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Sample records for transition circumstellar disks

  1. THE NATURE OF TRANSITION CIRCUMSTELLAR DISKS. II. SOUTHERN MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Romero, Gisela A.; Schreiber, Matthias R.; Rebassa-Mansergas, Alberto [Departamento de Fisica y Astronomia, Universidad de Valparaiso, Valparaiso (Chile); Cieza, Lucas A. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Merin, Bruno [Herschel Science Centre, ESAC (ESA), P.O. Box 78, 28691 Villanueva de la Canada, Madrid (Spain); Smith Castelli, Analia V. [Consejo Nacional de Investigaciones Cientificas y Tecnicas, Rivadavia 1917, C1033AAJ Buenos Aires (Argentina); Allen, Lori E. [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Morrell, Nidia [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile)

    2012-04-10

    Transition disk objects are pre-main-sequence stars with little or no near-IR excess and significant far-IR excess, implying inner opacity holes in their disks. Here we present a multifrequency study of transition disk candidates located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius. Complementing the information provided by Spitzer with adaptive optics (AO) imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy (Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and accretion rate for each object in our sample in order to identify the mechanism potentially responsible for its inner hole. We find that our transition disks show a rich diversity in their spectral energy distribution morphology, have disk masses ranging from {approx}<1 to 10 M{sub JUP}, and accretion rates ranging from {approx}<10{sup -11} to 10{sup -7.7} M{sub Sun} yr{sup -1}. Of the 17 bona fide transition disks in our sample, three, nine, three, and two objects are consistent with giant planet formation, grain growth, photoevaporation, and debris disks, respectively. Two disks could be circumbinary, which offers tidal truncation as an alternative origin of the inner hole. We find the same heterogeneity of the transition disk population in Lupus III, IV, and Corona Australis as in our previous analysis of transition disks in Ophiuchus while all transition disk candidates selected in Lupus V, VI turned out to be contaminating background asymptotic giant branch stars. All transition disks classified as photoevaporating disks have small disk masses, which indicates that photoevaporation must be less efficient than predicted by most recent models. The three systems that are excellent candidates for harboring giant planets potentially represent invaluable laboratories to study planet formation with the Atacama Large Millimeter/Submillimeter Array.

  2. [OI] in circumstellar disks

    Science.gov (United States)

    Sandell, Goran

    2018-01-01

    In the far-infrared, [OI] 63 micron is the most sensitive probe of gas in protoplanetary disks and has even been detected in several young debris disks.We have now obtained velocity resolved spectra (velocity resolution 0.1 km/s) using the heterodyne receiver GREAT on the Stratospheric Observatory for Infrared Astronomy (SOFIA) of five of the brightest circumstellar disks in the [OI] 63 micron line. Four of these are protoplanetary disks (AB Aur, HL Tau, HD 100546 and HD 97048), while one is a disk around an FS CMa star, HD 50138. Since all the stars are surrounded by disks in Keplerian rotation, our observations allow us to explore where the [OI] emission originates and the physical conditions of the [OI] emitting layers. In this presentation we present preliminary results of our findings.

  3. The Nature of Transition Circumstellar Disks. III. Perseus, Taurus, and Auriga

    Science.gov (United States)

    Cieza, Lucas A.; Schreiber, Matthias R.; Romero, Gisela A.; Williams, Jonathan P.; Rebassa-Mansergas, Alberto; Merín, Bruno

    2012-05-01

    As part of an ongoing program aiming to characterize a large number of Spitzer-selected transition disks (disks with reduced levels of near-IR and/or mid-IR excess emission), we have obtained (sub)millimeter wavelength photometry, high-resolution optical spectroscopy, and adaptive optics near-infrared imaging for a sample of 31 transition objects located in the Perseus, Taurus, and Auriga molecular clouds. We use these ground-based data to estimate disk masses, multiplicity, and accretion rates in order to investigate the mechanisms potentially responsible for their inner holes. Following our previous studies in other regions, we combine disk masses, accretion rates, and multiplicity data with other information, such as spectral energy distribution morphology and fractional disk luminosity, to classify the disks as strong candidates for the following categories: grain-growth-dominated disks (seven objects), giant planet-forming disks (six objects), photoevaporating disks (seven objects), debris disks (11 objects), and cicumbinary disks (one object, which was also classified as a photoevaporating disk). Combining our sample of 31 transition disks with those from our previous studies results in a sample of 74 transition objects that have been selected, characterized, and classified in a homogenous way. We discuss this combined high-quality sample in the context of the current paradigm of the evolution and dissipation of protoplanetary disks and use its properties to constrain different aspects of the key processes driving their evolution. We find that the age distribution of disks that are likely to harbor recently formed giant planets favors core accretion as the main planet formation mechanism and a ~2-3 Myr formation timescale. Based in part on observations made with the CFHT, under programs 09BH48, 09BH10, 10AH06, and 10BH97.

  4. Circumstellar disks around binary stars in Taurus

    International Nuclear Information System (INIS)

    Akeson, R. L.; Jensen, E. L. N.

    2014-01-01

    We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10 –4 M ☉ . We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F mm ∝M ∗ 1.5--2.0 to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

  5. Circumstellar disks around binary stars in Taurus

    Energy Technology Data Exchange (ETDEWEB)

    Akeson, R. L. [NASA Exoplanet Science Institute, IPAC/Caltech, Pasadena, CA 91125 (United States); Jensen, E. L. N. [Swarthmore College, Department of Physics and Astronomy, Swarthmore, PA 19081 (United States)

    2014-03-20

    We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10{sup –4} M {sub ☉}. We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F{sub mm}∝M{sub ∗}{sup 1.5--2.0} to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

  6. Circumstellar Gas in Young Planetary Debris Disks

    Science.gov (United States)

    Roberge, A.

    Circumstellar (CS) disks orbiting young stars fall into two categories: primordial disks, composed of unprocessed interstellar dust and gas, and debris disks, produced by the destruction of solid planetary bodies. In the first class, the most abundant gas is H_2; in the second, it appears that the H_2 gas has disappeared, possibly through incorporation into gas giant planets. The lifetime of H_2 gas in a CS disk is therefore of great importance, as it dictates the timescale for the formation of giant planets. FUSE observations of H_2 in CS disk systems have shown that FUV absorption spectroscopy may sensitively probe for small amounts of gas along the line of sight to the star. Most importantly, the FUSE non-detection of H_2 gas in the Beta Pictoris disk suggests that the primordial gas lifetime is less than about 12 Myr, and that gas giant planets must form very quickly. However, this suggestion is based on one system, and needs to be tested in additional systems with a range of ages, especially since there are indications that age is not the only factor in the evolution of a CS disk. We propose for FUSE observations of 3 additional debris disk systems, Fomalhaut, HD3003, and HD2884. Fomalhaut is an intermediate age debris disk, one of the Fabulous Four CS disks first discovered in 1984. The other two disks are younger, with ages similar to that of Beta Pic. All three stars are brighter in the FUV than Beta Pic, permitting us to sensitively probe for traces of H_2 gas. We will also measure the amount of secondary atomic gas produced from planetary bodies in these disks, in an effort to understand the entire evolution of CS gas in young planetary systems.

  7. A WISE survey of circumstellar disks in Taurus

    International Nuclear Information System (INIS)

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

    2014-01-01

    We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ∼M8 (M ≳ 0.03 M ☉ ).

  8. A WISE survey of circumstellar disks in Taurus

    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); Mamajek, E. E., E-mail: taran.esplin@psu.edu [Department of Physics and Astronomy, The University of Rochester, Rochester, NY 14627 (United States)

    2014-04-01

    We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ∼M8 (M ≳ 0.03 M {sub ☉}).

  9. WFIRST: CGI Detection and Characterization of Circumstellar Disks

    Science.gov (United States)

    Debes, John; Chen, Christine; Dawson, Bekki; Douglas, Ewan S.; Duchene, Gaspard; Jang-Condell, Hannah; hines, Dean C.; Lewis, Nikole K.; Macintosh, Bruce; Mazoyer, Johan; Meshkat, Tiffany; Nemati, Bijan; Patel, Rahul; Perrin, Marshall; Poteet, Charles; Pueyo, Laurent; Ren, Bin; Rizzo, Maxime; Roberge, Aki; Stark, Chris; Turnbull, Margaret

    2018-01-01

    The WFIRST Coronagraphic Instrument (CGI) will be capable of obtaining up to 5×10-9 contrast to an inner working angle of ~150 mas for a selection of medium band visible light filters using shaped pupil coronagraph and hybrid Lyot coronagraph designs. We present initial work at defining the scientific capabilities of the CGI with respect to different types of circumstellar disks, including warm exo-zodiacal disks, cold debris disks, and protoplanetary disks. With the above designs, CGI will be able to detect bright protoplanetary and debris disks with sizes of >100 AU beyond 500 pc. Additionally, it will be able to discover warm exozodiacal dust disks ten times more massive than that of the Solar System for over 100 nearby solar-type stars. Finally, it will be able to characterize resolved circumstellar dust disks in multiple filters of visible light, providing constraints on the size, shape, and composition of the dust.

  10. High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

    Science.gov (United States)

    Serabyn, G.; Grady, C. A.; Currie, T.

    2012-01-01

    We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.15" (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a spatial resolution of 0.1" (14 AU). It is inclined by 46 degrees plus or minus 2 degrees as the west side is nearest. Although SED modeling and sub-millimeter imagery suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at the limit of our inner working angle (23AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66 %) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh scattering nor Mie scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with the radii of 30 micrometers is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations and have grown in the circumstellar disk of UX Tau A.

  11. High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

    Science.gov (United States)

    Tanii, Ryoko; Itoh, Yoichi; Kudo, Tomoyuki; Hioki, Tomonori; Oasa, Yumiko; Gupta, Ranjan; Sen, Asoke K.; Wisniewski, John P.; Muto, Takayuki; Grady, Carol A.; Hashimoto, Jun; Fukagawa, Misato; Mayama, Satoshi; Hornbeck, Jeremy; Sitko, Michael L.; Russell, Ray W.; Werren, Chelsea; Curé, Michel; Currie, Thayne; Ohashi, Nagayoshi; Okamoto, Yoshiko; Momose, Munetake; Honda, Mitsuhiko; Inutsuka, Shu-ichi; Takeuchi, Taku; Dong, Ruobing; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph; Egner, Sebastian E.; Feldt, Markus; Fukue, Tsubasa; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kusakabe, Nobuhiko; Kuzuhara, Masayuki; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-ichi; Moro-Martín, Amaya; Nishimura, Tetsuro; Pyo, Tae-Soo; Serabyn, Eugene; Suto, Hiroshi; Suzuki, Ryuji; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    2012-12-01

    We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.''15 (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A, which extends to 120 AU, at a spatial resolution of 0.''1 (14 AU). It is inclined by 46° ± 2°, since the west side is nearest. Although SED modeling and sub-millimeter imagery have suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25-30 AU, we detect no evidence of a gap at the limit of our inner working angle (23 AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66%) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh-scattering nor Mie-scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with radii of 30μm is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations, and have grown in the circumstellar disk of UX Tau A.

  12. Studies of Young, Star-forming Circumstellar Disks

    Science.gov (United States)

    Bae, Jaehan

    2017-08-01

    Disks of gas and dust around forming stars - circumstellar disks - last only a few million years. This is a very small fraction of the entire lifetime of Sun-like stars, several billion years. Nevertheless, by the time circumstellar disks dissipate stars complete building up their masses, giant planets finish accreting gas, and terrestrial bodies are nearly fully grown and ready for their final assembly to become planets. Understanding the evolution of circumstellar disks are thus crucial in many contexts. Using numerical simulations as the primary tool, my thesis has focused on the studies of various physical processes that can occur throughout the lifetime of circumstellar disks, from their formation to dispersal. Chapters 2, 3, and 4 emphasize the importance of early evolution, during which time a forming star-disk system obtains mass from its natal cloud: the infall phase. In Chapter 2 and 3, I have modeled episodic outbursts of accretion in protostellar systems resulting from disk instabilities - gravitational instability and magnetorotational instability. I showed that outbursts occur preferentially during the infall phase, because the mass addition provides more favorable conditions for gravitational instability to initiate the outburst cycle, and that forming stars build up a significant fraction of their masses through repeated short-lived, episodic outbursts. The infall phase can also be important for the formation of planets. Recent ALMA observations revealed sets of bright and dark rings in circumstellar disks of young, forming stars, potentially indicating early formation of planets. In Chapter 4, I showed that infall streams can create radial pressure bumps near the outer edge of the mass landing on the disk, from which vortices can form, collecting solid particles very efficiently to make initial seeds of planets. The next three chapters highlight the role of planets in setting the observational appearance and the evolution of circumstellar disks

  13. Magnetic braking in weakly ionized circumstellar disks

    Science.gov (United States)

    Koenigl, A.

    1986-01-01

    Recent observations of disk-like mass distributions around newly formed stars have provided evidence for rapid rotation on scales similar to less than 0.1pc with specific angular momenta much higher than typical stellar values. A likely mechanism for the extraction of angular momentum from these regions is magnetic braking by means of Alfven waves that propagate into the lower-density ambient medium. However, because of the relatively high particle densities and the correspondingly low implied ionization fractions in these apparent disks, their constituent ions and neutrals need not be well coupled to each other and could develop large relative drift velocities. For this reason, previous treatments of magnetic braking that assumed perfect coupling between ions and neutrals have to be modified in this case. In particular, one has to take into account both the azimuthal drift that develops because only the ions are directly coupled to the magnetic field and the radial drift (or ambipolar diffusion) which leads to a redistribution (and leakage) of the magnetic flux. The results of a preliminary analysis of these effects are described.

  14. Circumstellar Disk Lifetimes In Numerous Galactic Young Stellar Clusters

    Science.gov (United States)

    Richert, A. J. W.; Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Broos, P. S.; Povich, M. S.; Bate, M. R.; Garmire, G. P.

    2018-04-01

    Photometric detections of dust circumstellar disks around pre-main sequence (PMS) stars, coupled with estimates of stellar ages, provide constraints on the time available for planet formation. Most previous studies on disk longevity, starting with Haisch, Lada & Lada (2001), use star samples from PMS clusters but do not consider datasets with homogeneous photometric sensitivities and/or ages placed on a uniform timescale. Here we conduct the largest study to date of the longevity of inner dust disks using X-ray and 1-8 {μ m} infrared photometry from the MYStIX and SFiNCs projects for 69 young clusters in 32 nearby star-forming regions with ages t ≤ 5 Myr. Cluster ages are derived by combining the empirical AgeJX method with PMS evolutionary models, which treat dynamo-generated magnetic fields in different ways. Leveraging X-ray data to identify disk-free objects, we impose similar stellar mass sensitivity limits for disk-bearing and disk-free YSOs while extending the analysis to stellar masses as low as M ˜ 0.1 M⊙. We find that the disk longevity estimates are strongly affected by the choice of PMS evolutionary model. Assuming a disk fraction of 100% at zero age, the inferred disk half-life changes significantly, from t1/2 ˜ 1.3 - 2 Myr to t1/2 ˜ 3.5 Myr when switching from non-magnetic to magnetic PMS models. In addition, we find no statistically significant evidence that disk fraction varies with stellar mass within the first few Myr of life for stars with masses <2 M⊙, but our samples may not be complete for more massive stars. The effects of initial disk fraction and star-forming environment are also explored.

  15. ALIGNMENT OF PROTOSTARS AND CIRCUMSTELLAR DISKS DURING THE EMBEDDED PHASE

    International Nuclear Information System (INIS)

    Spalding, Christopher; Batygin, Konstantin; Adams, Fred C.

    2014-01-01

    Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulence within cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation in the orientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling, such disk-tilting would provide a natural mechanism for the production of primordial spin-orbit misalignments in the resulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inner edge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretional angular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitational coupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. The joint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wandering widens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of the protostar's gaseous envelope. Accordingly, the processes described in this work provide an additional mechanism responsible for sculpting the stellar initial mass function

  16. Interaction of a Supernova with a Circumstellar Disk

    Science.gov (United States)

    McDowell, Austin T.; Duffell, Paul C.; Kasen, Daniel

    2018-03-01

    Interaction between a supernova (SN) ejecta and a dense circumstellar medium (CSM) can power a luminous light curve and create narrow emission lines in the spectra. While theoretical studies of interaction often assume a spherically symmetric CSM, there are observational indications that the gas surrounding some SNe has a disk-like geometry. Here, we use moving-mesh hydrodynamics simulations to study the interaction of an SN with a disk and determine how the dynamics and observable signatures may depend on the disk mass, thickness, and radial extent. We find that simple modifications to standard spherically-symmetric scaling laws can be used to describe the propagation and heating rate of the interaction shock. We use the resulting shock heating rates to derive approximate bolometric light curves, and provide analytic formulas that can be used to generate simple synthetic light curves for general supernova-disk interactions. For certain disk parameters and explosion energies, we are able to produce luminosities akin to those seen in super-luminous SNe. Because the SN ejecta can flow around and engulf the CSM disk, the interaction region may become embedded and, from certain viewing angles, the narrow emission lines indicative of interaction may be hidden.

  17. A High-mass Protobinary System with Spatially Resolved Circumstellar Accretion Disks and Circumbinary Disk

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, S.; Kluska, J.; Kreplin, A.; Bate, M.; Harries, T. J.; Hone, E.; Anugu, A. [School of Physics, Astrophysics Group, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Hofmann, K.-H.; Weigelt, G. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Monnier, J. D. [Department of Astronomy, University of Michigan, 311 West Hall, 1085 South University Avenue, Ann Arbor, MI 48109 (United States); De Wit, W. J. [ESO, Alonso de Cordova 3107, Vitacura, Santiago 19 (Chile); Wittkowski, M., E-mail: skraus@astro.ex.ac.uk [ESO, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany)

    2017-01-20

    High-mass multiples might form via fragmentation of self-gravitational disks or alternative scenarios such as disk-assisted capture. However, only a few observational constraints exist on the architecture and disk structure of high-mass protobinaries and their accretion properties. Here, we report the discovery of a close (57.9 ± 0.2 mas = 170 au) high-mass protobinary, IRAS17216-3801, where our VLTI/GRAVITY+AMBER near-infrared interferometry allows us to image the circumstellar disks around the individual components with ∼3 mas resolution. We estimate the component masses to ∼20 and ∼18 M {sub ⊙} and find that the radial intensity profiles can be reproduced with an irradiated disk model, where the inner regions are excavated of dust, likely tracing the dust sublimation region in these disks. The circumstellar disks are strongly misaligned with respect to the binary separation vector, which indicates that the tidal forces did not have time to realign the disks, pointing toward a young dynamical age of the system. We constrain the distribution of the Br γ and CO-emitting gas using VLTI/GRAVITY spectro-interferometry and VLT/CRIRES spectro-astrometry and find that the secondary is accreting at a higher rate than the primary. VLT/NACO imaging shows L ′-band emission on (3–4)× larger scales than the binary separation, matching the expected dynamical truncation radius for the circumbinary disk. The IRAS17216-3801 system is ∼3× more massive and ∼5× more compact than other high-mass multiplies imaged at infrared wavelength and the first high-mass protobinary system where circumstellar and circumbinary dust disks could be spatially resolved. This opens exciting new opportunities for studying star–disk interactions and the role of multiplicity in high-mass star formation.

  18. ALMA OBSERVATIONS OF HD 141569’s CIRCUMSTELLAR DISK

    Energy Technology Data Exchange (ETDEWEB)

    White, J. A.; Boley, A. C. [Department of Physics and Astronomy, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Hughes, A. M.; Flaherty, K. M. [Department of Astronomy, Van Vleck Observatory, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States); Ford, E. [Center for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802-2111 (United States); Wilner, D.; Payne, M. [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Corder, S., E-mail: jawhite@astro.ubc.ca [North American ALMA Science Center, National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA, 22903 (United States)

    2016-09-20

    We present ALMA band 7 (345 GHz) continuum and {sup 12}CO( J = 3-2) observations of the circumstellar disk surrounding HD 141569. At an age of about 5 Myr, the disk has a complex morphology that may be best interpreted as a nascent debris system with gas. Our 870 μ m ALMA continuum observations resolve a dust disk out to approximately 56 au from the star (assuming a distance of 116 pc) with 0.″38 resolution and 0.07 mJy beam{sup −1} sensitivity. We measure a continuum flux density for this inner material of 3.8 ± 0.4 mJy (including calibration uncertainties). The {sup 12}CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated {sup 12}CO(3-2) line flux density is 15.7 ± 1.6 Jy km s{sup −1}. We estimate the mass of the millimeter debris and {sup 12}CO(3-2) gas to be ≳0.04 M {sub ⊕} and ∼2 × 10{sup −3} M {sub ⊕}, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk (<50 au) has ∼160 M {sub ⊕} contained within objects less than 50 km in radius, depending on the planetesimal size distribution and density assumptions. Markov Chain Monte Carlo modeling of the system reveals a disk morphology with an inclination of 53.°4 centered around an M = 2.39 M {sub ⊙} host star ( M sin( i ) = 1.92 M {sub ⊙}). We discuss whether the gas in HD 141569's disk may be second generation. If it is, the system can be used to study the clearing stages of planet formation.

  19. Disk Detective: Discovery of New Circumstellar Disk Candidates through Citizen Science

    OpenAIRE

    Kuchner, Marc J.; Silverberg, Steven M.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; Garcia, Luciano; Jung, Dawoon; Lintott, Chris; McElwain, Michael; Padgett, Deborah L.; Rebull, Luisa M.; Wisniewski, John P.; Nesvold, Erika

    2016-01-01

    The Disk Detective citizen science project aims to find new stars with 22 μm excess emission from circumstellar dust using data from NASA's Wide-field Infrared Survey Explorer (WISE) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10 different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectr...

  20. Discovery of a Circumstellar Disk in the Lagoon Nebula

    Science.gov (United States)

    1997-04-01

    Circumstellar disks of gas and dust play a crucial role in the formation of stars and planets. Until now, high-resolution images of such disks around young stars within the Orion Nebula obtained with the Hubble Space Telescope (HST) constituted the most direct proof of their existence. Now, another circumstellar disk has been detected around a star in the Lagoon Nebula - also known as Messier 8 (M8) , a giant complex of interstellar gas and dust with many young stars in the southern constellation of Sagittarius and four times more distant than the Orion Nebula. The observations were carried out by an international team of scientists led by Bringfried Stecklum (Thüringer Landessternwarte, Tautenburg, Germany) [1] who used telescopes located at the ESO La Silla observatory and also observations from the HST archive. These new results are paving the road towards exciting research programmes on star formation which will become possible with the ESO Very Large Telescope. The harsh environment of circumstellar disks The existence of circumstellar disks has been inferred from indirect measurements of young stellar objects, such as the spectral energy distribution, the analysis of the profiles of individual spectral lines and measurements of the polarisation of the emitted light [2]. Impressive images of such disks in the Orion Nebula, known as proplyds (PROto-PLanetarY DiskS), have been obtained by the HST during the recent years. They have confirmed the interpretation of previous ground-based emission-line observations and mapping by radio telescopes. Moreover, they demonstrated that those disks which are located close to hot and massive stars are subject to heating caused by the intense radiation from these stars. Subsequently, the disks evaporate releasing neutral gas which streams off. During this process, shock fronts (regions with increased density) with tails of ionised gas result at a certain distance between the disk and the hot star. These objects appear on

  1. Grand-design Spiral Arms in a Young Forming Circumstellar Disk

    Energy Technology Data Exchange (ETDEWEB)

    Tomida, Kengo; Lin, Chia Hui [Department of Earth and Space Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Machida, Masahiro N. [Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, Nishi-ku, Fukuoka 819-0395 (Japan); Hosokawa, Takashi [Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Sakurai, Yuya, E-mail: tomida@vega.ess.sci.osaka-u.ac.jp [Department of Physics, The University of Tokyo, Tokyo 113-0033 (Japan)

    2017-01-20

    We study formation and long-term evolution of a circumstellar disk in a collapsing molecular cloud core using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues, and its radius becomes as large as 200 au toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum in the highly resistive disk. Although the spiral arms disappear in a few rotations as expected in a classical theory, new spiral arms form recurrently as the disk, soon becoming unstable again by gas accretion. Such recurrent spiral arms persist throughout the Class-0 and I phases. We then perform synthetic observations and compare our model with a recent high-resolution observation of a young stellar object Elias 2–27, whose circumstellar disk has grand-design spiral arms. We find good agreement between our theoretical model and the observation. Our model suggests that the grand-design spiral arms around Elias 2–27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.

  2. DISK DETECTIVE: DISCOVERY OF NEW CIRCUMSTELLAR DISK CANDIDATES THROUGH CITIZEN SCIENCE

    Energy Technology Data Exchange (ETDEWEB)

    Kuchner, Marc J.; McElwain, Michael; Padgett, Deborah L. [NASA Goddard Space Flight Center Exoplanets and Stellar Astrophysics Laboratory, Code 667 Greenbelt, MD 21230 (United States); Silverberg, Steven M.; Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy The University of Oklahoma 440 W. Brooks St. Norman, OK 73019 (United States); Bans, Alissa S. [Valparaiso University, Department of Physics and Astronomy, Neils Science Center, 1610 Campus Drive East, Valparaiso, IN 46383 (United States); Bhattacharjee, Shambo [International Space University 1 Rue Jean-Dominique Cassini F-67400 Illkirch-Graffenstaden (France); Kenyon, Scott J. [Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 (United States); Debes, John H. [Space Telescope Science Institute 3700 San Martin Dr. Baltimore, MD 21218 (United States); Currie, Thayne [National Astronomical Observatory of Japan 650 N A’ohokhu Place Hilo, HI 96720 (United States); García, Luciano [Observatorio Astronómico de Córdoba Universidad Nacional de Córdoba Laprida 854, X5000BGR, Córdoba (Argentina); Jung, Dawoon [Korea Aerospace Research Institute Lunar Exploration Program Office 169-84 Gwahak-ro, Yuseong-gu, Daejeon 34133 (Korea, Republic of); Lintott, Chris [Denys Wilkinson Building Keble Road Oxford, OX1 3RH (United Kingdom); Rebull, Luisa M. [Infrared Processing and Analaysis Center Caltech M/S 314-6 1200 E. California Blvd. Pasadena, CA 91125 (United States); Nesvold, Erika, E-mail: Marc.Kuchner@nasa.gov, E-mail: michael.w.mcelwain@nasa.gov, E-mail: deborah.l.padgett@nasa.gov, E-mail: carol.a.grady@nasa.gov, E-mail: silverberg@ou.edu, E-mail: wisniewski@ou.edu [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305 (United States); Collaboration: Disk Detective Collaboration; and others

    2016-10-20

    The Disk Detective citizen science project aims to find new stars with 22 μ m excess emission from circumstellar dust using data from NASA’s Wide-field Infrared Survey Explorer ( WISE ) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10 different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and protoplanetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137, and HD 218546) and a new detection of 22 μ m excess around the previously known debris disk host star HD 22128.

  3. Disk Detective: Discovery of New Circumstellar Disk Candidates Through Citizen Science

    Science.gov (United States)

    Kuchner, Marc J.; Silverberg, Steven M.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; Garcia, Luciano; Jung, Dawoon; Lintott, Chris; hide

    2016-01-01

    The Disk Detective citizen science project aims to find new stars with 22 micron excess emission from circumstellar dust using data from NASAs Wide-field Infrared Survey Explorer (WISE) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and proto planetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137,and HD 218546) and a new detection of 22 micron excess around the previously known debris disk host star HD 22128.

  4. DISK DETECTIVE: DISCOVERY OF NEW CIRCUMSTELLAR DISK CANDIDATES THROUGH CITIZEN SCIENCE

    International Nuclear Information System (INIS)

    Kuchner, Marc J.; McElwain, Michael; Padgett, Deborah L.; Silverberg, Steven M.; Wisniewski, John P.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; García, Luciano; Jung, Dawoon; Lintott, Chris; Rebull, Luisa M.; Nesvold, Erika

    2016-01-01

    The Disk Detective citizen science project aims to find new stars with 22 μ m excess emission from circumstellar dust using data from NASA’s Wide-field Infrared Survey Explorer ( WISE ) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10 different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and protoplanetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137, and HD 218546) and a new detection of 22 μ m excess around the previously known debris disk host star HD 22128.

  5. A deep Spitzer survey of circumstellar disks in the young double cluster, h and χ Persei

    Energy Technology Data Exchange (ETDEWEB)

    Cloutier, Ryan; Currie, Thayne; Jayawardhana, Ray [University of Toronto, 50 St. George Street, Toronto, ON, M5S 2J7 (Canada); Rieke, George H. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Kenyon, Scott J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02140 (United States); Balog, Zoltan, E-mail: cloutier@cita.utoronto.ca, E-mail: currie@astro.utoronto.ca, E-mail: grieke@as.arizona.edu, E-mail: skenyon@cfa.harvard.edu [Max Planck Institute for Astrophysics, Königstuhl 17, D-69117 Heidelberg (Germany)

    2014-12-01

    We analyze very deep Infrared Array Camera and Multiband Imaging Photometer for Spitzer (MIPS) photometry of ∼12, 500 members of the 14 Myr old Double Cluster, h and χ Persei, building upon our earlier, shallower Spitzer Cycle 1 studies. Numerous likely members show infrared (IR) excesses at 8 μm and 24 μm, indicative of circumstellar dust. The frequency of stars with 8 μm excess is at least 2% for our entire sample, slightly lower (higher) for B/A stars (later type, lower mass stars). Optical spectroscopy also identifies gas in about 2% of systems, but with no clear trend between the presence of dust and gas. Spectral energy distribution modeling of 18 sources with detections at optical wavelengths through MIPS 24 μm reveals a diverse set of disk evolutionary states, including a high fraction of transitional disks, though similar data for all disk-bearing members would provide constraints. Using Monte Carlo simulations, we combine our results with those for other young clusters to study the global evolution of dust/gas disks. For nominal cluster ages, the e-folding times (τ{sub 0}) for the frequency of warm dust and gas are 2.75 Myr and 1.75 Myr, respectively. Assuming a revised set of ages for some clusters, these timescales increase to 5.75 and 3.75 Myr, respectively, implying a significantly longer typical protoplanetary disk lifetime than previously thought. In both cases, the transitional disk duration, averaged over multiple evolutionary pathways, is ≈1 Myr. Finally, 24 μm excess frequencies for 4-6 M {sub ☉} stars appear lower than for 1-2.5 M {sub ☉} stars in other 10-30 Myr old clusters.

  6. Volatile-rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk

    NARCIS (Netherlands)

    Roberge, Aki; Welsh, Barry Y.; Kamp, Inga; Weinberger, Alycia J.; Grady, Carol A.

    2014-01-01

    We present Hubble Space Telescope Space Telescope Imaging Spectrograph far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing submillimeter CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying

  7. Observational constraints for the circumstellar disk of the B[e] star CPD-52 9243

    Science.gov (United States)

    Cidale, L. S.; Borges Fernandes, M.; Andruchow, I.; Arias, M. L.; Kraus, M.; Chesneau, O.; Kanaan, S.; Curé, M.; de Wit, W. J.; Muratore, M. F.

    2012-12-01

    Context. The formation and evolution of gas and dust environments around B[e] supergiants are still open issues. Aims: We intend to study the geometry, kinematics and physical structure of the circumstellar environment (CE) of the B[e] supergiant CPD-52 9243 to provide further insights into the underlying mechanism causing the B[e] phenomenon. Methods: The influence of the different physical mechanisms acting on the CE (radiation pressure, rotation, bi-stability or tidal forces) is somehow reflected in the shape and kinematic properties of the gas and dust regions (flaring, Keplerian, accretion or outflowing disks). To investigate these processes we mainly used quasi-simultaneous observations taken with high spatial resolution optical long-baseline interferometry (VLTI/MIDI), near-IR spectroscopy of CO bandhead features (Gemini/Phoenix and VLT/CRIRES) and optical spectra (CASLEO/REOSC). Results: High angular resolution interferometric measurements obtained with VLTI/MIDI provide strong support for the presence of a dusty disk(ring)-like structure around CPD-52 9243, with an upper limit for its inner edge of ~8 mas (~27.5 AU, considering a distance of 3.44 kpc to the star). The disk has an inclination angle with respect to the line of sight of 46 ± 7°. The study of CO first overtone bandhead evidences a disk structure in Keplerian rotation. The optical spectrum indicates a rapid outflow in the polar direction. Conclusions: The IR emission (CO and warm dust) indicates Keplerian rotation in a circumstellar disk while the optical line transitions of various species are consistent with a polar wind. Both structures appear simultaneously and provide further evidence for the proposed paradigms of the mass-loss in supergiant B[e] stars. The presence of a detached cold CO ring around CPD-52 9243 could be due to a truncation of the inner disk caused by a companion, located possibly interior to the disk rim, clearing the center of the system. More spectroscopic and

  8. The First 40 Million Years of Circumstellar Disk Evolution: The Signature of Terrestrial Planet Formation

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Huan Y. A.; Rieke, George H.; Su, Kate Y. L.; Gáspár, András, E-mail: hyameng@lpl.arizona.edu [Steward Observatory, Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2017-02-10

    We characterize the first 40 Myr of evolution of circumstellar disks through a unified study of the infrared properties of members of young clusters and associations with ages from 2 Myr up to ∼40 Myr: NGC 1333, NGC 1960, NGC 2232, NGC 2244, NGC 2362, NGC 2547, IC 348, IC 2395, IC 4665, Chamaeleon I, Orion OB1a and OB1b, Taurus, the β Pictoris Moving Group, ρ Ophiuchi, and the associations of Argus, Carina, Columba, Scorpius–Centaurus, and Tucana–Horologium. Our work features: (1) a filtering technique to flag noisy backgrounds; (2) a method based on the probability distribution of deflections, P ( D ), to obtain statistically valid photometry for faint sources; and (3) use of the evolutionary trend of transitional disks to constrain the overall behavior of bright disks. We find that the fraction of disks three or more times brighter than the stellar photospheres at 24 μ m decays relatively slowly initially and then much more rapidly by ∼10 Myr. However, there is a continuing component until ∼35 Myr, probably due primarily to massive clouds of debris generated in giant impacts during the oligarchic/chaotic growth phases of terrestrial planets. If the contribution from primordial disks is excluded, the evolution of the incidence of these oligarchic/chaotic debris disks can be described empirically by a log-normal function with the peak at 12–20 Myr, including ∼13% of the original population, and with a post-peak mean duration of 10–20 Myr.

  9. Variable Circumstellar Extinction in a Protoplanetary Disk with an Embedded Low-Mass Companion

    Science.gov (United States)

    Demidova, T. V.; Grinin, V. P.

    2017-06-01

    The motion of the low-mass companion embedded in a protoplanetary disk perturbs the disk matter periodically. It leads to the large-scale inhomogenity formation. Such structures in the disk have to influence on the propagation of the radiation from a star to an observer. If the protoplanetary disk is observed almost edge-on the structures will intersect the line of sight periodically. We use the hydrodynamic simulations of such disks to explore how an invisible low-mass companions in protoplanetary disks can affect on the circumstellar extinction and the light curves of the young star. The models with circular and eccentric, inclined and coplanar companions orbits were calculated. Our modification of the GADGET-2 code is used for the calculations. The column density of the test particles on the line of sight was calculated as a function of phase of the orbital period. If we propose the dust is well mixed with gas in the ratio 1:100 the column density function determines the behaviour the circumstellar extinction. Our calculations show the periodic variations of the circumstellar extinction can originate in the CB-disk as well in the CS-disk. The results can be used for the explanation of the cyclic activity of UX Ori type stars.

  10. Fe I in the β Pictoris circumstellar gas disk. I. Physical properties of the neutral iron gas

    Science.gov (United States)

    Vidal-Madjar, A.; Kiefer, F.; Lecavelier des Etangs, A.; Bourrier, V.; Ehrenreich, D.; Ferlet, R.; Hébrard, G.; Wilson, P. A.

    2017-10-01

    The young planetary system β Pictoris is surrounded by a circumstellar disk of dust and gas. Because both dust and gas have a lifetime shorter than the system age, they need to be replenished continuously. The gas composition is partly known, but its location and its origin are still a puzzle. The gas source could be the exocomets (or so-called falling and evaporating bodies, FEBs), which are observed as transient features in absorption lines of refractory elements (Mg, Ca, and Fe) when they transit in front of the star at several tens of stellar radii. Nearly 1700 high-resolution spectra of β Pictoris have been obtained from 2003 to 2015 using the HARPS spectrograph. In these spectra, the circumstellar disk is always detected as a stable component among the numerous variable absorption signatures of transiting exocomets. Summing all the 1700 spectra allowed us to reach a signal-to-noise ratio higher than 1000, which is an unprecedentedly high number for a β Pictoris spectrum. It revealed many weak Fe I absorption lines of the circumstellar gas in more than ten excited states. These weak lines bring new information on the physical properties of the neutral iron gas in the circumstellar disk. The population of the first excited levels follows a Boltzmann distribution with a slope consistent with a gas temperature of about 1300 K; this temperature corresponds to a distance to the star of 38 RStar and implies a turbulence of ξ 0.8 km s-1. A copy of the averaged spectrum (FITS file) is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A25

  11. MIGRATION OF PLANETS EMBEDDED IN A CIRCUMSTELLAR DISK

    International Nuclear Information System (INIS)

    Bromley, Benjamin C.; Kenyon, Scott J.

    2011-01-01

    Planetary migration poses a serious challenge to theories of planet formation. In gaseous and planetesimal disks, migration can remove planets as quickly as they form. To explore migration in a planetesimal disk, we combine analytic and numerical approaches. After deriving general analytic migration rates for isolated planets, we use N-body simulations to confirm these results for fast and slow migration modes. Migration rates scale as m -1 (for massive planets) and (1 + (e H /3) 3 ) -1 , where m is the mass of a planet and e H is the eccentricity of the background planetesimals in Hill units. When multiple planets stir the disk, our simulations yield the new result that large-scale migration ceases. Thus, growing planets do not migrate through planetesimal disks. To extend these results to migration in gaseous disks, we compare physical interactions and rates. Although migration through a gaseous disk is an important issue for the formation of gas giants, we conclude that migration has little impact on the formation of terrestrial planets.

  12. New circumstellar disk candidates around young low mass stars and brown dwarfs

    Science.gov (United States)

    Boucher, Anne; Lafrenière, David; Gagné, Jonathan; Malo, Lison; Doyon, Rene

    2015-12-01

    It is now common knowledge that circumstellar disks are signposts of past or ongoing planetary system formation. Their presence and their properties, in relation to those of their host star, also bear valuable information about the process of star formation itself. To address these questions, we started a project to uncover new circumstellar disks around newly identified low mass star and brown dwarf candidates in nearby young kinematic associations. Being near the stellar/substellar mass boundary, these hosts - and their potential disks - are particularly interesting to study both star and planet formation. We used a least squares approach to fit synthetic spectra to the observed photometric data of each star, covering from 0.8 µm up to 22 µm, and then identified candidates showing a significant excess compared to the best fits. We then carefully looked at the data for these candidates to filter out those biased by contaminants or other artefacts. We ended up with a list of 4 young stars and brown dwarfs strongly suspected of being surrounded by a disk. Here we will present our search method and some properties of our newly identified disk-bearing candidates.

  13. Evidence of Dissipation of Circumstellar Disks from L-band Spectra of Bright Galactic Be Stars

    Science.gov (United States)

    Sabogal, B. E.; Ubaque, K. Y.; García-Varela, A.; Álvarez, M.; Salas, L.

    2017-01-01

    We present L-band spectra of the Be stars γ Cas, ϕ Per, 28 Tau, θ CrB, 66 Oph, o Her, and 28 Cyg, obtained through use of the CID-InSb spectrograph with the 2.1-m telescope at OAN/UNAM San Pedro Martir Observatory. This is the first report of L-band spectra of o Her and θ CrB, and of the data obtained with this spectrograph. We obtain flux ratios of hydrogen lines for these stars, finding that they have optically thin envelopes, except by 66 Oph and θ CrB, which do not show evidence of a circumstellar disk. γ Cas and ϕ Per have flux ratio values of hydrogen lines closer to the optically thick case than the other stars. We use the line flux ratio diagram and optical spectra reported in the literature to study the life cycles of the disks. We find clear evidence of the dissipating process of the envelopes of 66 Oph and 28 Cyg, i.e., they are decaying stars. 28 Tau seems to have passed by a similar process. γ Cas and ϕ Per are stable stars because their circumstellar disks do not show notorious changes for many years. Finally, the stars in a build-up phase, whose envelopes are generated after a decaying phase or for the first time, have not yet been observed in the L-band. It would be useful to monitor more Be stars to observe this class of stars that probably change from a very tenuous envelope to an optically thick circumstellar disk. The line flux ratio diagram seems to confirm that late Be stars have more tenuous disks than early-type Be stars, as they tend to be separated at the left bottom and the top right parts of the diagram, respectively. Larger samples of Be stars are needed to confirm this hypothesis through a statistical analysis.

  14. DYNAMICS OF CIRCUMSTELLAR DISKS. III. THE CASE OF GG Tau A

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, Andrew F. [XCP-2, Mailstop T082, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Marzari, F., E-mail: andy.nelson@lanl.gov, E-mail: francesco.marzari@pd.infn.it [Università di Padova, Dipartimento di Fisica, via Marzolo 8, 35131 Padova (Italy)

    2016-08-20

    We present two-dimensional hydrodynamic simulations using the Smoothed Particle Hydrodynamic code, VINE, to model a self-gravitating binary system. We model configurations in which a circumbinary torus+disk surrounds a pair of stars in orbit around each other and a circumstellar disk surrounds each star, similar to that observed for the GG Tau A system. We assume that the disks cool as blackbodies, using rates determined independently at each location in the disk by the time dependent temperature of the photosphere there. We assume heating due to hydrodynamical processes and to radiation from the two stars, using rates approximated from a measure of the radiation intercepted by the disk at its photosphere. We simulate a suite of systems configured with semimajor axes of either a = 62 AU (“wide”) or a = 32 AU (“close”), and with assumed orbital eccentricity of either e = 0 or e = 0.3. Each simulation follows the evolution for ∼6500–7500 yr, corresponding to about three orbits of the torus around the center of mass. Our simulations show that strong, sharply defined spiral structures are generated from the stirring action of the binary and that, in some cases, these structures fragment into 1–2 massive clumps. The torus quickly fragments into several dozen such fragments in configurations in which either the binary is replaced by a single star of equal mass, or radiative heating is neglected. The spiral structures extend inwards to the circumstellar environment as large scale material streams for which most material is found on trajectories that return it to the torus on a timescale of 1–200 yr, with only a small fraction accreting into the circumstellar environment. The spiral structures also propagate outwards through the torus, generating net outwards mass flow, and eventually losing coherence at large distances from the stars. The torus becomes significantly eccentric in shape over most of its evolution. In all configurations, accretion onto the

  15. THE FIRST DETERMINATION OF THE VISCOSITY PARAMETER IN THE CIRCUMSTELLAR DISK OF A Be STAR

    Energy Technology Data Exchange (ETDEWEB)

    Carciofi, Alex C.; Bjorkman, Jon E.; Haubois, Xavier [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, 05508-900, Sao Paulo, SP (Brazil); Otero, Sebastian A. [American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138 (United States); Okazaki, Atsuo T. [Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062-8605 (Japan); Stefl, Stanislav; Rivinius, Thomas [European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19 (Chile); Baade, Dietrich, E-mail: carciofi@usp.br, E-mail: jon@physics.utoledo.edu [European Organisation for Astronomical Research in the Southern Hemisphere, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen (Germany)

    2012-01-15

    Be stars possess gaseous circumstellar decretion disks, which are well described using standard {alpha}-disk theory. The Be star 28 CMa recently underwent a long outburst followed by a long period of quiescence, during which the disk dissipated. Here we present the first time-dependent models of the dissipation of a viscous decretion disk. By modeling the rate of decline of the V-band excess, we determine that the viscosity parameter {alpha} = 1.0 {+-} 0.2, corresponding to a mass injection rate M-dot =(3.5{+-}1.3) Multiplication-Sign 10{sup -8} M{sub Sun} yr{sup -1}. Such a large value of {alpha} suggests that the origin of the turbulent viscosity is an instability in the disk whose growth is limited by shock dissipation. The mass injection rate is more than an order of magnitude larger than the wind mass-loss rate inferred from UV observations, implying that the mass injection mechanism most likely is not the stellar wind, but some other mechanism.

  16. Revealing the inclined circumstellar disk in the UX Ori system KK Ophiuchi

    Science.gov (United States)

    Kreplin, A.; Weigelt, G.; Kraus, S.; Grinin, V.; Hofmann, K.-H.; Kishimoto, M.; Schertl, D.; Tambovtseva, L.; Clausse, J.-M.; Massi, F.; Perraut, K.; Stee, Ph.

    2013-07-01

    We study the inner sub-AU region of the circumstellar environment of the UX Ori type star KK Oph with near-infrared VLTI/AMBER interferometry. We are particularly interested in the inclination of the star-disk system, and we will use this information to test the current standard picture for UX Ori stars. We recorded spectrally dispersed (R˜35) interferograms in the near-infrared H and K bands with the VLTI/AMBER instrument. The derived visibilities, closure phases and the SED of KK Oph were compared with two-dimensional geometric and radiative transfer models (RADMC). We obtained visibilities at four different position angles. Using two-dimensional geometric models, we derive an axis ratio ˜3.0 corresponding to an inclination of ˜70 degree. A fitted inclined ring model leads to a ring radius of 2.8 ± 0.2 mas, corresponding to 0.44 ± 0.03 AU at a distance of 160 pc, which is larger than the dust sublimation radius of ˜0.1 AU predicted for a dust sublimation temperature of 1500 K. Our derived two-dimensional RADMC model consists of a circumstellar disk with an inclination angle of ˜70 degree and an additional dust envelope. The finding of an ˜70 degree inclined disk around KK Oph is consistent with the prediction that UX Ori objects are seen under large inclination angles, and orbiting clouds in the line of sight cause the observed variability. Furthermore, our results suggest that the orbit of the companion KK Oph B and the disk plane are coplanar.

  17. Revealing the inclined circumstellar disk in the UX Orionis system KK Ophiuchi

    Science.gov (United States)

    Kreplin, A.; Weigelt, G.; Kraus, S.; Grinin, V.; Hofmann, K.-H.; Kishimoto, M.; Schertl, D.; Tambovtseva, L.; Clausse, J.-M.; Massi, F.; Perraut, K.; Stee, Ph.

    2013-03-01

    Aims: We study the inner sub-AU region of the circumstellar environment of the UX Ori-type star KK Oph with near-infrared VLTI/AMBER interferometry. We are particularly interested in the inclination of the star-disk system, and we use this information to test the current standard picture for UX Ori stars. Methods: We recorded spectrally dispersed (R ~ 35) interferograms in the near-infrared H and K bands with the VLTI/AMBER instrument. The derived visibilities, closure phases, and the spectral energy distribution of KK Oph were compared with two-dimensional geometric and radiative transfer models (RADMC). Results: We obtained visibilities at four different position angles. Using two-dimensional geometric models, we derive an axis ratio ~3.0 corresponding to an inclination of ~70°. A fitted inclined ring model leads to a ring radius of 2.8 ± 0.2 mas, corresponding to 0.44 ± 0.03 AU at a distance of 160 pc, which is larger than the dust sublimation radius of ~0.1 AU predicted for a dust sublimation temperature of 1500 K. Our derived two-dimensional RADMC model consists of a circumstellar disk with an inclination angle of ~70° and an additional dust envelope. Conclusions: The finding of an ~70° inclined disk around KK Oph is consistent with the prediction that UX Ori objects are seen under large inclination angles, and orbiting clouds in the line of sight cause the observed variability. Furthermore, our results suggest that the orbit of the companion KK Oph B and the disk plane are coplanar. Based on observations made with ESO telescopes at Paranal Observatory under program ID: 083.D-0224(C) and 088.C-0575(A).

  18. THE REINCARNATION OF INTERSTELLAR DUST: THE IMPORTANCE OF ORGANIC REFRACTORY MATERIAL IN INFRARED SPECTRA OF COMETARY COMAE AND CIRCUMSTELLAR DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, Hiroshi, E-mail: hiroshi_kimura@cps-jp.org [Graduate School of Science, Kobe University, c/o CPS (Center for Planetary Science), Chuo-ku Minatojima Minamimachi 7-1-48, Kobe 650-0047 (Japan)

    2013-09-20

    We consider the reincarnation of interstellar dust to be reborn in protoplanetary disks as aggregates consisting of submicron-sized grains with a crystalline or amorphous silicate core and an organic-rich carbonaceous mantle. We find that infrared spectra of reincarnated interstellar dust reproduce emission peaks at correct wavelengths where the peaks were observed in cometary comae, debris disks, and protoplanetary disks if the volume fraction of organic refractory meets the constraints on elemental abundances. We discuss what we can learn from the infrared spectra of reincarnated interstellar dust in cometary comae and circumstellar disks.

  19. The Reincarnation of Interstellar Dust: The Importance of Organic Refractory Material in Infrared Spectra of Cometary Comae and Circumstellar Disks

    Science.gov (United States)

    Kimura, Hiroshi

    2013-09-01

    We consider the reincarnation of interstellar dust to be reborn in protoplanetary disks as aggregates consisting of submicron-sized grains with a crystalline or amorphous silicate core and an organic-rich carbonaceous mantle. We find that infrared spectra of reincarnated interstellar dust reproduce emission peaks at correct wavelengths where the peaks were observed in cometary comae, debris disks, and protoplanetary disks if the volume fraction of organic refractory meets the constraints on elemental abundances. We discuss what we can learn from the infrared spectra of reincarnated interstellar dust in cometary comae and circumstellar disks.

  20. THE REINCARNATION OF INTERSTELLAR DUST: THE IMPORTANCE OF ORGANIC REFRACTORY MATERIAL IN INFRARED SPECTRA OF COMETARY COMAE AND CIRCUMSTELLAR DISKS

    International Nuclear Information System (INIS)

    Kimura, Hiroshi

    2013-01-01

    We consider the reincarnation of interstellar dust to be reborn in protoplanetary disks as aggregates consisting of submicron-sized grains with a crystalline or amorphous silicate core and an organic-rich carbonaceous mantle. We find that infrared spectra of reincarnated interstellar dust reproduce emission peaks at correct wavelengths where the peaks were observed in cometary comae, debris disks, and protoplanetary disks if the volume fraction of organic refractory meets the constraints on elemental abundances. We discuss what we can learn from the infrared spectra of reincarnated interstellar dust in cometary comae and circumstellar disks

  1. The inner circumstellar disk of the UX Orionis star V1026 Scorpii

    Science.gov (United States)

    Vural, J.; Kreplin, A.; Kishimoto, M.; Weigelt, G.; Hofmann, K.-H.; Kraus, S.; Schertl, D.; Dugué, M.; Duvert, G.; Lagarde, S.; Massi, F.

    2014-04-01

    Context. The UX Ori type variables (named after the prototype of their class) are intermediate-mass pre-main sequence objects. One of the most likely causes of their variability is the obscuration of the central star by orbiting dust clouds. Aims: We investigate the structure of the circumstellar environment of the UX Ori star V1026 Sco (HD 142666) and test whether the disk inclination is large enough to explain the UX Ori variability. Methods: We observed the object in the low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument and derived H- and K-band visibilities and closure phases. We modeled our AMBER observations, published Keck Interferometer observations, archival MIDI/VLTI visibilities, and the spectral energy distribution using geometric and temperature-gradient models. Results: Employing a geometric inclined-ring disk model, we find a ring radius of 0.15 ± 0.06 AU in the H band and 0.18 ± 0.06 AU in the K band. The best-fit temperature-gradient model consists of a star and two concentric, ring-shaped disks. The inner disk has a temperature of 1257+133-53 K at the inner rim and extends from 0.19 ± 0.01 AU to 0.23 ± 0.02 AU. The outer disk begins at 1.35+0.19-0.20 AU and has an inner temperature of 334+35-17 K. The derived inclination of 48.6+2.9-3.6° approximately agrees with the inclination derived with the geometric model (49 ± 5° in the K band and 50 ± 11° in the H band). The position angle of the fitted geometric and temperature-gradient models are 163 ± 9° (K band; 179 ± 17° in the H band) and 169.3+4.2-6.7°, respectively. Conclusions: The narrow width of the inner ring-shaped model disk and the disk gap might be an indication for a puffed-up inner rim shadowing outer parts of the disk. The intermediate inclination of ~50° is consistent with models of UX Ori objects where dust clouds in the inclined disk obscure the central star. Based on observations made with ESO telescopes at the La Silla Paranal Observatory

  2. IDENTIFYING NEARBY, YOUNG, LATE-TYPE STARS BY MEANS OF THEIR CIRCUMSTELLAR DISKS

    International Nuclear Information System (INIS)

    Schneider, Adam; Song, Inseok; Melis, Carl; Zuckerman, B.; Bessell, Mike

    2012-01-01

    It has recently been shown that a significant fraction of late-type members of nearby, very young associations (age ∼<10 Myr) display excess emission at mid-IR wavelengths indicative of dusty circumstellar disks. We demonstrate that the detection of mid-IR excess emission can be utilized to identify new nearby, young, late-type stars including two definite new members ('TWA 33' and 'TWA 34') of the TW Hydrae Association (TWA). Both new TWA members display mid-IR excess emission in the Wide-field Infrared Survey Explorer catalog and they show proper motion and youthful spectroscopic characteristics—namely, Hα emission, strong lithium absorption, and low surface gravity features consistent with known TWA members. We also detect mid-IR excess—the first unambiguous evidence of a dusty circumstellar disk—around a previously identified UV-bright, young, accreting star (2M1337) that is a likely member of the Lower-Centaurus Crux region of the Scorpius-Centaurus Complex.

