, John M.; Howard, Andrew W.

    2016-01-01

    We report the discovery of three low-mass double-lined eclipsing binaries in the pre-main sequence Upper Scorpius association, revealed by K2 photometric monitoring of the region over ˜78 days. The orbital periods of all three systems are K2 photometry plus multiple Keck/HIRES radial velocities (RVs) and spectroscopic flux ratios to determine fundamental stellar parameters for both the primary and secondary components of each system, along with the orbital parameters. We present tentative evidence that EPIC 203868608 is a hierarchical triple system comprised of an eclipsing pair of ˜25 MJup brown dwarfs with a wide M-type companion. If confirmed, it would constitute only the second double-lined eclipsing brown dwarf binary system discovered to date. The double-lined system EPIC 203710387 is composed of nearly identical M4.5-M5 stars with fundamentally determined masses and radii measured to better than 3% precision ({M}1=0.1183+/- 0.0028{M}⊙ , {M}2=0.1076+/- 0.0031{M}⊙ and {R}1=0.417+/- 0.010{R}⊙ , {R}2=0.450+/- 0.012{R}⊙ ) from combination of the light curve and RV time series. These stars have the lowest masses of any stellar mass double-lined eclipsing binary to date. Comparing our derived stellar parameters with evolutionary models, we suggest an age of ˜10-11 Myr for this system, in contrast to the canonical age of 3-5 Myr for the association. Finally, EPIC 203476597 is a compact single-lined system with a G8-K0 primary and a likely mid-K secondary whose lines are revealed in spectral ratios. Continued measurement of RVs and spectroscopic flux ratios will better constrain fundamental parameters and should elevate the objects to benchmark status. We also present revised parameters for the double-lined eclipsing binary UScoCTIO 5 ({M}1=0.3336+/- 0.0022{M}⊙ , {M}2=0.3200+/- 0.0022{M}⊙ and {R}1=0.862+/- 0.012, {R}2=0.852+/- 0.013{R}⊙ ), which are suggestive of a system age younger than previously reported. We discuss the implications of our

  2. Systematic NLTE study of the -2.6 < [Fe/H] < 0.2 F and G dwarfs in the solar neighbourhood. I. Stellar atmosphere parameters

    CERN Document Server

    Sitnova, T; Mashonkina, L; Chen, Y Q; Liu, F; Pakhomov, Yu; Tan, K; Bolte, M; Alexeeva, S; Grupp, F; Shi, J -R; Zhang, H -W

    2015-01-01

    We present atmospheric parameters for 51 nearby FG dwarfs uniformly distributed over the -2.60 60000) Shane/Hamilton and CFHT/ESPaDOnS observed spectra and non-local thermodynamic equilibrium (NLTE) line formation for Fe I and Fe II in the classical 1D model atmospheres. The spectroscopic method was tested with the 20 benchmark stars, for which there are multiple measurements of the infrared flux method (IRFM) Teff and their Hipparcos parallax error is -0.75, or Teff 4.20. NLTE analysis is crucial for the VMP turn-off and subgiant stars, for which the shift in log g between NLTE and LTE can be up to 0.5 dex. The obtained atmospheric parameters will be used in the forthcoming papers to determine NLTE abundances of important astrophysical elements from lithium to europium and to improve observational constraints on the chemo-dynamical models of the Galaxy evolution.

  3. Binary frequency of planet-host stars at wide separations: A new brown dwarf companion to a planet-host star

    CERN Document Server

    Lodieu, N; Bejar, V J S; Gauza, B; Ruiz, M T; Rebolo, R; Pinfield, D J; Martin, E L

    2014-01-01

    The aim of the project is to improve our knowledge on the multiplicity of planet-host stars at wide physical separations. We cross-matched approximately 6200 square degree area of the Southern sky imaged by the Visible Infrared Survey Telescope for Astronomy (VISTA) Hemisphere Survey (VHS) with the Two Micron All Sky Survey (2MASS) to look for wide common proper motion companions to known planet-host stars. We complemented our astrometric search with photometric criteria. We confirmed spectroscopically the co-moving nature of seven sources out of 16 companion candidates and discarded eight, while the remaining one stays as a candidate. Among these new wide companions to planet-host stars, we discovered a T4.5 dwarf companion at 6.3 arcmin (~9000 au) from HIP70849, a K7V star which hosts a 9 Jupiter mass planet with an eccentric orbit. We also report two new stellar M dwarf companions to one G and one metal-rich K star. We infer stellar and substellar binary frequencies for our complete sample of 37 targets of...

  4. Very Low Mass Stellar and Substellar Companions to Solar-Like Stars From MARVELS V: A Low Eccentricity Brown Dwarf from the Driest Part of the Desert, MARVELS-6b

    CERN Document Server

    De Lee, Nathan; Crepp, Justin R; Eastman, Jason; Esposito, Massimiliano; Femenía, Bruno; Fleming, Scott W; Gaudi, B Scott; Ghezzi, Luan; Hernández, Jonay I González; Lee, Brian L; Stassun, Keivan G; Wisniewski, John P; Wood-Vasey, W Michael; Agol, Eric; Prieto, Carlos Allende; Barnes, Rory; Bizyaev, Dmitry; Cargile, Phillip; Chang, Liang; Da Costa, Luiz N; De Mello, G F Porto; Ferreira, Leticia D; Gary, Bruce; Hebb, Leslie; Holtzman, Jon; Liu, Jian; Ma, Bo; Mack, Claude E; Mahadevan, Suvrath; Maia, Marcio A G; Nguyen, Duy Cuong; Oravetz, Audrey; Oravetz, Daniel J; Paegert, Martin; Pan, Kaike; Pepper, Joshua; Malanushenko, Elena; Malanushenko, Viktor; Rebolo, Rafael; Santiago, Basilio X; Schneider, Donald P; Bradley, Alaina C Shelden; Wan, Xiaoke; Wang, Ji; Zhao, Bo

    2013-01-01

    We describe the discovery of a likely brown dwarf (BD) companion with a minimum mass of 31.7 +/- 2.0 M_Jup to GSC 03546-01452 from the MARVELS radial velocity survey, which we designate as MARVELS-6b. For reasonable priors, our analysis gives a probability of 72% that MARVELS-6b has a mass below the hydrogen-burning limit of 0.072 M_Sun, and thus it is a high-confidence BD companion. It has a moderately long orbital period of 47.8929 +0.0063/-0.0062 days with a low eccentricty of 0.1442 +0.0078/-0.0073, and a semi-amplitude of 1644 +12/-13 m/s. Moderate resolution spectroscopy of the host star has determined the following parameters: T_eff = 5598 +/- 63, log g = 4.44 +/- 0.17, and [Fe/H] = +0.40 +/- 0.09. Based upon these measurements, GSC 03546-01452 has a probable mass and radius of M_star = 1.11 +/- 0.11 M_Sun and R_star = 1.06 +/- 0.23 R_Sun with an age consistent with less than ~6 Gyr at a distance of 219 +/- 21 pc from the Sun. Although MARVELS-6b is not observed to transit, we cannot definitively rule ...

  5. Planck cold clumps in the $\\lambda$ Orionis complex: I. Discovery of an extremely young Class 0 protostellar object and a proto-brown dwarf candidate in a bright rimmed clump PGCC G192.32-11.88

    CERN Document Server

    Liu, Tie; Kim, Kee-Tae; Wu, Yuefang; Lee, Chang Won; Lee, Jeong-Eun; Tatematsu, Kenichi; Choi, Minho; Juvela, Mika; Thompson, Mark; Goldsmith, Paul F; Liu, Sheng-yuan; Naomi, Hirano; Koch, Patrick; Henkel, Christian; Sanhueza, Patricio; He, JinHua; Rivera-Ingraham, Alana; Wang, Ke; Cunningham, Maria R; Tang, Ya-Wen; Lai, Shih-Ping; Yuan, Jinghua; Li, Di; Fuller, Gary; Kang, Miju; Luong, Quang Nguyen; Liu, Hauyu Baobab; Ristorcelli, Isabelle; Yang, Ji; Xu, Ye; Hirota, Tomoya; Mardones, Diego; Qin, Sheng-Li; Chen, Huei-Ru; Kwon, Woojin; Meng, FanYi; Zhang, Huawei; Kim, Mi-Ryang; Yi, Hee-Weon

    2015-01-01

    We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the $\\lambda$ Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32-11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound bright-rimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32-11.88 is externally heated and compressed. G192N probably has the lowest bolometric luminosity ($\\sim0.8$ L$_{\\sun}$) and accretion rate (6.3$\\times10^{-7}$ M$_{\\sun}$~yr$^{-1}$) when compared with other young Class 0 sources (e.g. PACS Bright Red sources (PBRs)) in the Orion complex. It has slightly larger internal luminosity ($0.21\\pm0.01$ L$_{\\sun}$) and outflow velocity ($\\sim$14 km~s$^{-1}$) than the predictions of first hydrostatic cores (FHSCs). G192N...

  6. Response of atmospheric biomarkers to NO(x)-induced photochemistry generated by stellar cosmic rays for earth-like planets in the habitable zone of M dwarf stars.

