WorldWideScience

Sample records for brown dwarf atmospheres

  1. Atmospheres of Brown Dwarfs

    Science.gov (United States)

    Wang, Ruoyan; Seay, Christopher

    2018-01-01

    We construct a grid of brown dwarf model atmospheres spanning a wide range of atmospheric metallicity (0.3x ≤ met ≤ 100x), C/O ratios (0.25x ≤ C/O ≤ 2.5x), and cloud properties, encompassing atmospheres of effective temperatures 200 ≤ Teff ≤ 2400 K and gravities 2.5 ≤ log g ≤ 5.5. We produce the expected temperature-pressure profiles and emergent spectra from an atmosphere in radiative-convective equilibrium. We can then compare our predicted spectra to observations and retrieval results to aid in their predictions and influence future missions and telescopic observations. In our poster we briefly describe our modeling methodology and present our progress on model grid construction, spanning solar and subsolar C/O and metallicity.

  2. FINGERING CONVECTION AND CLOUDLESS MODELS FOR COOL BROWN DWARF ATMOSPHERES

    International Nuclear Information System (INIS)

    Tremblin, P.; Amundsen, D. S.; 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 types 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 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 H 2 -H 2 , H 2 -He, H 2 O, CO, CO 2 , CH 4 , NH 3 , 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 NH 3 quenching are taken into account. T dwarf spectra still have some reddening in, e.g., J–H, compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust

  3. FINGERING CONVECTION AND CLOUDLESS MODELS FOR COOL BROWN DWARF ATMOSPHERES

    Energy Technology Data Exchange (ETDEWEB)

    Tremblin, P.; Amundsen, D. S.; Mourier, P.; Baraffe, I.; Chabrier, G.; Drummond, B. [Astrophysics Group, University of Exeter, EX4 4QL Exeter (United Kingdom); Homeier, D. [Ecole Normale Supérieure de Lyon, CRAL, UMR CNRS 5574, F-69364 Lyon Cedex 07 (France); Venot, O., E-mail: tremblin@astro.ex.ac.uk, E-mail: pascal.tremblin@cea.fr [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)

    2015-05-01

    This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral types 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 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 H{sub 2}-H{sub 2}, H{sub 2}-He, H{sub 2}O, CO, CO{sub 2}, CH{sub 4}, NH{sub 3}, 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 NH{sub 3} quenching are taken into account. T dwarf spectra still have some reddening in, e.g., J–H, compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust.

  4. Measuring Atmospheric Abundances and Rotation of a Brown Dwarf with a Measured Mass and Radius

    Science.gov (United States)

    Birkby, Jayne

    2015-08-01

    There are no cool brown dwarfs with both a well-characterized atmosphere and a measured mass and radius. LHS 6343, a brown dwarf transiting one member of an M+M binary in the Kepler field, provides the first opportunity to tie theoretical atmospheric models to the observed brown dwarf mass-radius diagram. We propose four half-nights of observations with NIRSPAO in 2015B to measure spectral features in LHS 6343 C by detecting the relative motions of absorption features during the system's orbit. In addition to abundances, we will directly measure the brown dwarf's projected rotational velocity and mass.

  5. A data-driven approach for retrieving temperatures and abundances in brown dwarf atmospheres

    OpenAIRE

    Line, MR; Fortney, JJ; Marley, MS; Sorahana, S

    2014-01-01

    © 2014. The American Astronomical Society. All rights reserved. Brown dwarf spectra contain a wealth of information about their molecular abundances, temperature structure, and gravity. We present a new data driven retrieval approach, previously used in planetary atmosphere studies, to extract the molecular abundances and temperature structure from brown dwarf spectra. The approach makes few a priori physical assumptions about the state of the atmosphere. The feasibility of the approach is fi...

  6. Understanding Brown Dwarf Variability

    Science.gov (United States)

    Marley, Mark S.

    2013-01-01

    Surveys of brown dwarf variability continue to find that roughly half of all brown dwarfs are variable. While variability is observed amongst all types of brown dwarfs, amplitudes are typically greatest for L-T transition objects. In my talk I will discuss the possible physical mechanisms that are responsible for the observed variability. I will particularly focus on comparing and contrasting the effects of changes in atmospheric thermal profile and cloud opacity. The two different mechanisms will produce different variability signatures and I will discuss the extent to which the current datasets constrain both mechanisms. By combining constraints from studies of variability with existing spectral and photometric datasets we can begin to construct and test self-consistent models of brown dwarf atmospheres. These models not only aid in the interpretation of existing objects but also inform studies of directly imaged giant planets.

  7. Sonora: A New Generation Model Atmosphere Grid for Brown Dwarfs and Young Extrasolar Giant Planets

    Science.gov (United States)

    Marley, Mark S.; Saumon, Didier; Fortney, Jonathan J.; Morley, Caroline; Lupu, Roxana Elena; Freedman, Richard; Visscher, Channon

    2017-01-01

    Brown dwarf and giant planet atmospheric structure and composition has been studied both by forward models and, increasingly so, by retrieval methods. While indisputably informative, retrieval methods are of greatest value when judged in the context of grid model predictions. Meanwhile retrieval models can test the assumptions inherent in the forward modeling procedure. In order to provide a new, systematic survey of brown dwarf atmospheric structure, emergent spectra, and evolution, we have constructed a new grid of brown dwarf model atmospheres. We ultimately aim for our grid to span substantial ranges of atmospheric metallilcity, C/O ratios, cloud properties, atmospheric mixing, and other parameters. Spectra predicted by our modeling grid can be compared to both observations and retrieval results to aid in the interpretation and planning of future telescopic observations. We thus present Sonora, a new generation of substellar atmosphere models, appropriate for application to studies of L, T, and Y-type brown dwarfs and young extrasolar giant planets. The models describe the expected temperature-pressure profile and emergent spectra of an atmosphere in radiative-convective equilibrium for ranges of effective temperatures and gravities encompassing 200 less than or equal to T(sub eff) less than or equal to 2400 K and 2.5 less than or equal to log g less than or equal to 5.5. In our poster we briefly describe our modeling methodology, enumerate various updates since our group's previous models, and present our initial tranche of models for cloudless, solar metallicity, and solar carbon-to-oxygen ratio, chemical equilibrium atmospheres. These models will be available online and will be updated as opacities and cloud modeling methods continue to improve.

  8. Brown dwarf distances and atmospheres: Spitzer Parallaxes and the Keck/NIRSPEC upgrade

    Science.gov (United States)

    Martin, Emily C.

    2018-01-01

    Advances in infrared technology have been essential towards improving our understanding of the solar neighborhood, revealing a large population of brown dwarfs, which span the mass regime between planets and stars. My thesis combines near-infrared (NIR) spectroscopic and astrometric analysis of nearby low-mass stars and brown dwarfs with instrumentation work to upgrade the NIRSPEC instrument for the Keck II Telescope. I will present results from a program using Spitzer/IRAC data to measure precise locations and distances to 22 of the coldest and closest brown dwarfs. These distances allow us to constrain absolute physical properties, such as mass, radius, and age, of free-floating planetary-mass objects through comparison to atmospheric and evolutionary models. NIR spectroscopy combined with the Spitzer photometry reveals a detailed look into the atmospheres of brown dwarfs and gaseous extrasolar planets. Additionally, I will discuss the improvements we are making to the NIRSPEC instrument at Keck. NIRSPEC is a NIR echelle spectrograph, capable of R~2000 and R~25,000 observations in the 1-5 μm range. As part of the upgrade, I performed detector characterization, optical design of a new slit-viewing camera, mechanical testing, and electronics design. NIRSPEC’s increased efficiency will allow us to obtain moderate- and high-resolution NIR spectra of objects up to a magnitude fainter than the current NIRSPEC design. Finally, I will demonstrate the utility of a NIR laser frequency comb as a high-resolution calibrator. This new technology will revolutionize precision radial velocity measurements in the coming decade.

  9. A SEARCH FOR PHOTOMETRIC VARIABILITY IN L- AND T-TYPE BROWN DWARF ATMOSPHERES

    International Nuclear Information System (INIS)

    Khandrika, Harish; Burgasser, Adam J.; Melis, Carl; Luk, Christopher; Bowsher, Emily; Swift, Brandon

    2013-01-01

    Using the Gemini infrared camera on the 3 m Shane telescope at Lick Observatory, we have searched for broadband J and K' photometric variability for a sample of 15 L- and T-type brown dwarfs, including 7 suspected spectral binaries. Four of the dwarfs—2MASS J0939–2448, 2MASS J1416+1348A, 2MASS J1711+2232, and 2MASS J2139+0220—exhibit statistically significant variations over timescales ranging from ∼0.5 hr to 6 days. Our detection of variability in 2MASS J2139+0220 confirms that reported by Radigan et al., and periodogram and phase dispersion minimization analysis also confirms a variability period of approximately 7.6 ± 0.2 hr. Remarkably, two of the four variables are known or candidate binary systems, including 2MASS J2139+0220, for which we find only marginal evidence of radial velocity variation over the course of a year. This result suggests that some spectral binary candidates may appear as such due to the blending of cloudy and non-cloudy regions in a single ''patchy'' atmosphere. Our results are consistent with an overall variability fraction of 35% ± 5%, with no clear evidence of greater variability among brown dwarfs at the L dwarf/T dwarf transition.

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

    International Nuclear Information System (INIS)

    Stark, C. R.; Helling, Ch.; Rimmer, P. B.; Diver, D. A.

    2013-01-01

    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, H 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

  11. 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.

  12. 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.

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

    DEFF Research Database (Denmark)

    Juncher, Diana

    M-dwarfs are very attractive targets when searching for new exoplanets. Unfortunately, they are also very difficult to model since their temperatures are low enough for dust clouds to form in their atmospheres. Because the properties of an exoplanet cannot be determined without knowing the proper......M-dwarfs are very attractive targets when searching for new exoplanets. Unfortunately, they are also very difficult to model since their temperatures are low enough for dust clouds to form in their atmospheres. Because the properties of an exoplanet cannot be determined without knowing......-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 their clouds and found that their synthetic spectra fit the observed spectra of mid to late type M-dwarfs and early type L-dwarfs well. With additional development into even cooler regimes, they could be used to characterize the atmospheres of exoplanets and aid us in our search for the kind of chemical...

  14. Benchmarking Brown Dwarf Models With a Non-irradiated Transiting Brown Dwarf in Praesepe

    Science.gov (United States)

    Beatty, Thomas; Marley, Mark; Line, Michael; Gizis, John

    2018-05-01

    We wish to use 9.4 hours of Spitzer time to observe two eclipses, one each at 3.6um and 4.5um, of the transiting brown dwarf AD 3116b. AD 3116b is a 54.2+/-4.3 MJ, 1.08+/-0.07 RJ object on a 1.98 day orbit about a 3200K M-dwarf. Uniquely, AD 3116 and its host star are both members of Praesepe, a 690+/-60 Myr old open cluster. AD 3116b is thus one of two transiting brown dwarfs for which we have a robust isochronal age that is not dependent upon brown dwarf evolutionary models, and the youngest brown dwarf for which this is the case. Importantly, the flux AD 3116b receives from its host star is only 0.7% of its predicted internal luminosity (Saumon & Marley 2008). This makes AD 3116b the first known transiting brown dwarf that simultaneously has a well-defined age, and that receives a negligible amount of external irradiation, and a unique laboratory to test radius and luminosity predictions from brown dwarf evolutionary models. Our goal is to measure the emission from the brown dwarf. AD 3116b should have large, 25 mmag, eclipse depths in the Spitzer bandpasses, and we expect to measure them with a precision of +/-0.50 mmag at 3.6um and +/-0.54 mmag at 4.5um. This will allow us to make measure AD 3116b?s internal effective temperature to +/-40K. We will also use the upcoming Gaia DR2 parallaxes to measure AD 3116b's absolute IRAC magnitudes and color, and hence determine the cloud properties of the atmosphere. As the only known brown dwarf with an independently measured mass, radius, and age, Spitzer measurements of AD 3116b's luminosity and clouds will provide a critical benchmark for brown dwarf observation and theory.

  15. The brown dwarf kinematics project

    Science.gov (United States)

    Faherty, Jackie K.

    2010-10-01

    Brown dwarfs are a recent addition to the plethora of objects studied in Astronomy. With theoretical masses between 13 and 75 MJupiter , they lack sustained stable Hydrogen burning so they never join the stellar main sequence. They have physical properties similar to both planets and low-mass stars so studies of their population inform on both. The distances and kinematics of brown dwarfs provide key statistical constraints on their ages, moving group membership, absolute brightnesses, evolutionary trends, and multiplicity. Yet, until my thesis, fundamental measurements of parallax and proper motion were made for only a relatively small fraction of the known population. To address this deficiency, I initiated the Brown Dwarf Kinematics (BDKP). Over the past four years I have re-imaged the majority of spectroscopically confirmed field brown dwarfs (or ultracool dwarfs---UCDs) and created the largest proper motion catalog for ultracool dwarfs to date. Using new astrometric information I examined population characteristics such as ages calculated from velocity dispersions and correlations between kinematics and colors. Using proper motions, I identified several new wide co-moving companions and investigated binding energy (and hence formation) limitations as well as the frequency of hierarchical companions. Concurrently over the past four years I have been conducting a parallax survey of 84 UCDs including those showing spectral signatures of youth, metal-poor brown dwarfs, and those within 20 pc of the Sun. Using absolute magnitude relations in J,H, and K, I identified overluminous binary candidates and investigated known flux-reversal binaries. Using current evolutionary models, I compared the MK vs J-K color magnitude diagram to model predictions and found that the low-surface gravity dwarfs are significantly red-ward and underluminous of predictions and a handful of late-type T dwarfs may require thicker clouds to account for their scatter.

  16. Unusual Slowly Rotating Brown Dwarfs Discovered through Precision Spitzer Photometry

    Science.gov (United States)

    Heinze, Aren; Metchev, S.

    2014-01-01

    Many brown dwarfs exhibit low-amplitude rotationally modulated variability due to photospheric inhomogeneities caused by condensate clouds in their atmospheres. The Spitzer Space Telescope 'Weather on Other Worlds' (WoW) project has monitored 44 brown dwarfs at unprecedented photometric precision from space. We present one of several important new results from WoW: the discovery of brown dwarfs with unexpectedly slow rotation periods. While most brown dwarfs have periods of 2-12 hours, we have identified two with well-constrained periods of 13±1 and >20 hours, respectively, and 2 others that show more tentative evidence of longer than 20-hour periods. By serving as almost non-rotating standards, these objects will allow more accurate calibration of spectroscopic measurements of brown dwarfs' projected rotational velocities. The existence of such slowly-rotating objects also constrains models of brown dwarf formation and angular momentum evolution.

  17. A Panchromatic View of Brown Dwarf Aurorae

    Energy Technology Data Exchange (ETDEWEB)

    Pineda, J. Sebastian [University of Colorado Boulder, Laboratory for Atmospheric and Space Physics, 3665 Discovery Drive, Boulder CO, 80303 (United States); Hallinan, Gregg; Kao, Melodie M. [California Institute of Technology, Department of Astronomy, 1200 E. California Avenue, Pasadena CA, 91125 (United States)

    2017-09-01

    Stellar coronal activity has been shown to persist into the low-mass star regime, down to late M-dwarf spectral types. However, there is now an accumulation of evidence suggesting that at the end of the main sequence, there is a transition in the nature of the magnetic activity from chromospheric and coronal to planet-like and auroral, from local impulsive heating via flares and MHD wave dissipation to energy dissipation from strong large-scale magnetospheric current systems. We examine this transition and the prevalence of auroral activity in brown dwarfs through a compilation of multiwavelength surveys of magnetic activity, including radio, X-ray, and optical. We compile the results of those surveys and place their conclusions in the context of auroral emission as a consequence of large-scale magnetospheric current systems that accelerate energetic electron beams and drive the particles to impact the cool atmospheric gas. We explore the different manifestations of auroral phenomena, like H α , in brown dwarf atmospheres and define their distinguishing characteristics. We conclude that large-amplitude photometric variability in the near-infrared is most likely a consequence of clouds in brown dwarf atmospheres, but that auroral activity may be responsible for long-lived stable surface features. We report a connection between auroral H α emission and quiescent radio emission in electron cyclotron maser instability pulsing brown dwarfs, suggesting a potential underlying physical connection between quiescent and auroral emissions. We also discuss the electrodynamic engines powering brown dwarf aurorae and the possible role of satellites around these systems both to power the aurorae and seed the magnetosphere with plasma.

  18. Brown Dwarf Variability: What's Varying and Why?

    Science.gov (United States)

    Marley, Mark Scott

    2014-01-01

    Surveys by ground based telescopes, HST, and Spitzer have revealed that brown dwarfs of most spectral classes exhibit variability. The spectral and temporal signatures of the variability are complex and apparently defy simplistic classification which complicates efforts to model the changes. Important questions include understanding if clearings are forming in an otherwise uniform cloud deck or if thermal perturbations, perhaps associated with breaking gravity waves, are responsible. If clouds are responsible how long does it take for the atmospheric thermal profile to relax from a hot cloudy to a cooler cloudless state? If thermal perturbations are responsible then what atmospheric layers are varying? How do the observed variability timescales compare to atmospheric radiative, chemical, and dynamical timescales? I will address such questions by presenting modeling results for time-varying partly cloudy atmospheres and explore the importance of various atmospheric processes over the relevant timescales for brown dwarfs of a range of effective temperatures. Regardless of the origin of the observed variability, the complexity seen in the atmospheres of the field dwarfs hints at the variability that we may encounter in the next few years in directly imaged young Jupiters. Thus understanding the nature of variability in the field dwarfs, including sensitivity to gravity and metallicity, is of particular importance for exoplanet characterization.

  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. Brown dwarfs as dark galactic halos

    International Nuclear Information System (INIS)

    Adams, F.C.; Walker, T.P.

    1990-01-01

    The possibility that the dark matter in galactic halos can consist of brown dwarf stars is considered. The radiative signature for such halos consisting solely of brown dwarfs is calculated, and the allowed range of brown dwarf masses, the initial mass function (IMF), the stellar properties, and the density distribution of the galactic halo are discussed. The prediction emission from the halo is compared with existing observations. It is found that, for any IMF of brown dwarfs below the deuterium burning limit, brown dwarf halos are consistent with observations. Brown dwarf halos cannot, however, explain the recently observed near-IR background. It is shown that future satellite missions will either detect brown dwarf halos or place tight constraints on the allowed range of the IMF. 30 refs

  1. Brown dwarfs and black holes

    International Nuclear Information System (INIS)

    Tarter, J.C.

    1978-01-01

    The astronomical missing-mass problem (the discrepancy between the dynamical mass estimate and the sum of individual masses in large groupings) is considered, and possible explanations are advanced. The existence of brown dwarfs (stars not massive enough to shine by nuclear burning) and black holes (extremely high density matter contraction such that gravitation allows no light emission) thus far provides the most plausible solutions

  2. Looking for the Coldest Atmospheres: a Search for Planetary Mass Companions around T and Y Brown Dwarfs

    Science.gov (United States)

    Fontanive, Clemence

    2017-08-01

    We propose to obtain WFC3/IR imaging of the very coolest brown dwarfs (T planetary-mass companions to these objects. Companions discovered by this program would likely be analogues of the 250 K brown dwarf WISE 0855 and would provide vital benchmark objects for theoretical models, closing the gap in mass and temperature between brown dwarfs and planets. Finding such an object as a member of a binary system would be even more valuable as it would allow for the measurement of dynamical masses. We recently placed the first constraints to date on the binary frequency for brown dwarfs with spectral types >T8. This program will triple our current sample size, a requirement in order to confirm our current results and compare substellar binary properties for various spectral type and age populations. The WFC3/IR plate will allow us to probe near equal-mass binaries down to separations of 0.2 (2-3 AU for the typical distances of our targets). True cool companions should show strong absorption around 1.4 um as a result of the deep water absorption band observed at that wavelength in substellar spectra. We therefore propose observations in the WFC3 F127M and F139M filters which will allow us to robustly identify bona fide candidates and distinguish them from background stars based on this spectral feature. Most of our targets lack suitable NGS AO guide stars or LGS AO tip-tilt stars to be observed with ground-based telescopes, and the 1.4 um water band is often unobservable from the ground due to telluric water absorption. WFC3 on HST is thus the only instrument suitable for these observations.

  3. 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

  4. Thermochemical modelling of brown dwarf discs

    NARCIS (Netherlands)

    Greenwood, A. J.; Kamp, I.; Waters, L. B. F. M.; Woitke, P.; Thi, W.-F.; Rab, Ch.; Aresu, G.; Spaans, M.

    The physical properties of brown dwarf discs, in terms of their shapes and sizes, are still largely unexplored by observations. ALMA has by far the best capabilities to observe these discs in sub-mm CO lines and dust continuum, while also spatially resolving some discs. To what extent brown dwarf

  5. 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.

  6. Microlensing Binaries with Candidate Brown Dwarf Companions

    DEFF Research Database (Denmark)

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

    2012-01-01

    masses of the brown dwarf companions are 0.02 ± 0.01 M⊙ and 0.019 ± 0.002 M⊙ for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively, and both companions are orbiting low-mass M dwarf host stars. More microlensing brown dwarfs are expected to be detected as the number of lensing events...

  7. AEOLUS: A MARKOV CHAIN MONTE CARLO CODE FOR MAPPING ULTRACOOL ATMOSPHERES. AN APPLICATION ON JUPITER AND BROWN DWARF HST LIGHT CURVES

    Energy Technology Data Exchange (ETDEWEB)

    Karalidi, Theodora; Apai, Dániel; Schneider, Glenn; Hanson, Jake R. [Steward Observatory, Department of Astronomy, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Pasachoff, Jay M., E-mail: tkaralidi@email.arizona.edu [Hopkins Observatory, Williams College, 33 Lab Campus Drive, Williamstown, MA 01267 (United States)

    2015-11-20

    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 5 μm 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-band HST light curves of 2MASS J21392676+0220226 and 2MASS J0136565+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.

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

    NARCIS (Netherlands)

    Montet, B.T.; Johnson, J.A.; Fortney, J.J.; Desert, J.-M.

    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

  9. 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

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

    OpenAIRE

    Montet, B.T.; Johnson, J.A.; Fortney, J.J.; Desert, J.-M.

    2016-01-01

    © 2016. The American Astronomical Society. All rights reserved.. 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 atmospher...

  11. The periodicities in the infrared excess of G29-38 - An oscillating brown dwarf?

    International Nuclear Information System (INIS)

    Marley, M.S.; Lunine, J.I.; Hubbard, W.B.

    1990-01-01

    The oscillatory behavior of brown dwarfs has been investigated. The observed periodicities in the infrared excess of the white dwarf Giclas 29-38 are consistent with low-degree, intermediate radial order p-mode oscillations of a brown dwarf companion to the white dwarf. These oscillation modes have the correct frequencies, act on observable layers of the atmosphere, and may be excited to sufficient amplitudes to explain the observations. 14 refs

  12. Atmospheric Habitable Zones in Y Dwarf Atmospheres

    Energy Technology Data Exchange (ETDEWEB)

    Yates, Jack S.; Palmer, Paul I. [School of GeoSciences, University of Edinburgh (United Kingdom); Biller, Beth; Cockell, Charles S., E-mail: j.s.yates@ed.ac.uk [Centre for Exoplanet Science, University of Edinburgh (United Kingdom)

    2017-02-20

    We use a simple organism lifecycle model to explore the viability of an atmospheric habitable zone (AHZ), with temperatures that could support Earth-centric life, which sits above an environment that does not support life. To illustrate our model, we use a cool Y dwarf atmosphere, such as WISE J085510.83–0714442.5, whose 4.5–5.2 μ m spectrum shows absorption features consistent with water vapor and clouds. We allow organisms to adapt to their atmospheric environment (described by temperature, convection, and gravity) by adopting different growth strategies that maximize their chance of survival and proliferation. We assume a constant upward vertical velocity through the AHZ. We found that the organism growth strategy is most sensitive to the magnitude of the atmospheric convection. Stronger convection supports the evolution of more massive organisms. For a purely radiative environment, we find that evolved organisms have a mass that is an order of magnitude smaller than terrestrial microbes, thereby defining a dynamical constraint on the dimensions of life that an AHZ can support. Based on a previously defined statistical approach, we infer that there are of the order of 10{sup 9} cool Y brown dwarfs in the Milky Way, and likely a few tens of these objects are within 10 pc from Earth. Our work also has implications for exploring life in the atmospheres of temperate gas giants. Consideration of the habitable volumes in planetary atmospheres significantly increases the volume of habitable space in the galaxy.

  13. Brown dwarfs in retrogradely precessing cataclysmic variables?

    Directory of Open Access Journals (Sweden)

    Martin E.L.

    2011-07-01

    Full Text Available We compare Smoothed Particle Hydrodynamic simulations of retrogradely precessing accretion disks that have a white dwarf primary and a main sequence secondary with observational data and with theory on retrograde precession via tidal torques like those by the Moon and the Sun on the Earth [1, 2]. Assuming the primary does not accrete much of the mass lost from the secondary, we identify the theoretical low mass star/brown dwarf boundary. We find no observational candidates in our study that could qualify as brown dwarfs.

  14. Search for brown dwarfs in the IRAS data bases

    International Nuclear Information System (INIS)

    Low, F.J.

    1986-01-01

    A report is given on the initial searches for brown dwarf stars in the IRAS data bases. The paper was presented to the workshop on 'Astrophysics of brown dwarfs', Virginia, USA, 1985. To date no brown dwarfs have been discovered in the solar neighbourhood. Opportunities for future searches with greater sensitivity and different wavelengths are outlined. (U.K.)

  15. 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

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

    International Nuclear Information System (INIS)

    Gizis, John E.; Castro, Philip J.; Faherty, Jacqueline K.; Liu, Michael C.; Aller, Kimberly M.; Shaw, John D.; Vrba, Frederick J.; Harris, Hugh C.; Deacon, Niall R.

    2012-01-01

    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. 0 2). Near-infrared photometry and spectroscopy reveals that this is one of the reddest (2MASS J – K s 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 (K s = 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.

  17. Characterizing Water Ice Clouds on the Coldest Known Brown Dwarf

    Science.gov (United States)

    Luhman, Kevin; Burgasser, Adam; Cushing, Michael; Esplin, Taran; Fortney, Jonathan; Hardegree-Ullman, Kevin; Marley, Mark; Morley, Caroline; Schneider, Adam; Trucks, Jesica

    2014-12-01

    We have conducted a search for high proper motion brown dwarfs using multi-epoch all-sky mid-infrared images from the WISE satellite. Through this work, we have discovered an object with a parallactic distance of 2.3 pc and a temperature of 250 K, making it the 4th closest neighbor of the Sun, and the coldest known brown dwarf. Because of its extreme proximity and temperature, it represents an unparalleled laboratory for studying planet-like atmospheres in an unexplored temperature regime. We propose to photometrically monitor this object with IRAC to 1) detect and characterize water ice clouds in its atmosphere via the short-term variations induced during rotation and 2) constrain the long-term evolution of its clouds across a period of months.

  18. Models of surface convection and dust clouds in brown dwarfs

    International Nuclear Information System (INIS)

    Freytag, B; Allard, F; Ludwig, H-G; Homeier, D; Steffen, M

    2008-01-01

    The influence of dust grains on the atmospheres of brown dwarfs is visible in observed spectra. To investigate what prevents the dust grains from falling down, or how fresh condensable material is mixed up in the atmosphere to allow new grains to form, we performed 2D radiation-hydrodynamics simulations with CO5BOLD of the upper part of the convection zone and the atmosphere containing the dust cloud layers. We find that unlike in models of Cepheids, the convective overshoot does not play a major role. Instead, the mixing in the dust clouds is controlled by gravity waves.

  19. POLARIMETRIC DETECTION OF EXOPLANETS TRANSITING T AND L BROWN DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Sengupta, Sujan, E-mail: sujan@iiap.res.in [Indian Institute of Astrophysics, Koramangala 2nd Block, Bangalore 560 034 (India)

    2016-10-01

    While scattering of light by atoms and molecules yields large amounts of polarization at the B-band of both T and L dwarfs, scattering by dust grains in the cloudy atmosphere of L dwarfs gives rise to significant polarization at the far-optical and infrared 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 profiles of these objects during the transit phase and estimate the peak amplitude of polarization that occurs during the inner contact points of the transit ingress/egress phase. It is found that peak polarization in the range of 0.2%–1.0% at I and J band may arise of cloudy L dwarfs occulted by Earth-size or larger exoplanets. Such an amount of polarization is higher than what can be produced by rotation-induced oblateness of even rapidly rotating L dwarfs. Hence, I suggest that time-resolved imaging polarization could be a potential technique for detecting transiting exoplanets around L dwarfs.

  20. POLARIMETRIC DETECTION OF EXOPLANETS TRANSITING T AND L BROWN DWARFS

    International Nuclear Information System (INIS)

    Sengupta, Sujan

    2016-01-01

    While scattering of light by atoms and molecules yields large amounts of polarization at the B-band of both T and L dwarfs, scattering by dust grains in the cloudy atmosphere of L dwarfs gives rise to significant polarization at the far-optical and infrared 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 profiles of these objects during the transit phase and estimate the peak amplitude of polarization that occurs during the inner contact points of the transit ingress/egress phase. It is found that peak polarization in the range of 0.2%–1.0% at I and J band may arise of cloudy L dwarfs occulted by Earth-size or larger exoplanets. Such an amount of polarization is higher than what can be produced by rotation-induced oblateness of even rapidly rotating L dwarfs. Hence, I suggest that time-resolved imaging polarization could be a potential technique for detecting transiting exoplanets around L dwarfs.

  1. Population II brown dwarfs and dark haloes

    International Nuclear Information System (INIS)

    Zinnecker, H.

    1986-01-01

    Opacity-limited fragmentation is investigated as a function of the dust-to-gas ratio and it is found that the characteristic protostellar mass Msub(*) is metallicity-dependent. This dependence is such that, for the low metallicity gas out of which the stars of Population II formed in the halo, Msub(*) is less than 0.1 M solar mass. If applicable, these theoretical considerations would predict that substellar masses have formed more frequently under the metal-poor conditions in the early Galaxy (Population II brown dwarfs). Thus the missing mass in the Galactic halo and in the dark haloes around other spirals may well reside in these metal-poor Population II brown dwarfs. (author)

  2. SPECTROSCOPY OF PUTATIVE BROWN DWARFS IN TAURUS

    International Nuclear Information System (INIS)

    Luhman, K. L.; Mamajek, E. E.

    2010-01-01

    Quanz and coworkers have reported the discovery of the coolest known member of the Taurus star-forming complex (L2 ± 0.5), and Barrado and coworkers have identified a possible protostellar binary brown dwarf in the same region. We have performed infrared spectroscopy on the former and the brighter component of the latter to verify their substellar nature. The resulting spectra do not exhibit the strong steam absorption bands that are expected for cool objects, demonstrating that they are not young brown dwarfs. The optical magnitudes and colors for these sources are also indicative of background stars rather than members of Taurus. Although the fainter component of the candidate protostellar binary lacks spectroscopy, we conclude that it is a galaxy rather than a substellar member of Taurus based on its colors and the constraints on its proper motion.

  3. SILICATE EVOLUTION IN BROWN DWARF DISKS

    International Nuclear Information System (INIS)

    Riaz, B.

    2009-01-01

    We present a compositional analysis of the 10 μm silicate spectra for brown dwarf disks in the Taurus and Upper Scorpius (UppSco) star-forming regions, using archival Spitzer/Infrared Spectrograph observations. A variety in the silicate features is observed, ranging from a narrow profile with a peak at 9.8 μm, to nearly flat, low-contrast features. For most objects, we find nearly equal fractions for the large-grain and crystalline mass fractions, indicating both processes to be active in these disks. The median crystalline mass fraction for the Taurus brown dwarfs is found to be 20%, a factor of ∼2 higher than the median reported for the higher mass stars in Taurus. The large-grain mass fractions are found to increase with an increasing strength in the X-ray emission, while the opposite trend is observed for the crystalline mass fractions. A small 5% of the Taurus brown dwarfs are still found to be dominated by pristine interstellar medium-like dust, with an amorphous submicron grain mass fraction of ∼87%. For 15% of the objects, we find a negligible large-grain mass fraction, but a >60% small amorphous silicate fraction. These may be the cases where substantial grain growth and dust sedimentation have occurred in the disks, resulting in a high fraction of amorphous submicron grains in the disk surface. Among the UppSco brown dwarfs, only usd161939 has a signal-to-noise ratio high enough to properly model its silicate spectrum. We find a 74% small amorphous grain and a ∼26% crystalline mass fraction for this object.

  4. A systematic search for brown dwarfs orbiting nearby stars

    International Nuclear Information System (INIS)

    Henry, T.J.; Mccarthy, D.W. Jr.

    1990-01-01

    Survey data for brown dwarf and stellar companions relative to known M dwarf stars within 5 pc north of -30 deg are analyzed. A region 0.2 to 5 arcsec in radius around 27 stars at the IR H and K bands are examined using IR speckle interferometry. The frequency of binary versus single M dwarfs in the solar neighborhood is examined. The IR mass-magnitude relations and mass-luminosity-age relation are studied. The data reveal that there are 19 single M dwarfs, 8 M dwarf binaries, 1 M dwarf triple system, and 1 M dwarf in a triple system for M dwarfs within 5 pc north of -30 deg. Also of the 27 M dwarfs studied none was found to have a brown dwarf companion. 64 refs

  5. Exploring Substellar Evolution with the Coldest Brown Dwarfs

    Science.gov (United States)

    Dupuy, Trent J.

    2017-01-01

    The coldest brown dwarfs are our best analogs to extrasolar gas-giant planets, representing the lowest mass products of star formation. Our view of such objects has been transformed over the last few years as new observations have revealed that the solar neighborhood is populated by much colder objects than previously recognized. At the center of efforts to discover and characterize these coldest substellar objects have been observations from NASA missions (WISE, Spitzer, HST) and the Keck Telescopes. I will review the tremendous progress made in this field over just the last few years thanks to major community efforts to overcome observational challenges in obtaining spectroscopy, photometry, and astrometry of these infrared-faint, optically invisible objects. Spectra from HST and Keck were key in establishing the much anticipated "Y" spectral type, extending the classic stellar classification scheme to atmospheres as cool as 300-400 K. Parallaxes and photometry from Spitzer and Keck have provided absolute fluxes, enabling robust temperature determinations and critical tests of model atmopheres. High-resolution imaging with Keck laser guide star adaptive optics (LGS AO) has been the most prolific resource for revealing tight companions among the coldest brown dwarfs. In fact, with continued orbit monitoring with Keck LGS AO and HST, these binary systems will ultimately provide dynamical masses that will allow the strongest tests of models and reveal if the coldest brown dwarfs are indeed "planetary mass" (less than about 13 Jupiter masses) as is currently thought.

  6. 37 NEW T-TYPE BROWN DWARFS IN THE CANADA-FRANCE BROWN DWARFS SURVEY

    International Nuclear Information System (INIS)

    Albert, Loic; Artigau, Etienne; Delorme, Philippe; Reyle, Celine; Forveille, Thierry; Delfosse, Xavier; Willott, Chris J.

    2011-01-01

    The Canada-France Brown Dwarfs Survey is an i'- and z'-band survey realized with MegaCam at the Canada-France-Hawaii Telescope that covers a surface area of 780 deg 2 . Image analysis is now completed while J-band follow-up campaigns are ∼90% done. The survey identified about 70 T dwarf candidates, of which 43 now have near-infrared spectra obtained with NIRI and GNIRS at Gemini and ISAAC at the Very Large Telescope. Six of these were previously published and we present here the 37 new discoveries, all T dwarfs. They range from T0 to T8.5 with four being of type T7 or later. Both newly identified T8 dwarfs are possibly high log (g) massive brown dwarfs of thin disk age. One T4.5 dwarf shows signs of sub-metallicity. We present proper motions and near-infrared photometry, and discuss about the most peculiar/interesting objects in some details.

  7. THE FIRST SPECTRUM OF THE COLDEST BROWN DWARF

    Energy Technology Data Exchange (ETDEWEB)

    Skemer, Andrew J.; Morley, Caroline V.; Fortney, Jonathan J. [University of California, Santa Cruz, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Allers, Katelyn N. [Bucknell University, 701 Moore Avenue, Lewisburg, PA 17837 (United States); Geballe, Thomas R. [Gemini Observatory, 670 North A’ohoku Place, Hilo, HI 96720 (United States); Marley, Mark S.; Lupu, Roxana [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Faherty, Jacqueline K. [Carnegie Institute for Science, Department of Terrestrial Magnetism, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Bjoraker, Gordon L. [NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)

    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 μ 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’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.

  8. 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

  9. Explaining millimeter-sized particles in brown dwarf disks

    NARCIS (Netherlands)

    Pinilla, P.; Birnstiel, T.; Benisty, M.; Ricci, L.; Natta, A.; Dullemond, C.P.; Dominik, C.; Testi, L.

    2013-01-01

    Context. Planets have been detected around a variety of stars, including low-mass objects, such as brown dwarfs. However, such extreme cases are challenging for planet formation models. Recent sub-millimeter observations of disks around brown dwarf measured low spectral indices of the continuum

  10. Brown dwarf accretion: Nonconventional star formation over very long timescales

    Directory of Open Access Journals (Sweden)

    Ćirković Milan M.

    2005-01-01

    Full Text Available We investigate the process of accretion of interstellar gas by the Galactic population of brown dwarfs over very long timescales typical for physical eschatology. In particular, we use the classical Hoyle-Lyttleton-Bondi accretion model to investigate the rate at which brown dwarfs collect enough additional mass to become red dwarfs, accretion-induced changes in the mass function of the low- mass objects, and the corresponding accretion heating of brown dwarfs. In addition, we show how we can make the definition of the final mass function for stellar objects more precise.

  11. An unsuccessful search for brown dwarf companions to white dwarf stars

    Science.gov (United States)

    Shipman, Harry L.

    1986-01-01

    The results of a survey to detect excess infrared emission from white dwarf stars which would be attributable to a low mass companion are reviewed. Neither a simple comparison of spectroscopically identified white dwarf stars with the IRAS Point Source Catalog nor the coadding of IRAS survey data resulted in a detection of a brown dwarf. The seven nearest stars where the most stringent limits to the presence of a brown dwarf were obtained are listed, and an effort to detect brown dwarfs in the solar neighborhood is discussed.

  12. EVIDENCE FOR ACCRETION IN A NEARBY, YOUNG BROWN DWARF

    International Nuclear Information System (INIS)

    Reiners, Ansgar

    2009-01-01

    We report on the discovery of the young, nearby, brown dwarf 2MASS J0041353-562112. The object has a spectral type of M7.5; it shows Li absorption and signatures of accretion, which implies that it still has a disk and suggests an age below 10 Myr. The space motion vector and position on the sky indicate that the brown dwarf is probably a member of the ∼20 Myr old Tuc-Hor association, or that it may be an ejected member of the ∼12 Myr old β Pic association; both would imply that 2MASS J0041353-562112 may in fact be older than 10 Myr. No accreting star or brown dwarf was previously known in these associations. Assuming an age of 10 Myr, the brown dwarf has a mass of about 30 M Jup and is located at 35 pc distance. The newly discovered object is the closest accreting brown dwarf known. Its membership to an association older than 10 Myr implies that either disks in brown dwarfs can survive as long as in more massive stars, perhaps even longer, or that star formation in Tuc-Hor or β Pic occurred more recently than previously thought. The history and evolution of this object can provide new fundamental insight into the formation process of stars, brown dwarfs, and planets.

  13. New Light on Dark Stars Red Dwarfs, Low-Mass Stars, Brown Dwarfs

    CERN Document Server

    Reid, I. Neill

    2005-01-01

    There has been very considerable progress in research into low-mass stars, brown dwarfs and extrasolar planets during the past few years, particularly since the fist edtion of this book was published in 2000. In this new edtion the authors present a comprehensive review of both the astrophysical nature of individual red dwarf and brown dwarf stars and their collective statistical properties as an important Galactic stellar population. Chapters dealing with the observational properies of low-mass dwarfs, the stellar mass function and extrasolar planets have been completely revised. Other chapters have been significantly revised and updated as appropriate, including important new material on observational techniques, stellar acivity, the Galactic halo and field star surveys. The authors detail the many discoveries of new brown dwarfs and extrasolar planets made since publication of the first edition of the book and provide a state-of-the-art review of our current knowledge of very low-mass stars, brown dwarfs a...

  14. Adaptive Optics Observations of Exoplanets, Brown Dwarfs, and Binary Stars

    Science.gov (United States)

    Hinkley, Sasha

    2012-04-01

    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. Further, the prevalence of aperture masking interferometry in the field of high contrast imaging is also allowing observers to sense massive, young planets at solar system scales (~3-30 AU)- separations out of reach to conventional direct imaging techniques. Such observations can provide snapshots at the earliest phases of planet formation-information essential for constraining formation mechanisms as well as evolutionary models of planetary mass companions. As a demonstration of the power of this technique, I briefly review recent aperture masking observations of the HR 8799 system. Moreover, all of the aforementioned techniques are already extremely adept at detecting low-mass stellar companions to their target stars, and I present some recent highlights.

  15. THE COLDEST BROWN DWARF (OR FREE-FLOATING PLANET)?: THE Y DWARF WISE 1828+2650

    International Nuclear Information System (INIS)

    Beichman, C.; Gelino, Christopher R.; Kirkpatrick, J. Davy; Marsh, Kenneth A.; Barman, Travis S.; Cushing, Michael C.; Wright, E. L.

    2013-01-01

    We have monitored the position of the cool Y dwarf WISEPA J182831.08+265037.8 using a combination of ground- and space-based telescopes and have determined its distance to be 11.2 +1.3 –1.0 pc. Its absolute H magnitude, M H = 22.21 +0.25 –0.22 mag, suggests a mass in the range 0.5-20 M Jup for ages of 0.1-10 Gyr with an effective temperature in the range 250-400 K. The broad range in mass is due primarily to the unknown age of the object. Since the high tangential velocity of the object, 51 ± 5 km s –1 , is characteristic of an old disk population, a plausible age range of 2-4 Gyr leads to a mass range of 3-6 M Jup based on fits to the (highly uncertain) COND evolutionary models. The range in temperature is due to the fact that no single model adequately represents the 1-5 μm spectral energy distribution (SED) of the source, failing by factors of up to five at either the short or long wavelength portions of the SED. The appearance of this very cold object may be affected by non-equilibrium chemistry or low temperature condensates forming clouds, two atmospheric processes that are known to be important in brown dwarf atmospheres but have proven difficult to model. Finally, we argue that there would have to be a very steep upturn in the number density of late-type Y-dwarfs to account for the putative population of objects suggested by recent microlensing observations. Whether WISE 1828+2650 sits at the low-mass end of the brown dwarf population or is the first example of a large number of 'free-floating' planets is not yet known.

  16. Brown dwarfs forming in discs: Where to look for them?

    Directory of Open Access Journals (Sweden)

    Stamatellos D.

    2011-07-01

    Full Text Available A large fraction of the observed brown dwarfs may form by gravitational fragmentation of unstable discs. This model reproduces the brown dwarf desert, and provides an explanation for the existence of planetary-mass objects and for the binary properties of low-mass objects. We have performed an ensemble of radiative hydrodynamic simulations and determined the statistical properties of the low-mass objects produced by gravitational fragmentation of discs. We suggest that there is a population of brown dwarfs loosely bound on wide orbits (100–5000 AU around Sun-like stars that surveys of brown dwarf companions should target. Our simulations also indicate that planetary-mass companions to Sun-like stars are unlikely to form by disc fragmentation.

  17. Youngest Brown Dwarf Yet in a Multiple Stellar System

    Science.gov (United States)

    2000-07-01

    Silla, as well as the 8.2-m VLT/ANTU telescope with the ISAAC multi-mode instrument at Paranal. The first step is to take high-resolution images of the stars from the ROSAT list to look for possible faint companions. However, any faint object found near one of the programme stars may of course be a completely unrelated fore- or background object and it is therefore imperative to check this by means of supplementary observations. Two methods are available. The first implies taking spectra of the companion candidates that demonstrate whether they are bona-fide Brown Dwarfs that display spectral lines typical for the cool atmospheres of this class, e.g., of Titanium Oxide (TiO) and Vanadium Oxide (VO). Infrared spectra are particularly useful for a measurement of the atmospheric temperature. The other involves obtaining a second image some years later. If the companion candidate and the brighter star belong to the same stellar system, they must move together on the sky or, as astronomers say, their measured "proper motions" must be (nearly) the same. If both checks are positive, the fainter object is most likely to be a bona-fide Brown Dwarf companion to the young and nearby star. To be absolutely certain, its orbital motion should also be detected, but it will be very slow and can only be perceived after several years of continued observations. VLT observations of TWA-5 B Two years ago, a faint companion candidate was found near one of the young and nearby stars included in the present programme and designated TWA-5 (also known as CoD -33 7795 ). It is about 12 million years old and is a member of a group of about a dozen young stars (of the "T Tauri"-type ), seen in the southern constellation Hydra (the Water-Snake) and grouped around the star TW Hya , the first to be found in this area ("TWA" means the "TW Hya Association"). The HIPPARCOS mission of the European Space Agency (ESA) measured a mean distance to some of these stars of ~ 180 light-years (55 parsec). This

  18. THE COOLEST ISOLATED BROWN DWARF CANDIDATE MEMBER OF TWA

    Energy Technology Data Exchange (ETDEWEB)

    Gagné, Jonathan; Lafrenière, David; Doyon, René; Malo, Lison; Artigau, Étienne [Département de Physique and Observatoire du Mont-Mégantic, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, Qc H3C 3J7 (Canada); Faherty, Jacqueline K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 (United States); Cruz, Kelle, E-mail: jonathan.gagne@astro.umontreal.ca, E-mail: jfaherty17@gmail.com [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10034 (United States)

    2014-04-10

    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 of 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 L0γ), 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 to have masses down to 11-15 M {sub Jup} at the age of TWA, which makes them compelling targets to study atmospheric properties in a regime similar to that of currently known imaged extrasolar planets.

  19. An L Band Spectrum of the Coldest Brown Dwarf

    Science.gov (United States)

    Morley, Caroline V.; Skemer, Andrew J.; Allers, Katelyn N.; Marley, Mark. S.; Faherty, Jacqueline K.; Visscher, Channon; Beiler, Samuel A.; Miles, Brittany E.; Lupu, Roxana; Freedman, Richard S.; Fortney, Jonathan J.; Geballe, Thomas R.; Bjoraker, Gordon L.

    2018-05-01

    The coldest brown dwarf, WISE 0855, is the closest known planetary-mass, free-floating object and has a temperature nearly as cold as the solar system gas giants. Like Jupiter, it is predicted to have an atmosphere rich in methane, water, and ammonia, with clouds of volatile ices. WISE 0855 is faint at near-infrared wavelengths and emits almost all its energy in the mid-infrared. Skemer et al. presented a spectrum of WISE 0855 from 4.5–5.1 μm (M band), revealing water vapor features. Here, we present a spectrum of WISE 0855 in the L band, from 3.4–4.14 μm. We present a set of atmosphere models that include a range of compositions (metallicities and C/O ratios) and water ice clouds. Methane absorption is clearly present in the spectrum. The mid-infrared color can be better matched with a methane abundance that is depleted relative to solar abundance. We find that there is evidence for water ice clouds in the M band spectrum, and we find a lack of phosphine spectral features in both the L and M band spectra. We suggest that a deep continuum opacity source may be obscuring the near-infrared flux, possibly a deep phosphorous-bearing cloud, ammonium dihyrogen phosphate. Observations of WISE 0855 provide critical constraints for cold planetary atmospheres, bridging the temperature range between the long-studied solar system planets and accessible exoplanets. The James Webb Space Telescope will soon revolutionize our understanding of cold brown dwarfs with high-precision spectroscopy across the infrared, allowing us to study their compositions and cloud properties, and to infer their atmospheric dynamics and formation processes.

  20. K2 Ultracool Dwarfs Survey. II. The White Light Flare Rate of Young Brown Dwarfs

    Science.gov (United States)

    Gizis, John E.; Paudel, Rishi R.; Mullan, Dermott; Schmidt, Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.

    2017-08-01

    We use Kepler K2 Campaign 4 short-cadence (one-minute) photometry to measure white light flares in the young, moving group brown dwarfs 2MASS J03350208+2342356 (2M0335+23) and 2MASS J03552337+1133437 (2M0355+11), and report on long-cadence (thirty-minute) photometry of a superflare in the Pleiades M8 brown dwarf CFHT-PL-17. The rotation period (5.24 hr) and projected rotational velocity (45 km s-1) confirm 2M0335+23 is inflated (R≥slant 0.20 {R}⊙ ) as predicted for a 0.06 {M}⊙ , 24 Myr old brown dwarf βPic moving group member. We detect 22 white light flares on 2M0335+23. The flare frequency distribution follows a power-law distribution with slope -α =-1.8+/- 0.2 over the range 1031 to 1033 erg. This slope is similar to that observed in the Sun and warmer flare stars, and is consistent with lower-energy flares in previous work on M6-M8 very-low-mass stars; taking the two data sets together, the flare frequency distribution for ultracool dwarfs is a power law over 4.3 orders of magnitude. The superflare (2.6× {10}34 erg) on CFHT-PL-17 shows higher-energy flares are possible. We detect no flares down to a limit of 2× {10}30 erg in the nearby L5γ AB Dor moving group brown dwarf 2M0355+11, consistent with the view that fast magnetic reconnection is suppressed in cool atmospheres. We discuss two multi-peaked flares observed in 2M0335+23, and argue that these complex flares can be understood as sympathetic flares, in which fast-mode magnetohydrodynamic waves similar to extreme-ultraviolet waves in the Sun trigger magnetic reconnection in different active regions.

  1. Searching for chemical signatures of brown dwarf formation

    Science.gov (United States)

    Maldonado, J.; Villaver, E.

    2017-06-01

    Context. Recent studies have shown that close-in brown dwarfs in the mass range 35-55 MJup are almost depleted as companions to stars, suggesting that objects with masses above and below this gap might have different formation mechanisms. Aims: We aim to test whether stars harbouring massive brown dwarfs and stars with low-mass brown dwarfs show any chemical peculiarity that could be related to different formation processes. Methods: Our methodology is based on the analysis of high-resolution échelle spectra (R 57 000) from 2-3 m class telescopes. We determine the fundamental stellar parameters, as well as individual abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Zn for a large sample of stars known to have a substellar companion in the brown dwarf regime. The sample is divided into stars hosting massive and low-mass brown dwarfs. Following previous works, a threshold of 42.5 MJup was considered. The metallicity and abundance trends of the two subsamples are compared and set in the context of current models of planetary and brown dwarf formation. Results: Our results confirm that stars with brown dwarf companions do not follow the well-established gas-giant planet metallicity correlation seen in main-sequence planet hosts. Stars harbouring massive brown dwarfs show similar metallicity and abundance distribution as stars without known planets or with low-mass planets. We find a tendency of stars harbouring less-massive brown dwarfs of having slightly higher metallicity, [XFe/Fe] values, and abundances of Sc II, Mn I, and Ni I than the stars having the massive brown dwarfs. The data suggest, as previously reported, that massive and low-mass brown dwarfs might present differences in period and eccentricity. Conclusions: We find evidence of a non-metallicity dependent mechanism for the formation of massive brown dwarfs. Our results agree with a scenario in which massive brown dwarfs are formed as stars. At high metallicities, the core

  2. MEASURING TINY MASS ACCRETION RATES ONTO YOUNG BROWN DWARFS

    International Nuclear Information System (INIS)

    Herczeg, Gregory J.; Cruz, Kelle L.; Hillenbrand, Lynne A.

    2009-01-01

    We present low-resolution Keck I/LRIS spectra spanning from 3200 to 9000 A of nine young brown dwarfs and three low-mass stars in the TW Hya Association and in Upper Sco. The optical spectral types of the brown dwarfs range from M5.5 to M8.75, though two have near-IR spectral types of early L dwarfs. We report new accretion rates derived from excess Balmer continuum emission for the low-mass stars TW Hya and Hen 3-600A and the brown dwarfs 2MASS J12073347-3932540, UScoCTIO 128, SSSPM J1102-3431, USco J160606.29-233513.3, DENIS-P J160603.9-205644, and Oph J162225-240515B, and upper limits on accretion for the low-mass star Hen 3-600B and the brown dwarfs UScoCTIO 112, Oph J162225-240515A, and USco J160723.82-221102.0. For the six brown dwarfs in our sample that are faintest at short wavelengths, the accretion luminosity or upper limit is measurable only when the image is binned over large wavelength intervals. This method extends our sensitivity to accretion rate down to ∼10 -13 M sun yr -1 for brown dwarfs. Since the ability to measure an accretion rate from excess Balmer continuum emission depends on the contrast between excess continuum emission and the underlying photosphere, for objects with earlier spectral types the upper limit on accretion rate is much higher. Absolute uncertainties in our accretion rate measurements of ∼3-5 include uncertainty in accretion models, brown dwarf masses, and distance. The accretion rate of 2 x 10 -12 M sun yr -1 onto 2MASS J12073347-3932540 is within 15% of two previous measurements, despite large changes in the Hα flux.

  3. JVLA Observations of Young Brown Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Rodríguez, Luis F.; Zapata, Luis A.; Palau, Aina, E-mail: l.rodriguez@crya.unam.mx, E-mail: l.zapata@crya.unam.mx, E-mail: a.palau@crya.unam.mx [Instituto de Radioastronomía y Astrofísica, UNAM, Apdo. Postal 3-72 (Xangari), 58089 Morelia, Michoacán, México (Mexico)

    2017-05-01

    We present sensitive 3.0 cm JVLA radio continuum observations of six regions of low-mass star formation that include twelve young brown dwarfs (BDs) and four young BD candidates. We detect a total of 49 compact radio sources in the fields observed, of which 24 have no reported counterparts and are considered new detections. Twelve of the radio sources show variability in timescales of weeks to months, suggesting gyrosynchrotron emission produced in active magnetospheres. Only one of the target BDs, FU Tau A, was detected. However, we detected radio emission associated with two of the BD candidates, WL 20S and CHLT 2. The radio flux densities of the sources associated with these BD candidates are more than an order of magnitude larger than expected for a BD and suggest a revision of their classification. In contrast, FU Tau A falls on the well-known correlation between radio luminosity and bolometric luminosity, suggesting that the emission comes from a thermal jet and that this BD seems to be forming as a scaled-down version of low-mass stars.

  4. New Brown Dwarf Discs in Upper Scorpius Observed with WISE

    Science.gov (United States)

    Dawson, P.; Scholz, A.; Ray, T. P.; Natta, A.; Marsh, K. A.; Padgett, D.; Ressler, M. E.

    2013-01-01

    We present a census of the disc population for UKIDSS selected brown dwarfs in the 5-10 Myr old Upper Scorpius OB association. For 116 objects originally identified in UKIDSS, the majority of them not studied in previous publications, we obtain photometry from the Wide-Field Infrared Survey Explorer data base. The resulting colour magnitude and colour colour plots clearly show two separate populations of objects, interpreted as brown dwarfs with discs (class II) and without discs (class III). We identify 27 class II brown dwarfs, 14 of them not previously known. This disc fraction (27 out of 116, or 23%) among brown dwarfs was found to be similar to results for K/M stars in Upper Scorpius, suggesting that the lifetimes of discs are independent of the mass of the central object for low-mass stars and brown dwarfs. 5 out of 27 discs (19 per cent) lack excess at 3.4 and 4.6 microns and are potential transition discs (i.e. are in transition from class II to class III). The transition disc fraction is comparable to low-mass stars.We estimate that the time-scale for a typical transition from class II to class III is less than 0.4 Myr for brown dwarfs. These results suggest that the evolution of brown dwarf discs mirrors the behaviour of discs around low-mass stars, with disc lifetimes of the order of 5 10 Myr and a disc clearing time-scale significantly shorter than 1 Myr.

  5. Mid-Infrared Observations of the White Dwarf Brown Dwarf Binary GD 1400

    OpenAIRE

    Farihi, J.; Zuckerman, B.; Becklin, E. E.