  3. The circumstellar disk of AB Aurigae: evidence for envelope accretion at late stages of star formation?

    Science.gov (United States)

    Tang, Y.-Wen; Guilloteau, S.; Piétu, V.; Dutrey, A.; Ohashi, N.; Ho, P. T. P.

    2012-11-01

    Aims: The circumstellar disk of AB Aurigae has garnered strong attention owing to the apparent existence of spirals at a relatively young stage and also the asymmetric disk traced in thermal dust emission. However, the physical conditions of the spirals are still not well understood. The origin of the asymmetric thermal emission is unclear. Methods: We observed the disk at 230 GHz (1.3 mm) in both the continuum and the spectral line 12CO J = 2 → 1 with IRAM 30-m, the Plateau de Bure interferometer, and the SubMillimeter Array to sample all spatial scales from 0.37 arcsec to about 50''. To combine the data obtained from these telescopes, several methods and calibration issues were checked and discussed. Results: The 1.3 mm continuum (dust) emission is resolved into inner disk and outer ring. The emission from the dust ring is highly asymmetric in azimuth, with intensity variations by a factor 3. Molecular gas at high velocities traced by the CO line is detected next to the stellar location. The inclination angle of the disk is found to decrease toward the center. On a larger scale, based on the intensity weighted dispersion and the integrated intensity map of 12CO J = 2 → 1, four spirals are identified, where two of them are also detected in the near infrared. The total gas mass of the 4 spirals (Mspiral) is 10-7 rotating with respect to the CO disk, and it only exhibits small radial motion. Conclusions: The wide gap, the warped disk, and the asymmetric dust ring suggest that there is an undetected companion with a mass of 0.03 M⊙ at a radius of 45 AU. The different spirals would, however, require multiple perturbing bodies. While viable from an energetic point of view, this mechanism cannot explain the apparent counter-rotation of the gas in the spirals. Although an hypothetical fly-by cannot be ruled out, the most likely explanation of the AB Aurigae system may be inhomogeneous accretion well above or below the main disk plane from the remnant envelope

  4. Young Stellar Associations Cleanup: A Deep Circumstellar Disk Census at Ages 8-12 Myrs

    Science.gov (United States)

    Rieke, George; Stapelfeldt, Karl; Hines, Dean; Plavchan, Peter; Rebull, Luisa; Stapefeldlt, Karl

    2008-03-01

    The transformation of primordial protoplanetary disks into optically thin debris disks takes place very early in a star's life. The youngest debris disks are therefore of great interest for disk evolution studies, as their properties can define the mechanisms and timescales for planet formation. In the age range 8-12 Myrs, three nearby young stellar associations are crucial to these studies: eta Chamaeleontis, TW Hydrae, and beta Pictoris. Spitzer/MIPS studies of these groups have found that both optically thick and thin disks are present at 8 Myrs, but only optically thin disks at 12 Myrs. Disk inner holes, diagnosed by the presence of 70 micron excess and absence of 24 micron excess, are found so far in only the beta Pictoris group. Disk fractions of 30-50% have been measured at 24 microns down to the photospheric limit. However, at 70 microns, the existing data are relatively shallow, probing to only to 3-20 times the photospheric limit, and providing a lower limit to the disk fraction > 30%. We propose to obtain much deeper measurements (10 cycles of 70 micron photometry) for 37 members of these groups not yet detected at 70 microns, and which are found in regions of low to medium background emission, In addition, we include 24 micron observations for two eta Cha members that fell outside the scan map region in the original study. The results of this program will allow an assessment of the frequency of disks down to Ld/Lstar ~0.0002 across the full membership of these young associations, thereby consolidating the Spitzer science legacy for early disk evolution.

  5. Asymmetric transition disks: Vorticity or eccentricity?

    NARCIS (Netherlands)

    Ataiee, S.; Pinilla, P.; Zsom, A.; Dullemond, C.P.; Dominik, C.; Ghanbari, J.

    2013-01-01

    Context. Transition disks typically appear in resolved millimeter observations as giant dust rings surrounding their young host stars. More accurate observations with ALMA have shown several of these rings to be in fact asymmetric: they have lopsided shapes. It has been speculated that these rings

  6. PROTOPLANETARY AND TRANSITIONAL DISKS IN THE OPEN STELLAR CLUSTER IC 2395

    Energy Technology Data Exchange (ETDEWEB)

    Balog, Zoltan [Max Planck Institute for Astronomy, Heidelberg, D-69117 (Germany); Siegler, Nick [NASA Exoplanet Exploration Program, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Rieke, G. H.; Su, K. Y. L.; Gáspár, András [Steward Observatory, 933 N. Cherry Ave, University of Arizona, Tucson, AZ 85721 (United States); Kiss, L. L. [Konkoly Observatory, Research Center for Astronomy and Earth Sciences, P.O. Box 67, H-1525 Budapest (Hungary); Muzerolle, James [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA (United States); Bell, Cameron P. M. [Institute for Astronomy, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093, Zürich (Switzerland); Vinkó, J. [Dept. of Optics and Quantum Electronics, University of Szeged, H-6720 Szeged (Hungary); Young, E. T., E-mail: balog@mpia-hd.mpg.de [NASA Ames SOFIA Science Center, N211, Mountain View, CA 94043 (United States)

    2016-11-20

    We present new deep UBVRI images and high-resolution multi-object optical spectroscopy of the young (∼6–10 Myr old), relatively nearby (800 pc) open cluster IC 2395. We identify nearly 300 cluster members and use the photometry to estimate their spectral types, which extend from early B to middle M. We also present an infrared imaging survey of the central region using the IRAC and MIPS instruments on board the Spitzer Space Telescope , covering the wavelength range from 3.6 to 24 μ m. Our infrared observations allow us to detect dust in circumstellar disks originating over a typical range of radii from ∼0.1 to ∼10 au from the central star. We identify 18 Class II, 8 transitional disk, and 23 debris disk candidates, respectively, 6.5%, 2.9%, and 8.3% of the cluster members with appropriate data. We apply the same criteria for transitional disk identification to 19 other stellar clusters and associations spanning ages from ∼1 to ∼18 Myr. We find that the number of disks in the transitional phase as a fraction of the total with strong 24 μ m excesses ([8] – [24] ≥ 1.5) increases from (8.4 ± 1.3)% at ∼3 Myr to (46 ± 5)% at ∼10 Myr. Alternative definitions of transitional disks will yield different percentages but should show the same trend.

  7. An ALMA continuum survey of circumstellar disks in the upper Scorpius OB association

    Energy Technology Data Exchange (ETDEWEB)

    Carpenter, John M.; Ricci, Luca; Isella, Andrea [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States)

    2014-05-20

    We present ALMA 880 μm continuum observations of 20 K- and M-type stars in the Upper Scorpius OB association (Upper Sco) that are surrounded by protoplanetary disks. These data are used to measure the dust content in disks around low-mass stars (0.1-1.6 M {sub ☉}) at a stellar age of 5-11 Myr. Thirteen sources were detected in the 880 μm dust continuum at ≥3σ with inferred dust masses between 0.3 and 52 M {sub ⊕}. The dust masses tend to be higher around the more massive stars, but the significance is marginal in that the probability of no correlation is p ≈ 0.03. The evolution in the dust content in disks was assessed by comparing the Upper Sco observations with published continuum measurements of disks around ∼1-2 Myr stars in the Class II stage in the Taurus molecular cloud. While the dust masses in the Upper Sco disks are on average lower than in Taurus, any difference in the dust mass distributions is significant at less than 3σ. For stellar masses between 0.49 M {sub ☉} and 1.6 M {sub ☉}, the mean dust mass in disks is lower in Upper Sco relative to Taurus by Δlog M {sub dust} = 0.44 ± 0.26.

  8. Spitzer and Variable Young Stars: Shining a Spotlight on Circumstellar Disks

    Science.gov (United States)

    Cody, Ann Marie; CSI 2264 Team

    2014-01-01

    Since its launch in 2003, the Spitzer Space Telescope has helped to uncover hundreds of disk bearing young stars in clusters by detecting their infrared excesses. Study of the spectral energy distributions of these objects has shed light on disk evolution, dispersal, and the relationship to planet formation. With the start of the Warm Spitzer Mission, mid-infrared time series observations have opened up a new window into the dynamic nature of these systems. Not only are young stellar objects (YSOs) highly variable, but so are their disks! I will review recent findings on mid-infrared variability in young stars, highlighting the Young Stellar Object Variability project and the joint Spitzer/CoRoT Coordinated Synoptic Investigation of NGC 2264. These efforts have resulted in a comprehensive census and categorization of YSO flux behavior at 0.5 through 4.5 microns, on timescales from hours to months. We now have evidence for multiple simultaneous variability mechanisms, supporting the picture of a highly dynamic star-disk system.

  9. A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48

    Energy Technology Data Exchange (ETDEWEB)

    Schworer, Guillaume; Lacour, Sylvestre; Du Foresto, Vincent Coudé [LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universits, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité (France); Huélamo, Nuria [Dpto. Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, P.O. Box 78, E-28691, Villanueva de la Cañada (Spain); Pinte, Christophe; Chauvin, Gaël [Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France CNRS, IPAG, F-38000 Grenoble (France); Ehrenreich, David [Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Versoix (Switzerland); Girard, Julien [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001 Vitacura, Santiago 19 (Chile); Tuthill, Peter [Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia)

    2017-06-20

    For one decade, the spectral type and age of the ρ Oph object IRS-48 were subject to debate and mystery. Modeling its disk with mid-infrared to millimeter observations led to various explanations to account for the complex intricacy of dust holes and gas-depleted regions. We present multi-epoch high-angular-resolution interferometric near-infrared data of spatially resolved emissions in the first 15 au of IRS-48, known to have very strong polycyclic aromatic hydrocarbon (PAH) emissions within this dust-depleted region. We make use of new Sparse-Aperture-Masking data to instruct a revised radiative-transfer model, where spectral energy distribution fluxes and interferometry are jointly fitted. Neutral and ionized PAH, very small grains (VSG), and classical silicates are incorporated into the model; new stellar parameters and extinction laws are explored. A bright (42 L {sub ⊙}) and hence large (2.5 R {sub ⊙}) central star with A {sub v} = 12.5 mag and R {sub v} = 6.5 requires less near-infrared excess: the inner-most disk at ≈1 au is incompatible with the interferometric data. The revised stellar parameters place this system on a 4 Myr evolutionary track, four times younger than the previous estimations, which is in better agreement with the surrounding ρ Oph region and disk-lifetime observations. The disk-structure solution converges to a classical-grain outer disk from 55 au combined with an unsettled and fully resolved VSG and PAH ring, between 11 and 26 au. We find two overluminosities in the PAH ring at color-temperatures consistent with the radiative transfer simulations; one follows a Keplerian circular orbit at 14 au. We show a depletion of a factor of ≈5 of classical dust grains up to 0.3 mm compared to very small particles: the IRS-48 disk is nearly void of dust grains in the first 55 au. A 3.5 M {sub Jup} planet on a 40 au orbit can qualitatively explain the new disk structure.

  10. SPITZER SPECTROSCOPY OF CIRCUMSTELLAR DISKS IN THE 5 Myr OLD UPPER SCORPIUS OB ASSOCIATION

    International Nuclear Information System (INIS)

    Dahm, S. E.; Carpenter, John M.

    2009-01-01

    We present mid-infrared spectra between 5.2 and 38 μm for 26 disk-bearing members of the ∼5 Myr old Upper Scorpius OB association obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. We find clear evidence for changes in the spectral characteristics of dust emission between the early-type (B+A) and late-type (K+M) infrared excess stars. The early-type members exhibit featureless continuum excesses that become apparent redward of ∼8 μm. In contrast, 10 and 20 μm silicate features or polycyclic aromatic hydrocarbon emission are present in all but one of the late-type excess members of Upper Scorpius. The strength of silicate emission among late-type Upper Scorpius members is spectral-type dependent, with the most prominent features being associated with K5-M2-type stars. By fitting the spectral energy distributions (SED) of a representative sample of low-mass stars with accretion disk models, we find that the SEDs are consistent with models having inner disk radii ranging from ∼0.2 to 1.2 AU. Complementary high-resolution (R ∼ 33, 000) optical (λλ4800-9200) spectra for the Upper Scorpius excess stars were examined for signatures of gaseous accretion. Of the 35 infrared excess stars identified in Upper Scorpius, only seven (all late-type) exhibit definitive signatures of accretion. Mass-accretion rates for these stars were estimated to range from 10 -11 to 10 -8.9 M sun yr -1 . Compared to Class II sources in Taurus-Auriga, the disk population in Upper Scorpius exhibits reduced levels of near- and mid-infrared excess emission and an order of magnitude lower mass-accretion rates. These results suggest that the disk structure has changed significantly over the 2-4 Myr in age separating these two stellar populations. The ubiquity of depleted inner disks in the Upper Scorpius excess sample implies that such disks are a common evolutionary pathway that persists for some time.

  11. Spiral Arms, Infall, and Misalignment of the Circumbinary Disk from the Circumstellar Disks in the Protostellar Binary System L1551 NE

    Energy Technology Data Exchange (ETDEWEB)

    Takakuwa, Shigehisa [Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065 (Japan); Saigo, Kazuya [ALMA Project Office, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Matsumoto, Tomoaki [Faculty of Humanity and Environment, Hosei University, Chiyoda-ku, Tokyo 102-8160 (Japan); Saito, Masao [Nobeyama Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano 384-1805 (Japan); Lim, Jeremy [Department of Physics, University of Hong Kong, Pokfulam Road (Hong Kong); Hanawa, Tomoyuki [Center for Frontier Science, Chiba University, Inage-ku, Chiba 263-8522 (Japan); Yen, Hsi-Wei; Ho, Paul T. P., E-mail: takakuwa@sci.kagoshima-u.ac.jp [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China)

    2017-03-01

    We report the ALMA Cycle 2 observations of the Class I binary protostellar system L1551 NE in the 0.9 mm continuum, C{sup 18}O (3–2), {sup 13}CO (3–2), SO (7{sub 8}–6{sub 7}), and CS (7–6) emission. At 0.″18 (=25 au) resolution, ∼4 times higher than that of our Cycle 0 observations, the circumbinary disk (CBD) as seen in the 0.9 mm emission is shown to be composed of a northern and a southern spiral arm, with the southern arm connecting to the circumstellar disk (CSD) around Source B. The western parts of the spiral arms are brighter than the eastern parts, suggesting the presence of an m = 1 spiral mode. In the C{sup 18}O emission, the infall gas motions in the interarm regions and the outward gas motions in the arms are identified. These observed features are well reproduced with our numerical simulations, where gravitational torques from the binary system impart angular momenta to the spiral-arm regions and extract angular momenta from the interarm regions. Chemical differentiation of the CBD is seen in the four molecular species. Our Cycle 2 observations have also resolved the CSDs around the individual protostars, and the beam-deconvolved sizes are 0.″29 × 0.″19 (=40 × 26 au) (P.A. = 144°) and 0.″26 × 0.″20 (=36 × 27 au) (P.A. = 147°) for Sources A and B, respectively. The position and inclination angles of these CSDs are misaligned with those of the CBD. The C{sup 18}O emission traces the Keplerian rotation of the misaligned disk around Source A.

  12. The Circumstellar Disk HD 169142: Gas, Dust, and Planets Acting in Concert?

    Science.gov (United States)

    Pohl, A.; Benisty, M.; Pinilla, P.; Ginski, C.; de Boer, J.; Avenhaus, H.; Henning, Th.; Zurlo, A.; Boccaletti, A.; Augereau, J.-C.; Birnstiel, T.; Dominik, C.; Facchini, S.; Fedele, D.; Janson, M.; Keppler, M.; Kral, Q.; Langlois, M.; Ligi, R.; Maire, A.-L.; Ménard, F.; Meyer, M.; Pinte, C.; Quanz, S. P.; Sauvage, J.-F.; Sezestre, É.; Stolker, T.; Szulágyi, J.; van Boekel, R.; van der Plas, G.; Villenave, M.; Baruffolo, A.; Baudoz, P.; Le Mignant, D.; Maurel, D.; Ramos, J.; Weber, L.

    2017-11-01

    HD 169142 is an excellent target for investigating signs of planet-disk interaction due to previous evidence of gap structures. We perform J-band (˜1.2 μm) polarized intensity imaging of HD 169142 with VLT/SPHERE. We observe polarized scattered light down to 0.″16 (˜19 au) and find an inner gap with a significantly reduced scattered-light flux. We confirm the previously detected double-ring structure peaking at 0.″18 (˜21 au) and 0.″56 (˜66 au) and marginally detect a faint third gap at 0.″70-0.″73 (˜82-85 au). We explore dust evolution models in a disk perturbed by two giant planets, as well as models with a parameterized dust size distribution. The dust evolution model is able to reproduce the ring locations and gap widths in polarized intensity but fails to reproduce their depths. However, it gives a good match with the ALMA dust continuum image at 1.3 mm. Models with a parameterized dust size distribution better reproduce the gap depth in scattered light, suggesting that dust filtration at the outer edges of the gaps is less effective. The pileup of millimeter grains in a dust trap and the continuous distribution of small grains throughout the gap likely require more efficient dust fragmentation and dust diffusion in the dust trap. Alternatively, turbulence or charging effects might lead to a reservoir of small grains at the surface layer that is not affected by the dust growth and fragmentation cycle dominating the dense disk midplane. The exploration of models shows that extracting planet properties such as mass from observed gap profiles is highly degenerate. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 095.C-0273.

  13. Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk Around PDS 70: Observations of the Disk

    Science.gov (United States)

    Hashimoto, J.; Dong, R.; Kudo, T.; Honda, M.; McClure, M. K.; Zhu, Z.; Muto, T.; Wisniewski, J.; Abe, L.; Brandner, W.; hide

    2012-01-01

    We present high-resolution H-band polarized intensity (FWHM=0".1:14AU) and L'-band imaging data(FWHM= 0".11:15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0".2) up to 210 AU (1".5). In both images, a giant inner gap is clearly resolved for the first time, and the radius of the gap is approx.70 AU. Our data show that the geometric center of the disk shifts by approx.6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a result of spectral energy distribution fitting by Monte Carlo radiative transfer modeling, we infer the existence of an optically thick inner disk at a few AU. Combining our observations and modeling, we classify the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the analysis of L'-band imaging data, we put an upper limit of approx.30 to approx.50 M(sub J) on the mass of companions within the gap. Taking into account the presence of the large and sharp gap, we suggest that the gap could be formed by dynamical interactions of sub-stellar companions or multiple unseen giant planets in the gap. Key words: planetary systems - polarization - protoplanetary disks - stars: individual (PDS 70) - stars: pre-main sequence.

  14. THE FIRST CIRCUMSTELLAR DISK IMAGED IN SILHOUETTE AT VISIBLE WAVELENGTHS WITH ADAPTIVE OPTICS: MagAO IMAGING OF ORION 218-354

    International Nuclear Information System (INIS)

    Follette, Katherine B.; Close, Laird M.; Males, Jared R.; Wu, Ya-Lin; Morzinski, Katie M.; Hinz, Philip; Rodigas, Timothy J.; Kopon, Derek; Puglisi, Alfio; Esposito, Simone; Riccardi, Armando; Pinna, Enrico; Xompero, Marco; Briguglio, Runa

    2013-01-01

    We present high-resolution adaptive optics (AO) corrected images of the silhouette disk Orion 218-354 taken with Magellan AO (MagAO) and its visible light camera, VisAO, in simultaneous differential imaging mode at Hα. This is the first image of a circumstellar disk seen in silhouette with AO and is among the first visible light AO results in the literature. We derive the disk extent, geometry, intensity, and extinction profiles and find, in contrast with previous work, that the disk is likely optically thin at Hα. Our data provide an estimate of the column density in primitive, ISM-like grains as a function of radius in the disk. We estimate that only ∼10% of the total submillimeter derived disk mass lies in primitive, unprocessed grains. We use our data, Monte Carlo radiative transfer modeling, and previous results from the literature to make the first self-consistent multiwavelength model of Orion 218-354. We find that we are able to reproduce the 1-1000 μm spectral energy distribution with a ∼2-540 AU disk of the size, geometry, small versus large grain proportion, and radial mass profile indicated by our data. This inner radius is a factor of ∼15 larger than the sublimation radius of the disk, suggesting that it is likely cleared in the very interior

  15. THE FIRST CIRCUMSTELLAR DISK IMAGED IN SILHOUETTE AT VISIBLE WAVELENGTHS WITH ADAPTIVE OPTICS: MagAO IMAGING OF ORION 218-354

    Energy Technology Data Exchange (ETDEWEB)

    Follette, Katherine B.; Close, Laird M.; Males, Jared R.; Wu, Ya-Lin; Morzinski, Katie M.; Hinz, Philip; Rodigas, Timothy J. [Steward Observatory, The University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721 (United States); Kopon, Derek [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Puglisi, Alfio; Esposito, Simone; Riccardi, Armando; Pinna, Enrico; Xompero, Marco; Briguglio, Runa [INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy)

    2013-09-20

    We present high-resolution adaptive optics (AO) corrected images of the silhouette disk Orion 218-354 taken with Magellan AO (MagAO) and its visible light camera, VisAO, in simultaneous differential imaging mode at Hα. This is the first image of a circumstellar disk seen in silhouette with AO and is among the first visible light AO results in the literature. We derive the disk extent, geometry, intensity, and extinction profiles and find, in contrast with previous work, that the disk is likely optically thin at Hα. Our data provide an estimate of the column density in primitive, ISM-like grains as a function of radius in the disk. We estimate that only ∼10% of the total submillimeter derived disk mass lies in primitive, unprocessed grains. We use our data, Monte Carlo radiative transfer modeling, and previous results from the literature to make the first self-consistent multiwavelength model of Orion 218-354. We find that we are able to reproduce the 1-1000 μm spectral energy distribution with a ∼2-540 AU disk of the size, geometry, small versus large grain proportion, and radial mass profile indicated by our data. This inner radius is a factor of ∼15 larger than the sublimation radius of the disk, suggesting that it is likely cleared in the very interior.

  16. ON THE TRANSITIONAL DISK CLASS: LINKING OBSERVATIONS OF T TAURI STARS AND PHYSICAL DISK MODELS

    International Nuclear Information System (INIS)

    Espaillat, C.; Andrews, S.; Qi, C.; Wilner, D.; Ingleby, L.; Calvet, N.; Hernández, J.; Furlan, E.; D'Alessio, P.; Muzerolle, J.

    2012-01-01

    Two decades ago 'transitional disks' (TDs) described spectral energy distributions (SEDs) of T Tauri stars with small near-IR excesses, but significant mid- and far-IR excesses. Many inferred this indicated dust-free holes in disks possibly cleared by planets. Recently, this term has been applied disparately to objects whose Spitzer SEDs diverge from the expectations for a typical full disk (FD). Here, we use irradiated accretion disk models to fit the SEDs of 15 such disks in NGC 2068 and IC 348. One group has a 'dip' in infrared emission while the others' continuum emission decreases steadily at all wavelengths. We find that the former have an inner disk hole or gap at intermediate radii in the disk and we call these objects 'transitional disks' and 'pre-transitional disks' (PTDs), respectively. For the latter group, we can fit these SEDs with FD models and find that millimeter data are necessary to break the degeneracy between dust settling and disk mass. We suggest that the term 'transitional' only be applied to objects that display evidence for a radical change in the disk's radial structure. Using this definition, we find that TDs and PTDs tend to have lower mass accretion rates than FDs and that TDs have lower accretion rates than PTDs. These reduced accretion rates onto the star could be linked to forming planets. Future observations of TDs and PTDs will allow us to better quantify the signatures of planet formation in young disks.

  17. Exploring the circumstellar disk-like structure of the B[e] supergiant LHA 120-S 73

    Czech Academy of Sciences Publication Activity Database

    Torres, A.F.; Cidale, L.S.; Kraus, Michaela; Arias, M.L.; Maravelias, Grigorios; Borges Fernandes, M.; Vallverdú, R.

    2016-01-01

    Roč. 58, č. 1 (2016), s. 120-122 E-ISSN 1669-9521 R&D Projects: GA MŠk(CZ) 7AMB14AR017; GA MŠk LG14013 Institutional support: RVO:67985815 Keywords : stars * early-type * circumstellar matter Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics http://www.astronomiaargentina.org.ar/b58/2016baaa...58...120T.pdf

  18. A DWARF TRANSITIONAL PROTOPLANETARY DISK AROUND XZ TAU B

    Energy Technology Data Exchange (ETDEWEB)

    Osorio, Mayra; Macías, Enrique; Anglada, Guillem; Gómez, José F. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Carrasco-González, Carlos; Galván-Madrid, Roberto; Zapata, Luis; Rodríguez, Luis F. [Instituto de Radioastronomía y Astrofísica UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán (Mexico); Calvet, Nuria [Department of Astronomy, University of Michigan, 825 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Nagel, Erick [Departamento de Astronomía, Universidad de Guanajuato, Guanajuato, Gto 36240 (Mexico); Torrelles, José M. [Institut de Ciències de l’Espai (CSIC)-Institut de Ciències del Cosmos (UB)/IEEC, Martí i Franquès 1, E-08028 Barcelona (Spain); Zhu, Zhaohuan, E-mail: osorio@iaa.es [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

    2016-07-01

    We report the discovery of a dwarf protoplanetary disk around the star XZ Tau B that shows all the features of a classical transitional disk but on a much smaller scale. The disk has been imaged with the Atacama Large Millimeter/submillimeter Array (ALMA), revealing that its dust emission has a quite small radius of ∼3.4 au and presents a central cavity of ∼1.3 au in radius that we attribute to clearing by a compact system of orbiting (proto)planets. Given the very small radii involved, evolution is expected to be much faster in this disk (observable changes in a few months) than in classical disks (observable changes requiring decades) and easy to monitor with observations in the near future. From our modeling we estimate that the mass of the disk is large enough to form a compact planetary system.

  19. A DWARF TRANSITIONAL PROTOPLANETARY DISK AROUND XZ TAU B

    International Nuclear Information System (INIS)

    Osorio, Mayra; Macías, Enrique; Anglada, Guillem; Gómez, José F.; Carrasco-González, Carlos; Galván-Madrid, Roberto; Zapata, Luis; Rodríguez, Luis F.; Calvet, Nuria; Nagel, Erick; Torrelles, José M.; Zhu, Zhaohuan

    2016-01-01

    We report the discovery of a dwarf protoplanetary disk around the star XZ Tau B that shows all the features of a classical transitional disk but on a much smaller scale. The disk has been imaged with the Atacama Large Millimeter/submillimeter Array (ALMA), revealing that its dust emission has a quite small radius of ∼3.4 au and presents a central cavity of ∼1.3 au in radius that we attribute to clearing by a compact system of orbiting (proto)planets. Given the very small radii involved, evolution is expected to be much faster in this disk (observable changes in a few months) than in classical disks (observable changes requiring decades) and easy to monitor with observations in the near future. From our modeling we estimate that the mass of the disk is large enough to form a compact planetary system.

  20. The Discovery of a Photoevaporation-Driven Molecular Outflow from the T Tauri Transitional Disk GM Aur

    NARCIS (Netherlands)

    Hornbeck, Jeremy; Grady, C. A.; Brown, A.; Ayres, T.; Apai, D.; Brittain, S.; Brown, J. M.; Hamaguchi, K.; Henning, T.; Herczeg, G.; Kamp, I.; Perrin, M.; Petre, R.; Schneider, G.; Sitko, M.; Walter, F.; Williger, G.; Wisniewski, J.; Woodgate, B.

    Circumstellar disks are not only a byproduct of star formation, but are also the place where planets form and migrate. The dominant gas-phase constituent of disks early in their evolution is H2, and its lifetime in the disk limits the time available for gas giant planet formation and migration. A

  1. Transition Disks – Grain Growth, Planets, or Photoevaporation?

    Directory of Open Access Journals (Sweden)

    Benisty M.

    2013-04-01

    Full Text Available In the past years, many transition disks have been detected via SED modeling or imaging. The disks feature dust cavities in their inner regions with sizes ranging from a few to more than 70 AU. The origin of those structures, however, remains mysterious. We will present how our recent simulation results, which include gap opening by a giant planet and effects of dust evolution, could explain these structures.

  2. Stirring up the dust: a dynamical model for halo-like dust clouds in transitional disks

    NARCIS (Netherlands)

    Krijt, S.; Dominik, C.

    2011-01-01

    Context. A small number of young stellar objects show signs of a halo-like structure of optically thin dust, in addition to a circumstellar disk. This halo or torus is located within a few AU of the star, but its origin has not yet been understood. Aims. A dynamically excited cloud of planetesimals

  3. TRANSITION DISK CHEMISTRY AND FUTURE PROSPECTS WITH ALMA

    International Nuclear Information System (INIS)

    Cleeves, L. Ilsedore; Bergin, Edwin A.; Bethell, Thomas J.; Calvet, Nuria; Fogel, Jeffrey K. J.; Sauter, Jürgen; Wolf, Sebastian

    2011-01-01

    We explore the chemical structure of a disk that contains a large central gap of R ∼ 45 AU, as is commonly seen in transitional disk systems. In our chemical model of a disk with a cleared inner void, the midplane becomes revealed to the central star so that it is directly irradiated. The midplane material at the truncation radius is permissive to reprocessed optical heating radiation, but opaque to the photodissociating ultraviolet, creating an environment abundant in gas-phase molecules. Thus the disk midplane, which would otherwise for a full disk be dominated by near complete heavy element freeze-out, should become observable in molecular emission. If this prediction is correct this has exciting prospects for observations with the Atacama Large Millimeter/Submillimeter Array, as the inner transition region should thus be readily detected and resolved, especially using high-J rotational transitions excited in the high density midplane gas. Therefore, such observations will potentially provide us with a direct probe of the physics and chemistry at this actively evolving interface.

  4. A tunnel and a traffic jam: How transition disks maintain a detectable warm dust component despite the presence of a large planet-carved gap

    Science.gov (United States)

    Pinilla, P.; Klarmann, L.; Birnstiel, T.; Benisty, M.; Dominik, C.; Dullemond, C. P.

    2016-01-01

    Context. Transition disks are circumstellar disks that show evidence of a dust cavity, which may be related to dynamical clearing by embedded planet(s). Most of these objects show signs of significant accretion, indicating that the inner disks are not truly empty, but that gas is still streaming through to the star. A subset of transition disks, sometimes called pre-transition disks, also shows a strong near-infrared excess, interpreted as an optically thick dusty belt located close to the dust sublimation radius within the first astronomical unit. Aims: We study the conditions for the survival and maintenance of such an inner disk in the case where a massive planet opens a gap in the disk. In this scenario, the planet filters out large dust grains that are trapped at the outer edge of the gap, while the inner regions of the disk may or may not be replenished with small grains. Methods: We combined hydrodynamical simulations of planet-disk interactions with dust evolution models that include coagulation and fragmentation of dust grains over a large range of radii and derived observational properties using radiative transfer calculations. We studied the role of the snow line in the survival of the inner disk of transition disks. Results: Inside the snow line, the lack of ice mantles in dust particles decreases the sticking efficiency between grains. As a consequence, particles fragment at lower collision velocities than in regions beyond the snow line. This effect allows small particles to be maintained for up to a few Myr within the first astronomical unit. These particles are closely coupled to the gas and do not drift significantly with respect to the gas. For lower mass planets (1 MJup), the pre-transition appearance can be maintained even longer because dust still trickles through the gap created by the planet, moves invisibly and quickly in the form of relatively large grains through the gap, and becomes visible again as it fragments and gets slowed down

  5. High-contrast direct imaging of exo-planets and circumstellar disks: from the self-coherent camera to NICI data analysis

    International Nuclear Information System (INIS)

    Mazoyer, Johan

    2014-01-01

    Out of the 1800 exo-planets detected to date, only 50 were by direct imaging. However, by allowing the observation of circumstellar disks and planets (sometimes simultaneously around the same star, as in the case of β-pictoris), this method is a fundamental tool for the understanding of planetary formation. In addition, direct access to the light of the detected objects allows spectroscopy, paving the way for the first time to the chemical and thermal analysis of their atmosphere and surface. However, direct imaging raises specific challenges: accessing objects fainter than their star (with a ration up to 10 -8 to 10 -11 ), and separated only by a fraction of arc-second. To obtain these values, several techniques must be implemented. A corona-graph, used in complement with a deformable mirror and active optical aberration correction methods, produces high-contrast images, which can be further processed by differential imaging techniques. My PhD thesis work took place at the intersection of these techniques. At first, I analyzed, in simulation and experimentally on the THD 'French acronym for very high contrast' bench of the Paris Observatory, the performance of the self-coherent camera, a wavefront sensing technique used to correct the optical aberrations in the focal plane. I managed to obtained high-contrast zones (called dark holes) with performance up to 3.10 -8 between 5 and 12?/D, in monochromatic light. I also started an analysis of the performance in narrow spectral bands. In the second part of my thesis, I applied the latest differential imaging techniques to high contrast images from another corona-graphic instrument, NICI. The processing of these data revealed unprecedented views of the dust disk orbiting HD 15115. (author)

  6. Disk

    NARCIS (Netherlands)

    P.A. Boncz (Peter); L. Liu (Lei); M. Tamer Özsu

    2008-01-01

    htmlabstractIn disk storage, data is recorded on planar, round and rotating surfaces (disks, discs, or platters). A disk drive is a peripheral device of a computer system, connected by some communication medium to a disk controller. The disk controller is a chip, typically connected to the CPU of

  7. FAST MODES AND DUSTY HORSESHOES IN TRANSITIONAL DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Mittal, Tushar; Chiang, Eugene [Department of Earth and Planetary Science, 307 McCone Hall, University of California, Berkeley, CA 94720-4767 (United States)

    2015-01-01

    The brightest transitional protoplanetary disks are often azimuthally asymmetric: their millimeter-wave thermal emission peaks strongly on one side. Dust overdensities can exceed ∼100:1, while gas densities vary by factors less than a few. We propose that these remarkable ALMA observations—which may bear on how planetesimals form—reflect a gravitational global mode in the gas disk. The mode is (1) fast—its pattern speed equals the disk's mean Keplerian frequency; (2) of azimuthal wavenumber m = 1, displacing the host star from the barycenter; and (3) Toomre-stable. We solve for gas streamlines including the indirect stellar potential in the frame rotating with the pattern speed, under the drastic simplification that gas does not feel its own gravity. Near corotation, the gas disk takes the form of a horseshoe-shaped annulus. Dust particles with aerodynamic stopping times much shorter or much longer than the orbital period are dragged by gas toward the horseshoe center. For intermediate stopping times, dust converges toward a ∼45° wide arc on the corotation circle. Particles that do not reach their final accumulation points within disk lifetimes, either because of gas turbulence or long particle drift times, conform to horseshoe-shaped gas streamlines. Our mode is not self-consistent because we neglect gas self-gravity; still, we expect that trends between accumulation location and particle size, similar to those we have found, are generically predicted by fast modes and are potentially observable. Unlike vortices, global modes are not restricted in radial width to the pressure scale height; their large radial and azimuthal extents may better match observations.

  8. WIND-DRIVEN ACCRETION IN TRANSITIONAL PROTOSTELLAR DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lile; Goodman, Jeremy J. [Princeton University Observatory, Princeton, NJ 08544 (United States)

    2017-01-20

    Transitional protostellar disks have inner cavities that are heavily depleted in dust and gas, yet most of them show signs of ongoing accretion, often at rates comparable to full disks. We show that recent constraints on the gas surface density in a few well-studied disk cavities suggest that the accretion speed is at least transsonic. We propose that this is the natural result of accretion driven by magnetized winds. Typical physical conditions of the gas inside these cavities are estimated for plausible X-ray and FUV radiation fields. The gas near the midplane is molecular and predominantly neutral, with a dimensionless ambipolar parameter in the right general range for wind solutions of the type developed by Königl, Wardle, and others. That is to say, the density of ions and electrons is sufficient for moderately good coupling to the magnetic field, but it is not so good that the magnetic flux needs to be dragged inward by the accreting neutrals.

  9. New Insights into the Nature of Transition Disks from a Complete Disk Survey of the Lupus Star-forming Region

    Science.gov (United States)

    van der Marel, Nienke; Williams, Jonathan P.; Ansdell, M.; Manara, Carlo F.; Miotello, Anna; Tazzari, Marco; Testi, Leonardo; Hogerheijde, Michiel; Bruderer, Simon; van Terwisga, Sierk E.; van Dishoeck, Ewine F.

    2018-02-01

    Transition disks with large dust cavities around young stars are promising targets for studying planet formation. Previous studies have revealed the presence of gas cavities inside the dust cavities, hinting at recently formed, giant planets. However, many of these studies are biased toward the brightest disks in the nearby star-forming regions, and it is not possible to derive reliable statistics that can be compared with exoplanet populations. We present the analysis of 11 transition disks with large cavities (≥20 au radius) from a complete disk survey of the Lupus star-forming region, using ALMA Band 7 observations at 0.″3 (22–30 au radius) resolution of the 345 GHz continuum, 13CO and C18O 3–2 observations, and the spectral energy distribution of each source. Gas and dust surface density profiles are derived using the physical–chemical modeling code DALI. This is the first study of transition disks of large cavities within a complete disk survey within a star-forming region. The dust cavity sizes range from 20 to 90 au radius, and in three cases, a gas cavity is resolved as well. The deep drops in gas density and large dust cavity sizes are consistent with clearing by giant planets. The fraction of transition disks with large cavities in Lupus is ≳ 11 % , which is inconsistent with exoplanet population studies of giant planets at wide orbits. Furthermore, we present a hypothesis of an evolutionary path for large massive disks evolving into transition disks with large cavities.

  10. TRANSITIONAL DISKS AND THEIR ORIGINS: AN INFRARED SPECTROSCOPIC SURVEY OF ORION A

    Energy Technology Data Exchange (ETDEWEB)

    Kim, K. H.; Watson, Dan M.; Manoj, P.; Forrest, W. J.; Arnold, Laura [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Najita, Joan; Furlan, Elise [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Sargent, Benjamin [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Espaillat, Catherine [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Muzerolle, James [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Megeath, S. T. [Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606 (United States); Calvet, Nuria [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Green, Joel D., E-mail: khkim@pas.rochester.edu [Department of Astronomy, University of Texas, 1 University Station, Austin, TX 78712 (United States)

    2013-06-01

    Transitional disks are protoplanetary disks around young stars, with inner holes or gaps which are surrounded by optically thick outer, and often inner, disks. Here we present observations of 62 new transitional disks in the Orion A star-forming region. These were identified using the Spitzer Space Telescope's Infrared Spectrograph and followed up with determinations of stellar and accretion parameters using the Infrared Telescope Facility's SpeX. We combine these new observations with our previous results on transitional disks in Taurus, Chamaeleon I, Ophiuchus, and Perseus, and with archival X-ray observations. This produces a sample of 105 transitional disks of ''cluster'' age 3 Myr or less, by far the largest hitherto assembled. We use this sample to search for trends between the radial structure in the disks and many other system properties, in order to place constraints on the possible origins of transitional disks. We see a clear progression of host-star accretion rate and the different disk morphologies. We confirm that transitional disks with complete central clearings have median accretion rates an order of magnitude smaller than radially continuous disks of the same population. Pre-transitional disks-those objects with gaps that separate inner and outer disks-have median accretion rates intermediate between the two. Our results from the search for statistically significant trends, especially related to M-dot , strongly support that in both cases the gaps are far more likely to be due to the gravitational influence of Jovian planets or brown dwarfs orbiting within the gaps, than to any of the photoevaporative, turbulent, or grain-growth processes that can lead to disk dissipation. We also find that the fraction of Class II YSOs which are transitional disks is large, 0.1-0.2, especially in the youngest associations.

  11. Tomographic Sounding of Protoplanetary and Transitional Disks: Using Inner Disk Variability at Near to Mid-IR Wavelengths to Probe Conditions in the Outer Disk

    Science.gov (United States)

    Grady, C. A.; Sitko, M.L.

    2013-01-01

    Spitzer synoptic monitoring of young stellar associations has demonstrated that variability among young stars and their disks is ubiquitous. The Spitzer studies have been limited by target visibility windows and cover only a short temporal baseline in years. A complementary approach is to focus on stars chosen for high-value observations (e.g. high-contrast imaging, interferometry, or access to wavelengths which are difficult to achieve from the ground) where the synoptic data can augment the imagery or interferometry as well as probing disk structure. In this talk, we discuss how synoptic data for two protoplanetary disks, MWC 480 and HD 163296, constrain the dust disk scale height, account for variable disk illumination, and can be used to locate emission features, such as the IR bands commonly associated with PAHs in the disk, as part of our SOFIA cycle 1 study. Similar variability is now known for several pre-transitional disks, where synoptic data can be used to identify inner disks which are not coplanar with the outer disk, and which may be relicts of giant planet-giant planet scattering events. Despite the logistical difficulties in arranging supporting, coordinated observations in tandem with high-value observations, such data have allowed us to place imagery in context, constrained structures in inner disks not accessible to direct imagery, and may be a tool for identifying systems where planet scattering events have occurred.

  12. Planetary accretion in circumstellar disks

    Science.gov (United States)

    Lissauer, Jack J.; Stewart, Glen R.

    1993-01-01

    The formation of terrestrial planets and the cores of Jovian planets is reviewed in the framework of the planetesimal hypothesis, wherein planets are assumed to grow via the pairwise accumulation of small solid bodies. Emphasis is placed on the dynamics of solid body accretion from kilometer size planetesimals to terrestrial type planets. This stage of planetary growth is least dependent on the characteristics of the evolutionary state of the central star. It is concluded that the evolution of the planetesimal size distribution is determined by the gravitationally enhanced collision cross-section, which favors collisions between planetesimals with smaller velocities. Runaway growth of the largest planetesimal in each accretion zone appears to be a likely outcome. The subsequent accumulation of the resulting protoplanets leads to a large degree of radial mixing in the terrestrial planet region, and giant impacts are probable.

  13. Circumstellar chemistry

    International Nuclear Information System (INIS)

    Glassgold, A.E.

    1989-01-01

    Circumstellar chemistry has a special role in astrochemistry because the astrophysical conditions in the circumstellar envelopes of red giants are frequently well known and clear tests of chemical models are feasible. Recent advances in astronomical observations now offer opportunities to test relevant theories of molecule formation, especially in carbon-rich environments. Many new molecules have recently been discovered using radio and infrared techniques and high spatial resolution maps obtained with large telescopes and interferometers indicate where complex molecules are being formed in these envelopes. A large body of observational data can be understood in terms of the photochemical model, which embraces relevant elements of equilibrium chemistry, photodissociation, and ion-molecule chemistry of the photo-products. A critical review of the photochemical model will be presented together with new results on the synthesis of hydrocarbon molecules and silicon and sulfur compounds

  14. Rings and Spirals Forming by Themselves: the Photoelectric Instability in Debris Disks and Transitional disks, Now with Radiation Pressure.

    Science.gov (United States)

    Kuchner, Marc J.; Richert, Alex J. W.; Lyra, Wladimir

    2018-01-01

    Previous models of the photoelectric instability (PeI) in optically-thin disks suggested that it could form narrow rings of dust with no need for planets to shepherd them. We used the Pencil Code to perform the new numerical models of this instability that include a spectrum of grain sizes and stellar radiation pressure. The new models show that the instability persists in the presence of radiation pressure, and at low gas levels it tends to create dust rings. At higher gas levels where at least some of the bound grains are well coupled to the gas, clumpy spiral structures form instead. Can these simulations explain the patterns you see in your favorite transitional disk or debris disk (e.g., HD 141569A)? Drop by to compare notes and disk images--just leave the planets at home.

  15. MID-INFRARED SPECTRA OF TRANSITIONAL DISKS IN THE CHAMAELEON I CLOUD

    International Nuclear Information System (INIS)

    Kim, K. H.; Watson, Dan M.; Manoj, P.; Forrest, W. J.; Sargent, B.; McClure, M. K.; Green, J. D.; Harrold, Samuel T.; Furlan, E.; Najita, J.; Espaillat, C.; Calvet, N.; Luhman, K. L.

    2009-01-01

    We present 5-40 μm Spitzer Infrared Spectrograph spectra of a collection of transitional disks, objects for which the spectral energy distribution (SED) indicates central clearings (holes) or gaps in the dust distribution, in the Chamaeleon I star-forming region. Like their counterparts in the Taurus-Auriga star-forming region that we have previously observed, the spectra of these young objects (1-3 Myr old) reveal that the central clearings or gaps are very sharp-edged, and are surrounded by optically thick dusty disks similar to those around other classical T Tauri stars in the Chamaeleon I association. Also like the Taurus transitional disks, the Chamaeleon I transitional disks have extremely large depletion factors for small dust grains in their gaps, compared to the full accretion disks whose SEDs are represented by the median SED of Class II objects in the region. We find that the fraction of transitional disks in the Chamaeleon I cloud is somewhat higher than that in the Taurus-Auriga cloud, possibly indicating that the frequency of transitional disks, on average, increases with cluster age. We also find a significant correlation between the stellar mass and the radius of the outer edge of the gap. We discuss the disk structures implied by the spectra and the constraints they place on gap-formation mechanisms in protoplanetary disks.

  16. EVIDENCE FOR DYNAMICAL CHANGES IN A TRANSITIONAL PROTOPLANETARY DISK WITH MID-INFRARED VARIABILITY

    International Nuclear Information System (INIS)

    Muzerolle, James; Flaherty, Kevin; Balog, Zoltan; Smith, Paul S.; Rieke, George H.; Furlan, Elise; Allen, Lori; Muench, August; Calvet, Nuria; D'Alessio, Paola; Megeath, S. Thomas; Sherry, William H.

    2009-01-01

    We present multi-epoch Spitzer Space Telescope observations of the transitional disk LRLL 31 in the 2-3 Myr old star-forming region IC 348. Our measurements show remarkable mid-infrared variability on timescales as short as one week. The infrared continuum emission exhibits systematic wavelength-dependent changes that suggest corresponding dynamical changes in the inner disk structure and variable shadowing of outer disk material. We propose several possible sources for the structural changes, including a variable accretion rate or a stellar or planetary companion embedded in the disk. Our results indicate that variability studies in the infrared can provide important new constraints on protoplanetary disk behavior.

  17. High-resolution submillimeter and near-infrared studies of the transition disk around Sz 91

    Energy Technology Data Exchange (ETDEWEB)

    Tsukagoshi, Takashi; Momose, Munetake [College of Science, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512 (Japan); Hashimoto, Jun [Department of Physics and Astronomy, The University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Kudo, Tomoyuki; Saito, Masao; Ohashi, Nagayoshi; Kawabe, Ryohei; Akiyama, Eiji [National Astronomical Observatory Japan (NAOJ), Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Andrews, Sean; Wilner, David [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kitamura, Yoshimi [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Yoshinodai 3-1-1, Sagamihara, Kanagawa 229-8510 (Japan); Abe, Lyu [Lboratoire Lagrange (UMR 7293), Université de Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d' Azur, 28 avenue Valrose, F-06108 Nice Cedex 2 (France); Brandner, Wolfgang [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Brandt, Timothy D. [Department of Astrophysical Sciences, Princeton University, Peyton Hall, Ivy Lane, Princeton, NJ 08544 (United States); Carson, Joseph [Department of Physics and Astronomy, College of Charleston, 58 Coming Street, Charleston, SC 29424 (United States); Currie, Thayne [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street M5S 3H4, Toronto, Ontario (Canada); Egner, Sebastian E.; Guyon, Olivier [Subaru Telescope, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Goto, Miwa [Universitäts-Sternwarte München, Ludwig-Maximilians-Universität, Scheinerstr. 1, D-81679 München (Germany); Grady, Carol, E-mail: ttsuka@mx.ibaraki.ac.jp [Exoplanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771 (United States); and others

    2014-03-10

    To reveal the structures of a transition disk around a young stellar object in Lupus, Sz 91 , we have performed aperture synthesis 345 GHz continuum and CO(3-2) observations with the Submillimeter Array (∼1''-3'' resolution) and high-resolution imaging of polarized intensity at the K{sub s} -band using the HiCIAO instrument on the Subaru Telescope (0.''25 resolution). Our observations successfully resolved the inner and outer radii of the dust disk to be 65 and 170 AU, respectively, which indicates that Sz 91 is a transition disk source with one of the largest known inner holes. The model fitting analysis of the spectral energy distribution reveals an H{sub 2} mass of 2.4 × 10{sup –3} M {sub ☉} in the cold (T < 30 K) outer part at 65 AU 3 × 10{sup –9} M {sub ☉}) of hot (T ∼ 180 K) dust possibly remains inside the inner hole of the disk. The structure of the hot component could be interpreted as either an unresolved self-luminous companion body (not directly detected in our observations) or a narrow ring inside the inner hole. Significant CO(3-2) emission with a velocity gradient along the major axis of the dust disk is concentrated on the Sz 91 position, suggesting a rotating gas disk with a radius of 420 AU. The Sz 91 disk is possibly a rare disk in an evolutionary stage immediately after the formation of protoplanets because of the large inner hole and the lower disk mass than other transition disks studied thus far.

  18. Interferometry from near-infrared to mm-wavelengths: the transition disk around TW Hydrae

    Science.gov (United States)

    Menu, Jonathan; van Boekel, Roy; Henning, Thomas; Benisty, Myriam; Chandler, Claire; Linz, Hendrik; Waelkens, Christoffel

    2013-07-01

    For over a decade, the structure of the inner "hole" in the transition disk of TW Hydrae has been a subject of strong debate. Observations at different wavelengths have been modeled largely on an individual basis, and by consequence the inferred size scales are not necessarily agreeing. The disagreement at different wavelengths can simply be an indication for inconsistency, but might as well point to radial changes in dust properties, e.g.~caused by dust growth or the disk interaction with a sub-stellar companion. To probe the innermost region of the protoplanetary disk, observations at the highest possible spatial resolution are required. We present new near- and mid-infrared (VLTI/PIONIER and VLTI/MIDI) and millimeter (VLA) interferometric data of TW Hya. On the basis of the new and archival data, we investigate the shortcomings of existing models, both on the inner-disk and the outer-disk scales. Using a genetic fitting algorithm, a detailed radiative-transfer model is determined that reproduces the multi-wavelength data set. The modeling work shows that: 1) the inner disk structure agrees with surface-density profiles following from hydrodynamical simulations for disks with a companion; 2) the (sub-)mm data agrees with a centrally concentrated large grain population. Considering the latter observation, we indicate that the inferred surface densities agree with results from dust-growth simulations in protoplanetary disks. A current "best model" is proposed.

  19. Robust Extraction of Circumstellar Structures with Nonnegative Matrix Factorization

    Science.gov (United States)

    Ren, Bin; Pueyo, Laurent; debes, John Henry; Ben Zhu, Guangtun; Duchene, Gaspard

    2018-01-01

    We apply the vectorized Non-negative Matrix Factorization (NMF) method to the post-processing of direct imaging data of exoplanetary systems such as circumstellar disks. NMF is an iterative approach that first creates a non-orthogonal and non-negative basis of components using the given reference images, then models a target with the components. The constructed model is then rescaled with a factor to compensate for the contribution from the disks. We compare NMF with existing methods (classical reference differential imaging method, and the Karhunen-Loeve image projection algorithm) using synthetic circumstellar disks, and demonstrate the superiority of NMF: with no need of prior selection of references, NMF can not only detect fainter circumstellar disks, but also better preserve their morphology. As an application to a real disk, we processed the archival Hubble Space Telescope STIS coronagraphic observations of HD 181327 with different methods and compared them.

  20. Characterizing the Evolution of Circumstellar Systems with the Hubble Space Telescope and the Gemini Planet Imager

    Science.gov (United States)

    Wolff, Schuyler; Schuyler G. Wolff

    2018-01-01

    The study of circumstellar disks at a variety of evolutionary stages is essential to understand the physical processes leading to planet formation. The recent development of high contrast instruments designed to directly image the structures surrounding nearby stars, such as the Gemini Planet Imager (GPI) and coronagraphic data from the Hubble Space Telescope (HST) have made detailed studies of circumstellar systems possible. In my thesis work I detail the observation and characterization of three systems. GPI polarization data for the transition disk, PDS 66 shows a double ring and gap structure with a temporally variable azimuthal asymmetry. This evolved morphology could indicate shadowing from some feature in the innermost regions of the disk, a gap-clearing planet, or a localized change in the dust properties of the disk. Millimeter continuum data of the DH Tau system places limits on the dust mass that is contributing to the strong accretion signature on the wide-separation planetary mass companion, DH Tau b. The lower than expected dust mass constrains the possible formation mechanism, with core accretion followed by dynamical scattering being the most likely. Finally, I present HST scattered light observations of the flared, edge-on protoplanetary disk ESO H$\\alpha$ 569. I combine these data with a spectral energy distribution to model the key structural parameters such as the geometry (disk outer radius, vertical scale height, radial flaring profile), total mass, and dust grain properties in the disk using the radiative transfer code MCFOST. In order to conduct this work, I developed a new tool set to optimize the fitting of disk parameters using the MCMC code \\texttt{emcee} to efficiently explore the high dimensional parameter space. This approach allows us to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in

  1. Exploring the Milky Way Disk Abundance Transition Zone Rgc 10 kpc with Open Clusters

    Science.gov (United States)

    Jacobson, Heather R.; Friel, E.; Pilachowski, C.