    Science.gov (United States)

    Grenfell, John Lee; Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A Beate C; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2012-12-01

    Understanding whether M dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N(2)), which leads to production of nitrogen oxides (NO(x)) in the planetary atmosphere, hence affecting biomarkers such as ozone (O(3)). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. This point should be further explored in future work with time-dependent models. We estimate the NO(x) production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O(3) formation proceeds via the reaction O+O(2)+M→O(3)+M. At high NO(x) abundances, the O atoms arise mainly from NO(2) photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O(2)). For the flaring case, O(3) is mainly destroyed via direct titration, NO+O(3)→NO(2)+O(2), and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O(3), Rayleigh scattering by the main atmospheric gases (O(2), N(2), and CO(2)) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O(3) survived all the stellar-activity scenarios considered except for the strong

  7. DISCOVERY OF AN ∼23 MJup BROWN DWARF ORBITING ∼700 AU FROM THE MASSIVE STAR HIP 78530 IN UPPER SCORPIUS

    International Nuclear Information System (INIS)

    We present the discovery of a substellar companion on a wide orbit around the ∼ 2.5 Msun star HIP 78530, which is a member of the 5 Myr old Upper Scorpius association. We have obtained follow-up imaging over two years and show that the companion and primary share common proper motion. We have also obtained JHK spectroscopy of the companion and confirm its low surface gravity, in accordance with the young age of the system. A comparison with DRIFT-PHOENIX synthetic spectra indicates an effective temperature of 2800 ± 200 K and a comparison with template spectra of young and old dwarfs indicates a spectral type of M8 ± 1. The mass of the companion is estimated to be 19-26 MJup based on its bolometric luminosity and the predictions of evolutionary models. The angular separation of the companion is 4.''5, which at the distance of the primary star, 156.7 pc, corresponds to a projected separation of ∼710 AU. This companion features one of the lowest mass ratios (∼0.009) of any known companion at separations greater than 100 AU.

  8. HIGH-CONTRAST 3.8 μm IMAGING OF THE BROWN DWARF/PLANET-MASS COMPANION TO GJ 758

    International Nuclear Information System (INIS)

    We present L'-band (3.8 μm) MMT/Clio high-contrast imaging data for the nearby star GJ 758, which was recently reported by Thalmann et al. to have one-possibly two-faint comoving companions (GJ 758B and 'C', respectively). GJ 758B is detected in two distinct data sets. Additionally, we report a possible detection of the object identified by Thalmann et al. as 'GJ 758C' in our more sensitive data set, though it is likely a residual speckle. However, if it is the same object as that reported by Thalmann et al. it cannot be a companion in a bound orbit. GJ 758B has an H - L' color redder than nearly all known L-T8 dwarfs. Based on comparisons with the COND evolutionary models, GJ 758B has T e ∼ 560 K+150K-90K and a mass ranging from ∼10-20 MJ if it is ∼1 Gyr old to ∼ 25-40 MJ if it is 8.7 Gyr old. GJ 758B is likely in a highly eccentric orbit, e ∼ 0.73+0.12-0.21, with a semimajor axis. Though GJ 758B is sometimes discussed within the context of exoplanet direct imaging, its mass is likely greater than the deuterium-burning limit and its formation may resemble that of binary stars rather than that of Jovian-mass planets.

  9. White Dwarf Critical Tests for Modified Gravity.

    Science.gov (United States)

    Jain, Rajeev Kumar; Kouvaris, Chris; Nielsen, Niklas Grønlund

    2016-04-15

    Scalar-tensor theories of gravity can lead to modifications of the gravitational force inside astrophysical objects. We exhibit that compact stars such as white dwarfs provide a unique setup to test beyond Horndeski theories of G^{3} type. We obtain stringent and independent constraints on the parameter ϒ characterizing the deviations from Newtonian gravity using the mass-radius relation, the Chandrasekhar mass limit, and the maximal rotational frequency of white dwarfs. We find that white dwarfs impose stronger constraints on ϒ than red and brown dwarfs. PMID:27127952

  10. White Dwarf Critical Tests for Modified Gravity

    Science.gov (United States)

    Jain, Rajeev Kumar; Kouvaris, Chris; Nielsen, Niklas Grønlund

    2016-04-01

    Scalar-tensor theories of gravity can lead to modifications of the gravitational force inside astrophysical objects. We exhibit that compact stars such as white dwarfs provide a unique setup to test beyond Horndeski theories of G3 type. We obtain stringent and independent constraints on the parameter ϒ characterizing the deviations from Newtonian gravity using the mass-radius relation, the Chandrasekhar mass limit, and the maximal rotational frequency of white dwarfs. We find that white dwarfs impose stronger constraints on ϒ than red and brown dwarfs.

  11. White Dwarf Critical Tests for Modified Gravity

    CERN Document Server

    Jain, Rajeev Kumar; Nielsen, Niklas Grønlund

    2015-01-01

    Scalar-tensor theories of gravity can lead to modifications of the gravitational force inside astrophysical objects. We exhibit that compact stars such as white dwarfs provide a unique set-up to test such deviations from Newtonian gravitational physics inside the stars. We obtain stringent and independent constraints on the parameter $\\Upsilon$ characterizing the deviations from gravity using the mass-radius relation, the Chandrasekhar mass limit and the maximal rotational frequency of white dwarfs. We find that white dwarfs impose stronger constraints on $\\Upsilon$ than the red and brown dwarfs.

  12. Reference study to characterise plasma and magnetic properties of ultra-cool atmospheres

    CERN Document Server

    Rodriguez-Barrera, M I; Stark, C R; Rice, A M

    2015-01-01

    Radio and X-ray emission from brown dwarfs suggest that an ionised gas and a magnetic field with a sufficient flux density must be present. We perform a reference study for late M-dwarfs, brown dwarfs and giant gas planet to identify which ultra-cool objects are most susceptible to plasma and magnetic processes. Only thermal ionisation is considered. We utilise the {\\sc Drift-Phoenix} model grid where the local atmospheric structure is determined by the global parameters T$_{\\rm eff}$, $\\log(g)$ and [M/H]. Our results show that it is not unreasonable to expect H$_{\\alpha}$ or radio emission to origin from Brown Dwarf atmospheres as in particular the rarefied upper parts of the atmospheres can be magnetically coupled despite having low degrees of thermal gas ionisation. Such ultra-cool atmospheres could therefore drive auroral emission without the need for a companion's wind or an outgassing moon. The minimum threshold for the magnetic flux density required for electrons and ions to be magnetised is well above...

  13. Habitability of terrestrial-mass planets in the HZ of M Dwarfs - I. H/He-dominated atmospheres

    Science.gov (United States)

    Owen, James E.; Mohanty, Subhanjoy

    2016-07-01

    The ubiquity of M dwarfs, combined with the relative ease of detecting terrestrial-mass planets around them, has made them prime targets for finding and characterizing planets in the `habitable zone' (HZ). However, Kepler finds that terrestrial-mass exoplanets are often born with voluminous H/He envelopes, comprising mass-fractions (Menv/Mcore) ≳1 per cent. If these planets retain such envelopes over Gyr time-scales, they will not be `habitable' even within the HZ. Given the strong X-ray/UV fluxes of M dwarfs, we study whether sufficient envelope mass can be photoevaporated away for these planets to become habitable. We improve upon previous work by using hydrodynamic models that account for radiative cooling as well as the transition from hydrodynamic to ballistic escape. Adopting a template active M dwarf XUV spectrum, including stellar evolution, and considering both evaporation and thermal evolution, we show that: (1) the mass-loss is (considerably) lower than previous estimates that use an `energy-limited' formalism and ignore the transition to Jeans escape; (2) at the inner edge of the HZ, planets with core mass ≲ 0.9 M⊕ can lose enough H/He to become habitable if their initial envelope mass-fraction is ˜1 per cent; (3) at the outer edge of the HZ, evaporation cannot remove a ˜1 per cent H/He envelope even from cores down to 0.8 M⊕. Thus, if planets form with bulky H/He envelopes, only those with low-mass cores may eventually be habitable. Cores ≳1 M⊕, with ≳1 per cent natal H/He envelopes, will not be habitable in the HZ of M dwarfs.

  14. Habitability of Terrestrial-Mass Planets in the HZ of M Dwarfs. I. H/He-Dominated Atmospheres

    CERN Document Server

    Owen, James E

    2016-01-01

    The ubiquity of M dwarfs, combined with the relative ease of detecting terrestrial-mass planets around them, has made them prime targets for finding and characterising planets in the "Habitable Zone" (HZ). However, Kepler has revealed that terrestrial-mass exoplanets are often born with voluminous H/He envelopes, comprising mass-fractions ($M_{env}/M_{core}$) $\\gtrsim 1$\\%. If these planets retain such envelopes over Gyr timescales, they will not be "habitable" even within the HZ. Given the strong X-ray/UV fluxes of M dwarfs, we study whether these planets can lose sufficient envelope-mass through photoevaporation to become habitable. We improve upon previous work by using hydrodynamic models that account for radiative cooling as well as the transition from hydrodynamic to ballistic escape. Adopting the XUV spectrum of the active M dwarf AD Leo as a template, including stellar evolution, and considering both evaporation and thermal evolution, we show that: (1) the envelope-mass lost is significantly lower tha...

  15. The Rotation Period and Magnetic Field of the T Dwarf 2MASSI J1047539+212423 Measured From Periodic Radio Bursts

    OpenAIRE

    Williams, P. K. G.; Berger, E.

    2015-01-01

    Periodic radio bursts from very low mass stars and brown dwarfs simultaneously probe their magnetic and rotational properties. The brown dwarf 2MASSI J1047539+212423 (2M 1047+21) is currently the only T dwarf (T6.5) detected at radio wavelengths. Previous observations of this source with the Arecibo observatory revealed intermittent, 100%-polarized radio pulses similar to those detected from other brown dwarfs, but were unable to constrain a pulse periodicity; previous VLA observations detect...