    2005-01-01

    Fluxes are measured for the DA white dwarf plus brown dwarf pair GD 1400 with the Infrared Array Camera on the {\\em Spitzer Space Telescope}. GD 1400 displays an infrared excess over the entire $3-8\\mu$m region consistent with the presence of a mid- to late-type L dwarf companion. A discussion is given regarding current knowledge of this unique system.

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

    Science.gov (United States)

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

    2016-05-01

    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 ± 0.21 ppt at 3.6 μm and 2.09 ± 0.08 ppt at 4.5 μm, corresponding to brightness temperatures of 1026 ± 57 K and 1249 ± 36 K, respectively. We then apply brown dwarf evolutionary models to infer a bolometric luminosity {log}({L}\\star /{L}⊙ )=-5.16+/- 0.04. Given the known physical properties of the brown dwarf and the two M dwarfs in the LHS 6343 system, these depths are consistent with models of a 1100 K T dwarf at an age of 5 Gyr and empirical observations of field T5-6 dwarfs with temperatures of 1070 ± 130 K. We investigate the possibility that the orbit of LHS 6343 C has been altered by the Kozai-Lidov mechanism and propose additional astrometric or Rossiter-McLaughlin measurements of the system to probe the dynamical history of the system.

  7. SURPRISINGLY WEAK MAGNETISM ON YOUNG ACCRETING BROWN DWARFS

    International Nuclear Information System (INIS)

    Reiners, A.; Basri, G.; Christensen, U. R.

    2009-01-01

    We have measured the surface magnetic flux on four accreting young brown dwarfs and one nonaccreting young very low mass (VLM) star utilizing high-resolution spectra of absorption lines of the FeH molecule. A magnetic field of 1-2 kG had been proposed for one of the brown dwarfs, Two Micron All Sky Survey (2MASS) J1207334-393254, because of its similarities to higher mass T Tauri stars as manifested in accretion and the presence of a jet. We do not find clear evidence for a kilogauss field in any of our young brown dwarfs but do find a 2 kG field on the young VLM star. Our 3σ upper limit for the magnetic flux in 2MASS J1207334-393254 just reaches 1 kG. We estimate the magnetic field required for accretion in young brown dwarfs given the observed rotations, and find that fields of only a few hundred gauss are sufficient for magnetospheric accretion. This predicted value is less than our observed upper limit. We conclude that magnetic fields in young brown dwarfs are a factor of 5 or more lower than in young stars of about one solar mass, and in older stars with spectral types similar to our young brown dwarfs. It is interesting that, during the first few million years, the fields scale down with mass in line with what is needed for magnetospheric accretion, yet no such scaling is observed at later ages within the same effective temperature range. This scaling is opposite to the trend in rotation, with shorter rotation periods for very young accreting brown dwarfs compared with accreting solar-mass objects (and very low Rossby numbers in all cases). We speculate that in young objects a deeper intrinsic connection may exist between magnetospheric accretion and magnetic field strength, or that magnetic field generation in brown dwarfs may be less efficient than in stars. Neither of these currently has an easy physical explanation.

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

    International Nuclear Information System (INIS)

    Buenzli, Esther; Apai, Dániel; Radigan, Jacqueline; Reid, I. Neill; Flateau, Davin

    2014-01-01

    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 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 min =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.

  9. Testing the Formation Pathway of a Transiting Brown Dwarf in a Middle-aged Cluster

    Science.gov (United States)

    Beatty, Thomas; Curtis, Jason; Morley, Caroline; Burrows, Adam; Montet, Benjamin; Wright, Jason

    2018-05-01

    We wish to use 15.7 hours of Spitzer time to observe two transits, one each at 3.6um and 4.5um, of the transiting brown dwarf CWW 89Ab (Nowak et al. 2017) to measure its nightside emission. This will allow us to either make the first positive identification of a brown dwarf that has formed through core accretion processes - or will provide a severe challenge to brown dwarf evolution models. CWW 89Ab is a 36.5+/-0.1 MJ, 0.937+/-0.042 RJ, brown dwarf on a 5.3 day orbit about a 5800K dwarf. The brown dwarf is a member of the 3.00+/-0.25 Gyr old open cluster Ruprecht 147 (Curtis et al. 2013). CWW 89Ab is one of two transiting brown dwarfs for which we have an isochronal age - giving us an age, a mass, and a radius that are all independent of evolutionary models. Surprisingly, Spitzer eclipse observations of CWW 89Ab (Beatty et al. 2018) show that the dayside emission requires an internal luminosity is 16 times higher than predicted by evolutionary models. In Beatty et al. (2018) we hypothesized that this is due to a stratospheric temperature inversion on CWW 89Ab's dayside. Atmospheric modeling by Molliere et al. (2015) shows that CWW 89Ab's temperature, an inversion can only happen if the atmospheric carbon-to-oxygen ratio (C/O) is close to one. Since we know that the abundances of Ruprecht 147 and CWW 89A itself (Curtis et al. 2018) are close to the Solar value of C/O 0.54, a super-stellar value of C/O 1 in CWW 89Ab would mean that the material used to form the brown dwarf was processed through CWW 89A's proto-planetary disk (Oberg et al. 2011). It would necessarily follow that CWW 89Ab formed via core accretion within the proto-planetary disk, and not through gravitational collapse. We wish to observe CWW 89Ab to determine if the dayside over-luminosity is caused by a temperature inversion. Since inversions are caused by direct stellar irradiation and impossible at night, the nightside emission should be consistent with Tint=850K if an inversion is the cause of the

  10. 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

  11. Meteorologies of brown dwarfs and extrasolar giant planets

    Science.gov (United States)

    Cooper, Curtis Steven

    2006-06-01

    This dissertation explores the consequences of atmospheric dynamics for observations of substellar mass objects (SMOs). Discussed first is the growth of cloud particles of various compositions in brown dwarfs of different surface gravities and effective temperatures. The structure of these objects is calculated with a one-dimensional radiative transfer model. To determine particle sizes, the timescales for microphysical growth processes, including nucleation, coagulation, and coalescence, are compared to the timescale for gravitational sedimentation. The model also allows for sustained uplifting of condensable vapor in convective regions. The results show that particle sizes vary greatly over the range of objects studied. In most cases, clouds on brown dwarfs do not dominate the opacity. Rather, they smooth the emergent spectrum and partially redistribute the radiative energy. The focus then shifts to extrasolar giant planets (EGPs). Results are presented from a three-dimensional model of atmospheric dynamics on the transiting Jupiter-like planet HD 209458b. As a close-in orbiter (known as a "roaster"), HD 209458b is super-heated on its dayside. Due to tidal locking of the interior, the dayside hemisphere faces the star in perpetuity, which leads to very different dynamics than is seen on Jupiter. The flow is characterized by an eastward supersonic jet ( u ~ 4 kms - 1 ) extending from the equator to the mid-latitudes. Temperature contrasts are ~500 K at the photosphere. At 220 mbar, winds blow the hottest regions downstream from the substellar point by ~60°, with direct implications for the infrared light curve. These simulations are extended to the study of carbon chemistry in HD 209458b's atmosphere by coupling the CO/CH 4 reaction kinetics to the dynamics. Disequilibrium results from slow reaction rates at low temperatures and pressures. Effective vertical quenching near the ~3 bar level leads to uniformly high concentrations of CO at the photosphere, even in

  12. 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.

  13. BROWN DWARF BINARIES FROM DISINTEGRATING TRIPLE SYSTEMS

    International Nuclear Information System (INIS)

    Reipurth, Bo; Mikkola, Seppo

    2015-01-01

    Binaries in which both components are brown dwarfs (BDs) are being discovered at an increasing rate, and their properties may hold clues to their origin. We have carried out 200,000 N-body simulations of three identical stellar embryos with masses drawn from a Chabrier IMF and embedded in a molecular core. The bodies are initially non-hierarchical and undergo chaotic motions within the cloud core, while accreting using Bondi–Hoyle accretion. The coupling of dynamics and accretion often leads to one or two dominant bodies controlling the center of the cloud core, while banishing the other(s) to the lower-density outskirts, leading to stunted growth. Eventually each system transforms either to a bound hierarchical configuration or breaks apart into separate single and binary components. The orbital motion is followed for 100 Myr. In order to illustrate 200,000 end-states of such dynamical evolution with accretion, we introduce the “triple diagnostic diagram,” which plots two dimensionless numbers against each other, representing the binary mass ratio and the mass ratio of the third body to the total system mass. Numerous freefloating BD binaries are formed in these simulations, and statistical properties are derived. The separation distribution function is in good correspondence with observations, showing a steep rise at close separations, peaking around 13 AU and declining more gently, reaching zero at separations greater than 200 AU. Unresolved BD triple systems may appear as wider BD binaries. Mass ratios are strongly peaked toward unity, as observed, but this is partially due to the initial assumptions. Eccentricities gradually increase toward higher values, due to the lack of viscous interactions in the simulations, which would both shrink the orbits and decrease their eccentricities. Most newborn triple systems are unstable and while there are 9209 ejected BD binaries at 1 Myr, corresponding to about 4% of the 200,000 simulations, this number has grown to

  14. BROWN DWARF BINARIES FROM DISINTEGRATING TRIPLE SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Reipurth, Bo [Institute for Astronomy and NASA Astrobiology Institute University of Hawaii, 640 N. Aohoku Place, Hilo, HI 96720 (United States); Mikkola, Seppo, E-mail: reipurth@ifa.hawaii.edu, E-mail: Seppo.Mikkola@utu.fi [Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö (Finland)

    2015-04-15

    Binaries in which both components are brown dwarfs (BDs) are being discovered at an increasing rate, and their properties may hold clues to their origin. We have carried out 200,000 N-body simulations of three identical stellar embryos with masses drawn from a Chabrier IMF and embedded in a molecular core. The bodies are initially non-hierarchical and undergo chaotic motions within the cloud core, while accreting using Bondi–Hoyle accretion. The coupling of dynamics and accretion often leads to one or two dominant bodies controlling the center of the cloud core, while banishing the other(s) to the lower-density outskirts, leading to stunted growth. Eventually each system transforms either to a bound hierarchical configuration or breaks apart into separate single and binary components. The orbital motion is followed for 100 Myr. In order to illustrate 200,000 end-states of such dynamical evolution with accretion, we introduce the “triple diagnostic diagram,” which plots two dimensionless numbers against each other, representing the binary mass ratio and the mass ratio of the third body to the total system mass. Numerous freefloating BD binaries are formed in these simulations, and statistical properties are derived. The separation distribution function is in good correspondence with observations, showing a steep rise at close separations, peaking around 13 AU and declining more gently, reaching zero at separations greater than 200 AU. Unresolved BD triple systems may appear as wider BD binaries. Mass ratios are strongly peaked toward unity, as observed, but this is partially due to the initial assumptions. Eccentricities gradually increase toward higher values, due to the lack of viscous interactions in the simulations, which would both shrink the orbits and decrease their eccentricities. Most newborn triple systems are unstable and while there are 9209 ejected BD binaries at 1 Myr, corresponding to about 4% of the 200,000 simulations, this number has grown to

  15. Characterizing a New Candidate Benchmark Brown Dwarf Companion in the β Pic Moving Group

    Science.gov (United States)

    Phillips, Caprice; Bowler, Brendan; Liu, Michael C.; Mace, Gregory N.; Sokal, Kimberly R.

    2018-01-01

    Benchmark brown dwarfs are objects that have at least two measured fundamental quantities such as luminosity and age, and therefore can be used to test substellar atmospheric and evolutionary models. Nearby, young, loose associations such as the β Pic moving group represent some of the best regions in which to identify intermediate-age benchmark brown dwarfs due to their well-constrained ages and metallicities. We present a spectroscopic study of a new companion at the hydrogen-burning limit orbiting a low-mass star at a separation of 9″ (650 AU) in the 23 Myr old β Pic moving group. The medium-resolution near-infrared spectrum of this companion from IRTF/SpeX shows clear signs of low surface gravity and yields an index-based spectral type of M6±1 with a VL-G gravity on the Allers & Liu classification system. Currently, there are four known brown dwarf and giant planet companions in the β Pic moving group: HR 7329 B, PZ Tel B, β Pic b, and 51 Eri b. Depending on its exact age and accretion history, this new object may represent the third brown dwarf companion and fifth substellar companion in this association.

  16. Direct Test of the Brown Dwarf Evolutionary Models Through Secondary Eclipse Spectroscopy of LHS 6343

    Science.gov (United States)

    Albert, Loic

    2015-10-01

    As the number of field Brown Dwarfs counts in the thousands, interpreting their physical parameters (mass, temperature, radius, luminosity, age, metallicity) relies as heavily as ever on atmosphere and evolutionary models. Fortunately, models are largely successful in explaining observations (colors, spectral types, luminosity), so they appear well calibrated in a relative sense. However, an absolute model-independent calibration is still lacking. Eclipsing BDs systems are a unique laboratory in this respect but until recently only one such system was known, 2M0535-05 - a very young (1 Gyr) - was identified (62.1+/-1.2 MJup, 0.783+/-0.011 RJup) transiting LHS6343 with a 12.7-day period. We propose to use WFC3 in drift scan mode and 5 HST orbits to determine the spectral type (a proxy for temperature) as well as the near-infrared luminosity of this brown dwarf. We conducted simulations that predict a signal-to-noise ratio ranging between 10 and 30 per resolution element in the peaks of the spectrum. These measurements, coupled with existing luminosity measurements with Spitzer at 3.6 and 4.5 microns, will allow us to trace the spectral energy distribution of the Brown Dwarf and directly calculate its blackbody temperature. It will be the first field Brown Dwarfs with simultaneous measurements of its radius, mass, luminosity and temperature all measured independently of models.

  17. White dwarf stars with chemically stratified atmospheres

    Science.gov (United States)

    Muchmore, D.

    1982-01-01

    Recent observations and theory suggest that some white dwarfs may have chemically stratified atmospheres - thin layers of hydrogen lying above helium-rich envelopes. Models of such atmospheres show that a discontinuous temperature inversion can occur at the boundary between the layers. Model spectra for layered atmospheres at 30,000 K and 50,000 K tend to have smaller decrements at 912 A, 504 A, and 228 A than uniform atmospheres would have. On the basis of their continuous extreme ultraviolet spectra, it is possible to distinguish observationally between uniform and layered atmospheres for hot white dwarfs.

  18. Search for brown dwarfs and late M dwarfs in the Hyades and the Pleiades

    International Nuclear Information System (INIS)

    Zuckerman, B.; Becklin, E.E.; Hawaii Univ., Honolulu)

    1987-01-01

    The J and K colors of 14 white dwarfs that are believed to be single stars and members of either the Hyades or Pleiades clusters or the Hyades supercluster were measured, and no indication of any excess 2.2 micron (K) emission above that expected from the white dwarf was found. Based on recently published theoretical cooling curves for brown dwarfs, the existence of any cool companion stars, with masses greater than approximately 0.03 solar mass within a radius of 6 arcsec of eight white dwarfs in the Hyades cluster and greater than approximately 0.015 solar mass toward the single white dwarf in the Pleiades, is ruled out. This latter limit, only 15 Jupiter masses, is probably the lowest that has yet been established for any star by purely infrared techniques. 21 references

  19. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zahnle, Kevin J.; Marley, Mark S., E-mail: Kevin.J.Zahnle@NASA.gov, E-mail: Mark.S.Marley@NASA.gov [NASA Ames Research Center, MS-245-3, Moffett Field, CA 94035 (United States)

    2014-12-10

    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 CH{sub 4} 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 CH{sub 4} 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 CH{sub 4}/CO, the NH{sub 3}/N{sub 2} ratio is insensitive to mixing, which makes NH{sub 3} a potential proxy for gravity. HCN may become interesting in high-gravity brown dwarfs with very strong vertical mixing. Detailed analysis of the CO-CH{sub 4} 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, CH{sub 4}, NH{sub 3}, HCN, and CO{sub 2} 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).

  1. Students Use VLA to Make Startling Brown-Dwarf Discovery

    Science.gov (United States)

    2001-03-01

    A group of summer students making a long-shot astronomical gamble with the National Science Foundation's (NSF) Very Large Array (VLA) have found the first radio emission ever detected from a brown dwarf, an enigmatic object that is neither a star nor a planet, but something in between. Their surprising discovery is forcing experts to re-think their theories about how brown dwarfs work. The Very Large Array "Many astronomers are surprised at this discovery, because they didn't expect such strong radio emission from this object," said Shri Kulkarni, a Caltech professor who was on the team that first discovered a brown dwarf in 1995, and advisor to one of the students. "What is so cool is that this is research that probably nobody else would have tried to do because of its low chance of success. That made it ideal for summer students -- we had almost nothing to lose," said Kate Becker, a student at Oberlin College in Ohio. "The radio emission these students discovered coming from this brown dwarf is 10,000 times stronger than anyone expected," said Dale Frail, an astronomer at the National Radio Astronomy Observatory (NRAO) in Socorro, NM. "This student project is going to open up a whole new area of research for the VLA," Frail added. The students, in addition to Becker, are: Edo Berger from Caltech; Steven Ball from New Mexico Tech in Socorro, NM; Melanie Clarke from Carleton College in Northfield, MN; Therese Fukuda from the University of Denver; Ian Hoffman from the University of New Mexico in Albuquerque; Richard Mellon from The Pennsylvania State University; Emmanuel Momjian from the University of Kentucky; Nathanial Murphy from Amherst College in Amherst, MA; Stacey Teng from the University of Maryland; Timothy Woodruff from Southwestern University in Georgetown, TX; Ashley Zauderer from Agnes Scott College in Decatur, GA; and Robert Zavala from New Mexico State University in Las Cruces, NM. Frail also is an author of the research paper, published in the March

  2. Backyard Worlds: Finding Nearby Brown Dwarfs Through Citizen Science

    Science.gov (United States)

    Kuchner, Marc

    Recent discoveries of cool brown dwarfs in the solar neighborhood and microlensing surveys both point to an undiscovered population of brown dwarfs and rogue planets in the solar neighborhood. We propose to develop and sustain a novel website that enables a unique and powerful citizen-science based search for these and other high-proper-motion objects at 3.5 and 4.6 microns. Through this search, we have an opportunity to discover new ultracool Y dwarfs, crucial links between star formation and planet formation, and also the Sun's nearest neighbors-potentially a system closer than Proxima Centauri. NASA's Wide-field Infrared Survey Explorer mission (WISE) is nominally sensitive enough to detect a 250 K brown dwarf to > 6 pc and even a Jupiter analog to > 0.6 pc. However, high proper motion objects like these can easily be confused with variable stars, electronic noise, latent images, optical ghosts, cosmic ray hits, and so on in the WISE archive. Computer-based searches for high-proper motion objects falter in dense star fields, necessitating visual inspection all candidates. Our citizen science project, called "Backyard Worlds: Planet 9", remedies this problem by engaging volunteers to visually inspect WISE and NEOWISE images. Roughly 104,000 participants have already begun using a preliminary version of the site to examine time-resolved co-adds of unWISE-processed images, four epochs spanning 2010 to 2014. They have already performed more than 3.6 million classifications of these images since the site's launch on February 15, 2017. Besides seeking new brown dwarfs and nearby stars, this site is also the most sensitive all-sky WISE-based search for a planet orbiting the Sun beyond Pluto (sometimes called Planet Nine). Preliminary analysis data from the site has resulted in the discovery of 13 brown dwarf candidates including 6 T dwarfs. We obtained a spectrum of one of these candidates and published it in Astrophysical Journal Letters, with four citizen scientists

  3. Hubble Space Telescope Imaging and Spectral Analysis of Two Brown Dwarf Binaries at the L Dwarf/T Dwarf Transition

    OpenAIRE

    Burgasser, Adam J.; Gagliuffi, Daniella C. Bardalez; Gizis, John E.

    2010-01-01

    We present a detailed examination of the brown dwarf multiples 2MASS J08503593+1057156 and 2MASS J17281150+3948593, both suspected of harboring components that straddle the L dwarf/T dwarf transition. Resolved photometry from Hubble Space Telescope/NICMOS show opposite trends in the relative colors of the components, with the secondary of 2MASS J0850+1057 being redder than its primary, while that of 2MASS J1728+3948 is bluer. We determine near-infrared component types by matching combined-lig...

  4. An atlas of L-T transition brown dwarfs with VLT/XShooter

    Science.gov (United States)

    Marocco, F.; Day-Jones, A. C.; Jones, H. R. A.; Pinfield, D. J.

    In this contribution we present the first results from a large observing campaign we are carrying out using VLT/Xshooter to obtain spectra of a large sample (˜250 objects) of L-T transition brown dwarfs. Here we report the results based on the first ˜120 spectra already obtained. The large sample, and the wide spectral coverage (300-2480 nm) given by Xshooter, will allow us to do a new powerful analysis, at an unprecedent level. By fitting the absorption lines of a given element (e.g. Na) at different wavelengths we can test ultracool atmospheric models and draw for the first time a 3D picture of stellar atmospheres at temperatures down to 1000K. Determining the atmospheric parameters (e.g. temperature, surface gravity and metallicity) of a big sample of brown dwarfs, will allow us to understand the role of these parameters on the formation of their spectra. The large number of objects in our sample also will allow us to do a statistical significant test of the birth rate and initial mass function predictions for brown dwarfs. Determining the shape of the initial mass function for very low mass objects is a fundamental task to improve galaxy models, as recent studies tep{2010Natur.468..940V} have shown that low-mass objects dominate in massive elliptical galaxies.

  5. Ultracool Subdwarfs: Metal-poor Stars and Brown Dwarfs Extending into the Late-type M, L and T Dwarf Regimes

    OpenAIRE

    Burgasser, Adam J.; Kirkpatrick, J. Davy; Lepine, Sebastien

    2004-01-01

    Recent discoveries from red optical proper motion and wide-field near-infrared surveys have uncovered a new population of ultracool subdwarfs -- metal-poor stars and brown dwarfs extending into the late-type M, L and possibly T spectral classes. These objects are among the first low-mass stars and brown dwarfs formed in the Galaxy, and are valuable tracers of metallicity effects in low-temperature atmospheres. Here we review the spectral, photometric, and kinematic properties of recent discov...

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

    OpenAIRE

    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.

  7. A BROWN DWARF CENSUS FROM THE SIMP SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Robert, Jasmin; Gagné, Jonathan; Artigau, Étienne; Lafrenière, David; Nadeau, Daniel; Doyon, René; Malo, Lison; Albert, Loïc; Simard, Corinne [Département de physique and Observatoire du Mont-Mégantic, Université de Montréal, Montréal, QC H3C 3J7 (Canada); Gagliuffi, Daniella C. Bardalez; Burgasser, Adam J., E-mail: jasmin@astro.umontreal.ca [Center for Astrophysics and Space Sciences, University of California San Diego, 9500 Gilman Dr., Mail Code 0424, La Jolla, CA 92093 (United States)

    2016-10-20

    We have conducted a near-infrared (NIR) proper motion survey, the Sondage Infrarouge de Mouvement Propre, in order to discover field ultracool dwarfs (UCD) in the solar neighborhood. The survey was conducted by imaging ∼28% of the sky with the Caméra PAnoramique Proche-InfraRouge both in the southern hemisphere at the Cerro Tololo Inter-American Observatory 1.5 m telescope, and in the northern hemisphere at the Observatoire du Mont-Mégantic 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 an NIR spectroscopic follow-up of 169 M, L, and T dwarfs. Among the sources discovered are 2 young field brown dwarfs, 6 unusually red M and L dwarfs, 25 unusually blue M and L dwarfs, 2 candidate unresolved L+T binaries, and 24 peculiar UCDs. Additionally, we add 9 L/T transition dwarfs (L6–T4.5) to the already known objects.

  8. Functionally enhanced brown adipose tissue in Ames dwarf mice.

    Science.gov (United States)

    Darcy, Justin; Bartke, Andrzej

    2017-01-02

    Reduced insulin-like growth factor 1/insulin signaling (IIS) has been linked to extended longevity in species ranging from yeast to mammals. In mammals, this is exemplified in Ames dwarf (Prop1 df/df ) mice, which have a 40%-60% increase in longevity (males and females, respectively) due to their recessive Prop1 loss-of-function mutation that results in lack of growth hormone (GH), thyroid-stimulating hormone and prolactin. Our laboratory has previously shown that Ames dwarf mice have functionally unique white adipose tissue (WAT) that improves, rather than impairs, insulin sensitivity. Because GH and thyroid hormone are integral to adipose tissue development and function, we hypothesized that brown adipose tissue (BAT) in Ames dwarf mice may also be functionally unique and/or enhanced. Here, we elaborate on our recent findings, which demonstrate that BAT is functionally enhanced in Ames dwarf mice, and suggest that BAT removal in these mice results in utilization of WAT depots as an energy source. We also discuss how our findings compare to those in other long-lived dwarf mice with altered IIS, which unlike Ames dwarf mice, are essentially euthyroid. Lastly, we provide some insights into the implications of these findings and discuss some of the necessary future work in this area.

  9. A BROWN DWARF CENSUS FROM THE SIMP SURVEY

    International Nuclear Information System (INIS)

    Robert, Jasmin; Gagné, Jonathan; 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, in order to discover field ultracool dwarfs (UCD) in the solar neighborhood. The survey was conducted by imaging ∼28% of the sky with the Caméra PAnoramique Proche-InfraRouge both in the southern hemisphere at the Cerro Tololo Inter-American Observatory 1.5 m telescope, and in the northern hemisphere at the Observatoire du Mont-Mégantic 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 an NIR spectroscopic follow-up of 169 M, L, and T dwarfs. Among the sources discovered are 2 young field brown dwarfs, 6 unusually red M and L dwarfs, 25 unusually blue M and L dwarfs, 2 candidate unresolved L+T binaries, and 24 peculiar UCDs. Additionally, we add 9 L/T transition dwarfs (L6–T4.5) to the already known objects.

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

    International Nuclear Information System (INIS)

    Luhman, K. L.; Allen, P. R.; Mamajek, E. E.; Muench, A. A.; Finkbeiner, D. P.

    2009-01-01

    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 M sun 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.

  11. Connecting Young Brown Dwarfs and Directly Imaged Gas-Giant Planets

    Science.gov (United States)

    Liu, Michael; Dupuy, Trent; Allers, Katelyn; Aller, Kimberly; Best, William; Magnier, Eugene

    2015-12-01

    Direct detections of gas-giant exoplanets and discoveries of young (~10-100 Myr) field brown dwarfs from all-sky surveys are strengthening the link between the exoplanet and brown dwarf populations, given the overlapping ages, masses, temperatures, and surface gravities. In light of the relatively small number of directly imaged planets and the modest associated datasets, the large census of young field brown dwarfsprovides a compelling laboratory for enriching our understanding of both classes of objects. However, work to date on young field objects has typically focused on individual discoveries.We present a large comprehensive study of the youngest field brown dwarfs, comprising both previously known objects and our new discoveries from the latest wide-field surveys (Pan-STARRS-1 and WISE). With masses now extending down to ~5 Jupiter masses, these objects have physical properties that largely overlap young gas-giant planets and thus are promising analogs for studying exoplanet atmospheres at unparalleled S/N, spectral resolution, and wavelength coverage. We combine high-quality spectra and parallaxes to determine spectral energy distributions, luminosities, temperatures, and ages for young field objects. We demonstrate that this population spans a continuum in the color-magnitude diagram, thereby forming a bridge between the hot and cool extremes of directly imaged planets. We find that the extremely dusty properties of the planets around 2MASS J1207-39 and HR 8799 do occur in some young brown dwarfs, but these properties do not have a simple correspondence with age, perhaps contrary to expectations. We find young field brown dwarfs can have unusually low temperatures and suggest a new spectral type-temperature scale appropriate for directly imaged planets.To help provide a reference for extreme-contrast imaging surveys, we establish a grid of spectral standards and benchmarks, based on membership in nearby young moving groups, in order to calibrate gravity

  12. Observational diagnostics of accretion on young stars and brown dwarfs

    Science.gov (United States)

    Stelzer, Beate; Argiroffi, Costanza

    I present a summary of recent observational constraints on the accretion properties of young stars and brown dwarfs with focus on the high-energy emission. In their T Tauri phase young stars assemble a few percent of their mass by accretion from a disk. Various observational signatures of disks around pre-main sequence stars and the ensuing accretion process are found in the IR and optical regime: e.g. excess emission above the stellar photosphere, strong and broad emission lines, optical veiling. At high energies evidence for accretion is less obvious, and the X-ray emission from stars has historically been ascribed to magnetically confined coronal plasmas. While being true for the bulk of the emission, new insight obtained from XMM-Newton and Chandra observations has unveiled contributions from accretion and outflow processes to the X-ray emission from young stars. Their smaller siblings, the brown dwarfs, have been shown to undergo a T Tauri phase on the basis of optical/IR observations of disks and measurements of accretion rates. Most re-cently, first evidence was found for X-rays produced by accretion in a young brown dwarf, complementing the suspected analogy between stars and substellar objects.

  13. Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B

    Science.gov (United States)

    Zhou, Yifan; Apai, Daniel; Metchev, Stanimir; Lew, Ben W. P.; Schneider, Glenn; Marley, Mark S.; Karalidi, Theodora; Manjavacas, Elena; Bedin, Luigi R.; Cowan, Nicolas B.; hide

    2018-01-01

    Time-resolved observations of brown dwarfs' rotational modulations provide powerful insights into the properties of condensate clouds in ultra-cool atmospheres. Multi-wavelength light curves reveal cloud vertical structures, condensate particle sizes, and cloud morphology, which directly constrain condensate cloud and atmospheric circulation models. We report results from Hubble Space Telescope/Wide Field Camera 3 (WFC3) near-infrared G141 taken in six consecutive orbits observations of HNPeg B, an L/T transition brown dwarf companion to a G0V type star. The best-fit sine wave to the 1.1 to 1.7 micron broadband light curve has the amplitude of and period of hour. The modulation amplitude has no detectable wavelength dependence except in the 1.4 micron water absorption band, indicating that the characteristic condensate particle sizes are large (greater than 1 micron). We detect significantly (4.4 sigma) lower modulation amplitude in the 1.4 micron water absorption band, and find that HN Peg B's spectral modulation resembles those of early T type brown dwarfs. We also describe a new empirical interpolation method to remove spectral contamination from the bright host star. This method may be applied in other high-contrast time-resolved observations with WFC3.

  14. 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.

  15. 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.

  16. An historical perspective - Brown is not a color. [astrophysics of infrared dwarf stars

    Science.gov (United States)

    Tarter, J. C.

    1986-01-01

    Major shifts in theoretical understanding of the star formation process and the possible components of the local mass density are reviewed. Those aspects of brown dwarf structure and evolution that are still not well enough understood are outlined, and the types of observations that might force the modification of current theories to accommodate the existence of brown dwarfs are suggested. The appropriateness of the name 'brown dwarf' is defended.

  17. Constraints on the brown dwarf mass function from optical and infrared searches

    International Nuclear Information System (INIS)

    Probst, R.G.

    1986-01-01

    Photometric surveys of faint proper motion stars and searches for infrared binary companions have identified a few very low luminosity objects. The author considers how these searches may constrain the brown dwarf mass function. An astrophysically plausible brown dwarf population is defined which yields a dark mass density = 0.5 x the observed density. Using the sensitivity and other limits of various surveys, the expected numbers of observable brown dwarfs are obtained from the model population for comparison with actual results. Reasonable improvement in search protocol could yield statistically significant tests of the brown dwarf mass function. (author)

  18. Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs. II. Properties of 11 T dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Line, Michael R. [School of Earth and Space Exploration, Arizona State University, Tempe AZ 85287 (United States); Marley, Mark S.; Freedman, Richard [NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035 (United States); Liu, Michael C. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Burningham, Ben [Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Morley, Caroline V. [Department of Astronomy, Harvard University, Cambridge, MA 02138 (United States); Hinkel, Natalie R. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Teske, Johanna [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Fortney, Jonathan J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Lupu, Roxana, E-mail: mrline@asu.edu [BAER Institute/NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035 (United States)

    2017-10-20

    Brown dwarf spectra are rich in information revealing of the chemical and physical processes operating in their atmospheres. We apply a recently developed atmospheric retrieval tool to an ensemble of late-T dwarf (600–800 K) near-infrared (1–2.5 μ m) spectra. With these spectra we are able to directly constrain the molecular abundances for the first time of H{sub 2}O, CH{sub 4}, CO, CO{sub 2}, NH{sub 3}, H{sub 2}S, and Na+K, surface gravity, effective temperature, thermal structure, photometric radius, and cloud optical depths. We find that ammonia, water, methane, and the alkali metals are present and that their abundances are well constrained in all 11 objects. We find no significant trend in the water, methane, or ammonia abundances with temperature, but find a very strong (>25 σ ) decreasing trend in the alkali metal abundances with decreasing effective temperature, indicative of alkali rainout. As expected from previous work, we also find little evidence for optically thick clouds. With the methane and water abundances, we derive the intrinsic atmospheric metallicity and carbon-to-oxygen ratios. We find in our sample that metallicities are typically subsolar (−0.4 < [ M /H] < 0.1 dex) and carbon-to-oxygen ratios are somewhat supersolar (0.4 < C/O < 1.2), different than expectations from the local stellar population. We also find that the retrieved vertical thermal profiles are consistent with radiative equilibrium over the photospheric regions. Finally, we find that our retrieved effective temperatures are lower than previous inferences for some objects and that some of our radii are larger than expectations from evolutionary models, possibly indicative of unresolved binaries. This investigation and method represent a new and powerful paradigm for using spectra to determine the fundamental chemical and physical processes governing cool brown dwarf atmospheres.

  19. Project DWARF - using eclipsing binaries for searching for exoplanets and brown dwarfs

    Science.gov (United States)

    Kudak, V.; Parimucha, Š.

    2016-12-01

    Project DWARF is a long-term observation campaign for about 60 selected eclipsing binaries aimed for detection of exoplanets or other objects (brown dwarfs) in low-mass detached binaries of different types (low-mass eclipsing binaries with M and K components, short-period binaries with sdB or sdO component, post-common-envelope systems containing a white dwarf). Existence of other bodies in systems are determined by analysing of O-C diagrams, constructed from observed minima times of binaries. Objects are selected with intention to determine minima with high precision. About 40 observatories are involved into the network at present time, mostly situated in Europe. The observations are made by small or middle class telescopes with apertures of 20-200 cm. In this contribution we give information about current status of the project, we present main goals and results of 4 years observations.

  20. WISE Y dwarfs as probes of the brown dwarf-exoplanet connection

    International Nuclear Information System (INIS)

    Beichman, C.; Gelino, Christopher R.; Kirkpatrick, J. Davy; Cushing, Michael C.; Dodson-Robinson, Sally; Marley, Mark S.; Morley, Caroline V.; Wright, E. L.

    2014-01-01

    We have determined astrometric positions for 15 WISE-discovered late-type brown dwarfs (six T8-9 and nine Y dwarfs) using the Keck-II telescope, the Spitzer Space Telescope, and the Hubble Space Telescope. Combining data from 8 to 20 epochs we derive parallactic and proper motions for these objects, which puts the majority within 15 pc. For ages greater than a few Gyr, as suggested from kinematic considerations, we find masses of 10-30 M Jup based on standard models for the evolution of low-mass objects with a range of mass estimates for individual objects, depending on the model in question. Three of the coolest objects have effective temperatures ∼350 K and inferred masses of 10-15 M Jup . Our parallactic distances confirm earlier photometric estimates and direct measurements and suggest that the number of objects with masses below about 15 M Jup must be flat or declining, relative to higher mass objects. The masses of the coldest Y dwarfs may be similar to those inferred for recently imaged planet-mass companions to nearby young stars. Objects in this mass range, which appear to be rare in both the interstellar and protoplanetary environments, may both have formed via gravitational fragmentation—the brown dwarfs in interstellar clouds and companion objects in a protoplanetary disk. In both cases, however, the fact that objects in this mass range are relatively infrequent suggests that this mechanism must be inefficient in both environments.

  1. POPULATION PROPERTIES OF BROWN DWARF ANALOGS TO EXOPLANETS

    International Nuclear Information System (INIS)

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

    2016-01-01

    We present a kinematic analysis of 152 low surface gravity M7-L8 dwarfs by adding 18 new parallaxes (including 10 for comparative field objects), 38 new radial velocities, and 19 new proper motions. We also add low- or moderate-resolution near-infrared spectra for 43 sources confirming their low surface gravity features. Among the full sample, we find 39 objects to be high-likelihood or new bona fide members of nearby moving groups, 92 objects to be ambiguous members and 21 objects that are non-members. Using this age-calibrated sample, we investigate trends in gravity classification, photometric color, absolute magnitude, color–magnitude, luminosity, and effective temperature. We find that gravity classification and photometric color clearly separate 5–130 Myr sources from >3 Gyr field objects, but they do not correlate one to one with the narrower 5–130 Myr age range. Sources with the same spectral subtype in the same group have systematically redder colors, but they are distributed between 1 and 4 σ from the field sequences and the most extreme outlier switches between intermediate- and low-gravity sources either confirmed in a group or not. The absolute magnitudes of low-gravity sources from the J band through W 3 show a flux redistribution when compared to equivalently typed field brown dwarfs that is correlated with spectral subtype. Low-gravity, late-type L dwarfs are fainter at J than the field sequence but brighter by W 3. Low-gravity M dwarfs are >1 mag brighter than field dwarfs in all bands from J through W 3. Clouds, which are a far more dominant opacity source for L dwarfs, are the likely cause. On color–magnitude diagrams, 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 . We conclude that low-gravity dwarfs carry an extreme version of the cloud conditions of field objects to lower

  2. Microlensing of unresolved stars as a brown dwarf detection method

    CERN Document Server

    Bouquet, Alain; Melchior, Anne-Laure; Giraud-Heraud, Yannick; Baillon, Paul

    1993-01-01

    We describe a project of brown dwarf detection in the dark halo of a galaxy using the microlensing effect. We argue that monitoring pixels instead of stars could provide an enhancement in the number of detectable events. We estimate the detection efficiency with a Monte-Carlo simulation. We expect a ten-fold increase with respect to current experiments. To assess the feasibility of this method we have determined the photometric precision of a pixel by comparing several pictures of a same field in the LMC. To be published in the Proceeding of the workshop 'The dark side of the universe...', Roma, Juin 1993,

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

    International Nuclear Information System (INIS)

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

    2012-01-01

    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 M 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 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 H and a plateau or dimming of [–0.2 to –0.3] mag is seen in M 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 JH and/or M 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 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. 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

  6. EROS 2 proper motion survey a field brown dwarf and an L dwarf companion to LHS 102

    CERN Document Server

    Goldman, B; Forveille, T; Afonso, C; Alard, C; Albert, J N; Andersen, J; Ansari, R; Aubourg, E; Bareyre, P; Bauer, F; Beaulieu, J P; Borsenberger, J; Bouquet, A; Char, S; Charlot, X; Couchot, F; Coutures, C; Derue, F; Ferlet, R; Fouqué, P; Glicenstein, J F; Gould, A; Graff, D S; Gros, M H; Haïssinski, J; Hamilton, J C; Hardin, D P; De Kat, J; Kim, A; Lasserre, T; Lesquoy, E; Loup, C; Magneville, C; Mansoux, B; Marquette, J B; Martín, E L; Maurice, E; Milshtein, A I; Moniez, M; Palanque-Delabrouille, Nathalie; Perdereau, O; Prévôt, L; Regnault, N; Rich, J; Spiro, Michel; Vidal-Madjar, A; Virgoux, L; Zylberajch, S

    1999-01-01

    We report the discovery of two L dwarfs (the new spectral class defined for dwarfs cooler than the M type) in a two-epoch CCD proper motion survey of 413 square degrees, complemented by infrared photometry from DENIS. One of them has a strong lithium line and is therefore a brown dwarf. The other is a common proper motion companion to the mid-M dwarf LHS 102 (GJ 1001), which has a well determined trigonometric parallax. LHS 102B is thus the coolest L dwarf of known distance and luminosity. Its infrared absolute photometry are very well reproduced by the Allard et al DUSTY models.

  7. Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B

    Science.gov (United States)

    Zhou, Yifan; Apai, Dániel; Metchev, Stanimir; Lew, Ben W. P.; Schneider, Glenn; Marley, Mark S.; Karalidi, Theodora; Manjavacas, Elena; Bedin, Luigi R.; Cowan, Nicolas B.; Miles-Páez, Paulo A.; Lowrance, Patrick J.; Radigan, Jacqueline; Burgasser, Adam J.

    2018-03-01

    Time-resolved observations of brown dwarfs’ rotational modulations provide powerful insights into the properties of condensate clouds in ultra-cool atmospheres. Multi-wavelength light curves reveal cloud vertical structures, condensate particle sizes, and cloud morphology, which directly constrain condensate cloud and atmospheric circulation models. We report results from Hubble Space Telescope/Wide Field Camera 3 near-infrared G141 taken in six consecutive orbits observations of HN Peg B, an L/T transition brown dwarf companion to a G0V type star. The best-fit sine wave to the 1.1–1.7 μm broadband light curve has an amplitude of 1.206% ± 0.025% and period of 15.4 ± 0.5 hr. The modulation amplitude has no detectable wavelength dependence except in the 1.4 μm water absorption band, indicating that the characteristic condensate particle sizes are large (>1 μm). We detect significantly (4.4σ) lower modulation amplitude in the 1.4 μm water absorption band and find that HN Peg B’s spectral modulation resembles those of early T type brown dwarfs. We also describe a new empirical interpolation method to remove spectral contamination from the bright host star. This method may be applied in other high-contrast time-resolved observations with WFC3.

  8. Brown dwarfs: at last filling the gap between stars and planets.

    Science.gov (United States)

    Zuckerman, B

    2000-02-01

    Until the mid-1990s a person could not point to any celestial object and say with assurance that "here is a brown dwarf." Now dozens are known, and the study of brown dwarfs has come of age, touching upon major issues in astrophysics, including the nature of dark matter, the properties of substellar objects, and the origin of binary stars and planetary systems.

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

    International Nuclear Information System (INIS)

    Wittenmyer, Robert A.; Endl, Michael; Cochran, William D.; Ramirez, Ivan; MacQueen, Phillip J.; Shetrone, Matthew; Reffert, Sabine

    2009-01-01

    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 ∼> 23 0 . This is the second rare close-in brown dwarf candidate discovered by the McDonald planet search program.

  10. Analytic Models of Brown Dwarfs and the Substellar Mass Limit

    Directory of Open Access Journals (Sweden)

    Sayantan Auddy

    2016-01-01

    Full Text Available We present the analytic theory of brown dwarf evolution and the lower mass limit of the hydrogen burning main-sequence stars and introduce some modifications to the existing models. We give an exact expression for the pressure of an ideal nonrelativistic Fermi gas at a finite temperature, therefore allowing for nonzero values of the degeneracy parameter. 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⊙–0.087M⊙. An analytic formula for the luminosity evolution allows us to estimate the time period of the nonsteady state (i.e., non-main-sequence nuclear burning for substellar objects. We also calculate the evolution of very low mass stars. We estimate that ≃11% of stars take longer than 107 yr to reach the main sequence, and ≃5% of stars take longer than 108 yr.

  11. Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey

    International Nuclear Information System (INIS)

    Martin, Emily C.; Mace, Gregory N.; McLean, Ian S.; Logsdon, Sarah E.; Rice, Emily L.; Kirkpatrick, J. Davy; Burgasser, Adam J.; McGovern, Mark R.; Prato, Lisa

    2017-01-01

    We combine 131 new medium-resolution ( R ∼ 2000) J -band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5–T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6–L7 objects in our sample by measuring the equivalent widths (EW) of the K i lines at 1.1692, 1.1778, and 1.2529 μ m, and the 1.2 μ m FeH J absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peak—at ∼L5 and T5—in K i EW as a function of spectral type. We analyze the K i EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6–L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.

  12. Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Emily C.; Mace, Gregory N.; McLean, Ian S.; Logsdon, Sarah E. [Department of Physics and Astronomy, University of California Los Angeles, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); Rice, Emily L. [Department of Engineering Science and Physics, College of Staten Island, 2800 Victory Boulevard, Staten Island, NY 10301 (United States); Kirkpatrick, J. Davy [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); McGovern, Mark R. [Math and Sciences Division, Antelope Valley College, 3041 West Avenue K, Lancaster, CA 93536 (United States); Prato, Lisa, E-mail: emartin@astro.ucla.edu [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)

    2017-03-20

    We combine 131 new medium-resolution ( R ∼ 2000) J -band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5–T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6–L7 objects in our sample by measuring the equivalent widths (EW) of the K i lines at 1.1692, 1.1778, and 1.2529 μ m, and the 1.2 μ m FeH{sub J} absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peak—at ∼L5 and T5—in K i EW as a function of spectral type. We analyze the K i EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6–L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.

  13. The Young and the Restless: Revealing the Turbulent, Cloudy Nature of Young Brown Dwarfs and Exoplanets

    Science.gov (United States)

    Faherty, Jacqueline; Cruz, Kelle; Rice, Emily; Gagne, Jonathan; Marley, Mark; Gizis, John

    2018-05-01

    Emerging as an important insight into cool-temperature atmospheric physics is evidence for a correlation between enhanced clouds and youth. With this Spitzer Cycle 14 large GO program, we propose to obtain qualifying evidence for this hypothesis using an age calibrated sample of brown dwarf-exoplanet analogs recently discovered and characterized by team members. Using Spitzer's unparalleled ability to conduct uninterrupted, high-cadence observations over numerous hours, we will examine the periodic brightness variations at 3.5 microns, where clouds are thought to be most disruptive to emergent flux. Compared to older sources, theory predicts that younger or lower-surface gravity objects will have cooler brightness temperatures at 3.5 microns and larger peak to peak amplitude variations due to higher altitude, more turbulent clouds. Therefore we propose to obtain light curves for 26 sources that span L3-L8 spectral types (Teff 2500-1700 K), 20-130 Myr ages, and predicted 8-30 MJup masses. Comparing to the variability trends and statistics of field (3-5 Gyr) Spitzer Space Telescope General Observer Proposal equivalents currently being monitored by Spitzer, we will have unequivocal evidence for (or against) the turbulent atmospheric nature of younger sources. Coupling this Spitzer dataset with the multitude of spectral information we have on each source, the light curves obtained through this proposal will form the definitive library of data for investigating atmosphere dynamics (rotation rates, winds, storms, changing cloud structures) in young giant exoplanets and brown dwarfs.

  14. Survival of a brown dwarf after engulfment by a red giant star.

    Science.gov (United States)

    Maxted, P F L; Napiwotzki, R; Dobbie, P D; Burleigh, M R

    2006-08-03

    Many sub-stellar companions (usually planets but also some brown dwarfs) orbit solar-type stars. These stars can engulf their sub-stellar companions when they become red giants. This interaction may explain several outstanding problems in astrophysics but it is unclear under what conditions a low mass companion will evaporate, survive the interaction unchanged or gain mass. Observational tests of models for this interaction have been hampered by a lack of positively identified remnants-that is, white dwarf stars with close, sub-stellar companions. The companion to the pre-white dwarf AA Doradus may be a brown dwarf, but the uncertain history of this star and the extreme luminosity difference between the components make it difficult to interpret the observations or to put strong constraints on the models. The magnetic white dwarf SDSS J121209.31 + 013627.7 may have a close brown dwarf companion but little is known about this binary at present. Here we report the discovery of a brown dwarf in a short period orbit around a white dwarf. The properties of both stars in this binary can be directly observed and show that the brown dwarf was engulfed by a red giant but that this had little effect on it.

  15. 50 years of brown dwarfs from prediction to discovery to forefront of research

    CERN Document Server

    2014-01-01

    The years 2012/2013 mark the 50th anniversary of the theoretical prediction that Brown Dwarfs, i.e. degenerate objects which are just not massive enough to sustain stable hydrogen fusion, exist. Some 20 years after their discovery, how Brown Dwarfs form is still one of the main open questions in the theory of star formation. In this volume, the pioneers of Brown Dwarf research review the history of the theoretical prediction and the subsequent discovery of Brown Dwarfs. After an introduction, written by Viki Joergens, reviewing Shiv Kumar's theoretical prediction of the existence of brown dwarfs, Takenori Nakano reviews his and Hayashi's calculation of the Hydrogen Burning Minimum Mass. Both predictions happened in the early 1960s. Jill Tarter then writes on the introduction of the term 'Brown Dwarf', before Ben Oppenheimer, Rafael Rebolo and Gibor Basri describe their first discovery of Brown Dwarfs in the 1990s. Lastly, Michael Cushing and Isabelle Baraffe describe the development of the field to the curren...

  16. Atmospheric studies of C2 white dwarfs

    Science.gov (United States)

    Swanson, Steven Roger

    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.

  17. Atmospheric studies of C2 white dwarfs

    International Nuclear Information System (INIS)

    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

  18. HUBBLE SPACE TELESCOPE IMAGING AND SPECTRAL ANALYSIS OF TWO BROWN DWARF BINARIES AT THE L DWARF/T DWARF TRANSITION

    International Nuclear Information System (INIS)

    Burgasser, Adam J.; Bardalez-Gagliuffi, Daniella C.; Gizis, John E.

    2011-01-01

    We present a detailed examination of the brown dwarf multiples 2MASS J08503593+1057156 and 2MASS J17281150+3948593, both suspected of harboring components that straddle the L dwarf/T dwarf transition. Resolved photometry from Hubble Space Telescope/NICMOS shows opposite trends in the relative colors of the components, with the secondary of 2MASS J0850+1057 being redder than its primary, while that of 2MASS J1728+3948 is bluer. We determine near-infrared component types by matching combined-light, near-infrared spectral data to binary templates, with component spectra scaled to resolved NICMOS and K p photometry. Combinations of L7 + L6 for 2MASS J0850+1057 and L5 + L6.5 for 2MASS J1728+3948 are inferred. Remarkably, the primary of 2MASS J0850+1057 appears to have a later-type classification compared to its secondary, despite being 0.8-1.2 mag brighter in the near-infrared, while the primary of 2MASS J1728+3948 is unusually early for its combined-light optical classification. Comparison to absolute magnitude/spectral type trends also distinguishes these components, with 2MASS J0850+1057A being ∼1 mag brighter and 2MASS J1728+3948A ∼ 0.5 mag fainter than equivalently classified field counterparts. We deduce that thick condensate clouds are likely responsible for the unusual properties of 2MASS J1728+3948A, while 2MASS J0850+1057A is either an inflated young brown dwarf or a tight unresolved binary, making it potentially part of a wide, low-mass, hierarchical quintuple system.

  19. ON THE RADII OF BROWN DWARFS MEASURED WITH AKARI NEAR-INFRARED SPECTROSCOPY

    International Nuclear Information System (INIS)

    Sorahana, S.; Yamamura, I.; Murakami, H.

    2013-01-01

    We derive the radii of 16 brown dwarfs observed by AKARI using their parallaxes and the ratios of observed to model fluxes. We find that the brown dwarf radius ranges between 0.64-1.13 R J with an average radius of 0.83 R J . We find a trend in the relation between radii and T eff ; the radius is at a minimum at T eff ∼ 1600 K, which corresponds to the spectral types of mid- to late-L. The result is interpreted by a combination of radius-mass and radius-age relations that are theoretically expected for brown dwarfs older than 10 8 yr.

  20. GPI Spectroscopy of the Mass, Age, and Metallicity Benchmark Brown Dwarf HD 4747 B

    Science.gov (United States)

    Crepp, Justin R.; Principe, David A.; Wolff, Schuyler; Giorla Godfrey, Paige A.; Rice, Emily L.; Cieza, Lucas; Pueyo, Laurent; Bechter, Eric B.; Gonzales, Erica J.

    2018-02-01

    The physical properties of brown dwarf companions found to orbit nearby, solar-type stars can be benchmarked against independent measures of their mass, age, chemical composition, and other parameters, offering insights into the evolution of substellar objects. The TRENDS high-contrast imaging survey has recently discovered a (mass/age/metallicity) benchmark brown dwarf orbiting the nearby (d = 18.69 ± 0.19 pc), G8V/K0V star HD 4747. We have acquired follow-up spectroscopic measurements of HD 4747 B using the Gemini Planet Imager to study its spectral type, effective temperature, surface gravity, and cloud properties. Observations obtained in the H-band and K 1-band recover the companion and reveal that it is near the L/T transition (T1 ± 2). Fitting atmospheric models to the companion spectrum, we find strong evidence for the presence of clouds. However, spectral models cannot satisfactorily fit the complete data set: while the shape of the spectrum can be well-matched in individual filters, a joint fit across the full passband results in discrepancies that are a consequence of the inherent color of the brown dwarf. We also find a 2σ tension in the companion mass, age, and surface gravity when comparing to evolutionary models. These results highlight the importance of using benchmark objects to study “secondary effects” such as metallicity, non-equilibrium chemistry, cloud parameters, electron conduction, non-adiabatic cooling, and other subtleties affecting emergent spectra. As a new L/T transition benchmark, HD 4747 B warrants further investigation into the modeling of cloud physics using higher resolution spectroscopy across a broader range of wavelengths, polarimetric observations, and continued Doppler radial velocity and astrometric monitoring.

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

    International Nuclear Information System (INIS)

    Stumpf, M. B.; Brandner, W.; Joergens, V.; Henning, Th.; Bouy, H.; Koehler, R.; Kasper, M.

    2010-01-01

    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 M Jup 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 (T eff ∼ 600-630 K) and least massive companion to any L or T dwarf.

  2. CLOUDS IN THE COLDEST BROWN DWARFS: FIRE SPECTROSCOPY OF ROSS 458C

    International Nuclear Information System (INIS)

    Burgasser, Adam J.; Simcoe, Robert A.; Bochanski, John J.; Saumon, Didier; Mamajek, Eric E.; McMurtry, Craig; Pipher, Judith L.; Forrest, William J.; Cushing, Michael C.; Marley, Mark S.

    2010-01-01

    Condensate clouds are a salient feature of L dwarf atmospheres, but have been assumed to play little role in shaping the spectra of the coldest T-type brown dwarfs. Here we report evidence of condensate opacity in the near-infrared spectrum of the brown dwarf candidate Ross 458C, obtained with the Folded-Port Infrared Echellette (FIRE) spectrograph at the Magellan Telescopes. These data verify the low-temperature nature of this source, indicating a T8 spectral classification, log 10 L bol /L sun = -5.62 ± 0.03, T eff = 650 ± 25 K, and a mass at or below the deuterium burning limit. The data also reveal enhanced emission at the K band associated with youth (low surface gravity) and supersolar metallicity, reflecting the properties of the Ross 458 system (age = 150-800 Myr, [Fe/H] = +0.2 to +0.3). We present fits of FIRE data for Ross 458C, the T9 dwarf ULAS J133553.45+113005.2, and the blue T7.5 dwarf SDSS J141624.08+134826.7B, to cloudless and cloudy spectral models from Saumon and Marley. For Ross 458C, we confirm a low surface gravity and supersolar metallicity, while the temperature differs depending on the presence (635 +25 -35 K) or absence (760 +70 -45 K) of cloud extinction. ULAS J1335+1130 and SDSS J1416+1348B have similar temperatures (595 +25 -45 K), but distinct surface gravities (log g = 4.0-4.5 cgs versus 5.0-5.5 cgs) and metallicities ([M/H] ∼ +0.2 versus -0.2). In all three cases, cloudy models provide better fits to the spectral data, significantly so for Ross 458C. These results indicate that clouds are an important opacity source in the spectra of young cold T dwarfs and should be considered when characterizing planetary-mass objects in young clusters and directly imaged exoplanets. The characteristics of Ross 458C suggest that it could itself be regarded as a planet, albeit one whose cosmogony does not conform with current planet formation theories.