    2009-01-01

    Recent studies of the radial chemical abundance distribution among stellar populations in the Galactic disk have shown a change in the abundance trend at galactocentric distance Rgc 10 kpc, as first noted by Twarog et al. (1997). Here the gradient in [Fe/H] with distance appears to vanish, with abundances of stars at greater distances dropping to [Fe/H] -0.3, independent of galactocentric distance. Much is still unknown about the exact nature of the transition from inner to outer disk, and it is still uncertain if the outer disk has had a distinct evolutionary history from that of the inner disk. While current chemical evolution models can well match the outer disk abundances (Cescutti et al. 2007), abundances of many more stars at Rgc 9-12 kpc must be determined to better characterize the nature of the transition from inner to outer disk. We have initiated a survey of abundances of 20 open clusters in this region using spectroscopy obtained with the WIYN, KPNO 4m, CTIO 4m and Hobby-Eberly telescopes. Chemical abundances are determined for Fe, O, Na, and alpha-elements, among others. Results for the survey to date are presented here.

  2. The Architecture of the LkCa 15 Transitional Disk Revealed By High-Contrast Imaging

    Science.gov (United States)

    Thalmann, C.; Mulders, G. D.; Hodapp, K.; Janson, M.; Grady, C.A.; Min, M.; de Juan Ovelar, M.; Carson, J.; Brandt, T.; Bonnefoy, M.; hide

    2014-01-01

    We present four new epochs of Ks-band images of the young pre-transitional disk around LkCa 15 and perform extensive forward modeling to derive the physical parameters of the disk. We find indications of strongly anisotropic scattering (Henyey-Greenstein g = 0.67 (+0.18/-0.11)) and a significantly tapered gap edge ("round wall") but see no evidence that the inner disk, whose existence is predicted by the spectral energy distribution, shadows the outer regions of the disk visible in our images.We marginally confirm the existence of an offset between the disk center and the star along the line of nodes; however, the magnitude of this offset (x = 27 (+19/-20) mas) is notably lower than that found in our earlier H-band images. Intriguingly, we also find an offset of y = 69 (+49/-25) mas perpendicular to the line of nodes at high significance. If confirmed by future observations, this would imply a highly elliptical - or otherwise asymmetric - disk gap with an effective eccentricity of e ˜ 0.3. Such asymmetry would most likely be the result of dynamical sculpting by one or more unseen planets in the system. Finally, we find that the bright arc of scattered light we see in direct imaging observations originates from the near side of the disk and appears brighter than the far side because of strong forward scattering.

  3. AN IONIZED OUTFLOW FROM AB AUR, A HERBIG AE STAR WITH A TRANSITIONAL DISK

    Energy Technology Data Exchange (ETDEWEB)

    Rodríguez, Luis F.; Zapata, Luis A.; Ortiz-León, Gisela N.; Loinard, Laurent [Centro de Radioastronomía y Astrofísica, UNAM, Apdo. Postal 3-72 (Xangari), 58089 Morelia, Michoacán (Mexico); Dzib, Sergio A. [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Macías, Enrique; Anglada, Guillem, E-mail: l.rodriguez@crya.unam.mx [Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, E-18080 Granada (Spain)

    2014-09-20

    AB Aur is a Herbig Ae star with a transitional disk. Transitional disks present substantial dust clearing in their inner regions, most probably because of the formation of one or more planets, although other explanations are still viable. In transitional objects, accretion is found to be about an order of magnitude smaller than in classical full disks. Since accretion is believed to be correlated with outflow activity, centimeter free-free jets are expected to be present in association with these systems, at weaker levels than in classical protoplanetary (full) systems. We present new observations of the centimeter radio emission associated with the inner regions of AB Aur and conclude that the morphology, orientation, spectral index, and lack of temporal variability of the centimeter source imply the presence of a collimated, ionized outflow. The radio luminosity of this radio jet is, however, about 20 times smaller than that expected for a classical system of similar bolometric luminosity. We conclude that centimeter continuum emission is present in association with stars with transitional disks, but at levels than are becoming detectable only with the upgraded radio arrays. On the other hand, assuming that the jet velocity is 300 km s{sup –1}, we find that the ratio of mass loss rate to accretion rate in AB Aur is ∼0.1, similar to that found for less evolved systems.

  4. A 40 Myr OLD GASEOUS CIRCUMSTELLAR DISK AT 49 CETI: MASSIVE CO-RICH COMET CLOUDS AT YOUNG A-TYPE STARS

    International Nuclear Information System (INIS)

    Zuckerman, B.; Song, Inseok

    2012-01-01

    The gaseous molecular disk that orbits the main-sequence A-type star 49 Ceti has been known since 1995, but the stellar age and the origin of the observed carbon monoxide molecules have been unknown. We now identify 49 Ceti as a member of the 40 Myr old Argus Association and present a colliding comet model to explain the high CO concentrations seen at 49 Ceti and the 30 Myr old A-type star HD 21997. The model suggests that massive—400 Earth mass—analogs of the Sun's Kuiper Belt are in orbit around some A-type stars, that these large masses are composed primarily of comet-like objects, and that these objects are rich in CO and perhaps also CO 2 . We identify additional early-type members of the Argus Association and the Tucana/Horologium and Columba Associations; some of these stars display excess mid-infrared emission as measured with the Widefield Infrared Survey Explorer.

  5. Spectroscopic Evolution of Disintegrating Planetesimals: Minute to Month Variability in the Circumstellar Gas Associated with WD 1145+017

    Energy Technology Data Exchange (ETDEWEB)

    Redfield, Seth; Cauley, P. Wilson; Duvvuri, Girish M. [Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459 (United States); Farihi, Jay [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Parsons, Steven G. [Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH (United Kingdom); Gänsicke, Boris T., E-mail: sredfield@wesleyan.edu [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2017-04-10

    With the recent discovery of transiting planetary material around WD 1145+017, a critical target has been identified that links the evolution of planetary systems with debris disks and their accretion onto the star. We present a series of observations, five epochs over a year, taken with Keck and the VLT, which for the first time show variability of circumstellar absorption in the gas disk surrounding WD 1145+017 on timescales of minutes to months. Circumstellar absorption is measured in more than 250 lines of 14 ions among 10 different elements associated with planetary composition, e.g., O, Mg, Ca, Ti, Cr, Mn, Fe, and Ni. Broad circumstellar gas absorption with a velocity spread of 225 km s{sup −1} is detected, but over the course of a year blueshifted absorption disappears, while redshifted absorption systematically increases. A correlation of equivalent width and oscillator strength indicates that the gas is not highly optically thick (median τ ≈ 2). We discuss simple models of an eccentric disk coupled with magnetospheric accretion to explain the basic observed characteristics of these high-resolution and high signal-to-noise observations. Variability is detected on timescales of minutes in the two most recent observations, showing a loss of redshifted absorption for tens of minutes, coincident with major transit events and consistent with gas hidden behind opaque transiting material. This system currently presents a unique opportunity to learn how the gas causing the spectroscopic, circumstellar absorption is associated with the ongoing accretion evidenced by photospheric contamination, as well as the transiting planetary material detected in photometric observations.

  6. SURFACE LAYER ACCRETION IN CONVENTIONAL AND TRANSITIONAL DISKS DRIVEN BY FAR-ULTRAVIOLET IONIZATION

    International Nuclear Information System (INIS)

    Perez-Becker, Daniel; Chiang, Eugene

    2011-01-01

    Whether protoplanetary disks accrete at observationally significant rates by the magnetorotational instability (MRI) depends on how well ionized they are. Disk surface layers ionized by stellar X-rays are susceptible to charge neutralization by small condensates, ranging from ∼0.01 μm sized grains to angstrom-sized polycyclic aromatic hydrocarbons (PAHs). Ion densities in X-ray-irradiated surfaces are so low that ambipolar diffusion weakens the MRI. Here we show that ionization by stellar far-ultraviolet (FUV) radiation enables full-blown MRI turbulence in disk surface layers. Far-UV ionization of atomic carbon and sulfur produces a plasma so dense that it is immune to ion recombination on grains and PAHs. The FUV-ionized layer, of thickness 0.01-0.1 g cm -2 , behaves in the ideal magnetohydrodynamic limit and can accrete at observationally significant rates at radii ∼> 1-10 AU. Surface layer accretion driven by FUV ionization can reproduce the trend of increasing accretion rate with increasing hole size seen in transitional disks. At radii ∼<1-10 AU, FUV-ionized surface layers cannot sustain the accretion rates generated at larger distance, and unless turbulent mixing of plasma can thicken the MRI-active layer, an additional means of transport is needed. In the case of transitional disks, it could be provided by planets.

  7. A RESOLVED NEAR-INFRARED IMAGE OF THE INNER CAVITY IN THE GM Aur TRANSITIONAL DISK

    Energy Technology Data Exchange (ETDEWEB)

    Oh, Daehyeon; Yang, Yi [Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 (Japan); Hashimoto, Jun; Kusakabe, Nobuhiko [Astrobiology Center of NINS 2-21-1, Osawa, Mitaka, Tokyo, 181-8588 (Japan); Carson, Joseph C. [Department of Physics and Astronomy, College of Charleston 66 George Street, Charleston, SC 29424 (United States); Janson, Markus [Department of Astronomy, Stockholm University, AlbaNova University Center SE-106 91 Stockholm (Sweden); Kwon, Jungmi; Nakagawa, Takao [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210 (Japan); Mayama, Satoshi [The Center for the Promotion of Integrated Sciences, SOKENDAI (The Graduate University for Advanced Studies), Shonan International Village, Hayama-cho, Miura-gun, Kanagawa 240-0193 (Japan); Uyama, Taichi [Department of Astronomy, The University of Tokyo 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan); Kudo, Tomoyuki; Currie, Thayne [Subaru Telescope, National Astronomical Observatory of Japan 650 North A’ohoku Place, Hilo, HI 96720 (United States); Abe, Lyu [Laboratoire Lagrange (UMR 7293), Universite de Nice-Sophia Antipolis, CNRS, Observatoire de la Coted’azur 28 avenue Valrose, F-06108 Nice Cedex 2 (France); Akiyama, Eiji [National Astronomical Observatory of Japan 2-21-1, Osawa, Mitaka, Tokyo, 181-8588 (Japan); Brandner, Wolfgang [Max Planck Institute for Astronomy, Köonigstuhl 17, D-69117 Heidelberg (Germany); Brandt, Timothy D.; Feldt, Markus [Astrophysics Department, Institute for Advanced Study Princeton, NJ (United States); Goto, Miwa [Universitats-Sternwarte Munchen, Ludwig-Maximilians-Universitat, Scheinerstr. 1, D-81679 Munchen (Germany); Grady, Carol A. [Exoplanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center Greenbelt, MD 20771 (United States); and others

    2016-11-01

    We present high-contrast H -band polarized intensity (PI) images of the transitional disk around the young solar-like star GM Aur. The near-infrared direct imaging of the disk was derived by polarimetric differential imaging using the Subaru 8.2 m Telescope and HiCIAO. An angular resolution and an inner working angle of 0.″07 and r ∼ 0.″05, respectively, were obtained. We clearly resolved a large inner cavity, with a measured radius of 18 ± 2 au, which is smaller than that of a submillimeter interferometric image (28 au). This discrepancy in the cavity radii at near-infrared and submillimeter wavelengths may be caused by a 3–4 M {sub Jup} planet about 20 au away from the star, near the edge of the cavity. The presence of a near-infrared inner cavity is a strong constraint on hypotheses for inner cavity formation in a transitional disk. A dust filtration mechanism has been proposed to explain the large cavity in the submillimeter image, but our results suggest that this mechanism must be combined with an additional process. We found that the PI slope of the outer disk is significantly different from the intensity slope obtained from HST /NICMOS, and this difference may indicate the grain growth process in the disk.

  8. Modeling the gas-phase chemistry of the transitional disk around HD 141569A

    OpenAIRE

    Jonkheid, B.; Kamp, I.; Augereau, J. -C.; van Dishoeck, E. F.

    2006-01-01

    Aims: The chemistry, distribution and mass of the gas in the transitional disk around the 5 Myr old B9.5 V star HD 141569A are constrained. Methods: A quasi 2-dimensional (2D) chemistry code for photon dominated regions (PDR) is used to calculate the chemistry and gas temperatures in the disk. The calculations are performed for several gas distributions, PAH abundances and values of the total gas mass. The resulting CO J=2-1 and J=3-2 emission lines are computed with a 2D radiative transfer c...

  9. 3.3 CM JVLA OBSERVATIONS OF TRANSITIONAL DISKS: SEARCHING FOR CENTIMETER PEBBLES

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-01-10

    We present sensitive (rms-noises ∼4–25 μ Jy) and high angular resolution (∼1″–2″) 8.9 GHz (3.3 cm) Karl G. Jansky Very Large Array radio continuum observations of 10 presumed transitional disks associated with young low-mass stars. We report the detection of radio continuum emission in 5 out of the 10 objects (RXJ1615, UX Tau A, LkCa15, RXJ1633, and SR 24s). In the case of LkCa15, the centimeter emission is extended, and has a similar morphology to that of the transitional disk observed at millimeter wavelengths with an inner depression. For these five detections, we construct the spectral energy distributions from the centimeter to submillimeter wavelengths, and find that they can be well fitted with a single (RXJ1633 and UX Tau A) or a two-component power law (LkCa15, RXJ1615, and SR 24s). For the cases where a single power law fits the data well, the centimeter emission is likely produced by optically thin dust with large grains (i.e., centimeter-size pebbles) present in the transitional disks. For the cases where a double power law fits the data, the centimeter emission might be produced by the combination of photoevaporation and a free–free jet. We conclude that RXJ1633 and UX Tau A are excellent examples of transitional disks where the structure of the emission from centimeter/millimeter pebbles can be studied. In the other cases, some other physical emitting mechanisms are also important in the centimeter regime.

  10. 3.3 CM JVLA OBSERVATIONS OF TRANSITIONAL DISKS: SEARCHING FOR CENTIMETER PEBBLES

    International Nuclear Information System (INIS)

    Zapata, Luis A.; Rodríguez, Luis F.; Palau, Aina

    2017-01-01

    We present sensitive (rms-noises ∼4–25 μ Jy) and high angular resolution (∼1″–2″) 8.9 GHz (3.3 cm) Karl G. Jansky Very Large Array radio continuum observations of 10 presumed transitional disks associated with young low-mass stars. We report the detection of radio continuum emission in 5 out of the 10 objects (RXJ1615, UX Tau A, LkCa15, RXJ1633, and SR 24s). In the case of LkCa15, the centimeter emission is extended, and has a similar morphology to that of the transitional disk observed at millimeter wavelengths with an inner depression. For these five detections, we construct the spectral energy distributions from the centimeter to submillimeter wavelengths, and find that they can be well fitted with a single (RXJ1633 and UX Tau A) or a two-component power law (LkCa15, RXJ1615, and SR 24s). For the cases where a single power law fits the data well, the centimeter emission is likely produced by optically thin dust with large grains (i.e., centimeter-size pebbles) present in the transitional disks. For the cases where a double power law fits the data, the centimeter emission might be produced by the combination of photoevaporation and a free–free jet. We conclude that RXJ1633 and UX Tau A are excellent examples of transitional disks where the structure of the emission from centimeter/millimeter pebbles can be studied. In the other cases, some other physical emitting mechanisms are also important in the centimeter regime.

  11. Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA

    Science.gov (United States)

    van der Marel, N.; van Dishoeck, E. F.; Bruderer, S.; Pérez, L.; Isella, A.

    2015-07-01

    Context. Transitional disks with large dust cavities are important laboratories in which to study planet formation and disk evolution. Cold gas may still be present inside these cavities, but quantying this gas is challenging. The gas content is important for constraining the origin of the dust cavity. Aims: We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of 12CO 6-5 and 690 GHz (Band 9) continuum of five well-studied transitional disks. In addition, we analyze previously published Band 7 observations of a disk in the 12CO 3-2 line and 345 GHz continuum. The observations are used to set constraints on the gas and dust surface density profiles, in particular, the drop δgas of the gas density inside the dust cavity. Methods: The physical-chemical modeling code DALI was used to simultaneously analyze the gas and dust images. We modeled SR21, HD 135344B, LkCa15, SR24S, and RX J1615-3255 (Band 9) and J1604-2130 (Band 7). The spectral energy distribution and continuum visibility curve constrain the dust surface density. Then we used the same model to calculate the 12CO emission, which we compared with the observations through spectra and intensity cuts. The amount of gas inside the cavity was quantified by varying the δgas parameter. Results: Model fits to the dust and gas indicate that gas is still present inside the dust cavity for all disks, but at a reduced level. The gas surface density drops inside the cavity by at least a factor 10, while the dust density drops by at least a factor 1000. Disk masses are comparable with previous estimates from the literature, cavity radii are found to be smaller than in the data obtained with the 345 GHz SubMillimeter Array. Conclusions: The derived gas surface density profiles suggest that the cavity was cleared by one or more companions in all cases, which trapped the millimeter-sized dust at the edge of the cavity. Appendix is available in electronic form at http://www.aanda.org

  12. Sulphur monoxide exposes a potential molecular disk wind from the planet-hosting disk around HD 100546

    Science.gov (United States)

    Booth, Alice S.; Walsh, Catherine; Kama, Mihkel; Loomis, Ryan A.; Maud, Luke T.; Juhász, Attila

    2018-03-01

    Sulphur-bearing volatiles are observed to be significantly depleted in interstellar and circumstellar regions. This missing sulphur is postulated to be mostly locked up in refractory form. With ALMA we have detected sulphur monoxide (SO), a known shock tracer, in the HD 100546 protoplanetary disk. Two rotational transitions: J = 77-66 (301.286 GHz) and J = 78-67 (304.078 GHz) are detected in their respective integrated intensity maps. The stacking of these transitions results in a clear 5σ detection in the stacked line profile. The emission is compact but is spectrally resolved and the line profile has two components. One component peaks at the source velocity and the other is blue-shifted by 5 km s-1. The kinematics and spatial distribution of the SO emission are not consistent with that expected from a purely Keplerian disk. We detect additional blue-shifted emission that we attribute to a disk wind. The disk component was simulated using LIME and a physical disk structure. The disk emission is asymmetric and best fit by a wedge of emission in the north-east region of the disk coincident with a "hot-spot" observed in the CO J = 3-2 line. The favoured hypothesis is that a possible inner disk warp (seen in CO emission) directly exposes the north-east side of the disk to heating by the central star, creating locally the conditions to launch a disk wind. Chemical models of a disk wind will help to elucidate why the wind is particularly highlighted in SO emission and whether a refractory source of sulphur is needed. An alternative explanation is that the SO is tracing an accretion shock from a circumplanetary disk associated with the proposed protoplanet embedded in the disk at 50 au. We also report a non-detection of SO in the protoplanetary disk around HD 97048.

  13. RESOLVING THE GAP AND AU-SCALE ASYMMETRIES IN THE PRE-TRANSITIONAL DISK OF V1247 ORIONIS

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, Stefan; Espaillat, Catherine; Wilner, David J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Ireland, Michael J. [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Sitko, Michael L.; Swearingen, Jeremy R.; Werren, Chelsea [Department of Physics, University of Cincinnati, Cincinnati, OH 45221 (United States); Monnier, John D.; Calvet, Nuria [Department of Astronomy, University of Michigan, 918 Dennison Building, Ann Arbor, MI 48109 (United States); Grady, Carol A. [Eureka Scientific Inc., Oakland, CA 94602 (United States); Harries, Tim J. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Hoenig, Sebastian F. [Department of Physics, University of California Santa Barbara, Broida Hall, Santa Barbara, CA 93106 (United States); Russell, Ray W. [The Aerospace Corporation, Los Angeles, CA 90009 (United States)

    2013-05-01

    Pre-transitional disks are protoplanetary disks with a gapped disk structure, potentially indicating the presence of young planets in these systems. In order to explore the structure of these objects and their gap-opening mechanism, we observed the pre-transitional disk V1247 Orionis using the Very Large Telescope Interferometer, the Keck Interferometer, Keck-II, Gemini South, and IRTF. This allows us to spatially resolve the AU-scale disk structure from near- to mid-infrared wavelengths (1.5-13 {mu}m), tracing material at different temperatures and over a wide range of stellocentric radii. Our observations reveal a narrow, optically thick inner-disk component (located at 0.18 AU from the star) that is separated from the optically thick outer disk (radii {approx}> 46 AU), providing unambiguous evidence for the existence of a gap in this pre-transitional disk. Surprisingly, we find that the gap region is filled with significant amounts of optically thin material with a carbon-dominated dust mineralogy. The presence of this optically thin gap material cannot be deduced solely from the spectral energy distribution, yet it is the dominant contributor at mid-infrared wavelengths. Furthermore, using Keck/NIRC2 aperture masking observations in the H, K', and L' bands, we detect asymmetries in the brightness distribution on scales of {approx}15-40 AU, i.e., within the gap region. The detected asymmetries are highly significant, yet their amplitude and direction changes with wavelength, which is not consistent with a companion interpretation but indicates an inhomogeneous distribution of the gap material. We interpret this as strong evidence for the presence of complex density structures, possibly reflecting the dynamical interaction of the disk material with sub-stellar mass bodies that are responsible for the gap clearing.

  14. Bit-mapped Holograms Using Phase Transition Mastering (PTM) and Blu-ray Disks

    International Nuclear Information System (INIS)

    Barnhart, Donald

    2013-01-01

    Due to recent advances made in data storage, cloud computing, and Blu-ray mastering technology, it is now straight forward to calculate, store, transfer, and print bitmapped holograms that use terabytes of data and tera-pixels of information. This presentation reports on the potential of using the phase transition mastering (PTM) process to construct bitmapped, computer generated holograms with spatial resolutions of 5000 line-pairs/mm (70 nm pixel width). In particular, for Blu-ray disk production, Sony has developed a complete process that could be alternately deployed in holographic applications. The PTM process uses a 405 nm laser to write phase patterns onto a layer of imperfect transition metal oxides that is deposited onto an 8 inch silicon wafer. After the master hologram has been constructed, its imprint can then be cheaply mass produced with the same process as Blu-ray disks or embossed holograms. Unlike traditional binary holograms made with expensive e-beam lithography, the PTM process has the potential for multiple phase levels using inexpensive optics similar to consumer-grade desktop Blu-ray writers. This PTM process could revolutionise holography for entertainment, industrial, and scientific applications.

  15. PANCHROMATIC IMAGING OF A TRANSITIONAL DISK: THE DISK OF GM AUR IN OPTICAL AND FUV SCATTERED LIGHT

    International Nuclear Information System (INIS)

    Hornbeck, J. B.; Williger, G. M.; Lauroesch, J. T.; Swearingen, J. R.; Sitko, M. L.; Champney, E. H.; Grady, C. A.; Brown, A.; Wisniewski, J. P.; Perrin, M. D.; Schneider, G.; Apai, D.; Brittain, S.; Brown, J. M.; Hamaguchi, K.; Henning, Th.; Lynch, D. K.; Russell, R. W.; Petre, R.; Walter, F. M.

    2016-01-01

    We have imaged GM Aurigae with the Hubble Space Telescope , detected its disk in scattered light at 1400 and 1650 Å, and compared these with observations at 3300 Å, 5550 Å, 1.1 μ m, and 1.6 μ m. The scattered light increases at shorter wavelengths. The radial surface brightness profile at 3300 Å shows no evidence of the 24 au radius cavity that has been previously observed in submillimeter observations. Comparison with dust grain opacity models indicates that the surface of the entire disk is populated with submicron grains. We have compiled a spectral energy distribution from 0.1 μ m to 1 mm and used it to constrain a model of the star + disk system that includes the submillimeter cavity using the Monte Carlo radiative transfer code by Barbara Whitney. The best-fit model image indicates that the cavity should be detectable in the F330W bandpass if the cavity has been cleared of both large and small dust grains, but we do not detect it. The lack of an observed cavity can be explained by the presence of submicron grains interior to the submillimeter cavity wall. We suggest one explanation for this that could be due to a planet of mass <9 M J interior to 24 au. A unique cylindrical structure is detected in the far-UV data from the Advanced Camera for Surveys/Solar Blind Channel. It is aligned along the system semiminor axis, but does not resemble an accretion-driven jet. The structure is limb brightened and extends 190 ± 35 au above the disk midplane. The inner radius of the limb brightening is 40 ± 10 au, just beyond the submillimeter cavity wall.

  16. PANCHROMATIC IMAGING OF A TRANSITIONAL DISK: THE DISK OF GM AUR IN OPTICAL AND FUV SCATTERED LIGHT

    Energy Technology Data Exchange (ETDEWEB)

    Hornbeck, J. B.; Williger, G. M.; Lauroesch, J. T. [Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292 (United States); Swearingen, J. R.; Sitko, M. L.; Champney, E. H. [Department of Physics, University of Cincinnati, 400 Geology/Physics Building, P.O. Box 210011, Cincinnati, OH 45221-0377 (United States); Grady, C. A. [Eureka Scientific, 2452 Delmer Street, Suite 100, Oakland, CA 96402 (United States); Brown, A. [CASA, University of Colorado, Boulder, CO 80309-0593 (United States); Wisniewski, J. P. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks Street, Norman, OK 73019 (United States); Perrin, M. D.; Schneider, G. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Apai, D. [Department of Astronomy and Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Brittain, S. [Department of Physics and Astronomy, Clemson University, 118 Kinard Laboratory, Clemson, SC 29634-0978 (United States); Brown, J. M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hamaguchi, K. [Department of Physics, UMBC, Baltimore, MD 21250 (United States); Henning, Th. [Max-Planck-Institut Für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Lynch, D. K.; Russell, R. W. [The Aerospace Corporation, Los Angeles, CA 90009 (United States); Petre, R. [NASA’s Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Walter, F. M., E-mail: jeremy.hornbeck@louisville.edu, E-mail: gmwill06@louisville.edu, E-mail: carol.a.grady@nasa.gov [Department of Physics and Astronomy, Z = 3800, Stony Brook University, Stony Brook, NY 11794-3800 (United States); and others

    2016-10-01

    We have imaged GM Aurigae with the Hubble Space Telescope , detected its disk in scattered light at 1400 and 1650 Å, and compared these with observations at 3300 Å, 5550 Å, 1.1 μ m, and 1.6 μ m. The scattered light increases at shorter wavelengths. The radial surface brightness profile at 3300 Å shows no evidence of the 24 au radius cavity that has been previously observed in submillimeter observations. Comparison with dust grain opacity models indicates that the surface of the entire disk is populated with submicron grains. We have compiled a spectral energy distribution from 0.1 μ m to 1 mm and used it to constrain a model of the star + disk system that includes the submillimeter cavity using the Monte Carlo radiative transfer code by Barbara Whitney. The best-fit model image indicates that the cavity should be detectable in the F330W bandpass if the cavity has been cleared of both large and small dust grains, but we do not detect it. The lack of an observed cavity can be explained by the presence of submicron grains interior to the submillimeter cavity wall. We suggest one explanation for this that could be due to a planet of mass <9 M {sub J} interior to 24 au. A unique cylindrical structure is detected in the far-UV data from the Advanced Camera for Surveys/Solar Blind Channel. It is aligned along the system semiminor axis, but does not resemble an accretion-driven jet. The structure is limb brightened and extends 190 ± 35 au above the disk midplane. The inner radius of the limb brightening is 40 ± 10 au, just beyond the submillimeter cavity wall.

  17. Radial decoupling of small and large dust grains in the transitional disk RX J1615.3-3255

    NARCIS (Netherlands)

    Kooistra, Robin; Kamp, Inga; Fukagawa, Misato; Ménard, François; Momose, Munetake; Tsukagoshi, Takashi; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Hashimoto, Jun; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph C.; Egner, Sebastian E.; Feldt, Markus; Goto, Miwa; Grady, Carol A.; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H.; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Wisniewski, John; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide; Currie, Thayne; Akiyama, Eiji; Mayama, Satoshi; Follette, Katherine B.; Nakagawa, Takao

    2017-01-01

    We present H-band (1.6 μm) scattered light observations of the transitional disk RX J1615.3-3255, located in the 1 Myr old Lupus association. From a polarized intensity image, taken with the HiCIAO instrument of the Subaru Telescope, we deduce the position angle and the inclination angle of the

  18. Chapter 3 Circumstellar Materials of Young Stellar Objects : Part II Formation Processes of Protostars : Origin of the Solar System

    OpenAIRE

    Shuji, SATO; National Astronomical Observatory

    1989-01-01

    We review observational evidence and evolution of circumstellar materials surrounding T Tauri stars and related low-mass young stars. Observations of broad-band photometry, polarization and spectrophotometry are reasonably understood in the context of evolution of circumstellar disks from protostars to T Tauri stars. We try to date the observed features based on the H-R diagrams.

  19. MID-INFRARED IMAGING OF THE TRANSITIONAL DISK OF HD 169142: MEASURING THE SIZE OF THE GAP

    Energy Technology Data Exchange (ETDEWEB)

    Honda, M. [Department of Mathematics and Physics, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293 (Japan); Maaskant, Koen; Waters, L. B. F. M.; Dominik, C.; Mulders, G. D. [Astronomical Institute Anton Pannekoek, University of Amsterdam, P.O. Box 94249, 1090 GE Amsterdam (Netherlands); Okamoto, Y. K. [Institute of Astrophysics and Planetary Sciences, Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan); Kataza, H. [Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan); Fukagawa, M. [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Tielens, A. G. G. M. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Min, M. [Astronomical Institute Utrecht, Utrecht University, P.O. Box 80000, 3508 TA Utrecht (Netherlands); Yamashita, T. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Fujiyoshi, T.; Fujiwara, H. [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Miyata, T.; Sako, S. [Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Sakon, I.; Onaka, T. [Department of Astronomy, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2012-06-20

    The disk around the Herbig Ae star HD 169142 was imaged and resolved at 18.8 and 24.5 {mu}m using Subaru/COMICS. We interpret the observations using a two-dimensional radiative transfer model and find evidence for the presence of a large gap. The mid-infrared images trace dust that is emitted at the onset of a strong rise in the spectral energy distribution (SED) at 20 {mu}m, and are therefore very sensitive to the location and characteristics of the inner wall of the outer disk and its dust. We determine the location of the wall to be 23{sup +3}{sub -5} AU from the star. An extra component of hot dust must exist close to the star. We find that a hydrostatic optically thick inner disk does not produce enough flux in the near-infrared, and an optically thin, geometrically thick component is our solution to fit the SED. Considering the recent findings of gaps and holes in a number of Herbig Ae/Be group I disks, we suggest that such disk structures may be common in group I sources. Classification as group I should be considered a strong case for classification as a transitional disk, though improved imaging surveys are needed to support this speculation.

  20. MID-INFRARED IMAGING OF THE TRANSITIONAL DISK OF HD 169142: MEASURING THE SIZE OF THE GAP

    International Nuclear Information System (INIS)

    Honda, M.; Maaskant, Koen; Waters, L. B. F. M.; Dominik, C.; Mulders, G. D.; Okamoto, Y. K.; Kataza, H.; Fukagawa, M.; Tielens, A. G. G. M.; Min, M.; Yamashita, T.; Fujiyoshi, T.; Fujiwara, H.; Miyata, T.; Sako, S.; Sakon, I.; Onaka, T.

    2012-01-01

    The disk around the Herbig Ae star HD 169142 was imaged and resolved at 18.8 and 24.5 μm using Subaru/COMICS. We interpret the observations using a two-dimensional radiative transfer model and find evidence for the presence of a large gap. The mid-infrared images trace dust that is emitted at the onset of a strong rise in the spectral energy distribution (SED) at 20 μm, and are therefore very sensitive to the location and characteristics of the inner wall of the outer disk and its dust. We determine the location of the wall to be 23 +3 –5 AU from the star. An extra component of hot dust must exist close to the star. We find that a hydrostatic optically thick inner disk does not produce enough flux in the near-infrared, and an optically thin, geometrically thick component is our solution to fit the SED. Considering the recent findings of gaps and holes in a number of Herbig Ae/Be group I disks, we suggest that such disk structures may be common in group I sources. Classification as group I should be considered a strong case for classification as a transitional disk, though improved imaging surveys are needed to support this speculation.

  1. VARIABILITY OF DISK EMISSION IN PRE-MAIN SEQUENCE AND RELATED STARS. III. EXPLORING STRUCTURAL CHANGES IN THE PRE-TRANSITIONAL DISK IN HD 169142

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Kevin R.; Sitko, Michael L.; Swearingen, Jeremy R.; Champney, Elizabeth H.; Johnson, Alexa N.; Werren, Chelsea [Department of Physics, University of Cincinnati, Cincinnati, OH 45221 (United States); Grady, Carol A. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Whitney, Barbara A. [Department of Astronomy, University of Wisconsin, 475 North CharterStreet, Madison, WI 53706-1582 (United States); Russell, Ray W. [The Aerospace Corporation, Los Angeles, CA 90009 (United States); Schneider, Glenn H. [Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, AZ 85721 (United States); Momose, Munetake [Ibaraki University, 310-0056 Ibaraki, Mito, Bunkyo, 11 (Japan); Muto, Takayuki [Kogakuin University, 1-24-2 Nishishinjuku, Shinjuku, Tokyo 163-8677 (Japan); Inoue, Akio K. [Osaka Sangyo University, College of General Education, 3-1-1 Nakagaito, Daito, Osaka 574-8530 (Japan); Lauroesch, James T.; Hornbeck, Jeremy [University of Louisville Research Foundation, Inc., 2301 South 3rd Street, Louisville, KY 40292 (United States); Brown, Alexander [Center for Astrophysics and Space Astronomy, Astrophysics Research Laboratory, 593 UCB, University of Colorado, Boulder, CO 80309-0593 (United States); Fukagawa, Misato [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Currie, Thayne M. [Oak Ridge Associated Universities, 100 ORAU Way, Oak Ridge, TN 37830-6218 (United States); Wisniewski, John P. [University of Oklahoma, 660 Parrington Oval, Norman, OK 73019 (United States); Woodgate, Bruce E., E-mail: wagnekr@mail.uc.edu, E-mail: sitkoml@ucmail.uc.edu, E-mail: swearijr@mail.uc.edu, E-mail: ehchampney@gmail.com, E-mail: astefank@andrew.cmu.edu, E-mail: ccwerren@yahoo.com, E-mail: carol.a.grady@nasa.gov, E-mail: bwhitney@astro.wisc.edu, E-mail: Ray.W.Russell@aero.org [NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)

    2015-01-10

    We present near-IR (NIR) and far-UV observations of the pre-transitional (gapped) disk in HD 169142 using NASA's Infrared Telescope Facility and Hubble Space Telescope. The combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between ∼1.5-10 μm over a maximum timescale of 10 yr. All observations known to us separate into two distinct states corresponding to a high near-IR state in the pre-2000 epoch and a low state in the post-2000 epoch, indicating activity within the ≲1 AU region of the disk. Through analysis of the Pa β and Br γ lines in our data we derive a mass accretion rate in 2013 May of M-dot ≈ (1.5-2.7) × 10{sup –9} M {sub ☉} yr{sup –1}. We present a theoretical modeling analysis of the disk in HD 169142 using Monte-Carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 yr of observations. We find that shifting the outer edge (r ≈ 0.3 AU) of the inner disk by 0.05 AU toward the star (in simulation of accretion and/or sculpting by forming planets) successfully reproduces the shift in NIR flux. We establish that the ∼40-70 AU dark ring imaged in the NIR by Quanz et al. and Momose et al. and at 7 mm by Osorio et al. may be reproduced with a 30% scaled density profile throughout the region, strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies.

  2. GAPS IN PROTOPLANETARY DISKS AS SIGNATURES OF PLANETS. II. INCLINED DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Jang-Condell, Hannah [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Turner, Neal J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

    2013-07-20

    We examine the observational appearance of partial gaps being opened by planets in protoplanetary disks, considering the effects of the inclination relative to the line of sight. We model the disks with static {alpha}-models with detailed radiative transfer, parameterizing the shape and size of the partially cleared gaps based on the results of hydrodynamic simulations. As in previous work, starlight falling across the gap leads to high surface brightness contrasts. The gap's trough is darkened by both shadowing and cooling, relative to the uninterrupted disk. The gap's outer wall is brightened by direct illumination and also by heating, which puffs it up so that it intercepts more starlight. In this paper, we examine the effects of inclination on resolved images of disks with and without gaps at a wide range of wavelengths. The scattering surface's offset from the disk midplane creates a brightness asymmetry along the axis of inclination, making the disk's near side appear brighter than the far side in scattered light. Finite disk thickness also causes the projected distances of equidistant points on the disk surface to be smaller on the near side of the disk as compared to the far side. Consequently, the gap shoulder on the near side of the disk should appear brighter and closer to the star than on the far side. However, if the angular resolution of the observation is coarser than the width of the brightened gap shoulder, then the gap shoulder on the far side may appear brighter because of its larger apparent size. We present a formula to recover the scale height and inclination angle of an imaged disk using simple geometric arguments and measuring disk asymmetries. Resolved images of circumstellar disks have revealed clearings and gaps, such as the transitional disk in LkCa 15. Models created using our synthetic imaging attempting to match the morphology of observed scattered light images of LkCa 15 indicate that the H-band flux deficit in

  3. Testing giant planet formation in the transitional disk of SAO 206462 using deep VLT/SPHERE imaging

    Science.gov (United States)

    Maire, A.-L.; Stolker, T.; Messina, S.; Müller, A.; Biller, B. A.; Currie, T.; Dominik, C.; Grady, C. A.; Boccaletti, A.; Bonnefoy, M.; Chauvin, G.; Galicher, R.; Millward, M.; Pohl, A.; Brandner, W.; Henning, T.; Lagrange, A.-M.; Langlois, M.; Meyer, M. R.; Quanz, S. P.; Vigan, A.; Zurlo, A.; van Boekel, R.; Buenzli, E.; Buey, T.; Desidera, S.; Feldt, M.; Fusco, T.; Ginski, C.; Giro, E.; Gratton, R.; Hubin, N.; Lannier, J.; Le Mignant, D.; Mesa, D.; Peretti, S.; Perrot, C.; Ramos, J. R.; Salter, G.; Samland, M.; Sissa, E.; Stadler, E.; Thalmann, C.; Udry, S.; Weber, L.

    2017-05-01

    Context. The SAO 206462 (HD 135344B) disk is one of the few known transitional disks showing asymmetric features in scattered light and thermal emission. Near-infrared scattered-light images revealed two bright outer spiral arms and an inner cavity depleted in dust. Giant protoplanets have been proposed to account for the disk morphology. Aims: We aim to search for giant planets responsible for the disk features and, in the case of non-detection, to constrain recent planet predictions using the data detection limits. Methods: We obtained new high-contrast and high-resolution total intensity images of the target spanning the Y to the K bands (0.95-2.3 μm) using the VLT/SPHERE near-infrared camera and integral field spectrometer. Results: The spiral arms and the outer cavity edge are revealed at high resolutions and sensitivities without the need for aggressive image post-processing techniques, which introduce photometric biases. We do not detect any close-in companions. For the derivation of the detection limits on putative giant planets embedded in the disk, we show that the knowledge of the disk aspect ratio and viscosity is critical for the estimation of the attenuation of a planet signal by the protoplanetary dust because of the gaps that these putative planets may open. Given assumptions on these parameters, the mass limits can vary from 2-5 to 4-7 Jupiter masses at separations beyond the disk spiral arms. The SPHERE detection limits are more stringent than those derived from archival NaCo/L' data and provide new constraints on a few recent predictions of massive planets (4-15 MJ) based on the spiral density wave theory. The SPHERE and ALMA data do not favor the hypotheses on massive giant planets in the outer disk (beyond 0.6''). There could still be low-mass planets in the outer disk and/or planets inside the cavity. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 095.C

  4. IMAGING THE INNER AND OUTER GAPS OF THE PRE-TRANSITIONAL DISK OF HD 169142 AT 7 mm

    Energy Technology Data Exchange (ETDEWEB)

    Osorio, Mayra; Anglada, Guillem; Macías, Enrique; Gómez, José F.; Mayen-Gijon, Juan M. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Carrasco-González, Carlos; Rodríguez, Luis F.; D' Alessio, Paola [Centro de Radioastronomía y Astrofísica, UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán (Mexico); Torrelles, José M. [Institut de Ciències de l' Espai (CSIC)-Institut de Ciències del Cosmos (UB)/IEEC, Martí i Franquès 1, E-08028 Barcelona (Spain); Calvet, Nuria [Department of Astronomy, University of Michigan, 825 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Nagel, Erick [Departamento de Astronomía, Universidad de Guanajuato, Guanajuato, Gto 36240 (Mexico); Dent, William R. F. [ALMA SCO, Alonso de Córdova 3107, Vitacura, Santiago (Chile); Quanz, Sascha P.; Reggiani, Maddalena, E-mail: osorio@iaa.es [Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich (Switzerland)

    2014-08-20

    We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ∼25-30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trapping of large dust grains. Our observations also reveal an outer annular gap at radii from ∼40 to ∼70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (millimeter/centimeter sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron-sized) dust grains. We model the broadband spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ∼0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects.

  5. IMAGING THE INNER AND OUTER GAPS OF THE PRE-TRANSITIONAL DISK OF HD 169142 AT 7 mm

    International Nuclear Information System (INIS)

    Osorio, Mayra; Anglada, Guillem; Macías, Enrique; Gómez, José F.; Mayen-Gijon, Juan M.; Carrasco-González, Carlos; Rodríguez, Luis F.; D'Alessio, Paola; Torrelles, José M.; Calvet, Nuria; Nagel, Erick; Dent, William R. F.; Quanz, Sascha P.; Reggiani, Maddalena

    2014-01-01

    We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ∼25-30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trapping of large dust grains. Our observations also reveal an outer annular gap at radii from ∼40 to ∼70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (millimeter/centimeter sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron-sized) dust grains. We model the broadband spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ∼0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects

  6. DISCOVERY OF Hα EMISSION FROM THE CLOSE COMPANION INSIDE THE GAP OF TRANSITIONAL DISK HD 142527

    International Nuclear Information System (INIS)

    Close, L. M.; Follette, K. B.; Males, J. R.; Apai, D.; Morzinski, K.; Rodigas, T. J.; Hinz, P.; Bailey, V.; Puglisi, A.; Xompero, M.; Briguglio, R.; Najita, J.; Weinberger, A. J.

    2014-01-01

    We utilized the new high-order 585 actuator Magellan Adaptive Optics system (MagAO) to obtain very high-resolution visible light images of HD 142527 with MagAO's VisAO science camera. In the median seeing conditions of the 6.5 m Magellan telescope (0.''5–0.''7), we find MagAO delivers 24%-19% Strehl at Hα (0.656 μm). We detect a faint companion (HD 142527B) embedded in this young transitional disk system at just 86.3 ± 1.9 mas (∼12 AU) from the star. The companion is detected in both Hα and a continuum filter (Δmag = 6.33 ± 0.20 mag at Hα and 7.50 ± 0.25 mag in the continuum filter). This provides confirmation of the tentative companion discovered by Biller and co-workers with sparse aperture masking at the 8 m Very Large Telescope. The Hα emission from the ∼0.25 solar mass companion (EW = 180 Å) implies a mass accretion rate of ∼5.9 × 10 –10 M sun yr –1 and a total accretion luminosity of 1.2% L sun . Assuming a similar accretion rate, we estimate that a 1 Jupiter mass gas giant could have considerably better (50-1000×) planet/star contrasts at Hα than at the H band (COND models) for a range of optical extinctions (3.4-0 mag). We suggest that ∼0.5-5 M jup extrasolar planets in their gas accretion phase could be much more luminous at Hα than in the NIR. This is the motivation for our new MagAO GAPplanetS survey for extrasolar planets

  7. DISCOVERY OF Hα EMISSION FROM THE CLOSE COMPANION INSIDE THE GAP OF TRANSITIONAL DISK HD 142527

    Energy Technology Data Exchange (ETDEWEB)

    Close, L. M.; Follette, K. B.; Males, J. R.; Apai, D.; Morzinski, K.; Rodigas, T. J.; Hinz, P.; Bailey, V. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Puglisi, A.; Xompero, M.; Briguglio, R. [INAF-Osservatorio Astrofisico di Arcetri, I-50125, Firenze (Italy); Najita, J. [NOAO, 950 N Cherry Ave. Tucson, AZ 85719 (United States); Weinberger, A. J., E-mail: lclose@as.arizona.edu [Carnegie Institution DTM, 5241 Broad Branch Rd, Washington, DC 20015 (United States)

    2014-02-01

    We utilized the new high-order 585 actuator Magellan Adaptive Optics system (MagAO) to obtain very high-resolution visible light images of HD 142527 with MagAO's VisAO science camera. In the median seeing conditions of the 6.5 m Magellan telescope (0.''5–0.''7), we find MagAO delivers 24%-19% Strehl at Hα (0.656 μm). We detect a faint companion (HD 142527B) embedded in this young transitional disk system at just 86.3 ± 1.9 mas (∼12 AU) from the star. The companion is detected in both Hα and a continuum filter (Δmag = 6.33 ± 0.20 mag at Hα and 7.50 ± 0.25 mag in the continuum filter). This provides confirmation of the tentative companion discovered by Biller and co-workers with sparse aperture masking at the 8 m Very Large Telescope. The Hα emission from the ∼0.25 solar mass companion (EW = 180 Å) implies a mass accretion rate of ∼5.9 × 10{sup –10} M {sub sun} yr{sup –1} and a total accretion luminosity of 1.2% L {sub sun}. Assuming a similar accretion rate, we estimate that a 1 Jupiter mass gas giant could have considerably better (50-1000×) planet/star contrasts at Hα than at the H band (COND models) for a range of optical extinctions (3.4-0 mag). We suggest that ∼0.5-5 M {sub jup} extrasolar planets in their gas accretion phase could be much more luminous at Hα than in the NIR. This is the motivation for our new MagAO GAPplanetS survey for extrasolar planets.

  8. THE STRUCTURE OF PRE-TRANSITIONAL PROTOPLANETARY DISKS. II. AZIMUTHAL ASYMMETRIES, DIFFERENT RADIAL DISTRIBUTIONS OF LARGE AND SMALL DUST GRAINS IN PDS 70 {sup ,}

    Energy Technology Data Exchange (ETDEWEB)

    Hashimoto, J.; Wisniewski, J. [Department of Physics and Astronomy, The University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Tsukagoshi, T. [College of Science, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512 (Japan); Brown, J. M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138 (United States); Dong, R. [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Muto, T. [Division of Liberal Arts, Kogakuin University, 1-24-2, Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677 (Japan); Zhu, Z. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Ohashi, N.; Kudo, T.; Egner, S.; Guyon, O. [Subaru Telescope, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Kusakabe, N.; Akiyama, E. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Abe, L. [Laboratoire Hippolyte Fizeau, UMR6525, Universite de Nice Sophia-Antipolis, 28, avenue Valrose, F-06108 Nice Cedex 02 (France); Brandner, W.; Carson, J.; Feldt, M. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Brandt, T. [Astrophysics Department, Institute for Advanced Study, Princeton, NJ (United States); Currie, T. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON (Canada); Grady, C. A., E-mail: jun.hashimoto@ou.edu [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); and others

    2015-01-20

    The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-μm size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations could help elucidate the origin of complicated structures of a disk. Here we report Submillimeter Array observations of the dust continuum at 1.3 mm and {sup 12}CO J = 2 → 1 line emission of the pre-transitional protoplanetary disk around the solar-mass star PDS 70. PDS 70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of ∼65 AU at NIR wavelengths. However, we found a larger gap in the disk with a radius of ∼80 AU at 1.3 mm. Emission from all three disk components (the gas and the small and large dust grains) in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.4. We suggest the asymmetries and different gap radii of the disk around PDS 70 are potentially formed by several (unseen) accreting planets inducing dust filtration.

  9. Exploring the Milky Way Disk Abundance Transition Zone R_{{GC}}˜10} kpc with Open Clusters

    Science.gov (United States)

    Jacobson, H. R.; Pilachowski, C. A.; Friel, E. D.

    2008-10-01

    Recent studies of the radial abundance distribution among stellar populations in the Galactic disk have shown a change in the abundance trend at galactocentric distance R_{GC}˜10 kpc, as first noted by Twarog et al. (1997). Here the gradient in [Fe/H] with distance appears to vanish, with abundances of stars at greater distances dropping to [Fe/H]˜-0.5, independent of galactocentric distance. Also, [α/Fe]>0 for R_{gc}>10 kpc, contrasted to the solar ratios exhibited by clusters interior to 10 kpc (Yong et al. 2005). This implies that the outer disk has undergone a different star formation history than the inner disk. However, abundances of many more stars at R_{GC}˜9-12 kpc must be determined to characterize the nature of the transition from inner to outer disk. To that end, we have initiated a spectroscopic survey of a large sample of open clusters in this region, which we describe here.

  10. Spectral Evidence for an Inner Carbon-rich Circumstellar Belt in the Young HD 36546 A-star System

    Energy Technology Data Exchange (ETDEWEB)

    Lisse, C. M. [JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723 (United States); Sitko, M. L. [Department of Physics, University of Cincinnati, Cincinnati, OH 45221-0011 and Space Science Institute, Boulder, CO 80301 (United States); Russell, R. W. [The Aerospace Corporation, Los Angeles, CA 90009 (United States); Marengo, M. [Department of Physics and Astronomy, 12 Physics Hall, Iowa State University, Ames, IA 50010 (United States); Currie, T. [Subaru Telescope, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Hilo, HI 96720 (United States); Melis, C. [Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093-0424 (United States); Mittal, T. [Department of Earth and Planetary Sciences, McCone Hall, University of California at Berkeley, Berkeley, CA 94720 (United States); Song, I., E-mail: carey.lisse@jhuapl.edu, E-mail: ron.vervack@jhuapl.edu, E-mail: sitkoml@ucmail.uc.edu, E-mail: ray.russell@aero.org, E-mail: mmarengo@iastate.edu, E-mail: currie@naoj.org, E-mail: cmelis@ucsd.edu, E-mail: tmittal2@berkeley.edu, E-mail: song@physast.uga.edu [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602-2451 (United States)

    2017-05-10

    Using the NASA/IRTF SpeX and BASS spectrometers we have obtained 0.7–13 μ m observations of the newly imaged 3–10 Myr old HD 36546 disk system. The SpeX spectrum is most consistent with the photospheric emission expected from an L {sub *} ∼ 20 L {sub ⊙}, solar abundance A1.5V star with little to no extinction, and excess emission from circumstellar dust detectable beyond 4.5 μ m. Non-detections of CO emission lines and accretion signatures point to the gas-poor circumstellar environment of a very old transition disk. Combining the SpeX + BASS spectra with archival WISE / AKARI / IRAS / Herschel photometry, we find an outer cold dust belt at ∼135 K and 20–40 au from the primary, likely coincident with the disk imaged by Subaru, and a new second inner belt with a temperature ∼570 K and an unusual, broad SED maximum in the 6–9 μ m region, tracing dust at 1.1–2.2 au. An SED maximum at 6–9 μ m has been reported in just two other A-star systems, HD 131488 and HD 121191, both of ∼10 Myr age. From Spitzer , we have also identified the ∼12 Myr old A7V HD 148657 system as having similar 5–35 μ m excess spectral features. The Spitzer data allows us to rule out water emission and rule in carbonaceous materials—organics, carbonates, SiC—as the source of the 6–9 μ m excess. Assuming a common origin for the four young A-star systems’ disks, we suggest they are experiencing an early era of carbon-rich planetesimal processing.

  11. EXTREMELY LARGE AND HOT MULTILAYER KEPLERIAN DISK AROUND THE O-TYPE PROTOSTAR W51N: THE PRECURSORS OF THE HCH II REGIONS?

    International Nuclear Information System (INIS)

    Zapata, Luis A.; Tang, Ya-Wen; Leurini, Silvia

    2010-01-01

    We present sensitive high angular resolution (0.''57-0.''78) SO, SO 2 , CO, C 2 H 5 OH, HC 3 N, and HCOCH 2 OH line observations at millimeter and submillimeter wavelengths of the young O-type protostar W51 North made with the Submillimeter Array. We report the presence of a large (about 8000 AU) and hot molecular circumstellar disk around this object, which connects the inner dusty disk with the molecular ring or toroid reported recently and confirms the existence of a single bipolar outflow emanating from this object. The molecular emission from the large disk is observed in layers with the transitions characterized by high excitation temperatures in their lower energy states (up to 1512 K) being concentrated closer to the central massive protostar. The molecular emission from those transitions with low or moderate excitation temperatures is found in the outermost parts of the disk and exhibits an inner cavity with an angular size of around 0.''7. We modeled all lines with a local thermodynamic equilibrium (LTE) synthetic spectrum. A detailed study of the kinematics of the molecular gas together with an LTE model of a circumstellar disk shows that the innermost parts of the disk are also Keplerian plus a contracting velocity. The emission of the HCOCH 2 OH reveals the possible presence of a warm 'companion' located to the northeast of the disk, however its nature is unclear. The emission of the SO and SO 2 is observed in the circumstellar disk as well as in the outflow. We suggest that the massive protostar W51 North appears to be in a phase before the presence of a hypercompact or an ultracompact H II (HC/UCH II) region and propose a possible sequence on the formation of the massive stars.