  16. Stark Broadening and White Dwarfs

    CERN Document Server

    Dimitrijevic, Milan S; Simic, Zoran; Sahal-Brechot, Sylvie

    2012-01-01

    White dwarf and pre-white dwarf atmospheres are one of the best examples for the application of Stark broadening research results in astrophysics, due to plasma conditions very favorable for this line broadening mechanism. For example in hot hydrogen-deficient (pre-) white dwarf stars Teff = 75 000 K - 180 000 K and log g = 5.5-8 [cgs]. Even for much cooler DA and DB white dwarfs with typical effective temperatures of 10 000 K - 20 000 K, Stark broadening is usually the dominant broadening mechanism. In this review, Stark broadening in white dwarf spectra is considered and the attention is drawn to the STARK-B database (http://stark-b.obspm.fr/), containing Stark broadening parameters needed for white dwarf spectra analysis and synthesis, as well as to the new search facilities which will provide the collective effort to develop Virtual Atomic and Molecular Data Center (VAMDC - http://vamdc.org/).

  17. DISCOVERY OF THE Y1 DWARF WISE J064723.23–623235.5

    Energy Technology Data Exchange (ETDEWEB)

    Kirkpatrick, J. Davy; Gelino, Christopher R.; Beichman, Charles A.; Mace, Gregory N. [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Cushing, Michael C.; Schneider, Adam [Department of Physics and Astronomy, MS 111, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606-3328 (United States); Tinney, C. G. [School of Physics, University of New South Wales, Sydney, NSW 2052 (Australia); Faherty, Jacqueline K., E-mail: davy@ipac.caltech.edu [Department of Astronomy, University of Chile, Camino El Observatorio 1515, Casilla 36-D Santiago (Chile)

    2013-10-20

    We present the discovery of a very cold, very low mass, nearby brown dwarf using data from the NASA Wide-field Infrared Survey Explorer (WISE). The object, WISE J064723.23–623235.5, has a very red WISE color of W1–W2 > 3.77 mag and a very red Spitzer Space Telescope color of ch1–ch2 = 2.82 ± 0.09 mag. In J{sub MKO} –ch2 color (7.58 ± 0.27 mag) it is one of the two or three reddest brown dwarfs known. Our grism spectrum from the Hubble Space Telescope (HST) confirms it to be the seventeenth Y dwarf discovered, and its spectral type of Y1 ± 0.5 makes it one of the four latest-type Y dwarfs classified. Astrometric imaging from Spitzer and HST, combined with data from WISE, provides a preliminary parallax of π = 115 ± 12 mas (d = 8.7 ± 0.9 pc) and proper motion of μ = 387 ± 25 mas yr{sup –1} based on 2.5 yr of monitoring. The spectrum implies a blue J–H color, for which model atmosphere calculations suggest a relatively low surface gravity. The best fit to these models indicates an effective temperature of 350-400 K and a mass of ∼5-30 M{sub Jup}. Kinematic analysis hints that this object may belong to the Columba moving group, which would support an age of ∼30 Myr and thus an even lower mass of <2 M{sub Jup}, but verification would require a radial velocity measurement not currently possible for a J = 22.7 mag brown dwarf.

  18. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. V. A LOW ECCENTRICITY BROWN DWARF FROM THE DRIEST PART OF THE DESERT, MARVELS-6b

    International Nuclear Information System (INIS)

    We describe the discovery of a likely brown dwarf (BD) companion with a minimum mass of 31.7 ± 2.0 MJup to GSC 03546-01452 from the MARVELS radial velocity survey, which we designate as MARVELS-6b. For reasonable priors, our analysis gives a probability of 72% that MARVELS-6b has a mass below the hydrogen-burning limit of 0.072 M☉, and thus it is a high-confidence BD companion. It has a moderately long orbital period of 47.8929+0.0063-0.0062 days with a low eccentricity of 0.1442+0.0078-0.0073, and a semi-amplitude of 1644+12-13 m s–1. Moderate resolution spectroscopy of the host star has determined the following parameters: Teff = 5598 ± 63, log g = 4.44 ± 0.17, and [Fe/H] = +0.40 ± 0.09. Based upon these measurements, GSC 03546-01452 has a probable mass and radius of M* = 1.11 ± 0.11 M☉ and R* = 1.06 ± 0.23 R☉ with an age consistent with less than ∼6 Gyr at a distance of 219 ± 21 pc from the Sun. Although MARVELS-6b is not observed to transit, we cannot definitively rule out a transiting configuration based on our observations. There is a visual companion detected with Lucky Imaging at 7.''7 from the host star, but our analysis shows that it is not bound to this system. The minimum mass of MARVELS-6b exists at the minimum of the mass functions for both stars and planets, making this a rare object even compared to other BDs. It also exists in an underdense region in both period/eccentricity and metallicity/eccentricity space.

  19. Atom-Rydberg-atom chemi-ionization processes in solar and DB white-dwarf atmospheres in the presence of (n - n')-mixing channels

    Science.gov (United States)

    Mihajlov, A. A.; Srećković, V. A.; Ignjatović, Lj. M.; Dimitrijević, M. S.

    2016-05-01

    In this paper, the rate coefficients of the chemi-ionization processes in H(1s) + H*(n, l) and He(1s2) + He*(n, l) collisions (where the principal quantum number n ≫ 1) are determined for the first time, taking into account the influence of the corresponding (n - n')-mixing processes. It is demonstrated that the inclusion of (n - n') mixing in the calculation influences the values of chemi-ionization rate coefficients significantly, particularly in the lower part of the block of Rydberg states. The interpretation of this influence is based on two existing methods of describing inelastic processes in symmetrical atom-Rydberg-atom collisions. The calculations of the chemi-ionization rate coefficients are performed for the temperature region that is characteristic of solar and DB white-dwarf atmospheres.

  20. An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres I. Formation of the G-band in metal-poor dwarf stars

    CERN Document Server

    Gallagher, A J; Bonifacio, P; Ludwig, H -G; Steffen, M; Spite, M

    2016-01-01

    Recent developments in the three-dimensional (3D) spectral synthesis code Linfor3D have meant that, for the first time, large spectral wavelength regions, such as molecular bands, can be synthesised with it in a short amount of time. A detailed spectral analysis of the synthetic G-band for several dwarf turn-off-type 3D atmospheres (5850 <= T_eff [K] <= 6550, 4.0 <= log g <= 4.5, -3.0 <= [Fe/H] <= -1.0) was conducted, under the assumption of local thermodynamic equilibrium. We also examine carbon and oxygen molecule formation at various metallicity regimes and discuss the impact it has on the G-band. Using a qualitative approach, we describe the different behaviours between the 3D atmospheres and the traditional one-dimensional (1D) atmospheres and how the different physics involved inevitably leads to abundance corrections, which differ over varying metallicities. Spectra computed in 1D were fit to every 3D spectrum to determine the 3D abundance correction. Early analysis revealed that the ...

  1. The Atmospheres of Directly Imaged Planets: Where Has All the Methane Gone?

    Science.gov (United States)

    Marley, Mark S.; Zahnle, Kevin

    2014-01-01

    Methane and ammonia both first appear at lower effective temperatures in brown dwarf atmospheres than equilibrium chemistry models would suggest. This has traditionally been understood as a consequence of vertical mixing timescales being shorter than chemical equilibration timescales in brown dwarf photospheres. Indeed the eddy diffusivity, a variable accounting for the vigor of vertical mixing, has become a standard part of the description of brown dwarf atmosphere models, along with Teff and log g. While some models have suggested that methane is less favored at lower gravity, the almost complete absence of methane in the atmospheres of directly imaged planets, such as those orbiting HR 8799, even at effective temperatures where methane is readily apparent in brown dwarf spectra, has been puzzling. To better understand the paucity of methane in low gravity atmospheres we have revisited the problem of methane chemistry and mixing. We employed a 1-D atmospheric chemistry code augmented with an updated and complete network of the chemical reactions that link CO to CH4. We find the methane abundance at altitudes at or above the effective photosphere is a strong function of surface gravity because higher g shifts the p-T structure to higher pressures (i.e., a given optical depth is proportional to p/g, a relation mitigated somewhat by pressure broadening). Thus quenching in more massive brown dwarfs occurs at a lower temperature and higher pressure, both favoring CH4. We predict that in the lowest mass young giant planets, methane will appear very late, at effective temperatures as low as 600 K rather than the 1200 K seen among field brown dwarfs. This methane deficiency has important implications for the interpretation of spectra as well as methane-based planetary companion searches, such as the NICI survey. The GPI and SPHERE surveys will test these ideas and probe atmospheric chemistry and composition in an entire new range of parameter space. A caveat is that

  2. Observational Constraints on the Origin of Metals in Cool DA-type White Dwarfs

    CERN Document Server

    Chary, R R; Becklin, E E

    1998-01-01

    We present ISOCAM 7 micron and 15 micron observations of 12 nearby white dwarfs, 6 of which have been found to have metals such as Ca, Mg and Fe in their photospheres. Our purpose was to search for an excess of infrared emission above the stellar photospheres. We find that none of the white dwarfs other than G29-38 shows a detectable infrared excess and this places strong constraints on the existence of a dusty disk around these stars. We conclude that ongoing accretion of the interstellar medium seems an unlikely explanation for the existence of metals in the photospheres of cool hydrogen atmosphere white dwarfs. The excess associated with G29-38 is 3.8+/-1.0 mJy and 2.9+/-0.6 mJy at 7 micron and 15 micron respectively. The broadband spectrum of this star strengthens the hypothesis that the infrared excess arises from a disk of particulate matter surrounding the white dwarf rather than from a cool brown dwarf companion.