  3. UNIFORM ATMOSPHERIC RETRIEVAL ANALYSIS OF ULTRACOOL DWARFS. I. CHARACTERIZING BENCHMARKS, Gl 570D AND HD 3651B

    Energy Technology Data Exchange (ETDEWEB)

    Line, Michael R.; Fortney, Jonathan J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Teske, Johanna [Carnegie DTM, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Burningham, Ben; Marley, Mark S., E-mail: mrline@ucsc.edu [NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035 (United States)

    2015-07-10

    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, Gl 570D and HD 3651B, to establish the validity of our upgraded forward model parameterization and Bayesian estimator. Our retrieved metallicities, gravities, and effective temperatures 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-oxygen ratios derived in the brown dwarfs and the host stars. Furthermore, we have for the first time unambiguously determined the presence of ammonia in the low-resolution spectra of these two late T dwarfs. We also show that the retrieved results are not significantly impacted by the possible presence of clouds, though some quantities are significantly impacted by uncertainties in photometry. This investigation represents a watershed study in establishing the utility of atmospheric retrieval approaches on brown dwarf spectra.

  4. Testing the existence of optical linear polarization in young brown dwarfs

    Science.gov (United States)

    Manjavacas, E.; Miles-Páez, P. A.; Zapatero-Osorio, M. R.; Goldman, B.; Buenzli, E.; Henning, T.; Pallé, E.; Fang, M.

    2017-07-01

    Linear polarization can be used as a probe of the existence of atmospheric condensates in ultracool dwarfs. Models predict that the observed linear polarization increases with the degree of oblateness, which is inversely proportional to the surface gravity. We aimed to test the existence of optical linear polarization in a sample of bright young brown dwarfs, with spectral types between M6 and L2, observable from the Calar Alto Observatory, and cataloged previously as low gravity objects using spectroscopy. Linear polarimetric images were collected in I and R band using CAFOS at the 2.2-m telescope in Calar Alto Observatory (Spain). The flux ratio method was employed to determine the linear polarization degrees. With a confidence of 3σ, our data indicate that all targets have a linear polarimetry degree in average below 0.69 per cent in the I band, and below 1.0 per cent in the R band, at the time they were observed. We detected significant (I.e. P/σ ≥ 3) linear polarization for the young M6 dwarf 2MASS J04221413+1530525 in the R band, with a degree of p* = 0.81 ± 0.17 per cent.

  5. DISCOVERY OF THREE DISTANT, COLD BROWN DWARFS IN THE WFC3 INFRARED SPECTROSCOPIC PARALLELS SURVEY

    International Nuclear Information System (INIS)

    Masters, D.; Siana, B.; McCarthy, P.; Hathi, N. P.; Dressler, A.; Burgasser, A. J.; Malkan, M.; Ross, N. R.; Scarlata, C.; Henry, A.; Colbert, J.; Atek, H.; Rafelski, M.; Teplitz, H.; Bunker, A.

    2012-01-01

    We present the discovery of three late-type (≥T4.5) brown dwarfs, including a probable Y dwarf, in the WFC3 Infrared Spectroscopic Parallels (WISP) survey. We use the G141 grism spectra to determine the spectral types of the dwarfs and derive distance estimates based on a comparison with nearby T dwarfs with known parallaxes. These are the most distant spectroscopically confirmed T/Y dwarfs, with the farthest at an estimated distance of ∼400 pc. We compare the number of cold dwarfs found in the WISP survey with simulations of the brown dwarf mass function. The number found is generally consistent with an initial stellar mass function dN/dM∝M –α with α = 0.0-0.5, although the identification of a Y dwarf is somewhat surprising and may be indicative of either a flatter absolute magnitude/spectral-type relation than previously reported or an upturn in the number of very-late-type brown dwarfs in the observed volume.

  6. 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...

  7. SPECTRAL VARIABILITY FROM THE PATCHY ATMOSPHERES OF T AND Y DWARFS

    International Nuclear Information System (INIS)

    Morley, Caroline V.; Fortney, Jonathan J.; Marley, Mark S.; Lupu, Roxana

    2014-01-01

    Brown dwarfs of a variety of spectral types have been observed to be photometrically variable. Previous studies have focused on objects at the L/T transition, where the iron and silicate clouds in L dwarfs break up or dissipate. However, objects outside of this transitional effective temperature regime also exhibit variability. Here, we present models for mid-late T dwarfs and Y dwarfs. We present models that include patchy salt and sulfide clouds as well as water clouds for the Y dwarfs. We find that for objects over 375 K, patchy cloud opacity would generate the largest amplitude variability within near-infrared spectral windows. For objects under 375 K, water clouds also become important and generate larger amplitude variability in the mid-infrared. We also present models in which we perturb the temperature structure at different pressure levels of the atmosphere to simulate hot spots. These models show the most variability in the absorption features between spectral windows. The variability is strongest at wavelengths that probe pressure levels at which the heating is the strongest. The most illustrative types of observations for understanding the physical processes underlying brown dwarf variability are simultaneous, multi-wavelength observations that probe both inside and outside of molecular absorption features

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

    International Nuclear Information System (INIS)

    Belu, Adrian R.; Selsis, Franck; Raymond, Sean N.; Bolmont, Emeline; Pallé, Enric; Street, Rachel; Sahu, D. K.; Anupama, G. C.; Von Braun, Kaspar; Figueira, Pedro; Ribas, Ignasi

    2013-01-01

    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 HZ o ut ). Habitable planets with P HZ o ut 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 +5.6 -1.4 % and 56 +31 -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 ∼1% of a five-year mission's lifetime spread over a contiguous segment only one-fifth to one-tenth of this duration.

  9. 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.

  10. A Population Study of Wide-Separation Brown Dwarf Companions to Main Sequence Stars

    Science.gov (United States)

    Smith, Jeffrey J.

    2005-01-01

    Increased interest in infrared astronomy has opened the frontier to study cooler objects that shed significant light on the formation of planetary systems. Brown dwarf research provides a wealth of information useful for sorting through a myriad of proposed formation theories. Our study combines observational data from 2MASS with rigorous computer simulations to estimate the true population of long-range (greater than 1000 AU) brown dwarf companions in the solar neighborhood (less than 25 pc from Earth). Expanding on Gizis et al. (2001), we have found the margin of error in previous estimates to be significantly underestimated after we included orbit eccentricity, longitude of pericenter, angle of inclination, field star density, and primary and secondary luminosities as parameters influencing the companion systems in observational studies. We apply our simulation results to current L- and T-dwarf catalogs to provide updated estimates on the frequency of wide-separation brown dwarf companions to main sequence stars.

  11. 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.

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

    International Nuclear Information System (INIS)

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

    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.

  13. WISE BROWN DWARF BINARIES: THE DISCOVERY OF A T5+T5 AND A T8.5+T9 SYSTEM

    International Nuclear Information System (INIS)

    Gelino, Christopher R.; Kirkpatrick, J. Davy; Griffith, Roger L.; Marsh, Kenneth A.; Cushing, Michael C.; Eisenhardt, Peter R.; Mainzer, Amanda K.; Skrutskie, Michael F.; Wright, Edward L.

    2011-01-01

    The multiplicity properties of brown dwarfs are critical empirical constraints for formation theories, while multiples themselves provide unique opportunities to test evolutionary and atmospheric models and examine empirical trends. Studies using high-resolution imaging cannot only uncover faint companions, but they can also be used to determine dynamical masses through long-term monitoring of binary systems. We have begun a search for the coolest brown dwarfs using preliminary processing of data from the Wide-field Infrared Survey Explorer and have confirmed many of the candidates as late-type T dwarfs. In order to search for companions to these objects, we are conducting observations using the Laser Guide Star Adaptive Optics system on Keck II. Here we present the first results of that search, including a T5 binary with nearly equal mass components and a faint companion to a T8.5 dwarf with an estimated spectral type of T9.

  14. 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.

  15. Exploring the brown dwarf desert: new substellar companions from the SDSS-III MARVELS survey

    Science.gov (United States)

    Grieves, Nolan; Ge, Jian; Thomas, Neil; Ma, Bo; Sithajan, Sirinrat; Ghezzi, Luan; Kimock, Ben; Willis, Kevin; De Lee, Nathan; Lee, Brian; Fleming, Scott W.; Agol, Eric; Troup, Nicholas; Paegert, Martin; Schneider, Donald P.; Stassun, Keivan; Varosi, Frank; Zhao, Bo; Jian, Liu; Li, Rui; Porto de Mello, Gustavo F.; Bizyaev, Dmitry; Pan, Kaike; Dutra-Ferreira, Letícia; Lorenzo-Oliveira, Diego; Santiago, Basílio X.; da Costa, Luiz N.; Maia, Marcio A. G.; Ogando, Ricardo L. C.; del Peloso, E. F.

    2017-06-01

    Planet searches using the radial velocity technique show a paucity of companions to solar-type stars within ˜5 au in the mass range of ˜10-80 MJup. This deficit, known as the brown dwarf desert, currently has no conclusive explanation. New substellar companions in this region help assess the reality of the desert and provide insight to the formation and evolution of these objects. Here, we present 10 new brown dwarf and 2 low-mass stellar companion candidates around solar-type stars from the Multi-object APO Radial Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digital Sky Survey III. These companions were selected from processed MARVELS data using the latest University of Florida Two Dimensional pipeline, which shows significant improvement and reduction of systematic errors over previous pipelines. The 10 brown dwarf companions range in mass from ˜13 to 76 MJup and have orbital radii of less than 1 au. The two stellar companions have minimum masses of ˜98 and 100 MJup. The host stars of the MARVELS brown dwarf sample have a mean metallicity of [Fe/H] = 0.03 ± 0.08 dex. Given our stellar sample we estimate the brown dwarf occurrence rate around solar-type stars with periods less than ˜300 d to be ˜0.56 per cent.

  16. The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

    Science.gov (United States)

    Reylé, C.; Delorme, P.; Willott, C. J.; Albert, L.; Delfosse, X.; Forveille, T.; Artigau, E.; Malo, L.; Hill, G. J.; Doyon, R.

    2010-11-01

    Context. Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope. Aims: Our objectives are to find ultracool brown dwarfs and to constrain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs. Methods: We identify candidates in CFHT/MegaCam i' and z' images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found ~50 T dwarfs and ~170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i'-z' colours, found in 780 square degrees. Results: We have currently completed the NIR follow-up on a large part of the survey for all candidates from mid-L dwarfs down to the latest T dwarfs known with utracool dwarfs' colours. This allows us to draw on a complete and well defined sample of 102 ultracool dwarfs to investigate the luminosity function and space density of field dwarfs. Conclusions: We found the density of late L5 to T0 dwarfs to be 2.0+0.8-0.7 × 10-3 objects pc-3, the density of T0.5 to T5.5 dwarfs to be 1.4+0.3-0.2 × 10-3 objects pc-3, and the density of T6 to T8 dwarfs to be 5.3+3.1-2.2 × 10-3 objects pc-3. We found that these results agree better with a flat substellar mass function. Three latest dwarfs at the boundary between T and Y dwarfs give the high density 8.3+9.0-5.1 × 10-3 objects pc-3. Although the uncertainties are very large this suggests that many brown dwarfs should be found in this late spectral type range, as expected from the cooling of brown dwarfs, whatever their mass, down to very low temperature. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by

  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. PHOTOMETRIC MONITORING OF THE COLDEST KNOWN BROWN DWARF WITH THE SPITZER SPACE TELESCOPE

    Energy Technology Data Exchange (ETDEWEB)

    Esplin, T. L.; Luhman, K. L. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Cushing, M. C.; Hardegree-Ullman, K. K.; Trucks, J. L.; Schneider, A. C. [Department of Physics and Astronomy, The University of Toledo, OH 43606 (United States); Burgasser, A. J., E-mail: taran.esplin@psu.edu [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States)

    2016-11-20

    Because WISE J085510.83-071442.5 (hereafter WISE 0855-0714) is the coldest known brown dwarf (∼250 K) and one of the Sun’s closest neighbors (2.2 pc), it offers a unique opportunity to study a planet-like atmosphere in an unexplored regime of temperature. To detect and characterize inhomogeneities in its atmosphere (e.g., patchy clouds, hot spots), we have performed time-series photometric monitoring of WISE 0855-0714 at 3.6 and 4.5 μ m with the Spitzer Space Telescope during two 23 hr periods that were separated by several months. For both bands, we have detected variability with peak-to-peak amplitudes of 4%–5% and 3%–4% in the first and second epochs, respectively. The light curves are semiperiodic in the first epoch for both bands, but they are more irregular in the second epoch. Models of patchy clouds have predicted a large increase in mid-infrared (mid-IR) variability amplitudes (for a given cloud covering fraction) with the appearance of water ice clouds at T {sub eff} < 375 K, so if such clouds are responsible for the variability of WISE 0855-0714, then its small amplitudes of variability indicate a very small deviation in cloud coverage between hemispheres. Alternatively, the similarity in mid-IR variability amplitudes between WISE 0855-0714 and somewhat warmer T and Y dwarfs may suggest that they share a common origin for their variability (i.e., not water clouds). In addition to our variability data, we have examined other constraints on the presence of water ice clouds in the atmosphere of WISE 0855-0714, including the recent mid-IR spectrum from Skemer et al. (2016). We find that robust evidence of such clouds is not yet available.

  19. White Dwarf Model Atmospheres: Synthetic Spectra for Super Soft Sources

    OpenAIRE

    Rauch, Thomas

    2011-01-01

    The T\\"ubingen NLTE Model-Atmosphere Package (TMAP) calculates fully metal-line blanketed white dwarf model atmospheres and spectral energy distributions (SEDs) at a high level of sophistication. Such SEDs are easily accessible via the German Astrophysical Virtual Observatory (GAVO) service TheoSSA. We discuss applications of TMAP models to (pre) white dwarfs during the hottest stages of their stellar evolution, e.g. in the parameter range of novae and super soft sources.

  20. White Dwarf Model Atmospheres: Synthetic Spectra for Supersoft Sources

    Science.gov (United States)

    Rauch, Thomas

    2013-01-01

    The Tübingen NLTE Model-Atmosphere Package (TMAP) calculates fully metal-line blanketed white dwarf model atmospheres and spectral energy distributions (SEDs) at a high level of sophistication. Such SEDs are easily accessible via the German Astrophysical Virtual Observatory (GAVO) service TheoSSA. We discuss applications of TMAP models to (pre) white dwarfs during the hottest stages of their stellar evolution, e.g. in the parameter range of novae and supersoft sources.

  1. Understanding of variability properties in very low mass stars and brown dwarfs

    Science.gov (United States)

    Mondal, Soumen; Ghosh, Samrat; Khata, Dhrimadri; Joshi, Santosh; Das, Ramkrishna

    2018-04-01

    We report on photometric variability studies of a L3.5 brown dwarf 2MASS J00361617+1821104 (2M0036+18) in the field and of four young brown dwarfs in the star-forming region IC 348. From muti-epoch observations, we found significant periodic variability in 2M0036+18 with a period of 2.66 ± 0.55 hours on one occasion while it seemed to be non-variable on three other occasions. An evolving dust cloud might cause such a scenario. Among four young brown dwarfs of IC 348 in the spectral range M7.25 - M8, one brown dwarf 2MASS J03443921+3208138 shows significant variability. The K-band spectra (2.0-2.4 μm) of nine very low mass stars (M1 - M9 V) are used to characterize the water band index (H20-K2). We found that it is strongly correlated with the surface temperature of M dwarfs.

  2. Model atmospheres for M (sub)dwarf stars. 1: The base model grid

    Science.gov (United States)

    Allard, France; Hauschildt, Peter H.

    1995-01-01

    We have calculated a grid of more than 700 model atmospheres valid for a wide range of parameters encompassing the coolest known M dwarfs, M subdwarfs, and brown dwarf candidates: 1500 less than or equal to T(sub eff) less than or equal to 4000 K, 3.5 less than or equal to log g less than or equal to 5.5, and -4.0 less than or equal to (M/H) less than or equal to +0.5. Our equation of state includes 105 molecules and up to 27 ionization stages of 39 elements. In the calculations of the base grid of model atmospheres presented here, we include over 300 molecular bands of four molecules (TiO, VO, CaH, FeH) in the JOLA approximation, the water opacity of Ludwig (1971), collision-induced opacities, b-f and f-f atomic processes, as well as about 2 million spectral lines selected from a list with more than 42 million atomic and 24 million molecular (H2, CH, NH, OH, MgH, SiH, C2, CN, CO, SiO) lines. High-resolution synthetic spectra are obtained using an opacity sampling method. The model atmospheres and spectra are calculated with the generalized stellar atmosphere code PHOENIX, assuming LTE, plane-parallel geometry, energy (radiative plus convective) conservation, and hydrostatic equilibrium. The model spectra give close agreement with observations of M dwarfs across a wide spectral range from the blue to the near-IR, with one notable exception: the fit to the water bands. We discuss several practical applications of our model grid, e.g., broadband colors derived from the synthetic spectra. In light of current efforts to identify genuine brown dwarfs, we also show how low-resolution spectra of cool dwarfs vary with surface gravity, and how the high-regulation line profile of the Li I resonance doublet depends on the Li abundance.

  3. Brown Adipose Tissue Function Is Enhanced in Long-Lived, Male Ames Dwarf Mice

    Science.gov (United States)

    McFadden, Samuel; Fang, Yimin; Huber, Joshua A.; Zhang, Chi; Sun, Liou Y.; Bartke, Andrzej

    2016-01-01

    Ames dwarf mice (Prop1df/df) are long-lived due to a loss of function mutation, resulting in deficiency of GH, TSH, and prolactin. Along with a marked extension of longevity, Ames dwarf mice have improved energy metabolism as measured by an increase in their oxygen consumption and heat production, as well as a decrease in their respiratory quotient. Along with alterations in energy metabolism, Ames dwarf mice have a lower core body temperature. Moreover, Ames dwarf mice have functionally altered epididymal white adipose tissue (WAT) that improves, rather than impairs, their insulin sensitivity due to a shift from pro- to anti-inflammatory cytokine secretion. Given the unique phenotype of Ames dwarf epididymal WAT, their improved energy metabolism, and lower core body temperature, we hypothesized that Ames dwarf brown adipose tissue (BAT) may function differently from that of their normal littermates. Here we use histology and RT-PCR to demonstrate that Ames dwarf mice have enhanced BAT function. We also use interscapular BAT removal to demonstrate that BAT is necessary for Ames dwarf energy metabolism and thermogenesis, whereas it is less important for their normal littermates. Furthermore, we show that Ames dwarf mice are able to compensate for loss of interscapular BAT by using their WAT depots as an energy source. These findings demonstrate enhanced BAT function in animals with GH and thyroid hormone deficiencies, chronic reduction of body temperature, and remarkably extended longevity. PMID:27740871

  4. Finding ultracool brown dwarfs with MegaCam on CFHT: method and first results

    Science.gov (United States)

    Delorme, P.; Willott, C. J.; Forveille, T.; Delfosse, X.; Reylé, C.; Bertin, E.; Albert, L.; Artigau, E.; Robin, A. C.; Allard, F.; Doyon, R.; Hill, G. J.

    2008-06-01

    Aims: We present the first results of a wide field survey for cool brown dwarfs with the MegaCam camera on the CFHT telescope, the Canada-France Brown Dwarf Survey, hereafter CFBDS. Our objectives are to find ultracool brown dwarfs and to constrain the field-brown dwarf mass function thanks to a larger sample of L and T dwarfs. Methods: We identify candidates in CFHT/MegaCam i' and z' images using optimised psf-fitting within Source Extractor, and follow them up with pointed near-infrared imaging on several telescopes. Results: We have so far analysed over 350 square degrees and found 770 brown dwarf candidates brighter than z'_AB=22.5. We currently have J-band photometry for 220 of these candidates, which confirms 37% as potential L or T dwarfs. Some are among the reddest and farthest brown dwarfs currently known, including an independent identification of the recently published ULAS J003402.77-005206.7 and the discovery of a second brown dwarf later than T8, CFBDS J005910.83-011401.3. Infrared spectra of three T dwarf candidates confirm their nature, and validate the selection process. Conclusions: The completed survey will discover ~100 T dwarfs and ~500 L dwarfs or M dwarfs later than M8, approximately doubling the number of currently known brown dwarfs. The resulting sample will have a very well-defined selection function, and will therefore produce a very clean luminosity function. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on observations made

  5. MID-INFRARED PHOTOMETRY OF COLD BROWN DWARFS: DIVERSITY IN AGE, MASS, AND METALLICITY

    International Nuclear Information System (INIS)

    Leggett, S. K.; Burningham, Ben; Jones, H. R. A.; Lucas, P. W.; Pinfield, D. J.; Saumon, D.; Marley, M. S.; Warren, S. J.; Smart, R. L.; Tamura, Motohide

    2010-01-01

    We present new Spitzer Infrared Array Camera (IRAC) photometry of 12 very late-type T dwarfs: nine have [3.6], [4.5], [5.8], and [8.0] photometry and three have [3.6] and [4.5] photometry only. 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. The online appendix provides a collation of MKO-system YJHKL'M' and IRAC photometry for a sample of M, L, and T dwarfs. Brown dwarfs with effective temperature (T eff ) below 700 K emit more than half their flux at wavelengths longer than 3 μm, and the ratio of the mid-infrared flux to the near-infrared flux becomes very sensitive to T eff at these low temperatures. We confirm that the color H (1.6 μm) - [4.5] is a good indicator of T eff with a relatively weak dependence on metallicity and gravity. Conversely, the colors H - K (2.2 μm) 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 12 dwarfs currently known with H- [4.5] >3.0, and 500 K ∼ eff ∼<800 K, 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] = +0.3. The small number of T8-T9 dwarfs found in the UK Infrared Telescope 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 Wide-Field Infrared

  6. Habitable planets around white and brown dwarfs: the perils of a cooling primary.

    Science.gov (United States)

    Barnes, Rory; Heller, René

    2013-03-01

    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; 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 constrain their early activity and UV emission very well. Nonetheless, both types of planets are at risk of never achieving habitable conditions, but planets orbiting white dwarfs may be less likely to sustain life than those orbiting brown dwarfs. We consider the future habitability of the planet candidates KOI 55.01 and 55.02 in these terms and find they are unlikely to become habitable.

  7. PROTOPLANETARY DISK MASSES FROM STARS TO BROWN DWARFS

    International Nuclear Information System (INIS)

    Mohanty, Subhanjoy; Mortlock, Daniel; Greaves, Jane; Pascucci, Ilaria; Apai, Daniel; Scholz, Aleks; Thompson, Mark; Lodato, Giuseppe; Looper, Dagny

    2013-01-01

    We present SCUBA-2 850 μm 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 3σ limits correspond to a dust mass of 1.2 M ⊕ in Taurus and a mere 0.2 M ⊕ in the TWA (3-10× deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, ρ 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 ∼100 AU for intermediate-mass stars, solar types, and VLMS, and ∼20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M * 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 ρ Oph intermediate-mass and solar-type stars evince an opacity index of β ∼ 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 μm 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 Bayesian analysis shows that the apparent disk-to-stellar mass ratio has a roughly

  8. The First Brown Dwarf Discovered by the Backyard Worlds: Planet 9 Citizen Science Project

    Science.gov (United States)

    Kuchner, Marc J.; Faherty, Jacqueline K.; Schneider, Adam C.; Meisner, Aaron M.; Filippazzo, Joseph C.; Gagne, Jonathan; Trouille, Laura; Silverberg, Steven M.; Castro, Rosa; Fletcher, Bob; hide

    2017-01-01

    The Wide-field Infrared Survey Explorer (WISE) is a powerful tool for finding nearby brown dwarfs and searching for new planets in the outer solar system, especially with the incorporation of NEOWISE and NEOWISE Reactivation data. However, so far, searches for brown dwarfs in WISE data have yet to take advantage of the full depth of the WISE images. To efficiently search this unexplored space via visual inspection, we have launched anew citizen science project, called "Backyard Worlds: Planet 9," which asks volunteers to examine short animations composed of difference images constructed from time-resolved WISE co adds. We report the first new substellar object discovered by this project, WISEA J110125.95+540052.8, a T5.5 brown dwarf located approximately 34 pc from the Sun with a total proper motion of approx.0. "7/ yr. WISEA J110125.95+540052.8 has a WISE W2 magnitude of W2 = 15.37+/- 0.09; our sensitivity to this source demonstrates the ability of citizen scientists to identify moving objects via visual inspection that are 0.9 mag fainter than the W2 single-exposure sensitivity, a threshold that has limited prior motion-based brown dwarf searches with WISE.

  9. The luminosity and mass functions of the Pleiades: low-mass stars and brown dwarfs

    International Nuclear Information System (INIS)

    Hambly, N.C.; Jameson, R.F.

    1991-01-01

    COSMOS measurements of R and I Schmidt plates are used to determine the luminosity function and hence mass function of the Pleiades open cluster. Star counts are made in the cluster and the field star contribution, measured outside the cluster, is subtracted. A lower limit of 30 brown dwarfs is found; the mass function is flat at the lowest masses. (author)

  10. A search for lithium in Pleiades brown dwarf candidates using the Keck hires echelle

    Science.gov (United States)

    Marcy, Geoffrey W.; Basri, Gibor; Graham, James R.

    1994-01-01

    We report Keck Observatory high-resolution echelle spectra of lithium at 670.8 nm in two of the lowest luminosity brown dwarf candidates in the Pleiades. These objects have estimated masses of 0.055 to 0.059 solar mass from their location on a color-magnitude diagram relative to theoretical isochrones. Stellar interior models predict that Li has not burned in them. However, we find no evidence of the Li line, at limits 100 to 1000 times below the initial abundance. This indicates that Li has in fact been depleted, presumably by nuclear processing as occurs in Pleiades stars. Interior models suggest that such large Li depletion occurs only for objects with M greater than 0.09 solar mass at the age of the Pleiades. Thus, it is unlikely that the candidates are brown dwarfs. The brown dwarf candidates present a conflict: either they have masses greater than suggested from their placement on the H-R diagram, or they do have the very low suggested masses but are nonetheless capable of destroying Li, in only 70 Myr. Until this dilemma is resolved, the photometric identification of brown dwarfs will remain difficult. Resolution may reside in higher T(sub eff) derived from optical and IR colors or in lower T(sub eff) in the interior models.

  11. VLA Observations of the Disk around the Young Brown Dwarf 2MASS J044427+2512

    Energy Technology Data Exchange (ETDEWEB)

    Ricci, L. [Department of Physics and Astronomy, Rice University, 6100 Main Street, Houston, TX 77005 (United States); Rome, H. [The Kinkaid School, 201 Kinkaid School Drive, Houston, TX 77024 (United States); Pinilla, P. [Department of Astronomy Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Facchini, S. [Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Birnstiel, T. [University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, D-81679 Munich (Germany); Testi, L., E-mail: luca.ricci@rice.edu [European Southern Observatory (ESO) Headquarters, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)

    2017-09-01

    We present multi-wavelength radio observations obtained with the VLA of the protoplanetary disk surrounding the young brown dwarf 2MASS J04442713+2512164 (2M0444) in the Taurus star-forming region. 2M0444 is the brightest known brown dwarf disk at millimeter wavelengths, making this an ideal target to probe radio emission from a young brown dwarf. Thermal emission from dust in the disk is detected at 6.8 and 9.1 mm, whereas the 1.36 cm measured flux is dominated by ionized gas emission. We combine these data with previous observations at shorter sub-mm and mm wavelengths to test the predictions of dust evolution models in gas-rich disks after adapting their parameters to the case of 2M0444. These models show that the radial drift mechanism affecting solids in a gaseous environment has to be either completely made inefficient, or significantly slowed down by very strong gas pressure bumps in order to explain the presence of mm/cm-sized grains in the outer regions of the 2M0444 disk. We also discuss the possible mechanisms for the origin of the ionized gas emission detected at 1.36 cm. The inferred radio luminosity for this emission is in line with the relation between radio and bolometric luminosity valid for for more massive and luminous young stellar objects, and extrapolated down to the very low luminosity of the 2M0444 brown dwarf.

  12. An expanded set of brown dwarf and very low mass star models

    Science.gov (United States)

    Burrows, A.; Hubbard, W. B.; Saumon, D.; Lunine, J. I.

    1993-01-01

    We present in this paper updated and improved theoretical models of brown dwarfs and late M dwarfs. The evolution and characteristics of objects between 0.01 and 0.2 solar mass are exhaustively investigated and special emphasis is placed on their properties at early ages. The dependence on the helium fraction, deuterium fraction, and metallicity of the masses, effective temperature and luminosities at the edge of the hydrogen main sequence are calculated. We derive luminosity functions for representative mass functions and compare our predictions to recent cluster data. We show that there are distinctive features in the theoretical luminosity functions that can serve as diagnostics of brown dwarf physics. A zero-metallicity model is presented as a bound to or approximation of a putative extreme halo population.

  13. 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.

  14. BROWN DWARFS IN YOUNG MOVING GROUPS FROM PAN-STARRS1. I. AB DORADUS

    Energy Technology Data Exchange (ETDEWEB)

    Aller, Kimberly M.; Liu, Michael C.; Magnier, Eugene A.; Best, William M. J.; Kotson, Michael C.; Burgett, William S.; Chambers, Kenneth C.; Hodapp, Klaus W.; Flewelling, Heather; Kaiser, Nick; Tonry, John L.; Wainscoat, Richard J.; Waters, Christopher [University of Hawaii, Institute of Astronomy, 2860 Woodlawn Drive, Honolulu, HI 96822 (United States); Metcalf, Nigel [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)

    2016-04-20

    Substellar members of young (≲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, Two Micron All Sky Survey (2MASS), and WISE to search for substellar members of the AB Dor Moving Group within ≈50 pc and with spectral types of late M to early L, corresponding to masses down to ≈30 M {sub Jup} at the age of the group (≈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; ≈30–100 M {sub 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 find four field brown dwarfs unassociated with the AB Dor Moving Group, three of which have int-g gravity classification. While signatures of youth are present in the spectra of our ≈125 Myr objects, neither their J – K nor W 1 – W 2 colors are significantly redder than field dwarfs with the same spectral types, unlike younger ultracool dwarfs. We also determined PS1 parallaxes for eight of our candidates and one previously identified AB Dor Moving Group candidate. Although radial velocities (and parallaxes, for some) are still needed to fully assess membership, these new objects provide valuable insight into the spectral characteristics and evolution of young brown dwarfs.

  15. EXTRASOLAR STORMS: PRESSURE-DEPENDENT CHANGES IN LIGHT-CURVE PHASE IN BROWN DWARFS FROM SIMULTANEOUS HST AND SPITZER OBSERVATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Hao; Apai, Dániel; Karalidi, Theodora [Department of Astronomy, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Marley, Mark S. [NASA Ames Research Center, Naval Air Station, Moffett Field, Mountain View, CA 94035 (United States); Flateau, Davin [Department of Planetary Sciences, 1629 E. University Blvd., Tucson, AZ 85721 (United States); Showman, Adam P. [Department of Planetary Sciences, University of Arizona, 1629 University Blvd., Tucson, AZ 85721 (United States); Metchev, Stanimir [The University of Western Ontario, Department of Physics and Astronomy, Centre for Planetary Science and Exploration, 1151 Richmond St., London, ON N6A 3K7 (Canada); Buenzli, Esther [Institute for Astronomy, ETH Zürich Wolfgang-Pauli-Str. 27, 8093 Zürich (Switzerland); Radigan, Jacqueline [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Artigau, Étienne [Département de Physique, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 (Canada); Lowrance, Patrick J. [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Burgasser, Adam J., E-mail: haoyang@email.arizona.edu, E-mail: apai@arizona.edu [Center for Astrophysics and Space Science, University of California, San Diego, La Jolla, CA 92093 (United States)

    2016-07-20

    We present Spitzer /Infrared Array Camera Ch1 and Ch2 monitoring of six brown dwarfs during eight different epochs over the course of 20 months. For four brown dwarfs, we also obtained simulataneous Hubble Space Telescope ( HST )/WFC3 G141 grism spectra during two epochs and derived light curves in five narrowband filters. Probing different pressure levels in the atmospheres, the multiwavelength 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 to 13 hr. 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. The phase differences between the two groups of light curves suggest that the modulations seen at lower and higher pressures may be introduced by different cloud layers.

  16. HUBBLE SPACE TELESCOPE SPECTROSCOPY OF BROWN DWARFS DISCOVERED WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER

    International Nuclear Information System (INIS)

    Schneider, Adam C.; Cushing, Michael C.; Kirkpatrick, J. Davy; Gelino, Christopher R.; Mace, Gregory N.; Wright, Edward L.; Eisenhardt, Peter R.; Skrutskie, M. F.; Griffith, Roger L.; Marsh, Kenneth A.

    2015-01-01

    We present a sample of brown dwarfs identified with the Wide-field Infrared Survey Explorer (WISE) for which we have obtained Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) near-infrared grism spectroscopy. The sample (22 in total) was observed with the G141 grism covering 1.10–1.70 μm, while 15 were also observed with the G102 grism, which covers 0.90–1.10 μm. The additional wavelength coverage provided by the G102 grism allows us to (1) search for spectroscopic features predicted to emerge at low effective temperatures (e.g.,ammonia bands) and (2) construct a smooth spectral sequence across the T/Y boundary. We find no evidence of absorption due to ammonia in the G102 spectra. Six of these brown dwarfs are new discoveries, three of which are found to have spectral types of T8 or T9. The remaining three, WISE J082507.35+280548.5 (Y0.5), WISE J120604.38+840110.6 (Y0), and WISE J235402.77+024015.0 (Y1), are the 19th, 20th, and 21st spectroscopically confirmed Y dwarfs to date. We also present HST grism spectroscopy and reevaluate the spectral types of five brown dwarfs for which spectral types have been determined previously using other instruments

  17. HUBBLE SPACE TELESCOPE SPECTROSCOPY OF BROWN DWARFS DISCOVERED WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER

    Energy Technology Data Exchange (ETDEWEB)

    Schneider, Adam C.; Cushing, Michael C. [Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606 (United States); Kirkpatrick, J. Davy; Gelino, Christopher R. [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Mace, Gregory N.; Wright, Edward L. [Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); Eisenhardt, Peter R. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 (United States); Skrutskie, M. F. [Department of Astronomy, University of Virginia, 530 McCormick Road, Charlottesville, VA 22904 (United States); Griffith, Roger L. [Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States); Marsh, Kenneth A., E-mail: Adam.Schneider@Utoledo.edu [School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA (United Kingdom)

    2015-05-10

    We present a sample of brown dwarfs identified with the Wide-field Infrared Survey Explorer (WISE) for which we have obtained Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) near-infrared grism spectroscopy. The sample (22 in total) was observed with the G141 grism covering 1.10–1.70 μm, while 15 were also observed with the G102 grism, which covers 0.90–1.10 μm. The additional wavelength coverage provided by the G102 grism allows us to (1) search for spectroscopic features predicted to emerge at low effective temperatures (e.g.,ammonia bands) and (2) construct a smooth spectral sequence across the T/Y boundary. We find no evidence of absorption due to ammonia in the G102 spectra. Six of these brown dwarfs are new discoveries, three of which are found to have spectral types of T8 or T9. The remaining three, WISE J082507.35+280548.5 (Y0.5), WISE J120604.38+840110.6 (Y0), and WISE J235402.77+024015.0 (Y1), are the 19th, 20th, and 21st spectroscopically confirmed Y dwarfs to date. We also present HST grism spectroscopy and reevaluate the spectral types of five brown dwarfs for which spectral types have been determined previously using other instruments.

  18. The chemical evolution of white dwarf atmospheres: Diffusion and accretion

    International Nuclear Information System (INIS)

    Vauclair, G.; Vauclair, S.; Greenstein, J.L.

    1979-01-01

    A study of diffusion processes in white dwarfs is presented. We are especially interested in the estimate of the diffusion time scales for C, N, O, Mg, and Ca along the cooling sequence. The effect of the radiative acceleration is important in hot white dwarfs while in cooler ones the thermal diffusion dominates the gravitational settling. In hot white dwarfs, there should be an observable amount of CNO elements unless they have previously left the stars by a selective wind. Observational tests of this result are discussed. The diffusion time scales are always short compared to the evolutionary time scales. It is shown that in both hydrogen and helium envelopes, the convection zone, even at its maximum depth, is not able to bring back to the stellar surface the metals which have previously diffused downwards. The diffusion alone predicts a complete absence of metals in white dwarf atmospheres and envelopes. As metals are observed in white dwarfs, at least at effective temperatures lower than 15,000 K, there must be some mechanism competing with diffusion. We investigate the competition between diffusion and accretion and propose a general scheme for the chemical evolution of white dwarf atmospheres along the cooling sequence. (orig.)

  19. 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.; hide

    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.

  20. A search for low-mass stars and brown dwarfs in the Pleiades

    International Nuclear Information System (INIS)

    Jameson, R.F.; Skillen, I.

    1989-01-01

    Seven areas of size 25 arcmin 2 each were imaged at R and I in the Pleiades. The objects observed are plotted on a colour-magnitude diagram. Comparison with theory using the age of the Pleiades shows that nine of these objects might be low-mass Pleiades members. Of these, five would then be brown dwarfs although this number reduces if an older age is assumed for the cluster. Equally, all these objects may be old M dwarfs which are not cluster members. We are not yet able to distinguish definitely between these two possibilities. (author)

  1. CLOUDLESS ATMOSPHERES FOR L/T DWARFS AND EXTRASOLAR GIANT PLANETS

    Energy Technology Data Exchange (ETDEWEB)

    Tremblin, P.; Amundsen, D. S.; Chabrier, G.; Baraffe, I.; Drummond, B.; Hinkley, S. [Astrophysics Group, University of Exeter, Exeter EX4 4QL (United Kingdom); Mourier, P. [Ecole Normale Supérieure de Lyon, CRAL, UMR CNRS 5574, F-69364 Lyon Cedex 07 (France); Venot, O., E-mail: tremblin@astro.ex.ac.uk, E-mail: pascal.tremblin@cea.fr [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)

    2016-02-01

    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/CH{sub 4} and N{sub 2}/NH{sub 3} 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/CH{sub 4} 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.

  2. 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.

  3. CLOUDLESS ATMOSPHERES FOR L/T DWARFS AND EXTRASOLAR GIANT PLANETS

    International Nuclear Information System (INIS)

    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/CH 4 and N 2 /NH 3 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/CH 4 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

  4. PARALLAXES AND PROPER MOTIONS OF ULTRACOOL BROWN DWARFS OF SPECTRAL TYPES Y AND LATE T

    International Nuclear Information System (INIS)

    Marsh, Kenneth A.; Kirkpatrick, J. Davy; Gelino, Christopher R.; Griffith, Roger L.; Wright, Edward L.; Cushing, Michael C.; Skrutskie, Michael F.; Eisenhardt, Peter R.

    2013-01-01

    We present astrometric measurements of 11 nearby ultracool brown dwarfs of spectral types Y and late-T, based on imaging observations from a variety of space-based and ground-based telescopes. These measurements have been used to estimate relative parallaxes and proper motions via maximum likelihood fitting of geometric model curves. To compensate for the modest statistical significance (∼ tan , assumed similar to that implied by previous observations of T dwarfs. Our estimated distances are therefore somewhat dependent on that assumption. Nevertheless, the results have yielded distances for five of our eight Y dwarfs and all three T dwarfs. Estimated distances in all cases are ∼> 3 pc. In addition, we have obtained significant estimates of V tan for two of the Y dwarfs; both are –1 , consistent with membership in the thin disk population. Comparison of absolute magnitudes with model predictions as a function of color shows that the Y dwarfs are significantly redder in J – H than predicted by a cloud-free model.

  5. SPITZER SPECTROSCOPY OF THE CIRCUMPRIMARY DISK IN THE BINARY BROWN DWARF 2MASS J04414489+2301513

    International Nuclear Information System (INIS)

    Adame, Lucia; Calvet, Nuria; McClure, M. K.; Hartmann, Lee; Luhman, K. L.; D'Alessio, Paola; Furlan, Elise; Forrest, William J.; Watson, Dan M.

    2011-01-01

    Using the Spitzer Infrared Spectrograph, we have performed mid-infrared spectroscopy on the young binary brown dwarf 2MASS J04414489+2301513 (15 AU) in the Taurus star-forming region. The spectrum exhibits excess continuum emission that likely arises from a circumstellar disk around the primary. Silicate emission is not detected in these data, indicating the presence of significant grain growth. This is one of the few brown dwarf disks at such a young age (∼1 Myr) that has been found to lack silicate emission. To quantitatively constrain the properties of the disk, we have compared the spectral energy distribution of 2MASS J04414489+2301513 to the predictions of our vertical structure codes for irradiated accretion disks. Our models suggest that the remaining atmospheric grains of moderately depleted layers may have grown to a size of ∼>5 μm. In addition, our model fits indicate an outer radius of 0.2-0.3 AU for the disk. The small size of this circumprimary disk could be due to truncation by the secondary. The absence of an outer disk containing a reservoir of small, primordial grains, combined with a weak turbulent mechanism, may be responsible for the advanced grain growth in this disk.

  6. Identification and characterization of low mass stars and brown dwarfs using Virtual Observatory tools

    Science.gov (United States)

    Aberasturi, Miriam

    2015-11-01

    Context: Two thirds of the stars in our galactic neighborhood (d searches. Brown dwarfs (BDs) are self-gravitating objects that do not get enough mass to maintain a sufficiently high temperature in their core for stable hydrogen fusion. They represent the link between low-mass stars and giant planets. Due to their low temperatures, BDs emit significant flux at mid-infrared wavelength which makes this range very adequate to look for this type of objects. The Virtual Observatory (VO) is an international initiative designed to help the astronomical community in the exploitation of the multi-wavelength information that resides in data archives. In the last years the Spanish Virtual Observatory is conducting a number of projects focused on the study of substellar objects taking advantage of Virtual Observatory tools for an easy data access and analysis of large area surveys. This is the framework where this thesis has been carried out. This dissertation addresses three problems in the framework of low-mass stars and brown dwarfs, namely, the search for brown dwarf candidates crossmatching catalogues (Chapter 4), the search for nearby bright M dwarfs and the subsequent spectroscopic characterization (Chapter 5), and a study of binarity in mid to late-T brown dwarfs (Chapter 6); the first two topics use Virtual Observatory tools. Aims and methodology:In the first paper we carried out a search of brown dwarfs in the sky area in common to the WISE, 2MASS Point Source and SDSS catalogues. A VO-workflow with the criteria that must accomplish our candidates was built using STILTS. The workflow returned 138 sources that were visually inspected. For the six new candidates that passed the inspection, proper motions were calculated using the positions and the different observing epochs of the catalogues previously quoted. Effective temperatures were estimated using VOSA and spectral types and distances using appropriate photometric calibrations. In the second publication we

  7. A T8.5 BROWN DWARF MEMBER OF THE ξ URSAE MAJORIS SYSTEM

    International Nuclear Information System (INIS)

    Wright, Edward L.; Mace, Gregory; McLean, Ian S.; Skrutskie, M. F.; Nelson, M. J.; Borish, H. J.; Kirkpatrick, J. Davy; Gelino, Christopher R.; Griffith, Roger L.; Jarrett, Tom; Marsh, Kenneth A.; Mainzer, Amanda K.; Eisenhardt, Peter R.; Tobin, John J.; Cushing, Michael C.

    2013-01-01

    The Wide-field Infrared Survey Explorer has revealed a T8.5 brown dwarf (WISE J111838.70+312537.9) that exhibits common proper motion with a solar-neighborhood (8 pc) quadruple star system—ξ Ursae Majoris. The angular separation is 8.'5, and the projected physical separation is ≈4000 AU. The sub-solar metallicity and low chromospheric activity of ξ UMa A argue that the system has an age of at least 2 Gyr. The infrared luminosity and color of the brown dwarf suggests the mass of this companion ranges between 14 and 38 M J for system ages of 2 and 8 Gyr, respectively.

  8. The BDNYC database of low-mass stars, brown dwarfs, and planetary mass companions

    Science.gov (United States)

    Cruz, Kelle; Rodriguez, David; Filippazzo, Joseph; Gonzales, Eileen; Faherty, Jacqueline K.; Rice, Emily; BDNYC

    2018-01-01

    We present a web-interface to a database of low-mass stars, brown dwarfs, and planetary mass companions. Users can send SELECT SQL queries to the database, perform searches by coordinates or name, check the database inventory on specified objects, and even plot spectra interactively. The initial version of this database contains information for 198 objects and version 2 will contain over 1000 objects. The database currently includes photometric data from 2MASS, WISE, and Spitzer and version 2 will include a significant portion of the publicly available optical and NIR spectra for brown dwarfs. The database is maintained and curated by the BDNYC research group and we welcome contributions from other researchers via GitHub.

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

    Science.gov (United States)

    Heller, René

    2013-01-01

    Abstract 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; 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 104 K. The situation is less clear for brown dwarfs, as observational data do not constrain their early activity and UV emission very well. Nonetheless, both types of planets are at risk of never achieving habitable conditions, but planets orbiting white dwarfs may be less likely to sustain life than those orbiting brown dwarfs. We consider the future habitability of the planet candidates KOI 55.01 and 55.02 in these terms and find they are unlikely to become habitable. Key Words: Extrasolar terrestrial planets—Habitability—Habitable zone—Tides—Exoplanets. Astrobiology 13, 279–291. PMID:23537137

  10. Detection of brown dwarfs by the micro-lensing of unresolved stars

    CERN Document Server

    Baillon, Paul; Giraud-Héraud, Yannick; Kaplan, J; Baillon, Paul; Bouquet, Alain; Giraud-Héraud, Yannick; Kaplan, Jean

    1993-01-01

    The presence of brown dwarfs in the dark galactic halo could be detected through their gravitational lensing effect and experiments under way monitor about one million stars to observe a few lensing events per year. We show that if the photon flux from a galaxy is measured with a good precision, it is not necessary to resolve the stars and besides more events could be observed.

  11. The Y-type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry, and Near-infrared Spectroscopy

    International Nuclear Information System (INIS)

    Leggett, S. K.; Tremblin, P.; Esplin, T. L.; Luhman, K. L.; Morley, Caroline V.

    2017-01-01

    The survey of the mid-infrared sky by the Wide-field Infrared Survey Explorer ( WISE ) led to the discovery of extremely cold, low-mass brown dwarfs, classified as Y dwarfs, which extend the T class to lower temperatures. Twenty-four Y dwarfs are known at the time of writing. Here we present improved parallaxes for four of these, determined using Spitzer images. We give new photometry for four late-type T and three Y dwarfs and new spectra of three Y dwarfs, obtained at Gemini Observatory. We also present previously unpublished photometry taken from HST , ESO, Spitzer , and WISE archives of 11 late-type T and 9 Y dwarfs. The near-infrared data are put onto the same photometric system, forming a homogeneous data set for the coolest brown dwarfs. We compare recent models to our photometric and spectroscopic data set. We confirm that nonequilibrium atmospheric chemistry is important for these objects. Nonequilibrium cloud-free models reproduce well the near-infrared spectra and mid-infrared photometry for the warmer Y dwarfs with 425 ≤ T eff (K) ≤ 450. A small amount of cloud cover may improve the model fits in the near-infrared for the Y dwarfs with 325 ≤ T eff (K) ≤ 375. Neither cloudy nor cloud-free models reproduce the near-infrared photometry for the T eff = 250 K Y dwarf W0855. We use the mid-infrared region, where most of the flux originates, to constrain our models of W0855. We find that W0855 likely has a mass of 1.5–8 Jupiter masses and an age of 0.3–6 Gyr. The Y dwarfs with measured parallaxes are within 20 pc of the Sun and have tangential velocities typical of the thin disk. The metallicities and ages we derive for the sample are generally solar-like. We estimate that the known Y dwarfs are 3 to 20 Jupiter-mass objects with ages of 0.6–8.5 Gyr.

  12. The Y-type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry, and Near-infrared Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Leggett, S. K. [Gemini Observatory, Northern Operations Center, 670 N. A’ohoku Place, Hilo, HI 96720 (United States); Tremblin, P. [Maison de la Simulation, CEA-CNRS-INRIA-UPS-UVSQ, USR 3441, Centre d’étude de Saclay, F-91191 Gif-Sur-Yvette (France); Esplin, T. L.; Luhman, K. L. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Morley, Caroline V., E-mail: sleggett@gemini.edu [Harvard-Smithsonian Center for Astrophysics, Harvard University, Cambridge, MA 02138 (United States)

    2017-06-20

    The survey of the mid-infrared sky by the Wide-field Infrared Survey Explorer ( WISE ) led to the discovery of extremely cold, low-mass brown dwarfs, classified as Y dwarfs, which extend the T class to lower temperatures. Twenty-four Y dwarfs are known at the time of writing. Here we present improved parallaxes for four of these, determined using Spitzer images. We give new photometry for four late-type T and three Y dwarfs and new spectra of three Y dwarfs, obtained at Gemini Observatory. We also present previously unpublished photometry taken from HST , ESO, Spitzer , and WISE archives of 11 late-type T and 9 Y dwarfs. The near-infrared data are put onto the same photometric system, forming a homogeneous data set for the coolest brown dwarfs. We compare recent models to our photometric and spectroscopic data set. We confirm that nonequilibrium atmospheric chemistry is important for these objects. Nonequilibrium cloud-free models reproduce well the near-infrared spectra and mid-infrared photometry for the warmer Y dwarfs with 425 ≤ T {sub eff} (K) ≤ 450. A small amount of cloud cover may improve the model fits in the near-infrared for the Y dwarfs with 325 ≤ T {sub eff} (K) ≤ 375. Neither cloudy nor cloud-free models reproduce the near-infrared photometry for the T {sub eff} = 250 K Y dwarf W0855. We use the mid-infrared region, where most of the flux originates, to constrain our models of W0855. We find that W0855 likely has a mass of 1.5–8 Jupiter masses and an age of 0.3–6 Gyr. The Y dwarfs with measured parallaxes are within 20 pc of the Sun and have tangential velocities typical of the thin disk. The metallicities and ages we derive for the sample are generally solar-like. We estimate that the known Y dwarfs are 3 to 20 Jupiter-mass objects with ages of 0.6–8.5 Gyr.

  13. ROTATION PERIODS OF YOUNG BROWN DWARFS: K2 SURVEY IN UPPER SCORPIUS

    Energy Technology Data Exchange (ETDEWEB)

    Scholz, Alexander [School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS (United Kingdom); Kostov, Veselin [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Jayawardhana, Ray [Faculty of Science, York University, 355 Lumbers Building, 4700 Keele Street, Toronto, ON M3J 1P2 (Canada); Mužić, Koraljka, E-mail: as110@st-andrews.ac.uk [Nucleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago (Chile)

    2015-08-20

    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 Keplerspace telescope’s K2 mission. The periods range from a few hours to two days (plus one outlier at five 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 light curves. 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 providing an important constraint on the mass dependence of the braking mechanism.

  14. ROTATION PERIODS OF YOUNG BROWN DWARFS: K2 SURVEY IN UPPER SCORPIUS

    International Nuclear Information System (INIS)

    Scholz, Alexander; Kostov, Veselin; Jayawardhana, Ray; Mužić, 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 Keplerspace telescope’s K2 mission. The periods range from a few hours to two days (plus one outlier at five 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 light curves. 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 providing an important constraint on the mass dependence of the braking mechanism

  15. VizieR Online Data Catalog: Brown dwarf surface gravities with Keck/NIRSPEC (Martin , 2017)

    Science.gov (United States)

    Martin, E. C.; Mace, G. N.; McLean, I. S.; Logsdon, S. E.; Rice, E. L.; Kirkpatrick, J. D.; Burgasser, A. J.; McGovern, M. R.; Prato, L.

    2017-10-01

    In this paper, we follow up on prior NIR spectroscopy by our group and use a modified Allers & Liu (A13, 2013ApJ...772...79A) method to determine surface gravities for 228 M, L, and T dwarfs. We present medium-resolution (R~20000) J-band spectra of 85 M dwarfs, 92 L dwarfs, and 51 T dwarfs obtained as part of the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS). Ninety-seven spectra were published previously in McLean+ (2003ApJ...596..561M), Burgasser+ (2003ApJ...592.1186B), McGovern+ (2004ApJ...600.1020M), Rice+ (2010ApJS..186...63R), Kirkpatrick+ (2010, J/ApJS/190/100), Luhman (2012ARA&A..50...65L), Thompson+ (2013PASP..125..809T), Mace+ (2013, J/ApJS/205/6), Mace+ (2013ApJ...777...36M), and Kirkpatrick+ (2014, J/ApJ/783/122), and the remaining 131 are presented here for the first time. Observation information (spanning 1999 Apr to 2015 Mar) for all of the targets in our sample is listed in Table 1. (4 data files).

  16. Pulsations in carbon-atmosphere white dwarfs: A new chapter in white dwarf asteroseismology

    International Nuclear Information System (INIS)

    Fontaine, G; Brassard, P; Dufour, P; Green, E M; Liebert, J

    2009-01-01

    We present some of the results of a survey aimed at exploring the asteroseismological potential of the newly-discovered carbon-atmosphere white dwarfs. We show that, in certains regions of parameter space, carbon-atmosphere white dwarfs may drive low-order gravity modes. We demonstrate that our theoretical results are consistent with the recent exciting discovery of luminosity variations in SDSS J1426+5752 and some null results obtained by a team of scientists at McDonald Observatory. We also present follow-up photometric observations carried out by ourselves at the Mount Bigelow 1.6-m telescope using the new Mont4K camera. The results of follow-up spectroscopic observations at the MMT are also briefly reported, including the surprising discovery that SDSS J1426+5752 is not only a pulsating star but that it is also a magnetic white dwarf with a surface field near 1.2 MG. The discovery of g-mode pulsations in SDSS J1426+5752 is quite significant in itself as it opens a fourth asteroseismological 'window', after the GW Vir, V777 Her, and ZZ Ceti families, through which one may study white dwarfs.