  12. Extremely Large and Hot Multilayer Keplerian Disk Around the O-type Protostar W51N: The Precursors of the HCH II Regions?

    Science.gov (United States)

    Zapata, Luis A.; Tang, Ya-Wen; Leurini, Silvia

    2010-12-01

    We present sensitive high angular resolution (0farcs57-0farcs78) SO, SO2, CO, C2H5OH, HC3N, and HCOCH2OH line observations at millimeter and submillimeter wavelengths of the young O-type protostar W51 North made with the Submillimeter Array. We report the presence of a large (about 8000 AU) and hot molecular circumstellar disk around this object, which connects the inner dusty disk with the molecular ring or toroid reported recently and confirms the existence of a single bipolar outflow emanating from this object. The molecular emission from the large disk is observed in layers with the transitions characterized by high excitation temperatures in their lower energy states (up to 1512 K) being concentrated closer to the central massive protostar. The molecular emission from those transitions with low or moderate excitation temperatures is found in the outermost parts of the disk and exhibits an inner cavity with an angular size of around 0farcs7. We modeled all lines with a local thermodynamic equilibrium (LTE) synthetic spectrum. A detailed study of the kinematics of the molecular gas together with an LTE model of a circumstellar disk shows that the innermost parts of the disk are also Keplerian plus a contracting velocity. The emission of the HCOCH2OH reveals the possible presence of a warm "companion" located to the northeast of the disk, however its nature is unclear. The emission of the SO and SO2 is observed in the circumstellar disk as well as in the outflow. We suggest that the massive protostar W51 North appears to be in a phase before the presence of a hypercompact or an ultracompact H II (HC/UCH II) region and propose a possible sequence on the formation of the massive stars.

  13. Disks around young stellar objects

    Indian Academy of Sciences (India)

    Keywords. Star formation; young stellar objects; circumstellar disks; exoplanets. Abstract. By 1939, when Chandrasekhar's classic monograph on the theory of Stellar Structure was published, although the need for recent star formation was fully acknowledged, no one had yet recognized an object that could be called a star ...

  14. SCATTERED LIGHT FROM DUST IN THE CAVITY OF THE V4046 Sgr TRANSITION DISK

    Energy Technology Data Exchange (ETDEWEB)

    Rapson, Valerie A.; Kastner, Joel H. [School of Physics and Astronomy, Rochester Institute of Technology, 1 Lomb Memorial Drive, Rochester, NY 14623-5603 (United States); Andrews, Sean M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hines, Dean C. [Space Telescope Science Institute, Baltimore, MD (United States); Macintosh, Bruce [Physics Department, Stanford University, Stanford, CA 94305 (United States); Millar-Blanchaer, Max [Department of Astronomy and Astrophysics, University of Toronto, ON, M5S 3H4 (Canada); Tamura, Motohide, E-mail: var5998@rit.edu [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan)

    2015-04-10

    We report the presence of scattered light from dust grains located in the giant planet formation region of the circumbinary disk orbiting the ∼20 Myr old close (∼0.045 AU separation) binary system V4046 Sgr AB based on observations with the new Gemini Planet Imager (GPI) instrument. These GPI images probe to within ∼7 AU of the central binary with a linear spatial resolution of ∼3 AU, and are therefore capable of revealing the dust disk structure within a region corresponding to the giant planets in our solar system. GPI imaging reveals a relatively narrow (FWHM ∼ 10 AU) ring of polarized near-infrared flux whose brightness peaks at ∼14 AU. This ∼14 AU radius ring is surrounded by a fainter outer halo of scattered light extending to ∼45 AU, which coincides with previously detected millimeter-wave thermal dust emission. The presence of small grains that efficiently scatter starlight well inside the millimeter-wavelength disk cavity supports current models of planet formation which suggest that planet–disk interactions can generate pressure traps that impose strong radial variations in the particle size distribution throughout the disk.

  15. THE DISK POPULATION OF THE TAURUS STAR-FORMING REGION

    International Nuclear Information System (INIS)

    Luhman, K. L.; Allen, P. R.; Espaillat, C.; Hartmann, L.; Calvet, N.

    2010-01-01

    We have analyzed nearly all images of the Taurus star-forming region at 3.6, 4.5, 5.8, 8.0, and 24 μm that were obtained during the cryogenic mission of the Spitzer Space Telescope (46 deg 2 ) and have measured photometry for all known members of the region that are within these data, corresponding to 348 sources, or 99% of the known stellar population. By combining these measurements with previous observations with the Spitzer Infrared Spectrograph and other facilities, we have classified the members of Taurus according to whether they show evidence of circumstellar disks and envelopes (classes I, II, and III). Through these classifications, we find that the disk fraction in Taurus, N(II)/N(II+III), is ∼75% for solar-mass stars and declines to ∼45% for low-mass stars and brown dwarfs (0.01-0.3 M sun ). This dependence on stellar mass is similar to that measured for Chamaeleon I, although the disk fraction in Taurus is slightly higher overall, probably because of its younger age (1 Myr versus 2-3 Myr). In comparison, the disk fraction for solar-mass stars is much lower (∼20%) in IC 348 and σ Ori, which are denser than Taurus and Chamaeleon I and are roughly coeval with the latter. These data indicate that disk lifetimes for solar-mass stars are longer in star-forming regions that have lower stellar densities. Through an analysis of multiple epochs of Spitzer photometry that are available for ∼200 Taurus members, we find that stars with disks exhibit significantly greater mid-infrared (mid-IR) variability than diskless stars, which agrees with the results of similar variability measurements for a smaller sample of stars in Chamaeleon I. The variability fraction for stars with disks is higher in Taurus than in Chamaeleon I, indicating that the IR variability of disks decreases with age. Finally, we have used our data in Taurus to refine the observational criteria for primordial, evolved, and transitional disks. The ratio of the number of evolved and

  16. The vertical metallicity gradient of the Milky Way disk: transitions in [α/Fe] populations

    International Nuclear Information System (INIS)

    Schlesinger, Katharine J.; Johnson, Jennifer A.; Rockosi, Constance M.; Lee, Young Sun; Beers, Timothy C.; Harding, Paul; Allende Prieto, Carlos; Bird, Jonathan C.; Schönrich, Ralph; Yanny, Brian; Schneider, Donald P.; Weaver, Benjamin A.; Brinkmann, Jon

    2014-01-01

    Using G dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey, we have determined the vertical metallicity gradient in the Milky Way's disk and examined how this gradient varies for different [α/Fe] subsamples. Our sample contains over 40,000 stars with low-resolution spectroscopy over 144 lines of sight. It also covers a significant disk volume, between ∼0.3 and 1.6 kpc from the Galactic plane, and allows us to examine the disk in situ, whereas previous analyses were more limited in scope. Furthermore, this work does not presuppose a disk structure, whether composed of a single complex population or distinct thin and thick disk components. We employ the SEGUE Stellar Parameter Pipeline to obtain estimates of stellar parameters, [Fe/H], and [α/Fe] and extract multiple volume-complete subsamples of approximately 1000 stars each. Based on SEGUE's target-selection algorithm, we adjust each subsample to determine an unbiased picture of disk chemistry; consequently, each individual star represents the properties of many. The metallicity gradient is –0.243 −0.053 +0.039 dex kpc –1 for the entire sample, which we compare to various literature results. This gradient stems from the different [α/Fe] populations inhabiting different ranges of height above the Galactic plane. Each [α/Fe] subsample shows little change in median [Fe/H] with height. If we associate [α/Fe] with age, the negligible gradients of our [α/Fe] subsamples suggest that stars formed in different epochs exhibit comparable vertical structure, implying similar star formation processes and evolution.

  17. ACCRETION-DRIVEN TURBULENCE AND THE TRANSITION TO GLOBAL INSTABILITY IN YOUNG GALAXY DISKS

    International Nuclear Information System (INIS)

    Elmegreen, Bruce G.; Burkert, Andreas

    2010-01-01

    A simple model of gas accretion in young galaxy disks suggests that fast turbulent motions can be driven by accretion energy for a time t acc ∼ 2(ε 0.5 GM 2 /ξV 3 ) 0.5 where ε is the fraction of the accretion energy going into disk turbulence, M and V are the galaxy mass and rotation speed, and ξ is the accretion rate. After t acc , accretion is replaced by disk instabilities as a source of turbulence driving, and shortly after that, energetic feedback by young stars should become important. The star formation rate equilibrates at the accretion rate after 1 to 2 t acc , depending on the star formation efficiency per dynamical time. The fast turbulence that is observed in high-redshift starburst disks is not likely to be driven by accretion because the initial t acc phase is over by the time the starburst is present. However, the high turbulent speeds that must have been present earlier, when the observed massive clumps first formed, could have been driven by accretion energy. The combined observations of a high relative velocity dispersion in the gas of z ∼ 2 clumpy galaxies and a gas mass comparable to the stellar mass suggest that either the star formation efficiency is fairly high, perhaps 10x higher than in local galaxies, or the observed turbulence is powered by young stars.

  18. Exploring Structures and Variability in the Pre-transitional Disk in HD 169142

    Science.gov (United States)

    Wagner, Kevin Robert; Sitko, Michael L.; Grady, Carol A.; Whitney, Barbara; Swearingen, Jeremy R.; Champney, Elizabeth H.; Johnson, Alexa N.; Warren, Chelsea C.; Russell, Ray W.; Schneider, Glenn; Momose, Muntake; Muto, Takayuki; Inoue, Akio K.; Lauroesch, James Thomas; Hornbeck, Jeremy; Brown, Alexander; Fukagawa, Misato; Currie, Thayne M.; Wisniewski, John P.; Woodgate, Bruce E.

    2015-01-01

    We present a theoretical modelling analysis of of the structures in the pre-transisitonal disk in HD 169142 using 3D Monte-Carlo radiative transfer simulation. The multi-epoch broadband spectral energy distribution (SED) exhibits clear evidence of changes to the inner (sub-AU) regions of the disk over a maximum timescale of 10 years with the additional constraint that the shadowing of the outer (>25 AU) disk is non-time-dependent. We find that changes to the inner dust rim (0.2 AU) cannot account for this behavior. Instead, we find that if the inner disk posses an optically thin body of small grains then changes to the outer edge of these structures may successfully reproduce the two states in the SED (analogous to what may be occurring due to accretion onto the central star or dynamical clearing by planets). Furthermore, we explore the density distributions of the outer disk structures as they are constrained by the SED and imaged surface brightness profiles, with the conclusion that a mid-plane density power law profile of r^{-2} and r^{-1} for the 35-70 AU and 70-250 AU regions, respectively, may reproduce the observations to the limit of our available complexity of structures within our modelling software. Finally, we find that a 0.3x density scaling of the 35-70 AU region reproduces the second gap imaged in the near-infrared and at 7 mm, strengthening the link to this structure being cleared by one or more planetary mass bodies.This work was supported by NASA ADAP grant NNX09AC73G, Hubble Space Telescope grant HST-GO-13032, the IR&D program at The Aerospace Corporation, and the University of Cincinnati Honors Program.

  19. HIGH-RESOLUTION 25 μM IMAGING OF THE DISKS AROUND HERBIG AE/BE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Honda, M. [Department of Mathematics and Physics, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293 (Japan); Maaskant, K. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Okamoto, Y. K. [Institute of Astrophysics and Planetary Sciences, Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan); Kataza, H. [Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan); Yamashita, T. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Miyata, T.; Sako, S.; Kamizuka, T. [Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Fujiyoshi, T.; Fujiwara, H. [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, Hawaii 96720 (United States); Sakon, I.; Onaka, T. [Department of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Mulders, G. D. [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Lopez-Rodriguez, E.; Packham, C. [Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249 (United States)

    2015-05-10

    We imaged circumstellar disks around 22 Herbig Ae/Be stars at 25 μm using Subaru/COMICS and Gemini/T-ReCS. Our sample consists of an equal number of objects from each of the two categories defined by Meeus et al.; 11 group I (flaring disk) and II (flat disk) sources. We find that group I sources tend to show more extended emission than group II sources. Previous studies have shown that the continuous disk is difficult to resolve with 8 m class telescopes in the Q band due to the strong emission from the unresolved innermost region of the disk. This indicates that the resolved Q-band sources require a hole or gap in the disk material distribution to suppress the contribution from the innermost region of the disk. As many group I sources are resolved at 25 μm, we suggest that many, but not all, group I Herbig Ae/Be disks have a hole or gap and are (pre-)transitional disks. On the other hand, the unresolved nature of many group II sources at 25 μm supports the idea that group II disks have a continuous flat disk geometry. It has been inferred that group I disks may evolve into group II through the settling of dust grains into the mid-plane of the protoplanetary disk. However, considering the growing evidence for the presence of a hole or gap in the disk of group I sources, such an evolutionary scenario is unlikely. The difference between groups I and II may reflect different evolutionary pathways of protoplanetary disks.

  20. HIGH-RESOLUTION 25 μM IMAGING OF THE DISKS AROUND HERBIG AE/BE STARS

    International Nuclear Information System (INIS)

    Honda, M.; Maaskant, K.; Okamoto, Y. K.; Kataza, H.; Yamashita, T.; Miyata, T.; Sako, S.; Kamizuka, T.; Fujiyoshi, T.; Fujiwara, H.; Sakon, I.; Onaka, T.; Mulders, G. D.; Lopez-Rodriguez, E.; Packham, C.

    2015-01-01

    We imaged circumstellar disks around 22 Herbig Ae/Be stars at 25 μm using Subaru/COMICS and Gemini/T-ReCS. Our sample consists of an equal number of objects from each of the two categories defined by Meeus et al.; 11 group I (flaring disk) and II (flat disk) sources. We find that group I sources tend to show more extended emission than group II sources. Previous studies have shown that the continuous disk is difficult to resolve with 8 m class telescopes in the Q band due to the strong emission from the unresolved innermost region of the disk. This indicates that the resolved Q-band sources require a hole or gap in the disk material distribution to suppress the contribution from the innermost region of the disk. As many group I sources are resolved at 25 μm, we suggest that many, but not all, group I Herbig Ae/Be disks have a hole or gap and are (pre-)transitional disks. On the other hand, the unresolved nature of many group II sources at 25 μm supports the idea that group II disks have a continuous flat disk geometry. It has been inferred that group I disks may evolve into group II through the settling of dust grains into the mid-plane of the protoplanetary disk. However, considering the growing evidence for the presence of a hole or gap in the disk of group I sources, such an evolutionary scenario is unlikely. The difference between groups I and II may reflect different evolutionary pathways of protoplanetary disks

  1. Molecular Gas in Debris Disks around Young A-type Stars

    Science.gov (United States)

    Moór, Attila; Curé, Michel; Kóspál, Ágnes; Ábrahám, Péter; Csengeri, Timea; Eiroa, Carlos; Gunawan, Diah; Henning, Thomas; Hughes, A. Meredith; Juhász, Attila; Pawellek, Nicole; Wyatt, Mark

    2017-11-01

    According to the current paradigm of circumstellar disk evolution, gas-rich primordial disks evolve into gas-poor debris disks that are composed of second-generation dust. To explore the transition between these phases, we searched for 12CO, 13CO, and C18O emission in seven dust-rich debris disks around young A-type stars, using the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 6. We discovered molecular gas in three debris disks. In all of these disks, the 12CO line was optically thick, highlighting the importance of less abundant molecules in reliable mass estimates. By supplementing our target list with literature data, we compiled a volume-limited sample of dust-rich debris disks around young A-type stars within 150 pc. We obtained a CO detection rate of 11/16 above a 12CO J = 2-1 line luminosity threshold of ˜1.4 × 104 Jy km s-1pc2 in the sample. This high incidence implies that the presence of CO gas in the bright debris disks around young A-type stars is more likely the rule than the exception. Interestingly, dust-rich debris disks around young FG-type stars exhibit, with the same detectability threshold as A-type stars, a significantly lower gas incidence. While the transition from the protoplanetary phase to the debris phase is associated with a drop in the dust content, our results exhibit a large spread in the CO mass in our debris sample, with peak values that are comparable to those in the protoplanetary Herbig Ae disks. In the particularly CO-rich debris systems, the gas may have a primordial origin, which is a characteristic of a hybrid disk.

  2. New Spatially Resolved Observations of the T Cha Transition Disk and Constraints on the Previously Claimed Substellar Companion

    Science.gov (United States)

    Sallum, S.; Eisner, J. A.; Close, Laird M.; Hinz, Philip M.; Skemer, Andrew J.; Bailey, Vanessa; Briguglio, Runa; Follette, Katherine B.; Males, Jared R.; Morzinski, Katie M.; Puglisi, Alfio; Rodigas, Timothy J.; Weinberger, Alycia J.; Xompero, Marco

    2015-03-01

    We present multi-epoch non-redundant masking observations of the T Cha transition disk, taken at the Very Large Telescope and Magellan in the H, Ks, and L' bands. T Cha is one of a small number of transition disks that host companion candidates discovered by high-resolution imaging techniques, with a putative companion at a position angle of 78°, separation of 62 mas, and contrast of ΔL' = 5.1 mag. We find comparable binary parameters in our re-reduction of the initial detection images, and similar parameters in the 2011 L', 2013 NaCo L', and 2013 NaCo Ks data sets. We find a close-in companion signal in the 2012 NaCo L' data set that cannot be explained by orbital motion, and a non-detection in the 2013 MagAO/Clio2 L' data. However, Monte Carlo simulations show that the best fits to the 2012 NaCo and 2013 MagAO/Clio2 followup data may be consistent with noise. There is also a significant probability of false non-detections in both of these data sets. We discuss physical scenarios that could cause the best fits, and argue that previous companion and scattering explanations are inconsistent with the results of the much larger data set presented here.

  3. NEW SPATIALLY RESOLVED OBSERVATIONS OF THE T Cha TRANSITION DISK AND CONSTRAINTS ON THE PREVIOUSLY CLAIMED SUBSTELLAR COMPANION

    International Nuclear Information System (INIS)

    Sallum, S.; Eisner, J. A.; Close, Laird M.; Hinz, Philip M.; Skemer, Andrew J.; Bailey, Vanessa; Follette, Katherine B.; Males, Jared R.; Morzinski, Katie M.; Briguglio, Runa; Puglisi, Alfio; Xompero, Marco; Rodigas, Timothy J.; Weinberger, Alycia J.

    2015-01-01

    We present multi-epoch non-redundant masking observations of the T Cha transition disk, taken at the Very Large Telescope and Magellan in the H, Ks, and L' bands. T Cha is one of a small number of transition disks that host companion candidates discovered by high-resolution imaging techniques, with a putative companion at a position angle of 78°, separation of 62 mas, and contrast of ΔL' = 5.1 mag. We find comparable binary parameters in our re-reduction of the initial detection images, and similar parameters in the 2011 L', 2013 NaCo L', and 2013 NaCo Ks data sets. We find a close-in companion signal in the 2012 NaCo L' data set that cannot be explained by orbital motion, and a non-detection in the 2013 MagAO/Clio2 L' data. However, Monte Carlo simulations show that the best fits to the 2012 NaCo and 2013 MagAO/Clio2 followup data may be consistent with noise. There is also a significant probability of false non-detections in both of these data sets. We discuss physical scenarios that could cause the best fits, and argue that previous companion and scattering explanations are inconsistent with the results of the much larger data set presented here

  4. NEW SPATIALLY RESOLVED OBSERVATIONS OF THE T Cha TRANSITION DISK AND CONSTRAINTS ON THE PREVIOUSLY CLAIMED SUBSTELLAR COMPANION

    Energy Technology Data Exchange (ETDEWEB)

    Sallum, S.; Eisner, J. A.; Close, Laird M.; Hinz, Philip M.; Skemer, Andrew J.; Bailey, Vanessa; Follette, Katherine B.; Males, Jared R.; Morzinski, Katie M. [Astronomy Department, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Briguglio, Runa; Puglisi, Alfio; Xompero, Marco [INAF-Osservatorio Astrofisico di Arcetri, I-50125 Firenze (Italy); Rodigas, Timothy J.; Weinberger, Alycia J., E-mail: ssallum@email.arizona.edu [Carnegie Institution DTM, 5241 Broad Branch Rd, Washington, DC 20015 (United States)

    2015-03-10

    We present multi-epoch non-redundant masking observations of the T Cha transition disk, taken at the Very Large Telescope and Magellan in the H, Ks, and L' bands. T Cha is one of a small number of transition disks that host companion candidates discovered by high-resolution imaging techniques, with a putative companion at a position angle of 78°, separation of 62 mas, and contrast of ΔL' = 5.1 mag. We find comparable binary parameters in our re-reduction of the initial detection images, and similar parameters in the 2011 L', 2013 NaCo L', and 2013 NaCo Ks data sets. We find a close-in companion signal in the 2012 NaCo L' data set that cannot be explained by orbital motion, and a non-detection in the 2013 MagAO/Clio2 L' data. However, Monte Carlo simulations show that the best fits to the 2012 NaCo and 2013 MagAO/Clio2 followup data may be consistent with noise. There is also a significant probability of false non-detections in both of these data sets. We discuss physical scenarios that could cause the best fits, and argue that previous companion and scattering explanations are inconsistent with the results of the much larger data set presented here.

  5. THE PROTOPLANETARY DISKS IN THE NEARBY MASSIVE STAR-FORMING REGION CYGNUS OB2

    International Nuclear Information System (INIS)

    Guarcello, M. G.; Drake, J. J.; Wright, N. J.; Hora, J. L.; Aldcroft, T.; Fruscione, A.; Kashyap, V. L.; Drew, J. E.; Gutermuth, R. A.; Naylor, T.; King, R.; García-Alvarez, D.

    2013-01-01

    The formation of stars in massive clusters is one of the main modes of the star formation process. However, the study of massive star-forming regions is hampered by their typically large distances to the Sun. One exception to this is the massive star-forming region Cygnus OB2 in the Cygnus X region, at the distance of ∼1400 pc. Cygnus OB2 hosts very rich populations of massive and low-mass stars, being the best target in our Galaxy to study the formation of stars, circumstellar disks, and planets in the presence of massive stars. In this paper, we combine a wide and deep set of photometric data, from the r band to 24 μm, in order to select the disk-bearing population of stars in Cygnus OB2 and identify the class I, class II, and stars with transition and pre-transition disks. We selected 1843 sources with infrared excesses in an area of 1° × 1° centered on Cyg OB2 in several evolutionary stages: 8.4% class I, 13.1% flat-spectrum sources, 72.9% class II, 2.3% pre-transition disks, and 3.3% transition disks. The spatial distribution of these sources shows a central cluster surrounded by an annular overdensity and some clumps of recent star formation in the outer region. Several candidate subclusters are identified, both along the overdensity and in the rest of the association

  6. DISK EVOLUTION IN THE THREE NEARBY STAR-FORMING REGIONS OF TAURUS, CHAMAELEON, AND OPHIUCHUS

    International Nuclear Information System (INIS)

    Furlan, E.; Watson, Dan M.; McClure, M. K.

    2009-01-01

    We analyze samples of Spitzer Infrared Spectrograph spectra of T Tauri stars in the Ophiuchus, Taurus, and Chamaeleon I star-forming regions, whose median ages lie in the <1-2 Myr range. The median mid-infrared spectra of objects in these three regions are similar in shape, suggesting, on average, similar disk structures. When normalized to the same stellar luminosity, the medians follow each other closely, implying comparable mid-infrared excess emission from the circumstellar disks. We use the spectral index between 13 and 31 μm and the equivalent width of the 10 μm silicate emission feature to identify objects whose disk configuration departs from that of a continuous, optically thick accretion disk. Transitional disks, whose steep 13-31 μm spectral slope and near-IR flux deficit reveal inner disk clearing, occur with about the same frequency of a few percent in all three regions. Objects with unusually large 10 μm equivalent widths are more common (20%-30%); they could reveal the presence of disk gaps filled with optically thin dust. Based on their medians and fraction of evolved disks, T Tauri stars in Taurus and Chamaeleon I are very alike. Disk evolution sets in early, since already the youngest region, the Ophiuchus core (L1688), has more settled disks with larger grains. Our results indicate that protoplanetary disks show clear signs of dust evolution at an age of a few Myr, even as early as ∼1 Myr, but age is not the only factor determining the degree of evolution during the first few million years of a disk's lifetime.

  7. Light-scattering models applied to circumstellar dust properties

    International Nuclear Information System (INIS)

    Koehler, Melanie; Mann, Ingrid

    2004-01-01

    Radiation pressure force, Poynting-Robertson effect, and collisions are important to determine the size distribution of dust in circumstellar debris disks with the two former parameters depending on the light-scattering properties of grains. We here present Mie and discrete-dipole approximation (DDA) calculations to describe the optical properties of dust particles around β Pictoris, Vega, and Fomalhaut in order to study the influence of the radiation pressure force. We find that the differences between Mie and DDA calculations are lower than 30% for all porosities. Therefore, Mie calculations can be used to determine the cut-off limits which contribute to the size distribution for the different systems

  8. DISCOVERY OF A COMPANION CANDIDATE IN THE HD 169142 TRANSITION DISK AND THE POSSIBILITY OF MULTIPLE PLANET FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Reggiani, Maddalena; Quanz, Sascha P.; Meyer, Michael R.; Amara, Adam; Avenhaus, Henning; Meru, Farzana [Institute for Astronomy, ETH Zurich, CH-8093 Zurich (Switzerland); Pueyo, Laurent; Wolff, Schuyler [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Absil, Olivier [Département d' Astrophysique, Géophysique et Océanographie, Université de Liège, 17 Allée du Six Août, B-4000 Liège (Belgium); Anglada, Guillem; Osorio, Mayra [Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Girard, Julien H.; Mawet, Dimitri; Milli, Julien [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001 Vitacura, Santiago 19 (Chile); Gonzalez, Carlos Carrasco [Centro de Radioastronomía y Astrofísica (UNAM), Apartado Postal 3-72 (Xangari), 58089 Morelia (Mexico); Graham, James [University of California, 644 Campbell Hall, Berkeley, CA (United States); Torrelles, Jose-Maria, E-mail: reggiani@phys.ethz.ch [Instituto de Ciencias del Espacio (CSIC)-UB/IEEC, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona (Spain)

    2014-09-01

    We present L'- and J-band high-contrast observations of HD 169142, obtained with the Very Large Telescope/NACO AGPM vector vortex coronagraph and the Gemini Planet Imager, respectively. A source located at 0.''156 ± 0.''032 north of the host star (P.A. = 7.°4 ± 11.°3) appears in the final reduced L' image. At the distance of the star (∼145 pc), this angular separation corresponds to a physical separation of 22.7 ± 4.7 AU, locating the source within the recently resolved inner cavity of the transition disk. The source has a brightness of L' = 12.2 ± 0.5 mag, whereas it is not detected in the J band (J >13.8 mag). If its L' brightness arose solely from the photosphere of a companion and given the J – L' color constraints, it would correspond to a 28-32 M {sub Jupiter} object at the age of the star, according to the COND models. Ongoing accretion activity of the star suggests, however, that gas is left in the inner disk cavity from which the companion could also be accreting. In this case, the object could be lower in mass and its luminosity enhanced by the accretion process and by a circumplanetary disk. A lower-mass object is more consistent with the observed cavity width. Finally, the observations enable us to place an upper limit on the L'-band flux of a second companion candidate orbiting in the disk annular gap at ∼50 AU, as suggested by millimeter observations. If the second companion is also confirmed, HD 169142 might be forming a planetary system, with at least two companions opening gaps and possibly interacting with each other.

  9. The Birth of Disks Around Protostars

    Science.gov (United States)

    Kohler, Susanna

    2017-03-01

    The dusty disks around young stars make the news regularly due to their appeal as the birthplace of early exoplanets. But how do disks like these first form and evolve around their newly born protostars? New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) are helping us to better understand this process.Formation from CollapseStars are born from the gravitational collapse of a dense cloud of molecular gas. Long before they start fusing hydrogen at their centers when they are still just hot overdensities in the process of contracting we call them protostars. These low-mass cores are hidden at the hearts of the clouds of molecular gas from which they are born.Aerial image of the Atacama Large Millimeter/submillimeter Array. [EFE/Ariel Marinkovic]During this contraction phase, before a protostar transitions to a pre-main-sequence star (which it does by blowing away its outer gas envelope, halting the stars growth), much of the collapsing material will spin into a centrifugally supported Keplerian disk that surrounds the young protostar. Later, these circumstellar disks will become the birthplace for young planets something for which weve seen observational evidence in recent years.But how do these Keplerian disks which eventually have scales of hundreds of AU first form and grow around protostars? We need observations of these disks in their early stages of formation to understand their birth and evolution a challenging prospect, given the obscuring molecular gas that hides them at these stages. ALMA, however, is up to the task: it can peer through to the center of the gas clouds to see the emission from protostellar cores and their surroundings.ALMA observations of the protostar Lupus 3 MMS. The molecular outflows from the protostar are shown in panel a. Panel b shows the continuum emission, which has a compact component that likely traces a disk surrounding the protostar. [Adapted from Yen et al. 2017]New Disks Revealed?In a recent

  10. On the Observability of Individual Population III Stars and Their Stellar-mass Black Hole Accretion Disks through Cluster Caustic Transits

    Science.gov (United States)

    Windhorst, Rogier A.; Timmes, F. X.; Wyithe, J. Stuart B.; Alpaslan, Mehmet; Andrews, Stephen K.; Coe, Daniel; Diego, Jose M.; Dijkstra, Mark; Driver, Simon P.; Kelly, Patrick L.; Kim, Duho

    2018-02-01

    We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-infrared surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z ≃ 7–17. Theoretical predictions and recent near-infrared power spectra provide tighter constraints on their sky signal. We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at z≳ 7. We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions. We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be μ ≃ {10}4{--}{10}5, with rise times of hours and decline times of ≲ 1 year for cluster transverse velocities of {v}T≲ 1000 km s‑1. Microlensing by intracluster-medium objects can modify transit magnifications but lengthen visibility times. Depending on BH masses, accretion-disk radii, and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Population III stars. To observe Population III caustic transits directly may require monitoring 3–30 lensing clusters to {AB}≲ 29 mag over a decade.

  11. Clearing Residual Planetesimals by Sweeping Secular Resonances in Transitional Disks: A Lone-planet Scenario for the Wide Gaps in Debris Disks around Vega and Fomalhaut

    Science.gov (United States)

    Zheng, Xiaochen; Lin, Douglas N. C.; Kouwenhoven, M. B. N.; Mao, Shude; Zhang, Xiaojia

    2017-11-01

    Extended gaps in the debris disks of both Vega and Fomalhaut have been observed. These structures have been attributed to tidal perturbations by multiple super-Jupiter gas giant planets. Within the current observational limits, however, no such massive planets have been detected. Here we propose a less stringent “lone-planet” scenario to account for the observed structure with a single eccentric gas giant and suggest that clearing of these wide gaps is induced by its sweeping secular resonance. With a series of numerical simulations, we show that the gravitational potential of the natal disk induces the planet to precess. At the locations where its precession frequency matches the precession frequency the planet imposes on the residual planetesimals, their eccentricity is excited by its resonant perturbation. Due to the hydrodynamic drag by the residual disk gas, the planetesimals undergo orbital decay as their excited eccentricities are effectively damped. During the depletion of the disk gas, the planet’s secular resonance propagates inward and clears a wide gap over an extended region of the disk. Although some residual intermediate-size planetesimals may remain in the gap, their surface density is too low to either produce super-Earths or lead to sufficiently frequent disruptive collisions to generate any observable dusty signatures. The main advantage of this lone-planet sweeping-secular-resonance model over the previous multiple gas giant tidal truncation scenario is the relaxed requirement on the number of gas giants. The observationally inferred upper mass limit can also be satisfied provided the hypothetical planet has a significant eccentricity. A significant fraction of solar or more massive stars bear gas giant planets with significant eccentricities. If these planets acquired their present-day kinematic properties prior to the depletion of their natal disks, their sweeping secular resonance would effectively impede the retention of neighboring

  12. HCO+ Detection of Dust-depleted Gas in the Inner Hole of the LkCa 15 Pre-transitional Disk

    NARCIS (Netherlands)

    Drabek-Maunder, E.; Mohanty, S.; Greaves, J.; Kamp, I.; Meijerink, R.; Spaans, M.; Thi, W. -F; Woitke, P.

    2016-01-01

    LkCa 15 is an extensively studied star in the Taurus region, known for its pre-transitional disk with a large inner cavity in the dust continuum and normal gas accretion rate. The most popular hypothesis to explain the LkCa 15 data invokes one or more planets to carve out the inner cavity, while gas

  13. Imaging of a transitional disk gap in reflected light: indications of planet formation around the young solar analog LkCa 15

    NARCIS (Netherlands)

    Thalmann, C.; Grady, C.A.; Gotto, M.; Min, M.

    2010-01-01

    We present H- and Ks-band imaging data resolving the gap in the transitional disk around LkCa 15, revealing the surrounding nebulosity. We detect sharp elliptical contours delimiting the nebulosity on the inside as well as the outside, consistent with the shape, size, ellipticity, and orientation of

  14. Hydrodynamical processes in planet-forming accretion disks

    Science.gov (United States)

    Lin, Min-Kai

    Understanding the physics of accretion flows in circumstellar disk provides the foundation to any theory of planet formation. The last few years have witnessed dramatic a revision in the fundamental fluid dynamics of protoplanetary accretion disks. There is growing evidence that the key to answering some of the most pressing questions, such as the origin of disk turbulence, mass transport, and planetesimal formation, may lie within, and intimately linked to, purely hydrodynamical processes in protoplanetary disks. Recent studies, including those from the proposal team, have discovered and highlighted the significance of several new hydrodynamical instabilities in the planet-forming regions of these disks. These include, but not limited to: the vertical shear instability, active between 10 to 100 AU; the zombie vortex instability, operating in regions interior to about 1AU; and the convective over-stability at intermediate radii. Secondary Rossbywave and elliptic instabilities may also be triggered, feeding off the structures that emerge from the above primary instabilities. The result of these hydrodynamic processes range from small-scale turbulence that transports angular momentum, to large-scale vortices that concentrate dust particles and enhance planetesimal formation. Hydrodynamic processes pertain to a wide range of disk conditions, meaning that at least one of these processes are active at any given disk location and evolutionary epoch. This remains true even after planet formation, which affects their subsequent orbital evolution. Hydrodynamical processes also have direct observable consequences. For example, vortices have being invoked to explain recent ALMA images of asymmetric `dust-traps' in transition disks. Hydrodynamic activities thus play a crucial role at every stage of planet formation and disk evolution. We propose to develop theoretical models of the above hydrodynamic processes under physical disk conditions by properly accounting for disk

  15. THE KOZAI-LIDOV MECHANISM IN HYDRODYNAMICAL DISKS

    International Nuclear Information System (INIS)

    Martin, Rebecca G.; Nixon, Chris; Armitage, Philip J.; Lubow, Stephen H.; Price, Daniel J.; Doğan, Suzan; King, Andrew

    2014-01-01

    We use three-dimensional hydrodynamical simulations to show that a highly misaligned accretion disk around one component of a binary system can exhibit global Kozai-Lidov cycles, where the inclination and eccentricity of the disk are interchanged periodically. This has important implications for accreting systems on all scales, for example, the formation of planets and satellites in circumstellar and circumplanetary disks, outbursts in X-ray binary systems, and accretion onto supermassive black holes

  16. STELLAR MASS DEPENDENT DISK DISPERSAL

    International Nuclear Information System (INIS)

    Kennedy, Grant M.; Kenyon, Scott J.

    2009-01-01

    We use published optical spectral and infrared (IR) excess data from nine young clusters and associations to study the stellar mass dependent dispersal of circumstellar disks. All clusters older than ∼3 Myr show a decrease in disk fraction with increasing stellar mass for solar to higher mass stars. This result is significant at about the 1σ level in each cluster. For the complete set of clusters we reject the null hypothesis-that solar and intermediate-mass stars lose their disks at the same rate-with 95%-99.9% confidence. To interpret this behavior, we investigate the impact of grain growth, binary companions, and photoevaporation on the evolution of disk signatures. Changes in grain growth timescales at fixed disk temperature may explain why early-type stars with IR excesses appear to evolve faster than their later-type counterparts. Little evidence that binary companions affect disk evolution suggests that photoevaporation is the more likely mechanism for disk dispersal. A simple photoevaporation model provides a good fit to the observed disk fractions for solar and intermediate-mass stars. Although the current mass-dependent disk dispersal signal is not strong, larger and more complete samples of clusters with ages of 3-5 Myr can improve the significance and provide better tests of theoretical models. In addition, the orbits of extra-solar planets can constrain models of disk dispersal and migration. We suggest that the signature of stellar mass dependent disk dispersal due to photoevaporation may be present in the orbits of observed extra-solar planets. Planets orbiting hosts more massive than ∼1.6 M sun may have larger orbits because the disks in which they formed were dispersed before they could migrate.

  17. CONSTRAINTS ON THE PRESENCE OF SiO GAS IN THE DEBRIS DISK OF HD 172555

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, T. L. [United States Naval Research Laboratory, Washington, DC 20375 (United States); Nilsson, R. [Astrophysics Department, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Chen, C. H.; Moerchen, M.; Banzatti, A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21212 (United States); Lisse, C. M. [Space Exploration Sector, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD, 20723 (United States); Käufl, H.-U., E-mail: thomaswilson1b@gmail.com [European Southern Observatory, K-Schwarzschild-str. 2, Garching, D-85748 (Germany)

    2016-08-01

    We have carried out two sets of observations to quantify the properties of SiO gas in the unusual HD 172555 debris disk: (1) a search for the J = 8–7 rotational transition from the vibrational ground state, carried out with the Atacama Pathfinder EXperiment (APEX) submillimeter telescope and heterodyne receiver at 863 μ m and (2) a search at 8.3 μ m for the P(17) ro-vibrational transition of gas phase SiO, carried out with the Very Large Telescope (VLT)/VISIR with a resolution, λ /Δ λ , of 30,000. The APEX measurement resulted in a 3.3 σ detection of an interstellar feature, but only an upper limit to emission at the radial velocity and line width expected from HD 172555. The VLT/VISIR result was also an upper limit. These were used to provide limits for the abundance of gas phase SiO for a range of temperatures. The upper limit from our APEX detection, assuming an 8000 K primary star photospheric excitation, falls more than an order of magnitude below the self-shielding stability threshold derived by Johnson et al. (2012). Our results thus favor a solid-state origin for the 8.3 μ m feature seen in the Spitzer IRS spectrum of the circumstellar excess emission and the production of circumstellar O i and Si i by SiO UV photolysis. The implications of these estimates are explored in the framework of models of the HD 172555 circumstellar disk.

  18. ACCRETION KINEMATICS THROUGH THE WARPED TRANSITION DISK IN HD 142527 FROM RESOLVED CO(6–5) OBSERVATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Casassus, S.; Marino, S.; Pérez, S.; Plas, G. van der; Christiaens, V.; Montesinos, Matías [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Roman, P.; Dunhill, A.; Cuadra, J.; Cieza, L.; Moral, Victor [Millennium Nucleus “Protoplanetary Disks,” Chile (Chile); Armitage, P. J. [JILA, University of Colorado and NIST, UCB 440, Boulder, CO 80309 (United States); Wootten, A., E-mail: scasassus@u.uchile.cl [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States)

    2015-10-01

    The finding of residual gas in the large central cavity of the HD 142527 disk motivates questions regarding the origin of its non-Keplerian kinematics and possible connections with planet formation. We aim to understand the physical structure that underlies the intra-cavity gaseous flows, guided by new molecular-line data in CO(6–5) with unprecedented angular resolutions. Given the warped structure inferred from the identification of scattered-light shadows cast on the outer disk, the kinematics are consistent, to first order, with axisymmetric accretion onto the inner disk occurring at all azimuths. A steady-state accretion profile, fixed at the stellar accretion rate, explains the depth of the cavity as traced in CO isotopologues. The abrupt warp and evidence for near free-fall radial flows in HD 142527 resemble theoretical models for disk tearing, which could be driven by the reported low-mass companion, whose orbit may be contained in the plane of the inner disk. The companion’s high inclination with respect to the massive outer disk could drive Kozai oscillations over long timescales; high-eccentricity periods may perhaps account for the large cavity. While shadowing by the tilted disk could imprint an azimuthal modulation in the molecular-line maps, further observations are required to ascertain the significance of azimuthal structure in the density field inside the cavity of HD 142527.

  19. The composition of circumstellar and interstellar dust

    NARCIS (Netherlands)

    Tielens, AGGM; Woodward, CE; Biscay, MD; Shull, JM

    2001-01-01

    A large number of solid dust components have been identified through analysis of stardust recovered from meteorites, and analysis of IR observations of circumstellar shells and the interstellar medium. These include graphite, hydrogenated amorphous carbon, diamond, PAHs, silicon-, iron-, and

  20. UV Spectroscopy of Star-Grazing Comets Within the 49 Ceti Debris Disk

    Science.gov (United States)

    Miles, Brittany E.; Roberge, Aki; Welsh, Barry

    2016-01-01

    We present the analysis of time-variable Doppler-shifted absorption features in far-UV spectra of the unusual 49 Ceti debris disk. This nearly edge-on disk is one of the brightest known and is one of the very few containing detectable amounts of circumstellar (CS) gas as well as dust. In our two visits of Hubble Space Telescope STIS spectra, variable absorption features are seen on the wings of lines arising from CII and CIV but not for any of the other CS absorption lines. Similar variable features have long been seen in spectra of the well-studied Beta Pictoris debris disk and attributed to the transits of star-grazing comets. We calculated the velocity ranges and apparent column densities of the 49 Cet variable gas, which appears to have been moving at velocities of tens to hundreds of kms(-1) relative to the central star. The velocities in the redshifted variable event seen in the second visit show that the maximum distances of the in falling gas at the time of transit were about 0.050.2 au from the central star. A preliminary attempt at a composition analysis of the redshifted event suggests that the C/O ratio in the in falling gas is super-solar, as it is in the bulk of the stable disk gas.

  1. Tracing Planets in Circumstellar Discs

    Directory of Open Access Journals (Sweden)

    Uribe Ana L.

    2013-04-01

    Full Text Available Planets are assumed to form in circumstellar discs around young stellar objects. The additional gravitational potential of a planet perturbs the disc and leads to characteristic structures, i.e. spiral waves and gaps, in the disc density profile. We perform a large-scale parameter study on the observability of these planet-induced structures in circumstellar discs in the (submm wavelength range for the Atacama Large (SubMillimeter Array (ALMA. On the basis of hydrodynamical and magneto-hydrodynamical simulations of star-disc-planet models we calculate the disc temperature structure and (submm images of these systems. These are used to derive simulated ALMA maps. Because appropriate objects are frequent in the Taurus-Auriga region, we focus on a distance of 140 pc and a declination of ≈ 20°. The explored range of star-disc-planet configurations consists of six hydrodynamical simulations (including magnetic fields and different planet masses, nine disc sizes with outer radii ranging from 9 AU to 225 AU, 15 total disc masses in the range between 2.67·10-7 M⊙ and 4.10·10-2 M⊙, six different central stars and two different grain size distributions, resulting in 10 000 disc models. At almost all scales and in particular down to a scale of a few AU, ALMA is able to trace disc structures induced by planet-disc interaction or the influence of magnetic fields in the wavelength range between 0.4...2.0 mm. In most cases, the optimum angular resolution is limited by the sensitivity of ALMA. However, within the range of typical masses of protoplane tary discs (0.1 M⊙...0.001 M⊙ the disc mass has a minor impact on the observability. At the distance of 140 pc it is possible to resolve discs down to 2.67·10-6 M⊙ and trace gaps in discs with 2.67·10-4 M⊙ with a signal-to-noise ratio greater than three. In general, it is more likely to trace planet-induced gaps in magneto-hydrodynamical disc models, because gaps are wider in the presence of

  2. Coronagraphic imaging of circumstellar material around evolved massive stars

    Science.gov (United States)

    Lomax, Jamie R.; Levesque, Emily; Wisniewski, John

    2018-01-01

    While many astronomical subfields (e.g. the solar, exoplanet, and disk communities) have been using coronagraphy to combat contrast ratio problems for years, the use of coronagraphic imaging techniques to probe the circumstellar environments of massive stars has been surprisingly underutilized. While current extreme adaptive optics coronagraphic imaging systems (e.g. GPI on Gemini South, SPHERE at the VLT, and SCExAO at Subaru) were built for the sole purpose of detecting exoplanets, their ability to provide large contrast ratios and small inner working angles means they can detect gas, dust, and companions that are closer to the central star than ever before. In this poster we present pilot studies of evolved massive stars using several coronagraphic imaging systems and summarize potential science gains this technique might provide.

  3. Effects of the Planetary Temperature on the Circumplanetary Disk and on the Gap

    Science.gov (United States)

    Szulágyi, J.

    2017-06-01

    Circumplanetary disks (CPDs) regulate the late accretion to the giant planet and serve as the birthplace for satellites. Understanding their characteristics via simulations also helps to prepare for their observations. Here we study disks around 1, 3, 5, and 10 M Jup planets with 3D global radiative hydrodynamic simulations with sub-planet peak resolution and various planetary temperatures. We found that as the 1 M Jup planet radiates away its formation heat, the circumplanetary envelope transitions to a disk between {T}p=6000 and 4000 K. In the case of 3-10 M Jup planets, a disk always forms. The temperature profile of the CPDs is very steep, the inner 1/6th is higher than the silicate condensation temperature, and the entire disk is higher than the water freezing point, making satellite formation impossible in this early stage (<1 Myr). Satellites might form much later and first in the outer parts of the disk, migrating inwards later on. Our disk masses are 1, 7, and 20 40× {10}-3 {M}{Jup} for the 1, 3, 5, and 10 M Jup gas giants, respectively, and we provide an empirical formula to estimate the subdisk masses based on the planet- and circumstellar disk (CSD) mass. Our finding is that the cooler the planet, the lower the temperature of the subdisk, and the higher the vertical influx velocities. The planetary gap is also both deeper and wider. We also show that the gaps in 2D and 3D are different. The subdisk eccentricity increases with {M}{{p}} and violently interacts with the CSD, making satellite-formation less likely when {M}{{p}}≳ 5{M}{Jup}.

  4. Polarimetric microlensing of circumstellar discs

    Science.gov (United States)

    Sajadian, Sedighe; Rahvar, Sohrab

    2015-12-01

    We study the benefits of polarimetry observations of microlensing events to detect and characterize circumstellar discs around the microlensed stars located at the Galactic bulge. These discs which are unresolvable from their host stars make a net polarization effect due to their projected elliptical shapes. Gravitational microlensing can magnify these signals and make them be resolved. The main aim of this work is to determine what extra information about these discs can be extracted from polarimetry observations of microlensing events in addition to those given by photometry ones. Hot discs which are closer to their host stars are more likely to be detected by microlensing, owing to more contributions in the total flux. By considering this kind of discs, we show that although the polarimetric efficiency for detecting discs is similar to the photometric observation, but polarimetry observations can help to constraint the disc geometrical parameters e.g. the disc inner radius and the lens trajectory with respect to the disc semimajor axis. On the other hand, the time-scale of polarimetric curves of these microlensing events generally increases while their photometric time-scale does not change. By performing a Monte Carlo simulation, we show that almost four optically thin discs around the Galactic bulge sources are detected (or even characterized) through photometry (or polarimetry) observations of high-magnification microlensing events during 10-yr monitoring of 150 million objects.

  5. THE EVOLUTION OF PROTOPLANETARY DISKS IN THE ARCHES CLUSTER

    International Nuclear Information System (INIS)

    Olczak, C.; Kaczmarek, T.; Pfalzner, S.; Harfst, S.; Portegies Zwart, S.

    2012-01-01

    Most stars form in a cluster environment. These stars are initially surrounded by disks from which potentially planetary systems form. Of all cluster environments, starburst clusters are probably the most hostile for planetary systems in our Galaxy. The intense stellar radiation and extreme density favor rapid destruction of circumstellar disks via photoevaporation and stellar encounters. Evolving a virialized model of the Arches cluster in the Galactic tidal field, we investigate the effect of stellar encounters on circumstellar disks in a prototypical starburst cluster. Despite its proximity to the deep gravitational potential of the Galactic center, only a moderate fraction of members escapes to form an extended pair of tidal tails. Our simulations show that encounters destroy one-third of the circumstellar disks in the cluster core within the first 2.5 Myr of evolution, preferentially affecting the least and most massive stars. A small fraction of these events causes rapid ejection and the formation of a weaker second pair of tidal tails that is overpopulated by disk-poor stars. Two predictions arise from our study. (1) If not destroyed by photoevaporation protoplanetary disks of massive late B- and early O-type stars represent the most likely hosts of planet formation in starburst clusters. (2) Multi-epoch K- and L-band photometry of the Arches cluster would provide the kinematically selected membership sample required to detect the additional pair of disk-poor tidal tails.

  6. A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527

    Energy Technology Data Exchange (ETDEWEB)

    Biller, Beth; Benisty, Myriam; Chauvin, Gael; Olofsson, Johan; Pott, Joerg-Uwe; Mueller, Andre; Bonnefoy, Mickaeel; Henning, Thomas [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany); Lacour, Sylvestre; Thebault, Philippe [LESIA, CNRS/UMR-8109, Observatoire de Paris, UPMC, Universite Paris Diderot, 5 place Jules Janssen, 92195 Meudon (France); Juhasz, Attila [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Sicilia-Aguilar, Aurora [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Cantoblanco, Madrid (Spain); Tuthill, Peter [School of Physics, University of Sydney, NSW 2006 (Australia); Crida, Aurelien, E-mail: biller@mpia.de [Universite de Nice - Sophia antipolis/C.N.R.S./Observatoire de la Cote d' Azur, Laboratoire Lagrange (UMR 7293), Boulevard de l' Observatoire, B.P. 4229 06304 NICE cedex 04 (France)

    2012-07-10

    With the uniquely high contrast within 0.''1 ({Delta}mag(L') = 5-6.5 mag) available using Sparse Aperture Masking with NACO at Very Large Telescope, we detected asymmetry in the flux from the Herbig Fe star HD 142527 with a barycenter emission situated at a projected separation of 88 {+-} 5 mas (12.8 {+-} 1.5 AU at 145 pc) and flux ratios in H, K, and L' of 0.016 {+-} 0.007, 0.012 {+-} 0.008, and 0.0086 {+-} 0.0011, respectively (3{sigma} errors), relative to the primary star and disk. After extensive closure-phase modeling, we interpret this detection as a close-in, low-mass stellar companion with an estimated mass of {approx}0.1-0.4 M{sub Sun }. HD 142527 has a complex disk structure, with an inner gap imaged in both the near and mid-IR as well as a spiral feature in the outer disk in the near-IR. This newly detected low-mass stellar companion may provide a critical explanation of the observed disk structure.

  7. 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

  8. The evolution of protostellar disks under the influence of external UV radiation and central stellar winds

    Science.gov (United States)

    Yorke, H. W.; Richling, S.

    2001-01-01

    The evolution and appearance of circumstellar disks in star forming regions can be influenced strongly by the radiation from nearby hot stars. Here we describe the results of numerical simulations of the evolution of protostellar disks and their immediate surroundings under the influence of external UV radiation.

  9. A deeply embedded young protoplanetary disk around L1489 IRS observed by the Submillimeter Array

    DEFF Research Database (Denmark)

    Brinch, C.; Crapsi, A.; Jørgensen, J. K.

    2007-01-01

    Context. Circumstellar disks are expected to form early in the process that leads to the formation of a young star, during the collapse of the dense molecular cloud core. Currently, it is not well understood at what stage of the collapse the disk is formed or how it subsequently evolves. Aims. We...

  10. Galaxy Disks

    NARCIS (Netherlands)

    van der Kruit, P. C.; Freeman, K. C.

    The disks of disk galaxies contain a substantial fraction of their baryonic matter and angular momentum, and much of the evolutionary activity in these galaxies, such as the formation of stars, spiral arms, bars and rings, and the various forms of secular evolution, takes place in their disks. The

  11. Transit of Mercury across the solar disk 9 May 1970 and fluctuations of radioemission at lambda = 8 mm

    International Nuclear Information System (INIS)

    Efanov, V.A.; Moiseev, I.G.; Severnyj, A.B.