  3. PROPERTIES OF THE COOLEST DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    SAUMON, DIDIER [Los Alamos National Laboratory; LEGGETT, SANDY K. [NON LANL; FREEDMAN, RICHARD S. [NON LANL; GEBALLE, THOMAS R. [NON LANL; GOLIMOWSKI, DAVID A. [NON LANL; LODIEU, NICOLAS [NON LANL; MARLEY, MARK S. [NON LANL; STEPHENS, DENISE [NON LANL; PINFIELD, DAVID J. [NON LANL; WARREN, STEPHEN J. [NON LANL

    2007-01-18

    Eleven years after the discovery of the first T dwarf, we have a population of ultracool L and T dwarfs that is large enough to show a range of atmospheric properties, as well as model atmospheres advanced enough to study these properties in detail. Since the last Cool Stars meeting, there have been observational developments which aid in these studies. they present recent mid-infrared photometry and spectroscopy from the Spitzer Space Telescope which confirms the prevalence of vertical mixing in the atmospheres of L and T dwarfs. Hence, the 700 K to 2200 K L and t dwarf photspheres require a large number of parameters for successful modeling: effective temperature, gravity, metallicity, grain sedimentation and vertical mixing efficiency. They also describe initial results of a search for ultracool dwarfs in the UKIRT Infrared Deep Sky Survey, and present the latest T dwarf found to date. They conclude with a discussion of the definition of the later-than-T spectral type, the Y dwarf.

  4. Gas Chromatography/Atmospheric Pressure Chemical Ionization-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry of Pyrolysis Oil from German Brown Coal.

    Science.gov (United States)

    Zuber, Jan; Kroll, Marius M; Rathsack, Philipp; Otto, Matthias

    2016-01-01

    Pyrolysis oil from the slow pyrolysis of German brown coal from Schöningen, obtained at a temperature of 500°C, was separated and analyzed using hyphenation of gas chromatography with an atmospheric pressure chemical ionization source operated in negative ion mode and Fourier transform ion cyclotron resonance mass spectrometry (GC-APCI-FT-ICR-MS). Development of this ultrahigh-resolving analysis method is described, that is, optimization of specific GC and APCI parameters and performed data processing. The advantages of GC-APCI-FT-ICR-MS hyphenation, for example, soft ionization, ultrahigh-resolving detection, and most important isomer separation, were demonstrated for the sample liquid. For instance, it was possible to separate and identify nine different propylphenol, ethylmethylphenol, and trimethylphenol isomers. Furthermore, homologous series of different acids, for example, alkyl and alkylene carboxylic acids, were verified, as well as homologous series of alkyl phenols, alkyl dihydroxy benzenes, and alkoxy alkyl phenols. PMID:27066076

  5. Gas Chromatography/Atmospheric Pressure Chemical Ionization-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry of Pyrolysis Oil from German Brown Coal

    Directory of Open Access Journals (Sweden)

    Jan Zuber

    2016-01-01

    Full Text Available Pyrolysis oil from the slow pyrolysis of German brown coal from Schöningen, obtained at a temperature of 500°C, was separated and analyzed using hyphenation of gas chromatography with an atmospheric pressure chemical ionization source operated in negative ion mode and Fourier transform ion cyclotron resonance mass spectrometry (GC-APCI-FT-ICR-MS. Development of this ultrahigh-resolving analysis method is described, that is, optimization of specific GC and APCI parameters and performed data processing. The advantages of GC-APCI-FT-ICR-MS hyphenation, for example, soft ionization, ultrahigh-resolving detection, and most important isomer separation, were demonstrated for the sample liquid. For instance, it was possible to separate and identify nine different propylphenol, ethylmethylphenol, and trimethylphenol isomers. Furthermore, homologous series of different acids, for example, alkyl and alkylene carboxylic acids, were verified, as well as homologous series of alkyl phenols, alkyl dihydroxy benzenes, and alkoxy alkyl phenols.

  6. Atmospheric Brown Clouds in the Himalayas: first two years of continuous observations at the Nepal-Climate Observatory at Pyramid (5079 m

    Directory of Open Access Journals (Sweden)

    P. Bonasoni

    2010-02-01

    Full Text Available South Asia is strongly influenced by the so-called Atmospheric Brown Cloud (ABC, a wide polluted layer extending from the Indian Ocean to the Himalayas during the winter and pre-monsoon seasons (November to April. This thick, grey-brown haze blanket substantially interacts with the incoming solar radiation, causing a cooling of the Earth's surface and a warming of the atmosphere, thus influencing the monsoon system and climate. In this area, the Himalayan region, particularly sensitive to climate change, offers a unique opportunity to detect global change processes and to analyse the influence of anthropogenic pollution on background atmospheric conditions through continuous monitoring activities.

    This paper provides a detailed description of the atmospheric conditions characterizing the high Himalayas, thanks to continuous observations begun in March 2006 at the Nepal Climate Observatory – Pyramid (NCO-P located at 5079 m a.s.l. on the southern foothills of Mt. Everest, in the framework of ABC-UNEP and SHARE-Ev-K2-CNR projects. Besides giving an overview of the measurement site and experimental activities, the work presents an in-depth characterization of meteorological conditions and air-mass circulation at NCO-P during the first two years of activity (March 2006–February 2008. The mean values of atmospheric pressure, temperature and wind speed recorded at the site were: 551 hPa, −3.0 °C, 4.7 m s−1, respectively. The highest seasonal values of temperature (1.7 °C and relative humidity (94% were registered during the monsoon season, which was also characterized by thick clouds present in about 80% of the afternoon hours and by a frequency of cloud-free sky less than 10%. The lowest temperature and relative humidity values were registered during winter, −6.3 °C and 22%, respectively, the season being characterised by mainly cloud-free sky conditions and rare thick clouds. The summer monsoon influenced

  7. Systematic Non-LTE Study of the -2.6 < [Fe/H] < 0.2 F and G dwarfs in the Solar Neighborhood. I. Stellar Atmosphere Parameters

    Science.gov (United States)

    Sitnova, T.; Zhao, G.; Mashonkina, L.; Chen, Y.; Liu, F.; Pakhomov, Yu.; Tan, K.; Bolte, M.; Alexeeva, S.; Grupp, F.; Shi, J.-R.; Zhang, H.-W.

    2015-08-01

    We present atmospheric parameters for 51 nearby F and G dwarf and subgiant stars uniformly distributed over the -2.60Yi et al. grid. Our final effective temperatures lie exactly in between the {T}{IRFM} scales of Alonso et al. and Casagrande et al., with a mean difference of +46 and -51 K, respectively. NLTE leads to higher surface gravity compared with that for LTE. The shift in log g is smaller than 0.1 dex for stars with [Fe/H] ≥slant -0.75, {T}{eff} ≤ 5750 K, or log g ≥ 4.20. NLTE analysis is crucial for the very metal-poor turnoff and subgiant stars, for which the shift in log g between NLTE and LTE can be up to 0.5 dex. The obtained accurate atmospheric parameters will be used in the forthcoming papers to determine NLTE abundances of important astrophysical elements from lithium to europium and to improve observational constraints on the chemodynamical models of the Galaxy evolution. Based on observations collected at the UCO/Lick Observatory, USA, and Canada-France-Hawaii Telescope.

  8. Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Greenhouse Effect in the Atmosphere of an Earthlike Planet Orbiting an M-Dwarf Star

    CERN Document Server

    Grenfell, J L; Patzer, B; Rauer, H; Segura, A; Stadelmann, A; Stracke, B; Titz, R; Von Paris, P; Grenfell, John Lee; Griessmeier, Jean-Mathias; Patzer, Beate; Rauer, Heike; Segura, Antigona; Stadelmann, Anja; Stracke, Barbara; Titz, Ruth; Paris, Philip von

    2007-01-01

    Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject to high levels of galactic cosmic rays (GCRs) which produce nitrogen oxides in earthlike atmospheres. We investigate to what extent this NOx may modify biomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well as related compounds such as water (H2O) (essential for life) and methane (CH4) (which has both abiotic and biotic sources) . Our model results suggest that such signals are robust, changing in the M-star world atmospheric column by up to 20% due to the GCR NOx effects compared to an M-star run without GCR effects and can therefore survive at least the effects of galactic cosmic rays. We have not however investigated stellar cosmic rays here. CH4 levels are about 10 times higher than on the Earth related to a lowering in hydroxyl (OH) in response to changes in UV. The increase is less than reported in previous studies. This difference arose partly because we used different biogenic input. For example, we employed 23% ...

  9. A new algorithm for brown and black carbon identification and organic carbon detection in fine atmospheric aerosols by a multi-wavelength Aethalometer

    Directory of Open Access Journals (Sweden)

    F. Esposito

    2012-02-01

    Full Text Available A novel approach for the analysis of aerosol absorption coefficient measurements is presented. A 7-wavelenghts aethalometer has been employed to identify brown carbon (BrC and black carbon (BC and to detect organic carbon (OC in fine atmospheric aerosols (PM2.5. The Magee Aethalometer estimates the BC content in atmospheric particulate by measuring the light attenuation in the aerosols accumulated on a quartz filter, at the standard wavelength λ = 0.88 μm. The known Magee algorithm is based on the hypothesis of a mass absorption coefficient inversely proportional to the wavelength. The new algorithm has been developed and applied to the whole spectral range; it verifies the spectral absorption behavior and, thus, it distinguishes between black and brown carbon. Moreover, it allows also to correct the absorption estimation at the UV wavelength commonly used to qualitatively detect the presence of mixed hydrocarbons. The algorithm has been applied to data collected in Agri Valley, located in Southern Italy, where torched crude oil undergoes a pre-treatment process.