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

    Science.gov (United States)

    2012-06-10

    a low surface gravity dwarf, Cal is a calibrator ultracool dwarf, SD is an ultracool subdwarf, B is a tight binary unresolved in 2MASS . d F indicates...procedure described in Vrba et al. (2004), we obtained 2MASS photometry for all reference stars. We com- pared with the intrinsic colors described in...140.5 ± 5.8 38.44 ± 2.83 −1191.00 ± 13.00 −115.00 ± 13.00 A 1 2MASS J0746+2000 86.2 ± 4.6 −355.9 ± 5.1 −63.7 ± 5.2 81.90 ± 0.30 −374.04 ± 0.31 −57.91

  18. THE FIRST HUNDRED BROWN DWARFS DISCOVERED BY THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE)

    International Nuclear Information System (INIS)

    Davy Kirkpatrick, J.; Gelino, Christopher R.; Griffith, Roger L.; Marsh, Kenneth A.; Tsai, Chao-Wei; Beichman, Charles A.; Cushing, Michael C.; Mainzer, A.; Eisenhardt, Peter R.; Bauer, James M.; Skrutskie, Michael F.; Wright, Edward L.; McLean, Ian S.; Lake, Sean E.; Petty, Sara M.; Thompson, Maggie A.; Benford, Dominic J.; Bridge, Carrie R.; Stanford, S. A.; Bailey, Vanessa

    2011-01-01

    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

  19. STABILITY OF CO2 ATMOSPHERES ON DESICCATED M DWARF EXOPLANETS

    International Nuclear Information System (INIS)

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

    2015-01-01

    We investigate the chemical stability of CO 2 -dominated atmospheres of desiccated M dwarf terrestrial exoplanets using a one-dimensional photochemical model. Around Sun-like stars, CO 2 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. We show that, for water-depleted M dwarf terrestrial planets, a catalytic cycle relying on H 2 O 2 photolysis can maintain a CO 2 atmosphere. However, this cycle breaks down for atmospheric hydrogen mixing ratios <1 ppm, resulting in ∼40% of the atmospheric CO 2 being converted to CO and O 2 on a timescale of 1 Myr. The increased O 2 abundance leads to high O 3 concentrations, the photolysis of which forms another CO 2 -regenerating catalytic cycle. For atmospheres with <0.1 ppm hydrogen, CO 2 is produced directly from the recombination of CO and O. These catalytic cycles place an upper limit of ∼50% on the amount of CO 2 that can be destroyed via photolysis, which is enough to generate Earth-like abundances of (abiotic) O 2 and O 3 . The conditions that lead to such high oxygen levels could be widespread on planets in the habitable zones of M dwarfs. Discrimination between biological and abiotic O 2 and O 3 in this case can perhaps be accomplished by noting the lack of water features in the reflectance and emission spectra of these planets, which necessitates observations at wavelengths longer than 0.95 μm

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

    Science.gov (United States)

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

    2011-10-01

    We have identified CFBDSIR J1458+1013 as a 0farcs11 (2.6 AU) physical binary using Keck laser guide star adaptive optics imaging and have measured a distance of 23.1 ± 2.4 pc to the system based on near-IR parallax data from the Canada-France-Hawaii Telescope. The integrated-light near-IR spectrum indicates a spectral type of T9.5, and model atmospheres suggest a slightly higher temperature and surface gravity than the T10 dwarf UGPS J0722-05. Thus, CFBDSIR J1458+1013AB is the coolest brown dwarf binary found 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 × 10-7 L sun makes it the least luminous known brown dwarf by a factor of 4-5. By comparing to evolutionary models and T9-T10 objects, we estimate a temperature of 370 ± 40 K and a mass of 6-15 M Jup for CFBDSIR J1458+1013B. At such extremes, atmospheric models predict the onset of novel photospheric processes, namely, the appearance of water clouds and the removal of strong alkali lines, but their impact on the emergent spectrum is highly uncertain. Our photometry shows that strong CH4 absorption persists in the H band, the J - K color is bluer than the latest known T dwarfs but not as blue as predicted by current models, and the J - H color delineates a possible inflection in the blueward trend for the latest T dwarfs. Given its low luminosity, atypical colors, and cold temperature, CFBDSIR J1458+1013B is a promising candidate for the hypothesized Y spectral class. However, regardless of its ultimate classification, CFBDSIR J1458+1013AB provides a new benchmark for measuring the properties of brown dwarfs and gas-giant planets, testing substellar models, and constraining the low-mass limit for star formation. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California

  1. Uniform Atmospheric Retrievals of Ultracool Late-T and Early-Y dwarfs

    Science.gov (United States)

    Garland, Ryan; Irwin, Patrick

    2018-01-01

    A significant number of ultracool (types of objects with a uniform retrieval method, we hope to elucidate any trends and (dis)similarities found in atmospheric parameters, such as chemical abundances, temperature-pressure profile, and cloud structure, for a sample of 7 ultracool brown dwarfs as we transition from hotter (~700K) to colder objects (~450K).We perform atmospheric retrievals on two late-T and five early-Y dwarfs. We use the NEMESIS atmospheric retrieval code coupled to a Nested Sampling algorithm, along with a standard uniform model for all of our retrievals. The uniform model assumes the atmosphere is described by a gray radiative-convective temperature profile, (optionally) a self-consistent Mie scattering cloud, and a number of relevant gases. We first verify our methods by comparing it to a benchmark retrieval for Gliese 570D, which is found to be consistent. Furthermore, we present the retrieved gaseous composition, temperature structure, spectroscopic mass and radius, cloud structure and the trends associated with decreasing temperature found in this small sample of objects.

  2. High-dispersion observations of H-alpha in the suspected brown dwarf, white dwarf binary system G29-38

    International Nuclear Information System (INIS)

    Liebert, J.; Saffer, R.A.; Pilachowski, C.A.

    1989-01-01

    High-dispersion spectroscopy of the H-alpha absorption line of the cool DA white dwarf G29-38 is reported. This is the star for which a recently detected IR excess has been suggested to be due to a possible brown dwarf companion. Three echelle spectra show no evidence for radial-velocity variations larger than about 1.1 + or - 8.7 km/s and are used to derive a weighted heliocentric radial velocity of 33.7 + or - 4.3 kms/s for the white dwarf. The observations of a sharp absorption-line core restricts the possible rotation of the white dwarf to 40 km/s or less and ensures that any surface magnetic field has a strength of 100,000 G or less. These results make it unlikely that the DA white dwarf has previously been in a cataclysmic variable accretion phase. 18 references

  3. Cloud Atlas: Discovery of Rotational Spectral Modulations in a Low-mass, L-type Brown Dwarf Companion to a Star

    Science.gov (United States)

    Manjavacas, Elena; Apai, Dániel; Zhou, Yifan; Karalidi, Theodora; Lew, Ben W. P.; Schneider, Glenn; Cowan, Nicolas; Metchev, Stan; Miles-Páez, Paulo A.; Burgasser, Adam J.; Radigan, Jacqueline; Bedin, Luigi R.; Lowrance, Patrick J.; Marley, Mark S.

    2018-01-01

    Observations of rotational modulations of brown dwarfs and giant exoplanets allow the characterization of condensate cloud properties. As of now, rotational spectral modulations have only been seen in three L-type brown dwarfs. We report here the discovery of rotational spectral modulations in LP261-75B, an L6-type intermediate surface gravity companion to an M4.5 star. As a part of the Cloud Atlas Treasury program, we acquired time-resolved Wide Field Camera 3 grism spectroscopy (1.1–1.69 μm) of LP261-75B. We find gray spectral variations with the relative amplitude displaying only a weak wavelength dependence and no evidence for lower-amplitude modulations in the 1.4 μm water band than in the adjacent continuum. The likely rotational modulation period is 4.78 ± 0.95 hr, although the rotational phase is not well sampled. The minimum relative amplitude in the white light curve measured over the whole wavelength range is 2.41% ± 0.14%. We report an unusual light curve, which seems to have three peaks approximately evenly distributed in rotational phase. The spectral modulations suggests that the upper atmosphere cloud properties in LP261-75B are similar to two other mid-L dwarfs of typical infrared colors, but differ from that of the extremely red L-dwarf WISE0047.

  4. A progress report on the carbon dominated atmosphere white dwarfs

    International Nuclear Information System (INIS)

    Dufour, P; Liebert, J; Swift, B; Sukhbold, T; Fontaine, G

    2009-01-01

    Recently, Dufour et al. (2007) reported the unexpected discovery that a few white dwarfs found in the Sloan Digital Sky Survey had an atmosphere dominated by carbon with little or no trace of hydrogen and helium. Here we present a progress report on these new objects based on new high signal-to-noise follow-up spectroscopic observations obtained at the 6.5m MMT telescope on Mount Hopkins, Arizona.

  5. FURTHER DEFINING SPECTRAL TYPE 'Y' AND EXPLORING THE LOW-MASS END OF THE FIELD BROWN DWARF MASS FUNCTION

    International Nuclear Information System (INIS)

    Davy Kirkpatrick, J.; Gelino, Christopher R.; Griffith, Roger L.; Marsh, Kenneth A.; Cushing, Michael C.; Mace, Gregory N.; Wright, Edward L.; McLean, Ian S.; Skrutskie, Michael F.; Eisenhardt, Peter R.; Mainzer, Amanda K.; Burgasser, Adam J.; Tinney, C. G.; Parker, Stephen; Salter, Graeme

    2012-01-01

    We present the discovery of another seven Y dwarfs from the Wide-field Infrared Survey Explorer (WISE). Using these objects, as well as the first six WISE Y dwarf discoveries from Cushing et al., we further explore the transition between spectral types T and Y. We find that the T/Y boundary roughly coincides with the spot where the J – H colors of brown dwarfs, as predicted by models, turn back to the red. Moreover, we use preliminary trigonometric parallax measurements to show that the T/Y boundary may also correspond to the point at which the absolute H (1.6 μm) and W2 (4.6 μm) magnitudes plummet. We use these discoveries and their preliminary distances to place them in the larger context of the solar neighborhood. We present a table that updates the entire stellar and substellar constituency within 8 pc of the Sun, and we show that the current census has hydrogen-burning stars outnumbering brown dwarfs by roughly a factor of six. This factor will decrease with time as more brown dwarfs are identified within this volume, but unless there is a vast reservoir of cold brown dwarfs invisible to WISE, the final space density of brown dwarfs is still expected to fall well below that of stars. We also use these new Y dwarf discoveries, along with newly discovered T dwarfs from WISE, to investigate the field substellar mass function. We find that the overall space density of late-T and early-Y dwarfs matches that from simulations describing the mass function as a power law with slope –0.5 < α < 0.0; however, a power law may provide a poor fit to the observed object counts as a function of spectral type because there are tantalizing hints that the number of brown dwarfs continues to rise from late-T to early-Y. More detailed monitoring and characterization of these Y dwarfs, along with dedicated searches aimed at identifying more examples, are certainly required.

  6. Atmospheric activity in red dwarf stars

    International Nuclear Information System (INIS)

    Pettersen, B.R.

    1986-01-01

    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

  7. Mapping radio emitting-region on low-mass stars and brown dwarfs

    Directory of Open Access Journals (Sweden)

    Hallinan G.

    2011-07-01

    Full Text Available Strong magnetic activity in ultracool dwarfs (UCDs, spectral classes later than M7 have emerged from a number of radio observations, including the periodic beams. The highly (up to 100% circularly polarized nature of the emission point to an effective amplification mechanism of the high-frequency electromagnetic waves – the electron cyclotron maser (ECM instability. Several anisotropic velocity distibution models of electrons, including the horseshoe distribution, ring shell distribution and the loss-cone distribution, are able to generate the ECM instability. A magnetic-field-aligned electric potential would play an significant role in the ECM process. We are developing a theoretical model in order to simulate ECM and apply this model to map the radio-emitting region on low-mass stars and brown dwarfs.

  8. The Next Generation Sky Survey and the Quest for Cooler Brown Dwarfs

    OpenAIRE

    Kirkpatrick, J. Davy

    2002-01-01

    The Next Generation Sky Survey (NGSS) is a proposed NASA MIDEX mission to map the entire sky in four infrared bandpasses - 3.5, 4.7, 12, and 23 um. The seven-month mission will use a 50-cm telescope and four-channel imager to survey the sky from a circular orbit above the Earth. Expected sensitivities will be half a million times that of COBE/DIRBE at 3.5 and 4.7 um and a thousand times that of IRAS at 12 and 23 um. NGSS will be particularly sensitive to brown dwarfs cooler than those present...

  9. EXPLORING THE ROLE OF SUB-MICRON-SIZED DUST GRAINS IN THE ATMOSPHERES OF RED L0–L6 DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Hiranaka, Kay; Cruz, Kelle L.; Baldassare, Vivienne F. [Hunter College, Department of Physics and Astronomy, City University of New York, 695 Park Ave, New York, NY 10065 (United States); Douglas, Stephanie T. [American Museum of Natural History, Department of Astrophysics, Central Park West at 79th Street, New York, NY 10024 (United States); Marley, Mark S., E-mail: khiranak@hunter.cuny.edu [NASA Ames Research Center, MS-245-3, Moffett Field, CA 94035 (United States)

    2016-10-20

    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 that 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 μ m) dust clouds but not sub-micron 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.

  10. Very Low-mass Stars and Brown Dwarfs in Upper Scorpius Using Gaia DR1: Mass Function, Disks, and Kinematics

    Science.gov (United States)

    Cook, Neil J.; Scholz, Aleks; Jayawardhana, Ray

    2017-12-01

    Our understanding of the brown dwarf population in star-forming regions is dependent on knowing distances and proper motions and therefore will be improved through the Gaia space mission. In this paper, we select new samples of very low-mass objects (VLMOs) in Upper Scorpius using UKIDSS colors and optimized proper motions calculated using Gaia DR1. The scatter in proper motions from VLMOs in Upper Scorpius is now (for the first time) dominated by the kinematic spread of the region itself, not by the positional uncertainties. With age and mass estimates updated using Gaia parallaxes for early-type stars in the same region, we determine masses for all VLMOs. Our final most complete sample includes 453 VLMOs of which ˜125 are expected to be brown dwarfs. The cleanest sample is comprised of 131 VLMOs, with ˜105 brown dwarfs. We also compile a joint sample from the literature that includes 415 VLMOs, out of which 152 are likely brown dwarfs. The disk fraction among low-mass brown dwarfs (M< 0.05 {M}⊙ ) is substantially higher than in more massive objects, indicating that disks around low-mass brown dwarfs survive longer than in low-mass stars overall. The mass function for 0.01< M< 0.1 {M}⊙ is consistent with the Kroupa Initial Mass Function. We investigate the possibility that some “proper motion outliers” have undergone a dynamical ejection early in their evolution. Our analysis shows that the color-magnitude cuts used when selecting samples introduce strong bias into the population statistics due to varying levels of contamination and completeness.

  11. How to find and type red/brown dwarf stars in near-infrared imaging space observatories

    Science.gov (United States)

    Willemn Holwerda, Benne; Ryan, Russell; Bridge, Joanna; Pirzkal, Nor; Kenworthy, Matthew; Andersen, Morten; Wilkins, Stephen; Trenti, Michele; Meshkat, Tiffany; Bernard, Stephanie; Smit, Renske

    2018-01-01

    Here we evaluate the near-infrared colors of brown dwarfs as observed with four major infrared imaging space observatories: the Hubble Space Telescope (HST), the James Webb Space Telescope (JWST), the EUCLID mission, and the WFIRST telescope. We use the splat ISPEX spectroscopic library to map out the colors of the M, L, and T-type brown dwarfs. We identify which color-color combination is optimal for identifying broad type and which single color is optimal to then identify the subtype (e.g., T0-9). We evaluate each observatory separately as well as the the narrow-field (HST and JWST) and wide-field (EULID and WFIRST) combinations.HST filters used thus far for high-redshift searches (e.g. CANDELS and BoRG) are close to optimal within the available filter combinations. A clear improvement over HST is one of two broad/medium filter combinations on JWST: pairing F140M with either F150W or F162M discriminates well between brown dwarf subtypes. The improvement of JWST the filter set over the HST one is so marked that any combination of HST and JWST filters does not improve the classification.The EUCLID filter set alone performs poorly in terms of typing brown dwarfs and WFIRST performs only marginally better, despite a wider selection of filters. A combined EUCLID and WFIRST observation, using WFIRST's W146 and F062 and EUCLID's Y-band, allows for a much better discrimination between broad brown dwarf categories. In this respect, WFIRST acts as a targeted follow-up observatory for the all-sky EUCLID survey. However, subsequent subtyping with the combination of EUCLID and WFIRST observations remains uncertain due to the lack of medium or narrow-band filters in this wavelength range. We argue that a medium band added to the WFIRST filter selection would greatly improve its ability to preselect against brown dwarfs in high-latitude surveys.

  12. 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.

  13. 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.

  14. A Statistical Study of Brown Dwarf Companions from the SDSS-III MARVELS Survey

    Science.gov (United States)

    Grieves, Nolan; Ge, Jian; Thomas, Neil; Ma, Bo; De Lee, Nathan M.; Lee, Brian L.; Fleming, Scott W.; Sithajan, Sirinrat; Varosi, Frank; Liu, Jian; Zhao, Bo; Li, Rui; Agol, Eric; MARVELS Team

    2016-01-01

    We present 23 new Brown Dwarf (BD) candidates from the Multi-object APO Radial-Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digital Sky Survey III (SDSS-III). The BD candidates were selected from the processed MARVELS data using the latest University of Florida 2D pipeline, which shows significant improvement and reduction of systematic errors over the 1D pipeline results included in the SDSS Data Release 12. This sample is the largest BD yield from a single radial velocity survey. Of the 23 candidates, 18 are around main sequence stars and 5 are around giant stars. Given a giant contamination rate of ~24% for the MARVELS survey, we find a BD occurrence rate around main sequence stars of ~0.7%, which agrees with previous studies and confirms the BD desert, while the BD occurrence rate around the MARVELS giant stars is ~0.6%. Preliminary results show that our new candidates around solar type stars support a two population hypothesis, where BDs are divided at a mass of ~42.5 MJup. BDs less massive than 42.5 MJup have eccentricity distributions consistent with planet-planet scattering models, where BDs more massive than 42.5 MJup have both period and eccentricity distributions similar to that of stellar binaries. Special Brown Dwarf systems such as multiple BD systems and highly eccentric BDs will also be presented.

  15. WISEP J004701.06+680352.1: An Intermediate Surface Gravity, Dusty Brown Dwarf in the AB Dor Moving Group

    Science.gov (United States)

    2015-02-01

    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...Key words: brown dwarfs – infrared: stars – stars: individual (WISEP J004701.06+680352.1, 2MASS J21481628+4003593) 1. INTRODUCTION One of the key...2M1207b (16.13, Gizis et al. 2007). Besides PSO J318-22, the best studied of the extremely red L dwarfs are 2MASS J21481628+4003593 (Looper et al

  16. THE BROWN DWARF KINEMATICS PROJECT (BDKP). IV. RADIAL VELOCITIES OF 85 LATE-M AND L DWARFS WITH MagE

    Energy Technology Data Exchange (ETDEWEB)

    Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Logsdon, Sarah E. [Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); Gagné, Jonathan [Institute for Research on Exoplanets (iREx), Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 (Canada); Bochanski, John J. [Rider University, 2083 Lawrenceville Road, Lawrenceville, NJ 08648 (United States); Faherty, Jaqueline K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 (United States); West, Andrew A. [Department of Astronomy, Boston University, 725 Commonwealth Avenue Boston, MA 02215 (United States); Mamajek, Eric E. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Schmidt, Sarah J. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Cruz, Kelle L., E-mail: aburgasser@ucsd.edu [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10034 (United States)

    2015-09-15

    Radial velocity measurements are presented for 85 late M- and L-type very low-mass stars and brown dwarfs obtained with the Magellan Echellette 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{sup −1}, 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 ± 0.2 Gyr for sources within 20 pc. We find signficantly different kinematic ages between late-M dwarfs (4.0 ± 0.2 Gyr) and L dwarfs (6.5 ± 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 with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313–4912012AB, a low-probability member of the β Pictoris Moving Group; and 2MASS J15104786–2818174, a moderate-probability member of the 30–50 Myr Argus Association.

  17. LHS 1610A: A Nearby Mid-M Dwarf with a Companion That Is Likely a Brown Dwarf

    Science.gov (United States)

    Winters, Jennifer G.; Irwin, Jonathan; Newton, Elisabeth R.; Charbonneau, David; Latham, David W.; Han, Eunkyu; Muirhead, Philip S.; Berlind, Perry; Calkins, Michael L.; Esquerdo, Gil

    2018-03-01

    We present the spectroscopic orbit of LHS 1610A, a newly discovered single-lined spectroscopic binary with a trigonometric distance placing it at 9.9 ± 0.2 pc. We obtained spectra with the TRES instrument on the 1.5 m Tillinghast Reflector at the Fred Lawrence Whipple Observatory located on Mt. Hopkins in AZ. We demonstrate the use of the TiO molecular bands at 7065–7165 Å to measure radial velocities and achieve an average estimated velocity uncertainty of 28 m s‑1. We measure the orbital period to be 10.6 days and calculate a minimum mass of 44.8 ± 3.2 M Jup for the secondary, indicating that it is likely a brown dwarf. We place an upper limit to 3σ of 2500 K on the effective temperature of the companion from infrared spectroscopic observations using IGRINS on the 4.3 m Discovery Channel Telescope. In addition, we present a new photometric rotation period of 84.3 days for the primary star using data from the MEarth-South Observatory, with which we show that the system does not eclipse.

  18. Inclusion of brown midrib dwarf pearl millet silage in the diet of lactating dairy cows.

    Science.gov (United States)

    Harper, M T; Melgar, A; Oh, J; Nedelkov, K; Sanchez, G; Roth, G W; Hristov, A N

    2018-06-01

    Brown midrib brachytic dwarf pearl millet (Pennisetum glaucum) forage harvested at the flag leaf visible stage and subsequently ensiled was investigated as a partial replacement of corn silage in the diet of high-producing dairy cows. Seventeen lactating Holstein cows were fed 2 diets in a crossover design experiment with 2 periods of 28 d each. Both diets had forage:concentrate ratios of 60:40. The control diet (CSD) was based on corn silage and alfalfa haylage, and in the treatment diet, 20% of the corn silage dry matter (corresponding to 10% of the dietary dry matter) was replaced with pearl millet silage (PMD). The effects of partial substitution of corn silage with pearl millet silage on dry matter intake, milk yield, milk components, fatty acid profile, apparent total-tract digestibility of nutrients, N utilization, and enteric methane emissions were analyzed. The pearl millet silage was higher in crude protein and neutral detergent fiber and lower in lignin and starch than the corn silage. Diet did not affect dry matter intake or energy-corrected milk yield, which averaged 46.7 ± 1.92 kg/d. The PMD treatment tended to increase milk fat concentration, had no effect on milk fat yield, and increased milk urea N. Concentrations and yields of milk protein and lactose were not affected by diet. Apparent total-tract digestibility of dry matter decreased from 66.5% in CSD to 64.5% in PMD. Similarly, organic matter and crude protein digestibility was decreased by PMD, whereas neutral- and acid-detergent fiber digestibility was increased. Total milk trans fatty acid concentration was decreased by PMD, with a particular decrease in trans-10 18:1. Urinary urea and fecal N excretion increased with PMD compared with CSD. Milk N efficiency decreased with PMD. Carbon dioxide emission was not different between the diets, but PMD increased enteric methane emission from 396 to 454 g/d and increased methane yield and intensity. Substituting corn silage with brown midrib dwarf

  19. Ensemble Atmospheric Properties of Small Planets around M Dwarfs

    Science.gov (United States)

    Guo, Xueying; Ballard, Sarah; Dragomir, Diana

    2018-01-01

    With the growing number of planets discovered by the Kepler mission and ground-base surveys, people start to try to understand the atmospheric features of those uncovered new worlds. While it has been found that hot Jupiters exhibit diverse atmosphere composition with both clear and cloudy/hazy atmosphere possible, similar studies on ensembles of smaller planets (Earth analogs) have been held up due to the faintness of most of their host stars. In this work, a sample of 20 Earth analogs of similar periods around M dwarfs with existing Kepler transit information and Spitzer observations is composed, complemented with previously studies GJ1214b and GJ1132b, as well as the recently announced 7 small planets in the TRAPPIST-1 system. We evaluate their transit depths with uncertainties on the Spitzer 4.5 micron band using the “pixel-level decorrelation” method, and together with their well analyzed Kepler data and Hubble data, we put constraints on their atmosphere haze slopes and cloud levels. Aside from improving the understanding of ensemble properties of small planets, this study will also provide clues of potential targets for detailed atmospheric studies using the upcoming James Webb Telescope.

  20. Infrared rotational light curves on Jupiter induced by wave activities and cloud patterns andimplications on brown dwarfs

    Science.gov (United States)

    Ge, Huazhi; Zhang, Xi; Fletcher, Leigh; Orton, Glenn S.; Sinclair, James Andrew; Fernandes,, Joshua; Momary, Thomas W.; Warren, Ari; Kasaba, Yasumasa; Sato, Takao M.; Fujiyoshi, Takuya

    2017-10-01

    Many brown dwarfs exhibit infrared rotational light curves with amplitude varying from a fewpercent to twenty percent (Artigau et al. 2009, ApJ, 701, 1534; Radigan et al. 2012, ApJ, 750,105). Recently, it was claimed that weather patterns, especially planetary-scale waves in thebelts and cloud spots, are responsible for the light curves and their evolutions on brown dwarfs(Apai et al. 2017, Science, 357, 683). Here we present a clear relationship between the direct IRemission maps and light curves of Jupiter at multiple wavelengths, which might be similar withthat on cold brown dwarfs. Based on infrared disk maps from Subaru/COMICS and VLT/VISIR,we constructed full maps of Jupiter and rotational light curves at different wavelengths in thethermal infrared. We discovered a strong relationship between the light curves and weatherpatterns on Jupiter. The light curves also exhibit strong multi-bands phase shifts and temporalvariations, similar to that detected on brown dwarfs. Together with the spectra fromTEXES/IRTF, our observations further provide detailed information of the spatial variations oftemperature, ammonia clouds and aerosols in the troposphere of Jupiter (Fletcher et al. 2016,Icarus, 2016 128) and their influences on the shapes of the light curves. We conclude that waveactivities in Jupiter’s belts (Fletcher et al. 2017, GRL, 44, 7140), cloud holes, and long-livedvortices such as the Great Red Spot and ovals control the shapes of IR light curves and multi-wavelength phase shifts on Jupiter. Our finding supports the hypothesis that observed lightcurves on brown dwarfs are induced by planetary-scale waves and cloud spots.

  1. WD0837+185: THE FORMATION AND EVOLUTION OF AN EXTREME MASS-RATIO WHITE-DWARF-BROWN-DWARF BINARY IN PRAESEPE

    International Nuclear Information System (INIS)

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

    2012-01-01

    There is a striking and unexplained dearth of brown dwarf companions in close orbits ( ☉ (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 separation to its current value. The initial and final orbital separations allow us to constrain the combination of the common envelope efficiency (α) and binding energy parameters (λ) for the AGB star to αλ ∼ 3. We examine the various formation scenarios and conclude that the substellar object was most likely captured by the white dwarf progenitor early in the life of the cluster, rather than forming in situ.

  2. Near-Infrared Spectroscopy of the Cool Brown Dwarf, SDSS 1624+00

    Science.gov (United States)

    Nakajima, Tadashi; Tsuji, Takashi; Maihara, Toshinori; Iwamuro, Fumihide; Motohara, Ken-taro; Taguchi, Tomoyuki; Hata, Ryuji; Tamura, Motohide; Yamashita, Takuya

    2000-02-01

    Using the Subaru Telescope, we have obtained multiple near-infrared spectra of the cool brown dwarf, SDSS 1624+00 (J162414.37+002915.8), in search of spectral variability in an 80 minute time span. We have found the suspected variability of water vapor absorption throughout the observations, which requires a confirmation with a longer time baseline. After coadding the spectra, we have obtained a high-quality spectrum covering from 1.05 to 1.8 mu m. There are three kinds of spectral indicators, the water vapor bands, methane band and K I lines at 1.243 and 1.252 mu m, which can be used to study the temperature and the presence of dust. We compare the spectra of SDSS 1624+00 and Gliese 229B, while paying special attention to these indicators. The shallower water vapor absorption of SDSS 1624+00 indicates that it is warmer and/or dustier. The shallower methane absorption suggests that SDSS 1624+00 is warmer. We interpret the deeper K I lines in SDSS 1624+00 as being the result of its higher temperature. With the help of model spectra, we conclude that SDSS 1624+00 is warmer and dustier than Gliese 229B. For the first time in a cool brown dwarf, a finite flux is seen at the bottom of the water vapor band between 1.34 and 1.42 mu m, which means that the 1.4 mu m band of water can be completely observed from the ground.

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

    International Nuclear Information System (INIS)

    Palle, E.; Garcia Munoz, A.; Zosorio, M. R. Zapatero

    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 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 (T eff ≤ ∼3100 K). For a twin of Earth around a star with T eff ∼ 3100 K (M4), for example, the spectral features of H 2 O, CH 4 , CO 2 , and O 2 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.

  4. THE SOLAR NEIGHBORHOOD. XXVIII. THE MULTIPLICITY FRACTION OF NEARBY STARS FROM 5 TO 70 AU AND THE BROWN DWARF DESERT AROUND M DWARFS

    International Nuclear Information System (INIS)

    Dieterich, Sergio B.; Henry, Todd J.; Golimowski, David A.; Krist, John E.; Tanner, Angelle M.

    2012-01-01

    We report on our analysis of Hubble Space Telescope/NICMOS snapshot high-resolution images of 255 stars in 201 systems within ∼10 pc 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 –1 , NICMOS can easily resolve binaries with subarcsecond separations in the 19.''5×19.''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 +3.5 –0.0 % for L companions to M dwarfs in the separation range of 5-70 AU, and 2.3 +5.0 –0.7 % for L and T companions to M dwarfs in the separation range of 10-70 AU. We also discuss trends in the color-magnitude diagrams using various color combinations and present astrometry for 19 multiple systems in our sample. Considering these results and results from several other studies, we argue that the so-called brown dwarf desert extends to binary systems with low-mass primaries and is largely independent of primary mass, mass ratio, and separations. While focusing on companion properties, we discuss how the qualitative agreement between observed companion mass functions and initial mass functions suggests that the paucity of brown dwarfs in either population may be due to a common cause and not due to binary formation mechanisms.

  5. THE SOLAR NEIGHBORHOOD. XXVIII. THE MULTIPLICITY FRACTION OF NEARBY STARS FROM 5 TO 70 AU AND THE BROWN DWARF DESERT AROUND M DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Dieterich, Sergio B.; Henry, Todd J. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302-4106 (United States); Golimowski, David A. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Krist, John E. [Jet Propulsion Laboratory, Pasadena, CA 91109 (United States); Tanner, Angelle M., E-mail: dieterich@chara.gsu.edu [Department of Physics and Astronomy, Mississippi State University, Starkville, MS 39762 (United States)

    2012-08-15

    We report on our analysis of Hubble Space Telescope/NICMOS snapshot high-resolution images of 255 stars in 201 systems within {approx}10 pc 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{sup -1}, NICMOS can easily resolve binaries with subarcsecond separations in the 19.''5 Multiplication-Sign 19.''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{sup +3.5}{sub -0.0}% for L companions to M dwarfs in the separation range of 5-70 AU, and 2.3{sup +5.0}{sub -0.7}% for L and T companions to M dwarfs in the separation range of 10-70 AU. We also discuss trends in the color-magnitude diagrams using various color combinations and present astrometry for 19 multiple systems in our sample. Considering these results and results from several other studies, we argue that the so-called brown dwarf desert extends to binary systems with low-mass primaries and is largely independent of primary mass, mass ratio, and separations. While focusing on companion properties, we discuss how the qualitative agreement between observed companion mass functions and initial mass functions suggests that the paucity of brown dwarfs in either population may be due to a common cause and not due to binary formation mechanisms.

  6. Possible Pleiades members with M of about 0.07 solar mass - identification of brown dwarf candidates of known age, distance, and metallicity

    International Nuclear Information System (INIS)

    Stauffer, J.; Hamilton, D.; Probst, R.; Rieke, G.; Mateo, M.

    1989-01-01

    A small number of very faint very red stars have been discovered in CCD frames taken near the center of the Pleiades cluster. The V, I, and K photometry for these stars is consistent with the expected luminosity and temperatures for brown dwarfs of mass about 0.07 solar mass at the distance and age of the Pleiades. It is concluded that these are the first identified single brown dwarfs of known age, distance, and metallicity. 16 refs

  7. Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

    Science.gov (United States)

    Marks, M.; Martín, E. L.; Béjar, V. J. S.; Lodieu, N.; Kroupa, P.; Manjavacas, E.; Thies, I.; Rebolo López, R.; Velasco, S.

    2017-08-01

    Context. One of the key questions of the star formation problem is whether brown dwarfs (BDs) form in the manner of stars directly from the gravitational collapse of a molecular cloud core (star-like) or whether BDs and some very low-mass stars (VLMSs) constitute a separate population that forms alongside stars comparable to the population of planets, for example through circumstellar disk (peripheral) fragmentation. Aims: For young stars in Taurus-Auriga the binary fraction has been shown to be large with little dependence on primary mass above ≈ 0.2 M⊙, while for BDs the binary fraction is computations. A small amount of dynamical processing of the stellar component was accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. Results: The binary fraction declines strongly in the transition region between star-like and peripheral formation, exhibiting characteristic features. The location of these features and the steepness of this trend depend on the mass limits for star-like and peripheral formation. Such a trend might be unique to low density regions, such as Taurus, which host binary populations that are largely unprocessed dynamically in which the binary fraction is large for stars down to M-dwarfs and small for BDs. Conclusions: The existence of a strong decline in the binary fraction - primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star-forming region. The binary fraction - primary mass diagram is a diagnostic of the (non-)continuity of star formation along the mass scale, the separateness of the stellar and BD populations, and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.

  8. Giant Planet Candidates, Brown Dwarfs, and Binaries from the SDSS-III MARVELS Planet Survey.

    Science.gov (United States)

    Thomas, Neil; Ge, Jian; Li, Rui; de Lee, Nathan M.; Heslar, Michael; Ma, Bo; SDSS-Iii Marvels Team

    2015-01-01

    We report the discoveries of giant planet candidates, brown dwarfs, and binaries from the SDSS-III MARVELS survey. The finalized 1D pipeline has provided 18 giant planet candidates, 16 brown dwarfs, and over 500 binaries. An additional 96 targets having RV variability indicative of a giant planet companion are also reported for future investigation. These candidates are found using the advanced MARVELS 1D data pipeline developed at UF from scratch over the past three years. This pipeline carefully corrects most of the instrument effects (such as trace, slant, distortion, drifts and dispersion) and observation condition effects (such as illumination profile, fiber degradation, and tracking variations). The result is long-term RV precisions that approach the photon limits in many cases for the ~89,000 individual stellar observations. A 2D version of the pipeline that uses interferometric information is nearing completion and is demonstrating a reduction of errors to half the current levels. The 2D processing will be used to increase the robustness of the detections presented here and to find new candidates in RV regions not confidently detectable with the 1D pipeline. The MARVELS survey has produced the largest homogeneous RV measurements of 3300 V=7.6-12 FGK stars with a well defined cadence of 27 RV measurements over 2 years. The MARVELS RV data and other follow-up data (photometry, high contrast imaging, high resolution spectroscopy and RV measurements) will explore the diversity of giant planet companion formation and evolution around stars with a broad range in metallicity (Fe/H -1.5-0.5), mass ( 0.6-2.5M(sun)), and environment (thin disk and thick disk), and will help to address the key scientific questions identified for the MARVELS survey including, but not limited to: Do metal poor stars obey the same trends for planet occurrence as metal rich stars? What is the distribution of giant planets around intermediate-mass stars and binaries? Is the 'planet desert

  9. NEW BROWN DWARF COMPANIONS TO YOUNG STARS IN SCORPIUS-CENTAURUS

    Energy Technology Data Exchange (ETDEWEB)

    Janson, Markus [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States); Jayawardhana, Ray; Bonavita, Mariangela [Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON (Canada); Girard, Julien H. [European Southern Observatory, Santiago (Chile); Lafreniere, David [Department of Physics, University of Montreal, Montreal, QC (Canada); Gizis, John [Department of Physics and Astronomy, University of Delaware, Newark, DE (United States); Brandeker, Alexis, E-mail: janson@astro.princeton.edu [Department of Astronomy, Stockholm University, Stockholm (Sweden)

    2012-10-10

    We present the discoveries of three faint companions to young stars in the Scorpius-Centaurus region, imaged with the NICI instrument on Gemini South. We have confirmed all three companions through common proper motion tests. Follow-up spectroscopy has confirmed two of them, HIP 65423 B and HIP 65517 B, to be brown dwarfs, while the third, HIP 72099 B, is more likely a very low mass star just above the hydrogen burning limit. The detection of wide companions in the mass range of {approx}40-100 M{sub jup} complements previous work in the same region, reporting detections of similarly wide companions with lower masses, in the range of {approx}10-30 M{sub jup}. Such low masses near the deuterium burning limit have raised the question of whether those objects formed like planets or stars. The existence of intermediate objects as reported here could represent a bridge between lower-mass companions and stellar companions, but in any case demonstrate that mass alone may not provide a clear-cut distinction for the formation of low-mass companions to stars.

  10. Extremely Low Mass: The Circumstellar Envelope of a Potential Proto-Brown Dwarf

    Science.gov (United States)

    Wiseman, Jennifer

    2011-01-01

    What is the environment for planet formation around extremely low mass stars? Is the environment around brown dwarfs and extremely low mass stars conducive and sufficiently massive for planet production? The determining conditions may be set very early in the process of the host object's formation. IRAS 16253-2429, the source of the Wasp-Waist Nebula seen in Spitzer IRAC images, is an isolated, very low luminosity ("VeLLO") Class 0 protostar in the nearby rho Ophiuchi cloud. We present VLA ammonia mapping observations of the dense gas envelope feeding the central core accreting system. We find a flattened envelope perpendicular to the outflow axis, and gas cavities that appear to cradle the outflow lobes as though carved out by the flow and associated (apparently precessing) jet, indicating environmental disruption. Based on the NH3 (1,1) and (2,2) emission distribution, we derive the mass, velocity fields and temperature distribution for the envelope. We discuss the combined evidence for this source to be one of the youngest and lowest mass sources in formation yet known, and discuss the ramifications for planet formation potential in this extremely low mass system.

  11. Characterizing the Cool KOIs. VII. Refined Physical Properties of the Transiting Brown Dwarf LHS 6343 C

    Science.gov (United States)

    Montet, Benjamin T.; Johnson, John Asher; Muirhead, Philip S.; Villar, Ashley; Vassallo, Corinne; Baranec, Christoph; Law, Nicholas M.; Riddle, Reed; Marcy, Geoffrey W.; Howard, Andrew W.; Isaacson, Howard

    2015-02-01

    We present an updated analysis of LHS 6343, a triple system in the Kepler field which consists of a brown dwarf transiting one member of a widely separated M+M binary system. By analyzing the full Kepler data set and 34 Keck/HIgh Resolution Echelle Spectrometer radial velocity observations, we measure both the observed transit depth and Doppler semiamplitude to 0.5% precision. With Robo-AO and Palomar/PHARO adaptive optics imaging as well as TripleSpec spectroscopy, we measure a model-dependent mass for LHS 6343 C of 62.1 ± 1.2 M Jup and a radius of 0.783 ± 0.011 R Jup. We detect the secondary eclipse in the Kepler data at 3.5σ, measuring ecos ω = 0.0228 ± 0.0008. We also derive a method to measure the mass and radius of a star and transiting companion directly, without any direct reliance on stellar models. The mass and radius of both objects depend only on the orbital period, stellar density, reduced semimajor axis, Doppler semiamplitude, eccentricity, and inclination, as well as the knowledge that the primary star falls on the main sequence. With this method, we calculate a mass and radius for LHS 6343 C to a precision of 3% and 2%, respectively.

  12. THE BIMODALITY OF ACCRETION IN T TAURI STARS AND BROWN DWARFS

    International Nuclear Information System (INIS)

    Vorobyov, E. I.; Basu, Shantanu

    2009-01-01

    We present numerical solutions of the collapse of prestellar cores that lead to the formation and evolution of circumstellar disks. The disk evolution is then followed for up to three million years. A variety of models of different initial masses and rotation rates allow us to study disk accretion around brown dwarfs and low-mass T Tauri stars (TTSs), with central object mass M * sun , as well as intermediate- and upper-mass TTSs (0.2 M sun * sun ). Our models include self-gravity and allow for nonaxisymmetric motions. In addition to the self-consistently generated gravitational torques, we introduce an effective turbulent α-viscosity with α = 0.01, which allows us particularly to model accretion in the low-mass regime where disk self-gravity is diminishing. A range of models with observationally motivated values of the initial ratio of rotational-to-gravitational energy yield a correlation between mass accretion rate M-dot and M * that is relatively steep, as observed. Additionally, our modeling reveals evidence for a bimodality in the M-dot - M * correlation, with a steeper slope at lower masses and a shallower slope at intermediate and upper masses, as also implied by observations. Furthermore, we show that the neglect of disk self-gravity leads to a much steeper M-dot - M * relation for intermediate- and upper-mass TTSs. This demonstrates that an accurate treatment of global self-gravity is essential to understanding observations of circumstellar disks.

  13. CFBDS J005910.90-011401.3: reaching the T-Y brown dwarf transition?

    Science.gov (United States)

    Delorme, P.; Delfosse, X.; Albert, L.; Artigau, E.; Forveille, T.; Reylé, C.; Allard, F.; Homeier, D.; Robin, A. C.; Willott, C. J.; Liu, M. C.; Dupuy, T. J.

    2008-05-01

    Aims: We report the discovery of CFBDS J005910.90-011401.3 (hereafter CFBDS0059), the coolest brown dwarf identified to date. Methods: We found CFBDS0059 using i' and z' images from the Canada-France-Hawaii Telescope (CFHT), and present optical and near-infrared photometry, Keck laser-guide-star adaptive optics imaging, and a complete near-infrared spectrum, from 1.0 to 2.2 μm. Results: A side-to-side comparison of the near-infrared spectra of CFBDS0059 and ULAS J003402.77-005206.7 (hereafter ULAS0034), previously the coolest known brown dwarf, indicates that CFBDS0059 is ~50 ± 15 K cooler. We estimate a temperature of T_eff ˜ 620 K and gravity of log g ~ 4.75. Evolutionary models translate these parameters into an age of 1-5 Gyr and a mass of 15-30 M_Jup. We estimate a photometric distance of ~13 pc, which puts CFBDS0059 within easy reach of accurate parallax measurements. Its large proper motion suggests membership in the older population of the thin disk. The spectra of both CFBDS0059 and ULAS J0034 show probable absorption by a wide ammonia band on the blue side of the H-band flux peak. If, as we expect, that feature deepens further for still lower effective temperatures, its appearance will become a natural breakpoint for the transition between the T spectral class and the new Y spectral type. Together, CFBDS0059 and ULAS J0034 would then be the first Y0 dwarfs. Based in part on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Also based on observations obtained

  14. Recent Variability Observations of Solar System Giant Planets: Fresh Context for Understanding Exoplanet and Brown Dwarf Weather

    Science.gov (United States)

    Marley, Mark Scott

    2016-01-01

    Over the past several years a number of high cadence photometric observations of solar system giant planets have been acquired by various platforms. Such observations are of interest as they provide points of comparison to the already expansive set of brown dwarf variability observations and the small, but growing, set of exoplanet variability observations. By measuring how rapidly the integrated light from solar system giant planets can evolve, variability observations of substellar objects that are unlikely to ever be resolved can be placed in a fuller context. Examples of brown dwarf variability observations include extensive work from the ground (e.g., Radigen et al. 2014), Spitzer (e.g., Metchev et al. 2015), Kepler (Gizis et al. 2015), and HST (Yang et al. 2015).Variability has been measured on the planetary mass companion to the brown dwarf 2MASS 1207b (Zhou et al. 2016) and further searches are planned in thermal emission for the known directly imaged planets with ground based telescopes (Apai et al. 2016) and in reflected light with future space based telescopes. Recent solar system variability observations include Kepler monitoring of Neptune (Simon et al. 2016) and Uranus, Spitzer observations of Neptune (Stauffer et al. 2016), and Cassini observations of Jupiter (West et al. in prep). The Cassini observations are of particular interest as they measured the variability of Jupiter at a phase angle of approximately 60 deg, comparable to the viewing geometry expected for space based direct imaging of cool extrasolar Jupiters in reflected light. These solar system analog observations capture many of the characteristics seen in brown dwarf variability, including large amplitudes and rapid light curve evolution on timescales as short as a few rotation periods. Simon et al. (2016) attribute such variations at Neptune to a combination of large scale, stable cloud structures along with smaller, more rapidly varying, cloud patches. The observed brown dwarf and

  15. 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

  16. EXTENDED MAGNETOSPHERES IN PRE-MAIN-SEQUENCE EVOLUTION: FROM T TAURI STARS TO THE BROWN DWARF LIMIT

    Energy Technology Data Exchange (ETDEWEB)

    Gomez de Castro, Ana I.; Marcos-Arenal, Pablo [Grupo de Investigacion Complutense AEGORA, Universidad Complutense de Madrid, 28040 Madrid (Spain)

    2012-04-20

    extended and dense stellar magnetosphere directly driven by local collisional processes. The brown dwarf 2MASS J12073346-3332539 has been found to follow the same flux-flux relations of the TTSs. Thus, TTS-normalized flux scaling laws seem to be extendable to the brown dwarf limit and can be used for identification/diagnosis purposes. We report the discovery of an inverse correlation between the C IV-normalized flux and the magnetospheric radius derived for stars with known magnetic fields. The normalized C IV flux is found to be {proportional_to}exp (- {alpha}r{sub mag}), with {alpha} = 0.5-0.7.

  17. 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.

  18. KNOW YOUR NEIGHBORHOOD: A DETAILED MODEL ATMOSPHERE ANALYSIS OF NEARBY WHITE DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Giammichele, N.; Bergeron, P. [Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation (United States); Dufour, P., E-mail: noemi.giammichele@astro.umontreal.ca, E-mail: pierre.bergeron@astro.umontreal.ca, E-mail: patrick.dufour@astro.umontreal.ca [Departement de Physique, Universite de Montreal, C.P. 6128, Succ. Centre-Ville, Montreal, Quebec H3C 3J7 (Canada)

    2012-04-01

    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, DB, DC, 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 presented. We provide, for the first time, a comprehensive analysis of the mass distribution and the chemical distribution of white dwarf stars in a volume-limited sample.

  19. Properties of submicron particles in Atmospheric Brown Clouds

    Science.gov (United States)

    Adushkin, V. V.; Chen, B. B.; Dubovskoi, A. N.; Friedrich, F.; Pernik, L. M.; Popel, S. I.; Weidler, P. G.

    2010-05-01

    The Atmospheric Brown Clouds (ABC) is an important problem of this century. Investigations of last years and satellite data show that the ABC (or brown gas, smog, fog) cover extensive territories including the whole continents and oceans. The brown gas consists of a mixture of particles of anthropogenic sulfates, nitrates, organic origin, black carbon, dust, ashes, and also natural aerosols such as sea salt and mineral dust. The brown color is a result of absorption and scattering of solar radiation by the anthropogenic black carbon, ashes, the particles of salt dust, and nitrogen dioxide. The investigation of the ABC is a fundamental problem for prevention of degradation of the environment. At present in the CIS in-situ investigations of the ABC are carried out on Lidar Station Teplokluchenka (Kyrgyz Republic). Here, we present the results of experimental investigation of submicron (nanoscale) particles originating from the ABC and the properties of the particles. Samples of dust precipitating from the ABC were obtained at the area of Lidar Station Teplokluchenka as well as scientific station of the Russian Academy of Sciences near Bishkek. The data for determination of the grain composition were obtained with the aid of the scanning electron microscopes JEOL 6460 LV and Philips XL 30 FEG. Analysis of the properties of the particles was performed by means of the X-ray diffraction using diffractometer Siemens D5000. The images of the grains were mapped. The investigation allows us to get (after the image processing) the grain composition within the dust particle size range of 60 nm to 700 μm. Distributions of nano- and microscale particles in sizes were constructed using Rozin-Rammler coordinates. Analysis of the distributions shows that the ABC contain submicron (nanoscale) particles; 2) at higher altitudes the concentration of the submicron (nanoscale) particles in the ABC is higher than at lower altitudes. The chemical compositions of the particles are shown to

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

    Science.gov (United States)

    Leggett, S. K.; Saumon, D.; 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.

    2012-04-01

    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 T eff ≈ 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 & 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 4.5 μm photometry and the Saumon & 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. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina); also based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; and also based on observations made at the UK Infrared Telescope

  1. White dwarfs in the WTS: Eclipsing binaries

    Directory of Open Access Journals (Sweden)

    Burleigh M.R.

    2013-04-01

    Full Text Available We have identified photometric white dwarf candidates in the WFCAM transit survey through a reduced proper motion versus colour approach. Box-fitting with parameters adjusted to detect the unique signature of a white dwarf + planet/brown dwarf transit/eclipse event was performed, as well as looking for variability due to the irradiation of the companions atmosphere by the white dwarf's high UV flux. We have also performed a simple sensitivity analysis in order to assess the ability of the survey to detect companions to white dwarfs via the transit method.

  2. First Large-scale Herbig-Haro Jet Driven by a Proto-brown Dwarf

    Science.gov (United States)

    Riaz, B.; Briceño, C.; Whelan, E. T.; Heathcote, S.

    2017-07-01

    We report the discovery of a new Herbig-Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The Hα image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ˜36 M Jup and a bolometric luminosity of ˜0.1 L ⊙. High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system.

  3. Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

    International Nuclear Information System (INIS)

    Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria; Greenwood, Aaron; Kamp, Inga; Henning, Thomas; Ménard, François; Dent, William R. F.; II, Neal J. Evans

    2017-01-01

    The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μ m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μ m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.

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

    International Nuclear Information System (INIS)

    Kraus, Adam L.; Ireland, Michael J.; Martinache, Frantz; Hillenbrand, Lynne A.

    2011-01-01

    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 M sun , 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 M sun ) is nearly log-flat over separations of 3-5000 AU, but lower-mass stars (0.25-0.7 M sun ) 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 = M B /M A ) 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.

  5. Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Greenwood, Aaron; Kamp, Inga [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Henning, Thomas [Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg (Germany); Ménard, François [Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble (France); Dent, William R. F. [Department of Engineering, Atacama Large Millimeter/submillimeter Array (ALMA) Santiago Central Offices, Alonso de Córdova 3107, Vitacura, Casilla 763 0355, Santiago (Chile); II, Neal J. Evans, E-mail: equant@lpl.arizona.edu [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States)

    2017-06-01

    The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μ m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μ m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.

  6. First Large-scale Herbig–Haro Jet Driven by a Proto-brown Dwarf

    Energy Technology Data Exchange (ETDEWEB)

    Riaz, B. [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Briceño, C.; Heathcote, S. [Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena (Chile); Whelan, E. T. [Maynooth University Department of Experimental Physics, National University of Ireland Maynooth, Maynooth Co. Kildare (Ireland)

    2017-07-20

    We report the discovery of a new Herbig–Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The H α image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ∼36 M {sub Jup} and a bolometric luminosity of ∼0.1 L {sub ⊙}. High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system.

  7. FIRST DETECTION OF THERMAL RADIOJETS IN A SAMPLE OF PROTO-BROWN DWARF CANDIDATES

    Energy Technology Data Exchange (ETDEWEB)

    Morata, Oscar [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan (China); Palau, Aina; González, Ricardo F. [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, P.O. Box 3-72, 58090 Morelia, Michoacán, México (Mexico); Gregorio-Monsalvo, Itziar de [Joint ALMA Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago (Chile); Ribas, Álvaro [European Space Astronomy Centre (ESA), P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Perger, Manuel [Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB—Facultat de Ciències, Torre C5—parell 2, E-08193 Bellaterra, Catalunya (Spain); Bouy, Hervé; Barrado, David; Huélamo, Nuria; Morales-Calderón, María [Centro de Astrobiología, INTA-CSIC, Dpto.Astrofísica, ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Eiroa, Carlos [Departamento de Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Bayo, Amelia, E-mail: omorata@asiaa.sinica.edu.tw [Max Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany); and others

    2015-07-01

    We observed with the Jansky Very Large Array at 3.6 and 1.3 cm a sample of 11 proto-brown dwarf (BD) candidates in Taurus in a search for thermal radio jets driven by the most embedded BDs. We detected for the first time four thermal radio jets in proto-BD candidates. We compiled data from UKIDSS, 2MASS, Spitzer, WISE, and Herschel to build the spectral energy distribution (SED) of the objects in our sample, which are similar to typical Class I SEDs of young stellar objects (YSOs). The four proto-BD candidates driving thermal radio jets also roughly follow the well-known trend of centimeter luminosity against bolometric luminosity determined for YSOs, assuming they belong to Taurus, although they present some excess of radio emission compared to the known relation for YSOs. Nonetheless, we are able to reproduce the flux densities of the radio jets modeling the centimeter emission of the thermal radio jets using the same type of models applied to YSOs, but with corresponding smaller stellar wind velocities and mass-loss rates, and exploring different possible geometries of the wind or outflow from the star. Moreover, we also find that the modeled mass outflow rates for the bolometric luminosities of our objects agree reasonably well with the trends found between the mass outflow rates and bolometric luminosities of YSOs, which indicates that, despite the “excess” centimeter emission, the intrinsic properties of proto-BDs are consistent with a continuation of those of very low-mass stars to a lower mass range. Overall, our study favors the formation of BDs as a scaled-down version of low-mass stars.

  8. A Search for Water Maser Emission from Brown Dwarfs and Low-luminosity Young Stellar Objects

    Energy Technology Data Exchange (ETDEWEB)

    Gómez, José F.; Manjarrez, Guillermo [Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Palau, Aina [Instituto de Radioastronomía y Astrofísica, UNAM, P.O. Box 3-72, 58090, Morelia, Michoacán, México (Mexico); Uscanga, Lucero [Departamento de Astronomía, Universidad de Guanajuato, A.P. 144, 36000 Guanajuato, Gto., México (Mexico); Barrado, David, E-mail: jfg@iaa.es [Centro de Astrobiología, INTA-CSIC, PO BOX 28692, ESAC Campus, E-208691 Villanueva de la Cañada, Madrid (Spain)

    2017-05-01

    We present a survey for water maser emission toward a sample of 44 low-luminosity young objects, comprising (proto-)brown dwarfs, first hydrostatic cores (FHCs), and other young stellar objects (YSOs) with bolometric luminosities lower than 0.4 L {sub ⊙}. Water maser emission is a good tracer of energetic processes, such as mass-loss and/or accretion, and is a useful tool to study these processes with very high angular resolution. This type of emission has been confirmed in objects with L {sub bol} ≳ 1 L {sub ⊙}. Objects with lower luminosities also undergo mass-loss and accretion, and thus, are prospective sites of maser emission. Our sensitive single-dish observations provided a single detection when pointing toward the FHC L1448 IRS 2E. However, follow-up interferometric observations showed water maser emission associated with the nearby YSO L1448 IRS 2 (a Class 0 protostar of L {sub bol} ≃ 3.6–5.3 L {sub ⊙}) and did not find any emission toward L1448 IRS 2E. The upper limits for water maser emission determined by our observations are one order of magnitude lower than expected from the correlation between water maser luminosities and bolometric luminosities found for YSOs. This suggests that this correlation does not hold at the lower end of the (sub)stellar mass spectrum. Possible reasons are that the slope of this correlation is steeper at L {sub bol} ≤ 1 L {sub ⊙} or that there is an absolute luminosity threshold below which water maser emission cannot be produced. Alternatively, if the correlation still stands at low luminosity, the detection rates of masers would be significantly lower than the values obtained in higher-luminosity Class 0 protostars.

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

    International Nuclear Information System (INIS)

    Spezzi, Loredana; Beccari, Giacomo; De Marchi, Guido; Andersen, Morten; Young, Erick T.; Paresce, Francesco; Dopita, Michael A.; Panagia, Nino; Bond, Howard E.; Balick, Bruce; 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.; Ryan, Russell E. Jr

    2011-01-01

    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 H 2 O 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.

  10. First Large-scale Herbig–Haro Jet Driven by a Proto-brown Dwarf

    International Nuclear Information System (INIS)

    Riaz, B.; Briceño, C.; Heathcote, S.; Whelan, E. T.

    2017-01-01

    We report the discovery of a new Herbig–Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The H α image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ∼36 M Jup and a bolometric luminosity of ∼0.1 L ⊙ . High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system.

  11. VARIABLE AND POLARIZED RADIO EMISSION FROM THE T6 BROWN DWARF WISEP J112254.73+255021.5

    Energy Technology Data Exchange (ETDEWEB)

    Williams, P. K. G.; Berger, E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gizis, J. E., E-mail: pwilliams@cfa.harvard.edu [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)

    2017-01-10

    Route and Wolszczan 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. Assuming that the radio emission of this T dwarf is periodically variable on ∼hour timescales, like other radio-active ultracool dwarfs, we infer a likely period of 116 minutes. However, our observation lasted only 162 minutes and so more data are needed to test this hypothesis. The handedness of the circular polarization switches twice 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.

  12. 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.

  13. A search for companions to brown dwarfs in the Taurus and Chamaeleon star-forming regions

    International Nuclear Information System (INIS)

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

    2014-01-01

    We have used WFPC2 on board the Hubble Space Telescope to obtain images of 47 members of the Taurus and Chamaeleon I star-forming regions that have spectral types of M6-L0 (M ∼ 0.01-0.1 M ☉ ). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. In these images, we have identified promising candidate companions to 2MASS J04414489+2301513 (ρ = 0.''105/15 AU), 2MASS J04221332+1934392 (ρ = 0.''05/7 AU), and ISO 217 (ρ = 0.''03/5 AU). We reported the first candidate in a previous study, showing that it has a similar proper motion as the primary in images from WFPC2 and Gemini adaptive optics. We have collected an additional epoch of data with Gemini that further supports that result. By combining our survey with previous high-resolution imaging in Taurus, Chamaeleon I, and Upper Sco (τ ∼ 10 Myr), we measure binary fractions of 14/93 = 0.15 −0.03 +0.05 for M4-M6 (M ∼ 0.1-0.3 M ☉ ) and 4/108 = 0.04 −0.01 +0.03 for >M6 (M ≲ 0.1 M ☉ ) at separations of >10 AU. Given the youth and low density of these regions, the lower binary fraction at later types is probably primordial rather than due to dynamical interactions among association members. The widest low-mass binaries (>100 AU) also appear to be more common in Taurus and Chamaeleon I than in the field, which suggests that the widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or that field brown dwarfs have been born predominantly in denser clusters where wide systems are disrupted or inhibited from forming.