    1975-01-01

    Radio-emission of the Sun was observed with the Crimea radio-telescope RT-22 during the passage of Mercury over the Sun disk on 9.05.1970. A modulation radiometer with sensitivity of approximately 1.5 deg K was used in observation. As a result of observations and correlational analysis two groups of inhomogeneities with charactetistic dimensions from 1'', 6 to 3'', 4 and from 17'' to 40'' and with brightness temperature from 9420 to 18250 deg K were revealed. Condensations were richer and colder in unperturbed regions in the Sun disk, than in active regions. Probably, the formation of condensations fo radio-emission inhomogeneities at the 8 mm wave was tightly connected with the magnetic field inhomogeneities, playing an essential part in the origin of radio-emission from separate finely structural condensations

  12. ALMA observations of the nearby AGB star L2 Puppis. II. Gas disk properties derived from 12CO and 13CO J = 3-2 emission

    Science.gov (United States)

    Homan, Ward; Richards, Anita; Decin, Leen; Kervella, Pierre; de Koter, Alex; McDonald, Iain; Ohnaka, Keiichi

    2017-05-01

    The circumstellar environment of the AGB star L2 Puppis was observed with ALMA in cycle 3, with a resolution of 15 × 18 mas. The molecular emission shows a differentially rotating disk, inclined to a nearly edge-on position. In the first paper in this series (Paper I) the molecular emission was analysed to accurately deduce the motion of the gas in the equatorial regions of the disk. In this work we model the optically thick 12CO J = 3-2 and the optically thin 13CO J = 3-2 rotational transition to constrain the physical conditions in the disk. To realise this effort we make use of the 3D NLTE radiative transfer code LIME. The temperature structure and velocity structure show a high degree of complexity, both radially and vertically. The radial H2 density profile in the disk plane is characterised by a power law with a slope of -3.1. We find a 12CO over 13CO abundance ratio of 10 inside the disk. Finally, estimations of the angular momentum in the disk surpass the expected available angular momentum of the star, strongly supporting the indirect detection of a compact binary companion reported in Paper I. We estimate the mass of the companion to be around 1 Jupiter mass.

  13. Protosteller Disks Under the Influence of Winds and UV Radiation

    Science.gov (United States)

    Yorke, H. W.

    2003-01-01

    Star formation and the creation of protostellar disks generally occur in a crowded environment. Nearby young stars and protostars can influence the disks of their closets neighbors by a combination of outflows and hard radiation. The central stars themselves can have a stellar wind and may produce sufficient UV and X-ray to ultimately destroy their surrounding disks. Here we describe the results of numerical simulations of the influence that an external UV source and a central star's wind can have on its circumstellar disk. The numerical method (axial symmetry assumed) is described elsewhere. We find that protostellar disks will be destroyed on a relatively short time scale ( 10(sup 5)yr) unless they are well shielded from O-stars. Initially isotropic T-Tauri winds do not significantly influence their disks, but instead are focused toward the rotation axis by the disk wind from photoevaporation.

  14. Magnetohydrodynamics of accretion disks

    International Nuclear Information System (INIS)

    Torkelsson, U.

    1994-04-01

    The thesis consists of an introduction and summary, and five research papers. The introduction and summary provides the background in accretion disk physics and magnetohydrodynamics. The research papers describe numerical studies of magnetohydrodynamical processes in accretion disks. Paper 1 is a one-dimensional study of the effect of magnetic buoyancy on a flux tube in an accretion disk. The stabilizing influence of an accretion disk corona on the flux tube is demonstrated. Paper 2-4 present numerical simulations of mean-field dynamos in accretion disks. Paper 11 verifies the correctness of the numerical code by comparing linear models to previous work by other groups. The results are also extended to somewhat modified disk models. A transition from an oscillatory mode of negative parity for thick disks to a steady mode of even parity for thin disks is found. Preliminary results for nonlinear dynamos at very high dynamo numbers are also presented. Paper 3 describes the bifurcation behaviour of the nonlinear dynamos. For positive dynamo numbers it is found that the initial steady solution is replaced by an oscillatory solution of odd parity. For negative dynamo numbers the solution becomes chaotic at sufficiently high dynamo numbers. Paper 4 continues the studies of nonlinear dynamos, and it is demonstrated that a chaotic solution appears even for positive dynamo numbers, but that it returns to a steady solution of mixed parity at very high dynamo numbers. Paper 5 describes a first attempt at simulating the small-scale turbulence of an accretion disk in three dimensions. There is only find cases of decaying turbulence, but this is rather due to limitations of the simulations than that turbulence is really absent in accretion disks

  15. Dust-trapping Vortices and a Potentially Planet-triggered Spiral Wake in the Pre-transitional Disk of V1247 Orionis

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, Stefan; Kreplin, Alexander; Young, Alison K.; Bate, Matthew R.; Harries, Tim T.; Willson, Matthew [University of Exeter, School of Physics, Astrophysics Group, Stocker Road, Exeter EX4 4QL (United Kingdom); Fukugawa, Misato [Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Nagoya (Japan); Muto, Takayuki [Division of Liberal Arts, Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677 (Japan); Sitko, Michael L. [Department of Physics, University of Cincinnati, Cincinnati, OH 45221 (United States); Grady, Carol [Eureka Scientific, 2452 Delmer Street, Suite 100, Oakland, CA 96402 (United States); Monnier, John D. [Department of Astronomy, University of Michigan, 311 West Hall, 1085 South University Avenue, Ann Arbor, MI 48109 (United States); Wisniewski, John, E-mail: skraus@astro.ex.ac.uk [Homer L. Dodge Department of Physics, University of Oklahoma, Norman, OK 73071 (United States)

    2017-10-10

    The radial drift problem constitutes one of the most fundamental problems in planet formation theory, as it predicts particles to drift into the star before they are able to grow to planetesimal size. Dust-trapping vortices have been proposed as a possible solution to this problem, as they might be able to trap particles over millions of years, allowing them to grow beyond the radial drift barrier. Here, we present ALMA 0.″04 resolution imaging of the pre-transitional disk of V1247 Orionis that reveals an asymmetric ring as well as a sharply confined crescent structure, resembling morphologies seen in theoretical models of vortex formation. The asymmetric ring (at 0.″17 = 54 au separation from the star) and the crescent (at 0.″38 = 120 au) seem smoothly connected through a one-armed spiral-arm structure that has been found previously in scattered light. We propose a physical scenario with a planet orbiting at ∼0.″3 ≈ 100 au, where the one-armed spiral arm detected in polarized light traces the accretion stream feeding the protoplanet. The dynamical influence of the planet clears the gap between the ring and the crescent and triggers two vortices that trap millimeter-sized particles, namely, the crescent and the bright asymmetry seen in the ring. We conducted dedicated hydrodynamics simulations of a disk with an embedded planet, which results in similar spiral-arm morphologies as seen in our scattered-light images. At the position of the spiral wake and the crescent we also observe {sup 12}CO(3-2) and H{sup 12}CO{sup +} (4-3) excess line emission, likely tracing the increased scale-height in these disk regions.

  16. Identifying Planet-Forming Disks Around Young Stars

    Science.gov (United States)

    Espaillat, C.

    2013-04-01

    In the past few years, several disks with inner holes that are relatively empty of small dust grains have been detected and are known as transitional disks. Spitzer identified a new class of “pre-transitional disks” with gaps; these objects have an optically thick inner disk separated from an optically thick outer disk by an optically thin disk gap. Here we review spectral observations which provided the first confirmations of gaps in the pre-transitional disks of LkCa 15 and UX Tau A. We also review the results of a Spitzer IRS study of variability in transitional and pre-transitional objects. The structure and behavior of pre-transitional and transitional disks may be a sign of young planets forming in these disks and future studies of these disks will provide constraints to aid in theoretical modeling of planet formation.

  17. Dust Disks Around Young Stellar Objects

    Directory of Open Access Journals (Sweden)

    Kyung-Won Suh

    2016-06-01

    Full Text Available To reproduce the spectral energy distributions (SEDs of young stellar objects (YSOs, we perform radiative transfer model calculations for the circumstellar dust disks with various shapes and many dust species. For eight sample objects of T Tauri and Herbig Ae/Be stars, we compare the theoretical model SEDs with the observed SEDs described by the infrared space observatory and Spitzer space telescope spectral data. We use the model, CGPLUS, for a passive irradiated circumstellar dust disk with an inner hole and an inner rim for the eight sample YSOs. We present model parameters for the dust disk, which reproduce the observed SEDs. We find that the model requires a higher mass, luminosity, and temperature for the central star for the Herbig Ae/Be stars than those for the T Tauri stars. Generally, the outer radius, total mass, thickness, and rim height of the theoretical dust disk for the Herbig Ae/Be stars are larger than those for the T Tauri stars.

  18. CHARACTERIZATION OF THE INNER DISK AROUND HD 141569 A FROM KECK/NIRC2 L-BAND VORTEX CORONAGRAPHY

    Energy Technology Data Exchange (ETDEWEB)

    Mawet, Dimitri; Bottom, Michael; Matthews, Keith [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Choquet, Élodie; Serabyn, Eugene [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Absil, Olivier; Huby, Elsa; Gonzalez, Carlos A. Gomez; Wertz, Olivier; Carlomagno, Brunella; Christiaens, Valentin; Defrère, Denis; Delacroix, Christian; Habraken, Serge; Jolivet, Aissa [Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, 19 Allée du Six Août, B-4000 Liège (Belgium); Femenia, Bruno [W. M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743 (United States); Lebreton, Jérémy [NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Forsberg, Pontus; Karlsson, Mikael [Department of Engineering Sciences, Ångström Laboratory, Uppsala University, Box 534, SE-751 21 Uppsala (Sweden); Milli, Julien, E-mail: dmawet@astro.caltech.edu [European Southern Observatory, Alonso de Cordóva 3107, Vitacura, Santiago (Chile); and others

    2017-01-01

    HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and complex circumstellar disk, likely still in a transition stage from protoplanetary to debris disk phase. Here, we present a new image of the third inner disk component of HD 141569 A made in the L ′ band (3.8 μ m) during the commissioning of the vector vortex coronagraph that has recently been installed in the near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory Keck II adaptive optics system. We used reference point-spread function subtraction, which reveals the innermost disk component from the inner working distance of ≃23 au and up to ≃70 au. The spatial scale of our detection roughly corresponds to the optical and near-infrared scattered light, thermal Q , N , and 8.6 μ m PAH emission reported earlier. We also see an outward progression in dust location from the L ′ band to the H band (Very Large Telescope/SPHERE image) to the visible ( Hubble Space Telescope ( HST )/STIS image), which is likely indicative of dust blowout. The warm disk component is nested deep inside the two outer belts imaged by HST-NICMOS in 1999 (at 406 and 245 au, respectively). We fit our new L ′-band image and spectral energy distribution of HD 141569 A with the radiative transfer code MCFOST. Our best-fit models favor pure olivine grains and are consistent with the composition of the outer belts. While our image shows a putative very faint point-like clump or source embedded in the inner disk, we did not detect any true companion within the gap between the inner disk and the first outer ring, at a sensitivity of a few Jupiter masses.

  19. Near-Infrared Imaging Polarimetry of Inner Region of GG Tau A Disk

    Science.gov (United States)

    Yang, Yi; Hashimoto, Jun; Hayashi, Saeko S.; Tamura, Motohide; Mayama, Satoshi; Rafikov, Roman; Akiyama, Eiji; Carson, Joseph C.; Janson, Markus; Kwon, Jungmi; hide

    2016-01-01

    By performing non-masked polarization imaging with Subaru HiCIAO, polarized scattered light from the inner region of the disk around the GGTau A system was successfully detected in the H band, with a spatial resolution of approximately0 07, revealing the complicated inner disk structures around this young binary. This paper reports the observation of an arc-like structure to the north of GG Tau Ab, and part of a circumstellar structure that is noticeable around GG Tau Aa, extending to a distance of approximately 28 au from the primary star. The speckle noise around GG Tau Ab constrains its disk radius to 13 au. Based on the size of the circumbinary ring and the circumstellar disk around GG Tau Aa, these mimajor axis of the binary's orbit is likely to be 62 au. A comparison of the present observations with previous Atacama Large Millimeter Array and near-infrared H2 emission observations suggests that the north arc could be part of a large streamer flowing from the circumbinary ring to sustain the circumstellar disks. According to the previous studies,the circumstellar disk around GG Tau Aa has enough mass and can sustain itself for a duration sufficient for planet formation; thus, our study indicates that planets can form within close (separation 100 au) young binary systems.

  20. VizieR Online Data Catalog: Database of circumstellar OH masers (Engels+, 2015)

    Science.gov (United States)

    Engels, D.; Bunzel, F.

    2015-08-01

    We present a new database of circumstellar OH masers at 1612, 1665, and 1667MHz in the Milky Way galaxy in tabular form. The database (version 2.4) contains 13655 observations and 2341 different stars detected in at least one transition and includes published data until end of 2014. Interferometric follow-up observations and monitor programs are stored in two auxiliary tables. (3 data files).

  1. The peculiar balmer decrement of SN 2009ip: Constraints on circumstellar geometry

    Energy Technology Data Exchange (ETDEWEB)

    Levesque, Emily M.; Stringfellow, Guy S.; Bally, John; Keeney, Brian A. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado 389-UCB, Boulder, CO 80309 (United States); Ginsburg, Adam G., E-mail: Emily.Levesque@colorado.edu [European Southern Observatory, ESO Headquarters, Karl-Schwarzschild-Strasse 2, D-95748 Garching bei München (Germany)

    2014-01-01

    We present optical and near-IR spectroscopic observations of the luminous blue variable SN 2009ip during its remarkable photometric evolution of 2012. The spectra sample three key points in the SN 2009ip light curve, corresponding to its initial brightening in August (2012-A) and its dramatic rebrightening in early October (2012-B). Based on line fluxes and velocities measured in our spectra, we find a surprisingly low I(Hα)/I(Hβ) ratio (∼1.3-1.4) in the 2012-B spectra. Such a ratio implies either a rare Case B recombination scenario where Hα, but not Hβ, is optically thick, or an extremely high density for the circumstellar material of n{sub e} > 10{sup 13} cm{sup –3}. The Hα line intensity yields a minimum radiating surface area of ≳20,000 AU{sup 2} in Hα at the peak of SN 2009ip's photometric evolution. Combined with the nature of this object's spectral evolution in 2012, a high circumstellar density and large radiating surface area imply the presence of a thin disk geometry around the central star (and, consequently, a possible binary companion), suggesting that the observed 2012-B rebrightening of SN 2009ip can be attributed to the illumination of the disk's inner rim by fast-moving ejecta produced by the underlying events of 2012-A.

  2. The peculiar balmer decrement of SN 2009ip: Constraints on circumstellar geometry

    International Nuclear Information System (INIS)

    Levesque, Emily M.; Stringfellow, Guy S.; Bally, John; Keeney, Brian A.; Ginsburg, Adam G.

    2014-01-01

    We present optical and near-IR spectroscopic observations of the luminous blue variable SN 2009ip during its remarkable photometric evolution of 2012. The spectra sample three key points in the SN 2009ip light curve, corresponding to its initial brightening in August (2012-A) and its dramatic rebrightening in early October (2012-B). Based on line fluxes and velocities measured in our spectra, we find a surprisingly low I(Hα)/I(Hβ) ratio (∼1.3-1.4) in the 2012-B spectra. Such a ratio implies either a rare Case B recombination scenario where Hα, but not Hβ, is optically thick, or an extremely high density for the circumstellar material of n e > 10 13 cm –3 . The Hα line intensity yields a minimum radiating surface area of ≳20,000 AU 2 in Hα at the peak of SN 2009ip's photometric evolution. Combined with the nature of this object's spectral evolution in 2012, a high circumstellar density and large radiating surface area imply the presence of a thin disk geometry around the central star (and, consequently, a possible binary companion), suggesting that the observed 2012-B rebrightening of SN 2009ip can be attributed to the illumination of the disk's inner rim by fast-moving ejecta produced by the underlying events of 2012-A.

  3. Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758

    Science.gov (United States)

    Reggiani, M.; Christiaens, V.; Absil, O.; Mawet, D.; Huby, E.; Choquet, E.; Gomez Gonzalez, C. A.; Ruane, G.; Femenia, B.; Serabyn, E.; Matthews, K.; Barraza, M.; Carlomagno, B.; Defrère, D.; Delacroix, C.; Habraken, S.; Jolivet, A.; Karlsson, M.; Orban de Xivry, G.; Piron, P.; Surdej, J.; Vargas Catalan, E.; Wertz, O.

    2018-03-01

    Context. Transition disks offer the extraordinary opportunity to look for newly born planets and to investigate the early stages of planet formation. Aim. In this context we observed the Herbig A5 star MWC 758 with the L'-band vector vortex coronagraph installed in the near-infrared camera and spectrograph NIRC2 at the Keck II telescope, with the aim of unveiling the nature of the spiral structure by constraining the presence of planetary companions in the system. Methods: Our high-contrast imaging observations show a bright (ΔL' = 7.0 ± 0.3 mag) point-like emission south of MWC 758 at a deprojected separation of 20 au (r = 0.''111 ± 0.''004) from the central star. We also recover the two spiral arms (southeast and northwest), already imaged by previous studies in polarized light, and discover a third arm to the southwest of the star. No additional companions were detected in the system down to 5 Jupiter masses beyond 0.''6 from the star. Results: We propose that the bright L'-band emission could be caused by the presence of an embedded and accreting protoplanet, although the possibility of it being an asymmetric disk feature cannot be excluded. The spiral structure is probably not related to the protoplanet candidate, unless on an inclined and eccentric orbit, and it could be due to one (or more) yet undetected planetary companions at the edge of or outside the spiral pattern. Future observations and additional simulations will be needed to shed light on the true nature of the point-like source and its link with the spiral arms. The reduced images (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A74

  4. Herniated Disk

    Science.gov (United States)

    ... It is often caused by natural aging and deterioration. To keep your disks and back in good ... Injury Prevention Crisis Situations Pets and Animals myhealthfinder Food and Nutrition Healthy Food Choices Weight Loss and ...

  5. Evidence for circumstellar obscuration of OB stars

    International Nuclear Information System (INIS)

    Bohannan, B.

    1975-01-01

    Reddish found a strong increase of color excess with increasing stellar luminosity: here referred to as the Reddish Effect: in ten young galactic clusters and associations. New photometric and spectroscopic observations drawn from the literature are combined with data used by Reddish to reconsider the color excess versus intrinsic magnitude diagrams of the same ten stellar groups. The reality of the Effect is questioned in all but one of the systems; this was accomplished by identifying possible foreground stars and by recognizing some of the brightest stars as supergiants, then applying correct intrinsic color indices. After careful reanalysis, the one stellar group to retain an indication of the Reddish Effect is Cygnus OB2. No correlation of reddening with luminosity was found for five additional very young stellar groups in the southern hemisphere; these groups should exhibit the Effect if it is a natural consequence of stellar evolution. Reddish ascribed the correlation to massive circumstellar remnants of material from which the stars formed. However, a peculiar dispersion in color excess could also be attributed to patchy dust within the stellar group. In several stellar systems previously identified as displaying the Reddish Effect, a correlation of observed color excess with dust and gas concentrations is noted on Palomar Sky Survey prints. If present, circumstellar dust clouds should []anifest their existence in modes other than a correlation of color excess with luminosity. The following possibilities are considered and all show negative results: correlation of color excess with spectral type; correlation of reddening slope E/subU//sub -//subB//E/subB//sub -//subV/ with spectral type; observable infrared excess. The preceding astrophysical arguments strongly imply that circumstellar dust remnants from stellar formation do not remain around stars during their main-sequence lifetimes. (auth)

  6. POLARIMETRY WITH THE GEMINI PLANET IMAGER: METHODS, PERFORMANCE AT FIRST LIGHT, AND THE CIRCUMSTELLAR RING AROUND HR 4796A

    International Nuclear Information System (INIS)

    Perrin, Marshall D.; Duchene, Gaspard; Graham, James R.; Kalas, Paul G.; Millar-Blanchaer, Max; Fitzgerald, Michael P.; Chilcote, Jeffrey; Wiktorowicz, Sloane J.; Dillon, Daren; Gavel, Donald; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale; De Rosa, Robert J.; Doyon, René; Dunn, Jennifer; Erikson, Darren

    2015-01-01

    We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point-spread function (PSF) subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side ≳ 9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring

  7. POLARIMETRY WITH THE GEMINI PLANET IMAGER: METHODS, PERFORMANCE AT FIRST LIGHT, AND THE CIRCUMSTELLAR RING AROUND HR 4796A

    Energy Technology Data Exchange (ETDEWEB)

    Perrin, Marshall D. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Duchene, Gaspard; Graham, James R.; Kalas, Paul G. [Astronomy Department, University of California, Berkeley, Hearst Field Annex B-20, Berkeley, CA 94720-3411 (United States); Millar-Blanchaer, Max [Department of Astronomy and Astrophysics, University of Toronto, Toronto ON M5S 3H4 (Canada); Fitzgerald, Michael P.; Chilcote, Jeffrey [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095 (United States); Wiktorowicz, Sloane J.; Dillon, Daren; Gavel, Donald [Department of Astronomy, UC Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Macintosh, Bruce; Bauman, Brian [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94040 (United States); Cardwell, Andrew; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale [Gemini Observatory, Casilla 603 La Serena (Chile); De Rosa, Robert J. [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287 (United States); Doyon, René [Department de Physique, Université de Montréal, Montréal QC H3C 3J7 (Canada); Dunn, Jennifer; Erikson, Darren [National Research Council of Canada Herzberg, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); and others

    2015-02-01

    We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point-spread function (PSF) subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side ≳ 9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring.

  8. Circumstellar ammonia in oxygen-rich evolved stars

    Science.gov (United States)

    Wong, K. T.; Menten, K. M.; Kamiński, T.; Wyrowski, F.; Lacy, J. H.; Greathouse, T. K.

    2018-04-01

    Context. The circumstellar ammonia (NH3) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH3 abundance in oxygen-rich stars is several orders of magnitude above that predicted by equilibrium chemistry. Aims: We would like to characterise the spatial distribution and excitation of NH3 in the oxygen-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420. Methods: We observed NH3 emission from the ground state in the inversion transitions near 1.3 cm with the Very Large Array (VLA) and submillimetre rotational transitions with the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel Space Observatory from all four targets. For IK Tau and VY CMa, we observed NH3 rovibrational absorption lines in the ν2 band near 10.5 μm with the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). We also attempted to search for the rotational transition within the excited vibrational state (v2 = 1) near 2 mm with the IRAM 30m Telescope. Non-LTE radiative transfer modelling, including radiative pumping to the vibrational state, was carried out to derive the radial distribution of NH3 in the CSEs of these targets. Results: We detected NH3 inversion and rotational emission in all four targets. IK Tau and VY CMa show blueshifted absorption in the rovibrational spectra. We did not detect vibrationally excited rotational transition from IK Tau. Spatially resolved VLA images of IK Tau and IRC +10420 show clumpy emission structures; unresolved images of VY CMa and OH 231.8+4.2 indicate that the spatial-kinematic distribution of NH3 is similar to that of assorted molecules, such as SO and SO2, that exhibit localised and clumpy emission. Our modelling shows that the NH3 abundance relative to molecular hydrogen is generally of the order of 10-7, which is a few times lower than previous estimates that were made without considering radiative

  9. Models for circumstellar nebulae around red and blue supergiants

    Science.gov (United States)

    Chita, S. M.

    2011-10-01

    In this thesis, we model the circumstellar medium of stars with initial masses of 8, 12, 18 and 20 solar masses, over their entire life from the main sequence until their supernova explosion. During the post-main-sequence stages, stars can evolve through several blue and red supergiant stages depending on their initial mass, composition and rotation rate. The models considered in the second Chapter have long-lasting RSG stages starting after the MS. In this phase, they develop shells of RSG wind material at the location where the free streaming RSG wind is stalled by the thermal pressure of the hot MS bubble, close to the central star. The RSG shells develop violent Rayleigh-Taylor instabilities. Once these start to grow non-linear, the RSG shell becomes highly structured as clumps form, and shell material mixes with material in the hot bubble. Later, the stars evolve to the BSG stage, during which the RSG shells are completely destroyed. These models return to the RSG stage, and build new RSG shells, which are more massive than those formed earlier. RSG shells are essential for our understanding of bipolar emission nebulae around BSGs. In the third Chapter are shown the results of the wind-wind interaction model of single star with 12 solar masses. On a time scale of a few 10000 yr, a BSG hour-glas shaped nebula expands into the sphere defined by the RSG shell. The faster polar parts of the hour glass hit the inner edge of the RSG shell first. The collision creates a pair of hot and dense polar caps. As time passes, the collision zone moves to lower latitudes of the RSG shell and becomes more confined in latitude. At the same time, the interaction of the BSG wind with the equatorial disk defines a second, ring shaped collision zone in the equatorial plane. These structures are reminiscent of the observed nebulae around the blue supergiant Sher 25. In the Chapter 3 we present calculations that predict the properties of the circumstellar medium for rapidly rotating

  10. Imaging polarimetry of circumstellar environments with the Extreme Polarimeter

    NARCIS (Netherlands)

    Rodenhuis, M.; Canovas, H.; Jeffers, S.V.; Min, M.; Keller, C.U.

    2010-01-01

    Three successful observation campaigns have been conducted with the Extreme Polarimeter, an imaging polarimeter for the study of circumstellar environments in scattered light at visible wavelengths. A contrast ratio between the central star and the circumstellar source of 10-5 can be achieved with

  11. Gas in Protoplanetary and Debris Disks: Insights from UV Spectroscopy

    Science.gov (United States)

    Roberge, Aki

    2008-01-01

    Over the last two decades, observations of protoplanetary and debris disks have played an important role in the new field of extrasolar planetary studies. Many are familiar with the extensive work on the cold circumstellar dust present in these disks done using infrared and sub-millimeter photometry and spectroscopy. However. UV spectroscopy has made some unique contributions by probing the elusive but vital gas component in protoplanetary and debris disks. In this talk, I will outline our picture of the evolution of protoplanetary disks and discuss the importance of the gas component. New insights obtained from UV spectroscopy will be highlighted, as well as some new puzzles. Finally, I will touch on upcoming studies of gas in protoplanetary and debris disks, some at UV wavelengths, some at far-IR and sub-mm wavelengths.

  12. Disks Surrounding Massive Stars: When Computational Models are Confronted by Observations

    Science.gov (United States)

    2010-01-01

    distribución espectral de enerǵıa y la polarización del continuo . Los modelos con es- tructura térmica precisa y campos de radiación son esenciales...circumstellar disks for Be stars, using a non-LTE radiative transfer code which incorporates a number of improvements over previous treatments of the disk...the other predicted observables. The code has a number of improvements over previous disk models available in the literature. For example, the disk

  13. Spectral energy distributions of T Tauri stars - disk flaring and limits on accretion

    International Nuclear Information System (INIS)

    Kenyon, S.J.; Hartmann, L.

    1987-01-01

    The Adams et al. (1987) conclusion that much of the IR excess emission in the spectral energy distribution of T Tauri stars arises from reprocessing of stellar radiation by a dusty circumstellar disk is presently supported by analyses conducted in light of various models of these stars' spectra. A low mass reprocessing disk can, however, produce these spectra as well as a massive accretion disk. The detection of possible boundary layer radiation in the optical and near-UV regions poses the strongest limits on accretion rates. Disk accretion in the T Tauri phase does not significantly modify stellar evolution. 85 references

  14. CORONAL MASS EJECTIONS AS A MECHANISM FOR PRODUCING IR VARIABILITY IN DEBRIS DISKS

    International Nuclear Information System (INIS)

    Osten, Rachel; Livio, Mario; Lubow, Steve; Pringle, J. E.; Soderblom, David; Valenti, Jeff

    2013-01-01

    Motivated by recent observations of short-timescale variations in the infrared emission of circumstellar disks, we propose that coronal mass ejections can remove dust grains on timescales as short as a few days. Continuous monitoring of stellar activity, coupled with infrared observations, can place meaningful constraints on the proposed mechanism.

  15. Testing the theory of grain growth and fragmentation by millimeter observations of protoplanetary disks

    NARCIS (Netherlands)

    Birnstiel, T.; Ricci, L.; Trotta, F.; Dullemond, C.P.; Natta, A.; Testi, L.; Dominik, C.; Henning, T.; Ormel, C.W.; Zsom, A.

    2010-01-01

    Context. Observations at sub-millimeter and mm wavelengths will in the near future be able to resolve the radial dependence of the mm spectral slope in circumstellar disks with a resolution of around a few AU at the distance of the closest star-forming regions. Aims. We aim to constrain physical

  16. IONIZATION AND DUST CHARGING IN PROTOPLANETARY DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Ivlev, A. V.; Caselli, P. [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstr. 1, D-85748 Garching (Germany); Akimkin, V. V., E-mail: ivlev@mpe.mpg.de [Institute of Astronomy of the Russian Academy of Sciences, Pyatnitskaya Street 48, 119017 Moscow (Russian Federation)

    2016-12-10

    Ionization–recombination balance in dense interstellar and circumstellar environments is a key factor for a variety of important physical processes, such as chemical reactions, dust charging and coagulation, coupling of the gas with magnetic field, and development of instabilities in protoplanetary disks. We determine a critical gas density above which the recombination of electrons and ions on the grain surface dominates over the gas-phase recombination. For this regime, we present a self-consistent analytical model, which allows us to calculate exactly the abundances of charged species in dusty gas, without making assumptions on the grain charge distribution. To demonstrate the importance of the proposed approach, we check whether the conventional approximation of low grain charges is valid for typical protoplanetary disks, and discuss the implications for dust coagulation and development of the “dead zone” in the disk. The presented model is applicable for arbitrary grain-size distributions and, for given dust properties and conditions of the disk, has only one free parameter—the effective mass of the ions, shown to have a small effect on the results. The model can be easily included in numerical simulations following the dust evolution in dense molecular clouds and protoplanetary disks.

  17. The circumstellar environments of B[e] Supergiants

    Science.gov (United States)

    Maravelias, G.; Kraus, M.; Cidale, L.; Arias, M. L.; Aret, A.; Borges Fernandes, M.

    2017-11-01

    The evolution of massive stars encompasses short-lived transition phases in which mass-loss is more enhanced and usually eruptive. A complex environment, combining atomic, molecular and dust regions, is formed around these stars. In particular, the circumstellar environment of B[e] Supergiants is not well understood. To address that, we have initiated a campaign to investigate their environments for a sample of Galactic and Magellanic Cloud sources. Using high-resolution optical and near-infrared spectra (MPG-ESO/FEROS, GEMINI/Phoenix and VLT/CRIRES, respectively), we examine a set of emission features ([OI], [CaII], CO bandheads) to trace the physical conditions and kinematics in their formation regions. We find that the B[e] Supergiants are surrounded by a series of rings of different temperatures and densities, a probable result of previous mass-loss events. In many cases the CO forms very close to the star, while we notice also an alternate mixing of densities and temperatures (which give rise to the different emission features) along the equatorial plane.

  18. Numerical models for the circumstellar medium around Betelgeuse

    Science.gov (United States)

    Mackey, J.; Mohamed, S.; Neilson, H. R.; Langer, N.; Meyer, D. M.-A.

    2013-05-01

    The nearby red supergiant (RSG) Betelgeuse has a complex circumstellar medium out to at least 0.5 parsecs from its surface, shaped by its mass-loss history within the past ≈ 0.1 Myr, its environment, and its motion through the interstellar medium (ISM). In principle its mass-loss history can be constrained by comparing hydrodynamic models with observations. Observations and numerical simulations indicate that Betelgeuse has a very young bow shock, hence the star may have only recently become a RSG. To test this possibility we calculated a stellar evolution model for a single star with properties consistent with Betelgeuse. We incorporated the resulting evolving stellar wind into 2D hydrodynamic simulations to model a runaway blue supergiant (BSG) undergoing the transition to a RSG near the end of its life. The collapsing BSG wind bubble induces a bow shock-shaped inner shell which at least superficially resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is the larger-scale retreating bow shock generated by the now defunct BSG wind's interaction with the ISM. We investigate whether this outer shell could explain the bar feature located (at least in projection) just in front of Betelgeuse's bow shock.

  19. CO/H{sub 2} abundance ratio ≈ 10{sup –4} in a protoplanetary disk

    Energy Technology Data Exchange (ETDEWEB)

    France, Kevin; McJunkin, Matthew [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309 (United States); Herczeg, Gregory J. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Penton, Steven V., E-mail: kevin.france@colorado.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States)

    2014-10-20

    The relative abundances of atomic and molecular species in planet-forming disks around young stars provide important constraints on photochemical disk models and provide a baseline for calculating disk masses from measurements of trace species. A knowledge of absolute abundances, those relative to molecular hydrogen (H{sub 2}), are challenging because of the weak rovibrational transition ladder of H{sub 2} and the inability to spatially resolve different emission components within the circumstellar environment. To address both of these issues, we present new contemporaneous measurements of CO and H{sub 2} absorption through the 'warm molecular layer' of the protoplanetary disk around the Classical T Tauri Star RW Aurigae A. We use a newly commissioned observing mode of the Hubble Space Telescope Cosmic Origins Spectrograph to detect warm H{sub 2} absorption in this region for the first time. An analysis of the emission and absorption spectrum of RW Aur shows components from the accretion region near the stellar photosphere, the molecular disk, and several outflow components. The warm H{sub 2} and CO absorption lines are consistent with a disk origin. We model the 1092-1117 Å spectrum of RW Aur to derive log{sub 10} N(H{sub 2}) = 19.90{sub −0.22}{sup +0.33} cm{sup –2} at T {sub rot}(H{sub 2}) = 440 ± 39 K. The CO A - X bands observed from 1410 to 1520 Å are best fit by log{sub 10} N(CO) = 16.1 {sub −0.5}{sup +0.3} cm{sup –2} at T {sub rot}(CO) = 200{sub −125}{sup +650} K. Combining direct measurements of the H I, H{sub 2}, and CO column densities, we find a molecular fraction in the warm disk surface of f {sub H2} ≥ 0.47 and derive a molecular abundance ratio of CO/H{sub 2} = 1.6{sub −1.3}{sup +4.7} × 10{sup –4}, both consistent with canonical interstellar dense cloud values.

  20. PLANETARY CONSTRUCTION ZONES IN OCCULTATION: DISCOVERY OF AN EXTRASOLAR RING SYSTEM TRANSITING A YOUNG SUN-LIKE STAR AND FUTURE PROSPECTS FOR DETECTING ECLIPSES BY CIRCUMSECONDARY AND CIRCUMPLANETARY DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Mamajek, Eric E.; Quillen, Alice C.; Pecaut, Mark J.; Moolekamp, Fred; Scott, Erin L. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627-0171 (United States); Kenworthy, Matthew A. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Cameron, Andrew Collier; Parley, Neil R. [School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS (United Kingdom)

    2012-03-15

    The large relative sizes of circumstellar and circumplanetary disks imply that they might be seen in eclipse in stellar light curves. We estimate that a survey of {approx}10{sup 4} young ({approx}10 million year old) post-accretion pre-main-sequence stars monitored for {approx}10 years should yield at least a few deep eclipses from circumplanetary disks and disks surrounding low-mass companion stars. We present photometric and spectroscopic data for a pre-main-sequence K5 star (1SWASP J140747.93-394542.6 = ASAS J140748-3945.7), a newly discovered {approx}0.9 M{sub Sun} member of the {approx}16 Myr old Upper Centaurus-Lupus subgroup of Sco-Cen at a kinematic distance of 128 {+-} 13 pc. This star exhibited a remarkably long, deep, and complex eclipse event centered on 2007 April 29 (as discovered in Super Wide Angle Search for Planets (SuperWASP) photometry, and with portions of the dimming confirmed by All Sky Automated Survey (ASAS) data). At least five multi-day dimming events of >0.5 mag are identified, with a >3.3 mag deep eclipse bracketed by two pairs of {approx}1 mag eclipses symmetrically occurring {+-}12 days and {+-}26 days before and after. Hence, significant dimming of the star was taking place on and off over at least a {approx}54 day period in 2007, and a strong >1 mag dimming event occurring over a {approx}12 day span. We place a firm lower limit on the period of 850 days (i.e., the orbital radius of the eclipser must be >1.7 AU and orbital velocity must be <22 km s{sup -1}). The shape of the light curve is similar to the lopsided eclipses of the Be star EE Cep. We suspect that this new star is being eclipsed by a low-mass object orbited by a dense inner disk, further girded by at least three dusty rings of optical depths near unity. Between these rings are at least two annuli of near-zero optical depth (i.e., gaps), possibly cleared out by planets or moons, depending on the nature of the secondary. For possible periods in the range 2.33-200 yr, the

  1. Mass loss of evolved massive stars: the circumstellar environment at high angular resolution

    International Nuclear Information System (INIS)

    Montarges, Miguel

    2014-01-01

    Mass loss of evolved stars is still largely mysterious, despite its importance as the main evolution engine for the chemical composition of the interstellar medium. For red supergiants (RSG), the triggering of the outflow and the mechanism of dust condensation remain unknown. Concerning red giant stars, we still do not know how their mass loss is able to form a bipolar planetary nebula. During my PhD thesis, I observed evolved stars with high angular resolution techniques. They allowed us to study the surface and the close environment of these stars, from where mass loss originates. With near-infrared interferometric observations, I characterized the water vapor and carbon monoxide envelope of the nearby RSG Betelgeuse. I also monitored a hot spot on its surface and analyzed the structure of its convection, as well as that of Antares (another very nearby supergiant) thanks to radiative hydrodynamical simulations. Diffraction-limited imaging techniques (near-infrared adaptive optics, ultraviolet space telescope) allowed me to observe the evolution of inhomogeneities in the circumstellar envelope of Betelgeuse and to discover a circumstellar disk around L2 Puppis, an asymptotic giant branch star. These multi-scale and multi-wavelength observations obtained at several epochs allowed us to monitor the evolution of the structures and to derive information on the dynamics of the stellar environment. With a wider stellar sample expected in the next few years, this observing program will allow a better understanding of the mass loss of evolved stars. (author)

  2. Observations of the circumstellar gas shells around Betelgeuse and Antares

    Science.gov (United States)

    Bernat, A. P.; Lambert, D. L.

    1975-01-01

    Results are presented on the direct observations of the circumstellar shell around alpha-Ori, along with new observations of the Ca II infrared triplet lines which provide lower limits for the Ca(+) shell radii for alpha-Ori and alpha-Sco (Antares). The 8542-A line in alpha-Ori does not show a circumstellar absorption core, and the shell radius limit is estimated to be at least 31 times stellar radius. A 108-mA circumstellar core is observed in the 8542-A line in Antares for which a shell radius equal to 4.0 times stellar radius is suggested. The discovery of circumstellar emission through resonance line scattering will provide valuable additional information on the physical conditions in the shell.

  3. Barium nucleosynthesis in the disk

    Energy Technology Data Exchange (ETDEWEB)

    Twarog, B.A.

    1981-11-15

    The history of Ba production in the disk is discussed, particularly with regard to the apparent constancy of the production rate of Ba relative to Fe over the lifetime of the disk. An infall model of the chemical evolution of Ba/Fe within the disk is constructed under the assumption that the mass function and star formation rate are independent of time and Ba is produced as purely a secondary element. The model not only satisfies the present constraints for the disk, but produces a (Ba/H)-(Fe/H) relation which is consistent with the available observational data. It is shown that the apparent constancy of the Ba/Fe ratio is an artifact of (1) an inadequate and insufficiently accurated data sample, and (2) secondary production of Ba within the disk which is 20 to 80 times less efficient relative to Fe than the production ratio for the halo. The model predicts that stars formed during the transition period between halo and disk should show a Ba/Fe excess relative to the Sun of about a factor of 2. It is concluded that the possible sources of the Ba/Fe overproduction in the halo relative to the disk are incompatible with present theoretical limits on the mass ranges for iron and barium production by stars.

  4. Resolving the inner disk of UX Orionis

    Science.gov (United States)

    Kreplin, A.; Madlener, D.; Chen, L.; Weigelt, G.; Kraus, S.; Grinin, V.; Tambovtseva, L.; Kishimoto, M.

    2016-05-01

    Aims: The cause of the UX Ori variability in some Herbig Ae/Be stars is still a matter of debate. Detailed studies of the circumstellar environment of UX Ori objects (UXORs) are required to test the hypothesis that the observed drop in photometry might be related to obscuration events. Methods: Using near- and mid-infrared interferometric AMBER and MIDI observations, we resolved the inner circumstellar disk region around UX Ori. Results: We fitted the K-, H-, and N-band visibilities and the spectral energy distribution (SED) of UX Ori with geometric and parametric disk models. The best-fit K-band geometric model consists of an inclined ring and a halo component. We obtained a ring-fit radius of 0.45 ± 0.07 AU (at a distance of 460 pc), an inclination of 55.6 ± 2.4°, a position angle of the system axis of 127.5 ± 24.5°, and a flux contribution of the over-resolved halo component to the total near-infrared excess of 16.8 ± 4.1%. The best-fit N-band model consists of an elongated Gaussian with a HWHM ~ 5 AU of the semi-major axis and an axis ration of a/b ~ 3.4 (corresponding to an inclination of ~72°). With a parametric disk model, we fitted all near- and mid-infrared visibilities and the SED simultaneously. The model disk starts at an inner radius of 0.46 ± 0.06 AU with an inner rim temperature of 1498 ± 70 K. The disk is seen under an nearly edge-on inclination of 70 ± 5°. This supports any theories that require high-inclination angles to explain obscuration events in the line of sight to the observer, for example, in UX Ori objects where orbiting dust clouds in the disk or disk atmosphere can obscure the central star. Based on observations made with ESO telescopes at Paranal Observatory under program IDs: 090.C-0769, 074.C-0552.

  5. Studies of Gas Disks in Binary Systems

    Science.gov (United States)

    de Val-Borro, Miguel

    There are over 300 exoplanets detected through radial velocity surveys and photometric studies showing a tremendous variety of masses, compositions and orbital parameters. Understanding the way these planets formed and evolved within the circumstellar disks they were initially embedded in is a crucial issue. In the first part of this thesis we study the physical interaction between a gaseous protoplanetary disk and an embedded planet using numerical simulations. In order to trust the results from simulations it is important to compare different methods. However, the standard test problems for hydrodynamic codes differ considerably from the case of a protoplanetary disk interacting with an embedded planet. We have carried out a code comparison in which the problem of a massive planet in a protoplanetary disk was studied with various numerical schemes. We compare the surface density, potential vorticity and azimuthally averaged density profiles at several times. There is overall good agreement between our codes for Neptune and Jupiter-sized planets. We performed simulations for each planet in an inviscid disk and including physical viscosity. The surface density profiles agree within about 5% for the grid-based schemes while the particle codes have less resolution in the low density regions and weaker spiral wakes. In Paper II, we study hydrodynamical instabilities in disks with planets. Vortices are generated close to the gap in our numerical models in agreement with the linear modal analysis. The vortices exert strong perturbations on the planet as they move along the gap and can change its migration rate. In addition, disk viscosity can be modified by the presence of vortices. The last part of this thesis studies the mass transfer in symbiotic binaries and close T Tauri binary systems. Our simulations of gravitationally focused wind accretion in binary systems show the formation of stream flows and enhanced accretion rates onto the compact component.

  6. CIRCUMSTELLAR SHELL FORMATION IN SYMBIOTIC RECURRENT NOVAE

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Kevin; Bildsten, Lars [Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106 (United States)

    2012-12-20

    We present models of spherically symmetric recurrent nova shells interacting with circumstellar material (CSM) in a symbiotic system composed of a red giant (RG) expelling a wind and a white dwarf accreting from this material. Recurrent nova eruptions periodically eject material at high velocities ({approx}> 10{sup 3} km s{sup -1}) into the RG wind profile, creating a decelerating shock wave as CSM is swept up. High CSM densities cause the shocked wind and ejecta to have very short cooling times of days to weeks. Thus, the late-time evolution of the shell is determined by momentum conservation instead of energy conservation. We compute and show evolutionary tracks of shell deceleration, as well as post-shock structure. After sweeping up all the RG wind, the shell coasts at a velocity {approx}100 km s{sup -1}, depending on system parameters. These velocities are similar to those measured in blueshifted CSM from the symbiotic nova RS Oph, as well as a few Type Ia supernovae that show evidence of CSM, such as 2006X, 2007le, and PTF 11kx. Supernovae occurring in such systems may not show CSM interaction until the inner nova shell gets hit by the supernova ejecta, days to months after the explosion.

  7. Recommended Rest Frequencies for Observed Interstellar Molecular Microwave Transitions - 2002 Revision

    Science.gov (United States)

    SRD 116 NIST Recommended Rest Frequencies for Observed Interstellar Molecular Microwave Transitions - 2002 Revision (Web, free access)   Critically evaluated transition frequencies for the molecular transitions detected in interstellar and circumstellar clouds are presented.

  8. MASSIVE PROTOPLANETARY DISKS IN ORION BEYOND THE TRAPEZIUM CLUSTER

    International Nuclear Information System (INIS)

    Mann, Rita K.; Williams, Jonathan P.

    2009-01-01

    We present Submillimeter Array 1 The Submillimeter Array is a joint project between the Submillimeter Astrophysical Observatory and the Academica Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academica Sinica. observations of the 880 μm continuum emission from three circumstellar disks around young stars in Orion that lie several arcminutes (∼> 1 pc) north of the Trapezium cluster. Two of the three disks are in the binary system 253-1536. Silhouette disks 216-0939 and 253-1536a are found to be more massive than any previously observed Orion disks, with dust masses derived from their submillimeter emission of 0.045 M sun and 0.066 M sun , respectively. The existence of these massive disks reveals that the disk mass distribution in Orion does extend to high masses, and that the truncation observed in the central Trapezium cluster is a result of photoevaporation due to the proximity of O-stars. 253-1536b has a disk mass of 0.018 M sun , making the 253-1536 system the first optical binary in which each protoplanetary disk is massive enough to potentially form solar systems.

  9. X-RAY EMISSION FROM STRONGLY ASYMMETRIC CIRCUMSTELLAR MATERIAL IN THE REMNANT OF KEPLER'S SUPERNOVA

    Energy Technology Data Exchange (ETDEWEB)

    Burkey, Mary T.; Reynolds, Stephen P.; Borkowski, Kazimierz J.; Blondin, John M., E-mail: reynolds@ncsu.edu [Department of Physics, North Carolina State University, Raleigh NC 27695-8202 (United States)

    2013-02-10

    Kepler's supernova remnant resulted from a thermonuclear explosion, but is interacting with circumstellar material (CSM) lost from the progenitor system. We describe a statistical technique for isolating X-ray emission due to CSM from that due to shocked ejecta. Shocked CSM coincides well in position with 24 {mu}m emission seen by Spitzer. We find most CSM to be distributed along the bright north rim, but substantial concentrations are also found projected against the center of the remnant, roughly along a diameter with position angle {approx}100 Degree-Sign . We interpret this as evidence for a disk distribution of CSM before the supernova, with the line of sight to the observer roughly in the disk plane. We present two-dimensional hydrodynamic simulations of this scenario in qualitative agreement with the observed CSM morphology. Our observations require Kepler to have originated in a close binary system with an asymptotic giant branch star companion.

  10. Levitation of dust at the surface of protoplanetary disks

    DEFF Research Database (Denmark)

    Wurm, Gerhard; Haack, Henning

    2009-01-01

    In recent years photophoretic forces acting on dust particles have been shown to be important for optically thin parts of protoplanetary disks. The optical surface (photosphere) of protoplanetary disks is a transitional region where the thermal radiation of the disk can escape. We show here...

  11. DYNAMICAL EVOLUTION OF VISCOUS DISKS AROUND Be STARS. I. PHOTOMETRY

    Energy Technology Data Exchange (ETDEWEB)

    Haubois, X.; Carciofi, A. C. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, Sao Paulo, SP 05508-900 (Brazil); Rivinius, Th. [European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19 (Chile); Okazaki, A. T. [Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062-8605 (Japan); Bjorkman, J. E., E-mail: xhaubois@astro.iag.usp.br [Ritter Observatory, Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States)

    2012-09-10

    Be stars possess gaseous circumstellar disks that modify in many ways the spectrum of the central B star. Furthermore, they exhibit variability at several timescales and for a large number of observables. Putting the pieces together of this dynamical behavior is not an easy task and requires a detailed understanding of the physical processes that control the temporal evolution of the observables. There is an increasing body of evidence that suggests that Be disks are well described by standard {alpha}-disk theory. This paper is the first of a series that aims at studying the possibility of inferring several disk and stellar parameters through the follow-up of various observables. Here we study the temporal evolution of the disk density for different dynamical scenarios, including the disk build-up as a result of a long and steady mass injection from the star, the disk dissipation that occurs after mass injection is turned off, as well as scenarios in which active periods are followed by periods of quiescence. For those scenarios, we investigate the temporal evolution of continuum photometric observables using a three-dimensional non-LTE radiative transfer code. We show that light curves for different wavelengths are specific of a mass loss history, inclination angle, and {alpha} viscosity parameter. The diagnostic potential of those light curves is also discussed.

  12. Characterizing Protoplanetary Disks in a Young Binary in Orion

    Science.gov (United States)

    Powell, Jonas; Hughes, A. Meredith; Mann, Rita; Flaherty, Kevin; Di Francesco, James; Williams, Jonathan

    2018-01-01

    Planetary systems form in circumstellar disks of gas and dust surrounding young stars. One open question in the study of planet formation involves understanding how different environments affect the properties of the disks and planets they generate. Understanding the properties of disks in high-mass star forming regions (SFRs) is critical since most stars - probably including our Sun - form in those regions. By comparing the disks in high-mass SFRs to those in better-studied low-mass SFRs we can learn about the role environment plays in planet formation. Here we present 0.5" resolution observations of the young two-disk binary system V2434 Ori in the Orion Nebula from the Atacama Large Millimeter/submillimeter Array (ALMA) in molecular line tracers of CO(3-2), HCN(4-3), HCO+(4-3) and CS(7-6). We model each disk’s mass, radius, temperature structure, and molecular abundances, by creating synthetic images using an LTE ray-tracing code and comparing simulated observations with the ALMA data in the visibility domain. We then compare our results to a previous study of molecular line emission from a single Orion proplyd, modeled using similar methods, and to previously characterized disks in low-mass SFRs to investigate the role of environment in disk chemistry and planetary system formation.

  13. Laboratory Studies Of Circumstellar Carbonaceous Grain Formation

    Science.gov (United States)

    Contreras, Cesar; Sciamma-O'Brien, Ella; Salama, Farid

    2014-06-01

    The study of the formation processes of dust is essential to understand the budget of extraterrestrial organic molecules. Although dust with all its components plays an important role in the evolution of interstellar (IS) chemistry and in the formation of organic molecules, little is known on the formation processes of carbonaceous dust. We report the progress that was recently achieved in this domain using NASA Ames’ COSmIC facility (Contreras & Salama 2013, ApJS, 208, 6). PAHs are important chemical building blocks of IS dust. They are detected in IDPs and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs are an important, ubiquitous component of the ISM. The formation of PAHs from smaller molecules has not been extensively studied. Therefore, we have performed laboratory experiments to study the dynamic processes of carbon grain formation, starting from the smallest hydrocarbon molecules into the formation of larger PAH and further into nanograins. Studies of IS dust analogs formed from a variety of PAH and hydrocarbon precursors as well as species that include the atoms O, N, and S, have recently been performed in our laboratory using the COSmIC facility to provide conditions that simulate IS and circumstellar environments. The species formed in the COSmiC chamber through a pulsed discharge nozzle plasma source are detected and characterized with a cavity ringdown spectrometer coupled to a time-of-flight mass spectrometer, thus providing both spectroscopic and ion mass information in-situ. Analysis of solid soot particles was also conducted using scanning electron microscopy at the UCSC/NASA Ames’ MACS facility. The SEM analysis of the deposition of soot from methane and acetylene precursors seeded in argon plasmas provide examples on the types of nanoparticles and micrograins that are produced in these gas mixtures under our experimental conditions. From these measurements, we derive information on

  14. The WIRED Survey. IV. New Dust Disks from the McCook & Sion White Dwarf Catalog

    Science.gov (United States)

    Hoard, D.W.; Debes, John H.; Wachter, Stefanie; Leisawitz, David T.; Cohen, Martin

    2013-01-01

    We have compiled photometric data from the Wide-field Infrared Survey Explorer All Sky Survey and other archival sources for the more than 2200 objects in the original McCook & Sion Catalog of Spectroscopically Identified White Dwarfs. We applied color-selection criteria to identify 28 targets whose infrared spectral energy distributions depart from the expectation for the white dwarf photosphere alone. Seven of these are previously known white dwarfs with circumstellar dust disks, five are known central stars of planetary nebulae, and six were excluded for being known binaries or having possible contamination of their infrared photometry. We fit white dwarf models to the spectral energy distributions of the remaining ten targets, and find seven new candidates with infrared excess suggesting the presence of a circumstellar dust disk. We compare the model dust disk properties for these new candidates with a comprehensive compilation of previously published parameters for known white dwarfs with dust disks. It is possible that the current census of white dwarfs with dust disks that produce an excess detectable at K-band and shorter wavelengths is close to complete for the entire sample of known WDs to the detection limits of existing near-IR all-sky surveys. The white dwarf dust disk candidates now being found using longer wavelength infrared data are drawn from a previously underrepresented region of parameter space, in which the dust disks are overall cooler, narrower in radial extent, and/or contain fewer emitting grains.

  15. SDP_golofs01_3: Stellar Disk Evolution

    Science.gov (United States)

    Olofsson, G.