    The Magee Aethalometer has been set to measure Aerosol absorption coefficients τaer (λ, t every 5 min. Wavelength dependence of τaer (λ, t has been analyzed by a best-fit technique and, excluding UV-wavelengths, both the absorption Angstrom coefficient α and the BC (or BrC concentration have been determined. Finally, daily histograms of α provide information on optical properties of carbonaceous aerosol, while the extrapolation at UV-wavelengths gives information on the presence of semivolatile organic carbon (OC particles.

  10. The Impact of Clouds and Hazes in Substellar Atmospheres

    Science.gov (United States)

    Morley, Caroline; Fortney, Jonathan J.; Marley, Mark S.

    2016-01-01

    The formation of clouds significantly alters the spectra of cool substellar atmospheres from terrestrial planets to brown dwarfs. In cool planets like Earth and Jupiter, volatile species like water and ammonia condense to form ice clouds. In hot planets and brown dwarfs, iron and silicates instead condense, forming dusty clouds. Irradiated methane-rich planets may have substantial hydrocarbon hazes. During my thesis, I have studied the impact of clouds and hazes in a variety of substellar objects. First, I present results for cool brown dwarfs including clouds previously neglected in model atmospheres. Model spectra that include sulfide and salt clouds can match the spectra of T dwarf atmospheres; water ice clouds will alter the spectra of the newest and coldest brown dwarfs, the Y dwarfs. These sulfide/salt and ice clouds potentially drive spectroscopic variability in these cool objects, and this variability should be distinguishable from variability caused by hot spots.Next, I present results for small, cool exoplanets between the size of Earth and Neptune, so-called super Earths. They likely have sulfide and salt clouds and also have photochemical hazes caused by stellar irradiation. Vast resources have been dedicated to characterizing the handful of super Earths accessible to current telescopes, yet of the planets smaller than Neptune studied to date, all have radii in the near-infrared consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. Very thick, lofted clouds of salts or sulfides in high metallicity (1000× solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes with a range of particle sizes also create featureless transmission spectra at lower metallicities. I show that despite these challenges, there are promising avenues for understanding this class of small planets: by observing the thermal emission and reflectivity of

  11. A brown dwarf orbiting an M-dwarf

    DEFF Research Database (Denmark)

    Bachelet, E.; Fouqué, P.; Albrow, M.D.;

    2012-01-01

    Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted. Aims. MOA 2009-BLG-411 was detected on August 5, 2009 by the M...

  12. Atmospheric electrification in dusty, reactive gases in the solar system and beyond

    CERN Document Server

    Helling, Ch; Honary, F; Diver, D A; Aplin, K; Dobbs-Dixon, I; Ebert, U; Inutsuka, S; Gordillo-Vazquez, F J; Littlefair, S

    2016-01-01

    Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. Instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) Brown Dwarfs which are amongst the oldest objects in the universe. Despite of this diversity, solar system planets, extrasolar planets and Brown Dwarfs have broadly similar global temperatures between 300K and 2500K. In consequence, clouds of different chemical species form in their atmospheres. While the details of these clouds differ, the fundamental physical processes are the same. Further to this, all these objects were observed to produce radio and X-ray emission. While both kinds of radiation are well studied on Earth and to a lesser extent on the solar system planets, the occurrence of emission that potentially originate from accelerated electrons o...

  13. 49 new T dwarfs identified using methane imaging

    OpenAIRE

    Cardoso, C. V.; Burningham, B.; Smart, R. L.; van Spaandonk, L.; Baker, D; Smith, L. C.; Andrei, A. H.; Bucciarelli, B.; Dhital, S; Jones, H.R.A.; Lattanzi, M.G.; Magazzu, A.; Pinfield, D. J.; Tinney, C. G.

    2015-01-01

    We present the discovery of 49 new photometrically classified T dwarfs from the combination of large infrared and optical surveys combined with follow-up TNG photometry. We used multi-band infrared and optical photometry from the UKIRT and Sloan Digital Sky Surveys to identify possible brown dwarf candidates, which were then confirmed using methane filter photometry. We have defined a new photometric conversion between CH4s - CH4l colour and spectral type for T4 to T8 brown dwarfs based on a ...

  14. Characterization of the atmosphere of the hot Jupiter HAT-P-32Ab and the M-dwarf companion HAT-P-32B

    CERN Document Server

    Zhao, Ming; Wright, Jason T; Knutson, Heather A; Burrows, Adam; Fortney, Johnathan; Ngo, Henry; Fulton, Benjamin J; Baranec, Christoph; Riddle, Reed; Law, Nicholas M; Muirhead, Philip S; Hinkley, Sasha; Showman, Adam P; Curtis, Jason; Burruss, Rick

    2014-01-01

    We report secondary eclipse photometry of the hot Jupiter HAT-P-32Ab, taken with Hale/WIRC in H and Ks bands and with Spitzer/IRAC at 3.6 and 4.5 micron. We carried out adaptive optics imaging of the planet host star HAT-P-32A and its companion HAT-P-32B in the near-IR and the visible. We clearly resolve the two stars from each other and find a separation of 2.923" +/- 0. 004" and a position angle 110.64 deg +/- 0.12 deg. We measure the flux ratios of the binary in g' r' i' z' and H & Ks bands, and determine Teff = 3565 +/- 82 K for the companion star, corresponding to an M1.5 dwarf. We use PHOENIX stellar atmosphere models to correct the dilution of the secondary eclipse depths of the hot Jupiter due to the presence of the M1.5 companion. We also improve the secondary eclipse photometry by accounting for the non-classical, flux-dependent nonlinearity of the WIRC IR detector in the H band. We measure planet-to-star flux ratios of 0.090 +/- 0.033%, 0.178 +/- 0.057%, 0.364 +/- 0.016%, and 0.438 +/- 0.020% i...

  15. The Effect of a Strong Stellar Flare on the Atmospheric Chemistry of an Earth-like Planet Orbiting an M dwarf

    CERN Document Server

    Segura, Antígona; Meadows, Victoria; Kasting, James; Hawley, Suzanne

    2010-01-01

    Main sequence M stars pose an interesting problem for astrobiology: their abundance in our galaxy makes them likely targets in the hunt for habitable planets, but their strong chromospheric activity produces high energy radiation and charged particles that may be detrimental to life. We studied the impact of the 1985 April 12 flare from the M dwarf, AD Leonis (AD Leo), simulating the effects from both UV radiation and protons on the atmospheric chemistry of a hypothetical, Earth-like planet located within its habitable zone. Based on observations of solar proton events and the Neupert effect we estimated a proton flux associated with the flare of $5.9\\times 10^{8}$ protons cm$^{-2}$ sr$^{-1}$ s$^{-1}$ for particles with energies >10 MeV. Then we calculated the abundance of nitrogen oxides produced by the flare by scaling the production of these compounds during a large solar proton event called the "Carrington event". The simulations were performed using a 1-D photochemical model coupled to a 1-D radiative/co...

  16. 49 new T dwarfs identified using methane imaging

    CERN Document Server

    Cardoso, C V; Smart, R L; van Spaandonk, L; Baker, D; Smith, L C; Andrei, A H; Bucciarelli, B; Dhital, S; Jones, H R A; Lattanzi, M G; Magazzu, A; Pinfield, D J; Tinney, C G

    2015-01-01

    We present the discovery of 49 new photometrically classified T dwarfs from the combination of large infrared and optical surveys combined with follow-up TNG photometry. We used multi-band infrared and optical photometry from the UKIRT and Sloan Digital Sky Surveys to identify possible brown dwarf candidates, which were then confirmed using methane filter photometry. We have defined a new photometric conversion between CH4s - CH4l colour and spectral type for T4 to T8 brown dwarfs based on a part of the sample that has been followed up using methane photometry and spectroscopy. Using methane differential photometry as a proxy for spectral type for T dwarfs has proved to be a very efficient technique. Of a subset of 45 methane selected brown dwarfs that were observed spectroscopically, 100% were confirmed as T dwarfs. Future deep imaging surveys will produce large samples of faint brown dwarf candidates, for which spectroscopy will not be feasible. When broad wavelength coverage is unavailable, methane imaging...

  17. Kinetic equilibrium of iron in the atmospheres of cool dwarf stars II. Weak Fe I lines in the solar spectrum

    CERN Document Server

    Gehren, T; Shi, J

    2001-01-01

    NLTE line formation calculations of FeI in the solar atmosphere are extended to include weak optical lines. Previously established atomic models are used to discriminate between different ways of treating collisional interaction processes. To derive a common solar FeI abundance from both strong and weak lines, fine-tuning of the microturbulence velocity parameter and the van-der- Waals damping constants is required. The solar FeI abundances based on all available f-values are dominated by the large scatter already found for the stronger lines. In particular the bulk of the data from the work of May et al. and O'Brian et al. is not adequate for accurate abundance work. Based on f-values measured by the Hannover and Oxford groups alone, the FeI LTE abundances are eps(FeI,Sun)=7.57 for the empirical and eps(FeI,Sun) = 7.48 ... 7.51 for the line-blanketed solar model. The solar Fe ionization equilibrium obtained for different atomic and atmospheric models rules out NLTE atomic models with a low efficiency of hydr...