  14. Globulettes as Seeds of Brown Dwarfs and Free-Floating Planetary-Mass Objects

    Science.gov (United States)

    Gahm, G. F.; Grenman, T.; Fredriksson, S.; Kristen, H.

    2007-04-01

    to form central low-mass objects long before the ionization front, driven by the impinging Lyman photons, has penetrated far into the globulette. Hence, the globulettes may be one source in the formation of brown dwarfs and free-floating planetary-mass objects in the galaxy. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

  15. A search for companions to brown dwarfs in the Taurus and Chamaeleon star-forming regions

    Energy Technology Data Exchange (ETDEWEB)

    Todorov, K. O.; Luhman, K. L. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Konopacky, Q. M. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); McLeod, K. K. [Whitin Observatory, Wellesley College, Wellesley, MA 02481 (United States); Apai, D.; Pascucci, I. [Department of Astronomy, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Ghez, A. M. [Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095 (United States); Robberto, M., E-mail: todorovk@phys.ethz.ch [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2014-06-10

    We have used WFPC2 on board the Hubble Space Telescope to obtain images of 47 members of the Taurus and Chamaeleon I star-forming regions that have spectral types of M6-L0 (M ∼ 0.01-0.1 M {sub ☉}). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. In these images, we have identified promising candidate companions to 2MASS J04414489+2301513 (ρ = 0.''105/15 AU), 2MASS J04221332+1934392 (ρ = 0.''05/7 AU), and ISO 217 (ρ = 0.''03/5 AU). We reported the first candidate in a previous study, showing that it has a similar proper motion as the primary in images from WFPC2 and Gemini adaptive optics. We have collected an additional epoch of data with Gemini that further supports that result. By combining our survey with previous high-resolution imaging in Taurus, Chamaeleon I, and Upper Sco (τ ∼ 10 Myr), we measure binary fractions of 14/93 = 0.15{sub −0.03}{sup +0.05} for M4-M6 (M ∼ 0.1-0.3 M {sub ☉}) and 4/108 = 0.04{sub −0.01}{sup +0.03} for >M6 (M ≲ 0.1 M {sub ☉}) at separations of >10 AU. Given the youth and low density of these regions, the lower binary fraction at later types is probably primordial rather than due to dynamical interactions among association members. The widest low-mass binaries (>100 AU) also appear to be more common in Taurus and Chamaeleon I than in the field, which suggests that the widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or that field brown dwarfs have been born predominantly in denser clusters where wide systems are disrupted or inhibited from forming.

  16. A Survey For Planetary-mass Brown Dwarfs in the Taurus and Perseus Star-forming Regions

    Energy Technology Data Exchange (ETDEWEB)

    Esplin, T. L.; Luhman, K. L., E-mail: taran.esplin@psu.edu [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)

    2017-10-01

    We present the initial results from a survey for planetary-mass brown dwarfs in the Taurus star-forming region. We have identified brown dwarf candidates in Taurus using proper motions and photometry from several ground- and space-based facilities. Through spectroscopy of some of the more promising candidates, we have found 18 new members of Taurus. They have spectral types ranging from mid-M to early-L, and they include the four faintest known members in extinction-corrected K{sub s}, which should have masses as low as ∼4–5 M {sub Jup} according to evolutionary models. Two of the coolest new members (M9.25, M9.5) have mid-IR excesses that indicate the presence of disks. Two fainter objects with types of M9–L2 and M9–L3 also have red mid-IR colors relative to photospheres at ≤L0, but since the photospheric colors are poorly defined at >L0, it is unclear whether they have excesses from disks. We also have obtained spectra of candidate members of the IC 348 and NGC 1333 clusters in Perseus that were identified by Luhman et al. Eight candidates are found to be probable members, three of which are among the faintest and least-massive known members of the clusters (∼5 M{sub Jup}).

  17. A Survey For Planetary-mass Brown Dwarfs in the Taurus and Perseus Star-forming Regions

    International Nuclear Information System (INIS)

    Esplin, T. L.; Luhman, K. L.

    2017-01-01

    We present the initial results from a survey for planetary-mass brown dwarfs in the Taurus star-forming region. We have identified brown dwarf candidates in Taurus using proper motions and photometry from several ground- and space-based facilities. Through spectroscopy of some of the more promising candidates, we have found 18 new members of Taurus. They have spectral types ranging from mid-M to early-L, and they include the four faintest known members in extinction-corrected K s , which should have masses as low as ∼4–5 M Jup according to evolutionary models. Two of the coolest new members (M9.25, M9.5) have mid-IR excesses that indicate the presence of disks. Two fainter objects with types of M9–L2 and M9–L3 also have red mid-IR colors relative to photospheres at ≤L0, but since the photospheric colors are poorly defined at >L0, it is unclear whether they have excesses from disks. We also have obtained spectra of candidate members of the IC 348 and NGC 1333 clusters in Perseus that were identified by Luhman et al. Eight candidates are found to be probable members, three of which are among the faintest and least-massive known members of the clusters (∼5 M Jup ).

  18. New Evidence for a Substellar Luminosity Problem: Dynamical Mass for the Brown Dwarf Binary Gl 417BC

    Science.gov (United States)

    Dupuy, Trent J.; Liu, Michael C.; Ireland, Michael J.

    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 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. 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.

  19. SCExAO and GPI Y JH band photometry and integral field spectroscopy of the young brown dwarf companion to HD 1160

    International Nuclear Information System (INIS)

    Garcia, Eugenio Victor; Currie, Thayne; Guyon, Olivier

    2017-01-01

    Here, we present high signal-to-noise ratio, precise Y JH photometry and Y band (0.957–1.120 μm) spectroscopy of HD 1160 B, a young substellar companion discovered from the Gemini NICI Planet Finding Campaign using the Subaru Coronagraphic Extreme Adaptive Optics instrument and the Gemini Planet Imager. HD 1160 B has typical mid-M dwarf-like infrared colors and a spectral type of M5.5_−_0_._5"+"1"."0, where the blue edge of our Y band spectrum rules out earlier spectral types. Atmospheric modeling suggests HD 1160 B has an effective temperature of 3000–3100 K, a surface gravity of log g = 4–4.5, a radius of 1.55 ± 0.10 R J, and a luminosity of log L/L _⊙ = –2.76 ± 0.05. Neither the primary's Hertzspring–Russell diagram position nor atmospheric modeling of HD 1160 B show evidence for a subsolar metallicity. Interpretation of the HD 1160 B spectroscopy depends on which stellar system components are used to estimate the age. Considering HD 1160 A, B and C jointly, we derive an age of 80–125 Myr, implying that HD 1160 B straddles the hydrogen-burning limit (70–90 M _J). If we consider HD 1160 A alone, younger ages (20–125 Myr) and a brown dwarf-like mass (35–90 M _J) are possible. Interferometric measurements of the primary, a precise Gaia parallax, and moderate-resolution spectroscopy can better constrain the system's age and how HD 1160 B fits within the context of (sub)stellar evolution.

  20. CLASSICAL T TAURI-LIKE OUTFLOW ACTIVITY IN THE BROWN DWARF MASS REGIME

    International Nuclear Information System (INIS)

    Whelan, E. T.; Ray, T. P.; Podio, L.; Bacciotti, F.; Randich, S.

    2009-01-01

    Over the last number of years, spectroscopic studies have strongly supported the assertion that protostellar accretion and outflow activity persist to the lowest masses. Indeed, previous to this work, the existence of three brown dwarf (BD) outflows had been confirmed by us. In this paper, we present the results of our latest investigation of BD outflow activity and report on the discovery of two new outflows. Observations to date have concentrated on studying the forbidden emission line (FEL) regions of young BDs and in all cases data have been collected using the UV-Visual Echelle Spectrometer (UVES) on the ESO Very Large Telescope. Offsets in the FEL regions are recovered using spectro-astrometry. Here, ISO-Oph 32 is shown to drive a blueshifted outflow with a radial velocity of 10-20 km s -1 and spectro-astrometric analysis constrains the position angle of this outflow to 240 0 ± 7 0 . The BD candidate, ISO-ChaI 217 is found to have a bipolar outflow bright in several key forbidden lines (V RAD = -20 km s -1 , +40 km s -1 ) and with a P.A. of 193 0 -209 0 . A striking feature of the ISO-ChaI 217 outflow is the strong asymmetry between the red- and blueshifted lobes. This asymmetry is revealed in the relative brightness of the two lobes (redshifted lobe is brighter), the factor of 2 difference in radial velocity (the redshifted lobe is faster) and the difference in the electron density (again higher in the red lobe). Such asymmetries are common in jets from low-mass protostars and the observation of a marked asymmetry at such a low mass ( sun ) supports the idea that BD outflow activity is scaled down from low-mass protostellar activity. Also note that although asymmetries are unexceptional, it is uncommon for the redshifted lobe to be the brightest as some obscuration by the accretion disk is assumed. This phenomenon has only been observed in one other source, the classical T Tauri (CTTS) star RW Aur. The physical mechanism responsible for the brightening of

  1. 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

  2. Top-of-atmosphere radiative forcing affected by brown carbon in the upper troposphere

    Science.gov (United States)

    Zhang, Yuzhong; Forrister, Haviland; Liu, Jiumeng; Dibb, Jack; Anderson, Bruce; Schwarz, Joshua P.; Perring, Anne E.; Jimenez, Jose L.; Campuzano-Jost, Pedro; Wang, Yuhang; Nenes, Athanasios; Weber, Rodney J.

    2017-07-01

    Carbonaceous aerosols affect the global radiative balance by absorbing and scattering radiation, which leads to warming or cooling of the atmosphere, respectively. Black carbon is the main light-absorbing component. A portion of the organic aerosol known as brown carbon also absorbs light. The climate sensitivity to absorbing aerosols rapidly increases with altitude, but brown carbon measurements are limited in the upper troposphere. Here we present aircraft observations of vertical aerosol distributions over the continental United States in May and June 2012 to show that light-absorbing brown carbon is prevalent in the troposphere, and absorbs more short-wavelength radiation than black carbon at altitudes between 5 and 12 km. We find that brown carbon is transported to these altitudes by deep convection, and that in-cloud heterogeneous processing may produce brown carbon. Radiative transfer calculations suggest that brown carbon accounts for about 24% of combined black and brown carbon warming effect at the tropopause. Roughly two-thirds of the estimated brown carbon forcing occurs above 5 km, although most brown carbon is found below 5 km. The highest radiative absorption occurred during an event that ingested a wildfire plume. We conclude that high-altitude brown carbon from biomass burning is an unappreciated component of climate forcing.

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

    Energy Technology Data Exchange (ETDEWEB)

    Mack, Claude E. III; Stassun, Keivan G.; De Lee, Nathan [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Ge, Jian; Fleming, Scott W. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL, 32611-2055 (United States); Deshpande, Rohit; Mahadevan, Suvrath [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Wisniewski, John P. [Homer L Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St, Norman, OK 73019 (United States); Gaudi, B. Scott; Eastman, Jason; Beatty, Thomas G. [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Observatorio Nacional, Rua Gal. Jose Cristino 77, Rio de Janeiro, RJ 20921-400 (Brazil); Gonzalez Hernandez, Jonay I.; Femenia, Bruno; Mata Sanchez, Daniel [Instituto de Astrofisica de Canarias (IAC), E-38205 La Laguna, Tenerife (Spain); Ferreira, Leticia; Porto de Mello, Gustavo [Laboratorio Interinstitucional de e-Astronomia-LIneA, Rua Gal. Jose Cristino 77, Rio de Janeiro, RJ 20921-400 (Brazil); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Agol, Eric [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195 (United States); Bizyaev, Dmitry, E-mail: claude.e.mack@vanderbilt.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); and others

    2013-05-15

    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 {approx}< 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 {approx} 50 M{sub 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 {approx} 0.8), its relatively long period (P {approx} 238 days), and the approximately perpendicular orientation of the semi-major axis with respect to the line of sight ({omega} {approx} 189 Degree-Sign ). As a result of these properties, for {approx}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 {approx} 0.3). Only during the {approx}5% of the orbit near periastron passage does the true, double-lined nature and large RV amplitude of {approx}15 km s{sup -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.

  4. Activity in Very Cool Stars: Magnetic Dissipation in Late M and L Dwarf Atmospheres

    Science.gov (United States)

    Mohanty, Subhanjoy; Basri, Gibor; Shu, Frank; Allard, France; Chabrier, Gilles

    2002-05-01

    Recent observations show that chromospheric Hα activity in late M and L dwarfs is much lower than in the earlier M types. This is particularly surprising given that the late M and L dwarfs are comparatively very rapid rotators: in the early M dwarfs, rapid rotation is associated with high activity levels. One possibility is that the drop-off in activity in the late M and L dwarfs is a result of very high electrical resistivities in their dense, cool, and predominantly neutral atmospheres.We calculate the magnetic field diffusivity in the atmospheres of objects with Teff in the range 3000-1500 K (mid M to late L) using the atmospheric structure models of Allard and Hauschildt. We find that the combination of very low ionization fraction and high density in these atmospheres results in very large resistivities and thus efficient field diffusion. While both ambipolar diffusion and Ohmic decay of currents due to ion-electron collisions occur, the primary diffusion effects are due to current decay through collisions of charged particles with neutrals. Moreover, the latter resistivity is a strong function of both effective temperature and optical depth, increasing rapidly as either Teff or optical depth decreases. This has two implications: (1) Any magnetic field present is increasingly decoupled from atmospheric fluid motions as one moves from mid M to L. In the late M and L dwarfs, atmospheric motions cannot lead to equilibrium field configurations very different from potential ones. That is, the magnitude of magnetic stresses generated by atmospheric motions is very small in these objects. We quantify this effect by a simple Reynolds number calculation. (2) Even if magnetic stresses are easily produced by fluid motions in the hot interior (where the coupling between field and matter is good), their propagation up through the atmosphere will be increasingly hampered by the growing atmospheric resistivity as one moves from mid M to late L. Thus both the generation and

  5. 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.

  6. OBSERVED VARIABILITY AT 1 and 4 μ m IN THE Y0 BROWN DWARF WISEP J173835.52+273258.9

    International Nuclear Information System (INIS)

    Leggett, S. K.; Cushing, Michael C.; Hardegree-Ullman, Kevin K.; Trucks, Jesica L.; Marley, M. S.; Morley, Caroline V.; Fortney, J. J.; Saumon, D.; Carey, S. J.; Gelino, C. R.; Kirkpatrick, J. D.; Gizis, J. E.; 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 400 K dwarf is at a distance of 8 pc and has a mass around 5 M Jupiter . We observed W1738 using two near-infrared filters at λ ≈ 1 μ m, Y and J , on Gemini Observatory and two mid-infrared filters at λ ≈ 4 μ m, [3.6] and [4.5], on the Spitzer observatory. Twenty-four hours were spent on the source by Spitzer on each of 2013 June 30 and October 30 UT. Between these observations, around 5 hr were spent on the source by Gemini on each of 2013 July 17 and August 23 UT. The mid-infrared light curves show significant evolution between the two observations separated by 4 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 hr and the other a period of 3.0 ± 0.1 hr. The near-infrared observations suggest variability with a ∼3.0 hr period, although only at a ≲2 σ confidence level. We interpret our results as showing that the Y dwarf has a 6.0 ± 0.1 hr rotation period, with one or more large-scale surface features being the source of variability. The peak-to-peak amplitude of the light curve at [4.5] is 3%. The amplitude of the near-infrared variability, if real, may be as high as 5%–30%. Intriguingly, this size of variability and the wavelength dependence can be reproduced by atmospheric models that include patchy KCl and Na 2 S clouds and associated small changes in surface temperature. The small number of large features, as well as the timescale for evolution of the features, is very similar to what is seen in the atmospheres of the solar system gas giants.

  7. OBSERVED VARIABILITY AT 1 and 4 μ m IN THE Y0 BROWN DWARF WISEP J173835.52+273258.9

    Energy Technology Data Exchange (ETDEWEB)

    Leggett, S. K. [Gemini Observatory, Northern Operations Center, 670 N. A’ohoku Place, Hilo, HI 96720 (United States); Cushing, Michael C.; Hardegree-Ullman, Kevin K.; Trucks, Jesica L. [The University of Toledo, 2801 West Bancroft Street, Mailstop 111, Toledo, OH 43606 (United States); Marley, M. S. [NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035 (United States); Morley, Caroline V.; Fortney, J. J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Saumon, D. [Los Alamos National Laboratory, P.O. Box 1663, MS F663, Los Alamos, NM 87545 (United States); Carey, S. J. [Spitzer Science Center, CalTech, Pasadena, CA 91125 (United States); Gelino, C. R.; Kirkpatrick, J. D. [IPAC, CalTech, Pasadena, CA 91125 (United States); Gizis, J. E. [University of Delaware, Newark, DE 19716 (United States); Mace, G. N., E-mail: sleggett@gemini.edu [University of Texas, Austin, TX 78712 (United States)

    2016-10-20

    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 400 K dwarf is at a distance of 8 pc and has a mass around 5 M {sub Jupiter}. We observed W1738 using two near-infrared filters at λ ≈ 1 μ m, Y and J , on Gemini Observatory and two mid-infrared filters at λ ≈ 4 μ m, [3.6] and [4.5], on the Spitzer observatory. Twenty-four hours were spent on the source by Spitzer on each of 2013 June 30 and October 30 UT. Between these observations, around 5 hr were spent on the source by Gemini on each of 2013 July 17 and August 23 UT. The mid-infrared light curves show significant evolution between the two observations separated by 4 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 hr and the other a period of 3.0 ± 0.1 hr. The near-infrared observations suggest variability with a ∼3.0 hr period, although only at a ≲2 σ confidence level. We interpret our results as showing that the Y dwarf has a 6.0 ± 0.1 hr rotation period, with one or more large-scale surface features being the source of variability. The peak-to-peak amplitude of the light curve at [4.5] is 3%. The amplitude of the near-infrared variability, if real, may be as high as 5%–30%. Intriguingly, this size of variability and the wavelength dependence can be reproduced by atmospheric models that include patchy KCl and Na{sub 2}S clouds and associated small changes in surface temperature. The small number of large features, as well as the timescale for evolution of the features, is very similar to what is seen in the atmospheres of the solar system gas giants.

  8. 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)

    Mack, Claude E. III; Stassun, Keivan G.; De Lee, Nathan; Ge, Jian; Fleming, Scott W.; Deshpande, Rohit; Mahadevan, Suvrath; Wisniewski, John P.; Gaudi, B. Scott; Eastman, Jason; Beatty, Thomas G.; Ghezzi, Luan; González Hernández, Jonay I.; Femenía, Bruno; Mata Sánchez, Daniel; Ferreira, Letícia; Porto de Mello, Gustavo; Crepp, Justin R.; Agol, Eric; Bizyaev, Dmitry

    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 ∼ 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.

  9. IDENTIFICATION OF A WIDE, LOW-MASS MULTIPLE SYSTEM CONTAINING THE BROWN DWARF 2MASS J0850359+105716

    International Nuclear Information System (INIS)

    Faherty, Jacqueline K.; Burgasser, Adam J.; Bochanski, John J.; Looper, Dagny L.; West, Andrew A.; Van der Bliek, Nicole S.

    2011-01-01

    We report our discovery of NLTT 20346 as an M5+M6 companion system to the tight binary (or triple) L dwarf 2MASS J0850359+105716. This nearby (∼31 pc), widely separated (∼7700 AU) quadruple system was identified through a cross-match of proper motion catalogs. Follow-up imaging and spectroscopy of NLTT 20346 revealed it to be a magnetically active M5+M6 binary with components separated by ∼2'' (50-80 AU). Optical spectroscopy of the components shows only moderate Hα emission corresponding to a statistical age of ∼5-7 Gyr for both M dwarfs. However, NLTT 20346 is associated with the XMM-Newton source J085018.9+105644, and based on X-ray activity the age of NLTT 20346 is between 250 and 450 Myr. Strong Li absorption in the optical spectrum of 2MASS J0850+1057 indicates an upper age limit of 0.8-1.5 Gyr, favoring the younger age for the primary. Using evolutionary models in combination with an adopted system age of 0.25-1.5 Gyr indicates a total mass for 2MASS J0850+1057 of 0.07 ± 0.02 M sun , if it is a binary. NLTT 20346/2MASS J0850+1057 joins a growing list of hierarchical systems containing brown dwarf binaries and is among the lowest binding energy associations found in the field. Formation simulations via gravitational fragmentation of massive extended disks have successfully produced a specific analog to this system.

  10. A Pan-STARRS1 Proper-Motion Survey for Young Brown Dwarfs in the Nearest Star-Forming Regions and a Reddening-Free Classification Method for Ultracool Dwarfs

    Science.gov (United States)

    Zhang, Zhoujian; Liu, Michael C.; Best, William M. J.; Magnier, Eugene; Aller, Kimberly

    2018-01-01

    Young brown dwarfs are of prime importance to investigate the universality of the initial mass function (IMF). Based on photometry and proper motions from the Pan-STARRS1 (PS1) 3π survey, we are conducting the widest and deepest brown dwarf survey in the nearby star-forming regions, Taurus–Auriga (Taurus) and Upper Scorpius (USco). Our work is the first to measure proper motions, a robust proxy of membership, for brown dwarf candidates in Taurus and USco over such a large area and long time baseline (≈ 15 year) with such high precision (≈ 4 mas yr-1). Since extinction complicates spectral classification, we have developed a new approach to quantitatively determine reddening-free spectral types, extinctions, and gravity classifications for mid-M to late-L ultracool dwarfs (≈ 100–5 MJup), using low-resolution near-infrared spectra. So far, our IRTF/SpeX spectroscopic follow-up has increased the substellar and planetary-mass census of Taurus by ≈ 50% and almost doubled the substellar census of USco, constituting the largest single increases of brown dwarfs and free-floating planets found in both regions to date. Most notably, our new discoveries reveal an older (> 10 Myr) low-mass population in Taurus, in accord with recent studies of the higher-mass stellar members. In addition, the mass function appears to differ between the younger and older Taurus populations, possibly due to incompleteness of the older stellar members or different star formation processes. Upon completion, our survey will establish the most complete substellar and planetary-mass census in both Taurus and USco associations, make a significant addition to the low-mass IMF in both regions, and deliver more comprehensive pictures of star formation histories.

  11. Highly Viscous States Affect the Browning of Atmospheric Organic Particulate Matter.

    Science.gov (United States)

    Liu, Pengfei; Li, Yong Jie; Wang, Yan; Bateman, Adam P; Zhang, Yue; Gong, Zhaoheng; Bertram, Allan K; Martin, Scot T

    2018-02-28

    Initially transparent organic particulate matter (PM) can become shades of light-absorbing brown via atmospheric particle-phase chemical reactions. The production of nitrogen-containing compounds is one important pathway for browning. Semisolid or solid physical states of organic PM might, however, have sufficiently slow diffusion of reactant molecules to inhibit browning reactions. Herein, organic PM of secondary organic material (SOM) derived from toluene, a common SOM precursor in anthropogenically affected environments, was exposed to ammonia at different values of relative humidity (RH). The production of light-absorbing organonitrogen imines from ammonia exposure, detected by mass spectrometry and ultraviolet-visible spectrophotometry, was kinetically inhibited for RH atmospheric brown carbon production and associated influences on energy balance.

  12. Precise atmospheric parameters for the shortest-period binary white dwarfs: gravitational waves, metals, and pulsations

    International Nuclear Information System (INIS)

    Gianninas, A.; Kilic, Mukremin; Dufour, P.; Bergeron, P.; Brown, Warren R.; Hermes, J. J.

    2014-01-01

    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.

  13. Precise atmospheric parameters for the shortest-period binary white dwarfs: gravitational waves, metals, and pulsations

    Energy Technology Data Exchange (ETDEWEB)

    Gianninas, A.; Kilic, Mukremin [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Dufour, P.; Bergeron, P. [Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, Québec H3C 3J7 (Canada); Brown, Warren R. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Hermes, J. J., E-mail: alexg@nhn.ou.edu [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2014-10-10

    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 {sub 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. On the Spectral Evolution of Helium-atmosphere White Dwarfs Showing Traces of Hydrogen

    Science.gov (United States)

    Rolland, B.; Bergeron, P.; Fontaine, G.

    2018-04-01

    We present a detailed spectroscopic analysis of 115 helium-line (DB) and 28 cool, He-rich hydrogen-line (DA) white dwarfs based on atmosphere fits to optical spectroscopy and photometry. We find that 63% of our DB population show hydrogen lines, making them DBA stars. We also demonstrate the persistence of pure DB white dwarfs with no detectable hydrogen feature at low effective temperatures. Using state-of-the art envelope models, we next compute the total quantity of hydrogen, M H, that is contained in the outer convection zone as a function of effective temperature and atmospheric H/He ratio. We find that some (T eff, M H) pairs cannot physically exist as a homogeneously mixed structure; such a combination can only occur as stratified objects of the DA spectral type. On that basis, we show that the values of M H inferred for the bulk of the DBA stars are too large and incompatible with the convective dilution scenario. We also present evidence that the hydrogen abundances measured in DBA and cool, helium-rich white dwarfs cannot be globally accounted for by any kind of accretion mechanism onto a pure DB star. We suggest that cool, He-rich DA white dwarfs are most likely created by the convective mixing of a DA star with a thin hydrogen envelope; they are not cooled down DBAs. We finally explore several scenarios that could account for the presence of hydrogen in DBA stars.

  15. 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.

  16. NEAR-INFRARED LIGHT CURVES OF THE BROWN DWARF ECLIPSING BINARY 2MASS J05352184-0546085: CAN SPOTS EXPLAIN THE TEMPERATURE REVERSAL?

    International Nuclear Information System (INIS)

    Gomez Maqueo Chew, Yilen; Stassun, Keivan G.; Prsa, Andrej; Mathieu, Robert D.

    2009-01-01

    We present near-infrared JHK S light curves for the double-lined eclipsing binary system Two Micron All Sky Survey J05352184 - 0546085, in which both components have been shown to be brown dwarfs with an age of ∼1 Myr. We analyze these light curves together with the previously published I C -band light curve and radial velocities to provide refined measurements of the system's physical parameters. The component masses and radii are here determined with an accuracy of ∼6.5% and ∼1.5%, respectively. In addition, we confirm the previous surprising finding that the primary brown dwarf has a cooler effective temperature than its lower mass companion. Next, we perform a detailed study of the residual variations in the out-of-eclipse phases of the light curves to ascertain the properties of any inhomogeneities (e.g., spots) on the surfaces of the brown dwarfs. Our analysis reveals two low-amplitude (∼0.02 mag) periodic signals, one attributable to the rotation of the primary with a period of 3.293 ± 0.001 d and the other to the rotation of the secondary with a period of 14.05 ± 0.05 d. Both periods are consistent with the measured vsin i and radii. Finally, we explore the effects on the derived physical parameters of the system when spots are included in the modeling of the light curves. The observed low-amplitude rotational modulations are well fitted by cool spots covering a small fraction (∼<10%) of the brown dwarfs' surfaces. Such small spots negligibly affect the physical properties of the brown dwarfs, and thus by themselves cannot explain the primary's unexpectedly low surface temperature. To mimic the observed ∼200 K suppression of the primary's temperature, our model requires that the primary possesses a very large spot coverage fraction of ∼65%. These spots must in addition be symmetrically distributed on the primary's surface so as not to produce photometric variations larger than observed. Altogether, a spot configuration in which the primary

  17. First Spectropolarimetric Measurement of a Brown Dwarf Magnetic Field in Molecular Bands

    Energy Technology Data Exchange (ETDEWEB)

    Kuzmychov, Oleksii; Berdyugina, Svetlana V. [Kiepenheuer-Institut für Sonnenphysik Schöneckstr, 6 D-79104 Freiburg (Germany); Harrington, David M., E-mail: oleksii@leibniz-kis.de [National Solar Observatory (Maui), 8 Kiopa’a Street Pukalani, HI 96768 (United States)

    2017-09-20

    We present the first measurements of the surface magnetic field of a late-M dwarf, LSR J1835+3259, with the help of the full-Stokes spectropolarimetry in the bands of diatomic molecules. Our measurements at different rotational phases of a dwarf yielded one 5 σ and two 3 σ magnetic field detections. The observational data have been obtained with the LRISp polarimeter at the Keck observatory on 2012 August 22 and 23. These data have been compared against synthetic full-Stokes spectra in the bands of the molecules CrH, FeH, and TiO, which have been calculated for a range of the stellar parameters and magnetic field strengths. Making use of χ {sup 2}-minimization and maximum likelihood estimation, we determine the net magnetic field strength B (and not flux Bf ) of LSR J1835+3259 to ∼5 kG with the help of the Paschen–Back effect in the CrH lines. Our measurements at different rotational phases suggest that the dwarf’s surface might be covered with strong small-scale magnetic fields. In addition, recent findings of the dwarf’s hydrogen emission and the Stokes V signal from the lower chromosphere indicate that its surface magnetic field might be changing rapidly giving rise to flare activity, similar to young dMe dwarfs. We substantiate the substellar origin of LSR J1835+3259 by making use of our own data as well as the photometric data from the all-sky surveys 2MASS and WISE .

  18. 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.

  19. Spectral Variability of Two Rapidly Rotating Brown Dwarfs: 2MASS J08354256-0819237 and 2MASS J18212815+1414010

    OpenAIRE

    Schlawin, Everett; Burgasser, Adam J.; Karalidi, Theodora; Gizis, John; Teske, Johanna

    2017-01-01

    L dwarfs exhibit low-level, rotationally-modulated photometric variability generally associated with heterogeneous, cloud-covered atmospheres. The spectral character of these variations yields insight into the particle sizes and vertical structure of the clouds. Here we present the results of a high precision, ground-based, near-infrared, spectral monitoring study of two mid-type L dwarfs that have variability reported in the literature, 2MASS J08354256-0819237 and 2MASS J18212815+1414010, us...

  20. The possible false-detection of a transiting brown dwarf candidate in the overlapping fields of Kepler and MARVELS

    Science.gov (United States)

    Reyes, Alan; Ge, Jian; Thomas, Neil; Ma, Bo; Heslar, Michael Francis; SDSS-III MARVELS Team

    2016-01-01

    While searching for exoplanets via the transit method, it has been documented that the periodicity of an unresolved background eclipsing binary (BEB) can be misinterpreted as the orbital companion of a target star. We explore the possibility that this false-positive contamination method can also occur in Doppler surveys if the angular separation between a BEB and a selected primary is under a certain threshold, dependent on the fiber diameter of the spectrometer instrument. The case example of this investigation is a K2 giant in the constellation Cygnus, in the region of overlap of the Kepler and MARVELS surveys. This star was originally flagged for potentially having a 5.56d period companion as per the Kepler transit photometry. It was also imbricated with radial velocity (RV) observations performed by the SDSS-III MARVELS survey, in which Doppler information was extracted from along the dispersion direction of the fiducially-calibrated, post-pipeline-rendered spectra. The 5.56d period was corroborated after testing its probability against that of others via a Lomb-Scargle periodogram analysis. The pipeline mass determination yielded a ~17 MJupiter companion, within the characteristic mass-range of brown dwarfs. The MARVELS results seem to constitute an independent discovery, and hence confirmation, of the brown dwarf candidate. However, a later investigation conducted by EXPERT, intent upon refining the system's physical parameters, failed to identify the RV signal of any companion whatsoever. EXPERT, with its superior resolving power (R=30,000 vs R=11,000 in MARVELS), finer fiber width (1.2 vs 1.9 arcsec), and higher degree of precision (~10 m/s), was expected to finalize the confirmation, but now offers a major challenge to previous models of the system. Additionally, high-resolution adaptive optics imaging reveals the presence of a distinct, close-in object. The object may itself be an unbound BEB, and thus the source of the period signals reported by Kepler

  1. The near-infrared outflow and cavity of the proto-brown dwarf candidate ISO-Oph 200

    Science.gov (United States)

    Whelan, E. T.; Riaz, B.; Rouzé, B.

    2018-03-01

    In this Letter a near-infrared integral field study of a proto-brown dwarf candidate is presented. A 0.''5 blue-shifted outflow is detected in both H2 and [Fe II] lines at Vsys = (–35 ± 2) km s-1 and Vsys = (–51 ± 5) km s-1 respectively. In addition, slower ( ±10 km s-1) H2 emission is detected out to <5.''4, in the direction of both the blue and red-shifted outflow lobes but along a different position angle to the more compact faster emission. It is argued that the more compact emission is a jet and the extended H2 emission is tracing a cavity. The source extinction is estimated at Av = 18 ± 1 mag and the outflow extinction at Av = 9 ± 0.4 mag. The H2 outflow temperature is calculated to be 1422 ± 255 K and the electron density of the [Fe II] outflow is measured at 10 000 cm-3. Furthermore, the mass outflow rate is estimated at Ṁout [H2] = 3.8 × 10-10 M⊙ yr-1 and Ṁout[Fe II] = 1 × 10-8 M⊙ yr-1. Ṁout[Fe II] takes a Fe depletion of 88% into account. The depletion is investigated using the ratio of the [Fe II] 1.257 μm and [P II] 1.188 μm lines. Using the Paβ and Brγ lines and a range in stellar mass and radius Ṁacc is calculated to be (3–10) × 10-8 M⊙ yr-/1. Comparing these rates puts the jet efficiency in line with predictions of magneto-centrifugal models of jet launching in low mass protostars. This is a further case of a brown dwarf outflow exhibiting analogous properties to protostellar jets. Based on Observations collected with SINFONI at the Very Large Telescope on Cerro Paranal (Chile), operated by the European Southern Observatory (ESO). Program ID: 097.C-0732(A).

  2. 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.

  3. The cool DA white dwarf G128-7: Atmospheric parameters and evolutionary consequences

    International Nuclear Information System (INIS)

    Wehrse, R.; Liebert, J.

    1980-01-01

    Atmospheric parameters are derived for the very cool DA white dwarf G128-7 (Gr283). The best fit to the models yields Tsub(eff) = 5800 0 K, [M/H] approx. 8.0 is found because of the implied formation of molecular hydrogen and its effects on the temperature stratification; at higher Tsub(eff), the molecule formation is unimportant and the H-lines show little gravity dependence. The dominance of non-DA spectral types for a sample of nearby, well observed white dwarfs with 13.0 0 K) leads us to conclude that the 3:1 ratio in favor of hydrogen atmospheres for hot white dwarfs is not preserved as the stars cool; this is evidence that convective mixing of the outer hydrogen layer has occured for some but not all stars. Results of recent theoretical investigations suggest that the surviving cool DA stars have larger initial hydrogen layer masses (>approx.10 -10 M) or higher than normal stallar masses. The latter possibility would be consistent with our inference for a higher than normal surface gravity in G128-7. (orig.) 891 WL/orig. 892 HIS

  4. PROBING THE FLARE ATMOSPHERES OF M DWARFS USING INFRARED EMISSION LINES

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Sarah J.; Kowalski, Adam F.; Hawley, Suzanne L.; Hilton, Eric J.; Wisniewski, John P.; Tofflemire, Benjamin M., E-mail: sjschmidt@astro.washington.edu [Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada (Canada)

    2012-01-20

    We present the results of a campaign to monitor active M dwarfs using infrared spectroscopy, supplemented with optical photometry and spectroscopy. We detected 16 flares during nearly 50 hr of observations on EV Lac, AD Leo, YZ CMi, and VB 8. The three most energetic flares also showed infrared emission, including the first reported detections of P{beta}, P{gamma}, He I {lambda}10830, and Br{gamma} during an M dwarf flare. The strongest flare ({Delta}u = 4.02 on EV Lac) showed emission from H{gamma}, H{delta}, He I {lambda}4471, and Ca II K in the UV/blue and P{beta}, P{gamma}, P{delta}, Br{gamma}, and He I {lambda}10830 in the infrared. The weaker flares ({Delta}u = 1.68 on EV Lac and {Delta}U = 1.38 on YZ CMi) were only observed with photometry and infrared spectroscopy; both showed emission from P{beta}, P{gamma}, and He I {lambda}10830. The strongest infrared emission line, P{beta}, occurred in the active mid-M dwarfs with a duty cycle of {approx}3%-4%. To examine the most energetic flare, we used the static NLTE radiative transfer code RH to produce model spectra based on a suite of one-dimensional model atmospheres. Using a hotter chromosphere than previous one-dimensional atmospheric models, we obtain line ratios that match most of the observed emission lines.

  5. Search for brown dwarfs by gravitational microlensing effect with the pixels method. Analysis of AGAPE and EROS collaborations data

    International Nuclear Information System (INIS)

    Melchior, Anne-Laure

    1995-01-01

    This work is involved in baryonic dark matter search in galactic halos. An important collect of observational data has been initiated to test the hypothesis that this dark mass is made of compact objects such as brown dwarfs or small mass stars. The gravitational microlensing effect allows to probe this distribution of this mass type along the line of sight of nearby galaxies such as the Large Magellanic Cloud. A new way to detect these microlensing events has been proposed by P. Baillon et al.: the pixel method. The aim is to detect the amplification of stars which are unresolved or too faint to be seen by classical analysis. First, we present this method and the simulations which allow to establish its feasibility. Then, we describe the pixel analysis of the 91-92 EROS data on the Large Magellanic Cloud. The selection of luminosity variations with a shape compatible with microlensing events allows us to study the sensitivity of this analysis. We see how these results allow us to validate the pixel method applied on a large volume of data. This also shows the possibility to find luminosity variations which escape classical analysis research. Strengthened by these results, we finally describe the analysis of the AGAPE 94 data on the Andromeda galaxy which uses the same pixel method. Being ten times farther away than the Large Magellanic Cloud, the Andromeda galaxy has very few resolved stars, making the pixel method the only way of looking for microlensing events. (author) [fr

  6. Microlensing discovery of a tight, low-mass-ratio planetary-mass object around an old field brown dwarf

    Energy Technology Data Exchange (ETDEWEB)

    Han, C.; Jung, Y. K. [Department of Physics, Chungbuk National University, Cheongju 371-763 (Korea, Republic of); Udalski, A.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Skowron, J.; Kozłowski, S.; Poleski, R.; Ulaczyk, K.; Wyrzykowski, Ł.; Pietrukowicz, P. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Sumi, T. [Department of Earth and Space Science, Osaka University, Osaka 560-0043 (Japan); Gaudi, B. S.; Gould, A. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Bennett, D. P. [University of Notre Dame, Department of Physics, 225 Nieuwland Science Hall, Notre Dame, IN 46556-5670 (United States); Tsapras, Y. [Las Cumbres Observatory Global Telescope Network, 6740B Cortona Dr, Goleta, CA 93117 (United States); Abe, F. [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601 (Japan); Bond, I. A. [Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland (New Zealand); Collaboration: OGLE Collaboration; MOA Collaboration; μFUN Collaboration; RoboNet Collaboration; and others

    2013-11-20

    Observations of accretion disks around young brown dwarfs (BDs) have led to the speculation that they may form planetary systems similar to normal stars. While there have been several detections of planetary-mass objects around BDs (2MASS 1207-3932 and 2MASS 0441-2301), these companions have relatively large mass ratios and projected separations, suggesting that they formed in a manner analogous to stellar binaries. We present the discovery of a planetary-mass object orbiting a field BD via gravitational microlensing, OGLE-2012-BLG-0358Lb. The system is a low secondary/primary mass ratio (0.080 ± 0.001), relatively tightly separated (∼0.87 AU) binary composed of a planetary-mass object with 1.9 ± 0.2 Jupiter masses orbiting a BD with a mass 0.022 M {sub ☉}. The relatively small mass ratio and separation suggest that the companion may have formed in a protoplanetary disk around the BD host in a manner analogous to planets.

  7. Radial velocities of very low mass stars and candidate brown dwarf members of the Hyades and Pleiades

    Science.gov (United States)

    Stauffer, John R.; Liebert, James; Giampapa, Mark; Macintosh, Bruce; Reid, Neill; Hamilton, Donald

    1994-01-01

    We have determined H alpha equivalent widths and radial velocities with 1 sigma accuracies of approximately 5 km s(exp -1) for approximately 20 candidate very low mass members of the Hyades and Pleiades clusters. The radial velocities for the Hyades sample suggest that nearly all of these stars are indeed highly probable members of the Hyades. The faintest stars in the Hyades sample have masses of order 0.1 solar mass. We also obtained radial velocities for four candidate very low mass members of the Pleiades and two objects that are candidate BD Pleiads. All of these stars have apparent V magnitudes fainter than the Hyades stars we observed, and the resultant radial velocity accuracy is worse. We believe that the three brighter stars are indeed likely very low mass stellar members of the Pleiades, whereas the status of the two brown dwarf candidates is uncertain. The Hyades stars we have observed and the three Pleiades very low mass stars are the lowest mass members of any open cluster whose membership has been confirmed by radial velocities and whose chromospheric activity has been measured. We see no change in chromospheric activity at the boundary where stars are expected to become fully convective (M approximately equals 0.3 solar mass) in either cluster. In the Pleiades, however, there may be a decrease in chromospheric activity for stars with (V-I)(sub K) greater than 3.5 (M less than or equal to 0.1 solar mass).

  8. MICROLENS TERRESTRIAL PARALLAX MASS MEASUREMENTS: A RARE PROBE OF ISOLATED BROWN DWARFS AND FREE-FLOATING PLANETS

    International Nuclear Information System (INIS)

    Gould, Andrew; Yee, Jennifer C.

    2013-01-01

    Terrestrial microlens parallax is one of the very few methods that can measure the mass and number density of isolated dark low-mass objects, such as old free-floating planets and brown dwarfs. Terrestrial microlens parallax can be measured whenever a microlensing event differs substantially as observed from two or more well-separated sites. If the lens also transits the source during the event, then its mass can be measured. We derive an analytic expression for the expected rate of such events and then use this to derive two important conclusions. First, the rate is directly proportional to the number density of a given population, greatly favoring low-mass populations relative to their contribution to the general microlensing rate, which further scales as M 1/2 where M is the lens mass. Second, the rate rises sharply as one probes smaller source stars, despite the fact that the probability of transit falls directly with source size. We propose modifications to current observing strategies that could yield a factor of 100 increase in sensitivity to these rare events.

  9. The Pan-STARRS1 Proper-motion Survey for Young Brown Dwarfs in Nearby Star-forming Regions. I. Taurus Discoveries and a Reddening-free Classification Method for Ultracool Dwarfs

    Science.gov (United States)

    Zhang, Zhoujian; Liu, Michael C.; Best, William M. J.; Magnier, Eugene A.; Aller, Kimberly M.; Chambers, K. C.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Metcalfe, N.; Wainscoat, R. J.; Waters, C.

    2018-05-01

    We are conducting a proper-motion survey for young brown dwarfs in the Taurus-Auriga molecular cloud based on the Pan-STARRS1 3π Survey. Our search uses multi-band photometry and astrometry to select candidates, and is wider (370 deg2) and deeper (down to ≈3 M Jup) than previous searches. We present here our search methods and spectroscopic follow-up of our high-priority candidates. Since extinction complicates spectral classification, we have developed a new approach using low-resolution (R ≈ 100) near-infrared spectra to quantify reddening-free spectral types, extinctions, and gravity classifications for mid-M to late-L ultracool dwarfs (≲100–3 M Jup in Taurus). We have discovered 25 low-gravity (VL-G) and the first 11 intermediate-gravity (INT-G) substellar (M6–L1) members of Taurus, constituting the largest single increase of Taurus brown dwarfs to date. We have also discovered 1 new Pleiades member and 13 new members of the Perseus OB2 association, including a candidate very wide separation (58 kau) binary. We homogeneously reclassify the spectral types and extinctions of all previously known Taurus brown dwarfs. Altogether our discoveries have thus far increased the substellar census in Taurus by ≈40% and added three more L-type members (≲5–10 M Jup). Most notably, our discoveries reveal an older (>10 Myr) low-mass population in Taurus, in accord with recent studies of the higher-mass stellar members. The mass function appears to differ between the younger and older Taurus populations, possibly due to incompleteness of the older stellar members or different star formation processes.

  10. 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.

  11. Testing Gravity Using Dwarf Stars

    OpenAIRE

    Sakstein, Jeremy

    2015-01-01

    Generic scalar-tensor theories of gravity predict deviations from Newtonian physics inside astrophysical bodies. In this paper, we point out that low mass stellar objects, red and brown dwarf stars, are excellent probes of these theories. We calculate two important and potentially observable quantities: the radius of brown dwarfs and the minimum mass for hydrogen burning in red dwarfs. The brown dwarf radius can differ significantly from the GR prediction and upcoming surveys that probe the m...

  12. 2MASS J0516288+260738: Discovery of the first eclipsing late K + Brown dwarf binary system?

    Science.gov (United States)

    Schuh, S. L.; Handler, G.; Drechsel, H.; Hauschildt, P.; Dreizler, S.; Medupe, R.; Karl, C.; Napiwotzki, R.; Kim, S.-L.; Park, B.-G.; Wood, M. A.; Paparó, M.; Szeidl, B.; Virághalmy, G.; Zsuffa, D.; Hashimoto, O.; Kinugasa, K.; Taguchi, H.; Kambe, E.; Leibowitz, E.; Ibbetson, P.; Lipkin, Y.; Nagel, T.; Göhler, E.; Pretorius, M. L.

    2003-11-01

    We report the discovery of a new eclipsing system less than one arcminute south of the pulsating DB white dwarf KUV 05134+2605. The object could be identified with the point source 2MASS J0516288+260738 published by the Two Micron All Sky Survey. We present and discuss the first light curves as well as some additional colour and spectral information. The eclipse period of the system is 1.29 d, and, assuming this to be identical to the orbital period, the best light curve solution yields a mass ratio of m2/m1=0.11, a radius ratio of r2/r1~ 1 and an inclination of 74o. The spectral anaylsis results in a Teff=4200 K for the primary. On this basis, we suggest that the new system probably consists of a late K + Brown dwarf (which would imply a system considerably younger than ~0.01 Gyr to have r2/r1~ 1), and outline possible future observations. This paper uses observations made at the Bohyunsan Optical Astronomy Observatory of Korea Astronomy Observatory, at the South African Astronomical Observatory (SAAO), at the 0.9 m telescope at Kitt Peak National Observatory recommissioned by the Southeastern Association for Research in Astronomy (SARA), at Gunma Astronomical Observatory established by Gunma prefecture, Japan, at the Florence and George Wise Observatory, operated by the Tel-Aviv University, Israel and at Piszkésteto, the mountain station of Konkoly Observatory of the Hungarian Academy of Science, Hungary. This publication makes use of data products from the Two Micron All Sky Survey, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center / California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The Digitized Sky Survey was produced at the Space Telescope Science Institute under US Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK

  13. A MULTIWAVELENGTH CHARACTERIZATION OF PROTO-BROWN-DWARF CANDIDATES IN SERPENS

    Energy Technology Data Exchange (ETDEWEB)

    Riaz, B.; Caselli, P. [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Vorobyov, E. [Institute of Astrophysics, University of Vienna, Vienna 1180 (Austria); Research Institute of Physics, Southern Federal University, Rostov-on-Don 344090 (Russian Federation); Harsono, D. [Universitt Heidelberg, Zentrum fr Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120, Heidelberg (Germany); Tikare, K. [IRAP, BP 44346-31028 Toulouse Cedex 4 (France); Gonzalez-Martin, O., E-mail: briaz@mpe.mpg.de [Instituto de Radioastronoma y Astrofsica (IRyA), UNAM, Antigua Carretera a Pátzcuaro # 8701, Col. Ex Hacienda San José de la Huerta, Morelia, Michoacán, C.P. 58089 (Mexico)

    2016-11-10

    We present results from a deep submillimeter survey in the Serpens Main and Serpens/G3–G6 clusters, conducted with the Submillimetre Common-User Bolometer Array (SCUBA-2) at the James Clerk Maxwell Telescope. We have combined near- and mid-infrared spectroscopy, Herschel PACS far-infrared photometry, submillimeter continuum, and molecular gas line observations, with the aim of conducting a detailed multiwavelength characterization of “proto-brown-dwarf” (proto-BD) candidates in Serpens. We have performed continuum and line radiative transfer modeling and have considered various classification schemes to understand the structure and the evolutionary stage of the system. We have identified four proto-BD candidates, of which the lowest-luminosity source has an L {sub bol} ∼ 0.05 L {sub ☉}. Two of these candidates show characteristics consistent with Stage 0/I systems, while the other two are Stage I-T/Class Flat systems with tenuous envelopes. Our work has also revealed a ∼20% fraction of misidentified Class 0/I/Flat sources that show characteristics consistent with Class II edge-on disk systems. We have set constraints on the mass of the central object using the measured bolometric luminosities and numerical simulations of stellar evolution. Considering the available gas+dust mass reservoir and the current mass of the central source, three of these candidates are likely to evolve into BDs.

  14. The First Simultaneous Microlensing Observations by Two Space Telescopes: Spitzer and Swift Reveal a Brown Dwarf in Event OGLE-2015-BLG-1319

    Science.gov (United States)

    Shvartzvald, Y.; Li, Z.; Udalski, A.; Gould, A.; Sumi, T.; Street, R. A.; Calchi Novati, S.; Hundertmark, M.; Bozza, V.; Beichman, C.; hide

    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 30-65M J brown dwarf orbiting a K dwarf in the microlensing event OGLE-2015-BLG-1319. The system is located at a distance of approximately 5 kpc toward the Galactic Bulge. The event was observed by several ground-based groups as well as by Spitzer and Swift, allowing a measurement of the physical properties. However, the event is still subject to an eight-fold degeneracy, in particular the well-known close-wide degeneracy, and thus the projected separation between the two lens components is either approximately 0.25 au or approximately 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 though Swift could not measure the microlens parallax with respect to ground-based observations for this event, it can be important for other events. Specifically, it is important for detecting nearby brown dwarfs and free-floating planets in high magnification events.

  15. Using brown midrib 6 dwarf forage sorghum silage and fall-grown oat silage in lactating dairy cow rations.

    Science.gov (United States)

    Harper, M T; Oh, J; Giallongo, F; Lopes, J C; Roth, G W; Hristov, A N

    2017-07-01

    Double cropping and increasing crop diversity could improve dairy farm economic and environmental sustainability. In this experiment, corn silage was partially replaced with 2 alternative forages, brown midrib-6 brachytic dwarf forage sorghum (Sorghum bicolor) or fall-grown oat (Avena sativa) silage, in the diet of lactating dairy cows. We investigated the effect on dry matter (DM) intake, milk yield (MY), milk components and fatty acid profile, apparent total-tract nutrient digestibility, N utilization, enteric methane emissions, and income over feed cost. We analyzed the in situ DM and neutral detergent fiber disappearance of the alternative forages versus corn silage and alfalfa haylage. Sorghum was grown in the summer and harvested in the milk stage. Oats were grown in the fall and harvested in the boot stage. Compared with corn silage, neutral detergent fiber and acid detergent fiber concentrations were higher in the alternative forages. Lignin content was highest for sorghum silage and similar for corn silage and oat silage. The alternative forages had less than 1% starch compared with the approximately 35% starch in the corn silage. Ruminal in situ DM effective degradability was similar, although statistically different, for corn silage and oat silage, but lower for sorghum silage. Diets with the alternative forages were fed in a replicated 3 × 3 Latin square design experiment with three 28-d periods and 12 Holstein cows. The control diet contained 44% (DM basis) corn silage. In the other 2 diets, sorghum or oat silages were included at 10% of dietary DM, replacing corn silage. Sorghum silage inclusion decreased DM intake, MY, and milk protein content but increased milk fat and maintained energy-corrected MY similar to the control. Oat silage had no effect on DM intake, MY, or milk components compared to the control. The oat silage diet increased apparent total-tract digestibility of dietary nutrients, except starch, whereas the sorghum diet slightly

  16. SPATIALLY RESOLVED OBSERVATIONS OF THE BIPOLAR OPTICAL OUTFLOW FROM THE BROWN DWARF 2MASS J12073347–3932540

    International Nuclear Information System (INIS)

    Whelan, E. T.; Ray, T. P.; Comeron, F.; Bacciotti, F.; Kavanagh, P. J.

    2012-01-01

    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 JUP BD 2MASS J12073347–3932540 are presented. The outflow was originally identified through the spectro-astrometric analysis of the [O I]λ6300 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 ∼65°. The [O I]λ6300 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.

  17. MARVELS-1b: A SHORT-PERIOD, BROWN DWARF DESERT CANDIDATE FROM THE SDSS-III MARVELS PLANET SEARCH

    International Nuclear Information System (INIS)

    Lee, Brian L.; Ge Jian; Fleming, Scott W.; Mahadevan, Suvrath; Sivarani, Thirupathi; Stassun, Keivan G.; Gary, Bruce; Pepper, Joshua; Gaudi, B. Scott; Eastman, Jason D.; Siverd, Robert J.; Barnes, Rory; Laws, Chris; Wisniewski, John P.; Wright, Jason; Ghezzi, Luan; Ogando, Ricardo L. C.; Maia, Marcio A. G.; Da Costa, Luiz Nicolaci; Porto de Mello, G. F.

    2011-01-01

    We present a new short-period brown dwarf (BD) candidate around the star TYC 1240-00945-1. This candidate was discovered in the first year of the Multi-object APO Radial Velocity Exoplanets Large-area Survey (MARVELS), which is part of the Sloan Digital Sky Survey (SDSS) III, and we designate the BD as MARVELS-1b. MARVELS uses the technique of dispersed fixed-delay interferometery to simultaneously obtain radial velocity (RV) measurements for 60 objects per field using a single, custom-built instrument that is fiber fed from the SDSS 2.5 m telescope. From our 20 RV measurements spread over a ∼370 day time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 2.533 ± 0.025 km s -1 , period P = 5.8953 ± 0.0004 days, and eccentricity consistent with circular. Independent follow-up RV data confirm the orbit. Adopting a mass of 1.37 ± 0.11 M sun for the slightly evolved F9 host star, we infer that the companion has a minimum mass of 28.0 ± 1.5 M Jup , a semimajor axis 0.071 ± 0.002 AU assuming an edge-on orbit, and is probably tidally synchronized. We find no evidence for coherent intrinsic variability of the host star at the period of the companion at levels greater than a few millimagnitudes. The companion has an a priori transit probability of ∼14%. Although we find no evidence for transits, we cannot definitively rule them out for companion radii ∼ Jup .

  18. Radial velocities of very low mass stars and candidate brown dwarf members of the Hyades and Pleiades, 2

    Science.gov (United States)

    Stauffer, John R.; Liebert, James; Giampapa, Mark

    1995-01-01

    We have determined H alpha equivalent widths and radial velocities with 1 sigma accuracies of approximately 5 km/s for approximately 20 candidate very low mass members of the Pleiades cluster and for a few proposed very low mass members of the Hyades. Most of the Pleiades targets were selected from the recent Hambly, Hawkins, and Jameson proper motion survey, where they were identified as probable Pleiades brown dwarfs with an age spread from 3 to 70 Myr. Our spectroscopic data and a reinterpretation of the photometric data confirm that these objects are indeed likely Pleiades members; however, we believe that they more likely have masses slightly above the hydrogen burning mass limit and that there is no firm evidence for an age spread amongst these stars. All of the very low mass Pleiades and Hyades members show H alpha in emission. However, the ratio of H alpha flux to biometric flux in the Pleiades shows a maximum near M(sub Bol) approximately equal to 9.5 (M approximately equal to 0.3 solar mass) and a sharp decrease to lower masses. This break occurs at the approximate mass where low mass stars are expected to become fully convective, and it is tempting to assume that the decrease in H alpha flux is caused by some change in the behavior of stellar dynamos at this mass. We do not see a similar break in activity at this mass in the Hyades. We discuss possible evolutionary explanations for this difference in the H alpha activity between the two clusters.

  19. Ascorbic acid and tissue browning in pears (Pyrus communis L. cvs Rocha and Conference) under controlled atmosphere conditions

    NARCIS (Netherlands)

    Veltman, R.H.; Kho, R.M.; Schaik, van A.C.R.; Sanders, M.G.; Oosterhaven, J.