    2010-03-01

    n a collaboration between the HSC, P. Harvey (Mission Scientist) and the three instrument consortia we propose to apply the full power of Herschel to investigate the properties of circum-stellar disks. The versatility of Herschel allows us to address several key questions: How do the disks evolve with time? Planets clearly form out of circum-stellar disks and there is growing evidence that the time scale is short, 1 - 10 Myr, for the main accretion phase. During this time period, the stellar radiation and stellar winds clean the disks from most of their dust and gas, eventually making them transparent. However, collisions and evaporation from comet- like bodies will continue to produce dust and gas. This activity declines with time, and we will pursue this scenario by observing a sample of IR excess stars of known age, ranging from a few million years to the age of the sun. Are there analogues to our Kuiper belt around nearby stars? The Kuiper belt is a dust belt surrounding the Sun, located outside the orbit of Neptune, which has a key role in stabilizing orbits of the KE-objects and this dynamical aspect makes it particularly interesting to search for stars that may host KE-belt analogues. Herschel offers a unique sensitivity beyond 100 m and we propose an extensive survey of nearby stars seeking cold dust emission. What will a closer IR look at the "Fabulous Four" (and some other resolved disks) reveal? Several nearby MS stars with IR excesses have circumstellar dust structures that can be resolved by Herschel. Imaging these structures in the six PACS+SPIRE bands will enable us to explore the dust properties, notably the size distribution and albedo.. What is the composition of young disks? We propose a detailed spectroscopic investigation of four bright disks, including a full spectral scan with PACS, an FTS scan at full resolution and HIFI observations of selected frequencies. The aim is to constrain the properties of both the dust and gas components.

  16. Improving signal-to-noise in the direct imaging of exoplanets and circumstellar disks with MLOCI

    Science.gov (United States)

    Wahhaj, Zahed; Cieza, Lucas A.; Mawet, Dimitri; Yang, Bin; Canovas, Hector; de Boer, Jozua; Casassus, Simon; Ménard, François; Schreiber, Matthias R.; Liu, Michael C.; Biller, Beth A.; Nielsen, Eric L.; Hayward, Thomas L.

    2015-09-01

    We present a new algorithm designed to improve the signal-to-noise ratio (S/N) of point and extended source detections around bright stars in direct imaging data.One of our innovations is that we insert simulated point sources into the science images, which we then try to recover with maximum S/N. This improves the S/N of real point sources elsewhere in the field. The algorithm, based on the locally optimized combination of images (LOCI) method, is called Matched LOCI or MLOCI. We show with Gemini Planet Imager (GPI) data on HD 135344 B and Near-Infrared Coronagraphic Imager (NICI) data on several stars that the new algorithm can improve the S/N of point source detections by 30-400% over past methods. We also find no increase in false detections rates. No prior knowledge of candidate companion locations is required to use MLOCI. On the other hand, while non-blind applications may yield linear combinations of science images that seem to increase the S/N of true sources by a factor >2, they can also yield false detections at high rates. This is a potential pitfall when trying to confirm marginal detections or to redetect point sources found in previous epochs. These findings are relevant to any method where the coefficients of the linear combination are considered tunable, e.g., LOCI and principal component analysis (PCA). Thus we recommend that false detection rates be analyzed when using these techniques. 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 (USA), the Science and Technology Facilities Council (UK), 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).

  17. Observational constraints for the circumstellar disk of the B[e] star CPD-52 9243

    Czech Academy of Sciences Publication Activity Database

    Cidale, L.S.; Borges Fernandes, M.; Andruchow, I.; Arias, M.L.; Kraus, Michaela; Chesneau, O.; Kanaan, S.; Curé, M.; de Wit, W.J.; Muratore, M.F.

    2012-01-01

    Roč. 548, November (2012), A72/1-A72/9 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GAP209/11/1198 Institutional support: RVO:67985815 Keywords : supergiants * stars * winds Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.084, year: 2012

  18. Mid-IR observations of circumstellar disks. I. Pre-main sequence objects

    Science.gov (United States)

    Schütz, O.; Meeus, G.; Sterzik, M. F.

    2005-02-01

    We present new N-band photometry and spectroscopy for a sample of eight pre-main sequence stars including T Tauri, Herbig Ae/Be stars and FU Ori objects using the ESO TIMMI2 camera at the La Silla observatory (Chile). For some objects this is their first N-band spectroscopic observation ever. The FU Ori stars V 346 Nor, V 883 Ori and Z CMa show a broad absorption band which we attribute to silicates, while for BBW 76 we find silicate emission. A comparison with ISO-SWS spectra of V 346 Nor and Z CMa taken in 1996/1997 reveals no differences in spectral shape. All T Tauri and Herbig Ae/Be stars possess N-band emission features. We model the emission spectra with a mixture of silicates consisting of different grain sizes and composition. The Herbig Ae star HD 34282 shows strong features of PAHs but none of silicate, while the emission spectrum of the Herbig Ae star HD 72106 resembles those of solar-system comets and known Herbig sources of evolved dust. We demonstrate that HD 72106 is host to highly processed silicates and find evidence for enstatite, which is not common in young objects. Evolved dust is also seen in the T Tauri stars HD 98800 and MP Mus. We further detected MP Mus at 1200 μm with the bolometer array SIMBA at the SEST in La Silla. The findings of our analysis are given in the context of previous dust studies of young stellar objects. Based on observations collected at the European Southern Observatory, La Silla, Chile (69.C-0073, 70.C-0468, 71.C-0001, 73.C-0372).

  19. A white dwarf explodes inside a dense circumstellar disk peeking at a puzzling supernova with spectropolarimetry

    CERN Multimedia

    2004-01-01

    "By measuring polarized light from an unusual exploding star, an international team of astrophysicists and astronomers has worked out the first detailed picture of a Type Ia supernova and the distinctive star system in which it exploded" (2 pages)

  20. The interaction of Type Ia supernovae with their circumstellar medium

    NARCIS (Netherlands)

    Chiotellis, A.

    2013-01-01

    This thesis is focused on the study of a specific class of supernovae, named Type Ia (or thermonuclear) supernovae. In particular, we attempt to gain information about their origin through the study of the interaction of these supernovae with circumstellar structures that have been shaped by their

  1. Models for circumstellar nebulae around red and blue supergiants

    NARCIS (Netherlands)

    Chita, S.M.|info:eu-repo/dai/nl/304832146

    2011-01-01

    In this thesis, we model the circumstellar medium of stars with initial masses of 8, 12, 18 and 20 solar masses, over their entire life from the main sequence until their supernova explosion. During the post-main-sequence stages, stars can evolve through several blue and red supergiant stages

  2. A study of the inner parts of protoplanetary disks observed by interferometry

    International Nuclear Information System (INIS)

    Anthonioz, Fabien

    2015-01-01

    Observing gas and dusty disks around young stars are of utmost importance for our knowledge about planetary formation. Observations of these disks bring unprecedented details about their structure and composition, and provide stronger and stronger constrains on planetary formation models. However, the inner parts of these disk are still barely known. Indeed, a 100 m diameter telescope would be required in order to resolve these inner region, for the closest young stars; nowadays, the construction of such telescope is impossible technologically and financially. By combining the light of pairs of telescopes, the interferometry technique is able to reach the sufficient resolving power, and permits us to observe the inner parts of circumstellar disks. My thesis has been focused on the observation and study of the inner part of TTauri's circumstellar disks. I present in this manuscript a statistical study on the environment around these stars, along with its modeling by taking into account thermal emission and light scattering of the disk. Finally, I present a more complete modelling for some of these stars, done by constraining spectroscopic, interferometric and photometric datasets with a radiative transfer code. (author)

  3. TOPOLOGIES OF CURRENT-FREE AXISYMMETRIC MAGNETOSPHERES IN STAR-DISK SYSTEMS

    International Nuclear Information System (INIS)

    Krasnopolsky, Ruben; Shang Hsien; Li ZhiYun

    2009-01-01

    Young stars are strongly magnetized. They interact with circumstellar disks through a shared magnetosphere. The interaction can have powerful effects on both the mass accretion from the disk to the star and the launch of magnetocentrifugal outflows. In this work, we show an extensive set of topological types of axisymmetric magnetospheres of the star-disk system, obtained numerically under the current-free assumption. We find that the topologies fall under a few broad categories, with different degrees of magnetic linkage between the star and the disk. A particularly interesting topology features a saddle point in the stellar corona, which enables to implement, this time in a simplified current-free form, the simultaneous existence of three regions of considerable astrophysical significance, as first proposed for X-winds. These regions are a 'funnel' region of inward-pointing field lines along which matter can flow from the inner part of the disk to the star, a region of outward-pointing open field lines that can drive a magnetocentrifugal wind, and an axial region of open stellar fields that allow stellar wind to escape. The Coronal Saddle point topology and other current-free configurations can serve as a starting point for full MHD simulations of the complex, dynamic, magnetic interaction between the young star and its circumstellar disk.

  4. Oscillations of disks

    CERN Document Server

    Kato, Shoji

    2016-01-01

    This book presents the current state of research on disk oscillation theory, focusing on relativistic disks and tidally deformed disks. Since the launch of the Rossi X-ray Timing Explorer (RXTE) in 1996, many high-frequency quasiperiodic oscillations (HFQPOs) have been observed in X-ray binaries. Subsequently, similar quasi-periodic oscillations have been found in such relativistic objects as microquasars, ultra-luminous X-ray sources, and galactic nuclei. One of the most promising explanations of their origin is based on oscillations in relativistic disks, and a new field called discoseismology is currently developing. After reviewing observational aspects, the book presents the basic characteristics of disk oscillations, especially focusing on those in relativistic disks. Relativistic disks are essentially different from Newtonian disks in terms of several basic characteristics of their disk oscillations, including the radial distributions of epicyclic frequencies. In order to understand the basic processes...

  5. MIT miniaturized disk bend test

    International Nuclear Information System (INIS)

    Harling, O.K.; Lee, M.; Sohn, D.S.; Kohse, G.; Lau, C.W.

    1983-01-01

    A miniaturized disk bend test (MDBT) using transmission electron microscopy specimens for the determination of various mechanical properties is being developed at MIT. Recent progress in obtaining strengths and ductilities of highly irradiated metal alloys is reviewed. Other mechanical properties can also be obtained using the MDBT approach. Progress in fatigue testing and in determination of the ductile-to-brittle transition temperature is reviewed briefly. 11 figures

  6. Probing for Exoplanets Hiding in Dusty Debris Disks: Disk Imaging, Characterization, and Exploration with HST-STIS Multi-roll Coronagraphy

    Science.gov (United States)

    Schneider, Glenn; Grady, Carol A.; Hines, Dean C.; Stark, Christopher C.; Debes, John; Carson, Joe; Kuchner, Marc J.; Perrin, Marshall; Weinberger, Alycia; Wisniewski, John P.; hide

    2014-01-01

    Spatially resolved scattered-light images of circumstellar debris in exoplanetary systems constrain the physical properties and orbits of the dust particles in these systems. They also inform on co-orbiting (but unseen) planets, the systemic architectures, and forces perturbing the starlight-scattering circumstellar material. Using HST/STIS broadband optical coronagraphy, we have completed the observational phase of a program to study the spatial distribution of dust in a sample of ten circumstellar debris systems, and one "mature" protoplanetrary disk all with HST pedigree, using PSF-subtracted multi-roll coronagraphy. These observations probe stellocentric distances greater than or equal to 5 AU for the nearest systems, and simultaneously resolve disk substructures well beyond corresponding to the giant planet and Kuiper belt regions within our own Solar System. They also disclose diffuse very low-surface brightness dust at larger stellocentric distances. Herein we present new results inclusive of fainter disks such as HD92945 (F (sub disk) /F (sub star) = 5x10 (sup -5) confirming, and better revealing, the existence of a narrow inner debris ring within a larger diffuse dust disk. Other disks with ring-like sub-structures and significant asymmetries and complex morphologies include: HD181327 for which we posit a spray of ejecta from a recent massive collision in an exo-Kuiper belt; HD61005 suggested to be interacting with the local ISM; HD15115 and HD32297, discussed also in the context of putative environmental interactions. These disks, and HD15745, suggest that debris system evolution cannot be treated in isolation. For AU Mic's edge-on disk we find out-of-plane surface brightness asymmetries at greater than or equal to 5 AU that may implicate the existence of one or more planetary perturbers. Time resolved images of the MP Mus proto-planetary disk provide spatially resolved temporal variability in the disk illumination. These and other new images from our HST

  7. Probing for exoplanets hiding in dusty debris disks: Disk imaging, characterization, and exploration with HST/STIS multi-roll coronagraphy

    Energy Technology Data Exchange (ETDEWEB)

    Schneider, Glenn; Hinz, Phillip M. [Steward Observatory and the Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Grady, Carol A. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Hines, Dean C.; Debes, John H.; Perrin, Marshall D.; Moro-Martin, Amaya [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Stark, Christopher C.; Kuchner, Marc J.; Woodgate, Bruce E. [NASA/Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Code 667, Greenbelt, MD 20771 (United States); Carson, Joe [Department of Physics and Astronomy, College of Charleston, 66 George Street, Charleston, SC 29424 (United States); Weinberger, Alycia J.; Rodigas, Timothy J. [Department of Terrestrial Magnetism, Carnegie Institute of Washington, 5241 Branch Road, NW, Washington, DC 20015 (United States); Wisniewski, John P. [H. L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Silverstone, Murray D. [Department of Physics and Astronomy, University of Alabama, P.O. Box 870324, Tuscaloosa, AL 35487-0324 (United States); Jang-Condell, Hannah [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Henning, Thomas [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Serabyn, Eugene [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Tamura, Motohide, E-mail: gschneider@as.arizona.edu [The University of Tokyo, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2014-10-01

    Spatially resolved scattered-light images of circumstellar debris in exoplanetary systems constrain the physical properties and orbits of the dust particles in these systems. They also inform on co-orbiting (but unseen) planets, the systemic architectures, and forces perturbing the starlight-scattering circumstellar material. Using Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) broadband optical coronagraphy, we have completed the observational phase of a program to study the spatial distribution of dust in a sample of 10 circumstellar debris systems and 1 'mature' protoplanetrary disk, all with HST pedigree, using point-spread-function-subtracted multi-roll coronagraphy. These observations probe stellocentric distances ≥5 AU for the nearest systems, and simultaneously resolve disk substructures well beyond corresponding to the giant planet and Kuiper Belt regions within our own solar system. They also disclose diffuse very low-surface-brightness dust at larger stellocentric distances. Herein we present new results inclusive of fainter disks such as HD 92945 (F {sub disk}/F {sub star} = 5 × 10{sup –5}), confirming, and better revealing, the existence of a narrow inner debris ring within a larger diffuse dust disk. Other disks with ring-like substructures and significant asymmetries and complex morphologies include HD 181327, for which we posit a spray of ejecta from a recent massive collision in an exo-Kuiper Belt; HD 61005, suggested to be interacting with the local interstellar medium; and HD 15115 and HD 32297, also discussed in the context of putative environmental interactions. These disks and HD 15745 suggest that debris system evolution cannot be treated in isolation. For AU Mic's edge-on disk, we find out-of-plane surface brightness asymmetries at ≥5 AU that may implicate the existence of one or more planetary perturbers. Time-resolved images of the MP Mus protoplanetary disk provide spatially resolved

  8. Friction and diffusion of a nano-colloidal disk in a two-dimensional solvent with a liquid-liquid transition.

    Science.gov (United States)

    Torres-Carbajal, Alexis; Castañeda-Priego, Ramón

    2018-03-07

    We report on the friction and diffusion of a single mobile nano-colloidal disk, whose size and mass are one and two orders of magnitude, respectively, greater than the molecules of the host solvent; all particles are restricted to move in a two-dimensional space. Using molecular dynamics simulations, the variation of the transport coefficients as a function of the thermodynamic state of the supporting fluid, in particular, around those states in the neighbourhood of the liquid-liquid phase coexistence, is investigated. The diffusion coefficient is determined through the fit of the mean-square displacement at long times and with the Green-Kubo relationship for the velocity autocorrelation function, whereas the friction coefficient is computed from the correlation of the fluctuating force. From the determination of the transport properties, the applicability of the Stokes-Einstein relation in two dimensions around the second critical point is discussed.

  9. Disk Storage Server

    CERN Multimedia

    This model was a disk storage server used in the Data Centre up until 2012. Each tray contains a hard disk drive (see the 5TB hard disk drive on the main disk display section - this actually fits into one of the trays). There are 16 trays in all per server. There are hundreds of these servers mounted on racks in the Data Centre, as can be seen.

  10. Observations of Circumstellar Thermochemical Equilibrium: The Case of Phosphorus

    Science.gov (United States)

    Milam, Stefanie N.; Charnley, Steven B.

    2011-01-01

    We will present observations of phosphorus-bearing species in circumstellar envelopes, including carbon- and oxygen-rich shells 1. New models of thermochemical equilibrium chemistry have been developed to interpret, and constrained by these data. These calculations will also be presented and compared to the numerous P-bearing species already observed in evolved stars. Predictions for other viable species will be made for observations with Herschel and ALMA.

  11. ALMA observations of the nearby AGB star L2 Puppis : II. Gas disk properties derived from 12CO and 13CO J = 3-2 emission

    NARCIS (Netherlands)

    Homan, W.; Richards, A.; Decin, L.; Kervella, P.; de Koter, A.; McDonald, I.; Ohnaka, K.

    The circumstellar environment of the AGB star L2 Puppis was observed with ALMA in cycle 3, with a resolution of 15 × 18 mas. The molecular emission shows a differentially rotating disk, inclined to a nearly edge-on position. In the first paper in this series (Paper I) the molecular emission was

  12. Ultraviolet extinction in M-supergiant circumstellar envelopes

    International Nuclear Information System (INIS)

    Buss, R.H. Jr.; Snow, T.P. Jr.

    1986-01-01

    Using International Ultraviolet (IUS) archival low-dispersion spectra, ultraviolet spectral extinctions were derived for the circumstellar envelopes of two M supergiants: HD 60414 and HD 213310. The observed stellar systems belong to a class of widely-separated spectroscopic binaries that are called VV Cephei stars. The total extinction was calculated by dividing the reddened fluxes with unreddened comparison fluxes of similar stars (g B2.5 for HD 213310 and a normalized s+B3 for HD 60414) from the reference atlas. After substracting the interstellar extinctions, which were estimated from the E(B-V) reddening of nearby stars, the resultant circumstellar extinctions were normalized at about 3.5 inverse microns. Not only is the 2175 A extinction bump absent in the circumstellar extinctions, but the far-ultraviolet extinction rise is also absent. The rather flat, ultraviolet extinction curves were interpreted as signatures of a population of noncarbonaceous, oxygen-rich grains with diameters larger than the longest observed wavelength

  13. MIPS Observations of the Fabulous Four Debris Disks

    Science.gov (United States)

    Su, K. Y. L.; Stansberry, J. A.; Rieke, G. H.; Trilling, D. E.; Stapelfeldt, K. R.; Werner, M. W.; Beichman, C.; Chen, C.; Marengo, M.; Megeath, T.; Backman, D.; van Cleve, J.

    2004-12-01

    The Multiband Imaging Photometer for Spitzer (MIPS) provides long-wavelength capability with imaging bands at 24, 70, and 160 um. We will present the MIPS images of the Fabulous Four Debris Disks: Beta Pictoris (A5 V), Epsilon Eridani (K2 V), Fomalhaut (A3 V) and Vega (A0 V). These systems discovered by IRAS possess large far-infrared excess emission above photosphere, indicating the existence of a circumstellar dusty disk. Given the main-sequence ages of these stars ( ˜12 Myr for Beta Pictoris, ˜730 Myr for Epsilon Eridani, ˜200 Myr for Fomalhaut, and ˜350 Myr for Vega), the dust in the systems could not be primordial as it would have been removed by radiation pressure and Poynting-Robertson drag on relatively short time scales ( ˜1E4 yr). The second-generation dust in such debris disks is thought to arise primarily from collisions between planetesimals (asteroids) and from cometary activity; however, details about the debris formation and evolution are not well understood. With the sensitivity and angular resolution of the Spitizer Space Telescope, the structures of these nearby debris disks were mapped in great detail to study the disks' spatial structures at mid- to far-infrared wavelengths. These high spatial resolution images provide unprecedented new constraints on the the dust properties in the systems and limits on the origin of dusty debris. Support for this work was provided by NASA through Contract Number 960785 issued by JPL/Caltech.

  14. VLTI/PIONIER images the Achernar disk swell

    Science.gov (United States)

    Dalla Vedova, G.; Millour, F.; Domiciano de Souza, A.; Petrov, R. G.; Moser Faes, D.; Carciofi, A. C.; Kervella, P.; Rivinius, T.

    2017-05-01

    Context. The mechanism of disk formation around fast-rotating Be stars is not well understood. In particular, it is not clear which mechanisms operate, in addition to fast rotation, to produce the observed variable ejection of matter. The star Achernar is a privileged laboratory to probe these additional mechanisms because it is close, presents B ⇌ Be phase variations on timescales ranging from 6 yr to 15 yr, a companion star was discovered around it, and probably presents a polar wind or jet. Aims: Despite all these previous studies, the disk around Achernar was never directly imaged. Therefore we seek to produce an image of the photosphere and close environment of the star. Methods: We used infrared long-baseline interferometry with the PIONIER instrument at the Very Large Telescope Interferometer (VLTI) to produce reconstructed images of the photosphere and close environment of the star over four years of observations. To study the disk formation, we compared the observations and reconstructed images to previously computed models of both the stellar photosphere alone (normal B phase) and the star presenting a circumstellar disk (Be phase). Results: The observations taken in 2011 and 2012, during the quiescent phase of Achernar, do not exhibit a disk at the detection limit of the instrument. In 2014, on the other hand, a disk was already formed and our reconstructed image reveals an extended H-band continuum excess flux. Our results from interferometric imaging are also supported by several Hα line profiles showing that Achernar started an emission-line phase sometime in the beginning of 2013. The analysis of our reconstructed images shows that the 2014 near-IR flux extends to 1.7-2.3 equatorial radii. Our model-independent size estimation of the H-band continuum contribution is compatible with the presence of a circumstellar disk, which is in good agreement with predictions from Be-disk models. Based on observations performed at ESO, Chile under VLTI

  15. Debris Disks And The Search For Life In The Universe

    Science.gov (United States)

    Cataldi, Gianni

    2016-04-01

    Circumstellar debris disks are the extrasolar analogues of the asteroid belt and the Kuiper belt. These disks consist of comets and leftover planetesimals that continuously collide to produce copious amounts of circumstellar dust that can be observed as infrared excess or in resolved imaging. As an obvious outcome of the planet formation process, debris disks can help us constrain planet formation theories and learn about the history of our own solar system. Structures in the disks such as gaps or warps can hint at the presence of planets. Thus, the study of debris disks is an important branch of exoplanetary science. In this thesis, some aspects of debris disks are considered in detail. A handful of debris disks show observable amounts of gas besides the dust. One such case is the edge-on debris disk around the young A-type star β Pictoris, where the gas is thought to be of secondary origin, i.e. derived from the dust itself. By observing this gas, we can thus learn something about the dust, and therefore about the building blocks of planets. In paper I, spectrally resolved observations of C II emission with Herschel/HIFI are presented. The line profile is used to constrain the spatial distribution of carbon gas in the disk, which helps understanding the gas producing mechanism. In paper II, we analyse C II and O I emission detected with Herschel/PACS and find that the oxygen must be located in a relatively dense region, possibly similar to the CO clump seen by ALMA. An upcoming analysis of our ALMA C I observations will give us a clearer picture of the system. Another famous debris disk is found around the nearby, 440 Myr old A-star Fomalhaut. Its morphology is that of an eccentric debris belt with sharp edges, suggesting shaping by a planet. However, gas-dust interactions may result in a similar morphology without the need to invoke planets. We test this possibility in paper III by analysing non-detections of C II and O I emission by Herschel/PACS. We find that

  16. FIRST IMAGES OF DEBRIS DISKS AROUND TWA 7, TWA 25, HD 35650, AND HD 377

    Energy Technology Data Exchange (ETDEWEB)

    Choquet, Élodie; Perrin, Marshall D.; Chen, Christine H.; Soummer, Rémi; Pueyo, Laurent; Hagan, James B.; Gofas-Salas, Elena; Golimowski, David A.; Hines, Dean C.; Mazoyer, Johan; Debes, John; Stark, Christopher C.; N’Diaye, Mamadou [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Rajan, Abhijith [Arizona State University, Phoenix, AZ 85004 (United States); Schneider, Glenn [Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Augereau, Jean-Charles [Univ. Grenoble Alpes, IPAG, F-38000 Grenoble (France); Wolff, Schuyler; Hsiao, Kevin, E-mail: choquet@stsci.edu [Johns Hopkins University, 3400 North Charles Street, Baltimore MD 21218 (United States)

    2016-01-20

    We present the first images of four debris disks observed in scattered light around the young (4–250 Myr old) M dwarfs TWA 7 and TWA 25, the K6 star HD 35650, and the G2 star HD 377. We obtained these images by reprocessing archival Hubble Space Telescope NICMOS coronagraph data with modern post-processing techniques as part of the Archival Legacy Investigation of Circumstellar Environments program. All four disks appear faint and compact compared with other debris disks resolved in scattered light. The disks around TWA 25, HD 35650, and HD 377 appear very inclined, while TWA 7's disk is viewed nearly face-on. The surface brightness of HD 35650's disk is strongly asymmetric. These new detections raise the number of disks resolved in scattered light around M and late-K stars from one (the AU Mic system) to four. This new sample of resolved disks enables comparative studies of heretofore scarce debris disks around low-mass stars relative to solar-type stars.

  17. Molecular Gas in Disks around Young Stars with ALMA

    Science.gov (United States)

    Hughes, A. Meredith; Factor, Samuel; Lieman-Sifry, Jesse; Flaherty, Kevin; Daley, Cail; Mann, Rita; Roberge, Aki; Di Francesco, James; Williams, Jonathan; Ricci, Luca; Matthews, Brenda; Bally, John; Johnstone, Doug; Kospal, Agnes; Moor, Attila; Kamp, Inga; Wilner, David; Andrews, Sean; Kastner, Joel H.; Abraham, Peter

    2018-01-01

    Molecular gas is a critical component of the planet formation process. In this poster, we present two analyses of the molecular gas component of circumstellar disks at extremes (young, old) of the pre-main sequence phase.(1) We characterize the molecular gas content of the disk around d216-0939, a pre-main sequence star in the Orion Nebula Cluster, using ALMA observations of CO(3-2), HCO+(4-3), and HCN(4-3) observed at 0.5" resolution. We model the density and temperature structure of the disk, returning abundances generally consistent with chemical modeling of protoplanetary disks, and obtain a dynamical mass measurement of the central star of 2.2+/-0.4 M_sun, which is inconsistent with the previously determined spectral type of K5. We also report the detection of a spatially unresolved high-velocity blue-shifted excess emission feature with a measurable position offset from the central star, consistent with an object in Keplerian orbit at 60+/-20 au. The feature is due to a local temperature and/or density enhancement consistent with either a hydrodynamic vortex or the expected signature of the envelope of a forming protoplanet within the disk, providing evidence that planet formation is ongoing within this massive and relatively isolated Orion proplyd. This work is published in Factor et al. (2017). (2) We present ~0.4" resolution images of CO(3-2) and associated continuum emission from the gas-bearing debris disk around the nearby A star 49 Ceti, observed with ALMA. We analyze the ALMA visibilities in tandem with the broadband spectral energy distribution to measure the radial surface density profiles of dust and gas emission from the system. The radial extent of the gas disk (~220 au) is smaller than that of the dust disk (~300 au), consistent with recent observations of other gas-bearing debris disks. While there are so far only three broad debris disks with well characterized radial dust profiles at millimeter wavelengths, 49 Ceti’s disk shows a markedly

  18. Radial Surface Density Profiles of Gas and Dust in the Debris Disk around 49 Ceti

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, A. Meredith; Lieman-Sifry, Jesse; Flaherty, Kevin M.; Daley, Cail M. [Department of Astronomy, Van Vleck Observatory, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States); Roberge, Aki [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States); Kóspál, Ágnes; Moór, Attila; Ábrahám, Peter [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 67, 1525 Budapest (Hungary); Kamp, Inga [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Wilner, David J.; Andrews, Sean M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States); Kastner, Joel H., E-mail: amhughes@astro.wesleyan.edu [Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

    2017-04-20

    We present ∼0.″4 resolution images of CO(3–2) and associated continuum emission from the gas-bearing debris disk around the nearby A star 49 Ceti, observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We analyze the ALMA visibilities in tandem with the broadband spectral energy distribution to measure the radial surface density profiles of dust and gas emission from the system. The dust surface density decreases with radius between ∼100 and 310 au, with a marginally significant enhancement of surface density at a radius of ∼110 au. The SED requires an inner disk of small grains in addition to the outer disk of larger grains resolved by ALMA. The gas disk exhibits a surface density profile that increases with radius, contrary to most previous spatially resolved observations of circumstellar gas disks. While ∼80% of the CO flux is well described by an axisymmetric power-law disk in Keplerian rotation about the central star, residuals at ∼20% of the peak flux exhibit a departure from axisymmetry suggestive of spiral arms or a warp in the gas disk. The radial extent of the gas disk (∼220 au) is smaller than that of the dust disk (∼300 au), consistent with recent observations of other gas-bearing debris disks. While there are so far only three broad debris disks with well characterized radial dust profiles at millimeter wavelengths, 49 Ceti’s disk shows a markedly different structure from two radially resolved gas-poor debris disks, implying that the physical processes generating and sculpting the gas and dust are fundamentally different.

  19. TRANSIT

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. TRANSIT. SYSTEM: DETERMINE 2D-POSITION GLOBALLY BUT INTERMITTENT (POST-FACTO). IMPROVED ACCURACY. PRINCIPLE: POLAR SATELLITES WITH INNOVATIONS OF: GRAVITY-GRADIENT ATTITUDE CONTROL; DRAG COMPENSATION. WORKS ...

  20. Evidence for Different Disk Mass Distributions between Early- and Late-type Be Stars in the BeSOS Survey

    International Nuclear Information System (INIS)

    Arcos, C.; Kanaan, S.; Curé, M.; Jones, C. E.; Sigut, T. A. A.

    2017-01-01

    The circumstellar disk density distributions for a sample of 63 Be southern stars from the BeSOS survey were found by modeling their H α emission line profiles. These disk densities were used to compute disk masses and disk angular momenta for the sample. Average values for the disk mass are 3.4 × 10"−"9 and 9.5 × 10"−"1"0 M _⋆ for early (B0–B3) and late (B4–B9) spectral types, respectively. We also find that the range of disk angular momentum relative to the star is (150–200) J _⋆/ M _⋆ and (100–150) J _⋆/ M _⋆, again for early- and late-type Be stars, respectively. The distributions of the disk mass and disk angular momentum are different between early- and late-type Be stars at a 1% level of significance. Finally, we construct the disk mass distribution for the BeSOS sample as a function of spectral type and compare it to the predictions of stellar evolutionary models with rapid rotation. The observed disk masses are typically larger than the theoretical predictions, although the observed spread in disk masses is typically large.

  1. Evidence for Different Disk Mass Distributions between Early- and Late-type Be Stars in the BeSOS Survey

    Energy Technology Data Exchange (ETDEWEB)

    Arcos, C.; Kanaan, S.; Curé, M. [Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso. Av. Gran Bretana 1111, Valparaíso (Chile); Jones, C. E.; Sigut, T. A. A. [Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada)

    2017-06-10

    The circumstellar disk density distributions for a sample of 63 Be southern stars from the BeSOS survey were found by modeling their H α emission line profiles. These disk densities were used to compute disk masses and disk angular momenta for the sample. Average values for the disk mass are 3.4 × 10{sup −9} and 9.5 × 10{sup −10} M {sub ⋆} for early (B0–B3) and late (B4–B9) spectral types, respectively. We also find that the range of disk angular momentum relative to the star is (150–200) J {sub ⋆}/ M {sub ⋆} and (100–150) J {sub ⋆}/ M {sub ⋆}, again for early- and late-type Be stars, respectively. The distributions of the disk mass and disk angular momentum are different between early- and late-type Be stars at a 1% level of significance. Finally, we construct the disk mass distribution for the BeSOS sample as a function of spectral type and compare it to the predictions of stellar evolutionary models with rapid rotation. The observed disk masses are typically larger than the theoretical predictions, although the observed spread in disk masses is typically large.

  2. Orbital Evolution of Moons in Weakly Accreting Circumplanetary Disks

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, Yuri I.; Gressel, Oliver [Niels Bohr International Academy, The Niels Bohr Institute, Blegdamsvej 17, DK-2100, Copenhagen Ø (Denmark); Kobayashi, Hiroshi [Department of Physics, Nagoya University, Furo-cho, Showa-ku, Nagoya, Aichi, 464-8602 (Japan); Takahashi, Sanemichi Z., E-mail: yuri.fujii@nbi.ku.dk [Astronomical Institute, Tohoku University, 6-3 Aramaki, Aoba-ku, Sendai, 980-8578 (Japan)

    2017-04-01

    We investigate the formation of hot and massive circumplanetary disks (CPDs) and the orbital evolution of satellites formed in these disks. Because of the comparatively small size-scale of the sub-disk, quick magnetic diffusion prevents the magnetorotational instability (MRI) from being well developed at ionization levels that would allow MRI in the parent protoplanetary disk. In the absence of significant angular momentum transport, continuous mass supply from the parental protoplanetary disk leads to the formation of a massive CPD. We have developed an evolutionary model for this scenario and have estimated the orbital evolution of satellites within the disk. We find, in a certain temperature range, that inward migration of a satellite can be stopped by a change in the structure due to the opacity transitions. Moreover, by capturing second and third migrating satellites in mean motion resonances, a compact system in Laplace resonance can be formed in our disk models.

  3. Accretion Disks around Young Stars: An Observational Perspective

    Science.gov (United States)

    Ménard, F.; Bertout, C.

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve this long standing mystery: how did our Solar System form? This chapter focuses on observational studies of the circumstellar environment, and in particular of circumstellar disks, associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of the typical star forming regions ( e.g. 140 pc for Taurus), a planetary system like ours (with diameter simeq50 AU out to Pluto, but excluding the Kuiper belt which could extend much farther out) subtends only 0.35''. Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1'' resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages we will attempt to describe, in a historical perpective, the road that led to the idea that most solar-like stars are surrounded by an accretion disk at one point in their early life and how, nowadays, their structural and physical parameters can be estimated from direct observations. We will follow by a short discussion of a few of the constraints available regarding the evolution and dissipation of these disks. This last topic is particularly relevant today

  4. Measurements of Volatile Circumstellar Isotopes: Effects of Fractionation vs. Nucleosynthesis

    Science.gov (United States)

    Milam, Stefanie

    The origin, evolution, and fate of our Universe and/or Galaxy have puzzled humankind for centuries. One approach to answering this question is to gain further understanding of stellar evolution, since stars are fundamental in galaxy development and evolution. A compilation of stellar composition can reveal the age, dynamics, and possibly the evolutionary state of a galaxy. In particular the volatile isotope ratios carry an imprint of stellar evolution and nucleosynthesis. Primitive materials, such as meteorites and IDPs, have revealed a component of ``atypical" isotopic signatures of these fundamental elements denoting a possible stellar origin. Understanding the processes by which these elements derive is essential for astrophysics on cosmochemical, galactic, stellar, and planetary scales. We propose to analyze data obtained from the Herschel Space Observatory of circumstellar envelopes to definitively measure C, N, and O isotope ratios and test current models of photo-selective isotope fractionation vs. nucleosynthetically determined values. This proposal augments data from the Herschel Space Observatory, primarily from the HIFISTARS program and MESS, though the entire Herschel archive will be searched for relevant data. The broader implications for this study include fundamental data necessary for furthering our current understanding of stellar nucleosynthesis, circumstellar chemistry, Galactic chemical evolution, and the origin of presolar grains found in primitive materials. We will focus on isotopologues of species formed in thermochemical equilibrium and trace their natal, nucleosynthetic isotope ratios. We will analyze Herschel data obtained for a survey of evolved stars with varying degrees of nuclear processing, evolutionary states, and envelope chemistry (e.g. oxygen-rich vs. carbon-rich). A full circumstellar model will be developed for each source to address specific affects that may influence either the ratios or chemistry. The isotope ratios of 12C

  5. High-Contrast Near-Infrared Imaging Polarimetry of the Protoplanetary Disk around RY Tau

    Science.gov (United States)

    Takami, Michihiro; Karr, Jennifer L.; Hashimoto, Jun; Kim, Hyosun; Wisenewski, John; Henning, Thomas; Grady, Carol; Kandori, Ryo; Hodapp, Klaus W.; Kudo, Tomoyuki; hide

    2013-01-01

    We present near-infrared coronagraphic imaging polarimetry of RY Tau. The scattered light in the circumstellar environment was imaged at H-band at a high resolution (approx. 0.05) for the first time, using Subaru-HiCIAO. The observed polarized intensity (PI) distribution shows a butterfly-like distribution of bright emission with an angular scale similar to the disk observed at millimeter wavelengths. This distribution is offset toward the blueshifted jet, indicating the presence of a geometrically thick disk or a remnant envelope, and therefore the earliest stage of the Class II evolutionary phase. We perform comparisons between the observed PI distribution and disk models with: (1) full radiative transfer code, using the spectral energy distribution (SED) to constrain the disk parameters; and (2) monochromatic simulations of scattered light which explore a wide range of parameters space to constrain the disk and dust parameters. We show that these models cannot consistently explain the observed PI distribution, SED, and the viewing angle inferred by millimeter interferometry. We suggest that the scattered light in the near-infrared is associated with an optically thin and geometrically thick layer above the disk surface, with the surface responsible for the infrared SED. Half of the scattered light and thermal radiation in this layer illuminates the disk surface, and this process may significantly affect the thermal structure of the disk.

  6. Numerical models for the circumstellar medium around Betelgeuse

    OpenAIRE

    Mackey, Jonathan; Mohamed, Shazrene; Neilson, Hilding R.; Langer, Norbert; Meyer, Dominique M. -A.

    2013-01-01

    The nearby red supergiant (RSG) Betelgeuse has a complex circumstellar medium out to at least 0.5 parsecs from its surface, shaped by its mass-loss history within the past 0.1 Myr, its environment, and its motion through the interstellar medium (ISM). In principle its mass-loss history can be constrained by comparing hydrodynamic models with observations. Observations and numerical simulations indicate that Betelgeuse has a very young bow shock, hence the star may have only recently become a ...

  7. THE SPITZER INFRARED SPECTROGRAPH SURVEY OF PROTOPLANETARY DISKS IN ORION A. I. DISK PROPERTIES

    Energy Technology Data Exchange (ETDEWEB)

    Kim, K. H. [Korea Astronomy and Space Science Institute (KASI), 776, Daedeokdae-ro, Yuseong-gu, Daejeon 305-348 (Korea, Republic of); Watson, Dan M.; Manoj, P.; Forrest, W. J. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Furlan, Elise [Infrared Processing and Analysis Center, Caltech, 770 S. Wilson Avenue, Pasadena, CA 91125 (United States); Najita, Joan [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Sargent, Benjamin [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Dr., Rochester, NY 14623 (United States); Hernández, Jesús [Centro de Investigaciones de Astronomía, Apdo. Postal 264, Mérida 5101-A (Venezuela, Bolivarian Republic of); Calvet, Nuria [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Adame, Lucía [Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, Av. Universidad S/N, San Nicolás de los Garza, Nuevo León, C.P. 66451, México (Mexico); Espaillat, Catherine [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Megeath, S. T. [Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606 (United States); Muzerolle, James, E-mail: quarkosmos@kasi.re.kr [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

    2016-09-01

    We present our investigation of 319 Class II objects in Orion A observed by Spitzer /IRS. We also present the follow-up observations of 120 of these Class II objects in Orion A from the Infrared Telescope Facility/SpeX. We measure continuum spectral indices, equivalent widths, and integrated fluxes that pertain to disk structure and dust composition from IRS spectra of Class II objects in Orion A. We estimate mass accretion rates using hydrogen recombination lines in the SpeX spectra of our targets. Utilizing these properties, we compare the distributions of the disk and dust properties of Orion A disks with those of Taurus disks with respect to position within Orion A (Orion Nebular Cluster [ONC] and L1641) and with the subgroups by the inferred radial structures, such as transitional disks (TDs) versus radially continuous full disks (FDs). Our main findings are as follows. (1) Inner disks evolve faster than the outer disks. (2) The mass accretion rates of TDs and those of radially continuous FDs are statistically significantly displaced from each other. The median mass accretion rate of radially continuous disks in the ONC and L1641 is not very different from that in Taurus. (3) Less grain processing has occurred in the disks in the ONC compared to those in Taurus, based on analysis of the shape index of the 10 μ m silicate feature ( F {sub 11.3}/ F {sub 9.8}). (4) The 20–31 μ m continuum spectral index tracks the projected distance from the most luminous Trapezium star, θ {sup 1} Ori C. A possible explanation is UV ablation of the outer parts of disks.

  8. Reprocessing in Luminous Disks

    Science.gov (United States)

    Bell, K. Robbins; DeVincenzi, Donald L. (Technical Monitor)

    1999-01-01

    We develop and investigate a procedure that accounts for disk reprocessing of photons that originate in the disk itself. Surface temperatures and simple, black body spectral energy distributions (SEDs) of protostellar disks are calculated. In disks that flare with radius, reprocessing of stellar photons results in temperature profiles considerably shallower than r(sup -3/4). Including the disk as a radiation source (as in the case of actively secreting disks) along with the stellar source further flattens the temperature profile. Disks that flare strongly near the star and then smoothly curve over and become shadowed at some distance ("decreasing curvature" disks) exhibit nearly power-law temperature profiles which result in power-law infrared SEDs with slopes in agreement with typical observations of young stellar objects. Disk models in which the photospheric thickness is controlled by the local opacity and in which the temperature decreases with radius naturally show this shape. Uniformly flaring models do not match observations as well; progressively stronger reprocessing at larger radii leads to SEDs that flatten toward the infrared or even have a second peak at the wavelength corresponding (through the Wien law) to the temperature of the outer edge of the disk. In FU Orionis outbursting systems, the dominant source of energy is the disk itself. The details of the reprocessing depend sensitively on the assumed disk shape and emitted temperature profile. The thermal instability outburst models of Bell Lin reproduce trends in the observed SEDs of Fuors with T varies as r(sup -3/4) in the inner disk (r approx. less than 0.25au corresponding to lambda approx. less than 10 microns) and T varies as r(sup -1/2) in the outer disk. Surface irradiation during outburst and quiescence is compared in the region of planet formation (1 - 10 au). The contrast between the two phases is diminished by the importance of the reprocessing of photons from the relatively high mass

  9. Are young supernova remnants interacting with circumstellar gas

    International Nuclear Information System (INIS)

    Chevalier, R.A.

    1982-01-01

    The young remnants of galactic Type I supernovae (SN 1006, SN 1572, and SN 1604) appear to be interacting with moderately dense gas (n/sub O/> or =0.1 cm -3 ). If the gas in the ambient interstellar medium, the observations suggest that gas of this density is fairly pervasive. If the gas is circumstellar, there are important implications for the progenitors of Type I supernovae. A plausible density distribution for circumstellar gas is rhoinfinityr -2 . The expansion of a supernova into such a medium is examined and is compared with expansion into a uniform medium. The two cases can be distinguished on the basis of their density profiles and their rates of expansion. Currently available data factor the hypothesis of expansion in a uniform medium for all three Type I remnants; the evidence is the strongest for SN 1572 and the weakest for SN 1604. Further X-ray and radio observations of the galactic remnants and of extragalactic Type I supernovae should serve to test this hypothesis

  10. A Neptune-sized transiting planet closely orbiting a 5–10-million-year-old star.

    Science.gov (United States)

    David, Trevor J; Hillenbrand, Lynne A; Petigura, Erik A; Carpenter, John M; Crossfield, Ian J M; Hinkley, Sasha; Ciardi, David R; Howard, Andrew W; Isaacson, Howard T; Cody, Ann Marie; Schlieder, Joshua E; Beichman, Charles A; Barenfeld, Scott A

    2016-06-30

    Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and gas disk from which they formed. The precise ages of meteorites indicate that planetesimals—the building blocks of planets—are produced within the first million years of a star’s life. Fully formed planets are frequently detected on short orbital periods around mature stars. Some theories suggest that the in situ formation of planets close to their host stars is unlikely and that the existence of such planets is therefore evidence of large-scale migration. Other theories posit that planet assembly at small orbital separations may be common. Here we report a newly born, transiting planet orbiting its star with a period of 5.4 days. The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times that of Jupiter (at 99.7 per cent confidence), with a true mass likely to be similar to that of Neptune. The star is 5–10 million years old and has a tenuous dust disk extending outward from about twice the Earth–Sun separation, in addition to the fully formed planet located at less than one-twentieth of the Earth–Sun separation.

  11. Herschel's "Cold Debris Disks": Background Galaxies or Quiescent Rims of Planetary Systems?

    Science.gov (United States)

    Krivov, A. V.; Eiroa, C.; Loehne, T.; Marshall, J. P.; Montesinos, B.; DelBurgo, C.; Absil, O.; Ardila, D.; Augereau, J.-C.; Bayo, A.; hide

    2013-01-01

    Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around approx, 100 micron or shorter. However, 6 out of 31 excess sources studied in the Herschel Open Time Key Programme, DUNES, have been seen to show significant-and in some cases extended-excess emission at 160 micron, which is larger than the 100 micron excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We re-address these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than approx. 100 micron, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but

  12. MEANS 2: Microstructure- and Micromechanism-Sensitive Property Models for Advanced Turbine Disk and Blade Systems

    National Research Council Canada - National Science Library

    Pollock, Tresa M; Mills, Michael J

    2008-01-01

    This effort has focused on verification and refinement of the mechanism transitions at intermediate temperatures in the disk alloy Rene 104, with the observation of microtwinning, continuous faulting...

  13. Resonantly driven nonlinear density waves in protostellar disks

    Science.gov (United States)

    Yuan, Chi; Cassen, Pat

    1994-01-01

    Recent observations of binary, pre-main-sequence, solar-type stars provide evidence that such systems may coexist with circumstellar disks. The binary disk systems, besides being of general interest for the study of star formation, potentially provide useful tests of companion-disk interaction theories prominent in current hypotheses of planet formation. In this paper, we apply an asymptotic analysis of the nonlinear, resonant interaction of a stellar companion with a disk to understand the dependence of such interactions on the properties of the system: the binary mass ratio, the physical properties of the disk, and the effective dissipation (treated herein as viscosity). The method is based on a WKBJ approximation and exploits the conditions that the disk is thin and much less massive than the primary, but does not require that the companion-induced disturbance be small. Both isothermal and adiabatic responses are treated. Only circular orbit resonances are considered in this paper. It is demonstrated that the temperature of the disk as well as the relative mass of the companion affects the degree of nonlinearity, and that nonlinearity promotes high wave compression ratios, long wavelengths, and increased propagation distances. Nevertheless, the total torque exerted between the companion and the disk is well represented by linear theory. The amplitudes of density disturbances are reduced by viscosity and nonisothermality. Because resonant interactions are generally strong and capable of driving rapid evolution, one might expect observations of systems undergoing strong, resonant-driven evolution to be rare. In this connection, it is pointed out that the m = 1 resonance is distinguished by being anomalously weaker than the others and is therefore of observational interest. It is speculated that, in conditions of intrinsically small dissipation, the propagation of resonant-driven density waves is limited by the tendency of their wavelength to diminish with distance

  14. Linear stability of magnetized massive protoplanetary disks

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Min-Kai, E-mail: mklin924@cita.utoronto.ca [Canadian Institute for Theoretical Astrophysics, 60 Saint George Street, Toronto, ON M5S 3H8 (Canada)

    2014-07-20

    Magnetorotational instability (MRI) and gravitational instability (GI) are the two principle routes to turbulent angular momentum transport in accretion disks. Protoplanetary disks (PPDs) may develop both. This paper aims to reinvigorate interest in the study of magnetized massive PPDs, starting from the basic issue of stability. The local linear stability of a self-gravitating, uniformly magnetized, differentially rotating, three-dimensional stratified disk subject to axisymmetric perturbations is calculated numerically. The formulation includes resistivity. It is found that the reduction in the disk thickness by self-gravity (SG) can decrease MRI growth rates; the MRI becomes global in the vertical direction, and MRI modes with small radial length scales are stabilized. The maximum vertical field strength that permits the MRI in a strongly self-gravitating polytropic disk with polytropic index Γ = 1 is estimated to be B{sub z,max}≃c{sub s0}Ω√(μ{sub 0}/16πG), where c{sub s0} is the midplane sound speed and Ω is the local angular velocity. In massive disks with layered resistivity, the MRI is not well localized to regions where the Elsasser number exceeds unity. For MRI modes with radial length scales on the order of the disk thickness, SG can enhance density perturbations, an effect that becomes significant in the presence of a strong toroidal field, and which depends on the symmetry of the underlying MRI mode. In gravitationally unstable disks where GI and MRI growth rates are comparable, the character of unstable modes can transition smoothly between MRI and GI. Implications for nonlinear simulations are discussed briefly.

  15. A SELF-CONSISTENT MODEL OF THE CIRCUMSTELLAR DEBRIS CREATED BY A GIANT HYPERVELOCITY IMPACT IN THE HD 172555 SYSTEM

    International Nuclear Information System (INIS)

    Spectral modeling of the large infrared excess in the Spitzer IRS spectra of HD 172555 suggests that there is more than 10 19 kg of submicron dust in the system. Using physical arguments and constraints from observations, we rule out the possibility of the infrared excess being created by a magma ocean planet or a circumplanetary disk or torus. We show that the infrared excess is consistent with a circumstellar debris disk or torus, located at ∼6 AU, that was created by a planetary scale hypervelocity impact. We find that radiation pressure should remove submicron dust from the debris disk in less than one year. However, the system's mid-infrared photometric flux, dominated by submicron grains, has been stable within 4% over the last 27 years, from the Infrared Astronomical Satellite (1983) to WISE (2010). Our new spectral modeling work and calculations of the radiation pressure on fine dust in HD 172555 provide a self-consistent explanation for this apparent contradiction. We also explore the unconfirmed claim that ∼10 47 molecules of SiO vapor are needed to explain an emission feature at ∼8 μm in the Spitzer IRS spectrum of HD 172555. We find that unless there are ∼10 48 atoms or 0.05 M ⊕ of atomic Si and O vapor in the system, SiO vapor should be destroyed by photo-dissociation in less than 0.2 years. We argue that a second plausible explanation for the ∼8 μm feature can be emission from solid SiO, which naturally occurs in submicron silicate ''smokes'' created by quickly condensing vaporized silicate.

  16. A SELF-CONSISTENT MODEL OF THE CIRCUMSTELLAR DEBRIS CREATED BY A GIANT HYPERVELOCITY IMPACT IN THE HD 172555 SYSTEM

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, B. C.; Melosh, H. J. [Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907 (United States); Lisse, C. M. [JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723 (United States); Chen, C. H. [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Wyatt, M. C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Thebault, P. [LESIA, Observatoire de Paris, F-92195 Meudon Principal Cedex (France); Henning, W. G. [NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States); Gaidos, E. [Department of Geology and Geophysics, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Elkins-Tanton, L. T. [Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC 20015 (United States); Bridges, J. C. [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Morlok, A., E-mail: johns477@purdue.edu [Department of Physical Sciences, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)

    2012-12-10

    Spectral modeling of the large infrared excess in the Spitzer IRS spectra of HD 172555 suggests that there is more than 10{sup 19} kg of submicron dust in the system. Using physical arguments and constraints from observations, we rule out the possibility of the infrared excess being created by a magma ocean planet or a circumplanetary disk or torus. We show that the infrared excess is consistent with a circumstellar debris disk or torus, located at {approx}6 AU, that was created by a planetary scale hypervelocity impact. We find that radiation pressure should remove submicron dust from the debris disk in less than one year. However, the system's mid-infrared photometric flux, dominated by submicron grains, has been stable within 4% over the last 27 years, from the Infrared Astronomical Satellite (1983) to WISE (2010). Our new spectral modeling work and calculations of the radiation pressure on fine dust in HD 172555 provide a self-consistent explanation for this apparent contradiction. We also explore the unconfirmed claim that {approx}10{sup 47} molecules of SiO vapor are needed to explain an emission feature at {approx}8 {mu}m in the Spitzer IRS spectrum of HD 172555. We find that unless there are {approx}10{sup 48} atoms or 0.05 M{sub Circled-Plus} of atomic Si and O vapor in the system, SiO vapor should be destroyed by photo-dissociation in less than 0.2 years. We argue that a second plausible explanation for the {approx}8 {mu}m feature can be emission from solid SiO, which naturally occurs in submicron silicate ''smokes'' created by quickly condensing vaporized silicate.

  17. The photochemistry of carbon-rich circumstellar shells

    Science.gov (United States)

    Huggins, P. J.; Glassgold, A. E.