  18. Atmospheric Brown Clouds in the Himalayas: first two years of continuous observations at the Nepal Climate Observatory-Pyramid (5079 m

    Directory of Open Access Journals (Sweden)

    P. Bonasoni

    2010-08-01

    and, for coarse particles, during the post-monsoon (0.07 cm−3. At NCO-P, the synoptic-scale circulation regimes present three principal contributions: Westerly, South-Westerly and Regional, as shown by the analysis of in-situ meteorological parameters and 5-day LAGRANTO back-trajectories.

    The influence of the brown cloud (AOD>0.4 extending over Indo–Gangetic Plains up to the Himalayan foothills has been evaluated by analysing the in-situ concentrations of the ABC constituents. This analysis revealed that brown cloud hot spots mainly influence the South Himalayas during the pre-monsoon, in the presence of very high levels of atmospheric compounds (BC: 1974.1 ng m−3, PM1: 23.5 μg m−3, scattering coefficient: 57.7 Mm−1, coarse particles: 0.64 cm−3, O3: 69.2 ppbv, respectively. During this season 20% of the days were characterised by a strong brown cloud influence during the afternoon, leading to a 5-fold increased in the BC and PM1 values, in comparison with seasonal means. Our investigations provide clear evidence that, especially during the pre-monsoon, the southern side of the high Himalayan valleys represent a "direct channel" able to transport brown cloud pollutants up to 5000 m a.s.l., where the pristine atmospheric composition can be strongly influenced.

  19. A large spectroscopic sample of L and T dwarfs from UKIDSS LAS: peculiar objects, binaries, and space density

    CERN Document Server

    Marocco, F; Day-Jones, A C; Pinfield, D J; Lucas, P W; Burningham, B; Zhang, Z H; Smart, R L; Gomes, J I; Smith, L

    2015-01-01

    We present the spectroscopic analysis of a large sample of late-M, L, and T dwarfs from UKIDSS. Using the YJHK photometry from ULAS and the red-optical photometry from SDSS we selected a sample of 262 brown dwarf candidates and we followed-up 196 of them using X-shooter on the VLT. The large wavelength coverage (0.30-2.48 $\\mu$m) and moderate resolution (R~5000-9000) of X-shooter allowed us to identify peculiar objects including 22 blue L dwarfs, 2 blue T dwarfs, and 2 low gravity M dwarfs. Using a spectral indices-based technique we identified 27 unresolved binary candidates, for which we determined the spectral type of the potential components via spectral deconvolution. The spectra allowed us to measure the equivalent width of the prominent absorption features and to compare them to atmospheric models. Cross-correlating the spectra with a radial velocity standard, we measured the radial velocity for our targets, and we determined the distribution of the sample, which is centred at -1.7$\\pm$1.2 km s$^{-1}$ ...

  20. Characterization of the atmosphere of the hot Jupiter HAT-P-32Ab and the M-dwarf companion HAT-P-32B

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Ming; Wright, Jason T.; Curtis, Jason [Department of Astronomy and Astrophysics, Pennsylvania State University, PA 16802 (United States); O' Rourke, Joseph G.; Knutson, Heather A.; Ngo, Henry [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Burrows, Adam [Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544 (United States); Fortney, Johnathan [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Fulton, Benjamin J.; Baranec, Christoph [Institute for Astronomy, University of Hawai' i at Mānoa, Hilo, HI 96720-2700 (United States); Riddle, Reed; Hinkley, Sasha [Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Law, Nicholas M. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 (United States); Muirhead, Philip S. [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Showman, Adam P. [Department of Planetary Sciences and Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Burruss, Rick, E-mail: mingzhao@psu.edu [Jet Propulsion Laboratory, California Institute of Technology, CA 91109 (United States)

    2014-12-01

    We report secondary eclipse photometry of the hot Jupiter HAT-P-32Ab, taken with Hale/Wide-field Infra-Red Camera (WIRC) in H and K{sub S} bands and with Spitzer/IRAC at 3.6 and 4.5 μm. We carried out adaptive optics imaging of the planet host star HAT-P-32A and its companion HAT-P-32B in the near-IR and the visible. We clearly resolve the two stars from each other and find a separation of 2.''923 ± 0.''004 and a position angle 110.°64 ± 0.°12. We measure the flux ratios of the binary in g'r'i'z' and H and K{sub S} bands, and determine T {sub eff}= 3565 ± 82 K for the companion star, corresponding to an M1.5 dwarf. We use PHOENIX stellar atmosphere models to correct the dilution of the secondary eclipse depths of the hot Jupiter due to the presence of the M1.5 companion. We also improve the secondary eclipse photometry by accounting for the non-classical, flux-dependent nonlinearity of the WIRC IR detector in the H band. We measure planet-to-star flux ratios of 0.090% ± 0.033%, 0.178% ± 0.057%, 0.364% ± 0.016%, and 0.438% ± 0.020% in the H, K{sub S} , 3.6 and 4.5 μm bands, respectively. We compare these with planetary atmospheric models, and find they prefer an atmosphere with a temperature inversion and inefficient heat redistribution. However, we also find that the data are equally well described by a blackbody model for the planet with T {sub p} = 2042 ± 50 K. Finally, we measure a secondary eclipse timing offset of 0.3 ± 1.3 minutes from the predicted mid-eclipse time, which constrains e = 0.0072{sub −0.0064}{sup +0.0700} when combined with radial velocity data and is more consistent with a circular orbit.

  1. Characterization of the atmosphere of the hot Jupiter HAT-P-32Ab and the M-dwarf companion HAT-P-32B

    International Nuclear Information System (INIS)

    We report secondary eclipse photometry of the hot Jupiter HAT-P-32Ab, taken with Hale/Wide-field Infra-Red Camera (WIRC) in H and KS bands and with Spitzer/IRAC at 3.6 and 4.5 μm. We carried out adaptive optics imaging of the planet host star HAT-P-32A and its companion HAT-P-32B in the near-IR and the visible. We clearly resolve the two stars from each other and find a separation of 2.''923 ± 0.''004 and a position angle 110.°64 ± 0.°12. We measure the flux ratios of the binary in g'r'i'z' and H and KS bands, and determine T eff= 3565 ± 82 K for the companion star, corresponding to an M1.5 dwarf. We use PHOENIX stellar atmosphere models to correct the dilution of the secondary eclipse depths of the hot Jupiter due to the presence of the M1.5 companion. We also improve the secondary eclipse photometry by accounting for the non-classical, flux-dependent nonlinearity of the WIRC IR detector in the H band. We measure planet-to-star flux ratios of 0.090% ± 0.033%, 0.178% ± 0.057%, 0.364% ± 0.016%, and 0.438% ± 0.020% in the H, KS , 3.6 and 4.5 μm bands, respectively. We compare these with planetary atmospheric models, and find they prefer an atmosphere with a temperature inversion and inefficient heat redistribution. However, we also find that the data are equally well described by a blackbody model for the planet with T p = 2042 ± 50 K. Finally, we measure a secondary eclipse timing offset of 0.3 ± 1.3 minutes from the predicted mid-eclipse time, which constrains e = 0.0072−0.0064+0.0700 when combined with radial velocity data and is more consistent with a circular orbit.

  2. Measuring M dwarf Winds with DAZ White Dwarfs

    CERN Document Server

    Debes, J H

    2006-01-01

    Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, show evidence for ongoing accretion of material onto their surfaces. Some DAZs are known to have unresolved M dwarf companions, which could account for the observed accretion through a stellar wind. I combine observed Ca abundances of the DAZs with information on the orbital separation of their M dwarf companions to infer the mass loss rate of the M dwarfs. I find that for three of the six known DAZs with M dwarf companions, a stellar wind can plausibly explain the observed accretion on the white dwarfs assuming Bondi-Hoyle accretion of solar abundance stellar winds on the order of 10$^{-14}-10^{-16}\\Msun$ yr$^{-1}$. The rest of the sample have companions with orbits $\\gtorder$ 1~AU, and require companion mass loss rates of $> 10^{-11}\\Msun$ yr$^{-1}$. I conclude that there must be an alternative explanation for accretion of material onto DAZs with widely separated companions. The inferred winds for two of the close binaries are orders of magn...

  3. Temperature and salinity profiles from CTD casts from the NOAA Ship RONALD H. BROWN in the NE and SE Pacific as part of the East Pacific Investigations of Climate Processes in support of the Coupled Ocean-Atmosphere from 05 September 2001 to 25 October 2001 (NODC Accession 0000657)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — CTD and other data were collected from the NOAA Ship RONALD H. BROWN in the NE and SE Pacific from 05 September 2001 to 25 October 2001. CTD data consist of...