    2000-01-01

    The relationships between storage gas composition and ascorbic acid (AA) levels, and between AA levels and the development of internal browning, were studied in 'Conference' and 'Rocha' pears (Pyrus communis L.). In both cultivars, AA levels declined under (browning-inducing) controlled atmosphere

  20. A Candidate Wide Brown Dwarf Binary in the Argus Association: 2MASS J14504216–7841413 and 2MASS J14504113–7841383

    OpenAIRE

    Burgasser, Adam J.; Looper, Dagny L.; Kirkpatrick, J. Davy

    2017-01-01

    Widely-separated (≳100 au) multiples are rare among the lowest mass stars and brown dwarfs (Caballero 2007; Kraus & Hillenbrand 2009), and often (but not exclusively) associated with young (≾100 Myr), nearby stellar associations (e.g., Close et al. 2007). We report the discovery of a wide, very low mass, and potentially young binary, 2MASS J14504216–7841413 and 2MASS J14504113–7841383 (hereafter 2MASS J1450–7841AB). The primary was initially identified in the DENIS (Epchtein et al. 1997) and ...

  1. SIMP J2154–1055: A NEW LOW-GRAVITY L4β BROWN DWARF CANDIDATE MEMBER OF THE ARGUS ASSOCIATION

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-01

    We present SIMP J21543454–1055308, a new L4β brown dwarf identified in the SIMP survey that displays signs of low gravity in its near-infrared spectrum. Using BANYAN II, we show that it is a candidate member of the Argus association, albeit with a 21% probability that it is a contaminant from the field. Measurements of radial velocity and parallax will be needed to verify its membership. If it is a member of Argus (age 30-50 Myr), then this object would have a planetary mass of 10 ± 0.5 M {sub Jup}.

  2. THE NIRSPEC ULTRACOOL DWARF RADIAL VELOCITY SURVEY

    International Nuclear Information System (INIS)

    Blake, Cullen H.; Charbonneau, David; White, Russel J.

    2010-01-01

    We report the results of an infrared Doppler survey designed to detect brown dwarf and giant planetary companions to a magnitude-limited sample of ultracool dwarfs. Using the NIRSPEC spectrograph on the Keck II telescope, we obtained approximately 600 radial velocity (RV) measurements over a period of six years of a sample of 59 late-M and L dwarfs spanning spectral types M8/L0 to L6. A subsample of 46 of our targets has been observed on three or more epochs. We rely on telluric CH 4 absorption features in Earth's atmosphere as a simultaneous wavelength reference and exploit the rich set of CO absorption features found in the K-band spectra of cool stars and brown dwarfs to measure RVs and projected rotational velocities. For a bright, slowly rotating M dwarf standard we demonstrate an RV precision of 50 m s -1 and for slowly rotating L dwarfs we achieve a typical RV precision of approximately 200 m s -1 . This precision is sufficient for the detection of close-in giant planetary companions to mid-L dwarfs as well as more equal mass spectroscopic binary systems with small separations (a +0.7 -0.6 Gyr, similar to that of nearby sun-like stars. We simulate the efficiency with which we detect spectroscopic binaries and find that the rate of tight (a +8.6 -1.6 %, consistent with recent estimates in the literature of a tight binary fraction of 3%-4%.

  3. Discovery of Three Pulsating, Mixed-atmosphere, Extremely Low-mass White Dwarf Precursors

    Science.gov (United States)

    Gianninas, A.; Curd, Brandon; Fontaine, G.; Brown, Warren R.; Kilic, Mukremin

    2016-05-01

    We report the discovery of pulsations in three mixed-atmosphere, extremely low-mass white dwarf (ELM WD, M ≤slant 0.3 M ⊙) 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 timescale with theoretical predictions of p-mode pulsations in mixed-atmosphere ≈0.18 M ⊙ 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, timeseries 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. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil).

  4. THE DISCOVERY OF Y DWARFS USING DATA FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE)

    International Nuclear Information System (INIS)

    Cushing, Michael C.; Mainzer, A.; Eisenhardt, Peter R.; Kirkpatrick, J. Davy; Gelino, Christopher R.; Griffith, Roger L.; Marsh, Kenneth A.; Beichman, Charles A.; Skrutskie, Michael F.; Burgasser, Adam J.; Prato, Lisa A.; Simcoe, Robert A.; Marley, Mark S.; Freedman, Richard S.; Saumon, D.; Wright, Edward L.

    2011-01-01

    We present the discovery of seven ultracool brown dwarfs identified with the Wide-field Infrared Survey Explorer (WISE). Near-infrared spectroscopy reveals deep absorption bands of H 2 O and CH 4 that indicate all seven of the brown dwarfs have spectral types later than UGPS J072227.51–054031.2, the latest-type T dwarf currently known. The spectrum of WISEP J182831.08+265037.8 is distinct in that the heights of the J- and H-band peaks are approximately equal in units of f λ , so we identify it as the archetypal member of the Y spectral class. The spectra of at least two of the other brown dwarfs exhibit absorption on the blue wing of the H-band peak that we tentatively ascribe to NH 3 . These spectral morphological changes provide a clear transition between the T dwarfs and the Y dwarfs. In order to produce a smooth near-infrared spectral sequence across the T/Y dwarf transition, we have reclassified UGPS 0722–05 as the T9 spectral standard and tentatively assign WISEP J173835.52+273258.9 as the Y0 spectral standard. In total, six of the seven new brown dwarfs are classified as Y dwarfs: four are classified as Y0, one is classified as Y0 (pec?), and WISEP J1828+2650 is classified as >Y0. We have also compared the spectra to the model atmospheres of Marley and Saumon and infer that the brown dwarfs have effective temperatures ranging from 300 K to 500 K, making them the coldest spectroscopically confirmed brown dwarfs known to date.

  5. Automatic parameterization and analysis of stellar atmospheres: a study of the DA white dwarfs

    International Nuclear Information System (INIS)

    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 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

  6. 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.

  7. Softening behaviour of brown coal ashes. Influence of ash components and gas atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Hegermann, R; Huettinger, K J [Karlsruhe Univ. (T.H.) (Germany, F.R.). Inst. fuer Chemische Technik

    1990-03-01

    The softening behaviour of brown coal ashes during gasification is important for three reasons: (1) Formation of large agglomerates, (2) inactivation of catalytically active ash components, (3) encapsulation of parts of the coal. The softening behaviour of the ashes was studied with a high temperature dilatometer at ambient pressure in various atmospheres (air, CO{sub 2}, Ar/H{sub 2}O, Ar, H{sub 2}/H{sub 2}O, H{sub 2}) using a push-rod with a conical tip. The heating rate was 5 Kmin{sup -1}, the final temperature 1000deg C, the residence time 1 h. (orig.).

  8. 3D MODEL ATMOSPHERES FOR EXTREMELY LOW-MASS WHITE DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Tremblay, P.-E. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); Gianninas, A.; Kilic, M. [Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK, 73019 (United States); Ludwig, H.-G. [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Steffen, M. [Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Freytag, B. [Department of Physics and Astronomy at Uppsala University, Regementsvägen 1, Box 516, SE-75120 Uppsala (Sweden); Hermes, J. J., E-mail: tremblay@stsci.edu [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2015-08-20

    We present an extended grid of mean three-dimensional (3D) spectra for low-mass, pure-hydrogen atmosphere DA white dwarfs (WDs). We use CO5BOLD radiation-hydrodynamics 3D simulations covering T{sub eff} = 6000–11,500 K and log g = 5–6.5 (g in cm s{sup −2}) to derive analytical functions to convert spectroscopically determined 1D temperatures and surface gravities to 3D atmospheric parameters. Along with the previously published 3D models, the 1D to 3D corrections are now available for essentially all known convective DA WDs (i.e., log g = 5–9). For low-mass WDs, the correction in temperature is relatively small (a few percent at the most), but the surface gravities measured from the 3D models are lower by as much as 0.35 dex. We revisit the spectroscopic analysis of the extremely low-mass (ELM) WDs, and demonstrate that the 3D models largely resolve the discrepancies seen in the radius and mass measurements for relatively cool ELM WDs in eclipsing double WD and WD + millisecond pulsar binary systems. We also use the 3D corrections to revise the boundaries of the ZZ Ceti instability strip, including the recently found ELM pulsators.

  9. DEEP NEAR-INFRARED IMAGING OF THE ρ Oph CLOUD CORE: CLUES TO THE ORIGIN OF THE LOWEST-MASS BROWN DWARFS

    International Nuclear Information System (INIS)

    Marsh, Kenneth A.; Plavchan, Peter; Kirkpatrick, J. Davy; Lowrance, Patrick J.; Cutri, Roc M.; Velusamy, Thangasamy

    2010-01-01

    A search for young substellar objects in the ρ Oph cloud core region has been made with the aid of multiband profile-fitting point-source photometry of the deep-integration Combined Calibration Scan images of the 2MASS extended mission in the J, H, and K s bands, and Spitzer IRAC images at 3.6, 4.5, 5.8, and 8.0 μm. The field of view of the combined observations was 1 0 x 9.'3, and the 5σ limiting magnitude at J was 20.5. Comparison of the observed spectral energy distributions with the predictions of the COND and DUSTY models, for an assumed age of 1 Myr, supports the identification of many of the sources with brown dwarfs and enables the estimation of effective temperature, T eff . The cluster members are then readily distinguishable from background stars by their locations on a plot of flux density versus T eff . The range of estimated T eff values extends down to ∼750 K which, based on the COND model, would suggest the presence of objects of sub-Jupiter mass. The results also suggest that the mass function for the ρ Oph cloud resembles that of the σ Orionis cluster based on a recent study, with both rising steadily toward lower masses. The other main result from our study is the apparent presence of a progressive blueward skew in the distribution of J - H and H - K s colors, such that the blue end of the range becomes increasingly bluer with increasing magnitude. We suggest that this behavior might be understood in terms of the 'ejected stellar embryo' hypothesis, whereby some of the lowest-mass brown dwarfs could escape to locations close to the front edge of the cloud, and thereby be seen with less extinction.

  10. 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)

    Kniazev, A. Y.; Vaisanen, P.; Potter, S. B.; Crawford, S.; Gulbis, A. A. S.; Mužić, K.; Mehner, A.; Boffin, H. M. J.; Melo, C.; Ivanov, V. D.; Girard, J.; Mawet, D.; Schmidtobreick, L.; Kurtev, R.; Borissova, J.; Huelamo, N.; Minniti, D.; Ishibashi, K.; Beletsky, Y.; Buckley, D. A. H.

    2013-01-01

    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 (V rad ∼ 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 JHK S 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.

  11. BINARIES DISCOVERED BY THE MUCHFUSS PROJECT: SDSS J08205+0008-AN ECLIPSING SUBDWARF B BINARY WITH A BROWN DWARF COMPANION

    International Nuclear Information System (INIS)

    Geier, S.; Schaffenroth, V.; Drechsel, H.; Heber, U.; Kupfer, T.; Tillich, A.; Oestensen, R. H.; Smolders, K.; Degroote, P.; Maxted, P. F. L.; Barlow, B. N.; Gaensicke, B. T.; Marsh, T. R.; Napiwotzki, R.

    2011-01-01

    Hot subdwarf B stars (sdBs) are extreme horizontal branch stars believed to originate from close binary evolution. Indeed about half of the known sdB stars are found in close binaries with periods ranging from a few hours to a few days. The enormous mass loss required to remove the hydrogen envelope of the red-giant progenitor almost entirely can be explained by common envelope ejection. A rare subclass of these binaries are the eclipsing HW Vir binaries where the sdB is orbited by a dwarf M star. Here, we report the discovery of an HW Vir system in the course of the MUCHFUSS project. A most likely substellar object (≅0.068 M sun ) was found to orbit the hot subdwarf J08205+0008 with a period of 0.096 days. Since the eclipses are total, the system parameters are very well constrained. J08205+0008 has the lowest unambiguously measured companion mass yet found in a subdwarf B binary. This implies that the most likely substellar companion has not only survived the engulfment by the red-giant envelope, but also triggered its ejection and enabled the sdB star to form. The system provides evidence that brown dwarfs may indeed be able to significantly affect late stellar evolution.

  12. Estimation of genetic variability and selection response for clutch length in dwarf brown-egg layers carrying or not the naked neck gene

    Directory of Open Access Journals (Sweden)

    Tixier-Boichard Michèle

    2003-03-01

    Full Text Available Abstract In order to investigate the possibility of using the dwarf gene for egg production, two dwarf brown-egg laying lines were selected for 16 generations on average clutch length; one line (L1 was normally feathered and the other (L2 was homozygous for the naked neck gene NA. A control line from the same base population, dwarf and segregating for the NA gene, was maintained during the selection experiment under random mating. The average clutch length was normalized using a Box-Cox transformation. Genetic variability and selection response were estimated either with the mixed model methodology, or with the classical methods for calculating genetic gain, as the deviation from the control line, and the realized heritability, as the ratio of the selection response on cumulative selection differentials. Heritability of average clutch length was estimated to be 0.42 ± 0.02, with a multiple trait animal model, whereas the estimates of the realized heritability were lower, being 0.28 and 0.22 in lines L1 and L2, respectively. REML estimates of heritability were found to decline with generations of selection, suggesting a departure from the infinitesimal model, either because a limited number of genes was involved, or their frequencies were changed. The yearly genetic gains in average clutch length, after normalization, were estimated to be 0.37 ± 0.02 and 0.33 ± 0.04 with the classical methods, 0.46 ± 0.02 and 0.43 ± 0.01 with animal model methodology, for lines L1 and L2 respectively, which represented about 30% of the genetic standard deviation on the transformed scale. Selection response appeared to be faster in line L2, homozygous for the NA gene, but the final cumulated selection response for clutch length was not different between the L1 and L2 lines at generation 16.

  13. The Development of New Atmospheric Models for K and M DwarfStars with Exoplanets

    Science.gov (United States)

    Linsky, Jeffrey L.

    2018-01-01

    The ultraviolet and X-ray emissions of host stars play critical roles in the survival and chemical composition of the atmospheres of their exoplanets. The need to measure and understand this radiative output, in particular for K and M dwarfs, is the main rationale for computing a new generation of stellar models that includes magnetically heated chromospheres and coronae in addition to their photospheres. We describe our method for computing semi-empirical models that includes solutions of the statistical equilibrium equations for 52 atoms and ions and of the non-LTE radiative transfer equations for all important spectral lines. The code is an offspring of the Solar Radiation Physical Modelling system (SRPM) developed by Fontenla et al. (2007--2015) to compute one-dimensional models in hydrostatic equilibrium to fit high-resolution stellar X-ray to IR spectra. Also included are 20 diatomic molecules and their more than 2 million spectral lines. Our-proof-of-concept model is for the M1.5 V star GJ 832 (Fontenla et al. ApJ 830, 154 (2016)). We will fit the line fluxes and profiles of X-ray lines and continua observed by Chandra and XMM-Newton, UV lines observed by the COS and STIS instruments on HST (N V, C IV, Si IV, Si III, Mg II, C II, and O I), optical lines (including H$\\alpha$, Ca II, Na I), and continua. These models will allow us to compute extreme-UV spectra, which are unobservable but required to predict the hydrodynamic mass-loss rate from exoplanet atmospheres, and to predict panchromatic spectra of new exoplanet host stars discovered after the end of the HST mission.This work is supported by grant HST-GO-15038 from the Space Telescope Science Institute to the Univ. of Colorado

  14. VARIABILITY IN HOT CARBON-DOMINATED ATMOSPHERE (HOT DQ) WHITE DWARFS: RAPID ROTATION?

    Energy Technology Data Exchange (ETDEWEB)

    Williams, Kurtis A.; Bierwagen, Michael [Department of Physics and Astrophysics, Texas A and M University-Commerce, P.O. Box 3011, Commerce, TX, 75429 (United States); Montgomery, M. H.; Winget, D. E.; Falcon, Ross E., E-mail: Kurtis.Williams@tamuc.edu [Department of Astronomy, University of Texas, 1 University Station C1400, Austin, TX, 78712 (United States)

    2016-01-20

    Hot white dwarfs (WDs) with carbon-dominated atmospheres (hot DQs) are a cryptic class of WDs. 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 WDs. 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-day photometric variation; we do not observe any short-term variability. Monoperiodicity is rare among pulsating WDs, so we contemplate whether the photometric variability is due to rotation rather than pulsations; similar hypotheses have been raised by other researchers. If the variability is due to rotation, then hot DQ WDs as a class contain many rapid rotators. Given the lack of companions to these stars, the origin of any fast rotation is unclear—both massive progenitor stars and double degenerate merger remnants are possibilities. We end with suggestions of future work that would best clarify the nature of these rare, intriguing objects.

  15. 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.

  16. A CONSTRAINT ON BROWN DWARF FORMATION VIA EJECTION: RADIAL VARIATION OF THE STELLAR AND SUBSTELLAR MASS FUNCTION OF THE YOUNG OPEN CLUSTER IC 2391

    International Nuclear Information System (INIS)

    Boudreault, S.; Bailer-Jones, C. A. L.

    2009-01-01

    We present the stellar and substellar mass function (MF) of the open cluster IC 2391, plus its radial dependence, and use this to put constraints on the formation mechanism of brown dwarfs (BDs). Our multi-band optical and infrared photometric survey with spectroscopic follow-up covers 11 deg 2 , making it the largest survey of this cluster to date. We observe a radial variation in the MF over the range 0.072-0.3 M sun , but no significant variation in the MF below the substellar boundary at the three cluster radius intervals is analyzed. This lack of radial variation for low masses is what we would expect with the ejection scenario for BD formation, although considering that IC 2391 has an age about three times older than its crossing time, we expect that BDs with a velocity greater than the escape velocity have already escaped the cluster. Alternatively, the variation in the MF of the stellar objects could be an indication that they have undergone mass segregation via dynamical evolution. We also observe a significant variation across the cluster in the color of the (background) field star locus in color-magnitude diagrams and conclude that this is due to variable background extinction in the Galactic plane. From our preliminary spectroscopic follow-up, to confirm BD status and cluster membership, we find that all candidates are M dwarfs (in either the field or the cluster), demonstrating the efficiency of our photometric selection method in avoiding contaminants (e.g., red giants). About half of our photometric candidates for which we have spectra are spectroscopically confirmed as cluster members; two are new spectroscopically confirmed BD members of IC 2391.

  17. Transiting exoplanets from the CoRoT space mission . VI. CoRoT-Exo-3b: the first secure inhabitant of the brown-dwarf desert

    Science.gov (United States)

    Deleuil, M.; Deeg, H. J.; Alonso, R.; Bouchy, F.; Rouan, D.; Auvergne, M.; Baglin, A.; Aigrain, S.; Almenara, J. M.; Barbieri, M.; Barge, P.; Bruntt, H.; Bordé, P.; Collier Cameron, A.; Csizmadia, Sz.; de La Reza, R.; Dvorak, R.; Erikson, A.; Fridlund, M.; Gandolfi, D.; Gillon, M.; Guenther, E.; Guillot, T.; Hatzes, A.; Hébrard, G.; Jorda, L.; Lammer, H.; Léger, A.; Llebaria, A.; Loeillet, B.; Mayor, M.; Mazeh, T.; Moutou, C.; Ollivier, M.; Pätzold, M.; Pont, F.; Queloz, D.; Rauer, H.; Schneider, J.; Shporer, A.; Wuchterl, G.; Zucker, S.

    2008-12-01

    Context: The CoRoT space mission routinely provides high-precision photometric measurements of thousands of stars that have been continuously observed for months. Aims: The discovery and characterization of the first very massive transiting planetary companion with a short orbital period is reported. Methods: A series of 34 transits was detected in the CoRoT light curve of an F3V star, observed from May to October 2007 for 152 days. The radius was accurately determined and the mass derived for this new transiting, thanks to the combined analysis of the light curve and complementary ground-based observations: high-precision radial-velocity measurements, on-off photometry, and high signal-to-noise spectroscopic observations. Results: CoRoT-Exo-3b has a radius of 1.01 ± 0.07 R_Jup and transits around its F3-type primary every 4.26 days in a synchronous orbit. Its mass of 21.66 ± 1.0 M_Jup, density of 26.4 ± 5.6 g cm-3, and surface gravity of logg = 4.72 clearly distinguish it from the regular close-in planet population, making it the most intriguing transiting substellar object discovered so far. Conclusions: With the current data, the nature of CoRoT-Exo-3b is ambiguous, as it could either be a low-mass brown-dwarf or a member of a new class of “superplanets”. Its discovery may help constrain the evolution of close-in planets and brown-dwarfs better. Finally, CoRoT-Exo-3b confirms the trend that massive transiting giant planets (M ≥ 4 M_Jup) are found preferentially around more massive stars than the Sun. The CoRoT space mission, launched on December 27th 2006, has been developed and is operating by CNES, with the contribution of Austria, Belgium, Brasil, ESA, Germany and Spain. The first CoRoT data will be available to the public in February 2009 from the CoRoT archive: http://idoc-corot.ias.u-psud.fr/ Table of the COROT photometry is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb

  18. A STUDY OF THE DIVERSE T DWARF POPULATION REVEALED BY WISE

    International Nuclear Information System (INIS)

    Mace, Gregory N.; Wright, Edward L.; McLean, Ian S.; Davy Kirkpatrick, J.; Gelino, Christopher R.; Griffith, Roger L.; Mix, Katholeen; Beichman, Charles A.; Lowrance, Patrick J.; Cushing, Michael C.; Skrutskie, Michael F.; Marsh, Kenneth A.; Eisenhardt, Peter R.; Thompson, Maggie A.; Bailey, Vanessa; Hinz, Philip M.; Knox, Russell P.; Bloom, Joshua S.; Burgasser, Adam J.; Fortney, Jonathan J.

    2013-01-01

    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. Effect of Grinding at Modified Atmosphere or Vacuum on Browning, Antioxidant Capacities, and Oxidative Enzyme Activities of Apple.

    Science.gov (United States)

    Kim, Ah-Na; Lee, Kyo-Yeon; Kim, Hyun-Jin; Chun, Jiyeon; Kerr, William L; Choi, Sung-Gil

    2018-01-01

    This study evaluated the effects of grinding at atmospheric pressure (control), under vacuum (∼2.67 kPa), or with modified atmosphere (N 2 and CO 2 ) on the browning, antioxidant activity, phenolics, and oxidative enzyme activity of apples as a function of time. The control group was affected most, showing distinct browning and losing most of the antioxidant activity and concentrations of the main phenolic compounds. The modified atmosphere groups retained color, antioxidant activity, and phenolic compounds better than the control group. Least changes were obtained with vacuum grinding, particularly in terms of preventing enzymatic browning and oxidation of antioxidants apples. At 12 h after grinding, vacuum-ground apples retained total phenolic contents 5.32, 1.54, and 1.49 times higher than control, nitrogen gas, and carbon dioxide gas-ground samples, respectively. The oxidative enzyme activity, including that of polyphenol oxidase and peroxidase, decreased in the control and modified atmosphere group, but they were maintained in the samples ground under the vacuum. In this study, we found that grinding with modified atmosphere or vacuum conditions could effectively prevent browning as well as loss of phenolic compounds and antioxidant activity of ground apples. These results can help scientists and engineers build better grinding systems for retaining nutrient and quality factors of ground apples. In addition, these results may be useful to other fruit and vegetable industries that wish to retain fresh-like quality and nutritional value during grinding and storage. © 2017 Institute of Food Technologists®.

  20. Brown Carbon and Black Carbon in the Smoky Atmosphere during Boreal Forest Fires

    Science.gov (United States)

    Gorchakov, G. I.; Karpov, A. V.; Pankratova, N. V.; Semoutnikova, E. G.; Vasiliev, A. V.; Gorchakova, I. A.

    2017-12-01

    We have investigated the variability of smoke aerosol absorbing ability with variations in the content of brown carbon (BrC) and black carbon (BC). Using monitoring data on radiative characteristics of smoke aerosol at AERONET stations and the spatial distribution of aerosol optical depth (AOD) obtained by the MODIS spectrometer ( Terra satellite), we have detected large-scale smokes during boreal forest fires in Russia and Canada (1995-2012). The spatial distribution (50°-70° N, 95°-125° W) and temporal variability (at AERONET station Fort McMurray) of AOD during the smoking of a part of Canada in July 2012 have been analyzed. AOD probability distributions for July 14-18, 2012, and an estimate of aerosol radiative forcing of smoke aerosol at the upper boundary of the atmosphere have been obtained. We have proposed a technique for the diagnostics of BrC and BC in smoke aerosol particles from the spectral dependence of the imaginary part of the refractive index. At a wavelength of 440 nm, the contributions of BrC and BC to the smokeaerosol absorbing abitity can be comparable in magnitude. In many cases, the absorption spectra of smoke aerosol can be adequately approximated by either power or exponential functions. The presence of BrC in smoke-aerosol particles highly extends the variety of observed absorption spectra in a smoky atmosphere and spectral dependences of single scattering albedo. In the spectral range of 440-1020 nm, the radiative characteristics of smoke aerosol are largely contributed by its fine mode.

  1. Further Evidence of a Brown Dwarf Orbiting the Post-Common Envelope Eclipsing Binary V470 Cam (HS 0705+6700

    Directory of Open Access Journals (Sweden)

    Bogensberger David

    2017-12-01

    Full Text Available Several post-common envelope binaries have slightly increasing, decreasing or oscillating orbital periods. One of several possible explanations is light travel-time changes, caused by the binary centre-of-mass being perturbed by the gravitational pull of a third body. Further studies are necessary because it is not clear how a third body could have survived subdwarf progenitor mass-loss at the tip of the Red Giant Branch, or formed subsequently. Thirty-nine primary eclipse times for V470 Cam were secured with the Philip Wetton Telescope during the period 2016 November 25th to 2017 January 27th. Available eclipse timings suggest a brown dwarf tertiary having a mass of at least 0.0236(40 M⊙, an elliptical orbit with an eccentricity of 0.376(98 and an orbital period of 11.77(67 years about the binary centreof- mass. The mass and orbit suggest a hybrid formation, in which some ejected material from the subdwarf progenitor was accreted on to a precursor tertiary component, although additional observations would be needed to confirm this interpretation and investigate other possible origins for the binary orbital period change.

  2. EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?

    International Nuclear Information System (INIS)

    Baraffe, I.; Chabrier, G.; Gallardo, J.

    2009-01-01

    We present evolutionary models for young low-mass stars and brown dwarfs taking into account episodic phases of accretion at early stages of the evolution, a scenario supported by recent large surveys of embedded protostars. An evolution including short episodes of vigorous accretion followed by longer quiescent phases can explain the observed luminosity spread in H-R diagrams of star-forming regions at ages of a few Myr, for objects ranging from a few Jupiter masses to a few tenths of a solar mass. The gravitational contraction of these accreting objects strongly departs from the standard Hayashi track at constant T eff . The best agreement with the observed luminosity scatter is obtained if most of the accretion shock energy is radiated away. The obtained luminosity spread at 1 Myr in the H-R diagram is equivalent to what can be misinterpreted as an ∼10 Myr age spread for non-accreting objects. We also predict a significant spread in radius at a given T eff , as suggested by recent observations. These calculations bear important consequences for our understanding of star formation and early stages of evolution and on the determination of the initial mass function for young (≤ a few Myr) clusters. Our results also show that the concept of a stellar birthline for low-mass objects has no valid support.

  3. NEW EXTINCTION AND MASS ESTIMATES FROM OPTICAL PHOTOMETRY OF THE VERY LOW MASS BROWN DWARF COMPANION CT CHAMAELEONTIS B WITH THE MAGELLAN AO SYSTEM

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Ya-Lin; Close, Laird M.; Males, Jared R.; Morzinski, Katie M.; Follette, Katherine B.; Bailey, Vanessa; Rodigas, Timothy J.; Hinz, Philip [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Barman, Travis S. [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States); Puglisi, Alfio; Xompero, Marco; Briguglio, Runa, E-mail: yalinwu@email.arizona.edu [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy)

    2015-03-01

    We used the Magellan adaptive optics 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 Y{sub S}. With our new photometry and T {sub eff} ∼ 2500 K derived from the shape of its K-band spectrum, we find that CT Cha B has A{sub V} = 3.4 ± 1.1 mag, and a mass of 14-24 M{sub J} according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates that the companion has significant Hα emission and a mass accretion rate ∼6 × 10{sup –10} M {sub ☉} yr{sup –1}, 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 adaptive optics photometry (r', i', z', Y{sub S}) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions.

  4. Why the dark matter of galaxies is clumps of micro­ brown­dwarfs and not Cold Dark Matter

    Science.gov (United States)

    Gibson, Carl H.

    Observations of quasar microlensing by Schild 1996 show the baryonic dark matter BDM of galaxies is micro-brown-dwarfs, primordial hydrogen-helium planets formed at the plasma to gas transition 10^13 seconds, in trillion-planet clumps termed proto-globular-star-clusters PGCs. Large photon-viscosity {nu} of the plasma permits supercluster-mass gravitational fragmentation at 10^12 seconds when the horizon scale L_H = ct is matched by the Schwarz viscous scale L_SV of Gibson 1996. Voids begin expansion at sonic speeds c/ 3^1/2, where c is light speed and t is time, explaining 10^25 meter size regions observed to be devoid of all matter, either BDM or non-baryonic NBDM. Most of the NBDM is weakly-collisional, strongly-diffusive, neutrino-like particles. If cold NBDM (CDM) is assumed, it must soon become warm and diffuse because it is weakly-collisional. It cannot clump and its clumps cannot clump. CDM is ruled out with 99% confidence by local-group satellite observations of Kroupa et al. 2010. The satellites are clusters of PGCs. PGCs are recaptured by the Galaxy on an accretion disk as they freeze and diffuse from its core to form its BDM halo. Stars form by viscous mergers of primordial gas planets within PGCs. Stars die by overeating mBDs, making the first chemicals, oceans and life at 2-8 Myr.

  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)

    Becker, Andreas; Lorenzen, Winfried; Schöttler, Manuel; Redmer, Ronald; Fortney, Jonathan J.; Nettelmann, Nadine

    2014-01-01

    We present new equations of state (EOSs) for hydrogen and helium covering a wide range of temperatures from 60 K to 10 7 K and densities from 10 –10 g cm –3 to 10 3 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. Outer atmospheres of cool stars. XII - A survey of IUE ultraviolet emission line spectra of cool dwarf stars

    Science.gov (United States)

    Linsky, J. L.; Bornmann, P. L.; Carpenter, K. G.; Hege, E. K.; Wing, R. F.; Giampapa, M. S.; Worden, S. P.

    1982-01-01

    Quantitative information is obtained on the chromospheres and transition regions of M dwarf stars, in order to determine how the outer atmospheres of dMe stars differ from dM stars and how they compare with the outer atmospheres of quiet and active G and K type dwarfs. IUE spectra of six dMe and four dM stars, together with ground-based photometry and spectroscopy of the Balmer and Ca II H and K lines, show no evidence of flares. It is concluded, regarding the quiescent behavior of these stars, that emission-line spectra resemble that of the sun and contain emission lines formed in regions with 4000-20,000 K temperatures that are presumably analogous to the solar chromosphere, as well as regions with temperatures of 20,000-200,000 K that are presumably analogous to the solar transition region. Emission-line surface fluxes are proportional to the emission measure over the range of temperatures at which the lines are formed.

  7. Non-LTE line-blanketed model atmospheres of hot stars. 2: Hot, metal-rich white dwarfs

    Science.gov (United States)

    Lanz, T.; Hubeny, I.

    1995-01-01

    We present several model atmospheres for a typical hot metal-rich DA white dwarf, T(sub eff) = 60,000 K, log g = 7.5. We consider pure hydrogen models, as well as models with various abundances of two typical 'trace' elements-carbon and iron. We calculte a number of Local Thermodynamic Equilibrium (LTE) and non-LTE models, taking into account the effect of numerous lines of these elements on the atmospheric structure. We demostrate that while the non-LTE effects are notvery significant for pure hydrogen models, except for describing correctly the central emission in H-alpha they are essential for predicting correctly the ionization balance of metals, such as carbon and iron. Previously reported discrepancies in LTE abundances determinations using C III and C IV lines are easily explained by non-LTE effects. We show that if the iron abundance is larger than 10(exp -5), the iron line opacity has to be considered not only for the spectrum synthesis, but also in the model construction itself. For such metal abundances, non-LTE metal line-blanketed models are needed for detailed abundance studies of hot, metal-rich white dwarfs. We also discuss the predicted Extreme Ultraviolet (EUV) spectrum and show that it is very sensitive to metal abundances, as well as to non-LTE effects.

  8. High-Contrast 3.8 Micron Imaging of the Brown Dwarf/Planet-Mass Companion to GJ 758

    Science.gov (United States)

    Currie, Thayne M.; Bailey, Vanessa; Fabrycky, Daniel; Murray-Clay, Ruth; Rodigas, Timothy; Hinz, Phil

    2011-01-01

    We present L' band (3.8 Micron) MMT/Clio high-contrast imaging data for the nearby star GJ 758, which was recently reported by Thalmann et al. (2009) to have one - possibly two - faint comoving companions (GJ 7588 and "C", respectively). GJ 758B is detected in two distinct datasets. Additionally, we report a \\textit{possible} detection of the object identified by Thalmann et al as "GJ 758C" in our more sensitive dataset, 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 7588 has a H-L' color redder than nearly all known L-T8 dwarfs. 8ased on comparisons with the COND evolutionary models, GJ 7588 has Te approx. 560 K (+150 K, -90 K) and a mass ranging from approx.10-20 Mj if it is approx.1 Gyr old to approx. 25-40 Mj if it is 8.7 Gyr old. GJ 7588 is likely in a highly eccentric orbit, e approx. 0.73 (+0.12,-0.21), with a semimajor axis of approx. 44 AU (+32 AU, -14 AU). Though GJ 7588 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. 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.

  10. 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.

  11. 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 - others:GA AV ČR(CZ) IAA301630901 Program:IA 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

  12. VizieR Online Data Catalog: Binary white dwarfs atmospheric parameters (Gianninas+, 2014)

    Science.gov (United States)

    Gianninas, A.; Dufour, P.; Kilic, M.; Brown, W. R.; Bergeron, P.; Hermes, J. J.

    2017-04-01

    The sample that we analyze includes a total of 61 ELM WD binaries from the ELM Survey (Brown et al. 2013, J/ApJ/769/66). The bulk of this sample is comprised of the 58 ELM WDs listed in Table 3 of Brown et al. (2013, J/ApJ/769/66), but also includes three additional ELM WDs that have been published in separate papers since then. The spectra of these 61 ELM WDs were obtained using five distinct setups on two different telescopes. A total of 57 targets were observed with the 6.5m MMT telescope with the Blue Channel spectrograph (Schmidt et al. 1989PASP..101..713S). The four remaining targets were observed using the Fred Lawrence Whipple Observatory's (FLWO) 1.5m Tilinghast telescope equipped with the FAST spectrograph (Fabricant et al. 1998PASP..110...79F) and the 600 line/mm grating. (2 data files).

  13. Transfer of gaseous iodine from atmosphere to rough rice, brown rice and polished rice

    International Nuclear Information System (INIS)

    Sumiya, Misako; Uchida, Shigeo; Muramatsu, Yasuyuki; Ohmomo, Yoichiro; Yamaguchi, Shuho; Obata, Hitoshi.

    1987-01-01

    Experiments were carried out in order to obtain information required for establishing transfer coefficients of gaseous iodine (I 2 ) to rough rice, brown rice and polished rice. The gaseous iodine deposited on young rice plants before the heading period was scarcely found in the rough rice harvested at the full ripe stage. The biological half life of iodine in hull, however, was much slower than that in leaves of 14 days. The translocation of iodine from leaves and stalks to rough rice was not clearly recognized. Therefore, it was deduced that iodine found in brown rice mainly should originate from that deposited on the hull. The distribution ratios of iodine between rough rice and brown rice, and between brown rice and polished rice were 100:4 and 100:30 on 100 grains basis, respectively. If average normalized deposition velocity (V d(m) ) or derived deposition velocity (V s ) are given, the transfer coefficients of gaseous iodine to rough rice (TF r ), brown rice (TF b ) and polished rice (TF p ) could be calculated. (author)

  14. Theoretical oscillation frequencies for solar-type dwarfs from stellar models with <3D >-atmospheres

    DEFF Research Database (Denmark)

    Jørgensen, Andreas Christ Sølvsten; Weiss, Achim; Mosumgaard, Jakob Rorsted

    2017-01-01

    We present a new method for replacing the outermost layers of stellar models with interpolated atmospheres based on results from 3D simulations, in order to correct for structural inadequacies of these layers. This replacement is known as patching. Tests, based on 3D atmospheres from three......, and the mismatch in T-eff and log g between the un-patched model and patched 3D atmosphere. We find the eigen frequencies to be unaltered by the patching depth deep within the adiabatic region, while changing the patching quantity or the employed atmosphere grid leads to frequency shifts that may exceed 1 mu Hz....... Likewise, the eigen frequencies are sensitive to mismatches in T-eff or log g. A thorough investigation of the accuracy of a new scheme, for interpolating mean 3D stratifications within the atmosphere grids, is furthermore performed. Throughout large parts of the atmosphere grids, our interpolation scheme...

  15. A SEARCH FOR L/T TRANSITION DWARFS WITH PAN-STARRS1 AND WISE. II. L/T TRANSITION ATMOSPHERES AND YOUNG DISCOVERIES

    International Nuclear Information System (INIS)

    Best, William M. J.; Liu, Michael C.; Magnier, Eugene A.; Aller, Kimberly M.; Chambers, K. C.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.; Deacon, Niall R.; Redstone, Joshua; Burgett, W. S.; Draper, P.; Metcalfe, N.

    2015-01-01

    The evolution of brown dwarfs from L to T spectral types is one of the least understood aspects of the ultracool population, partly for lack of a large, well-defined, and well-characterized sample in the L/T transition. To improve the existing census, we have searched ≈28,000 deg 2 using the Pan-STARRS1 and Wide-field Infrared Survey Explorer surveys for L/T transition dwarfs within 25 pc. We present 130 ultracool dwarf discoveries with estimated distances ≈9–130 pc, including 21 that were independently discovered by other authors and 3 that were previously identified as photometric candidates. Seventy-nine of our objects have near-IR spectral types of L6–T4.5, the most L/T transition dwarfs from any search to date, and we have increased the census of L9–T1.5 objects within 25 pc by over 50%. The color distribution of our discoveries provides further evidence for the “L/T gap,” a deficit of objects with (J − K) MKO  ≈ 0.0–0.5 mag in the L/T transition, and thus reinforces the idea that the transition from cloudy to clear photospheres occurs rapidly. Among our discoveries are 31 candidate binaries based on their low-resolution spectral features. Two of these candidates are common proper motion companions to nearby main sequence stars; if confirmed as binaries, these would be rare benchmark systems with the potential to stringently test ultracool evolutionary models. Our search also serendipitously identified 23 late-M and L dwarfs with spectroscopic signs of low gravity implying youth, including 10 with vl-g or int-g gravity classifications and another 13 with indications of low gravity whose spectral types or modest spectral signal-to-noise ratio do not allow us to assign formal classifications. Finally, we identify 10 candidate members of nearby young moving groups (YMG) with spectral types L7–T4.5, including three showing spectroscopic signs of low gravity. If confirmed, any of these would be among the coolest known YMG members and would

  16. THE DYNAMICAL EVOLUTION OF LOW-MASS HYDROGEN-BURNING STARS, BROWN DWARFS, AND PLANETARY-MASS OBJECTS FORMED THROUGH DISK FRAGMENTATION

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yun; Kouwenhoven, M. B. N. [Department of Astronomy, School of Physics, Peking University, Yiheyuan Lu 5, Haidian Qu, Beijing 100871 (China); Stamatellos, D. [Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE (United Kingdom); Goodwin, S. P., E-mail: yunli@pku.edu.cn [Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

    2015-06-01

    Theory and simulations suggest that it is possible to form low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) via disk fragmentation. As disk fragmentation results in the formation of several bodies at comparable distances to the host star, their orbits are generally unstable. Here, we study the dynamical evolution of these objects. We set up the initial conditions based on the outcomes of the smoothed-particle hydrodynamics simulations of Stamatellos and Whitworth, and for comparison we also study the evolution of systems resulting from lower-mass fragmenting disks. We refer to these two sets of simulations as set 1 and set 2, respectively. At 10 Myr, approximately half of the host stars have one companion left, and approximately 22% (set 1) to 9.8% (set 2) of the host stars are single. Systems with multiple secondaries in relatively stable configurations are common (about 30% and 44%, respectively). The majority of the companions are ejected within 1 Myr with velocities mostly below 5 km s{sup −1}, with some runaway escapers with velocities over 30 km s{sup −1}. Roughly 6% (set 1) and 2% (set 2) of the companions pair up into very low-mass binary systems, resulting in respective binary fractions of 3.2% and 1.2%. The majority of these pairs escape as very low-mass binaries, while others remain bound to the host star in hierarchical configurations (often with retrograde inner orbits). Physical collisions with the host star (0.43 and 0.18 events per host star for set 1 and set 2, respectively) and between companions (0.08 and 0.04 events per host star for set 1 and set 2, respectively) are relatively common and their frequency increases with increasing disk mass. Our study predicts observable properties of very low-mass binaries, low-mass hierarchical systems, the BD desert, and free-floating BDs and PMOs in and near young stellar groupings, which can be used to distinguish between different formation scenarios of very low

  17. FIRE SPECTROSCOPY OF FIVE LATE-TYPE T DWARFS DISCOVERED WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER

    International Nuclear Information System (INIS)

    Burgasser, Adam J.; Cushing, Michael C.; Mainzer, A.; Bauer, James M.; Kirkpatrick, J. Davy; Gelino, Christopher R.; Griffith, Roger L.; Marsh, Kenneth A.; Looper, Dagny L.; Tinney, Christopher; Simcoe, Robert A.; Bochanski, John J.; Skrutskie, Michael F.; Thompson, Maggie A.; Wright, Edward L.

    2011-01-01

    We present the discovery of five late-type T dwarfs identified with the Wide-field Infrared Survey Explorer (WISE). Low-resolution near-infrared spectroscopy obtained with the Magellan Folded-port InfraRed Echellette reveal strong H 2 O and CH 4 absorption in all five sources, and spectral indices and comparison to spectral templates indicate classifications ranging from T5.5 to T8.5:. The spectrum of the latest-type source, WISE J1812+2721, is an excellent match to that of the T8.5 companion brown dwarf Wolf 940B. WISE-based spectrophotometric distance estimates place these T dwarfs at 12-13 pc from the Sun, assuming they are single. Preliminary fits of the spectral data to the atmosphere models of Saumon and Marley indicate effective temperatures ranging from 600 K to 930 K, both cloudy and cloud-free atmospheres, and a broad range of ages and masses. In particular, two sources show evidence of both low surface gravity and cloudy atmospheres, tentatively supporting a trend noted in other young brown dwarfs and exoplanets. In contrast, the high proper motion T dwarf WISE J2018-7423 exhibits a suppressed K-band peak and blue spectrophotometric J - K colors indicative of an old, massive brown dwarf; however, it lacks the broadened Y-band peak seen in metal-poor counterparts. These results illustrate the broad diversity of low-temperature brown dwarfs that will be uncovered with WISE.

  18. 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

  19. Dwarf Mice and Aging.

    Science.gov (United States)

    Masternak, Michal M; Darcy, Justin; Victoria, Berta; Bartke, Andrzej

    2018-01-01

    Dwarf mice have been studied for many decades, however, the focus of these studies shifted in 1996 when it was shown by Brown-Borg and her coworkers that Ames dwarf (Prop1 df ) mice are exceptionally long-lived. Since then, Snell dwarf (Pit1 dw ) and growth hormone receptor knockout (GHR-KO, a.k.a. Laron dwarf) mice were also shown to be exceptionally long-lived, presumably due to their growth hormone (GH)-deficiency or -resistance, respectively. What is of equal importance in these dwarf mice is their extended health span, that is, these animals have a longer period of life lived free of frailty and age-related diseases. This review article focuses on recent studies conducted in these dwarf mice, which concerned brown and white adipose tissue biology, microRNA (miRNA) profiling, as well as early-life dietary and hormonal interventions. Results of these studies identify novel mechanisms linking reduced GH action with extensions of both life span and health span. Copyright © 2017. Published by Elsevier Inc.

  20. 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.

  1. Comparative study of the banana pulp browning process of 'Giant Dwarf' and FHIA-23 during fruit ripening based on image analysis and the polyphenol oxidase and peroxidase biochemical properties.

    Science.gov (United States)

    Escalante-Minakata, Pilar; Ibarra-Junquera, Vrani; Ornelas-Paz, José de Jesús; García-Ibáñez, Victoria; Virgen-Ortíz, José J; González-Potes, Apolinar; Pérez-Martínez, Jaime D; Orozco-Santos, Mario

    2018-01-01

    This work presents a novel method to associate the polyphenol oxidase (PPO) and the peroxidase (POD) activities with the ripening-mediated color changes in banana peel and pulp by computational image analysis. The method was used to follow up the de-greening of peel and browning of homogenized pulp from 'Giant Dwarf' (GD: Musa AAA, subgroup Cavendish) and FHIA-23 (tetraploid hybrid, AAAA) banana cultivars. In both cultivars, the color changes of peel during the ripening process clearly showed four stages, which were used to group the fruit into ripening stages. The PPO and POD were extracted from pulp of fruit at these ripening stages, precipitated, and partially purified by gel filtration chromatography. Moreover, the pulp browning was digitally monitored after homogenization for a span time of up to 120 min. The browning level was higher for GD than FHIA-23 tissues. This fact correlated with an 11.7-fold higher PPO activity in the GD cultivar, as compared with that of FHIA-23. POD activity was 8.1 times higher for GD as compared that that of FHIA-23.

  2. 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.

  3. TWO EXTRAORDINARY SUBSTELLAR BINARIES AT THE T/Y TRANSITION AND THE Y-BAND FLUXES OF THE COOLEST BROWN DWARFS {sup ,}

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Michael C.; Bowler, Brendan P.; Best, William M. J. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Dupuy, Trent J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Leggett, S. K. [Gemini Observatory, 670 North A' ohoku Place, Hilo, HI 96720 (United States)

    2012-10-10

    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 ( Almost-Equal-To 0.''8, 8-15 AU), large near-IR flux ratios ( Almost-Equal-To 2-3 mag), and small mass ratios ( Almost-Equal-To 0.5) compared to previously known field ultracool binaries. 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 Almost-Equal-To 400 K and being planetary-mass binaries if their ages are {approx}<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 the color drop arises from a change in temperature, not surface gravity or metallicity variations among the field population. Thus, the T/Y transition established by near-IR spectra coincides with a significant change in the Almost-Equal-To 1 {mu}m fluxes of ultracool photospheres. One explanation is the depletion of potassium, whose broad absorption wings dominate the far-red optical spectra of T dwarfs. This large color change suggests that far-red data may be valuable for classifying objects of {approx}<500 K.

  4. A PATCHY CLOUD MODEL FOR THE L TO T DWARF TRANSITION

    International Nuclear Information System (INIS)

    Marley, Mark S.; Saumon, Didier; Goldblatt, Colin

    2010-01-01

    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.

  5. Effect of modified atmosphere packaging on chilling-induced peel browning in banana

    NARCIS (Netherlands)

    Nguyen, T.B.T.; Ketsa, S.; Doorn, van W.G.

    2004-01-01

    Sucrier bananas (Musa AA Group; cultivar locally known as Kluai Khai) were stored at 10degreesC, which results in chilling injury (CI). Fruit was held in packages with and without a modified atmosphere (MA). Oxygen levels in the MA packages were about 12% while CO2 concentrations were about 4%. MA

  6. A Physical Model-based Correction for Charge Traps in the Hubble Space Telescope ’s Wide Field Camera 3 Near-IR Detector and Its Applications to Transiting Exoplanets and Brown Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yifan; Apai, Dániel; Schneider, Glenn [Department of Astronomy/Steward Observatory, The University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Lew, Ben W. P., E-mail: yzhou@as.arizona.edu [Department of Planetary Science/Lunar and Planetary Laboratory, The University of Arizona, 1640 E. University Boulevard, Tucson, AZ 85718 (United States)

    2017-06-01

    The Hubble Space Telescope Wide Field Camera 3 (WFC3) near-IR channel is extensively used in time-resolved observations, especially for transiting exoplanet spectroscopy as well as brown dwarf and directly imaged exoplanet rotational phase mapping. The ramp effect is the dominant source of systematics in the WFC3 for time-resolved observations, which limits its photometric precision. Current mitigation strategies are based on empirical fits and require additional orbits to help the telescope reach a thermal equilibrium . We show that the ramp-effect profiles can be explained and corrected with high fidelity using charge trapping theories. We also present a model for this process that can be used to predict and to correct charge trap systematics. Our model is based on a very small number of parameters that are intrinsic to the detector. We find that these parameters are very stable between the different data sets, and we provide best-fit values. Our model is tested with more than 120 orbits (∼40 visits) of WFC3 observations and is proved to be able to provide near photon noise limited corrections for observations made with both staring and scanning modes of transiting exoplanets as well as for starting-mode observations of brown dwarfs. After our model correction, the light curve of the first orbit in each visit has the same photometric precision as subsequent orbits, so data from the first orbit no longer need to be discarded. Near-IR arrays with the same physical characteristics (e.g., JWST/NIRCam ) may also benefit from the extension of this model if similar systematic profiles are observed.

  7. Effect of Solar Radiation on the Optical Properties and Molecular Composition of Laboratory Proxies of Atmospheric Brown Carbon

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hyun Ji; Aiona, Paige K.; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey

    2014-09-02

    Sources, optical properties, and chemical composition of atmospheric brown carbon (BrC) aerosol are uncertain, making it challenging to estimate its contribution to radiative forcing. Furthermore, optical properties of BrC may change significantly during its atmospheric aging. We examined the effect of solar photolysis on the molecular composition, mass absorption coefficient, and fluorescence of secondary organic aerosol prepared by high-NOx photooxidation of naphthalene (NAP SOA). The aqueous solutions of NAP SOA was observed to photobleach with an effective half-time of ~15 hours (with sun in its zenith) for the loss of the near-UV (300 -400 nm) absorbance. The molecular composition of NAP SOA was significantly modified by photolysis, with the average SOA formula changing from C14.1H14.5O5.1N0.08 to C11.8H14.9O4.5N0.02 after 4 hours of irradiation. The average O/C ratio did not change significantly, however, suggesting that it is not a good metric for assessing the extent of photolysis-driven aging in NAP SOA (and in BrC in general). In contrast to NAP SOA, the photolysis of BrC material produced by aqueous reaction of limonene+O3 SOA (LIM/O3 SOA) with ammonium sulfate was much faster, but it did not result in a significant change in the molecular level composition. The characteristic absorbance of the aged LIM/O3 SOA in the 450-600 nm range decayed with an effective half-time of <0.5 hour. This result emphasizes the highly variable and dynamic nature of different types of atmospheric BrC.

  8. SpeX Spectroscopy of Unresolved Very Low-Mass Binaries. I. Identification of Seventeen Candidate Binaries Straddling the L Dwarf/T Dwarf Transition

    OpenAIRE

    Burgasser, Adam J.; Cruz, Kelle L.; Cushing, Michael C.; Gelino, Christopher R.; Looper, Dagny L.; Faherty, Jacqueline K.; Kirkpatrick, J. Davy; Reid, I. Neill

    2009-01-01

    We report the identification of 17 candidate brown dwarf binaries whose components straddle the L dwarf/T dwarf transition. These sources were culled from a large near-infrared spectral sample of L and T dwarfs observed with the Infrared Telescope Facility SpeX spectrograph. Candidates were selected on the basis of spectral ratios which segregate known (resolved) L dwarf/T dwarf pairs from presumably single sources. Composite templates, constructed by combining 13581 pairs of absolute flux-ca...

  9. Near-infrared light absorption by brown carbon in the ambient atmosphere

    Science.gov (United States)

    Chung, C.; Hoffer, A.; Beres, N. D.; Moosmüller, H.; Liu, C.; Green, M.; Kim, S. W.; Engelbrecht, J. P.; Gelencser, A.

    2017-12-01

    Organic aerosols have been assumed to have little-to-no absorption in the red and near-infrared spectral regions of solar radiation, even though a class of organic aerosols were shown to absorb significantly in these spectral regions. Here, we show that ambient atmospheric data from commonly-used 7-wavelength aethalometers contain evidence of abundant near-infrared light absorption by organic aerosol. This evidence comes from the absorption Ångström exponent over 880 950 nm, which often exceeds values explainable by fresh or coated black carbon, or mineral dust. This evidence is not due to an artifact from the instrument random errors or biases, either. The best explanation for these large 880/950 nm absorption Ångström exponent values in the aethalometer data is near-infrared light absorption by tar balls. Tar balls are among common particles from forest fire.

  10. Stark Broadening and White Dwarfs

    Directory of Open Access Journals (Sweden)

    Dimitrijević Milan S.

    2011-12-01

    Full Text Available White dwarf and pre-white dwarfs are the best types of stars for the application of Stark broadening research results in astrophysics, since in the atmospheres of these stars physical conditions are very favorable for this line broadening mechanism - in hot hydrogen-deficient white dwarfs and pre-white dwarfs Teff = 75 000–180 000 K and log g = 5.5–8 [cgs]. Even for much cooler DA and DB white dwarfs with the typical effective temperatures 10 000-20 000 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 the parameters needed for analysis and synthesis of white dwarf spectra, as well as for the collective efforts to develop the Virtual Atomic and Molecular Data Center.

  11. Pulsations in white dwarf stars

    OpenAIRE

    Van Grootel, Valérie; Fontaine, Gilles; Brassard, Pierre; Dupret, Marc-Antoine

    2017-01-01

    I will present a description of the six distinct families of pulsating white dwarfs that are currently known. Pulsations are present at various stages of the evolution (from hot, pre-white dwarfs to cool white dwarfs), at various stellar masses, and for various atmospheric compositions. In all of them, a mechanism linked to opacity changes along the evolution drives the oscillations. The existence of these oscillations offers the opportunity to apply asteroseismology for constraining physics ...

  12. 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

  13. 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

    Science.gov (United States)

    Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A. Beate C.; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2012-01-01

    Abstract 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 (NOx) in the planetary atmosphere, hence affecting biomarkers such as ozone (O3). 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 NOx production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O3 formation proceeds via the reaction O+O2+M→O3+M. At high NOx abundances, the O atoms arise mainly from NO2 photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O2). For the flaring case, O3 is mainly destroyed via direct titration, NO+O3→NO2+O2, and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O3, Rayleigh scattering by the main atmospheric gases (O2, N2, and CO2) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O3 survived all the stellar-activity scenarios considered except for the strong case, whereas the biomarker

  14. A Search for Coronal Emission at the Bottom of the Main-Sequence: Stars and Brown Dwarf Candidates with Spectral Types Later than M7 and the Rotation-Activity Relation

    Science.gov (United States)

    Stringfellow, Guy

    2004-01-01

    This program intended to test whether the lowest mass stars at the bottom end of the main sequence and the lower mass brown dwarfs have coronae. If they have coronae, what are the coronal characteristics and what drives them? In the classical dynamo picture, the closed magnetic loop structure is generated near the boundary of the convective envelope and the radiative core. Stars with mass below 0.30 Msun however are fully convective, and the nature of the dynamo responsible for the generation of the coronae in this regime is poorly understood. Previous results from the ROSAT mission (e.g., Fleming et al. 1993, 1995; Schmitt et al. 1995) had confirmed three very important characteristics of M-star coronae: (1) a very high percentage of all M dwarfs have coronae (of order 85% in the local 7 pc sample), (2) those M dwarfs showing high chromospheric activity, such as having the Balmer series in emission or large/numerous optical flaring, indeed exhibit the highest coronal activity, and (3) that the maximum saturation boundary in X-ray luminosity, which amounts to 0.0001-0.001 for Lx/Lbol for the dMe stars, extends down to the current detection limit, through spectral types M7. It was likely that the incompleteness noted for result (1) above was simply a detection limit problem; for more distant sources, the X-ray fainter dM stars will drop below detection thresholds before the more X-ray luminous dMe stars. The latest stars for which direct detection of the corona had been successful were of spectral type dM7 (e.g., VB8, LHS 3003). This program proposed to obtain ROSAT HRI observations for a large number of the coolest known (at that time) stars at the bottom of the main-sequence, which had spectral types of M9 or later. Three stars were approved for observations with ROSAT-HRI totaling 180 ksec. The goal was to obtain X-ray detections or low upper limits for the three approved stars.