    1982-01-01

    The effect of ambient ultraviolet photons on the chemical structure of carbon-rich, circumstellar envelopes is investigated with a simple formulation of the time-dependent, photochemical rate equations valid for optically thick shells. Molecules injected into the shielded inner envelope are broken down when they reach the outer regions where ambient ultraviolet photons can penetrate. A quantitative description of the abundance variations is obtained for the case of uniform expansion by detailed consideration of the shielding of the radiation by the dust and molecules of the envelope. Representative results are presented to illustrate the role of shielding in defining the extent of molecular envelopes, the formation of C I and C II shells by photodestruction of carbon-bearing molecules, and the development of layered chemical structures from the photobreakup of polyatomic molecules. Photochemistry makes the outer parts of thick, carbon-rich envelopes into complex regions containing radicals, ions, and atoms which are of considerable observational and theoretical interest.

  18. Astrobiological Effects of Stellar Radiation in Circumstellar Environments

    Science.gov (United States)

    Cuntz, Manfred; Gurdemir, Levent; Guinan, Edward F.; Kurucz, Robert L.

    2006-10-01

    The centerpiece of all life on Earth is carbon-based biochemistry. Previous scientific research has suggested that biochemistry based on carbon may also play a decisive role in extraterrestrial life forms, i.e., alien life outside of Earth, if existent. In the following, we explore if carbon-based macromolecules (such as DNA) in the environments of stars other than the Sun are able to survive the effects of energetic stellar radiation, such as UV-C in the wavelength band between 200 and 290 nm. We focus on main-sequence stars akin to the Sun, but of hotter (F-type stars) and cooler (K- and M-type stars) surface temperature. Emphasis is placed on investigating the radiative environment in stellar habitable zones (HZs). Stellar habitable zones have an important relevance in astrobiology because they constitute circumstellar regions in which a planet of suitable size can have surface temperatures for water to exist in liquid form.

  19. Disks, Microjets, Windblown Bubbles, and Outflows in the Orion Nebula

    Science.gov (United States)

    Bally, John; O'Dell, C. R.; McCaughrean, Mark J.

    2000-06-01

    New deep narrowband images of the Orion Nebula obtained with WFPC2 on the Hubble Space Telescope (HST) and spectra taken with the HIRES spectrometer at the Keck Observatory are presented. We report eight new circumstellar disks seen in silhouette against the background nebular light and about 30 dark disks embedded within the bright proplyds rimmed by ionization fronts. Deep narrowband λ6300 Å images reveal skins of glowing [O I] emission associated with several disks embedded within bright proplyds. [O I] emission also surrounds one dark disk not surrounded by an ionization front; this object may be embedded within the photon-dominated, mostly neutral region behind the ionization front of the Orion Nebula. The intensity and morphology of the [O I] emission provides support for the photon-dominated-region models of externally irradiated circumstellar disks in which soft UV powers photoablation of the disk surface. Dozens of outflows powered by young stars have been discovered on the new images. More than 20 stellar jets emerge from the externally irradiated circumstellar disks or their associated young stars embedded within the Nebula. Most are one-sided (monopolar) subarcsecond-scale microjets, too small to be seen on ground-based images against the bright background nebular light. Additionally, wide-angle winds from 10 young stars in the outskirts of the Nebula power large-scale bow shocks facing the Trapezium OB stars. These shocks may be produced by wind-wind interactions where the T-Tauri winds interact with the outflow of plasma from the core of M42. The largest such structure, associated with the star LL Ori, contains a number of compact high-proper-motion clumps moving almost tangentially to the bow shock. The new data are combined with older HST images to determine proper motions for many nebular features. Neither the LL Ori type bow shocks in the outskirts of the nebula nor the Hα + [O III] arcs that surround many proplyds near the Trapezium show

  20. Study at radio wavelengths of circumstellar envelopes around red giants

    International Nuclear Information System (INIS)

    Do Thi Hoai

    2015-01-01

    The thesis studies mass losing AGB stars and their circumstellar environments, with focus on the development of stellar outflows and their interaction with the surrounding medium. It uses emission from two tracers: carbon monoxide (CO), through its rotational lines in the millimeter range, probes the inner regions of the circumstellar shells out to photodissociation distances, while atomic hydrogen (HI, 21 cm) is better suited to the study of the external regions. The high spectral and spatial resolutions achieved in radio observations allow for a detailed exploration of the kinematics of the relatively slow outflows of red giants. After having introduced the subject, I discuss the case of an S-type star (RS Cnc) that has been observed in CO with the IRAM telescopes, as well as in HI with the VLA, concentrating on the modelling of the spatially resolved CO line profiles and illustrating the complementarity between HI and CO. Results of the CO modelling of other AGB stars observed at IRAM (EP Aqr, XHer and RXBoo) and of a post-AGB star observed with ALMA, the Red Rectangle, are also presented. The formation of the HI line profile in various cases of mass losing AGB stars, in particular YCVn for which a model is presented, is studied next, exploring several effects that might explain the lack of detected emission from stars with high mass loss rates. Similarities between the bipolar outflows of the AGB stars that have been studied, all having mass loss rates in the region of 10 -7 solar masses per year and displaying nearly spherical morphologies are discussed together with the information on the gas temperature obtained from the simultaneous observation of two CO lines. (author)

  1. Circumstellar grain extinction properties of recently discovered post AGB stars

    International Nuclear Information System (INIS)

    Buss, R.H. Jr.; Lamers, H.J.G.L.M.; Snow, T.P. Jr.

    1989-01-01

    The circumstellar grains of two hot evolved post asymptotic giant branch (post AGB) stars, HD 89353 and HD 213985 were examined. From ultraviolet spectra, energy balance of the flux, and Kurucz models, the extinction around 2175 A was derived. With visual spectra, an attempt was made to detect 6614 A diffuse band absorption arising from the circumstellar grains so that we could examine the relationship of these features to the infrared features. For both stars, we did not detect any diffuse band absorption at 6614 A, implying the carrier of this diffuse band is not the carrier of the unidentified infrared features not of the 2175 A bump. The linear ultraviolet extinction of the carbon-rich star HD 89353 was determined to continue across the 2175 A region with no sign of the bump; for HD 213985 it was found to be the reverse: a strong, wide bump in the mid-ultraviolet. The 213985 bump was found to be positioned at 2340 A, longward of its usual position in the interstellar medium. Since HD 213985 was determined to have excess carbon, the bump probably arises from a carbonaceous grain. Thus, in view of the ultraviolet and infrared properties of the two post AGB stars, ubiquitous interstellar infrared emission features do not seem to be associated with the 2175 A bump. Instead, the infrared features seem related to the linear ultraviolet extinction component: hydrocarbon grains of radius less than 300 A are present with the linear HD 89353 extinction; amorphous anhydrous carbonaceous grains of radius less than 50 A might cause the shifted ultraviolet extinction bump of HD 213985

  2. Planetary systems in polarized light: Debris disk observations and instrumentation

    Science.gov (United States)

    Millar-Blanchaer, Maxwell A.

    Understanding planet formation is one of the major challenges of modern astronomy. Polarimetry is a powerful tool with which we can confront this challenge. In particular, polarimetric observations can be useful for imaging debris disks and characterizing exoplanet atmospheres. With that in mind, this thesis has been constructed with two main aspects: i) observational studies of two debris disk systems, beta Pic and HD 157587, using the Gemini Planet Imager and ii) the characterization and testing of a new type of diffraction grating, called a polarization grating, that we plan to use for future observations of exoplanet atmospheres. The Gemini Planet Imager is a high-contrast imager that includes a polarimetry mode designed to image circumstellar disks. Here we detail the development of new data analysis techniques that reduce systematics and noise in processed GPI data. We apply these techniques to observations of the beta Pic and HD 157587 debris disks and then fit each disk image to a geometric disk model. The beta Pic disk model's morphology cannot be explained by interactions with the planet beta Pic b, and the presence of a second planet could be invoked to explain the discrepancy. In the case of HD 157587, the disk model's geometric centre is offset from the location of the star, which could be explained by a perturbing planet. Characterization of the planets' interactions with their debris disks is a critical method to gain more information about these two systems. The second component of this thesis focuses on polarization gratings, thin film optical devices that can simultaneously act as polarizing beam splitters and as spectral dispersive elements. Moreover, they can be designed for high diffraction efficiency across a broad wavelength range. These features make polarization gratings useful for many types of astronomical observations. We have carried out laboratory and on-sky test observations using a polarization grating optimized for visible

  3. Photoionization Models for the Inner Gaseous Disks of Herbig Be Stars: Evidence against Magnetospheric Accretion?

    Energy Technology Data Exchange (ETDEWEB)

    Patel, P.; Sigut, T. A. A.; Landstreet, J. D., E-mail: ppatel54@uwo.ca [Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada)

    2017-02-20

    We investigate the physical properties of the inner gaseous disks of three hot Herbig B2e stars, HD 76534, HD 114981, and HD 216629, by modeling CFHT-ESPaDOns spectra using non-LTE radiative transfer codes. We assume that the emission lines are produced in a circumstellar disk heated solely by photospheric radiation from the central star in order to test whether the optical and near-infrared emission lines can be reproduced without invoking magnetospheric accretion. The inner gaseous disk density was assumed to follow a simple power-law in the equatorial plane, and we searched for models that could reproduce observed lines of H i (H α and H β ), He i, Ca ii, and Fe ii. For the three stars, good matches were found for all emission line profiles individually; however, no density model based on a single power-law was able to reproduce all of the observed emission lines. Among the single power-law models, the one with the gas density varying as ∼10{sup −10}( R {sub *}/ R ){sup 3} g cm{sup −3} in the equatorial plane of a 25 R {sub *} (0.78 au) disk did the best overall job of representing the optical emission lines of the three stars. This model implies a mass for the H α -emitting portion of the inner gaseous disk of ∼10{sup −9} M {sub *}. We conclude that the optical emission line spectra of these HBe stars can be qualitatively reproduced by a ≈1 au, geometrically thin, circumstellar disk of negligible mass compared to the central star in Keplerian rotation and radiative equilibrium.

  4. Disk Defect Data

    Data.gov (United States)

    National Aeronautics and Space Administration — How Data Was Acquired: The data presented is from a physical simulator that simulated engine disks. Sample Rates and Parameter Description: All parameters are...

  5. Verbatim Floppy Disk

    CERN Multimedia

    1976-01-01

    Introduced under the name "Verbatim", Latin for "literally", these disks that sized more than 5¼ inches have become almost universal on dedicated word processing systems and personal computers. This format was replaced more slowly by the 3½-inch format, introduced for the first time in 1982. Compared to today, these large format disks stored very little data. In reality, they could only contain a few pages of text.

  6. Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

    Science.gov (United States)

    Bai, Xue-Ning

    2017-08-01

    The gas dynamics of weakly ionized protoplanetary disks (PPDs) are largely governed by the coupling between gas and magnetic fields, described by three non-ideal magnetohydrodynamical (MHD) effects (Ohmic, Hall, ambipolar). Previous local simulations incorporating these processes have revealed that the inner regions of PPDs are largely laminar and accompanied by wind-driven accretion. We conduct 2D axisymmetric, fully global MHD simulations of these regions (˜1-20 au), taking into account all non-ideal MHD effects, with tabulated diffusion coefficients and approximate treatment of external ionization and heating. With the net vertical field aligned with disk rotation, the Hall-shear instability strongly amplifies horizontal magnetic field, making the overall dynamics dependent on initial field configuration. Following disk formation, the disk likely relaxes into an inner zone characterized by asymmetric field configuration across the midplane, which smoothly transitions to a more symmetric outer zone. Angular momentum transport is driven by both MHD winds and laminar Maxwell stress, with both accretion and decretion flows present at different heights, and modestly asymmetric winds from the two disk sides. With anti-aligned field polarity, weakly magnetized disks settle into an asymmetric field configuration with supersonic accretion flow concentrated at one side of the disk surface, and highly asymmetric winds between the two disk sides. In all cases, the wind is magneto-thermal in nature, characterized by a mass loss rate exceeding the accretion rate. More strongly magnetized disks give more symmetric field configuration and flow structures. Deeper far-UV penetration leads to stronger and less stable outflows. Implications for observations and planet formation are also discussed.

  7. Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Xue-Ning, E-mail: xbai@cfa.harvard.edu [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-51, Cambridge, MA 02138 (United States)

    2017-08-10

    The gas dynamics of weakly ionized protoplanetary disks (PPDs) are largely governed by the coupling between gas and magnetic fields, described by three non-ideal magnetohydrodynamical (MHD) effects (Ohmic, Hall, ambipolar). Previous local simulations incorporating these processes have revealed that the inner regions of PPDs are largely laminar and accompanied by wind-driven accretion. We conduct 2D axisymmetric, fully global MHD simulations of these regions (∼1–20 au), taking into account all non-ideal MHD effects, with tabulated diffusion coefficients and approximate treatment of external ionization and heating. With the net vertical field aligned with disk rotation, the Hall-shear instability strongly amplifies horizontal magnetic field, making the overall dynamics dependent on initial field configuration. Following disk formation, the disk likely relaxes into an inner zone characterized by asymmetric field configuration across the midplane, which smoothly transitions to a more symmetric outer zone. Angular momentum transport is driven by both MHD winds and laminar Maxwell stress, with both accretion and decretion flows present at different heights, and modestly asymmetric winds from the two disk sides. With anti-aligned field polarity, weakly magnetized disks settle into an asymmetric field configuration with supersonic accretion flow concentrated at one side of the disk surface, and highly asymmetric winds between the two disk sides. In all cases, the wind is magneto-thermal in nature, characterized by a mass loss rate exceeding the accretion rate. More strongly magnetized disks give more symmetric field configuration and flow structures. Deeper far-UV penetration leads to stronger and less stable outflows. Implications for observations and planet formation are also discussed.

  8. Mass distributions in disk galaxies

    NARCIS (Netherlands)

    Martinsson, Thomas; Verheijen, Marc; Bershady, Matthew; Westfall, Kyle; Andersen, David; Swaters, Rob

    We present results on luminous and dark matter mass distributions in disk galaxies from the DiskMass Survey. As expected for normal disk galaxies, stars dominate the baryonic mass budget in the inner region of the disk; however, at about four optical scale lengths (hR ) the atomic gas starts to

  9. 2TB hard disk drive

    CERN Multimedia

    This particular object was used up until 2012 in the Data Centre. It slots into one of the Disk Server trays. Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes (link is external). They were originally called "fixed disks" or "Winchesters" (a code name used for a popular IBM product). They later became known as "hard disks" to distinguish them from "floppy disks (link is external)." Hard disks have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies.

  10. Protoplanetary disks studied with 2-Dimensional imaging polarimetry

    International Nuclear Information System (INIS)

    Hajjar, R.; Bastien, P.

    2000-01-01

    Full text: This paper describes a method devised to determine density profiles of disks around Young Stellar Objects (YSOs), since this is crucial for the determination of the possible creation of planets based on theories of the proto solar nebula. It is based on the determination of the position of null polarization points in maps of YSOs as a function of wavelength. This information is interpreted in terms of variation in optical depth then converted to densities based on opacity tables for published grain models. This method has been used on a number of YSOs, namely HL Tau, the archetypal low mass T tauri protostar and showed a density profile compatible with previous models based on the spectral energy distribution of T Tauri stars. We will also explore the possibility of combining this method with millimeter and submillimeter data in order to better constraint grain models circumstellar matter distribution around YSOs

  11. DM ORI: A YOUNG STAR OCCULTED BY A DISTURBANCE IN ITS PROTOPLANETARY DISK

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, Joseph E.; Stassun, Keivan G.; Lund, Michael B.; Weintraub, David A. [Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 (United States); Cargile, Phillip [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Shappee, Benjamin J. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Siverd, Robert J. [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Santa Barbara, CA 93117 (United States); Pepper, Joshua [Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015 (United States); Kochanek, Christopher S.; Gaudi, B. Scott; Stanek, Krzysztof Z.; Holoien, Thomas W.-S. [Department of Astronomy, The Ohio State University, Columbus, OH 43210 (United States); James, David [Cerro Tololo InterAmerican Observatory, Casilla 603, La Serena (Chile); Kuhn, Rudolf B. [South African Astronomical Observatory, P.O. Box 9, Observatory 7935 (South Africa); Beatty, Thomas G. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Prieto, Jose L. [Nucleo de Astronoma de la Facultad de Ingeniera, Universidad Diego Portales, Av. Ejercito 441, Santiago (Chile); Feldman, Daniel M.; Espaillat, Catherine C. [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)

    2016-11-01

    In some planet formation theories, protoplanets grow gravitationally within a young star’s protoplanetary disk, a signature of which may be a localized disturbance in the disk’s radial and/or vertical structure. Using time-series photometric observations by the Kilodegree Extremely Little Telescope South project and the All-Sky Automated Survey for SuperNovae, combined with archival observations, we present the discovery of two extended dimming events of the young star, DM Ori. This young system faded by ∼1.5 mag from 2000 March to 2002 August and then again in 2013 January until 2014 September (depth ∼1.7 mag). We constrain the duration of the 2000–2002 dimming to be < 860 days, and the event in 2013–2014 to be < 585 days, separated by ∼12.5 years. A model of the spectral energy distribution indicates a large infrared excess consistent with an extensive circumstellar disk. Using basic kinematic arguments, we propose that DM Ori is likely being periodically occulted by a feature (possibly a warp or perturbation) in its circumstellar disk. In this scenario, the occulting feature is located >6 au from the host star, moving at ∼14.6 km s{sup −1} and is ∼4.9 au in width. This localized structure may indicate a disturbance such as that which may be caused by a protoplanet early in its formation.

  12. The excess infrared emission of Herbig Ae/Be stars - Disks or envelopes?

    Science.gov (United States)

    Hartmann, Lee; Kenyon, Scott J.; Calvet, Nuria

    1993-01-01

    It is suggested that the near-IR emission in many Herbig Ae/Be stars arises in surrounding dusty envelopes, rather than circumstellar disks. It is shown that disks around Ae/Be stars are likely to remain optically thick at the required accretion rates. It is proposed that the IR excesses of many Ae/Be stars originate in surrounding dust nebulae instead of circumstellar disks. It is suggested that the near-IR emission of the envelope is enhanced by the same processes that produce anomalous strong continuum emission at temperatures of about 1000 K in reflection nebulae surrounding hot stars. This near-IR emission could be due to small grains transiently heated by UV photons. The dust envelopes could be associated with the primary star or a nearby companion star. Some Ae/Be stars show evidence for the 3.3-6.3-micron emission features seen in reflection nebulae around hot stars, which lends further support to this suggestion.

  13. Source to Accretion Disk Tilt

    OpenAIRE

    Montgomery, M. M.; Martin, E. L.

    2010-01-01

    Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source to cause and maintain disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through...

  14. Comparison of Disk Diffusionand

    Directory of Open Access Journals (Sweden)

    Mohsen Rezazadeh

    2014-08-01

    Full Text Available Background: Increasing prevalence of Methicillin-resistant Staphylococcus aureus (MRSA in different communities is clearly visible. Because of this, treatment of patients with infections caused by those bacteria has fallen into critical troubles .Current study, therefore, is aimed to compare phenotypic (disk diffusion and genotypic (PCR methods for fast diagnosis of methicillin-resistant strains, isolated from patients of Arak Central Hospital Materials and Methods:In a cross sectional study whithin one year of period , a total of 100 samples were taken and tested from the patients of Arak hospital (located in the central part of Iran . Isolates' sensitivity to Cefoxitin Disk and Oxacillin was confirmed through disk diffusion. Using PCR , the isolates were tested for the presence of mecA gene. Results were compared from the points of sensitivity and specificity by application of chi square test in SPSS software.. Results: Seventy five 75% out of the total 100 samples (through oxacillin disk diffusion method , already isolated from patients were resistant to oxacillin. Meanwhile, 83(83% of cefoxitin disk diffusion method samples’ were resistant to cefoxitin. Three resistant samples to cefoxitin were negative for mecA gene and 80 (80% samples were positive for mecA gene using PCR. Sensitivity were respectively 93.75% , 100% , and specificity were 100% and 100% , 85% , 100 Conclusion: Findings indicate that oxacillin disk diffusion method is a simple phenotypic method, however, it has lower sensitivity compared to cefoxitin disk diffusion and polymerase chain reaction (PCR methods. Therfore, it is not recommended for detection of Methicillin-resistant Staphylococcus aureus (MRSA. Existence of strains resistant to cefoxitin without mecA gene, shows the outset of another type of resistance or mutation in Methicillin-resistant Staphylococcus aureus (MRSA .

  15. Circumstellar matter and the nature of the SN1987A progenitor star

    International Nuclear Information System (INIS)

    Chevalier, R.A.; Fransson, C.

    1987-01-01

    The radio observations of the supernova SN1987A can be interpreted in terms of its interaction with circumstellar matter. The early turn-on of the radio emission implies a relatively low density circumstellar medium. The optical properties of the supernova imply that the progenitor star had a smaller radius than that of a typical type II supernova progenitor. The mass loss properties are consistent with this hypothesis. The authors predict the thermal X-ray luminosity of the supernova, and note that it is below the current upper limit. A bright infrared dust echo is not expected. Weak ultraviolet emission lines from circumstellar gas may be visible. Although the circumstellar density is low, it is possible that the progenitor star did lose a substantial fraction of its mass prior to the supernova explosion. (author)

  16. Studying Notable Debris Disks In L-band with the Vortex Coronagraph

    Science.gov (United States)

    Patel, Rahul; Beichman, Charles; Choquet, Elodie; Mawet, Dimitri; Meshkat, Tiffany; ygouf, marie

    2018-01-01

    Resolved images of circumstellar disks are integral to our understanding of planetary systems, as the micron sized dust grains that comprise the disk are born from the collisional grinding of planetesimals by larger planets in the system. Resolved images are essential to determining grain properties that might otherwise be degenerate from analyzing the star’s spectral energy distribution. Though the majority of scattered light images of disks are obtained at optical and near-IR wavelengths, only a few have been imaged in the thermal IR at L-band. Probing the spatial features of disks at L-band opens up the possibility of constraining additional grain properties, such as water/ice features.Here, we present the results of our effort to image the disks of a few notable systems at L-band using the NIRC2 imager at Keck, in conjunction with the newly commissioned vector vortex coronagraph. The vortex, along with the QACITS fine guiding program installed at Keck, enables us to probe the small ~lambda/D angular separations of these systems, and reach contrasts of 1/100,000. We will discuss the systems that have been imaged, and lessons learned while imaging in L-band. Our analysis of these disks reveal features previously unseen, and will lay the foundation for followup studies by missions such as JWST at similar wavelengths from space.

  17. Disk Masses in the Embedded and T Tauri Phases of Stellar Evolution

    Science.gov (United States)

    Vorobyov, E. I.

    2009-02-01

    Motivated by a growing concern that masses of circumstellar disks may have been systematically underestimated by conventional observational methods, we present a numerical hydrodynamics study of time-averaged disk masses (langM drang) around low-mass Class 0, Class I, and Class II objects. Mean disk masses (\\overline{M}_d) are then calculated by weighting the time-averaged disk masses according to the corresponding stellar masses using a power-law weight function with a slope typical for the Kroupa initial mass function of stars. Two distinct types of disks are considered: self-gravitating disks, in which mass and angular momentum are redistributed exclusively by gravitational torques, and viscous disks, in which both the gravitational and viscous torques are at work. We find that self-gravitating disks have mean masses that are slowly increasing along the sequence of stellar evolution phases. More specifically, Class 0/I/II self-gravitating disks have mean masses \\overline{M}_d=0.09, 0.10, and 0.12 M sun, respectively. Viscous disks have similar mean masses (\\overline{M}_d=0.10-0.11 M sun) in the Class 0/I phases but almost a factor of 2 lower mean mass in the Class II phase (\\overline{M}_d,CII=0.06 M_⊙). In each evolution phase, time-averaged disk masses show a large scatter around the mean value. Our obtained mean disk masses are larger than those recently derived by Andrews & Williams and Brown et al., regardless of the physical mechanisms of mass transport in the disk. The difference is especially large for Class II disks, for which we find \\overline{M}_d,CII=0.06-0.12 M sun but Andrews & Williams report median masses of the order 3 × 10-3 M sun. When Class 0/I/II systems are considered altogether, a least-squares best fit yields the following relation between the time-averaged disk and stellar masses, langM drang = (0.2 ± 0.05)langM *rang1.3±0.15. The dependence of langM drang on langM *rang becomes progressively steeper along the sequence of

  18. PLANETESIMAL DISK MICROLENSING

    International Nuclear Information System (INIS)

    Heng, Kevin; Keeton, Charles R.

    2009-01-01

    Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

  19. ON THE GRAVITATIONAL STABILITY OF GRAVITO-TURBULENT ACCRETION DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Min-Kai; Kratter, Kaitlin M., E-mail: minkailin@email.arizona.edu [Department of Astronomy and Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2016-06-20

    Low mass, self-gravitating accretion disks admit quasi-steady, “gravito-turbulent” states in which cooling balances turbulent viscous heating. However, numerical simulations show that gravito-turbulence cannot be sustained beyond dynamical timescales when the cooling rate or corresponding turbulent viscosity is too large. The result is disk fragmentation. We motivate and quantify an interpretation of disk fragmentation as the inability to maintain gravito-turbulence due to formal secondary instabilities driven by: (1) cooling, which reduces pressure support; and/or (2) viscosity, which reduces rotational support. We analyze the axisymmetric gravitational stability of viscous, non-adiabatic accretion disks with internal heating, external irradiation, and cooling in the shearing box approximation. We consider parameterized cooling functions in 2D and 3D disks, as well as radiative diffusion in 3D. We show that generally there is no critical cooling rate/viscosity below which the disk is formally stable, although interesting limits appear for unstable modes with lengthscales on the order of the disk thickness. We apply this new linear theory to protoplanetary disks subject to gravito-turbulence modeled as an effective viscosity, and cooling regulated by dust opacity. We find that viscosity renders the disk beyond ∼60 au dynamically unstable on radial lengthscales a few times the local disk thickness. This is coincident with the empirical condition for disk fragmentation based on a maximum sustainable stress. We suggest turbulent stresses can play an active role in realistic disk fragmentation by removing rotational stabilization against self-gravity, and that the observed transition in behavior from gravito-turbulent to fragmenting may reflect instability of the gravito-turbulent state itself.

  20. New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars

    Science.gov (United States)

    Ziurys, L. M.; Schmidt, D. R.; Bernal, J. J.

    2018-04-01

    PO and PN have been newly identified in several oxygen-rich circumstellar envelopes, using the Submillimeter Telescope of the Arizona Radio Observatory. The J = 5 → 4 and J = 6 → 5 transitions of PN near 235 and 282 GHz, and the lambda doublets originating in the J = 5.5 → 4.5 and J = 6.5 → 5.5 lines of PO at 240 and 284 GHz, have been detected toward the shells of asymptotic giant branch (AGB) stars TX Cam and R Cas. A similar set of lines has been observed toward the supergiant NML Cyg, and new transitions of these two molecules were also measured toward the AGB star IK Tau. Along with the previous data from VY Canis Majoris (VY CMa), these spectral lines were analyzed using the non-local thermodynamic equilibrium (non-LTE) circumstellar modeling code, ESCAPADE. For the AGB stars, peak abundances found for PN and PO were f ∼ (1–2) × 10‑8 and (0.5–1) × 10‑7, respectively, while those for the supergiants were f(PN) ∼ (0.3–0.7) × 10‑8 and f(PO) ∼ (5–7) × 10‑8. PN was well modeled with a spherical radial distribution, suggesting formation near the stellar photosphere, perhaps enhanced by shocks. PO was best reproduced by a shell model, indicating a photochemical origin, except for VY CMa. Overall, the abundance of PO is a factor of 5–20 greater than that of PN. This study suggests that phosphorus-bearing molecules are common in O-rich envelopes, and that a significant amount of phosphorus (>20%) remains in the gas phase.

  1. Relativistic, accreting disks

    International Nuclear Information System (INIS)

    Abramowicz, M.A; Jaroszynski, M.; Sikora, M.

    1978-01-01

    An analytic theory of the hydrodynamical structure of accreting disks (without self-gravitation but with pressure) orbiting around and axially symmetric, stationary, compact body (e.g. black hole) is presented. The inner edge of the marginally stable accreting disk (i.e. disk with constant angular momentum density) has a sharp cusp located on the equatorial plane between rsub(ms) and rsub(mb). The existence of the cusp is also typical for any angular momentum distribution. The physical importance of the cusp follows from the close analogy with the case of a close binary system (L 1 Lagrange point on the Roche lobe). The existence of the cusp is thus a crucial phenomenon in such problems as boundary condition for the viscous stresses, accretion rate etc. (orig.) [de

  2. Premixed direct injection disk

    Science.gov (United States)

    York, William David; Ziminsky, Willy Steve; Johnson, Thomas Edward; Lacy, Benjamin; Zuo, Baifang; Uhm, Jong Ho

    2013-04-23

    A fuel/air mixing disk for use in a fuel/air mixing combustor assembly is provided. The disk includes a first face, a second face, and at least one fuel plenum disposed therebetween. A plurality of fuel/air mixing tubes extend through the pre-mixing disk, each mixing tube including an outer tube wall extending axially along a tube axis and in fluid communication with the at least one fuel plenum. At least a portion of the plurality of fuel/air mixing tubes further includes at least one fuel injection hole have a fuel injection hole diameter extending through said outer tube wall, the fuel injection hole having an injection angle relative to the tube axis. The invention provides good fuel air mixing with low combustion generated NOx and low flow pressure loss translating to a high gas turbine efficiency, that is durable, and resistant to flame holding and flash back.

  3. The Effects of Protostellar Disk Turbulence on CO Emission Lines: A Comparison Study of Disks with Constant CO Abundance versus Chemically Evolving Disks

    Science.gov (United States)

    Yu, Mo; Evans, Neal J., II; Dodson-Robinson, Sarah E.; Willacy, Karen; Turner, Neal J.

    2017-12-01

    Turbulence is the leading candidate for angular momentum transport in protoplanetary disks and therefore influences disk lifetimes and planet formation timescales. However, the turbulent properties of protoplanetary disks are poorly constrained observationally. Recent studies have found turbulent speeds smaller than what fully-developed MRI would produce (Flaherty et al.). However, existing studies assumed a constant CO/H2 ratio of 10-4 in locations where CO is not frozen-out or photo-dissociated. Our previous studies of evolving disk chemistry indicate that CO is depleted by incorporation into complex organic molecules well inside the freeze-out radius of CO. We consider the effects of this chemical depletion on measurements of turbulence. Simon et al. suggested that the ratio of the peak line flux to the flux at line center of the CO J = 3-2 transition is a reasonable diagnostic of turbulence, so we focus on that metric, while adding some analysis of the more complex effects on spatial distribution. We simulate the emission lines of CO based on chemical evolution models presented in Yu et al., and find that the peak-to-trough ratio changes as a function of time as CO is destroyed. Specifically, a CO-depleted disk with high turbulent velocity mimics the peak-to-trough ratios of a non-CO-depleted disk with lower turbulent velocity. We suggest that disk observers and modelers take into account the possibility of CO depletion when using line profiles or peak-to-trough ratios to constrain the degree of turbulence in disks. Assuming that {CO}/{{{H}}}2={10}-4 at all disk radii can lead to underestimates of turbulent speeds in the disk by at least 0.2 km s-1.

  4. ABUNDANT CIRCUMSTELLAR SILICA DUST AND SiO GAS CREATED BY A GIANT HYPERVELOCITY COLLISION IN THE ∼12 MYR HD172555 SYSTEM

    International Nuclear Information System (INIS)

    Lisse, C. M.; Chen, C. H.; Wyatt, M. C.; Morlok, A.; Song, I.; Bryden, G.; Sheehan, P.

    2009-01-01

    The fine dust detected by infrared (IR) emission around the nearby β Pic analog star HD172555 is very peculiar. The dust mineralogy is composed primarily of highly refractory, nonequilibrium materials, with approximately three quarters of the Si atoms in silica (SiO 2 ) species. Tektite and obsidian lab thermal emission spectra (nonequilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a -3.95±0.10 . While IR photometry of the system has stayed stable since the 1983 IRAS mission, this steep a size distribution, with abundant micron-sized particles, argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 ± 0.6 AU (equivalent to 1.9 ± 0.2 AU from the Sun), within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 x 10 19 -2 x 10 20 kg, equivalent to a 150-200 km radius asteroid. Significant emission features centered at 4 and 8 μm due to fluorescing SiO gas are also found. Roughly 10 22 kg of SiO gas, formed by vaporizing silicate rock, is also present in the system, and a separate population of very large, cool grains, massing 10 21 -10 22 kg and equivalent to the largest sized asteroid currently found in the solar system's main asteroid belt, dominates the solid circumstellar material by mass. The makeup of the observed dust and gas, and the noted lack of a dense circumstellar gas disk, strong stellar X-ray activity, and an extended disk of β meteoroids argues that the source of the observed circumstellar materials is a giant hypervelocity (>10 km s -1 ) impact between large rocky planetesimals, similar to the ones which formed the Moon and which stripped the surface crustal material off of Mercury's surface.

  5. Characterizing Debris Disks in the Late Stages of Planet Formation

    Science.gov (United States)

    White, Jacob

    2018-01-01

    The planet formation process shapes the morphology and grain size distribution of circumstellar disks, encoding the formation history of a given system. Remnants of planet formation, such as comets and asteroids, collisionally evolve and can replenish the dust and small solids that would otherwise be cleared on short timescales. These grains are observed through reprocessed starlight at submm to cm wavelengths.The spectrum of the mm/cm emission reveals details of the grain population. However, one confounding parameter in studying these grains around stars is the stars themselves. The emission from stars in the mm/cm is nontrivial and generally not well-constrained. I will present examples of debris systems (HD 141569 and Fomalhaut) studied by ALMA and the VLA, in which unconstrained stellar emission may be contributing to the observed flux densities. Such contamination in turn biases the inferred emission from the disk and the corresponding dust properties. In some cases, the behavior of the observed A/B stars can exhibit an emission profile that has similarities to that of the Sun's mm/cm emission, although the same processes are not thought to necessarily occur in the atmospheres of massive stars.To address the uncertainty in stellar emission at mm/cm wavelengths, we present ongoing radio observations (JCMT, SMA, VLA) of Sirius A, which is a bright, nearby star with no known debris. We seek to use this system to set an observationally determined standard for stellar atmosphere modeling and debris disk studies around A stars, as well as to take the first step toward characterizing potential intrinsic uncertainty in stellar emission at these wavelengths. This talk will highlight the effort to characterize stellar atmospheres through a project known as MESAS (Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths) which is imperative to the success of current and future debris disk studies.

  6. Resolved Millimeter Observations of the HR 8799 Debris Disk

    Science.gov (United States)

    Wilner, David J.; MacGregor, Meredith A.; Andrews, Sean M.; Hughes, A. Meredith; Matthews, Brenda; Su, Kate

    2018-03-01

    We present 1.3 mm observations of the debris disk surrounding the HR 8799 multi-planet system from the Submillimeter Array to complement archival ALMA observations that spatially filtered away the bulk of the emission. The image morphology at 3.″8 (150 au) resolution indicates an optically thin circumstellar belt, which we associate with a population of dust-producing planetesimals within the debris disk. The interferometric visibilities are fit well by an axisymmetric radial power-law model characterized by a broad width, ΔR/R ≳ 1. The belt inclination and orientation parameters are consistent with the planet orbital parameters within the mutual uncertainties. The models constrain the radial location of the inner edge of the belt to {R}in}={104}-12+8 au. In a simple scenario where the chaotic zone of the outermost planet b truncates the planetesimal distribution, this inner edge location translates into a constraint on the planet b mass of {M}pl}={5.8}-3.1+7.9 M Jup. This mass estimate is consistent with infrared observations of the planet luminosity and standard hot-start evolutionary models, with the uncertainties allowing for a range of initial conditions. We also present new 9 mm observations of the debris disk from the Very Large Array and determine a millimeter spectral index of 2.41 ± 0.17. This value is typical of debris disks and indicates a power-law index of the grain size distribution q = 3.27 ± 0.10, close to predictions for a classical collisional cascade.

  7. Characterizing Debris Disks and the Late Stages of Planet Formation

    Science.gov (United States)

    White, Jacob

    2017-10-01

    The planet formation process shapes the morphology and grain size distribution of circumstellar disks, encoding the formation history of a given system. Remnants of planet formation, such as comets and asteroids, collisionally evolve and can replenish the dust and small solids that would otherwise be cleared on short timescales. These grains are observed through reprocessed starlight at submm to cm wavelengths.The spectrum of the mm/cm emission reveals details of the grain population. However, one confounding parameter in studying these grains around stars is the stars themselves. The emission from stars in the mm/cm is nontrivial and generally not well-constrained. I will present examples of debris systems (HD 141569 and Fomalhaut) studied by ALMA and the VLA, in which unconstrained stellar emission may be contributing to the observed flux densities. Such contamination in turn biases the inferred emission from the disk and the corresponding dust properties. In some cases, the behavior of the observed A/B stars can exhibit an emission profile that has similarities to that of the Sun's mm/cm emission, although the same processes are not thought to necessarily occur in the atmospheres of massive stars.To address the uncertainty in stellar emission at mm/cm wavelengths, we present ongoing radio observations (JCMT, SMA, VLA) of Sirius A, which is a bright, nearby star with no known debris. We seek to use this system to set an observationally determined standard for stellar atmosphere modeling and debris disk studies around A stars, as well as to take the first step toward characterizing potential intrinsic uncertainty in stellar emission at these wavelengths. This talk will highlight the effort to characterize stellar atmospheres through a project known as MESAS (Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths) which is imperative to the success of current and future debris disk studies.

  8. ALMA observations of the nearby AGB star L2 Puppis II. Gas disk properties derived from 12CO and 13CO J = 3–2 emission

    OpenAIRE

    Homan, Ward; Richards, Anita; Decin, Leen; Kervella , Pierre; de Koter, Alex; Mcdonald, Iain; Ohnaka, Keiichi

    2017-01-01

    The circumstellar environment of the AGB star L2 Puppis was observed with ALMA in cycle 3, with a resolution of 15 × 18 mas. The molecular emission shows a differentially rotating disk, inclined to a nearly edge-on position. In the first paper in this series (Paper I) the molecular emission was analysed to accurately deduce the motion of the gas in the equatorial regions of the disk. In this work we model the optically thick 12CO J = 3-2 and the optically thin 13CO J = 3-2 rotational transiti...

  9. Effect of Different Angular Momentum Transport Mechanisms on the Radial Volatile Distribution in Protoplanetary Disks

    Science.gov (United States)

    Kalyaan, Anusha; Desch, Steven

    2018-01-01

    How circumstellar disks evolve and transport angular momentum is a mystery even until today. Magnetorotational instability (MRI; [1]) earlier thought to be a primary driver of disk evolution, has been found to be not as strong a candidate in cold insufficiently ionized protoplanetary disks where non-ideal MHD effects take over to efficiently suppress the instability [2][3]. In the past few years, recent studies have proposed different mechanisms such as magnetically-driven disk winds [4][5], convective overstability [6], and the vertical shear instability (VSI)[7] to be likely drivers of disk evolution. In this work, we consider numerically [8] and/or parametrically derived radial α profiles of three different mechanisms of angular momentum transport (hydrodynamic instabilities such as VSI, disk winds, and MRI) to understand how the underlying disk structure changes and evolves with each mechanism. We overlay our snowline model that incorporates the advection and diffusion of volatiles as well as radial drift of solids [9] to understand how different α profiles can affect the distribution of water in the disk. References: [1] Balbus, S.A., & Hawley, J.F.,1998, Rev. of Mod. Phys., 70, 1 [2] Bai, X.-N., & Stone, J.M. 2011, ApJ, 736, 144 [3] Bai, X.-N., & Stone, J.M., 2013, ApJ, 769, 76 [4] Bai, X.-N., 2016, ApJ, 821, 80 [5] Suzuki, T.K., Ogihara, M., Morbidelli, A., Crida, A., & Guillot, T., 2016, A&A, 596, A74 [6] Klahr, H., & Hubbard, A. 2014, ApJ, 788, 21 [7] Stoll, M.H.R., & Kley, W. 2014, A&A, 572, A77 [8] Kalyaan, A., Desch, S.J., & Monga, N., 2015, ApJ, 815, 112 [9] Desch, S.J., Estrada, P.R., Kalyaan, A., & Cuzzi, J.N., 2017, ApJ, 840, 86

  10. Identifying Likely Disk-hosting M dwarfs with Disk Detective

    Science.gov (United States)

    Silverberg, Steven; Wisniewski, John; Kuchner, Marc J.; Disk Detective Collaboration

    2018-01-01

    M dwarfs are critical targets for exoplanet searches. Debris disks often provide key information as to the formation and evolution of planetary systems around higher-mass stars, alongside the planet themselves. However, less than 300 M dwarf debris disks are known, despite M dwarfs making up 70% of the local neighborhood. The Disk Detective citizen science project has identified over 6000 new potential disk host stars from the AllWISE catalog over the past three years. Here, we present preliminary results of our search for new disk-hosting M dwarfs in the survey. Based on near-infrared color cuts and fitting stellar models to photometry, we have identified over 500 potential new M dwarf disk hosts, nearly doubling the known number of such systems. In this talk, we present our methodology, and outline our ongoing work to confirm systems as M dwarf disks.

  11. MEASURING ORGANIC MOLECULAR EMISSION IN DISKS WITH LOW-RESOLUTION SPITZER SPECTROSCOPY

    International Nuclear Information System (INIS)

    Teske, Johanna K.; Najita, Joan R.; Carr, John S.; Pascucci, Ilaria; Apai, Daniel; Henning, Thomas

    2011-01-01

    We explore the extent to which Spitzer Infrared Spectrograph (IRS) spectra taken at low spectral resolution can be used in quantitative studies of organic molecular emission from disks surrounding low-mass young stars. We use Spitzer IRS spectra taken in both the high- and low-resolution modules for the same sources to investigate whether it is possible to define line indices that can measure trends in the strength of the molecular features in low-resolution data. We find that trends in the HCN emission strength seen in the high-resolution data can be recovered in low-resolution data. In examining the factors that influence the HCN emission strength, we find that the low-resolution HCN flux is modestly correlated with stellar accretion rate and X-ray luminosity. Correlations of this kind are perhaps expected based on recent observational and theoretical studies of inner disk atmospheres. Our results demonstrate the potential of using the large number of low-resolution disk spectra that reside in the Spitzer archive to study the factors that influence the strength of molecular emission from disks. Such studies would complement results for the much smaller number of circumstellar disks that have been observed at high resolution with IRS.

  12. Hydrogenated Benzene in Circumstellar Environments: Insights into the Photostability of Super-hydrogenated PAHs

    Science.gov (United States)

    Quitián-Lara, Heidy M.; Fantuzzi, Felipe; Nascimento, Marco A. C.; Wolff, Wania; Boechat-Roberty, Heloisa M.

    2018-02-01

    Polycyclic aromatic hydrocarbons (PAHs), comprised of fused benzene (C6H6) rings, emit infrared radiation (3–12 μm) due to the vibrational transitions of the C–H bonds of the aromatic rings. The 3.3 μm aromatic band is generally accompanied by the band at 3.4 μm assigned to the vibration of aliphatic C–H bonds of compounds such as PAHs with an excess of peripheral H atoms (H n –PAHs). Herein we study the stability of fully hydrogenated benzene (or cyclohexane, C6H12) under the impact of stellar radiation in the photodissociation region (PDR) of NGC 7027. Using synchrotron radiation and time-of-flight mass spectrometry, we investigated the ionization and dissociation processes at energy ranges of UV (10–200 eV) and soft X-rays (280–310 eV). Density Functional Theory (DFT) calculations were used to determine the most stable structures and the relevant low-lying isomers of singly charged C6H12 ions. Partial Ion Yield (PIY) analysis gives evidence of the higher tendency toward dissociation of cyclohexane in comparison to benzene. However, because of the high photoabsorption cross-section of benzene at the C1s resonance edge, its photodissociation and photoionization cross-sections are enhanced, leading to a higher efficiency of dissociation of benzene in the PDR of NGC 7027. We suggest that a similar effect is experienced by PAHs in X-ray photon-rich environments, which ultimately acts as an auxiliary protection mechanism of super-hydrogenated polycyclic hydrocarbons. Finally, we propose that the single photoionization of cyclohexane could enhance the abundance of branched molecules in interstellar and circumstellar media.

  13. 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.

  14. Exploring Our Galaxy's Thick Disk

    Science.gov (United States)

    Kohler, Susanna

    2017-12-01

    What is the structure of the Milky Ways disk, and how did it form? A new study uses giant stars to explore these questions.A View from the InsideSchematic showing an edge-on, not-to-scale view of what we think the Milky Ways structurelookslike. The thick disk is shown in yellow and the thin disk is shown in green. [Gaba p]Spiral galaxies like ours are often observed to have disks consisting of two components: a thin disk that lies close to the galactic midplane, and a thick disk that extends above and below this. Past studies have suggested that the Milky Ways disk hosts the same structure, but our position embedded in the Milky Way makes this difficult to confirm.If we can measure the properties of a broad sample of distant tracer stars and use this to better understand the construction of the Milky Ways disk, then we can start to ask additional questions like, how did the disk components form? Formation pictures for the thick disk generally fall into two categories:Stars in the thick disk formed within the Milky Way either in situ or by migrating to their current locations.Stars in the thick disk formed in satellite galaxies around the Milky Way and then accreted when the satellites were disrupted.Scientists Chengdong Li and Gang Zhao (NAO Chinese Academy of Sciences, University of Chinese Academy of Sciences) have now used observations of giant stars which can be detected out to great distances due to their brightness to trace the properties of the Milky Ways thick disk and address the question of its origin.Best fits for the radial (top) and vertical (bottom) metallicity gradients of the thick-disk stars. [Adapted from Li Zhao 2017]Probing OriginsLi and Zhao used data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in China to examine a sample of 35,000 giant stars. The authors sorted these stars into different disk components halo, thin disk, and thick disk based on their kinematic properties, and then explored how the orbital and

  15. DVD - digital versatile disks

    Energy Technology Data Exchange (ETDEWEB)

    Gaunt, R.

    1997-05-01

    An international standard has emerged for the first true multimedia format. Digital Versatile Disk (by its official name), you may know it as Digital Video Disks. DVD has applications in movies, music, games, information CD-ROMS, and many other areas where massive amounts of digital information is needed. Did I say massive amounts of data? Would you believe over 17 gigabytes on a single piece of plastic the size of an audio-CD? That`s the promise, at least, by the group of nine electronics manufacturers who have agreed to the format specification, and who hope to make this goal a reality by 1998. In this major agreement, which didn`t come easily, the manufacturers will combine Sony and Phillip`s one side double-layer NMCD format with Toshiba and Matsushita`s double sided Super-Density disk. By Spring of this year, they plan to market the first 4.7 gigabyte units. The question is: Will DVD take off? Some believe that read-only disks recorded with movies will be about as popular as video laser disks. They say that until the eraseable/writable DVD arrives, the consumer will most likely not buy it. Also, DVD has a good market for replacement of CD- Roms. Back in the early 80`s, the international committee deciding the format of the audio compact disk decided its length would be 73 minutes. This, they declared, would allow Beethoven`s 9th Symphony to be contained entirely on a single CD. Similarly, today it was agreed that playback length of a single sided, single layer DVD would be 133 minutes, long enough to hold 94% of all feature-length movies. Further, audio can be in Dolby`s AC-3 stereo or 5.1 tracks of surround sound, better than CD-quality audio (16-bits at 48kHz). In addition, there are three to five language tracks, copy protection and parental ``locks`` for R rated movies. DVD will be backwards compatible with current CD-ROM and audio CD formats. Added versatility comes by way of multiple aspect rations: 4:3 pan-scan, 4:3 letterbox, and 16:9 widescreen. MPEG

  16. Discussing the low fraction of disk-bearing T Tauri stars discovered near to the Sh2-296 nebula

    Science.gov (United States)

    Gregorio-Hetem, Jane

    2015-08-01

    A multiband study has been developed by our team in the direction of young star clusters associated to the Sh2-296 nebula aiming to unveil the star formation history of this galactic molecular cloud that shows a mixing of different age stellar groups. A sample of 58 pre-main sequence stars has been recently discovered by us in this region (Fernandes et al. 2015, MNRAS in press), based on optical spectral features. Only 41% of the sample shows evidence of IR excess revealing the presence of circumstellar disks. It is interesting to note that the targets were revealed by their strong X-ray emission, typically found in T Tauri stars (TTs) (Santos-Silva et al. 2015, in preparation) . In this case, it would be expected a larger number of disk-bearing stars and also the fraction of circumstellar emission (fc = Ldisk/Ltotal ) should be more significant in these objects. However, we verified that only 12% of the sample has fc > 30%. This low fraction is quite rare compared to most young star-forming regions, suggesting that some external factor has accelerated the disc dissipation. In the present work we explore the circumstellar structure of a subsample of 8 TTs associated to Sh2-296. The TTs were selected on the basis of their high circumstellar emission, which is estimated by SED fitting that uses near- to mid-IR data extracted from available catalogues (WISE, AKARI, MSX). The circumstellar characteristics are confronted to interstellar environment by comparing the stellar spatial distribution with 12CO maps (Nanten Survey, Fukui et al. ). Most of the TTs are projected against moderate molecular emission (33 Jy), but some of them are found in regions of lower levels of gas distribution (3.8 Jy). The similarities and differences found among the studied objects are discussed in order to better understand the formation and evolution of protostellar disks of the selected sample and their role in the star formation scenario nearby Sh2-296

  17. SPATIALLY RESOLVING THE HK Tau B EDGE-ON DISK FROM 1.2 TO 4.7 μm: A UNIQUE SCATTERED LIGHT DISK

    International Nuclear Information System (INIS)

    McCabe, C.; Duchene, G.; Pinte, C.; Menard, F.; Stapelfeldt, K. R.; Ghez, A. M.

    2011-01-01

    We present spatially resolved scattered light images of the circumstellar disk around HK Tau B at 3.8 and 4.7 μm taken with the Keck Telescope Laser Guide Star Adaptive Optics (AO) system, and 1.6-2.12 μm images taken with the Very Large Telescope/NACO AO system. Combined with previously published optical Hubble Space Telescope data, we investigate the spatially resolved scattered light properties of this edge-on circumstellar disk and probe for the presence of large grains. The 0.6-3.8 μm scattered light observations reveal strong, and in some cases, unusual, wavelength dependencies in the observed disk morphology. The separation between the two scattered light nebulae, which is directly proportional to the disk-mass-opacity product, decreases by 30% between 0.6 and 3.8 μm. Over the same wavelength range, the FWHM of the disk nebulosity declines by a factor of two, while the flux ratio between the two nebulae increases by a factor of ∼8. No other disk known to date shows a flux ratio that increases with wavelength. Both the FWHM and nebula flux ratio are affected by the scattering phase function and the observed behavior can most readily be explained by a phase function that becomes more forward throwing with wavelength. The multi-wavelength scattered light observations also confirm the asymmetric nature of the disk and show that the level of asymmetry is a function of wavelength. We use the MCFOST radiative transfer code to model the disk at four wavelengths, corresponding to the I, H, Ks, and L' bandpasses. A single power-law grain size distribution can recreate the observed disk properties simultaneously at all four wavelengths. Bayesian analysis of the dust parameters finds a 99% probability that the maximum grain size is 5.5 μm or larger. We also find that the grain size distribution is steep, with a 99% probability of a power-law index of 4.2 or larger, suggesting that these large grains are a small fraction of the overall dust population. The best

  18. The formation of rings and gaps in magnetically coupled disk-wind systems: ambipolar diffusion and reconnection

    Science.gov (United States)

    Suriano, Scott S.; Li, Zhi-Yun; Krasnopolsky, Ruben; Shang, Hsien

    2018-03-01

    Radial substructures in circumstellar disks are now routinely observed by ALMA. There is also growing evidence that disk winds drive accretion in such disks. We show through 2D (axisymmetric) simulations that rings and gaps develop naturally in magnetically coupled disk-wind systems on the scale of tens of au, where ambipolar diffusion (AD) is the dominant non-ideal MHD effect. In simulations where the magnetic field and matter are moderately coupled, the disk remains relatively laminar with the radial electric current steepened by AD into a thin layer near the midplane. The toroidal magnetic field sharply reverses polarity in this layer, generating a large magnetic torque that drives fast accretion, which drags the poloidal field into a highly pinched radial configuration. The reconnection of this pinched field creates magnetic loops where the net poloidal magnetic flux (and thus the accretion rate) is reduced, yielding dense rings. Neighbouring regions with stronger poloidal magnetic fields accrete faster, forming gaps. In better magnetically coupled simulations, the so-called `avalanche accretion streams' develop continuously near the disk surface, rendering the disk-wind system more chaotic. Nevertheless, prominent rings and gaps are still produced, at least in part, by reconnection, which again enables the segregation of the poloidal field and the disk material similar to the more diffusive disks. However, the reconnection is now driven by the non-linear growth of MRI channel flows. The formation of rings and gaps in rapidly accreting yet laminar disks has interesting implications for dust settling and trapping, grain growth, and planet formation.