  4. THREE NEW ECLIPSING WHITE-DWARF-M-DWARF BINARIES DISCOVERED IN A SEARCH FOR TRANSITING PLANETS AROUND M-DWARFS

    International Nuclear Information System (INIS)

    We present three new eclipsing white-dwarf/M-dwarf binary systems discovered during a search for transiting planets around M-dwarfs. Unlike most known eclipsing systems of this type, the optical and infrared emission is dominated by the M-dwarf components, and the systems have optical colors and discovery light curves consistent with being Jupiter-radius transiting planets around early M-dwarfs. We detail the PTF/M-dwarf transiting planet survey, part of the Palomar Transient Factory (PTF). We present a graphics processing unit (GPU)-based box-least-squares search for transits that runs approximately 8 × faster than similar algorithms implemented on general purpose systems. For the discovered systems, we decompose low-resolution spectra of the systems into white-dwarf and M-dwarf components, and use radial velocity measurements and cooling models to estimate masses and radii for the white dwarfs. The systems are compact, with periods between 0.35 and 0.45 days and semimajor axes of approximately 2 R☉ (0.01 AU). The M-dwarfs have masses of approximately 0.35 M☉, and the white dwarfs have hydrogen-rich atmospheres with temperatures of around 8000 K and have masses of approximately 0.5 M☉. We use the Robo-AO laser guide star adaptive optics system to tentatively identify one of the objects as a triple system. We also use high-cadence photometry to put an upper limit on the white-dwarf radius of 0.025 R☉ (95% confidence) in one of the systems. Accounting for our detection efficiency and geometric factors, we estimate that 0.08%-0.05%+0.10% (90% confidence) of M-dwarfs are in these short-period, post-common-envelope white-dwarf/M-dwarf binaries where the optical light is dominated by the M-dwarf. The lack of detections at shorter periods, despite near-100% detection efficiency for such systems, suggests that binaries including these relatively low-temperature white dwarfs are preferentially found at relatively large orbital radii. Similar eclipsing binary

  5. Atmospheric Electrification in Dusty, Reactive Gases in the Solar System and Beyond

    Science.gov (United States)

    Helling, Christiane; Harrison, R. Giles; Honary, Farideh; Diver, Declan A.; Aplin, Karen; Dobbs-Dixon, Ian; Ebert, Ute; Inutsuka, Shu-ichiro; Gordillo-Vazquez, Francisco J.; Littlefair, Stuart

    2016-04-01

    Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. Instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) brown dwarfs which are amongst the oldest objects in the Universe. Despite this diversity, solar system planets, extrasolar planets and brown dwarfs have broadly similar global temperatures between 300 and 2500 K. In consequence, clouds of different chemical species form in their atmospheres. While the details of these clouds differ, the fundamental physical processes are the same. Further to this, all these objects were observed to produce radio and X-ray emissions. While both kinds of radiation are well studied on Earth and to a lesser extent on the solar system planets, the occurrence of emissions that potentially originate from accelerated electrons on brown dwarfs, extrasolar planets and protoplanetary disks is not well understood yet. This paper offers an interdisciplinary view on electrification processes and their feedback on their hosting environment in meteorology, volcanology, planetology and research on extrasolar planets and planet formation.

  6. Atmospheric Electrification in Dusty, Reactive Gases in the Solar System and Beyond

    Science.gov (United States)

    Helling, Christiane; Harrison, R. Giles; Honary, Farideh; Diver, Declan A.; Aplin, Karen; Dobbs-Dixon, Ian; Ebert, Ute; Inutsuka, Shu-ichiro; Gordillo-Vazquez, Francisco J.; Littlefair, Stuart

    2016-07-01

    Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. Instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) brown dwarfs which are amongst the oldest objects in the Universe. Despite this diversity, solar system planets, extrasolar planets and brown dwarfs have broadly similar global temperatures between 300 and 2500 K. In consequence, clouds of different chemical species form in their atmospheres. While the details of these clouds differ, the fundamental physical processes are the same. Further to this, all these objects were observed to produce radio and X-ray emissions. While both kinds of radiation are well studied on Earth and to a lesser extent on the solar system planets, the occurrence of emissions that potentially originate from accelerated electrons on brown dwarfs, extrasolar planets and protoplanetary disks is not well understood yet. This paper offers an interdisciplinary view on electrification processes and their feedback on their hosting environment in meteorology, volcanology, planetology and research on extrasolar planets and planet formation.

  7. White dwarf-red dwarf binaries in the Galaxy

    NARCIS (Netherlands)

    Besselaar, E.J.M. van den

    2007-01-01

    This PhD thesis shows several studies on white dwarf - red dwarf binaries. White dwarfs are the end products of most stars and red dwarfs are normal hydrogen burning low-mass stars. White dwarf - red dwarf binaries are both blue (white dwarf) and red (red dwarf). Together with the fact that they are

  8. LHS 2803B: A VERY WIDE MID-T DWARF COMPANION TO AN OLD M DWARF IDENTIFIED FROM PAN-STARRS1

    International Nuclear Information System (INIS)

    We report the discovery of a wide (∼1400 AU projected separation), common proper motion companion to the nearby M dwarf LHS 2803 (PSO J207.0300-13.7422). This object was discovered during our census of the local T dwarf population using Pan-STARRS1 and Two Micron All Sky Survey data. Using the Infrared Telescope Facility/SpeX near-infrared spectroscopy, we classify the secondary to be spectral type T5.5. University of Hawaii 2.2 m/SuperNova Integral Field Spectrograph optical spectroscopy indicates that the primary has a spectral type of M4.5, with approximately solar metallicity and no measurable Hα emission. We use this lack of activity to set a lower age limit for the system of 3.5 Gyr. Using a comparison with chance alignments of brown dwarfs and nearby stars, we conclude that the two objects are unlikely to be a chance association. The primary's photometric distance of 21 pc and its proper motion implies thin disk kinematics. Based on these kinematics and its metallicity, we set an upper age limit for the system of 10 Gyr. Evolutionary model calculations suggest that the secondary has a mass of 72±47 MJup, temperature of 1120 ± 80 K, and log g = 5.4 ± 0.1 dex. Model atmosphere fitting to the near-IR spectrum gives similar physical parameters of 1100 K and log g = 5.0.

  9. A Targeted Search for Peculiarly Red L and T Dwarfs in SDSS, 2MASS, and WISE: Discovery of a Possible L7 Member of the TW Hydrae Association

    CERN Document Server

    Kellogg, Kendra; Geissler, Kerstin; Hicks, Shannon; Kirkpatrick, J Davy; Kurtev, Radostin

    2015-01-01

    We present first results from a targeted search for brown dwarfs with unusual red colors indicative of peculiar atmospheric characteristics. These include objects with low surface gravities or with unusual dust content or cloud properties. From a positional cross-match of SDSS, 2MASS and WISE, we have identified 40 candidate peculiar early L to early T dwarfs that are either new objects or have not been identified as peculiar through prior spectroscopy. Using low resolution spectra, we confirm that 10 of the candidates are either peculiar or potential L/T binaries. With a J-Ks color of 2.62 +/- 0.15 mag, one of the new objects --- the L7 dwarf 2MASS J11193254-1137466 --- is among the reddest field dwarfs currently known. Its proper motion and photometric parallax indicate that it is a possible member of the TW Hydrae moving group. If confirmed, it would its lowest-mass (5--6 MJup) free-floating member. We also report a new T dwarf, 2MASS J22153705+2110554, that was previously overlooked in the SDSS footprint....

  10. New White Dwarf Stars in the Sloan Digital Sky Survey Data Release 10

    CERN Document Server

    Kepler, S O; Koester, Detlev; Ourique, Gustavo; Kleinman, Scot J; Romero, Alejandra Daniela; Nitta, Atsuko; Eisenstein, Daniel J; Costa, José Eduardo da Silveira; Külebi, Baybars; Jordan, Stefan; Dufour, Patrick; Giommi, Paolo; Rebassa-Mansergas, Alberto

    2014-01-01

    We report the discovery of 9 088 new spectroscopically confirmed white dwarfs and subdwarfs in the Sloan Digital Sky Survey Data Release 10. We obtain Teff, log g and mass for hydrogen atmosphere white dwarf stars (DAs) and helium atmosphere white dwarf stars (DBs), and estimate the calcium/helium abundances for the white dwarf stars with metallic lines (DZs) and carbon/helium for carbon dominated spectra DQs. We found 1 central star of a planetary nebula, 2 new oxygen spectra on helium atmosphere white dwarfs, 71 DQs, 42 hot DO/PG1159s, 171 white dwarf+main sequence star binaries, 206 magnetic DAHs, 327 continuum dominated DCs, 397 metal polluted white dwarfs, 450 helium dominated white dwarfs, 647 subdwarfs and 6887 new hydrogen dominated white dwarf stars.

  11. Deep z-band observations of the coolest Y dwarf

    Energy Technology Data Exchange (ETDEWEB)

    Kopytova, Taisiya G.; Crossfield, Ian J. M.; Deacon, Niall R.; Brandner, Wolfgang; Buenzli, Esther; Bayo, Amelia; Schlieder, Joshua E.; Manjavacas, Elena; Kopon, Derek [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Biller, Beth A., E-mail: kopytova@mpia.de [Institute for Astronomy, University of Edinburgh, Blackford Hill View, Edinburgh EH9 3HJ (United Kingdom)

    2014-12-10

    WISE J085510.83-071442.5 (hereafter, WISE 0855-07) is the coolest Y dwarf known to date and is located at a distance of 2.31 ± 0.08 pc, giving it the fourth largest parallax of any known star or brown dwarf system. We report deep z-band observations of WISE 0855-07 using FORS2 on UT1/Very Large Telescope. We do not detect any counterpart to WISE 0855-07 in our z-band images and estimate a brightness upper limit of AB mag > 24.8 (F {sub ν} < 0.45 μJy) at 910 ± 65 nm with 3σ confidence. We combine our z-band upper limit with previous near- and mid-infrared photometry to place constraints on the atmospheric properties of WISE 0855-07 via comparison to models which implement water clouds in the atmospheres of T {sub eff} < 300 K substellar objects. We find that none of the available models that implement water clouds can completely reproduce the observed spectral energy distribution of WISE 0855-07. Every model significantly disagrees with the (3.6 μm/4.5 μm) flux ratio and at least one other bandpass. Since methane is predicted to be the dominant absorber at 3-4 μm, these mismatches might point to an incorrect or incomplete treatment of methane in current models. We conclude that (a) WISE0855-07 has T {sub eff} ∼ 200-250 K, (b) <80% of its surface is covered by clouds, and (c) deeper observations, and improved models of substellar evolution, atmospheres, clouds, and opacities will be necessary to better characterize this object.