  15. Characterizing the Resolved M6 Dwarf Twin LP 318-218AB

    Science.gov (United States)

    Moreno Hilario, Elizabeth; Burgasser, Adam J.; Bardalez Gagliuffi, Daniella; Tamiya, Tomoki

    2017-01-01

    The lowest-mass stars and brown dwarfs are among the most common objects in the Milky Way Galaxy, but theories of their formation and evolution remain poorly constrained. Binary systems are important for understanding the formation of these objects and for making direct orbit and mass measurements to validate evolutionary theories. We report the discovery of LP 318-218, a high proper motion late M dwarf, as a near equal-brightness binary system with a separation of 0.72 arcseconds. Resolved near-infrared spectroscopy confirms the components as nearly identical M6 twins. We using our resolved photometry and spectroscopy to estimate the distance, projected separation and tangential velocity of the system, and confirm common proper motion. We also perform atmosphere model fits to the resolved spectra to assess their physical properties. We place LP 318-218 in context with other widely-separated late M dwarf binaries.

  16. The effect of a strong stellar flare on the atmospheric chemistry of an earth-like planet orbiting an M dwarf.

    Science.gov (United States)

    Segura, Antígona; Walkowicz, Lucianne M; Meadows, Victoria; Kasting, James; Hawley, Suzanne

    2010-09-01

    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 × 10⁸ 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 with a 1-D photochemical model coupled to a 1-D radiative/convective model. Our results indicate that the UV radiation emitted during the flare does not produce a significant change in the ozone column depth of the planet. When the action of protons is included, the ozone depletion reaches a maximum of 94% two years after the flare for a planet with no magnetic field. At the peak of the flare, the calculated UV fluxes that reach the surface, in the wavelength ranges that are damaging for life, exceed those received on Earth during less than 100 s. Therefore, flares may not present a direct hazard for life on the surface of an orbiting habitable planet. Given that AD Leo is one of the most magnetically active M dwarfs known, this conclusion should apply to planets around other M dwarfs with lower levels of chromospheric activity.

  17. Effects of a high O2 dynamic-controlled atmosphere technology on the browning of postharvest white mushroom ( Agaricus bisporus) in relation to energy metabolism.

    Science.gov (United States)

    Li, Ling; Sun, Han; Kitazawa, Hiroaki; Wang, Xiangyou

    2017-07-01

    Browning is one of the main problems in senescence of mushrooms, and it is also one of the most important attributes accounting for the loss of the quality and reduction in market value. In order to study the relationship between the energy metabolism and the browning of white mushroom under high O 2 dynamic-controlled atmosphere (HO-DCA), mushrooms were stored in 100% O 2 (SCA1), 80% O 2  + 20% CO 2 (SCA2), 100% O 2 for three days and then transferred into the treatment of 80% O 2  + 20% CO 2 (HO-DCA) at 2 ± 1 ℃ and air as control. In this study, adenosine triphosphate (ATP) content, energy charge level, sensory evaluation, browning of surface and flesh, cell membrane integrity, exogenous ATP, polyphenol oxidase (PPO) and peroxidase (POD) activity and genes encoding PPO of the white mushroom were investigated. These were all closely related to the browning of products. The optimal storage condition of the HO-DCA treatment could delay the browning of pericarp and flesh tissues of the mushrooms, inhibit PPO activity and reduce the relative expression levels of the three genes encoding PPO. Meanwhile, it maintained moderate POD activity, good sensory properties and cell membrane integrity in a certain extent and thus slowed down the senescence of mushrooms. Results indicated that there was a positive correlation between the ATP content and whitening index ( r = 0.901). In addition, HO-DCA maintained a higher ATP level, prolonged the storage time to 28 days and it might be an ideal strategy for preserving the quality of mushroom during storage.

  18. A low-temperature companion to a white dwarf star

    Science.gov (United States)

    Becklin, E. E.; Zuckerman, B.

    1988-01-01

    An infrared object located about 120 AU from the white dwarf GD165 has been discovered. With the exception of the possible brown dwarf companion to Giclas 29-38 reported last year, the companion to GD165 is the coolest (2100 K) dwarf star ever reported and, according to some theoretical models, it should be a substellar brown dwarf with a mass between 0.06 and 0.08 solar mass. These results, together with newly discovered low-mass stellar companions to white dwarfs, change the investigation of very low-mass stars from the study of a few chance objects to that of a statistical distribution. In particular, it appears that very low-mass stars and perhaps even brown dwarfs could be quite common in the Galaxy.

  19. Pressure shifts and abundance gradients in the atmosphere of the DAZ white dwarf GALEX J193156.8+011745

    Czech Academy of Sciences Publication Activity Database

    Vennes, Stephane; Kawka, Adela; Németh, Péter

    2011-01-01

    Roč. 413, č. 4 (2011), s. 2545-2553 ISSN 0035-8711 R&D Projects: GA AV ČR(CZ) IAA300030908; GA AV ČR IAA301630901; GA ČR GAP209/10/0967; GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars abundances * individual star GALEX J193156.8+011745 * white dwarf s Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.900, year: 2011

  20. 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

    Energy Technology Data Exchange (ETDEWEB)

    De Lee, Nathan; Stassun, Keivan G.; Cargile, Phillip [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Ge, Jian; Fleming, Scott W.; Lee, Brian L.; Chang Liang [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Eastman, Jason; Gaudi, B. Scott [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I.; Allende Prieto, Carlos [Instituto de Astrofisica de Canarias (IAC), E-38205 La Laguna, Tenerife (Spain); Ghezzi, Luan [Observatorio Nacional, Rua Gal. Jose Cristino 77, Rio de Janeiro, RJ 20921-400 (Brazil); Wisniewski, John P. [H L Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St Norman, OK 73019 (United States); Wood-Vasey, W. Michael [Pittsburgh Particle physics, Astrophysics, and Cosmology Center (PITT PACC), Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Agol, Eric; Barnes, Rory [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195 (United States); Bizyaev, Dmitry, E-mail: nathan.delee@vanderbilt.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); and others

    2013-06-15

    We describe the discovery of a likely brown dwarf (BD) companion with a minimum mass of 31.7 {+-} 2.0 M{sub 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{sub Sun }, and thus it is a high-confidence BD companion. It has a moderately long orbital period of 47.8929{sup +0.0063}{sub -0.0062} days with a low eccentricity of 0.1442{sup +0.0078}{sub -0.0073}, and a semi-amplitude of 1644{sup +12}{sub -13} m s{sup -1}. Moderate resolution spectroscopy of the host star has determined the following parameters: T{sub 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{sub *} = 1.11 {+-} 0.11 M{sub Sun} and R{sub *} = 1.06 {+-} 0.23 R{sub Sun} with an age consistent with less than {approx}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.

  1. 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)

    De Lee, Nathan; Stassun, Keivan G.; Cargile, Phillip; Ge, Jian; Fleming, Scott W.; Lee, Brian L.; Chang Liang; Crepp, Justin R.; Eastman, Jason; Gaudi, B. Scott; Esposito, Massimiliano; Femenía, Bruno; González Hernández, Jonay I.; Allende Prieto, Carlos; Ghezzi, Luan; Wisniewski, John P.; Wood-Vasey, W. Michael; Agol, Eric; Barnes, Rory; Bizyaev, Dmitry

    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 ☉ , 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: 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 * = 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.

  2. 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

    Science.gov (United States)

    Ma, Bo; Ge, Jian; Wolszczan, Alex; Muterspaugh, Matthew W.; Lee, Brian; Henry, Gregory W.; Schneider, Donald P.; Martín, Eduardo L.; Niedzielski, Andrzej; Xie, Jiwei; Fleming, Scott W.; Thomas, Neil; Williamson, Michael; Zhu, Zhaohuan; Agol, Eric; Bizyaev, Dmitry; Nicolaci da Costa, Luiz; Jiang, Peng; Martinez Fiorenzano, A. F.; González Hernández, Jonay I.; 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

    2016-11-01

    We report the detections of a giant planet (MARVELS-7b) and a brown dwarf (BD) candidate (MARVELS-7c) around the primary star in the close binary system, HD 87646. To the best of our knowledge, it is the first close binary system with more than one substellar circumprimary companion that has been discovered. 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 the Exoplanet Tracker at the Kitt Peak National Observatory, the High Resolution Spectrograph at the Hobby Eberley telescope, the “Classic” spectrograph at the Automatic Spectroscopic Telescope at the Fairborn Observatory, and MARVELS from SDSS-III confirmed this giant planet discovery and revealed the existence of a long-period BD in this binary. HD 87646 is a close binary with a separation of ˜22 au between the two stars, estimated using the Hipparcos catalog and our newly acquired AO image from PALAO on the 200 inch Hale Telescope at Palomar. The primary star in the binary, HD 87646A, has {T}{eff} = 5770 ± 80 K, log g = 4.1 ± 0.1, and [Fe/H] = -0.17 ± 0.08. The derived minimum masses of the two substellar companions of HD 87646A are 12.4 ± 0.7 {M}{Jup} and 57.0 ± 3.7 {M}{Jup}. The periods are 13.481 ± 0.001 days and 674 ± 4 days and the measured eccentricities are 0.05 ± 0.02 and 0.50 ± 0.02 respectively. Our dynamical simulations show that the system is stable if the binary orbit has a large semimajor axis and a low eccentricity, which can be verified with future astrometry observations.

  3. Infrared photometry of cool white dwarfs

    International Nuclear Information System (INIS)

    Wickramasinghe, D.T.; Allen, D.A.; Bessell, M.S.

    1982-01-01

    The results are presented of a search for the effects of pressure induced H 2 dipole opacity on the infrared JHK magnitudes of cool white dwarfs. LHS 1126 is found to be a very cool (Tsub(e) approximately 4250 K) DC white dwarf with a H rich atmospheric composition dominated by H 2 dipole opacity in the infrared. JHK photometry also favours a H rich atmospheric composition for the DK white dwarfs LP 658-2 and W 489. The surprisingly high proportion of hydrogen rich white dwarfs in the sample appears to suggest that the mechanism which inhibits the accretion of hydrogen in the hotter helium stars becomes less effective at low (Tsub(e) approximately 3 + ion in cool hydrogen rich white dwarf atmospheres is pointed out and it is suggested that the opacity due to this ion may be responsible for the blanketing observed in the U and B magnitudes of some cool white dwarfs. (author)

  4. 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

  5. Thermogravimetric study of the combustion of Tetraselmis suecica microalgae and its blend with a Victorian brown coal in O2/N2 and O2/CO2 atmospheres.

    Science.gov (United States)

    Tahmasebi, Arash; Kassim, Mohd Asyraf; Yu, Jianglong; Bhattacharya, Sankar

    2013-12-01

    The combustion characteristics of microalgae, brown coal and their blends under O2/N2 and O2/CO2 atmospheres were studied using thermogravimetry. In microalgae combustion, two peaks at 265 and 485°C were attributable to combustion of protein and carbohydrate with lipid, respectively. The DTG profile of coal showed one peak with maximum mass loss rate at 360°C. Replacement of N2 by CO2 delayed the combustion of coal and microalgae. The increase in O2 concentration did not show any effect on combustion of protein at the first stage of microalgae combustion. However, between 400 and 600°C, with the increase of O2 partial pressure the mass loss rate of microalgae increased and TG and DTG curves of brown coal combustion shifted to lower temperature zone. The lowest and highest activation energy values were obtained for coal and microalgae, respectively. With increased microalgae/coal ratio in the blends, the activation energy increased due to synergy effect. Copyright © 2013 Elsevier Ltd. All rights reserved.

  6. Atmospheric Brown Clouds in the Himalayas: first two years of continuous observations at the Nepal-Climate Observatory at Pyramid (5079 m)

    Science.gov (United States)

    Bonasoni, P.; Laj, P.; Marinoni, A.; Sprenger, M.; Angelini, F.; Arduini, J.; Bonafè, U.; Calzolari, F.; Colombo, T.; Decesari, S.; di Biagio, C.; di Sarra, A. G.; Evangelisti, F.; Duchi, R.; Facchini, M. C.; Fuzzi, S.; Gobbi, G. P.; Maione, M.; Panday, A.; Roccato, F.; Sellegri, K.; Venzac, H.; Verza, G. P.; Villani, P.; Vuillermoz, E.; Cristofanelli, P.

    2010-02-01

    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 the rain precipitation (seasonal mean 237 mm), while

  7. Biomarker response to galactic cosmic ray-induced NOx and the methane greenhouse effect in the atmosphere of an Earth-like planet orbiting an M dwarf star.

    Science.gov (United States)

    Grenfell, John Lee; Griessmeier, Jean-Mathias; Patzer, Beate; Rauer, Heike; Segura, Antigona; Stadelmann, Anja; Stracke, Barbara; Titz, Ruth; Von Paris, Philip

    2007-02-01

    Planets orbiting in the habitable zone of M dwarf stars are subject to high levels of galactic cosmic rays (GCRs), which produce nitrogen oxides (NOx) in Earth-like atmospheres. We investigate to what extent these NO(Mx) species 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 due to GCR NOx effects by up to 20% compared to an M star run without GCR effects, and can therefore survive at least the effects of GCRs. We have not, however, investigated stellar cosmic rays here. CH4 levels are about 10 times higher on M star worlds than on Earth because of a lowering in hydroxyl (OH) in response to changes in the ultraviolet. The higher levels of CH4 are less than reported in previous studies. This difference arose partly because we used different biogenic input. For example, we employed 23% lower CH4 fluxes compared to those studies. Unlike on Earth, relatively modest changes in these fluxes can lead to larger changes in the concentrations of biomarker and related species on the M star world. We calculate a CH4 greenhouse heating effect of up to 4K. O3 photochemistry in terms of the smog mechanism and the catalytic loss cycles on the M star world differs considerably compared with that of Earth.

  8. VERY-LOW-MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. III. A SHORT-PERIOD BROWN DWARF CANDIDATE AROUND AN ACTIVE G0IV SUBGIANT

    Energy Technology Data Exchange (ETDEWEB)

    Ma Bo; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Wang Ji [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States); Barnes, Rory; Agol, Eric [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Dutra-Ferreira, Leticia; Porto de Mello, G. F. [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 Lctea S/N, E-38200 La Laguna (Spain); Gaudi, B. Scott [Department of Astronomy, 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); Hebb, Leslie; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Wisniewski, John P. [Homer L Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St, Norman, OK 73019 (United States); Bizyaev, Dmitry, E-mail: boma@astro.ufl.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); and others

    2013-01-01

    We present an eccentric, short-period brown dwarf candidate orbiting the active, slightly evolved subgiant star TYC 2087-00255-1, which has effective temperature T{sub eff} = 5903 {+-} 42 K, surface gravity log (g) = 4.07 {+-} 0.16 (cgs), and metallicity [Fe/H] = -0.23 {+-} 0.07. This candidate was discovered using data from the first two years of the Multi-object APO Radial Velocity Exoplanets Large-area Survey, which is part of the third phase of Sloan Digital Sky Survey. From our 38 radial velocity measurements spread over a two-year time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 3.571 {+-} 0.041 km s{sup -1}, period P = 9.0090 {+-} 0.0004 days, and eccentricity e = 0.226 {+-} 0.011. Adopting a mass of 1.16 {+-} 0.11 M{sub Sun} for the subgiant host star, we infer that the companion has a minimum mass of 40.0 {+-} 2.5 M{sub Jup}. Assuming an edge-on orbit, the semimajor axis is 0.090 {+-} 0.003 AU. The host star is photometrically variable at the {approx}1% level with a period of {approx}13.16 {+-} 0.01 days, indicating that the host star spin and companion orbit are not synchronized. Through adaptive optics imaging we also found a point source 643 {+-} 10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 M{sub Sun} if it is physically associated with TYC 2087-00255-1 and has the same age. Future proper motion observation should be able to resolve if this tertiary object is physically associated with TYC 2087-00255-1 and make TYC 2087-00255-1 a triple body system. Core Ca II H and K line emission indicate that the host is chromospherically active, at a level that is consistent with the inferred spin period and measured v{sub rot}sin i, but unusual for a subgiant of this T{sub eff}. This activity could be explained by ongoing tidal spin-up of the host star by the companion.

  9. 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...

  10. 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.

  11. The late-M dwarfs

    International Nuclear Information System (INIS)

    Bessell, M.S.

    1991-01-01

    Far-red spectra and VRIJHK photometry have been obtained for a sample of late-M dwarfs selected on the basis of large reduced red magnitudes from the LHS Catalog. Half of the stars in the three faintest 1 mag bins are late-M stars, the other red stars are metallic-hydride subdwarfs. Relations between various colors for the late-M dwarfs are investigated. Of all the colors I - K most reliably correlates with spectral type. FeH bands near 9900 A are clearly seen in the spectra of all dwarf stars later than M5. Two stars cooler than VB10, and similar in temperature to LHS2924 have been identified; both have H-alpha in emission and appear variable in magnitude and R - I color; one is a flare star. The other stars are of earlier spectral type and resemble W359 and VB8. The observed MI, I - K main sequence is in good agreement with the IG theoretical main sequence of Stringfellow, and the faintest stars could be about 0.09 solar mass red dwarfs or lower mass brown dwarfs. 65 refs

  12. Brown dwarfs in wide-field surveys

    Directory of Open Access Journals (Sweden)

    Lodieu N.

    2011-07-01

    Full Text Available In this invited talk, I briefly summarise early photometric and proper motion surveys carried out in the nearest and youngest open clusters to introduce the motivation behind the Galactic Cluster component of the UKIRT Infrared Deep Sky Survey. Afterwards, I focus on the latest results that we obtained in the Upper Sco association and in the Pleiades. To finish, I show a comparison of the luminosity and mass functions obtained in the Upper Sco association, the Pleiades cluster, and σ Orionis from the homogeneous set of data publicly available from the Galactic Clusters Survey.

  13. Dynamics of Tidally Locked, Ultrafast Rotating Atmospheres

    Science.gov (United States)

    Tan, Xianyu; Showman, Adam P.

    2017-10-01

    Tidally locked gas giants, which exhibit a novel regime of day-night thermal forcing and extreme stellar irradiation, are typically in several-day orbits, implying slow rotation and a modest role for rotation in the atmospheric circulation. Nevertheless, there exist a class of gas-giant, highly irradiated objects - brown dwarfs orbiting white dwarfs in extremely tight orbits - whose orbital and hence rotation periods are as short as 1-2 hours. Spitzer phase curves and other observations have already been obtained for this fascinating class of objects, which raise fundamental questions about the role of rotation in controlling the circulation. So far, most modeling studies have investigated rotation periods exceeding a day, as appropriate for typical hot Jupiters. In this work we investigate the dynamics of tidally locked atmospheres in shorter rotation periods down to about two hours. With increasing rotation rate (decreasing rotation period), we show that the width of the equatorial eastward jet decreases, consistent with the narrowing of wave-mean-flow interacting region due to decrease of the equatorial deformation radius. The eastward-shifted equatorial hot spot offset decreases accordingly, and the westward-shifted hot regions poleward of the equatorial jet associated with Rossby gyres become increasingly distinctive. At high latitudes, winds becomes weaker and more geostrophic. The day-night temperature contrast becomes larger due to the stronger influence of rotation. Our simulated atmospheres exhibit small-scale variability, presumably caused by shear instability. Unlike typical hot Jupiters, phase curves of fast-rotating models show an alignment of peak flux to secondary eclipse. Our results have important implications for phase curve observations of brown dwarfs orbiting white dwarfs in ultra tight orbits.

  14. Calculation of Brown Carbon Optical Properties in the Fifth version Community Atmospheric Model (CAM5) and Validation with a Case Study in Kanpur, India

    Science.gov (United States)

    Xu, L.; Peng, Y.; Ram, K.

    2017-12-01

    The presence of absorbing component of organic carbon in atmospheric aerosols (Brown Carbon, BrC) has recently received much attention to the scientific community because of its absorbing nature, especially in the UV and Visible region. Attempts to account for BrC in radiative forcing calculations in climate model are rather scarce, primarily due to observational constrain as well as its incorporation in the model-based studies. Due to non-treatment of BrC in the off-line models, there exists a large discrepancy between model- and observational- based estimate of direct radiative effect of carbonaceous aerosols. In this study, we have included BrC absorption and optical characteristics in the fifth version of Community Atmospheric Model (CAM5) for the better understanding of radiative impact of BrC over northern India, also for improving the performance of aerosol radiative calculation in climate model. We have used the inputs of aerosol chemical composition measurements conducted at an urban site, Kanpur, in the Indo-Gangetic Plain (IGP) during 2007-2008 to construct the optical properties of BrC in CAM5 model. Model radiative simulations of sensitive tests showed good agreement with observations. Effects of varying imaginary part of BrC refractive index, relative mass ratio of BrC to organic aerosol in combination with core-shell mixing style of BrC with other anthropogenic aerosols are also analyzed for understanding BrC impact on simulated aerosol absorption in model.

  15. Topics in white dwarf astrophysics

    International Nuclear Information System (INIS)

    Hintzen, P.M.N.

    1975-01-01

    This study was designed to investigate the apparent deficiency, compared to theoretical predictions, of cool degenerate stars. Two approaches to the problem were employed: a spectroscopic survey designed to identify red degenerates, and a model atmospheres study of the spectroscopic and photometric differences between red dwarfs and red degenerate stars. On computed atmospheric models for white dwarfs at the temperatures under investigation. Line profiles obtained from these models indicate that degenerate stars with T/sub e/ approximately 6000 0 K and depleted surface metals would be extremely difficult to identify spectroscopically. Their hydrogen and calcium line profiles would strongly resemble those of classical sub-dwarfs. Three apparently degenerate stars whose spectral features match our predictions have been identified. These results indicate that the existence of the previously postulated deficiency of red degenerate stars is uncertain

  16. 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.

  17. 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

  18. A Paradigm Shift in Substellar Classification: Understanding the Apparent Diversity of Substellar Atmospheres through Viewing Geometry

    Science.gov (United States)

    Metchev, Stanimir; Apai, Daniel; Radigan, Jacqueline; Heinze, Aren; Marley, Mark; Artigau, Etienne; Plavchan, Peter; Burgasser, Adam

    2014-12-01

    Results from our Cycle 8 Spitzer Exploration Science program Weather on Other Worlds (WOW) have suggested a potential transformative result for understanding the atmospheric and evolutionary properties of substellar objects. We have found tentative evidence for a correlation between atmospheric appearance and viewing geometry - much as in the now established AGN unification models. In particular, we have found that among L6-T8 dwarfs only those with J-K colors redder than the median are variable. Since apparent variability is enhanced for equator-on viewing geometries, we interpret this as a latitudinal dependence in appearance: redder L6-T8 dwarfs are seen closer to equator-on, and bluer ones are closer to pole-on. This result has the potential to solve the long-standing problem of cloud dissipation in L and T dwarfs: by explaining the broad range in spectroscopic appearance and near-infrared colors of L and T dwarfs as a geometric effect, rather than related to atmospheric dynamics. The implications are substantially broader, and touch on a range of issues in substellar astrophysics, such as the calibration of substellar effective temperatures and bolometric luminosities, and the modeling of ultracool atmospheres and substellar evolution - both of which will require at least a 2-D treatment. We propose an Exploration Science program to map the correspondence between spin-axis orientation, substellar colors, and spectral type. All of the L and T dwarfs in our proposed sample will have measured projected (vsini) rotational velocities within a year. By obtaining photometric periods through sensitive staring observations with Spitzer, and by using the fact that the radii of >1 Gyr-old brown dwarfs are approximately age-independent, we will be able to solve for the spin axis orientations. We will correlate these with variability amplitude, near-infrared colors, and spectral types, to solve for the meridional dependence in the spectroscopic appearance of L and T dwarfs.

  19. Calibrating Detailed Chemical Analysis of M dwarfs

    Science.gov (United States)

    Veyette, Mark; Muirhead, Philip Steven; Mann, Andrew; Brewer, John; Allard, France; Homeier, Derek

    2018-01-01

    The ability to perform detailed chemical analysis of Sun-like F-, G-, and K-type stars is a powerful tool with many applications including studying the chemical evolution of the Galaxy, assessing membership in stellar kinematic groups, and constraining planet formation theories. Unfortunately, complications in modeling cooler stellar atmospheres has hindered similar analysis of M-dwarf stars. Large surveys of FGK abundances play an important role in developing methods to measure the compositions of M dwarfs by providing benchmark FGK stars that have widely-separated M dwarf companions. These systems allow us to empirically calibrate metallicity-sensitive features in M dwarf spectra. However, current methods to measure metallicity in M dwarfs from moderate-resolution spectra are limited to measuring overall metallicity and largely rely on astrophysical abundance correlations in stellar populations. In this talk, I will discuss how large, homogeneous catalogs of precise FGK abundances are crucial to advancing chemical analysis of M dwarfs beyond overall metallicity to direct measurements of individual elemental abundances. I will present a new method to analyze high-resolution, NIR spectra of M dwarfs that employs an empirical calibration of synthetic M dwarf spectra to infer effective temperature, Fe abundance, and Ti abundance. This work is a step toward detailed chemical analysis of M dwarfs at a similar precision achieved for FGK stars.

  20. Temperature and salinity profiles from CTD casts from 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 2001-09-05 to 2001-10-25 (NODC Accession 0000657)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — CTD and other data were collected from NOAA Ship RONALD H. BROWN in the NE and SE Pacific from 05 September 2001 to 25 October 2001. CTD data consist of temperature...

  1. LHS 2803B: A VERY WIDE MID-T DWARF COMPANION TO AN OLD M DWARF IDENTIFIED FROM PAN-STARRS1

    International Nuclear Information System (INIS)

    Deacon, Niall R.; Liu, Michael C.; Magnier, Eugene A.; Bowler, Brendan P.; Mann, Andrew W.; Burgett, William S.; Chambers, Ken C.; Kaiser, Nick; Kudritzki, Rolf-Peter; Morgan, Jeff S.; Tonry, John L.; Wainscoat, Richard J.; Redstone, Joshua A.; Hodapp, Klaus W.; Price, Paul A.

    2012-01-01

    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± 4 7 M Jup , 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.

  2. Cloudless Atmospheres for Young Low-Gravity Substellar Objects

    Science.gov (United States)

    Tremblin, P.; Chabrier, G.; Baraffe, I.; Liu, Michael C.; Magnier, E. A.; Lagage, P.-O.; De Oliveira, C. Alves; Burgasser, A. J.; Amundsen, D. S.; Drummond, B.

    2017-01-01

    Atmospheric modeling of low-gravity (VL-G) young brown dwarfs remains challenging. The presence of very thick clouds is a possible source of this challenge, because of their extremely red near-infrared (NIR) spectra, but no cloud models provide a good fit to the data with a radius compatible with the evolutionary models for these objects. We show that cloudless atmospheres assuming a temperature gradient reduction caused by fingering convection provide a very good model to match the observed VL-G NIR spectra. The sequence of extremely red colors in the NIR for atmospheres with effective temperatures from approx. 2000 K down to approx. 1200 K is very well reproduced with predicted radii typical of young low-gravity objects. Future observations with NIRSPEC and MIRI on the James Webb Space Telescope (JWST) will provide more constraints in the mid-infrared, helping to confirm or refute whether or not the NIR reddening is caused by fingering convection. We suggest that the presence or absence of clouds will be directly determined by the silicate absorption features that can be observed with MIRI. JWST will therefore be able to better characterize the atmosphere of these hot young brown dwarfs and their low-gravity exoplanet analogs.

  3. 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

    Energy Technology Data Exchange (ETDEWEB)

    Kellogg, Kendra; Metchev, Stanimir [Western University, Centre for Planetary and Space Exploration, 1151 Richmond St, London, ON N6A 3K7 (Canada); Geißler, Kerstin; Hicks, Shannon [Stony Brook University, Stony Brook, NY 11790 (United States); Kirkpatrick, J. Davy [Infrared Processing and Analysis Center, Mail Code 100-22, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Kurtev, Radostin, E-mail: kkellogg@uwo.ca, E-mail: smetchev@uwo.ca [Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Ave. Gran Bretaña 1111, Playa Ancha, Casilla 53, Valparaíso (Chile)

    2015-12-15

    We present the 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 − K{sub s} 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 be the lowest-mass (5–6 M{sub Jup}) free-floating member. We also report a new T dwarf, 2MASS J22153705+2110554, that was previously overlooked in the SDSS footprint. These new discoveries demonstrate that despite the considerable scrutiny already devoted to the SDSS and 2MASS surveys, our exploration of these data sets is not yet complete.

  4. 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

    International Nuclear Information System (INIS)

    Kellogg, Kendra; Metchev, Stanimir; Geißler, Kerstin; Hicks, Shannon; Kirkpatrick, J. Davy; Kurtev, Radostin

    2015-01-01

    We present the 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 − K s 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 be the lowest-mass (5–6 M Jup ) free-floating member. We also report a new T dwarf, 2MASS J22153705+2110554, that was previously overlooked in the SDSS footprint. These new discoveries demonstrate that despite the considerable scrutiny already devoted to the SDSS and 2MASS surveys, our exploration of these data sets is not yet complete

  5. 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)

  6. Radiation of dwarf novae

    International Nuclear Information System (INIS)

    Bruch, A.

    1987-01-01

    The nature of dwarf novae with their components white dwarf star, cool star, accretion disk, boundary layer and hot spot is investigated. It is shown that very different physical states and processes occur in the components of dwarf novae. Spectroscopical and photometrical observations are carried out. For better understanding the radiation portions of the single dwarf novae components are separated from the total electromagnetic spectrum recieved from the dwarf novae. The model assumptions are compared with the observations and verified

  7. Strain characterization of West African Dwarf goats of Ogun State II ...

    African Journals Online (AJOL)

    The West African Dwarf (WAD) goat presents variable coat colours, ranging from black, brown, gray, red and white and sometimes combinations of these variety of patterns. In this study, strains of West African Dwarf (WAD) goat were characterized using linear body measurement. The WAD goat included the chocolate, white ...

  8. 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].

  9. Measuring the surface inhomogeneity of metals on accreting white dwarfs

    International Nuclear Information System (INIS)

    Montgomery, M H; Hippel, T von; Thompson, S E

    2009-01-01

    Due to the short settling times of metals in DA white dwarf atmospheres, any white dwarfs with photospheric metals must be actively accreting. It is therefore natural to expect that the metals may not be deposited uniformly on the surface of the star. We present calculations showing how the temperature variations associated with white dwarf pulsations lead to an observable diagnostic of the surface metal distribution, and we show what constraints current data sets are able to provide.

  10. SDSS DR7 WHITE DWARF CATALOG

    Energy Technology Data Exchange (ETDEWEB)

    Kleinman, S. J.; Nitta, A. [Gemini Observatory, 670 North A' ohoku Place, Hilo, HI 96720 (United States); Kepler, S. O.; Pelisoli, Ingrid; Pecanha, Viviane; Costa, J. E. S. [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS (Brazil); Koester, D. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Kiel, D-24098 Kiel (Germany); Krzesinski, J. [Mt. Suhora Observatory, Pedagogical University of Cracow, ul. Podchorazych 2, 30-084 Cracow (Poland); Dufour, P.; Lachapelle, F.-R.; Bergeron, P. [Departement de Physique, Universite de Montreal, C. P. 6128, Succ. Centre-Ville, Montreal, Quebec H3C 3J7 (Canada); Yip, Ching-Wa [Department of Physics and Astronomy, The Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218 (United States); Harris, Hugh C. [United States Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86001-8521 (United States); Eisenstein, Daniel J. [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, MS 20, Cambridge, MA 02138 (United States); Althaus, L.; Corsico, A., E-mail: hch@nofs.navy.mil [Facultad de Ciencias Astronomicas y Geofisicas, Paseo del Bosque S/N, (1900) La Plata (Argentina)

    2013-01-15

    We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA and 1011 DB white dwarf spectra from 12,843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated log g if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.

  11. ON THE EVOLUTION OF MAGNETIC WHITE DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Tremblay, P.-E. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Fontaine, G.; Brassard, P. [Département de Physique, Université de Montréal, C. P. 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7 (Canada); Freytag, B. [Department of Physics and Astronomy at Uppsala University, Regementsvägen 1, Box 516, SE-75120 Uppsala (Sweden); Steiner, O. [Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, D-79104 Freiburg (Germany); Ludwig, H.-G. [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Steffen, M. [Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Wedemeyer, S., E-mail: tremblay@stsci.edu [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo (Norway)

    2015-10-10

    We present the first radiation magnetohydrodynamic simulations of the atmosphere of white dwarf stars. We demonstrate that convective energy transfer is seriously impeded by magnetic fields when the plasma-β parameter, the thermal-to-magnetic-pressure ratio, becomes smaller than unity. The critical field strength that inhibits convection in the photosphere of white dwarfs is in the range B = 1–50 kG, which is much smaller than the typical 1–1000 MG field strengths observed in magnetic white dwarfs, implying that these objects have radiative atmospheres. We have employed evolutionary models to study the cooling process of high-field magnetic white dwarfs, where convection is entirely suppressed during the full evolution (B ≳ 10 MG). We find that the inhibition of convection has no effect on cooling rates until the effective temperature (T{sub eff}) reaches a value of around 5500 K. In this regime, the standard convective sequences start to deviate from the ones without convection due to the convective coupling between the outer layers and the degenerate reservoir of thermal energy. Since no magnetic white dwarfs are currently known at the low temperatures where this coupling significantly changes the evolution, the effects of magnetism on cooling rates are not expected to be observed. This result contrasts with a recent suggestion that magnetic white dwarfs with T{sub eff} ≲ 10,000 K cool significantly slower than non-magnetic degenerates.

  12. SEARCHING FOR BINARY Y DWARFS WITH THE GEMINI MULTI-CONJUGATE ADAPTIVE OPTICS SYSTEM (GeMS)

    International Nuclear Information System (INIS)

    Opitz, Daniela; Tinney, C. G.; Faherty, Jacqueline K.; Sweet, Sarah; Gelino, Christopher R.; Kirkpatrick, J. Davy

    2016-01-01

    The NASA Wide-field Infrared Survey Explorer (WISE) has discovered almost all the known members of the new class of Y-type brown dwarfs. Most of these Y dwarfs have been identified as isolated objects in the field. It is known that binaries with L- and T-type brown dwarf primaries are less prevalent than either M-dwarf or solar-type primaries, they tend to have smaller separations and are more frequently detected in near-equal mass configurations. The binary statistics for Y-type brown dwarfs, however, are sparse, and so it is unclear if the same trends that hold for L- and T-type brown dwarfs also hold for Y-type ones. In addition, the detection of binary companions to very cool Y dwarfs may well be the best means available for discovering even colder objects. We present results for binary properties of a sample of five WISE Y dwarfs with the Gemini Multi-Conjugate Adaptive Optics System. We find no evidence for binary companions in these data, which suggests these systems are not equal-luminosity (or equal-mass) binaries with separations larger than ∼0.5–1.9 AU. For equal-mass binaries at an age of 5 Gyr, we find that the binary binding energies ruled out by our observations (i.e., 10 42 erg) are consistent with those observed in previous studies of hotter ultra-cool dwarfs

  13. Haematological and physiological parameters of West African dwarf ...

    African Journals Online (AJOL)

    Twenty four West African Dwarf (WAD) goats of both sexes (12 bucks and 12 does) raised under intensive system and weighing between 5 and 11 kg with different coat colours (Black, Brown, Tan and White) were used for this study to evaluate the effects of sex and coat colour on their haematological and physiological ...

  14. A DARK SPOT ON A MASSIVE WHITE DWARF

    Energy Technology Data Exchange (ETDEWEB)

    Kilic, Mukremin; Gianninas, Alexandros; Curd, Brandon; Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019 (United States); Bell, Keaton J.; Winget, D. E.; Winget, K. I. [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Brown, Warren R. [Smithsonian Astrophysical Observatory, 60 Garden St., Cambridge, MA 02138 (United States); Hermes, J. J. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Dufour, Patrick [Institut de recherche sur les exoplanétes (iREx), Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, QC H3C 3J7 (Canada)

    2015-12-01

    We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98+292801.9 (hereafter J1529+2928). We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity, which place it near the ZZ Ceti instability strip. Instead of pulsations, we detect photometric dips from this white dwarf every 38 minutes. Follow-up optical spectroscopy observations with Gemini reveal no significant radial velocity variations, ruling out stellar and brown dwarf companions. A disintegrating planet around this white dwarf cannot explain the observed light curves in different filters. Given the short period, the source of the photometric dips must be a dark spot that comes into view every 38 minutes due to the rotation of the white dwarf. Our optical spectroscopy does not show any evidence of Zeeman splitting of the Balmer lines, limiting the magnetic field strength to B < 70 kG. Since up to 15% of white dwarfs display kG magnetic fields, such eclipse-like events should be common around white dwarfs. We discuss the potential implications of this discovery on transient surveys targeting white dwarfs, like the K2 mission and the Large Synoptic Survey Telescope.

  15. The Young L Dwarf 2MASS J11193254-1137466 Is a Planetary-mass Binary

    Science.gov (United States)

    Best, William M. J.; Liu, Michael C.; Dupuy, Trent J.; Magnier, Eugene A.

    2017-07-01

    We have discovered that the extremely red, low-gravity L7 dwarf 2MASS J11193254-1137466 is a 0.″14 (3.6 au) binary using Keck laser guide star adaptive optics imaging. 2MASS J11193254-1137466 has previously been identified as a likely member of the TW Hydrae Association (TWA). Using our updated photometric distance and proper motion, a kinematic analysis based on the BANYAN II model gives an 82% probability of TWA membership. At TWA’s 10 ± 3 Myr age and using hot-start evolutionary models, 2MASS J11193254-1137466AB is a pair of {3.7}-0.9+1.2 {M}{Jup} brown dwarfs, making it the lowest-mass binary discovered to date. We estimate an orbital period of {90}-50+80 years. One component is marginally brighter in K band but fainter in J band, making this a probable flux-reversal binary, the first discovered with such a young age. We also imaged the spectrally similar TWA L7 dwarf WISEA J114724.10-204021.3 with Keck and found no sign of binarity. Our evolutionary model-derived {T}{eff} estimate for WISEA J114724.10-204021.3 is ≈230 K higher than for 2MASS J11193254-1137466AB, at odds with the spectral similarity of the two objects. This discrepancy suggests that WISEA J114724.10-204021.3 may actually be a tight binary with masses and temperatures very similar to 2MASS J11193254-1137466AB, or further supporting the idea that near-infrared spectra of young ultracool dwarfs are shaped by factors other than temperature and gravity. 2MASS J11193254-1137466AB will be an essential benchmark for testing evolutionary and atmospheric models in the young planetary-mass regime.

  16. PREFACE: 16th European White Dwarfs Workshop

    Science.gov (United States)

    Garcia-Berro, Enrique; Hernanz, Margarita; Isern, Jordi; Torres, Santiago

    2009-07-01

    The 16th European Workshop on White Dwarfs was held in Barcelona, Spain, from 30 June to 4 July 2008 at the premises of the UPC. Almost 120 participants from Europe (France, Germany, United Kingdom, Italy, and several others), America (USA, Canada, Argentina, Brazil, and Chile), and other continents (Australia, South Africa, . . . ) attended the workshop. Among these participants were the most relevant specialists in the field. The topics covered by the conference were: White dwarf structure and evolution Progenitors and Planetary Nebulae White dwarfs in binaries: cataclysmic variables, double degenerates and other binaries White dwarfs, dust disks and planetary systems Atmospheres, chemical composition, magnetic fields Variable white dwarfs White dwarfs in stellar clusters and the halo White Dwarfs as SNIa progenitors The programme included 54 talks, and 45 posters. The oral presentations were distributed into the following sessions: Luminosity function, mass function and populations White dwarf structure and evolution White dwarf ages White dwarf catalogs and surveys Central stars of planetary nebulae Supernovae progenitors White dwarfs in novae and CVs Physical processes in white dwarfs and magnetic white dwarfs Disks, dust and planets around white dwarfs Pulsating white dwarfs Additionally we had a special open session about Spitzer and white dwarfs. The Proceedings of the 16th European Workshop on White Dwarfs are representative of the current state-of-the-art of the research field and include new and exciting results. We acknowledge the very positive attitude of the attendants to the workshop, which stimulated very fruitful discussions that took place in all the sessions and after the official schedule. Also, the meeting allowed new collaborations tp start that will undoubtedly result in significant advances in the research field. We also acknowledge the willingness of the participants to deliver their contributions before the final deadline. We sincerely

  17. Browns Ferry

    International Nuclear Information System (INIS)

    Wood, J.

    1996-01-01

    In 1986, the US Nuclear Regulatory Commission (NRC) established a ''watch list'' of power reactors requiring special attention which included the three BWR units at Brown's Ferry owned by the Tennessee Valley Authority (TVA). The reactors has been closed down voluntarily by the TVA in 1985 in order to deal with a backlog of maintenance and regulatory issues. Intended as short-term, the shutdown was indefinitely extended when the nature and extent of the design changes, accompanying documentation and retrofitting required to satisfy the NRC became apparent. The recovery programme for Unit 2 was completed by 1991 and the reactor returned to service under a dedicated operating staff. Meanwhile, a separate, dedicated, recovery team was set up to manage Unit 3 which was returned to service in December 1995. Browns Ferry 2 was removed from the NRC watch list in June 1992 and Units 1 and 3 in June 1996. Units 2 and 3 have both operated successfully since restart but Unit 1 is currently mothballed and TVA has no plans to bring it back into service. (UK)

  18. The Missing Link: Early Methane ("T") Dwarfs in the Sloan Digital Sky Survey.

    Science.gov (United States)

    Leggett; Geballe; Fan; Schneider; Gunn; Lupton; Knapp; Strauss; McDaniel; Golimowski; Henry; Peng; Tsvetanov; Uomoto; Zheng; Hill; Ramsey; Anderson; Annis; Bahcall; Brinkmann; Chen; Csabai; Fukugita; Hennessy; Hindsley; Ivezic; Lamb; Munn; Pier; Schlegel; Smith; Stoughton; Thakar; York

    2000-06-10

    We report the discovery of three cool brown dwarfs that fall in the effective temperature gap between the latest L dwarfs currently known, with no methane absorption bands in the 1-2.5 µm range, and the previously known methane (T) dwarfs, whose spectra are dominated by methane and water. The newly discovered objects were detected as very red objects in the Sloan Digital Sky Survey imaging data and have JHK colors between the red L dwarfs and the blue Gl 229B-like T dwarfs. They show both CO and CH(4) absorption in their near-infrared spectra in addition to H(2)O, with weaker CH(4) absorption features in the H and K bands than those in all other methane dwarfs reported to date. Due to the presence of CH(4) in these bands, we propose that these objects are early T dwarfs. The three form part of the brown dwarf spectral sequence and fill in the large gap in the overall spectral sequence from the hottest main-sequence stars to the coolest methane dwarfs currently known.

  19. HIP 38939B: A NEW BENCHMARK T DWARF IN THE GALACTIC PLANE DISCOVERED WITH Pan-STARRS1

    International Nuclear Information System (INIS)

    Deacon, Niall R.; Liu, Michael C.; Magnier, Eugene A.; Bowler, Brendan P.; Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Kaiser, N.; Morgan, J. S.; Sweeney, W. E.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.; Redstone, Joshua; Goldman, Bertrand; Price, P. A.

    2012-01-01

    We report the discovery of a wide brown dwarf companion to the mildly metal-poor ([Fe/H] = –0.24), low Galactic latitude (b = 1. 0 88) K4V star HIP 38939. The companion was discovered by its common proper motion with the primary and its red optical (Pan-STARRS1) and blue infrared (Two Micron All Sky Survey) colors. It has a projected separation of 1630 AU and a near-infrared spectral type of T4.5. As such it is one of only three known companions to a main-sequence star which have early/mid T spectral types of (the others being HN Peg B and ε Indi B). Using chromospheric activity we estimate an age for the primary of 900± 1900 600 Myr. This value is also in agreement with the age derived from the star's weak ROSAT detection. Comparison with evolutionary models for this age range indicates that HIP 38939B falls in the mass range 38 ± 20 M Jup with an effective temperature range of 1090 ± 60 K. Fitting our spectrum with atmospheric models gives a best-fitting temperature of 1100 K. We include our object in an analysis of the population of benchmark T dwarfs and find that while older atmospheric models appeared to overpredict the temperature of the coolest objects compared to evolutionary models, more recent atmospheric models provide better agreement.

  20. HIP 38939B: A NEW BENCHMARK T DWARF IN THE GALACTIC PLANE DISCOVERED WITH Pan-STARRS1

    Energy Technology Data Exchange (ETDEWEB)

    Deacon, Niall R.; Liu, Michael C.; Magnier, Eugene A.; Bowler, Brendan P.; Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Kaiser, N.; Morgan, J. S.; Sweeney, W. E.; Tonry, J. L.; Wainscoat, R. J.; Waters, C. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Redstone, Joshua [Facebook, 1601 S. California Avenue, Palo Alto, CA 94304 (United States); Goldman, Bertrand [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Price, P. A., E-mail: deacon@mpia.de [Princeton University Observatory, 4 Ivy Lane, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States)

    2012-08-20

    We report the discovery of a wide brown dwarf companion to the mildly metal-poor ([Fe/H] = -0.24), low Galactic latitude (b = 1.{sup 0}88) K4V star HIP 38939. The companion was discovered by its common proper motion with the primary and its red optical (Pan-STARRS1) and blue infrared (Two Micron All Sky Survey) colors. It has a projected separation of 1630 AU and a near-infrared spectral type of T4.5. As such it is one of only three known companions to a main-sequence star which have early/mid T spectral types of (the others being HN Peg B and {epsilon} Indi B). Using chromospheric activity we estimate an age for the primary of 900{+-}{sup 1900}{sub 600} Myr. This value is also in agreement with the age derived from the star's weak ROSAT detection. Comparison with evolutionary models for this age range indicates that HIP 38939B falls in the mass range 38 {+-} 20 M{sub Jup} with an effective temperature range of 1090 {+-} 60 K. Fitting our spectrum with atmospheric models gives a best-fitting temperature of 1100 K. We include our object in an analysis of the population of benchmark T dwarfs and find that while older atmospheric models appeared to overpredict the temperature of the coolest objects compared to evolutionary models, more recent atmospheric models provide better agreement.

  1. The solar neighborhood. XXXIV. A search for planets orbiting nearby M dwarfs using astrometry

    International Nuclear Information System (INIS)

    Lurie, John C.; Henry, Todd J.; Ianna, Philip A.; Jao, Wei-Chun; Quinn, Samuel N.; Winters, Jennifer G.; Koerner, David W.; Riedel, Adric R.; Subasavage, John P.

    2014-01-01

    Astrometric measurements are presented for seven nearby stars with previously detected planets: six M dwarfs (GJ 317, GJ 667C, GJ 581, GJ 849, GJ 876, and GJ 1214) and one K dwarf (BD-10 -3166). Measurements are also presented for six additional nearby M dwarfs without known planets, but which are more favorable to astrometric detections of low mass companions, as well as three binary systems for which we provide astrometric orbit solutions. Observations have baselines of 3 to 13 years, and were made as part of the RECONS long-term astrometry and photometry program at the CTIO/SMARTS 0.9 m telescope. We provide trigonometric parallaxes and proper motions for all 16 systems, and perform an extensive analysis of the astrometric residuals to determine the minimum detectable companion mass for the 12 M dwarfs not having close stellar secondaries. For the six M dwarfs with known planets, we are not sensitive to planets, but can rule out the presence of all but the least massive brown dwarfs at periods of 2–12 years. For the six more astrometrically favorable M dwarfs, we conclude that none have brown dwarf companions, and are sensitive to companions with masses as low as 1 M Jup for periods longer than two years. In particular, we conclude that Proxima Centauri has no Jovian companions at orbital periods of 2–12 years. These results complement previously published M dwarf planet occurrence rates by providing astrometrically determined upper mass limits on potential super-Jupiter companions at orbits of two years and longer. As part of a continuing survey, these results are consistent with the paucity of super-Jupiter and brown dwarf companions we find among the over 250 red dwarfs within 25 pc observed longer than five years in our astrometric program.

  2. The solar neighborhood. XXXIV. A search for planets orbiting nearby M dwarfs using astrometry

    Energy Technology Data Exchange (ETDEWEB)

    Lurie, John C. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Henry, Todd J.; Ianna, Philip A. [RECONS Institute, Chambersburg, PA 17201 (United States); Jao, Wei-Chun; Quinn, Samuel N.; Winters, Jennifer G. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302 (United States); Koerner, David W. [Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86011 (United States); Riedel, Adric R. [Department of Astrophysics, American Museum of Natural History, New York, NY 10034 (United States); Subasavage, John P., E-mail: lurie@uw.edu [United States Naval Observatory, Flagstaff, AZ 86001 (United States)

    2014-11-01

    Astrometric measurements are presented for seven nearby stars with previously detected planets: six M dwarfs (GJ 317, GJ 667C, GJ 581, GJ 849, GJ 876, and GJ 1214) and one K dwarf (BD-10 -3166). Measurements are also presented for six additional nearby M dwarfs without known planets, but which are more favorable to astrometric detections of low mass companions, as well as three binary systems for which we provide astrometric orbit solutions. Observations have baselines of 3 to 13 years, and were made as part of the RECONS long-term astrometry and photometry program at the CTIO/SMARTS 0.9 m telescope. We provide trigonometric parallaxes and proper motions for all 16 systems, and perform an extensive analysis of the astrometric residuals to determine the minimum detectable companion mass for the 12 M dwarfs not having close stellar secondaries. For the six M dwarfs with known planets, we are not sensitive to planets, but can rule out the presence of all but the least massive brown dwarfs at periods of 2–12 years. For the six more astrometrically favorable M dwarfs, we conclude that none have brown dwarf companions, and are sensitive to companions with masses as low as 1 M{sub Jup} for periods longer than two years. In particular, we conclude that Proxima Centauri has no Jovian companions at orbital periods of 2–12 years. These results complement previously published M dwarf planet occurrence rates by providing astrometrically determined upper mass limits on potential super-Jupiter companions at orbits of two years and longer. As part of a continuing survey, these results are consistent with the paucity of super-Jupiter and brown dwarf companions we find among the over 250 red dwarfs within 25 pc observed longer than five years in our astrometric program.

  3. A heating mechanism for the chromospheres of M dwarf stars

    Science.gov (United States)

    Giampapa, M. S.; Golub, L.; Rosner, R.; Vaiana, G.; Linsky, J. L.; Worden, S. P.

    1981-01-01

    The atmospheric structure of the dwarf M-stars which is especially important to the general field of stellar chromospheres and coronae was investigated. The M-dwarf stars constitute a class of objects for which the discrepancy between the predictions of the acoustic wave chromospheric/coronal heating hypothesis and the observations is most vivid. It is assumed that they represent a class of stars where alternative atmospheric heating mechanisms, presumably magnetically related, are most clearly manifested. Ascertainment of the validity of a hypothesis to account for the origin of the chromospheric and transition region line emission in M-dwarf stars is proposed.

  4. NEW COOLING SEQUENCES FOR OLD WHITE DWARFS

    International Nuclear Information System (INIS)

    Renedo, I.; Althaus, L. G.; GarcIa-Berro, E.; Miller Bertolami, M. M.; Romero, A. D.; Corsico, A. H.; Rohrmann, R. D.

    2010-01-01

    We present full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs. This is done by evolving white dwarf progenitors from the zero-age main sequence, through the core hydrogen-burning phase, the helium-burning phase, and the thermally pulsing asymptotic giant branch phase to the white dwarf stage. Complete evolutionary sequences are computed for a wide range of stellar masses and for two different metallicities, Z = 0.01, which is representative of the solar neighborhood, and Z = 0.001, which is appropriate for the study of old stellar systems, like globular clusters. During the white dwarf cooling stage, we self-consistently compute the phase in which nuclear reactions are still important, the diffusive evolution of the elements in the outer layers and, finally, we also take into account all the relevant energy sources in the deep interior of the white dwarf, such as the release of latent heat and the release of gravitational energy due to carbon-oxygen phase separation upon crystallization. We also provide colors and magnitudes for these sequences, based on a new set of improved non-gray white dwarf model atmospheres, which include the most up-to-date physical inputs like the Lyα quasi-molecular opacity. The calculations are extended down to an effective temperature of 2500 K. Our calculations provide a homogeneous set of evolutionary cooling tracks appropriate for mass and age determinations of old DA white dwarfs and for white dwarf cosmochronology of the different Galactic populations.

  5. A METHANE IMAGING SURVEY FOR T DWARF CANDIDATES IN ρ OPHIUCHI

    International Nuclear Information System (INIS)

    Haisch, Karl E.; Barsony, Mary; Tinney, Chris

    2010-01-01

    We report on the results of the first deep, wide-field, near-infrared methane imaging survey of the ρ Ophiuchi cloud core to search for T dwarfs. Among the 6587 objects detected, 22 were identified as T dwarf candidates. Brown dwarf models indicate that at the age and distance of the ρ Ophiuchi cloud, these T dwarf candidates have masses between 1 and 2 Jupiter masses. If confirmed as genuine T dwarfs, these objects would be the youngest, lowest mass, and lowest gravity free-floating objects ever directly observed. The existence of these candidates suggests that the initial mass function of the ρ Ophiuchi cloud extends well into the regime of planetary mass objects. A large fraction (59% ± 16%) of our T dwarf candidates appear to be surrounded by circumstellar disks, and thus represents the lowest mass objects yet found to harbor circumstellar disks.

  6. LHS 2803B: A VERY WIDE MID-T DWARF COMPANION TO AN OLD M DWARF IDENTIFIED FROM PAN-STARRS1

    Energy Technology Data Exchange (ETDEWEB)

    Deacon, Niall R. [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Liu, Michael C.; Magnier, Eugene A.; Bowler, Brendan P.; Mann, Andrew W.; Burgett, William S.; Chambers, Ken C.; Kaiser, Nick; Kudritzki, Rolf-Peter; Morgan, Jeff S.; Tonry, John L.; Wainscoat, Richard J. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Redstone, Joshua A. [Facebook, 1601 Willow Road, Menlo Park, CA 94025 (United States); Hodapp, Klaus W. [Institute for Astronomy, University of Hawaii, 640 North Aohoku Place, Hilo, HI 96720 (United States); Price, Paul A., E-mail: deacon@mpia.de [Princeton University Observatory, 4 Ivy Lane, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States)

    2012-09-20

    We report the discovery of a wide ({approx}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 H{alpha} 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{+-}{sup 4}{sub 7} M{sub Jup}, 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.

  7. White Dwarf Stars

    OpenAIRE

    Kepler, S. O.; Romero, Alejandra Daniela; Pelisoli, Ingrid; Ourique, Gustavo

    2017-01-01

    White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5000 to 39000. This number includes only white dwarf stars with log g >= 6.5 stars, i.e., excluding the Extremely Low Mass white dw...

  8. A Survey for Hα Emission from Late L Dwarfs and T Dwarfs

    Science.gov (United States)

    Pineda, J. Sebastian; Hallinan, Gregg; Kirkpatrick, J. Davy; Cotter, Garret; Kao, Melodie M.; Mooley, Kunal

    2016-07-01

    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 Å) survey with the Keck telescopes looking for Hα 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 Hα detection rate of 9.2±{}2.13.5% 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 auroral radio emission from Kao et al., suggesting that geometrical selection effects due to the beaming of the radio emission are small or absent. We also provide the first detection of Hα emission from 2MASS 0036+1821, previously notable as the only electron cyclotron maser radio source without a confirmed detection of Hα emission. Finally, we also establish optical standards for spectral types T3 and T4, filling in the previous gap between T2 and T5. 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.