  12. A non-grey analytical model for irradiated atmospheres. II: Analytical vs. numerical solutions

    CERN Document Server

    Parmentier, Vivien; Fortney, Jonathan J; Marley, Mark S

    2013-01-01

    The recent discovery and characterization of the diversity of the atmospheres of exoplanets and brown dwarfs calls for the development of fast and accurate analytical models. In this paper we first quantify the accuracy of the analytical solution derived in paper I for an irradiated, non-grey atmosphere by comparing it to a state-of-the-art radiative transfer model. Then, using a grid of numerical models, we calibrate the different coefficients of our analytical model for irradiated solar-composition atmospheres of giant exoplanets and brown dwarfs. We show that the so-called Eddington approximation used to solve the angular dependency of the radiation field leads to relative errors of up to 5% on the temperature profile. For grey or semi-grey atmospheres we show that the presence of a convective zone has a limited effect on the radiative atmosphere above it and leads to modifications of the radiative temperature profile of order 2%. However, for realistic non-grey planetary atmospheres, the presence of a con...

  13. Naming Disney's Dwarfs.

    Science.gov (United States)

    Sidwell, Robert T.

    1980-01-01

    Discusses Disney's version of the folkloric dwarfs in his production of "Snow White" and weighs the Disney rendition of the dwarf figure against the corpus of traits and behaviors pertaining to dwarfs in traditional folklore. Concludes that Disney's dwarfs are "anthropologically true." (HOD)

  14. WASP-80b has a dayside within the T-dwarf range

    CERN Document Server

    Triaud, Amaury H M J; Ehrenreich, David; Herrero, Enrique; Lendl, Monika; Anderson, David R; Cameron, Andrew Collier; Delrez, Laetitia; Demory, Brice-Olivier; Hellier, Coel; Heng, Keving; Jehin, Emmanuel; Maxted, Pierre F L; Pollacco, Don; Queloz, Didier; Ribas, Ignasi; Smalley, Barry; Smith, Alexis M S; Udry, Stephane

    2015-01-01

    WASP-80b is a missing link in the study of exo-atmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterisation, thanks to its host star's properties. We observed the planet through transit and during occultation with Warm Spitzer. Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 $\\mu$m Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L-T transition, our results would imply this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour-magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of thos...

  15. A Survey for H-alpha Emission from Late L dwarfs and T dwarfs

    CERN Document Server

    Pineda, J Sebastian; Kirkpatrick, J Davy; Cotter, Garret; Kao, Melodie M; Mooley, Kunal

    2016-01-01

    Recently, studies of brown dwarfs have demonstrated that they possess strong magnetic fields and have the potential to produce radio and optical auroral emissions powered by magnetospheric currents. This emission provides the only window on magnetic fields in the coolest brown dwarfs and identifying additional benchmark objects is key to constraining dynamo theory in this regime. To this end, we conducted a new red optical (6300 - 9700 Angstrom) survey with the Keck telescopes looking for H-alpha emission from a sample of late L dwarfs and T dwarfs. Our survey gathered optical spectra for 29 targets, 18 of which did not have previous optical spectra in the literature, greatly expanding the number of moderate resolution (R~2000) spectra available at these spectral types. Combining our sample with previous surveys, we confirm an H-alpha detection rate of 9.2 (+3.5/-2.1) % for L and T dwarfs in the optical spectral range of L4 - T8. This detection rate is consistent with the recently measured detection rate for ...

  16. Characterizing Exoplanet Atmospheres : A Complete Line List for Phosphine

    Science.gov (United States)

    Sousa-Silva, C.; Yurchenko, S. N.; Tennyson, J.

    2013-09-01

    The ability to characterise the atmospheres of cool stars, brown dwarfs and exoplanets requires fundamental data for all species contributing significantly to their opacity. However, with notable exceptions such as water and ammonia, existing molecular line lists are not sufficiently accurate or complete to allow for a full spectroscopic analysis of these bodies. ExoMol (www.exomol.com [1]) is a project that aims to rectify this by generating comprehensive line lists for all molecules likely to be detected in the atmospheres of cool astrophysical objects in the foreseeable future. The spectral data is generated by employing ab initio quantum mechanical methods, performing empirical refinement based on experimental spectroscopic data and harnessing high performance computing. Here we present our work on phosphine, (PH3), an equilateral pyramidal molecule (the phosphorus analogue to ammonia). Phosphine is known to be important for the atmospheres of giant-planets, cool stars and many other astronomical bodies. Rotational transition features of phosphine have been found in the far- infrared spectra of Saturn and Jupiter [2, 3], where it is a marker for vertical convection zones. A computed room temperature line list of phosphine is presented here [4], illustrated in the accompanying figure 1. This line list is a precursor to a high temperature equivalent to be produced in the near future, necessary for the analysis of cool stars and brown dwarfs. All the transitions' energy levels and Einstein A-coefficients were computed using the program TROVE [5].

  17. The Galactic M Dwarf Flare Rate

    OpenAIRE

    Hilton, Eric J.; Hawley, Suzanne L.; Kowalski, Adam F.; Holtzman, Jon

    2010-01-01

    M dwarfs are known to flare on timescales from minutes to hours, with flux increases of several magnitudes in the blue/near-UV. These frequent, powerful events, which are caused by magnetic reconnection, will have a strong observational signature in large, time-domain surveys. The radiation and particle fluxes from flares may also exert a significant influence on the atmospheres of orbiting planets, and affect their habitability. We present a statistical model of flaring M dwarfs in the Galax...

  18. SDSS J111010.01+011613.1: A New Planetary-Mass T Dwarf Member of the AB Doradus Moving Group

    CERN Document Server

    Gagné, Jonathan; Faherty, Jacqueline K; Lafrenière, David; Doyon, René; Filippazzo, Joseph C; Bowsher, Emily; Nicholls, Christine P

    2015-01-01

    We present a new radial velocity measurement that, together with a trigonometric parallax, proper motion and signs of low gravity from the literature, confirms that SDSS J111010.01+011613.1 is a new T5.5 bona fide member of AB Doradus. Fitting $\\lambda/\\Delta\\lambda$ $\\approx$ 6000 FIRE spectroscopy in the 1.20-1.33 $\\mu$m region to BT-Settl atmosphere models yielded a radial velocity of $7.5 \\pm 3.8$ km s$^{-1}$. At such a young age (110-130 Myr), current evolution models predict a mass of $\\sim$ 10-12 $M_{\\mathrm{Jup}}$, thus placing SDSS J1110+0116 well into the planetary-mass regime. We compare the fundamental properties of SDSS J1110+0116 with a sequence of seven recently identified M8-T5 brown dwarf bona fide or high-confidence candidate members of AB Doradus. We also note that its near-infrared $J-K$ color is redder than field T5-T6 brown dwarfs, however its absolute $J$-band magnitude is similar to them. SDSS J1110+0116 is one of the few age-calibrated T dwarfs known to date, as well as one of the coo...

  19. Attribution of aerosol light absorption to black carbon, brown carbon, and dust in China ? interpretations of atmospheric measurements during EAST-AIRE

    OpenAIRE

    Yang, M.; S. G. Howell; Zhuang, J.; Huebert, B. J.

    2008-01-01

    Black carbon, brown carbon, and mineral dust are three of the most important light absorbing aerosols. Their optical properties differ greatly and are distinctive functions of the wavelength of light. Most optical instruments that quantify light absorption, however, are unable to distinguish one type of absorbing aerosol from another. It is thus instructive to separate total absorption from these different light absorbers to gain a better understanding of the optical characteristics of each a...

  20. First T dwarfs in the VISTA Hemisphere Survey

    CERN Document Server

    Lodieu, N; Day-Jones, A; Scholz, R -D; Marocco, F; Koposov, S; Navascues, D Barrado y; Lucas, P W; Cruz, P; Lillo, J; Jones, H; Perez-Garrido, A; Ruiz, M T; Pinfield, D; Rebolo, R; Bejar, V J S; Boudreault, S; Emerson, J P; Banerji, M; Gonzalez-Solares, E; Hodgkin, S T; McMahon, R; Canty, J; Contreras, C

    2012-01-01

    The aim of the project is to improve our current knowledge of the density of T dwarfs and the shape of the substellar initial mass function by identifying a magnitude-limited sample of T dwarfs in the full southern sky. We present the results of a photometric search aimed at discovering cool brown dwarfs in the Southern sky imaged at infrared wavelengths by the Visible and Infrared Survey Telescope for Astronomy (VISTA) and the Wide Infrared Survey Explorer (WISE) satellite mission. We combined the first data release (DR1) of the VISTA Hemisphere Survey (VHS) and the WISE preliminary data release to extract candidates with red mid-infrared colours and near- to mid-infrared colours characteristics of cool brown dwarfs. The VHS DR1 vs WISE search returned tens of T dwarf candidates, 13 of which are presented here, including two previously published in the literature and five new ones confirmed spectroscopically with spectral types between T4.5 and T8. We estimate that the two T6 dwarfs lie within 16 pc and the ...