  9. Pulsations in white dwarfs: Selected topics

    Directory of Open Access Journals (Sweden)

    Saio H.

    2013-03-01

    Full Text Available This paper presents a very brief overview of the observed properties of g-mode pulsations in variable white dwarfs. We then discuss a few selected topics: Excitation mechanisms (kappa- and convection- mechanisms, and briefly the effect of a strong magnetic field (∼ 1 MG on g-modes as recently found in a hot DQ (carbon-rich atmosphere white dwarf. In the discussion of excitation mechanisms, a simple interpretation for the convection mechanism is given.

  10. Stroemgren photometry of southern white dwarfs

    International Nuclear Information System (INIS)

    Bessell, M.S.; Wickramasinghe, D.T.

    1978-01-01

    Colours of southern white dwarfs in the uvby (Stroemgren four-colour) system have been obtained. The results are compared with those of Graham. The extensive absolute photometry of white dwarfs published by Greenstein has also been transferred into the four-colour system and both sets of results are compared with model atmosphere calculations. The scatter in log (g) is higher than previously supposed, and the evidence for an increase in at the cooler (Tsub(e) < 10 000 K) end of the DA sequence is discussed. (author)

  11. Temperature and salinity profiles from CTD casts from NOAA Ship RONALD H. BROWN in the SE Pacific (limit -140 W) as part of the East Pacific Investigations of Climate Processes in the Coupled Ocean-Atmosphere from 2001-02-01 to 2001-03-08 (NODC Accession 0000660)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — CTD and other data were collected from NOAA Ship RONALD H. BROWN in the SE Pacific (limit-140 W) from from 01 February 2001 to 08 March 2001. CTD data consist of...

  12. Temperature and salinity profiles from CTD casts from NOAA Ship RONALD H. BROWN and NOAA Ship KA'IMIMOANA in the NE and SW Pacific as part of the Global Ocean-Atmosphere-Land System (GOALS) / Pan American Climate Studies (PACS) from 2001-01-14 to 2001-12-05 (NODC Accession 0000658)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — CTD and other data were collected from NOAA Ship RONALD H. BROWN and NOAA Ship KA'IMIMOANA in the NE and SW Pacific from 14 January 2001 to 05 December 2001. CTD...

  13. The Orbit of the L Dwarf + T Dwarf Spectral Binary SDSS J080531.84+481233.0

    Science.gov (United States)

    Burgasser, Adam J.; Blake, Cullen H.; Gelino, Christopher R.; Sahlmann, Johannes; Bardalez Gagliuffi, Daniella

    2016-08-01

    SDSS J080531.84+481233.0 is a closely separated, very-low-mass (VLM) binary identified through combined-light spectroscopy and confirmed as an astrometric variable. Here we report four years of radial velocity monitoring observations of the system that reveal significant and periodic variability, confirming the binary nature of the source. We infer an orbital period of 2.02 ± 0.03 years, a semimajor axis of 0.76{}-0.06+0.05 au, and an eccenticity of 0.46 ± 0.05, consistent with the amplitude of astrometric variability and prior attempts to resolve the system. Folding in constraints based on the spectral types of the components (L4 ± 0.7 and T5.5 ± 1.1), corresponding effective temperatures, and brown dwarf evolutionary models, we further constrain the orbital inclination of this system to be nearly edge-on (90° ± 19°), and deduce a large system mass ratio (M 2/M 1 = {0.86}-0.12+0.10), substellar components (M 1 = {0.057}-0.014+0.016 M ⊙, M 2 = {0.048}-0.010+0.008 M ⊙), and a relatively old system age (minimum age = {4.0}-1.2+1.9 Gyr). The measured projected rotational velocity of the primary ({V}{rot}\\sin I = 34.1 ± 0.7 km s-1) implies that this inactive source is a rapid rotator (period ≲ 3 hr) and a viable system for testing spin-orbit alignment in VLM multiples. Robust model-independent constraints on the component masses may be possible through measurement of the reflex motion of the secondary at wavelengths in which it contributes a greater proportion of the combined luminence, while the system may also be resolvable through sparse-aperature mask interferometry with adaptive optics. The combination of well-determined component atmospheric properties and masses near and/or below the hydrogen minimum mass make SDSS J0805+4812AB an important system for future tests of brown dwarf evolutionary models. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California

  14. Searching for white dwarfs candidates in Sloan Digital Sky Survey Data

    International Nuclear Information System (INIS)

    Nalezyty, Miroslaw; Majczyna, Agnieszka; Ciechanowska, Anna; Madej, Jerzy

    2009-01-01

    Large amount of observational spectroscopic data are recently available from different observational projects, like Sloan Digital Sky Survey. It's become more urgent to identify white dwarfs stars based on data itself i.e. without modelling white dwarf atmospheres. In particular, existing methods of white dwarfs identification presented in Kleinman et al. (2004) and in Eisenstein et al. (2006) did not allow to find all the white dwarfs in examined data. We intend to test various criteria of searching for white dwarf candidates, based on photometric and spectral features.

  15. Hemlock Dwarf Mistletoe (FIDL)

    Science.gov (United States)

    Paul E. Hennon; Jerome S. Beatty; Diane Hildebrand

    2001-01-01

    Hemlock dwarf mistletoe, Arceuthobium tsugense (Rosendahl) G.N. Jones, causes a serious disease of western hemlock and several other tree species along the Pacific Coast of North America. This small, seed-bearing plant lives exclusively as a parasite on living trees. Throughout its range, hemlock dwarf mistletoe occurs in patch-like patterns in the forests. Some...

  16. Larch Dwarf Mistletoe (FIDL)

    Science.gov (United States)

    Jerome S. Beatty; Gregory M. Filip; Robert L. Mathiason

    1997-01-01

    Larch dwarf mistletoe (Arceuthobium laricis (Piper) St. John) is a common and damaging parasite of western larch (Larix occidentalis Nutt.) in the Pacific Northwest and southern British Columbia. Larch dwarf mistletoe occurs commonly throughout the range of western larch in British Columbia, northern and central Idaho, western Montana and east of the Cascades in...

  17. Pithy brown core in ‘d’Anjou’ pear (Pyrus communis L.) fruit developing during controlled atmosphere storage at pO2 determined by monitoring chlorophyll fluorescense

    Science.gov (United States)

    Physiological responses and fruit quality of ‘d’Anjou’ pear fruit from five orchard lots were evaluated after cold storage in air or controlled atmospheres (CA) with the oxygen (O2) concentration based on assessment of fruit chlorophyll fluorescence (CF) or standard conditions (1.5 kPa O2). The pCO2...

  18. Throwing Icebergs at White Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Stephan, Alexander P.; Naoz, Smadar; Zuckerman, B., E-mail: alexpstephan@astro.ucla.edu [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)

    2017-08-01

    White dwarfs (WDs) have atmospheres that are expected to consist nearly entirely of hydrogen and helium, since heavier elements will sink out of sight on short timescales. However, observations have revealed atmospheric pollution by heavier elements in about a quarter to a half of all WDs. While most of the pollution can be accounted for with asteroidal or dwarf planetary material, recent observations indicate that larger planetary bodies, as well as icy and volatile material from Kuiper belt analog objects, are also viable sources of pollution. The commonly accepted pollution mechanisms, namely scattering interactions between planetary bodies orbiting the WDs, can hardly account for pollution by objects with large masses or long-period orbits. Here we report on a mechanism that naturally leads to the emergence of massive body and icy and volatile material pollution. This mechanism occurs in wide binary stellar systems, where the mass loss of the planets’ host stars during post main sequence stellar evolution can trigger the Eccentric Kozai–Lidov mechanism. This mechanism leads to large eccentricity excitations, which can bring massive and long-period objects close enough to the WDs to be accreted. We find that this mechanism readily explains and is consistent with observations.

  19. Star Formation in Dwarf-Dwarf Mergers: Fueling Hierarchical Assembly

    Science.gov (United States)

    Stierwalt, Sabrina; Johnson, K. E.; Kallivayalil, N.; Patton, D. R.; Putman, M. E.; Besla, G.; Geha, M. C.

    2014-01-01

    We present early results from the first systematic study a sample of isolated interacting dwarf pairs and the mechanisms governing their star formation. Low mass dwarf galaxies are ubiquitous in the local universe, yet the efficiency of gas removal and the enhancement of star formation in dwarfs via pre-processing (i.e. dwarf-dwarf interactions occurring before the accretion by a massive host) are currently unconstrained. Studies of Local Group dwarfs credit stochastic internal processes for their complicated star formation histories, but a few intriguing examples suggest interactions among dwarfs may produce enhanced star formation. We combine archival UV imaging from GALEX with deep optical broad- and narrow-band (Halpha) imaging taken with the pre- One Degree Imager (pODI) on the WIYN 3.5-m telescope and with the 2.3-m Bok telescope at Steward Observatory to confirm the presence of stellar bridges and tidal tails and to determine whether dwarf-dwarf interactions alone can trigger significant levels of star formation. We investigate star formation rates and global galaxy colors as a function of dwarf pair separation (i.e. the dwarf merger sequence) and dwarf-dwarf mass ratio. This project is a precursor to an ongoing effort to obtain high spatial resolution HI imaging to assess the importance of sequential triggering caused by dwarf-dwarf interactions and the subsequent affect on the more massive hosts that later accrete the low mass systems.

  20. THE 5 GHz ARECIBO SEARCH FOR RADIO FLARES FROM ULTRACOOL DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Route, Matthew; Wolszczan, Alexander, E-mail: mroute@astro.psu.edu, E-mail: alex@astro.psu.edu [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States)

    2013-08-10

    We present the results of a 4.75 GHz survey of 33 brown dwarfs and one young exoplanetary system for flaring radio emission, conducted with the 305 m Arecibo radio telescope. The goal of this program was to detect and characterize the magnetic fields of objects cooler than spectral type L3.5, the coolest brown dwarf detected prior to our survey. We have also attempted to detect flaring radio emission from the HR 8799 planetary system, guided by theoretical work indicating that hot, massive exoplanets may have strong magnetic fields capable of generating radio emission at GHz frequencies. We have detected and confirmed radio flares from the T6.5 dwarf 2MASS J10475385+2124234. This detection dramatically extends the temperature range over which brown dwarfs appear to be at least sporadic radio-emitters, from 1900 K (L3.5) down to 900 K (T6.5). It also demonstrates that the utility of radio detection as a unique tool to study the magnetic fields of substellar objects extends to the coolest dwarfs, and, plausibly to hot, massive exoplanets. We have also identified a single, 3.6{sigma} flare from the L1 dwarf, 2MASS J1439284+192915. This detection is tentative and requires confirmation by additional monitoring observations.

  1. New Y and T Dwarfs from WISE Identified by Methane Imaging

    Science.gov (United States)

    Tinney, C. G.; Kirkpatrick, J. Davy; Faherty, Jacqueline K.; Mace, Gregory N.; Cushing, Mike; Gelino, Christopher R.; Burgasser, Adam J.; Sheppard, Scott S.; Wright, Edward L.

    2018-06-01

    We identify new Y- and T-type brown dwarfs from the WISE All Sky data release using images obtained in filters that divide the traditional near-infrared H and J bands into two halves—specifically {CH}}4{{s}} and CH4l in the H and J2, and J3 in the J. This proves to be very effective at identifying cool brown dwarfs via the detection of their methane absorption, as well as providing preliminary classification using methane colors and WISE -to-near-infrared colors. New and updated calibrations between T/Y spectral types and {CH}}4{{s}}–CH4l J3–W2, and {CH}}4{{s}}–W2 colors are derived, producing classification estimates good to a few spectral sub-types. We present photometry for a large sample of T and Y dwarfs in these filters, together with spectroscopy for 23 new ultra-cool dwarfs—2 Y dwarfs and 21 T dwarfs. We identify a further 8 new cool brown dwarfs, which we have high confidence are T dwarfs based on their methane photometry. We find that, for objects observed on a 4 m class telescope at J-band magnitudes of ∼20 or brighter, {CH}}4{{s}}–CH4l is the more powerful color for detecting objects and then estimating spectral types. Due to the lower sky background in the J-band, the J3 and J2 bands are more useful for identifying fainter cool dwarfs at J ≳ 22. The J3–J2 color is poor at estimating spectral types. But fortunately, once J3–J2 confirms that an object is a cool dwarf, the J3–W2 color is very effective at estimating approximate spectral types.

  2. A search for southern ultracool dwarfs in young moving groups

    Directory of Open Access Journals (Sweden)

    Deacon N.R.

    2011-07-01

    Full Text Available We have constructed an 800-strong red object catalogue by cross-referencing optical and infrared catalogues with an extensive proper motion catalogue compiled for red objects in the southern sky to obtain proper motions. We have applied astrometric and photometric constraints to the catalogue in order to select ultracool dwarf moving group candidates. 132 objects were found to be candidates of a moving group. From this candidate list we present initial results. Using spectroscopy we have obtained reliable spectral types and space motions, and by association with moving groups we can infer an age and composition. the further study of the remainder of our candidates will provide a large sample of young brown dwarfs and confirmed members will provide benchmark ultracool dwarfs. These will make suitable targets of AO planet searches.

  3. The not-so-extreme white dwarf of the CV GD 552

    International Nuclear Information System (INIS)

    Unda-Sanzana, E; Hinojosa-Goni; Marsh, T R; Gaensicke, B T; Maxted, P F L; Morales-Rueda, L; Dhillon, V S; Thoroughgood, T D; Watson, C A; Tremou, E

    2009-01-01

    GD 552 is a cataclysmic binary which was previously believed to be composed of an M-star and a white dwarf, the latter having an extreme mass of 1.4 solar masses. In a recent paper we showed that this is not compatible with new observational evidence and presented an alternative model in which the white dwarf has a typical mass and the companion is a brown dwarf, making the system a likely member of the elusive group of CVs which have already evolved through minimum orbital period. Here we present additional spectroscopical evidence supporting this conclusion by means of skew mapping.

  4. RED DWARF DYNAMO RAISES PUZZLE OVER INTERIORS OF LOWEST-MASS STARS

    Science.gov (United States)

    2002-01-01

    NASA's Hubble Space Telescope has uncovered surprising evidence that powerful magnetic fields might exist around the lowest mass stars in the universe, which are near the threshold of stellar burning processes. 'New theories will have to be developed to explain how these strong fields are produced, since conventional models predict that these low mass red dwarfs should have very weak or no magnetic fields,' says Dr. Jeffrey Linsky of the Joint Institute for Laboratory Astrophysics (JILA) in Boulder, Colorado. 'The Hubble observations provide clear evidence that very low mass red dwarf stars must have some form of dynamo to amplify their magnetic fields.' His conclusions are based upon Hubble's detection of a high-temperature outburst, called a flare, on the surface of the extremely small, cool red dwarf star Van Biesbroeck 10 (VB10) also known as Gliese 752B. Stellar flares are caused by intense, twisted magnetic fields that accelerate and contain gasses which are much hotter than a star's surface. Explosive flares are common on the Sun and expected for stars that have internal structures similar to our Sun's. Stars as small as VB10 are predicted to have a simpler internal structure than that of the Sun and so are not expected to generate the electric currents required for magnetic fields that drive flares. Besides leading to a clearer understanding of the interior structure of the smallest red dwarf stars known, these unexpected results might possibly shed light on brown dwarf stars. A brown dwarf is a long-sought class of astronomical object that is too small to shine like a star through nuclear fusion processes, but is too large to be considered a planet. 'Since VB10 is nearly a brown dwarf, it is likely brown dwarfs also have strong magnetic fields,' says Linsky. 'Additional Hubble searches for flares are needed to confirm this prediction.' A QUARTER-MILLION DEGREE TORCH The star VB10 and its companion star Gliese 752A make up a binary system located 19 light

  5. Progenitors of white dwarfs

    International Nuclear Information System (INIS)

    Drilling, J.S.; Schoenberner, D.

    1985-01-01

    Direct observational evidence is presented which indicates that the immediate progenitors of white dwarfs are the central stars of planetary nebulae (approximately 70%), other post-AGB objects (approximately 30%), and post-HB objects not massive enough to climb the AGB (approximately 0.3%). The combined birth rate for these objects is in satisfactory agreement with the death rate of main-sequence stars and the birth rate of white dwarfs

  6. Dwarfs in ancient Egypt.

    Science.gov (United States)

    Kozma, Chahira

    2006-02-15

    Ancient Egypt was one of the most advanced and productive civilizations in antiquity, spanning 3000 years before the "Christian" era. Ancient Egyptians built colossal temples and magnificent tombs to honor their gods and religious leaders. Their hieroglyphic language, system of organization, and recording of events give contemporary researchers insights into their daily activities. Based on the record left by their art, the ancient Egyptians documented the presence of dwarfs in almost every facet of life. Due to the hot dry climate and natural and artificial mummification, Egypt is a major source of information on achondroplasia in the old world. The remains of dwarfs are abundant and include complete and partial skeletons. Dwarfs were employed as personal attendants, animal tenders, jewelers, and entertainers. Several high-ranking dwarfs especially from the Old Kingdom (2700-2190 BCE) achieved important status and had lavish burial places close to the pyramids. Their costly tombs in the royal cemeteries and the inscriptions on their statutes indicate their high-ranking position in Egyptian society and their close relation to the king. Some of them were Seneb, Pereniankh, Khnumhotpe, and Djeder. There were at least two dwarf gods, Ptah and Bes. The god Ptah was associated with regeneration and rejuvenation. The god Bes was a protector of sexuality, childbirth, women, and children. He was a favored deity particularly during the Greco-Roman period. His temple was recently excavated in the Baharia oasis in the middle of Egypt. The burial sites and artistic sources provide glimpses of the positions of dwarfs in daily life in ancient Egypt. Dwarfs were accepted in ancient Egypt; their recorded daily activities suggest assimilation into daily life, and their disorder was not shown as a physical handicap. Wisdom writings and moral teachings in ancient Egypt commanded respect for dwarfs and other individuals with disabilities. Copyright (c) 2005 Wiley-Liss, Inc.

  7. The K Dwarf Advantage for Biosignatures

    Science.gov (United States)

    Arney, Giada; Domagal-Goldman, Shawn David; Meadows, Victoria

    2018-01-01

    Biosignature detection is typically studied in the context of an atmosphere in chemical disequilibrium. Oxygen (O2) and methane (CH4) are generally considered the “canonical” biosignature disequilibrium pair. However, the modern CH4 concentration poses a major detection challenge to future direct imaging telescopes, and it has been difficult for Earth to accumulate spectrally detectable quantities of O2 and CH4 over its history (Olson et al 2016, Reinhard et al 2017). Even the lower atmospheric levels of O2 typical of the Earth’s Proterozoic eon (0.01-1% of the modern O2 amount) may have resulted in a reduced photochemical lifetime of CH4 due to decreased UV shielding of CH4 (Claire et al 2006, Goldblatt et al 2006). However, while the above is true for an Earthlike planet orbiting a sunlike star, the situation changes for other stars. For instance, Segura et al (2005) found longer photochemical lifetimes for CH4 in the atmospheres of Earthlike planets orbiting M dwarfs. M dwarfs, however, present several barriers to planetary habitability including desiccation during the stellar super-luminous pre-main sequence phase (Lugar and Barnes 2015) and tidal locking. K dwarfs, which comprise about 12% of all main sequence stars, avoid these M dwarf hazards, and will be important targets for future exoplanet direct imaging missions. Using a photochemical model, we find CH4 and O2 are simultaneously detectable in the atmospheres of K dwarf planets with various O2 concentrations ranging between Proterozoic levels and modern O2 amounts. For instance, for a planet with an Earth-like CH4 surface flux (1 x 1011 molecules/cm2/s) and a Proterozoic-like O2 level (1% of modern), the planet generates a CH4 surface mixing ratio of 1x10-5 for a planet orbiting the sun, and 1.5x10-4 – an order of magnitude more CH4 – for a planet orbiting a K6V star. This is enough to produce detectable CH4 and O2 for the planet orbiting the K6V star. We discuss the implications of this

  8. [Human brown adipose tissue].

    Science.gov (United States)

    Virtanen, Kirsi A; Nuutila, Pirjo

    2015-01-01

    Adult humans have heat-producing and energy-consuming brown adipose tissue in the clavicular region of the neck. There are two types of brown adipose cells, the so-called classic and beige adipose cells. Brown adipose cells produce heat by means of uncoupler protein 1 (UCP1) from fatty acids and sugar. By applying positron emission tomography (PET) measuring the utilization of sugar, the metabolism of brown fat has been shown to multiply in the cold, presumably influencing energy consumption. Active brown fat is most likely present in young adults, persons of normal weight and women, least likely in obese persons.

  9. NEAR-INFRARED PHOTOMETRY OF Y DWARFS: LOW AMMONIA ABUNDANCE AND THE ONSET OF WATER CLOUDS

    International Nuclear Information System (INIS)

    Leggett, S. K.; Morley, Caroline V.; Marley, M. S.; Saumon, D.

    2015-01-01

    We present new near-infrared photometry for seven late-type T dwarfs and nine Y-type dwarfs, and lower limit magnitudes for a tenth Y dwarf, obtained at Gemini Observatory. We also present a reanalysis of H-band imaging data from the Keck Observatory Archive, for an 11th Y dwarf. These data are combined with earlier MKO-system photometry, Spitzer and WISE mid-infrared photometry, and available trigonometric parallaxes, to create a sample of late-type brown dwarfs that includes 10 T9-T9.5 dwarfs or dwarf systems, and 16 Y dwarfs. We compare the data to our models, which include updated H 2 and NH 3 opacity, as well as low-temperature condensate clouds. The models qualitatively reproduce the trends seen in the observed colors; however, there are discrepancies of around a factor of two in flux for the Y0-Y1 dwarfs, with T eff ≈ 350-400 K. At T eff ∼ 400 K, the problems could be addressed by significantly reducing the NH 3 absorption, for example by halving the abundance of NH 3 possibly by vertical mixing. At T eff ∼ 350 K, the discrepancy may be resolved by incorporating thick water clouds. The onset of these clouds might occur over a narrow range in T eff , as indicated by the observed small change in 5 μm flux over a large change in J – W2 color. Of the known Y dwarfs, the reddest in J –W2 are WISEP J182831.08+265037.8 and WISE J085510.83–071442.5. We interpret the former as a pair of identical 300-350 K dwarfs, and the latter as a 250 K dwarf. If these objects are ∼3 Gyr old, their masses are ∼10 and ∼5 Jupiter-masses, respectively

  10. The quiescent chromospheres and transition regions of active dwarf stars - What are we learning from recent observations and models?

    Science.gov (United States)

    Linsky, J. L.

    1983-01-01

    Progress in understanding active dwarf stars based on recent IUE, Einstein, and ground-based observations is reviewed. The extent of magnetic field control over nonflare phenomena in active dwarf stars is considered, and the spatial homogeneity and time variability of active dwarf atmospheres is discussed. The possibility that solar like flux tubes can explain enhanced heating in active dwarf stars in examined, and the roles of systematic flows in active dwarf star atmospheres are considered. The relation between heating rates in different layers of active dwarf stars is summarized, and the mechanism of chromosphere and transition region heating in these stars are discussed. The results of one-component and two-component models of active dwarf stars are addressed.

  11. Do micro brown dwarf detections explain the galactic dark matter?

    NARCIS (Netherlands)

    Nieuwenhuizen, T.M.; Schild, R.E; Gibson, C.H.

    2011-01-01

    The baryonic dark matter dominating the structures of galaxies is widely considered as mysterious, but hints for it have been in fact detected in several astronomical observations at optical, infrared, and radio wavelengths. We call attention to the pattern of star formation in a galaxy merger, the

  12. A Dark Spot on a Massive White Dwarf

    Science.gov (United States)

    Kilic, Mukremin; Gianninas, Alexandros; Bell, Keaton J.; Curd, Brandon; Brown, Warren R.; Hermes, J. J.; Dufour, Patrick; Wisniewski, John P.; Winget, D. E.; Winget, K. I.

    2015-12-01

    We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98+292801.9 (hereafter J1529+2928). We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity, which place it near the ZZ Ceti instability strip. Instead of pulsations, we detect photometric dips from this white dwarf every 38 minutes. Follow-up optical spectroscopy observations with Gemini reveal no significant radial velocity variations, ruling out stellar and brown dwarf companions. A disintegrating planet around this white dwarf cannot explain the observed light curves in different filters. Given the short period, the source of the photometric dips must be a dark spot that comes into view every 38 minutes due to the rotation of the white dwarf. Our optical spectroscopy does not show any evidence of Zeeman splitting of the Balmer lines, limiting the magnetic field strength to B Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  13. KECK NIRSPEC RADIAL VELOCITY OBSERVATIONS OF LATE-M DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Tanner, Angelle; White, Russel [Department of Astronomy, Georgia State University, One Park Place, Atlanta, GA 30303 (United States); Bailey, John [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Blake, Cullen [Department of Astrophysical Sciences, Princeton University, Peyton Hall, Ivy Lane, Princeton, NJ 08544 (United States); Blake, Geoffrey [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Cruz, Kelle [Department of Physics and Astronomy, Hunter College, 695 Park Avenue, New York, NY 10065 (United States); Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Kraus, Adam [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

    2012-11-15

    We present the results of an infrared spectroscopic survey of 23 late-M dwarfs with the NIRSPEC echelle spectrometer on the Keck II telescope. Using telluric lines for wavelength calibration, we are able to achieve measurement precisions of down to 45 m s{sup -1} for our late-M dwarfs over a one- to four-year long baseline. Our sample contains two stars with radial velocity (RV) variations of >1000 m s{sup -1}. While we require more measurements to determine whether these RV variations are due to unseen planetary or stellar companions or are the result of starspots known to plague the surface of M dwarfs, we can place upper limits of <40 M{sub J} sin i on the masses of any companions around those two M dwarfs with RV variations of <160 m s{sup -1} at orbital periods of 10-100 days. We have also measured the rotational velocities for all the stars in our late-M dwarf sample and offer our multi-order, high-resolution spectra over 2.0-2.4 {mu}m to the atmospheric modeling community to better understand the atmospheres of late-M dwarfs.

  14. KECK NIRSPEC RADIAL VELOCITY OBSERVATIONS OF LATE-M DWARFS

    International Nuclear Information System (INIS)

    Tanner, Angelle; White, Russel; Bailey, John; Blake, Cullen; Blake, Geoffrey; Cruz, Kelle; Burgasser, Adam J.; Kraus, Adam

    2012-01-01

    We present the results of an infrared spectroscopic survey of 23 late-M dwarfs with the NIRSPEC echelle spectrometer on the Keck II telescope. Using telluric lines for wavelength calibration, we are able to achieve measurement precisions of down to 45 m s –1 for our late-M dwarfs over a one- to four-year long baseline. Our sample contains two stars with radial velocity (RV) variations of >1000 m s –1 . While we require more measurements to determine whether these RV variations are due to unseen planetary or stellar companions or are the result of starspots known to plague the surface of M dwarfs, we can place upper limits of J sin i on the masses of any companions around those two M dwarfs with RV variations of –1 at orbital periods of 10-100 days. We have also measured the rotational velocities for all the stars in our late-M dwarf sample and offer our multi-order, high-resolution spectra over 2.0-2.4 μm to the atmospheric modeling community to better understand the atmospheres of late-M dwarfs.

  15. Using Laboratory Methods to Better Understand Refractory Cloud Formation in Exoplanet Atmospheres

    Science.gov (United States)

    Kohler, E.; Ferguson, F.

    2017-12-01

    The high number of extrasolar planets found in recent years has brought a new importance to planetary atmospheres. These recently discovered planets show a large diversity in their masses, temperatures, orbital periods, and other properties. With such a diverse mix of planetary parameters, it is safe to assume that the atmospheric properties are just as varied. Recent literature suggests silicates and metals as possible condensates in extrasolar planetary atmospheres as well as the atmospheres of brown dwarfs. While theoretical studies have laid the foundation of cloud formation analysis, their findings still need to be validated via experiments. A verification of the condensation and vaporization predictions of refractory materials needs to be found in order to assist global circulation models in being as accurate as possible. The stability of minerals identified in the literature as potential candidates, will be tested in a thermogravimetric balance. The minerals will be pumped under vacuum for twenty-four hours under room temperature and then heated to a predetermined high temperature, dependent on the expected vaporization temperature of that sample. If there is apparent mass loss, then the temperature will be lowered at preset durations and mass measurements will be taken in similar measured increments. The data will be processed by a computer program in order to calculate the mass loss as a function of temperature. The current cloud formation and global circulation models are very important to the field of planetary science but their accuracy is hindered by the lack of experimental data. The aim of this work is to investigate the mineral stability of potential condensates in an effort to explain the formation of refractory clouds in the atmospheres of extrasolar planets and brown dwarfs.

  16. Periodic optical variability of radio-detected ultracool dwarfs

    International Nuclear Information System (INIS)

    Harding, L. K.; Golden, A.; Singh, Navtej; Sheehan, B.; Butler, R. F.; Hallinan, G.; Boyle, R. P.; Zavala, R. T.

    2013-01-01

    A fraction of very low mass stars and brown dwarfs are known to be radio active, in some cases producing periodic pulses. Extensive studies of two such objects have also revealed optical periodic variability, and the nature of this variability remains unclear. Here, we report on multi-epoch optical photometric monitoring of six radio-detected dwarfs, spanning the ∼M8-L3.5 spectral range, conducted to investigate the ubiquity of periodic optical variability in radio-detected ultracool dwarfs. This survey is the most sensitive ground-based study carried out to date in search of periodic optical variability from late-type dwarfs, where we obtained 250 hr of monitoring, delivering photometric precision as low as ∼0.15%. Five of the six targets exhibit clear periodicity, in all cases likely associated with the rotation period of the dwarf, with a marginal detection found for the sixth. Our data points to a likely association between radio and optical periodic variability in late-M/early-L dwarfs, although the underlying physical cause of this correlation remains unclear. In one case, we have multiple epochs of monitoring of the archetype of pulsing radio dwarfs, the M9 TVLM 513–46546, spanning a period of 5 yr, which is sufficiently stable in phase to allow us to establish a period of 1.95958 ± 0.00005 hr. This phase stability may be associated with a large-scale stable magnetic field, further strengthening the correlation between radio activity and periodic optical variability. Finally, we find a tentative spin-orbit alignment of one component of the very low mass binary, LP 349–25.

  17. Periodic optical variability of radio-detected ultracool dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Harding, L. K.; Golden, A.; Singh, Navtej; Sheehan, B.; Butler, R. F. [Centre for Astronomy, National University of Ireland, Galway, University Road, Galway (Ireland); Hallinan, G. [Cahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Boyle, R. P. [Vatican Observatory Research Group, Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Zavala, R. T., E-mail: lkh@astro.caltech.edu [United States Naval Observatory, Flagstaff Station, Flagstaff, AZ 86001 (United States)

    2013-12-20

    A fraction of very low mass stars and brown dwarfs are known to be radio active, in some cases producing periodic pulses. Extensive studies of two such objects have also revealed optical periodic variability, and the nature of this variability remains unclear. Here, we report on multi-epoch optical photometric monitoring of six radio-detected dwarfs, spanning the ∼M8-L3.5 spectral range, conducted to investigate the ubiquity of periodic optical variability in radio-detected ultracool dwarfs. This survey is the most sensitive ground-based study carried out to date in search of periodic optical variability from late-type dwarfs, where we obtained 250 hr of monitoring, delivering photometric precision as low as ∼0.15%. Five of the six targets exhibit clear periodicity, in all cases likely associated with the rotation period of the dwarf, with a marginal detection found for the sixth. Our data points to a likely association between radio and optical periodic variability in late-M/early-L dwarfs, although the underlying physical cause of this correlation remains unclear. In one case, we have multiple epochs of monitoring of the archetype of pulsing radio dwarfs, the M9 TVLM 513–46546, spanning a period of 5 yr, which is sufficiently stable in phase to allow us to establish a period of 1.95958 ± 0.00005 hr. This phase stability may be associated with a large-scale stable magnetic field, further strengthening the correlation between radio activity and periodic optical variability. Finally, we find a tentative spin-orbit alignment of one component of the very low mass binary, LP 349–25.

  18. Solar system astrophysics planetary atmospheres and the outer solar system

    CERN Document Server

    Milone, Eugene F

    2008-01-01

    Solar System Astrophysics opens with coverage of the atmospheres, ionospheres and magnetospheres of the Earth, Venus and Mars and the magnetosphere of Mercury. The book then provides an introduction to meteorology and treating the physics and chemistry of these areas in considerable detail. What follows are the structure, composition, particle environments, satellites, and rings of Jupiter, Saturn, Uranus and Neptune, making abundant use of results from space probes. Solar System Astrophysics follows the history, orbits, structure, origin and demise of comets and the physics of meteors and provides a thorough treatment of meteorites, the asteroids and, in the outer solar system, the Kuiper Belt objects. The methods and results of extrasolar planet searches, the distinctions between stars, brown dwarfs, and planets, and the origins of planetary systems are examined. Historical introductions precede the development and discussion in most chapters. A series of challenges, useful as homework assignments or as foc...

  19. New inner boundaries of the habitable zones around M dwarfs

    Science.gov (United States)

    Bin, Jiayu; Tian, Feng; Liu, Lei

    2018-06-01

    Two general circulation models CAM4 and CAM5 are used to study the climate of ocean planets around M dwarfs with different effective temperatures. The atmospheres in CAM5 simulations are warmer and contain more water vapor than those in CAM4 under identical model settings, a result likely caused by improved treatments of radiation and possibly clouds in CAM5. The inner boundary of the habitable zones of M dwarfs based on CAM5 simulations, expressed as a second order polynomial function, are farther away from the stars than what are suggested by previous works and the corresponding atmospheres are in the moist greenhouse state.

  20. NOAA Ship Ronald Brown Underway Meteorological Data, Quality Controlled

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NOAA Ship Ronald Brown Underway Meteorological Data (delayed ~10 days for quality control) are from the Shipboard Automated Meteorological and Oceanographic System...

  1. NOAA Ship Ronald Brown Underway Meteorological Data, Near Real Time

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NOAA Ship Ronald Brown Underway Meteorological Data (Near Real Time, updated daily) are from the Shipboard Automated Meteorological and Oceanographic System (SAMOS)...

  2. Strain characterization of West African Dwarf Goats of Ogun State I ...

    African Journals Online (AJOL)

    Characterization of West African Dwarf goat is an approach to a sustainable use of its great potentials. In this study, strains of WAD goat were characterized using linear body measurement. The WAD goat included the gold (brown), black, buckskin and chaimose of ages 1, 2, 3 and 4 years,raised under extensive system of ...

  3. Asteroseismology of White Dwarf Stars

    Science.gov (United States)

    Hansen, Carl J.

    1997-01-01

    The primary purpose of this investigation has been to study various aspects of multimode pulsations in variable white dwarfs. In particular, nonlinear interactions among pulsation modes in white dwarfs (and, to some extent, in other variable stars), analysis of recent observations where such interactions are important, and preliminary work on the effects of crystallization in cool white dwarfs are reported.

  4. A Volume-Limited Sample of L and T Dwarfs Defined by Parallaxes

    Science.gov (United States)

    Best, William M. J.; Liu, Michael C.; Magnier, Eugene; Dupuy, Trent

    2018-01-01

    Volume-limited samples are the gold standard for stellar population studies, as they enable unbiased measurements of space densities and luminosity functions. Parallaxes are the most direct measures of distance and are therefore essential for defining high-confidence volume limited samples. Previous efforts to model the local brown dwarf population were hampered by samples based on a small number of parallaxes. We are using UKIRT/WFCAM to conduct the largest near-infrared program to date to measure parallaxes and proper motions of L and T dwarfs. For the past 3+ years we have monitored over 350 targets, ≈90% of which are too faint to be observed by Gaia. We present preliminary results from our observations. Our program more than doubles the number of known L and T dwarf parallaxes, defining a volume-limited sample of ≈400 L0-T6 dwarfs out to 25 parsecs, the first L and T dwarf sample of this size and depth based entirely on parallaxes. Our sample will combine with the upcoming stellar census from Gaia DR2 parallaxes to form a complete volume-limited sample of nearby stars and brown dwarfs.

  5. An Analysis of Coordinated Observations from NOAA’s Ronald H. Brown Ship and G-IV Aircraft in a Landfalling Atmospheric River over the North Pacific during CalWater-2015

    Energy Technology Data Exchange (ETDEWEB)

    Neiman, Paul J. [Physical Sciences Division, NOAA/Earth System Research Laboratory, Boulder, Colorado; Gaggini, Natalie [Science and Technology Corporation, and NOAA/Earth System Research Laboratory, Boulder, Colorado; Fairall, Christopher W. [Physical Sciences Division, NOAA/Earth System Research Laboratory, Boulder, Colorado; Aikins, Joshua [Cooperative Institute for Research in the Environmental Sciences, and NOAA/Earth System Research Laboratory, Boulder, Colorado; Spackman, J. Ryan [Science and Technology Corporation, and NOAA/Earth System Research Laboratory, Boulder, Colorado; Leung, L. Ruby [Pacific Northwest National Laboratory, Richland, Washington; Fan, Jiwen [Pacific Northwest National Laboratory, Richland, Washington; Hardin, Joseph [Pacific Northwest National Laboratory, Richland, Washington; Nalli, Nicholas R. [I. M. Systems Group, NOAA/NESDIS/STAR, College Park, Maryland; White, Allen B. [Physical Sciences Division, NOAA/Earth System Research Laboratory, Boulder, Colorado

    2017-09-01

    Using a diverse suite of mobile observing platforms deployed on NOAA’s Ronald H. Brown (RHB) research vessel and G-IV research aircraft during the CalWater-2015 field campaign, this study describes the structure and evolution of a long-lived atmospheric river (AR) modulated by six frontal waves over the northeastern Pacific on 20-25 January 2015. Satellite observations and reanalysis diagnostics provided synoptic-scale context, illustrating the warm, moist southwesterly airstream within the quasi-stationary AR situated between an upper-level trough and ridge. The AR remained offshore of the U.S. West Coast but made landfall across British Columbia where heavy precipitation and high melting levels occurred, resulting in flooding. Forty-seven rawinsondes launched from the RHB provided a comprehensive thermodynamic and kinematic depiction of the AR, including an upward intrusion of strong water-vapor transport in the low-level moist southwesterly flow during the passage of frontal waves 2 through 6. A collocated 1290-MHz wind profiler showed an abrupt frontal transition from southwesterly to northerly flow below 1 km MSL coinciding with the tail-end of AR conditions. Shipborne radar and disdrometer observations in the AR uniquely captured key microphysical characteristics of shallow warm rain, convection, and deep mixed-phase precipitation. Continuous and novel observations of sea-surface fluxes documented persistent ocean-surface evaporation into the AR and sensible-heat transfer from the AR into the ocean. The G-IV aircraft coordinated with the RHB and flew directly over the ship. Dropsonde and radar spatial analyses complemented the temporal depictions of the AR from the RHB. The AR characteristics varied, depending on the location of the cross section through the frontal waves.

  6. Stringent limits on the ionized mass loss from A and F dwarfs

    International Nuclear Information System (INIS)

    Brown, A.; Veale, A.; Judge, P.; Bookbinder, J.A.; Hubeny, I.

    1990-01-01

    Following the suggestion of Willson et al. (1987) that A- and F-type main-sequence stars might undergo significant mass loss due to pulsationally driven winds, upper limits to the ionized mass loss from A and F dwarfs have been obtained using VLA observations. These stringent upper limits show that the level of ionized mass loss would have at most only a small effect on stellar evolution. Radiative-equilibrium atmospheric and wind models for early A dwarfs indicate that it is highly likely that a wind flowing from such stars would be significantly ionized. In addition, late A and early F dwarfs exhibit chromospheric emission indicative of significant nonradiative heating. The present mass-loss limits are thus representative of the total mass-loss rates for these stars. It is concluded that A and F dwarfs are not losing sufficient mass to cause A dwarfs to evolve into G dwarfs. 24 refs

  7. The population of single and binary white dwarfs of the Galactic bulge

    Science.gov (United States)

    Torres, S.; García-Berro, E.; Cojocaru, R.; Calamida, A.

    2018-05-01

    Recent Hubble Space Telescope observations have unveiled the white dwarf cooling sequence of the Galactic bulge. Although the degenerate sequence can be well fitted employing the most up-to-date theoretical cooling sequences, observations show a systematic excess of red objects that cannot be explained by the theoretical models of single carbon-oxygen white dwarfs of the appropriate masses. Here, we present a population synthesis study of the white dwarf cooling sequence of the Galactic bulge that takes into account the populations of both single white dwarfs and binary systems containing at least one white dwarf. These calculations incorporate state-of-the-art cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient atmospheres, for both white dwarfs with carbon-oxygen and helium cores, and also take into account detailed prescriptions of the evolutionary history of binary systems. Our Monte Carlo simulator also incorporates all the known observational biases. This allows us to model with a high degree of realism the white dwarf population of the Galactic bulge. We find that the observed excess of red stars can be partially attributed to white dwarf plus main sequence binaries, and to cataclysmic variables or dwarf novae. Our best fit is obtained with a higher binary fraction and an initial mass function slope steeper than standard values, as well as with the inclusion of differential reddening and blending. Our results also show that the possible contribution of double degenerate systems or young and thick-discbulge stars is negligible.

  8. Thomson scattering in magnetic fields. [of white dwarf stars

    Science.gov (United States)

    Whitney, Barbara

    1989-01-01

    The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.

  9. Semi-dwarf mutants for rice improvement

    International Nuclear Information System (INIS)

    Othman, Ramli; Osman, Mohammad; Ibrahim, Rusli

    1990-01-01

    Full text: MARDI and the National University of Malaysia embarked on a programme to induce resistance against blast in rice in 1978. MARDI also obtained semi dwarf mutants of cvs 'Mahsuri', 'Muda', 'Pongsu seribu' and 'Jarum Mas', which are under evaluation. The popular local rice variety 'Manik' was subjected to gamma irradiation (15-40 krad) and 101 promising semidwarf mutants have been obtained following selection in M 2 -M 6 . 29 of them show grain yields of 6.0-7.3 t/ha, compared with 5.7t for 'Manik'. Other valuable mutants were found showing long grain, less shattering, earlier maturity, and glutinous endosperm. One mutant, resistant to brown plant hopper yields 6.3t/ha. (author)

  10. Lodgepole Pine Dwarf Mistletoe

    Science.gov (United States)

    Frank G. Hawksworth; Oscar J. Dooling

    1984-01-01

    Lodgepole pine dwarf mistletoe (Arceuthobium americanum Nutt. ex Engelm.) is a native, parasitic, seed plant that occurs essentially throughout the range of lodgepole pine in North America. It is the most damaging disease agent in lodgepole pine, causing severe growth loss and increased tree mortality. Surveys in the Rocky Mountains show that the parasite is found in...

  11. Sagittarius Dwarf Galaxy

    Science.gov (United States)

    Ibata, R.; Murdin, P.

    2000-11-01

    The Sagittarius DWARF GALAXY is the closest member of the Milky Way's entourage of satellite galaxies. Discovered by chance in 1994, its presence had previously been overlooked because it is largely hidden by the most crowded regions of our own Galaxy with which it is merging....

  12. Dwarf Eye Disorder

    Science.gov (United States)

    Science Teacher, 2005

    2005-01-01

    Johns Hopkins researchers at the Wilmer Eye Institute have discovered what appears to be the first human gene mutation that causes extreme farsightedness. The researchers report that nanophthalmos, Greek for "dwarf eye," is a rare, potentially blinding disorder caused by an alteration in a gene called MFRP that helps control eye growth and…

  13. Fir dwarf mistletoe (FIDL).

    Science.gov (United States)

    Gregory M. Filip; Jerome S. Beatty; Robert L. Mathiasen

    2000-01-01

    Fir dwarf mistletoe (Arceuthobium abietinum Engelmann ex Munz) is a common and damaging parasite of white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), and California red fir (A. magnifica A. Murr.) in the western...

  14. Dwarf Elliptical Galaxies

    Science.gov (United States)

    Caldwell, N.; Murdin, P.

    2000-11-01

    DWARF SPHEROIDAL GALAXIES were first identified by Shapley, who had noticed two very diffuse collections of stars on Harvard patrol plates. Although these systems had about as many stars as a GLOBULAR CLUSTER, they were of much lower density, and hence much larger radius, and thus were considered distinct galaxies. These two, named Fornax and Sculptor after the constellations in which they ap...

  15. A Predicted Astrometric Microlensing Event by a Nearby White Dwarf

    Science.gov (United States)

    McGill, Peter; Smith, Leigh C.; Wyn Evans, N.; Belokurov, Vasily; Smart, R. L.

    2018-04-01

    We used the Tycho-Gaia Astrometric Solution catalogue, part of Gaia Data Release 1, to search for candidate astrometric microlensing events expected to occur within the remaining lifetime of the Gaia satellite. Our search yielded one promising candidate. We predict that the nearby DQ type white dwarf LAWD 37 (WD 1142-645) will lens a background star and will reach closest approach on November 11th 2019 (± 4 days) with impact parameter 380 ± 10 mas. This will produce an apparent maximum deviation of the source position of 2.8 ± 0.1 mas. In the most propitious circumstance, Gaia will be able to determine the mass of LAWD 37 to ˜3%. This mass determination will provide an independent check on atmospheric models of white dwarfs with helium rich atmospheres, as well as tests of white dwarf mass radius relationships and evolutionary theory.

  16. ROTATIONAL VELOCITIES FOR M DWARFS

    International Nuclear Information System (INIS)

    Jenkins, J. S.; Ramsey, L. W.; Jones, H. R. A.; Pavlenko, Y.; Barnes, J. R.; Pinfield, D. J.; Gallardo, J.

    2009-01-01

    We present spectroscopic rotation velocities (v sin i) for 56 M dwarf stars using high-resolution Hobby-Eberly Telescope High Resolution Spectrograph red spectroscopy. In addition, we have also determined photometric effective temperatures, masses, and metallicities ([Fe/H]) for some stars observed here and in the literature where we could acquire accurate parallax measurements and relevant photometry. We have increased the number of known v sin i values for mid M stars by around 80% and can confirm a weakly increasing rotation velocity with decreasing effective temperature. Our sample of v sin is peak at low velocities (∼3 km s -1 ). We find a change in the rotational velocity distribution between early M and late M stars, which is likely due to the changing field topology between partially and fully convective stars. There is also a possible further change in the rotational distribution toward the late M dwarfs where dust begins to play a role in the stellar atmospheres. We also link v sin i to age and show how it can be used to provide mid-M star age limits. When all literature velocities for M dwarfs are added to our sample, there are 198 with v sin i ≤ 10 km s -1 and 124 in the mid-to-late M star regime (M3.0-M9.5) where measuring precision optical radial velocities is difficult. In addition, we also search the spectra for any significant Hα emission or absorption. Forty three percent were found to exhibit such emission and could represent young, active objects with high levels of radial-velocity noise. We acquired two epochs of spectra for the star GJ1253 spread by almost one month and the Hα profile changed from showing no clear signs of emission, to exhibiting a clear emission peak. Four stars in our sample appear to be low-mass binaries (GJ1080, GJ3129, Gl802, and LHS3080), with both GJ3129 and Gl802 exhibiting double Hα emission features. The tables presented here will aid any future M star planet search target selection to extract stars with low v

  17. Observations of M dwarfs beyond 2.2 μm

    International Nuclear Information System (INIS)

    Berriman, G.

    1987-01-01

    This paper presents the first systematic spectroscopic observations of M dwarfs beyond 2.2μm. The coolest dwarfs show strong water absorption in the 3μm window, and beyond 4μm, the energy distributions of all the stars fall slightly less steeply than the Rayleigh-Jeans tail of a blackbody. Spectra between 1 and 4μm are essential in deriving accurate luminosities of M dwarfs, and possibly in deriving accurate effective temperatures too. New values reported here are not in general well explained by theoretical models of hydrogen burning stars. This is especially true for those cooler than 3000K: in the HR diagram they lie closer to brown dwarfs, in contrast to recent results based only on photometry. (author)

  18. Photometry, Astrometry, and Discoveries of Ultracool Dwarfs in the Pan-STARRS 3π Survey

    Science.gov (United States)

    Best, William M. J.; Magnier, Eugene A.; Liu, Michael C.; Deacon, Niall; Aller, Kimberly; Zhang, Zhoujian; Pan-STARRS1 Builders

    2018-01-01

    The Pan-STARRS1 3π Survey (PS1)'s far-red optical sensitivity makes it an exceptional new resource for discovering and characterizing ultracool dwarfs. We present a PS1-based catalog of photometry and proper motions of nearly 10,000 M, L, and T dwarfs, along with our analysis of the kinematics of nearby M6-T9 dwarfs, building a comprehensive picture of the local ultracool population. We highlight some especially interesting ultracool discoveries made with PS1, including brown dwarfs with spectral types in the enigmatic L/T transition, wide companions to main sequence stars that serve as age and metallicity bechmarks for substellar models, and free-floating members of the nearby young moving groups and star-forming regions with masses down to ≈5 MJup. With its public release, PS1 will continue to be a vital tool for studying the ultracool population.

  19. Brown adipocyte function

    DEFF Research Database (Denmark)

    Winther, Sally

    . The first part of this thesis explores this by identifying and investigating two novel kinase regulators of brown adipocyte function. Study 1 demonstrates that spleen tyrosine kinase is a hitherto undescribed regulator of brown adipocyte differentiation and activation. Study 2 identifies glycogen synthase...

  20. Theoretical models for asteroseismology of DA white dwarf stars

    Energy Technology Data Exchange (ETDEWEB)

    Bradley, P.A. [XTA, MS B220, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    1996-09-01

    Because white dwarfs are the most common end state of stellar evolution, determining their internal structure will yield many clues about the final stages of stellar evolution and the physics of matter under extreme conditions. We present the results of our parametric survey of evolutionary models of compositionally stratified white dwarfs with hydrogen surface layers (DA white dwarfs) and provide a comprehensive set of theoretical {ital g}-mode pulsation periods for comparison to observations of pulsating DA white dwarfs. This survey complements the previous survey of helium atmosphere (DB) white dwarf periods of Bradley, Winget, & Wood. We show how to use the periods of low-overtone and/or trapped modes to constrain the internal structure of pulsating DA white dwarfs by utilizing their sensitivity to the total stellar mass and the location of the hydrogen/helium transition zone. We use G117-B15A as an example to demonstrate the potential of our models for asteroseismology; we suggest that G117-B15A has a mass of 0.55 {ital M}{sub {circle_dot}} and a hydrogen layer mass of {approx_equal}1.5{times}10{sup {minus}4} {ital M}{sub {asterisk}}. {copyright} {ital 1996 The American Astronomical Society.}

  1. The habitability of planets orbiting M-dwarf stars

    Science.gov (United States)

    Shields, Aomawa L.; Ballard, Sarah; Johnson, John Asher

    2016-12-01

    The prospects for the habitability of M-dwarf planets have long been debated, due to key differences between the unique stellar and planetary environments around these low-mass stars, as compared to hotter, more luminous Sun-like stars. Over the past decade, significant progress has been made by both space- and ground-based observatories to measure the likelihood of small planets to orbit in the habitable zones of M-dwarf stars. We now know that most M dwarfs are hosts to closely-packed planetary systems characterized by a paucity of Jupiter-mass planets and the presence of multiple rocky planets, with roughly a third of these rocky M-dwarf planets orbiting within the habitable zone, where they have the potential to support liquid water on their surfaces. Theoretical studies have also quantified the effect on climate and habitability of the interaction between the spectral energy distribution of M-dwarf stars and the atmospheres and surfaces of their planets. These and other recent results fill in knowledge gaps that existed at the time of the previous overview papers published nearly a decade ago by Tarter et al. (2007) and Scalo et al. (2007). In this review we provide a comprehensive picture of the current knowledge of M-dwarf planet occurrence and habitability based on work done in this area over the past decade, and summarize future directions planned in this quickly evolving field.

  2. Nearby Red Dwarfs are Sexy for Planets and Life

    Science.gov (United States)

    Henry, T. J.; Jao, W.-C.; Subasavage, J. P.; RECONS Team

    2005-12-01

    The RECONS group continues to discover many nearby red dwarfs in the southern sky through a combination of proper motion surveys, literature review, and ultimately, our parallax program CTIOPI. Already, we have measured the first accurate parallaxes for 11 of the nearest 100 stellar systems, including four within 5 parsecs of the Sun. These nearby red dwarfs are prime candidates for NASA's Space Interferometry Mission (SIM) because the astrometric perturbations are largest for planets orbiting stars of low mass that are nearby. In addition, new multiple red dwarf systems can be targeted for mass determinations, thereby providing points on a comprehensive mass-luminosity relation for the most populous members of the Galaxy. Recent atmospheric modeling of planets orbiting red dwarfs indicates that even if the planets are tidally locked, heat distribution is highly effective in keeping the worlds balmy over the entire surface. Red dwarfs are therefore "back on the table" as viable hosts of life-bearing planets. Given their ubiquity, red dwarfs are being seriously considered as prime SETI targets, and will allow us to answer not only the question "Are We Alone?" but "Just How Alone Are We?" This work has been supported by the National Science Foundation, NASA's Space Interferometry Mission, and Georgia State University.

  3. THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Michael C. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Dupuy, Trent J. [The University of Texas at Austin, Department of Astronomy, 2515 Speedway C1400, Austin, TX 78712 (United States); Allers, Katelyn N., E-mail: mliu@ifa.hawaii.edu [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States)

    2016-12-10

    We present a large, uniform analysis of young (≈10–150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (vl-g) late-M and L dwarfs form a continuous sequence in IR color–magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity (vl-g) objects have the most uniform photometric behavior, while intermediate gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. Notable individual objects in our sample include high-velocity (≳100 km s{sup −1}) int-g objects, very red late-L dwarfs with high surface gravities, candidate disk-bearing members of the MBM20 cloud and β  Pic moving group, and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102

  4. Temperatures and luminosities of white dwarfs in dwarf novae

    International Nuclear Information System (INIS)

    Smak, J.

    1984-01-01

    Far ultraviolet radiation observed in dwarf novae at minimum can only be attributed to their white dwarfs. In three systems white dwarfs are detected directly through their eclipses. These data are used to determine the effective temperatures and luminosities of white dwarfs. The resulting temperatures range from about logT e = 4.1 to about 4.9, with typical values of about 4.5. The luminosities range from about logL 1 = 31.0 to about 33.5 and show correlation with the average accretion rates. Radiation from white dwarfs is likely to be the source of excitation of the emission lines from disks. It is also argued that the heating by the white dwarf can significantly modify the structure of the innermost parts of the disk and, particularly, inhibit the incidence of thermal instability in that region. 26 refs., 2 figs., 1 tab. (author)

  5. Four faint T dwarfs from the UKIRT Infrared Deep Sky Survey (UKIDSS) Southern Stripe

    Science.gov (United States)

    Chiu, Kuenley; Liu, Michael C.; Jiang, Linhua; Allers, Katelyn N.; Stark, Daniel P.; Bunker, Andrew; Fan, Xiaohui; Glazebrook, Karl; Dupuy, Trent J.

    2008-03-01

    We present the optical and near-infrared photometry and spectroscopy of four faint T dwarfs newly discovered from the UKIDSS first data release. The sample, drawn from an imaged area of ~136 deg2 to a depth of Y = 19.9 (5σ, Vega), is located in the Sloan Digital Sky Survey (SDSS) Southern Equatorial Stripe, a region of significant future deep imaging potential. We detail the selection and followup of these objects, three of which are spectroscopically confirmed brown dwarfs ranging from type T2.5 to T7.5, and one is photometrically identified as early T. Their magnitudes range from Y = 19.01 to 19.88 with derived distances from 34 to 98 pc, making these among the coldest and faintest brown dwarfs known. The T7.5 dwarf appears to be single based on 0.05-arcsec images from Keck laser guide star adaptive optics. The sample brings the total number of T dwarfs found or confirmed by UKIDSS data in this region to nine, and we discuss the projected numbers of dwarfs in the future survey data. We estimate that ~240 early and late T dwarfs are discoverable in the UKIDSS Large Area Survey (LAS) data, falling significantly short of published model projections and suggesting that initial mass functions and/or birth rates may b