  19. Radio Supernovae: Circum-Stellar Investigation (C.S.I.) of Supernova Progenitor Stars

    Science.gov (United States)

    2009-02-24

    ar X iv :0 90 2. 40 59 v1 [ as tr o- ph .H E ] 2 4 Fe b 20 09 Radio Supernovae : Circum-Stellar Investigation (C.S.I.) of Supernova Progenitor...FEB 2009 2. REPORT TYPE 3. DATES COVERED 00-00-2009 to 00-00-2009 4. TITLE AND SUBTITLE Radio Supernovae : Circum-Stellar Investigation (C.S.I...of Supernova Progenitor Stars 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f

  20. Warm H2O and OH Disk Emission in V1331 Cyg

    Science.gov (United States)

    Doppmann, Greg W.; Najita, Joan R.; Carr, John S.; Graham, James R.

    2011-09-01

    We present high-resolution (R = 24, 000) L-band spectra of the young intermediate-mass star V1331 Cyg obtained with NIRSPEC on the Keck II telescope. The spectra show strong, rich emission from water and OH that likely arises from the warm surface region of the circumstellar disk. We explore the use of the new BT2 water line list in fitting the spectra, and we find that it does a much better job than the well-known HITRAN water line list in the observed wavelength range and for the warm temperatures probed by our data. By comparing the observed spectra with synthetic disk emission models, we find that the water and OH emission lines have similar widths (FWHM ~= 18 km s-1). If the line widths are set by disk rotation, the OH and water emission lines probe a similar range of disk radii in this source. The water and OH emission are consistent with thermal emission for both components at a temperature ~1500 K. The column densities of the emitting water and OH are large, ~1021 cm-2 and ~1020 cm-2, respectively. Such a high column density of water is more than adequate to shield the disk midplane from external UV irradiation in the event of complete dust settling out of the disk atmosphere, enabling chemical synthesis to continue in the midplane despite a harsh external UV environment. The large OH-to-water ratio is similar to expectations for UV irradiated disks, although the large OH column density is less easily accounted for. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  1. Audit: Automated Disk Investigation Toolkit

    Directory of Open Access Journals (Sweden)

    Umit Karabiyik

    2014-09-01

    Full Text Available Software tools designed for disk analysis play a critical role today in forensics investigations. However, these digital forensics tools are often difficult to use, usually task specific, and generally require professionally trained users with IT backgrounds. The relevant tools are also often open source requiring additional technical knowledge and proper configuration. This makes it difficult for investigators without some computer science background to easily conduct the needed disk analysis. In this paper, we present AUDIT, a novel automated disk investigation toolkit that supports investigations conducted by non-expert (in IT and disk technology and expert investigators. Our proof of concept design and implementation of AUDIT intelligently integrates open source tools and guides non-IT professionals while requiring minimal technical knowledge about the disk structures and file systems of the target disk image.

  2. A NEW ALGORITHM FOR SELF-CONSISTENT THREE-DIMENSIONAL MODELING OF COLLISIONS IN DUSTY DEBRIS DISKS

    International Nuclear Information System (INIS)

    Stark, Christopher C.; Kuchner, Marc J.

    2009-01-01

    We present a new 'collisional grooming' algorithm that enables us to model images of debris disks where the collision time is less than the Poynting-Robertson (PR) time for the dominant grain size. Our algorithm uses the output of a collisionless disk simulation to iteratively solve the mass flux equation for the density distribution of a collisional disk containing planets in three dimensions. The algorithm can be run on a single processor in ∼1 hr. Our preliminary models of disks with resonant ring structures caused by terrestrial mass planets show that the collision rate for background particles in a ring structure is enhanced by a factor of a few compared to the rest of the disk, and that dust grains in or near resonance have even higher collision rates. We show how collisions can alter the morphology of a resonant ring structure by reducing the sharpness of a resonant ring's inner edge and by smearing out azimuthal structure. We implement a simple prescription for particle fragmentation and show how PR drag and fragmentation sort particles by size, producing smaller dust grains at smaller circumstellar distances. This mechanism could cause a disk to look different at different wavelengths, and may explain the warm component of dust interior to Fomalhaut's outer dust ring seen in the resolved 24 μm Spitzer image of this system.

  3. IBM 3390 Hard Disk Platter

    CERN Multimedia

    1991-01-01

    The 3390 disks rotated faster than those in the previous model 3380. Faster disk rotation reduced rotational delay (ie. the time required for the correct area of the disk surface to move to the point where data could be read or written). In the 3390's initial models, the average rotational delay was reduced to 7.1 milliseconds from 8.3 milliseconds for the 3380 family.

  4. Disk storage at CERN

    CERN Document Server

    Mascetti, L; Chan, B; Espinal, X; Fiorot, A; Labrador, H Gonz; Iven, J; Lamanna, M; Presti, G Lo; Mościcki, JT; Peters, AJ; Ponce, S; Rousseau, H; van der Ster, D

    2015-01-01

    CERN IT DSS operates the main storage resources for data taking and physics analysis mainly via three system: AFS, CASTOR and EOS. The total usable space available on disk for users is about 100 PB (with relative ratios 1:20:120). EOS actively uses the two CERN Tier0 centres (Meyrin and Wigner) with 50:50 ratio. IT DSS also provide sizeable on-demand resources for IT services most notably OpenStack and NFS-based clients: this is provided by a Ceph infrastructure (3 PB) and few proprietary servers (NetApp). We will describe our operational experience and recent changes to these systems with special emphasis to the present usages for LHC data taking, the convergence to commodity hardware (nodes with 200-TB each with optional SSD) shared across all services. We also describe our experience in coupling commodity and home-grown solution (e.g. CERNBox integration in EOS, Ceph disk pools for AFS, CASTOR and NFS) and finally the future evolution of these systems for WLCG and beyond.

  5. [Disk calcifications in children].

    Science.gov (United States)

    Schmit, P; Fauré, C; Denarnaud, L

    1985-05-01

    It is not unusual for intervertebral disk calcifications to be detected in pediatric practice, the 150 or so cases reported in the literature probably representing only a small proportion of lesions actually diagnosed. Case reports of 33 children with intervertebral disk calcifications were analyzed. In the majority of these patients (31 of 33) a diagnosis of "idiopathic" calcifications had been made, the cervical localization of the lesions being related to repeated ORL infections and/or trauma. A pre-existing pathologic factor was found in two cases (one child with juvenile rheumatoid arthritis treated by corticoids and one child with Williams and Van Beuren's syndrome). An uncomplicated course was noted in 31 cases, the symptomatology (pain, spinal stiffness and febricula) improving after several days. Complications developed in two cases: one child had very disabling dysphagia due to an anteriorly protruding cervical herniated disc and surgery was necessary; the other child developed cervicobrachial neuralgia due to herniated disc protrusion into the cervical spinal canal, but symptoms regressed within several days although calcifications persisted unaltered. These findings and the course of the rare complications documented in the literature suggest the need for the most conservative treatment possible in cases of disc calcifications in children.

  6. Disk MHD generator study

    Science.gov (United States)

    Retallick, F. D.

    1980-10-01

    Directly-fired, separately-fired, and oxygen-augmented MHD power plants incorporating a disk geometry for the MHD generator were studied. The base parameters defined for four near-optimum-performance MHD steam power systems of various types are presented. The finally selected systems consisted of (1) two directly fired cases, one at 1920 K (2996F) preheat and the other at 1650 K (2500 F) preheat, (2) a separately-fired case where the air is preheated to the same level as the higher temperature directly-fired cases, and (3) an oxygen augmented case with the same generator inlet temperature of 2839 (4650F) as the high temperature directly-fired and separately-fired cases. Supersonic Mach numbers at the generator inlet, gas inlet swirl, and constant Hall field operation were specified based on disk generator optimization. System pressures were based on optimization of MHD net power. Supercritical reheat stream plants were used in all cases. Open and closed cycle component costs are summarized and compared.

  7. Mind the gap : gas and dust in planet-forming disks

    NARCIS (Netherlands)

    Marel, Nienke van der

    2015-01-01

    This thesis discusses the structure of gas and dust in protoplanetary disks around young stars, in which the planets are formed, using ALMA (Atacama Large Millimeter/submillimeter Array) observations. Primary targets of this study are the so-called 'transition disks', with a central cavity in the

  8. Open clusters. III. Fundamental parameters of B stars in NGC 6087, NGC 6250, NGC 6383, and NGC 6530 B-type stars with circumstellar envelopes

    Science.gov (United States)

    Aidelman, Y.; Cidale, L. S.; Zorec, J.; Panei, J. A.

    2018-02-01

    Context. Stellar physical properties of star clusters are poorly known and the cluster parameters are often very uncertain. Methods: Our goals are to perform a spectrophotometric study of the B star population in open clusters to derive accurate stellar parameters, search for the presence of circumstellar envelopes, and discuss the characteristics of these stars. The BCD spectrophotometric system is a powerful method to obtain stellar fundamental parameters from direct measurements of the Balmer discontinuity. To this end, we wrote the interactive code MIDE3700. The BCD parameters can also be used to infer the main properties of open clusters: distance modulus, color excess, and age. Furthermore, we inspected the Balmer discontinuity to provide evidence for the presence of circumstellar disks and identify Be star candidates. We used an additional set of high-resolution spectra in the Hα region to confirm the Be nature of these stars. Results: We provide Teff, log g, Mv, Mbol, and spectral types for a sample of 68 stars in the field of the open clusters NGC 6087, NGC 6250, NGC 6383, and NGC 6530, as well as the cluster distances, ages, and reddening. Then, based on a sample of 230 B stars in the direction of the 11 open clusters studied along this series of three papers, we report 6 new Be stars, 4 blue straggler candidates, and 15 B-type stars (called Bdd) with a double Balmer discontinuity, which indicates the presence of circumstellar envelopes. We discuss the distribution of the fraction of B, Be, and Bdd star cluster members per spectral subtype. The majority of the Be stars are dwarfs and present a maximum at the spectral type B2-B4 in young and intermediate-age open clusters (San Juan, Argentina.Tables 1, 2, 9-16 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A30

  9. The Chemistry of Protostellar Jet-Disk Systems

    Science.gov (United States)

    Codella, Claudio

    2017-11-01

    The birth of a Sun-like star is a complex game played by several participants whose respective roles are not yet entirely clear. On the one hand, the star-to-be accretes matter from a collapsing envelope. The gravitational energy released in the process heats up the material surrounding the protostar, creating warm regions enriched by interstellar complex organic molecules (iCOMs, at least 6 atoms) called hot-corinos. On the other hand, the presence of angular momentum and magnetic fields leads to two consequences: (i) the formation of circumstellar disks; and (ii) substantial episodes of matter ejection, as e.g. collimated jets. Thanks to the combination of the high-sensitivities and high-angular resolu- tions provided by the advent of new telescopes such as ALMA and NOEMA, it is now possible to image in details the earliest stages of the Sun-like star formation, thus inspecting the inner ( effects connected with the accreting disk. In other words, it is time to study the protostellar jet-disk system as a whole. Several still unanswered questions can be addressed. What is the origin of the chemically enriched hot corinos: are they jet-driven shocked regions? What is the origin of the ejections: are they due to disk or stellar winds? Shocks are precious tool to attack these questions, given they enrich the gas phase with the species deposited onto the dust mantles and/or locked in the refractory dust cores. Basically, we have to deal with two kind of shocks: (i) high-velocity shocks produced by protostellar jets, and (ii) slow accretion shocks located close to the centrifugal barrier of the accretion disks. Both shocks are factories of iCOMs, which can be then efficiently used to follow both the kinematics and the chemistry of the inner protostellar systems. With this in mind, we will discuss recent results obtained in the framework of different observational campaigns at mm and sub-mm wavelengths.

  10. THE SPINDLE: AN IRRADIATED DISK AND BENT PROTOSTELLAR JET IN ORION

    Energy Technology Data Exchange (ETDEWEB)

    Bally, John; Youngblood, Allison; Ginsburg, Adam, E-mail: John.Bally@colorado.edu, E-mail: Allison.Youngblood@colorado.edu, E-mail: Adam.Ginsburg@colorado.edu [Department of Astrophysical and Planetary Sciences, University of Colorado, UCB 389, Boulder, CO 80309 (United States)

    2012-09-10

    We present Hubble Space Telescope observations of a bent, pulsed Herbig-Haro jet, HH 1064, emerging from the young star Parenago 2042 embedded in the H II region NGC 1977 located about 30' north of the Orion Nebula. This outflow contains eight bow shocks in the redshifted western lobe and five bow shocks in the blueshifted eastern lobe. Shocks within a few thousand AU of the source star exhibit proper motions of {approx}160 km s{sup -1} but motions decrease with increasing distance. Parenago 2042 is embedded in a proplyd-a photoevaporating protoplanetary disk. A remarkable set of H{alpha} arcs resembling a spindle surround the redshifted (western) jet. The largest arc with a radius of 500 AU may trace the ionized edge of a circumstellar disk inclined by {approx}30 Degree-Sign . The spindle may be the photoionized edge of either a {approx}3 km s{sup -1} FUV-driven wind from the outer disk or a faster MHD-powered flow from an inner disk. The HH 1064 jet appears to be deflected north by photoablation of the south-facing side of a mostly neutral jet beam. V2412 Ori, located 1' west of Parenago 2042 drives a second bent flow, HH 1065. Both HH 1064 and 1065 are surrounded by LL Ori-type bows marking the boundary between the outflow cavity and the surrounding nebula.

  11. Improved Constraints on the Disk around MWC 349A from the 23 m LBTI

    Energy Technology Data Exchange (ETDEWEB)

    Sallum, S.; Eisner, J. A.; Hinz, P. M.; Sheehan, P. D. [Astronomy Department, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Skemer, A. J. [Astronomy Department, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Tuthill, P. G. [School of Physics, University of Sydney, Sydney, NSW 2006 (Australia); Young, J. S., E-mail: ssallum@email.arizona.edu [Cavendish Laboratory, University of Cambridge, J J Thompson Avenue, Cambridge (United Kingdom)

    2017-07-20

    We present new spatially resolved observations of MWC 349A from the Large Binocular Telescope Interferometer (LBTI), a 23 m baseline interferometer made up of two, co-mounted 8 m telescopes. MWC 349A is a B[e] star with an unknown evolutionary state. Proposed scenarios range from a young stellar object, to a B[e] supergiant, to a tight binary system. Radio continuum and recombination line observations of this source revealed a sub-arcsecond bipolar outflow surrounding an ∼100 mas circumstellar disk. Follow-up infrared studies detected the disk, and suggested that it may have skew and an inner clearing. Our new infrared interferometric observations, which have more than twice the resolution of previously published data sets, support the presence of both skew and a compact infrared excess. They rule out inner clearings with radii greater than ∼14 mas. We show the improvements in disk parameter constraints provided by LBTI, and discuss the inferred disk parameters in the context of the posited evolutionary states for MWC 349A.

  12. The Temperature and Distribution of Organic Molecules in the Inner Regions of T Tauri Disks

    Science.gov (United States)

    Mandell, Avi

    2012-01-01

    "High-resolution NIR spectroscopic observations of warm molecular gas emission from young circumstellar disks allow us to constrain the temperature and composition of material in the inner planet-forming region. By combining advanced data reduction algorithms with accurate modeling of the terrestrial atmospheric spectrum and a novel double-differencing data analysis technique, we have achieved very high-contrast measurements (S/N approx. 500-1000) of molecular emission at 3 microns. In disks around low-mass stars, we have achieved the first detections of emission from HCN and C2H2 at near-infrared wavelengths from several bright T Tauri stars using the CRIRES spectrograph on the Very Large Telescope and NIRSPEC spectrograph on the Keck Telescope. We spectrally resolve the line shape, showing that the emission has both a Keplerian and non-Keplerian component as observed previously for CO emission. We used a simplified single-temperature local thermal equilibrium (LTE) slab model with a Gaussian line profile to make line identifications and determine a best-fit temperature and initial abundance ratios, and we then compared these values with constraints derived from a detailed disk radiative transfer model assuming LTE excitation but utilizing a realistic temperature and density structure. Abundance ratios from both sets of models are consistent with each other and consistent with expected values from theoretical chemical models, and analysis of the line shapes suggests that the molecular emission originates from within a narrow region in the inner disk (R < 1 AU)."

  13. Driving of Accretion Disk Variability by the Disk Dynamo

    Science.gov (United States)

    Hogg, J. Drew; Reynolds, Christopher S.

    2016-04-01

    Variability is a ubiquitous feature of emission from accreting objects, but many questions remain as to how the variability is driven and how it relates to the underlying accretion physics. In this talk I will discuss recent results from a long, semi-global MHD simulation of a thin accretion disk around a black hole used to perform a detailed study of the fluctuations in the internal disk stress and the influence these fluctuations have on the accretion flow. In the simulation, low frequency fluctuations of the effective α-parameter in the disk are linked to oscillations of the disk dynamo. These fluctuations in the effective alpha parameter drive “propagating fluctuations” in mass accretion rate through the disk that qualitatively resemble the variability from astrophysical black hole systems. The mass accretion rate has several of the ubiquitous phenomenological properties of black hole variability, including log-normal flux distributions, RMS-flux relationships, and radial coherence.

  14. Disks around young stellar objects

    Indian Academy of Sciences (India)

    flattened disk around the central young stellar object and planets form in these disks by processes that involve growth of dust grains and their sedimentation, collisions and coag- ulation of planetesimals, accretion of gaseous material and gravitational instabilities on various time-scales as proposed in different models.

  15. Stochastic disks that roll

    Science.gov (United States)

    Holmes-Cerfon, Miranda

    2016-11-01

    We study a model of rolling particles subject to stochastic fluctuations, which may be relevant in systems of nano- or microscale particles where rolling is an approximation for strong static friction. We consider the simplest possible nontrivial system: a linear polymer of three disks constrained to remain in contact and immersed in an equilibrium heat bath so the internal angle of the polymer changes due to stochastic fluctuations. We compare two cases: one where the disks can slide relative to each other and the other where they are constrained to roll, like gears. Starting from the Langevin equations with arbitrary linear velocity constraints, we use formal homogenization theory to derive the overdamped equations that describe the process in configuration space only. The resulting dynamics have the formal structure of a Brownian motion on a Riemannian or sub-Riemannian manifold, depending on if the velocity constraints are holonomic or nonholonomic. We use this to compute the trimer's equilibrium distribution with and without the rolling constraints. Surprisingly, the two distributions are different. We suggest two possible interpretations of this result: either (i) dry friction (or other dissipative, nonequilibrium forces) changes basic thermodynamic quantities like the free energy of a system, a statement that could be tested experimentally, or (ii) as a lesson in modeling rolling or friction more generally as a velocity constraint when stochastic fluctuations are present. In the latter case, we speculate there could be a "roughness" entropy whose inclusion as an effective force could compensate the constraint and preserve classical Boltzmann statistics. Regardless of the interpretation, our calculation shows the word "rolling" must be used with care when stochastic fluctuations are present.

  16. HERSCHEL's ''COLD DEBRIS DISKS'': BACKGROUND GALAXIES OR QUIESCENT RIMS OF PLANETARY SYSTEMS?

    Energy Technology Data Exchange (ETDEWEB)

    Krivov, A. V.; Loehne, T.; Mutschke, H.; Neuhaeuser, R. [Astrophysikalisches Institut und Universitaetssternwarte, Friedrich-Schiller-Universitaet Jena, Schillergaesschen 2-3, D-07745 Jena (Germany); Eiroa, C.; Marshall, J. P.; Mustill, A. J. [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Montesinos, B. [Departamento de Astrofisica, Centro de Astrobiologia (CAB, CSIC-INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Del Burgo, C. [Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Apartado Postal 51 y 216, 72000 Puebla, Pue. (Mexico); Absil, O. [Institut d' Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout 17, B-4000 Liege (Belgium); Ardila, D. [NASA Herschel Science Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Augereau, J.-C.; Ertel, S.; Lebreton, J. [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d' Astrophysique de Grenoble (IPAG), UMR 5274, F-38041 Grenoble (France); Bayo, A. [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Bryden, G. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Danchi, W. [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics, Code 667, Greenbelt, MD 20771 (United States); Liseau, R. [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992, Onsala (Sweden); Mora, A. [ESA-ESAC Gaia SOC, P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Pilbratt, G. L., E-mail: krivov@astro.uni-jena.de [ESA Astrophysics and Fundamental Physics Missions Division, ESTEC/SRE-SA, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands); and others

    2013-07-20

    Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around {approx}100 {mu}m or shorter. However, 6 out of 31 excess sources studied in the Herschel Open Time Key Programme, DUNES, have been seen to show significant-and in some cases extended-excess emission at 160 {mu}m, which is larger than the 100 {mu}m excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We re-address these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than {approx}100 {mu}m, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller

  17. Particle trapping and snow lines in the Trappist-1 disk

    Science.gov (United States)

    White, Kevin; Desch, Steven; Kalyaan, Anusha

    2018-01-01

    The Trappist-1 system has 7 transiting planets with constrained masses and radii (Gillon et al. 2017; Wang et al. 2017), and represents a laboratory for understanding planet formation in M dwarf disks. All the planets are about 1 ME, consistent with the pebble isolation masses in M dwarf disks, in the same way ~ 30 ME Jupiter’s core matches the pebble isolation mass in the solar nebula (Ormel et al. 2017). Trappist-1 f, g, and h are apparently ice-rich (> 50%), but planets b and c are ice, suggesting they formed inside the snow line in Trappist-1’s disk (Unterborn et al. 2017). Earth formed inside the snow line in the solar nebula, but is only ~ 0.1wt% water, much drier than Trappist-1 b and c. If the pebbles excluded by Jupiter were icy, this would explain the dryness of the inner solar system (Morbidelli et al. 2016). This raises the question why the Trappist-1 inner disk was not equally dry. We have calculated the efficiency by which pebbles are trapped in the pressure maxima outside of planet-opened disk gaps, comparing the rates of radial diffusion vs. radial drift (as in Desch et al. 2017). We find that while Jupiter can exclude particles mm-sized or larger, only for particles > cm-sized does radial drift act faster than radial diffusion in the Trappist-1 pressure maxima. Pressure maxima in M dwarf disks are relatively leaky particle traps, possibly admitting more icy pebbles and water into the inner disk. We predict lower emission contrast between rings and gaps in M dwarf disks observable by ALMA.

  18. Hydrogen Cyanide In Protoplanetary Disks

    Science.gov (United States)

    Walker, Ashley L.; Oberg, Karin; Cleeves, L. Ilsedore

    2018-01-01

    The chemistry behind star and planet formation is extremely complex and important in the formation of habitable planets. Life requires molecules containing carbon, oxygen, and importantly, nitrogen. Hydrogen cyanide, or HCN, one of the main interstellar nitrogen carriers, is extremely dangerous here on Earth. However, it could be used as a vital tool for tracking the chemistry of potentially habitable planets. As we get closer to identifying other habitable planets, we must understand the beginnings of how those planets are formed in the early protoplanetary disk. This project investigates HCN chemistry in different locations in the disk, and what this might mean for forming planets at different distances from the star. HCN is a chemically diverse molecule. It is connected to the formation for other more complex molecules and is commonly used as a nitrogen tracer. Using computational chemical models we look at how the HCN abundance changes at different locations. We use realistic and physically motivated conditions for the gas in the protoplanetary disk: temperature, density, and radiation (UV flux). We analyze the reaction network, formation, and destruction of HCN molecules in the disk environment. The disk environment informs us about stability of habitable planets that are created based on HCN molecules. We reviewed and compared the difference in the molecules with a variety of locations in the disk and ultimately giving us a better understanding on how we view protoplanetary disks.

  19. ALMA observations of the nearby AGB star L$_{\\rm 2}$ Puppis. II. Gas disk properties derived from $^{\\rm 12}$CO and $^{\\rm13}$CO $J=$3$-$2 emission

    OpenAIRE

    Homan, Ward; Richards, Anita; Decin, Leen; Kervella, Pierre; de Koter, Alex; McDonald, Iain; Ohnaka, Keiichi

    2018-01-01

    The circumstellar environment of the AGB star L$_{\\rm 2}$ Puppis was observed with ALMA in cycle 3, with a resolution of $15 \\times 18 \\rm\\ mas$. The molecular emission shows a differentially rotating disk, inclined to a nearly edge-on position. In the first paper in this series (paper I) the molecular emission was analysed to accurately deduce the motion of the gas in the equatorial regions of the disk. In this work we model the optically thick $^{\\rm 12}$CO $J=$3$-$2 and the optically thin ...

  20. Near-IR High-Resolution Imaging Polarimetry of the SU Aur Disk: Clues for Tidal Tails?

    Science.gov (United States)

    De Leon, Jerome; Michihiro, Takami; Karr, Jennifer; Hashimoto, Jun; Kudo, Tomoyuki; Sitko, Michael; Mayama, Satoshi; Kusakabe, Nobuyuki; Grady, Carol A.; McElwain, Michael W.

    2015-01-01

    We present new high-resolution (approximately 0.09) H-band imaging observations of the circumstellar disk around the T Tauri star SU Aur. Our observations with Subaru-HiCIAO have revealed the presence of scattered light as close as 0.15 (approximately 20 AU) to the star. Within our image, we identify bright emission associated with a disk with a minimum radius of approximately 90 AU, an inclination of approximately 35 deg from the plane of the sky, and an approximate PA of 15 deg for the major axis. We find a brightness asymmetry between the northern and southern sides of the disk due to a non-axisymmetric disk structure. We also identify a pair of asymmetric tail structures extending east and west from the disk. The western tail extends at least 2. 5 (350 AU) from the star, and is probably associated with a reflection nebula previously observed at optical and near-IR wavelengths. The eastern tail extends at least 1 (140 AU) at the present signal-to-noise. These tails are likely due to an encounter with an unseen brown dwarf, but our results do not exclude the explanation that these tails are outflow cavities or jets.

  1. 8-inch IBM floppy disk

    CERN Multimedia

    1971-01-01

    The 8-inch floppy disk was a magnetic storage disk for the data introduced commercially by IBM in 1971. It was designed by an IBM team as an inexpensive way to load data into the IBM System / 370. Plus it was a read-only bare disk containing 80 KB of data. The first read-write version was introduced in 1972 by Memorex and could contain 175 KB on 50 tracks (with 8 sectors per track). Other improvements have led to various coatings and increased capacities. Finally, it was surpassed by the mini diskette of 5.25 inches introduced in 1976.

  2. The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

    Energy Technology Data Exchange (ETDEWEB)

    Hogg, J. Drew; Reynolds, Christopher S. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

    2017-07-10

    Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, i.e., state transitions in galactic black hole binaries (GBHBs), and large systems, i.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ − ϕ stress that is less than the generic r − ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.

  3. SUBMILLIMETER POLARIZATION OBSERVATION OF THE PROTOPLANETARY DISK AROUND HD 142527

    Energy Technology Data Exchange (ETDEWEB)

    Kataoka, Akimasa; Dullemond, Cornelis P.; Pohl, Adriana [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Tsukagoshi, Takashi; Momose, Munetake [College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan); Nagai, Hiroshi [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Muto, Takayuki [Division of Liberal Arts, Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677 (Japan); Fukagawa, Misato [Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602 (Japan); Shibai, Hiroshi [Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Hanawa, Tomoyuki [Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 263-8522 (Japan); Murakawa, Koji, E-mail: kataoka@uni-heidelberg.de [College of General Education, Osaka Sangyo University, 3-1-1, Nakagaito, Daito, Osaka 574-8530 (Japan)

    2016-11-10

    We present the polarization observations toward the circumstellar disk around HD 142527 by using Atacama Large Millimeter/submillimeter Array at the frequency of 343 GHz. The beam size is 0.″51 × 0.″44, which corresponds to the spatial resolution of ∼71 × 62 au. The polarized intensity displays a ring-like structure with a peak located on the east side with a polarization fraction of P = 3.26 ± 0.02%, which is different from the peak of the continuum emission from the northeast region. The polarized intensity is significantly weaker at the peak of the continuum where P = 0.220 ± 0.010%. The polarization vectors are in the radial direction in the main ring of the polarized intensity, while there are two regions outside at the northwest and northeast areas where the vectors are in the azimuthal direction. If the polarization vectors represent the magnetic field morphology, the polarization vectors indicate the toroidal magnetic field configuration on the main ring and the poloidal fields outside. On the other hand, the flip of the polarization vectors is predicted by the self-scattering of thermal dust emission due to the change of the direction of thermal radiation flux. Therefore, we conclude that self-scattering of thermal dust emission plays a major role in producing polarization at millimeter wavelengths in this protoplanetary disk. Also, this puts a constraint on the maximum grain size to be approximately 150 μ m if we assume compact spherical dust grains.

  4. Radio emission from young supernova remnants - Effects of an inhomogeneous circumstellar medium

    Science.gov (United States)

    Dickel, John R.; Eilek, Jean A.; Jones, Eric M.; Reynolds, Stephen P.

    1989-01-01

    The evolution of young supernova remnants has been modeled using a one-dimensional hydrodynamics code. Rayleigh-Taylor instabilities and the growth of Rayleigh-Taylor fingers have been included in the code. Turbulent dynamo amplification of magnetic fields and both turbulent and shock acceleration of relativistic electrons have been included macroscopically. From this, the distribution of synchrotron luminosity in the remnant has been calculated. It is found that the radio morphology of model remnants expanding into a homogeneous medium does not agree with observations. Expansion into a circumstellar medium with many small cloudlets does produce radio shells which agree with observations. It is suggested that supernova remnants reflect the interaction of ejected matter with a cloudy circumstellar medium.

  5. Herbig stars' near-infrared excess: An origin in the protostellar disk's magnetically supported atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Turner, N. J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Benisty, M.; Dullemond, C. P. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Hirose, S., E-mail: neal.turner@jpl.nasa.gov [Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showamachi, Kanazawa-ku, Yokohama, Kanagawa 236-0001 (Japan)

    2014-01-01

    Young stars with masses 2-8 times solar, the Herbig Ae and Be stars, often show a near-infrared excess too large to explain with a hydrostatically supported circumstellar disk of gas and dust. At the same time, the accretion flow carrying the circumstellar gas to the star is thought to be driven by magnetorotational turbulence, which, according to numerical MHD modeling, yields an extended low-density atmosphere supported by the magnetic fields. We demonstrate that the base of the atmosphere can be optically thick to the starlight and that the parts lying near 1 AU are tall enough to double the fraction of the stellar luminosity reprocessed into the near-infrared. We generate synthetic spectral energy distributions (SEDs) using Monte Carlo radiative transfer calculations with opacities for submicron silicate and carbonaceous grains. The synthetic SEDs closely follow the median Herbig SED constructed recently by Mulders and Dominik and, in particular, match the large near-infrared flux, provided the grains have a mass fraction close to interstellar near the disk's inner rim.

  6. A Rigidly Rotating Magnetosphere Model for the Circumstellar Environments of Magnetic OB Stars

    Science.gov (United States)

    Townsend, R.; Owocki, S.; Groote, D.

    2005-11-01

    We report on a new model for the circumstellar environments of rotating, magnetic hot stars. This model predicts the channeling of wind plasma into a corotating magnetosphere, where -- supported against gravity by centrifugal forces -- it can steadily accumulate over time. We apply the model to the B2p star σ Ori E, demonstrating that it can simultaneously reproduce the spectroscopic, photometric and magnetic variations exhibited by the star.

  7. Chaotic Dynamics of Falling Disks: from Maxwell to Bar Tricks.

    Science.gov (United States)

    Field, Stuart

    1998-03-01

    Understanding the motion of flat objects falling in a viscous medium dates back to at least Newton and Maxwell, and is relevant to problems in meteorology, sedimentology, aerospace and chemical engineering, and nori/disks/pub.html>bar wagering strategies. Recent theoretical studies have emphasized the role played by deterministic chaos. Here we nori/falling.html>report(S. B. Field, M. Klaus, M. G. Moore, and F. Nori, Nature 388), 252 (1997) experimental observations and theoretical analysis of the dynamics of disks falling in water/glycerol mixtures. We find four distinct types of motion, and map out a ``phase diagram'' in the appropriate variables. The apparently complex behavior of the disks can be reduced to a series of one-dimensional maps which display a discontinuity at the crossover from periodic and chaotic motion. This discontinuity leads to an unusual intermittency transition between the two behaviors, which has not previously been observed experimentally in any system.

  8. The Fabulous Four Debris Disks

    Science.gov (United States)

    Werner, Michael; Stapelfeldt, Karl

    2004-09-01

    This program is a comprehensive study of the four bright debris disks that were spatially resolved by IRAS: Beta Pictoris, Epsilon Eridani, Fomalhaut, and Vega. All SIRTF instruments and observing modes will be used. The program has three major objectives: (1) Study of the disk spatial structure from MIPS and IRAC imaging; (2) Study of the dust grain composition using the IRS and MIPS SED mode; and (3) companion searches using IRAC. The data from this program should lead to a detailed understanding of these four systems, and will provide a foundation for understanding all of the debris disks to be studied with SIRTF. Images and spectra will be compared with models for disk structure and dust properties. Dynamical features indicative of substellar companions' effects on the disks will be searched for. This program will require supporting observations of PSF stars, some of which have been included explicitly. In the majority of cases, the spectral observations require a preferred orientation to align the slits along the disk position angles. Detector saturation issues are still being worked for this program, and will lead to AOR modifications in subsequent submissions. The results from this program will be analyzed collaboratively by the IRAC, IRS, and MIPS teams and by general GTOs Jura and Werner.

  9. Tracing the evolution of protoplanetary disks

    NARCIS (Netherlands)

    Maaskant, Koen Maarten

    2014-01-01

    This thesis presents new insights of protoplanetary disk evolution. It focuses on the characterisation of several elements in the earliest phases of planet formation in protoplanetary disks: the connection between the SED and disk gaps (Chapters 2, 3 and 4), PAHs in the gas flows in disk gaps

  10. Influence of nuclear burning of the stability of degenerate and nondegenerate accretion disks

    International Nuclear Information System (INIS)

    Taam, R.E.; Fryxell, B.A.

    1985-01-01

    The structure and stability of accretion disks composed of hydrogen-rich matter rotating about a central neutron star have been investigated for known sources of viscosity. Two general classes of solutions have been found. For one class the energy generated in the disk is provided by hydrogen burning, whereas for the other class the gravitational binding energy released by viscous dissipation dominates. The former solutions are thermally unstable (stable) whenever hydrogen burns via the normal CNO cycle ( pp chain) in a partially or fully degenerate region of the disk. Solutions characterized by nuclear burning via the β-limited CNO cycle or by viscous dissipation only are always stable. On the basis of a local analysis it is shown that modulations of the mass flow in the disk are possible for a range of mass inflow rates into the disk. In such circumstances the disk can undergo a phase transition from a cold, low-viscosity state to a hot, high-viscosity state as a result of the thermonuclear flash instability. Phase transitions from the hot state to the cold state also occur whenever the mass input rate into the disk is less than the equilibrium mass flow rate corresponding to the hot state. It is also shown that for sufficiently high mass flow rates all the hydrogen-rich matter can be processed to helium in the inner regions of the disk before it can be accreted by a neutron star

  11. A HUBBLE SPACE TELESCOPE SURVEY OF H{sub 2} EMISSION IN THE CIRCUMSTELLAR ENVIRONMENTS OF YOUNG STARS

    Energy Technology Data Exchange (ETDEWEB)

    France, Kevin; Schindhelm, Eric; Brown, Alexander [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309 (United States); Herczeg, Gregory J. [Max-Planck-Institut fuer extraterrestriche Physik, Postfach 1312, D-85741 Garching (Germany); Abgrall, Herve; Roueff, Evelyne [LUTH and UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, Place J. Janssen, F-92195 Meudon (France); Alexander, Richard D. [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Bergin, Edwin A. [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Brown, Joanna M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Linsky, Jeffrey L. [JILA, University of Colorado and NIST, 440 UCB, Boulder, CO 80309 (United States); Yang Hao, E-mail: kevin.france@colorado.edu [Institute of Astrophysics, Central China Normal University, Wuhan, Hubei 430079 (China)

    2012-09-10

    The formation timescale and final architecture of exoplanetary systems are closely related to the properties of the molecular disks from which they form. Observations of the spatial distribution and lifetime of the molecular gas at planet-forming radii (a < 10 AU) are important for understanding the formation and evolution of exoplanetary systems. Toward this end, we present the largest spectrally resolved survey of H{sub 2} emission around low-mass pre-main-sequence stars compiled to date. We use a combination of new and archival far-ultraviolet spectra from the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph instruments on the Hubble Space Telescope to sample 34 T Tauri stars (27 actively accreting Classical T Tauri Stars and 7 non-accreting Weak-lined T Tauri Stars) with ages ranging from {approx}1 to 10 Myr. We observe fluorescent H{sub 2} emission, excited by Ly{alpha} photons, in 100% of the accreting sources, including all of the transitional disks in our sample (CS Cha, DM Tau, GM Aur, UX Tau A, LkCa 15, HD 135344B, and TW Hya). The spatial distribution of the emitting gas is inferred from spectrally resolved H{sub 2} line profiles. Some of the emitting gas is produced in outflowing material, but the majority of H{sub 2} emission appears to originate in a rotating disk. For the disk-dominated targets, the H{sub 2} emission originates predominately at a {approx}< 3 AU. The emission line widths and inner molecular radii are found to be roughly consistent with those measured from mid-IR CO spectra.

  12. Shadows and spirals in the protoplanetary disk HD 100453

    Science.gov (United States)

    Benisty, M.; Stolker, T.; Pohl, A.; de Boer, J.; Lesur, G.; Dominik, C.; Dullemond, C. P.; Langlois, M.; Min, M.; Wagner, K.; Henning, T.; Juhasz, A.; Pinilla, P.; Facchini, S.; Apai, D.; van Boekel, R.; Garufi, A.; Ginski, C.; Ménard, F.; Pinte, C.; Quanz, S. P.; Zurlo, A.; Boccaletti, A.; Bonnefoy, M.; Beuzit, J. L.; Chauvin, G.; Cudel, M.; Desidera, S.; Feldt, M.; Fontanive, C.; Gratton, R.; Kasper, M.; Lagrange, A.-M.; LeCoroller, H.; Mouillet, D.; Mesa, D.; Sissa, E.; Vigan, A.; Antichi, J.; Buey, T.; Fusco, T.; Gisler, D.; Llored, M.; Magnard, Y.; Moeller-Nilsson, O.; Pragt, J.; Roelfsema, R.; Sauvage, J.-F.; Wildi, F.

    2017-01-01

    Context. Understanding the diversity of planets requires studying the morphology and physical conditions in the protoplanetary disks in which they form. Aims: We aim to study the structure of the 10 Myr old protoplanetary disk HD 100453, to detect features that can trace disk evolution and to understand the mechanisms that drive these features. Methods: We observed HD 100453 in polarized scattered light with VLT/SPHERE at optical (0.6 μm, 0.8 μm) and near-infrared (1.2 μm) wavelengths, reaching an angular resolution of 0.02'', and an inner working angle of 0.09''. Results: We spatially resolve the disk around HD 100453, and detect polarized scattered light up to 0.42'' ( 48 au). We detect a cavity, a rim with azimuthal brightness variations at an inclination of 38° with respect to our line of sight, two shadows and two symmetric spiral arms. The spiral arms originate near the location of the shadows, close to the semi major axis. We detect a faint feature in the SW that can be interpreted as the scattering surface of the bottom side of the disk, if the disk is tidally truncated by the M-dwarf companion currently seen at a projected distance of 119 au. We construct a radiative transfer model that accounts for the main characteristics of the features with an inner and outer disk misaligned by 72°. The azimuthal brightness variations along the rim are well reproduced with the scattering phase function of the model. While spirals can be triggered by the tidal interaction with the companion, the close proximity of the spirals to the shadows suggests that the shadows could also play a role. The change in stellar illumination along the rim induces an azimuthal variation of the scale height that can contribute to the brightness variations. Conclusions: Dark regions in polarized images of transition disks are now detected in a handful of disks and often interpreted as shadows due to a misaligned inner disk. However, the origin of such a misalignment in HD 100453, and

  13. First exoplanet and disk results with the PALM-3000 adaptive optics system

    Science.gov (United States)

    Dekany, Richard; Burruss, Rick; Shelton, J. Chris; Oppenheimer, Ben; Vasisht, Gautam; Metchev, Stanimir; Roberts, Jennifer; Tesch, Jonathan; Truong, Tuan; Milburn, Jennifer; Hale, David; Baranec, Christoph; Hildebrandt, Sergi; Wahl, Matthew; Beichman, Chas; Hillenbrand, Lynne; Patel, Rahul; Hinkley, Sasha; Cady, Eric; Parry, Ian

    2013-12-01

    We describe the status of the PALM-3000 adaptive optics facility instrument for the Hale telescope at Palomar Observatory. Since first light in June 2011, PALM-3000 has made significant advances in both performance and sensitivity. Using Strehl ratio as our performance metric, we present results in 64x64 and 32x32 wavefront sensor pupil sampling modes on a range of guide stars from V ~ 3 to 12. We describe our automated reconstructor pipeline tool, which incorporates pupil illumination and an optimal-estimator Baysian approach which serve to boost faint guide star performance. We conclude by presenting initial high-contrast circumstellar disk results from the PHARO vector vortex coronagraph and exoplanet spectra from the P1640 integral field spectrograph.

  14. SDMS-based Disk Encryption Method

    OpenAIRE

    An, Dokjun; Ri, Myongchol; Choe, Changil; Han, Sunam; Kim, Yongmin

    2012-01-01

    We propose a disk encryption method, called secure disk mixed system (SDMS) in this paper, for data protection of disk storages such as USB flash memory, USB hard disk and CD/DVD. It is aimed to solve temporal and spatial limitation problems of existing disk encryption methods and to control security performance flexibly according to the security requirement of system. SDMS stores data by encrypting with different encryption key per sector and updates sector encryption keys each time data is ...

  15. Covering and piercing disks with two centers

    KAUST Repository

    Ahn, Heekap

    2011-01-01

    We consider new versions of the two-center problem where the input consists of a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. We give exact and approximation algorithms for these versions. © 2011 Springer-Verlag.

  16. Covering and piercing disks with two centers

    KAUST Repository

    Ahn, Heekap

    2013-04-01

    We give exact and approximation algorithms for two-center problems when the input is a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in D intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. © 2012 Elsevier B.V.

  17. Scour around a perforated disk modeling a marine hydrokinetic device

    Science.gov (United States)

    Beninati, M. L.; Soliani, G.; Zhou, C. C.; Krane, M.; Fontaine, A.

    2013-12-01

    A study was conducted to investigate the behavior of scour hole dimensions and scour rates around a bottom-mounted cylindrical support structure of a perforated disk. The experiments focus on collecting temporal variations of scour depth around the support structure of the perforated disk for two scour regimes: transitional (ReD = 8500 and 9400) and live-bed (ReD = 10200). A perforated disk is used to approximate the drag of a submerged, horizontal axis, marine hydrokinetic (MHK) turbine. The goal is to compare the scour behavior around a perforated disk to that of a marine hydrokinetic (MHK) device. This study is motivated by the need to predict the environmental effect of MHK devices on an erodible bed. Testing is conducted in the small-scale hydraulic flume facility (1.2 m wide, 0.38 m deep, and 9.75 m long) at Bucknell University. The base of the support structure is marked incrementally to allow for time based observations of changes in scour depth. Bed form topologies are then acquired after a three hour time interval using a 2D sediment bed profiler. Experimental results show that scour rate is dependent on flow speed. Additionally, an increase in scour hole size occurs as the scour conditions are varied from transitional to live-bed.

  18. Disorder in the Disk: The Influence of Accretion Disk Thickness on the Large-scale Magnetic Dynamo.

    Science.gov (United States)

    Hogg, J. Drew; Reynolds, Christopher S.

    2018-01-01

    The evolution of the magnetic field from the enigmatic large-scale dynamo is often considered a central feature of the accretion disk around a black hole. The resulting low-frequency oscillations introduced from the growth and decay of the field strength, along with the change in field orientation, are thought to be intimately tied to variability from the disk. Several factors are at play, but the dynamo can either be directly tied to observable signatures through modulation of the heating rate, or indirectly as the source of quasiperiodic oscillations, the driver of nonlinear structure from propagating fluctuations in mass accretion rate, or even the trigger of state transitions. We present a selection of results from a recent study of this process using a suite of four global, high-resolution, MHD accretion disk simulations. We systematically vary the scale height ratio and find the large-scale dynamo fails to develop above a scale height ratio of h/r ≥ 0.2. Using “butterfly” diagrams of the azimuthal magnetic field, we show the large-scale dynamo exists in the thinner accretion disk models, but fails to excite when the scale height ratio is increased, a feature which is also reflected in 2D Fourier transforms. Additionally, we calculate the dynamo α-parameter through correlations in the averaged magnetic field and turbulent electromotive force, and also generate synthetic light curves from the disk cooling. Using our emission proxy, we find the disks have markedly different characters as photometric fluctuations are larger and less ordered when the disk is thicker and the dynamo is absent.

  19. RESOLVING THE PLANET-HOSTING INNER REGIONS OF THE LkCa 15 DISK

    Energy Technology Data Exchange (ETDEWEB)

    Thalmann, C.; Garufi, A.; Quanz, S. P.; Daemgen, S.; Engler, N. [ETH Zurich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, 8093 Zurich (Switzerland); Janson, M. [Department of Astronomy, Stockholm University, SE-106 91 Stockholm (Sweden); Boccaletti, A. [LESIA, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC Paris 6, Sorbonne Université, 5 place Jules Janssen, F-92195 Meudon CEDEX (France); Sissa, E.; Gratton, R.; Desidera, S. [INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy); Salter, G.; Langlois, M. [Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Benisty, M.; Bonnefoy, M.; Chauvin, G.; Lagrange, A.-M.; Lannier, J. [Université Grenoble Alpes, IPAG, F-38000 Grenoble (France); Dominik, C. [Anton Pannekoek Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Feldt, M.; Henning, T., E-mail: thalmann@phys.ethz.ch [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); and others

    2016-09-10

    LkCa 15 hosts a pre-transitional disk as well as at least one accreting protoplanet orbiting in its gap. Previous disk observations have focused mainly on the outer disk, which is cleared inward of ∼50 au. The planet candidates, on the other hand, reside at orbital radii around 15 au, where disk observations have been unreliable until recently. Here, we present new J -band imaging polarimetry of LkCa 15 with SPHERE IRDIS, yielding the most accurate and detailed scattered-light images of the disk to date down to the planet-hosting inner regions. We find what appear to be persistent asymmetric structures in the scattering material at the location of the planet candidates, which could be responsible at least for parts of the signals measured with sparse-aperture masking. These images further allow us to trace the gap edge in scattered light at all position angles and search the inner and outer disks for morphological substructure. The outer disk appears smooth with slight azimuthal variations in polarized surface brightness, which may be due to shadowing from the inner disk or a two-peaked polarized phase function. We find that the near-side gap edge revealed by polarimetry matches the sharp crescent seen in previous ADI imaging very well. Finally, the ratio of polarized disk to stellar flux is more than six times larger in the J -band than in the RI bands.

  20. Ultrafast disk lasers and amplifiers

    Science.gov (United States)

    Sutter, Dirk H.; Kleinbauer, Jochen; Bauer, Dominik; Wolf, Martin; Tan, Chuong; Gebs, Raphael; Budnicki, Aleksander; Wagenblast, Philipp; Weiler, Sascha

    2012-03-01

    Disk lasers with multi-kW continuous wave (CW) output power are widely used in manufacturing, primarily for cutting and welding applications, notably in the automotive industry. The ytterbium disk technology combines high power (average and/or peak power), excellent beam quality, high efficiency, and high reliability with low investment and operating costs. Fundamental mode picosecond disk lasers are well established in micro machining at high throughput and perfect precision. Following the world's first market introduction of industrial grade 50 W picosecond lasers (TruMicro 5050) at the Photonics West 2008, the second generation of the TruMicro series 5000 now provides twice the average power (100 W at 1030 nm, or 60 W frequency doubled, green output) at a significantly reduced footprint. Mode-locked disk oscillators achieve by far the highest average power of any unamplified lasers, significantly exceeding the 100 W level in laboratory set-ups. With robust long resonators their multi-microjoule pulse energies begin to compete with typical ultrafast amplifiers. In addition, significant interest in disk technology has recently come from the extreme light laser community, aiming for ultra-high peak powers of petawatts and beyond.

  1. Magnetorotational Instability in Eccentric Disks

    Science.gov (United States)

    Chan, Chi-Ho; Krolik, Julian H.; Piran, Tsvi

    2018-03-01

    Eccentric disks arise in such astrophysical contexts as tidal disruption events, but it is unknown whether the magnetorotational instability (MRI), which powers accretion in circular disks, operates in eccentric disks as well. We examine the linear evolution of unstratified, incompressible MRI in an eccentric disk orbiting a point mass. We consider vertical modes of wavenumber k on a background flow with uniform eccentricity e and vertical Alfvén speed {v}{{A}} along an orbit with mean motion n. We find two mode families, one with dominant magnetic components, the other with dominant velocity components. The former is unstable at {(1-e)}3 {f}2≲ 3, where f\\equiv {{kv}}{{A}}/n, and the latter at e ≳ 0.8. For f 2 ≲ 3, MRI behaves much like in circular disks, but the growth per orbit declines slowly with increasing e; for f 2 ≳ 3, modes grow by parametric amplification, which is resonant for 0 energy transport happen chiefly near pericenter, where orbital shear dominates magnetic tension.

  2. SN 2007bg: the complex circumstellar medium around one of the most radio-luminous broad-lined Type Ic supernovae

    Science.gov (United States)

    Salas, P.; Bauer, F. E.; Stockdale, C.; Prieto, J. L.

    2013-01-01

    In this paper we present the results of the radio light curve and X-ray observations of broad-lined Type Ic (Ic-BL) SN 2007bg. The light curve shows three distinct phases of spectral and temporal evolution, implying that the supernova (SN) shock likely encountered at least three different circumstellar medium regimes. We interpret this as the progenitor of SN 2007bg having at least two distinct mass-loss episodes (i.e. phases 1 and 3) during its final stages of evolution, yielding a highly stratified circumstellar medium. Modelling the phase 1 light curve as a freely expanding, synchrotron-emitting shell, self-absorbed by its own radiating electrons, requires a progenitor mass-loss rate of skew4dot{M}≈ 1.9× 10^{-6}(v_w/1000 km s^{-1}) M⊙ yr-1 for the last t ˜ 20(vw/1000 km s-1) yr before explosion and a total energy of the radio-emitting ejecta of E ≈ 1 × 1048 erg 10 d after explosion. This places SN 2007bg among the most energetic Type Ib/c events. We interpret the second phase as a sparser `gap' region between the two winds stages. Phase 3 shows a second absorption turn-on before rising to a peak luminosity 2.6 times higher than in phase 1. Assuming this luminosity jump is due to a circumstellar medium density enhancement from a faster previous mass-loss episode, we estimate that the phase 3 mass-loss rate could be as high as skew4dot{M}lesssim 4.3× 10^{-4}(v_w/1000 km s^{-1}) M⊙ yr-1. The phase 3 wind would have transitioned directly into the phase 1 wind for a wind speed difference of ≈2. In summary, the radio light curve provides robust evidence for dramatic global changes in at least some Ic-BL progenitors just prior (˜10-1000 yr) to explosion. The observed luminosity of this SN is the highest observed for a non-gamma-ray-burst Ic-BL SN, reaching L8.46 GHz ≈ 1 × 1029 erg Hz-1 s-1, ˜567 d after explosion.

  3. Shadows and cavities in protoplanetary disks: HD 163296, HD 141569A, and HD 150193A in polarized light

    Science.gov (United States)

    Garufi, A.; Quanz, S. P.; Schmid, H. M.; Avenhaus, H.; Buenzli, E.; Wolf, S.

    2014-08-01

    Context. The morphological evolution of dusty disks around young (a few Myr old) stars is pivotal for a better understanding of planet formation. Since both dust grains and the global disk geometry evolve on short timescales, high-resolution imaging of a sample of objects may provide important indications about this evolution. Aims: We enlarge the sample of protoplanetary disks imaged in polarized light with high-resolution imaging (≲0.2″) by observing the Herbig Ae/Be stars HD 163296, HD 141569A, and HD 150193A. We combine our data with previous datasets to understand the larger context of their morphology. Methods: Polarimetric differential imaging is an attractive technique with which to image at near-IR wavelengths a significant fraction of the light scattered by the circumstellar material. The unpolarized stellar light is canceled out by combining two simultaneous orthogonal polarization states. This allowed us to achieve an inner working angle and an angular resolution as low as ~0.1″. Results: We report a weak detection of the disk around HD 163296 in the H and KS bands. The disk is resolved as a broken ring structure with a significant surface brightness drop inward of 0.6″. No sign of extended polarized emission is detected from the disk around HD 141569A and HD 150193A. Conclusions: We propose that the absence of scattered light in the inner 0.6″ around HD 163296 and the non-detection of the disk around HD 150193A may be due to similar geometric factors. Since these disks are known to be flat or only moderately flared, self-shadowing by the disk inner wall is the favored explanation. We show that the polarized brightness of a number of disks is indeed related to their flaring angle. Other scenarios (such as dust grain growth or interaction with icy molecules) are also discussed. On the other hand, the non-detection of HD 141569A is consistent with previous datasets that revealed a huge cavity in the dusty disk. Based on observations collected at

  4. Dynamic Young Stars and their Disks: A Temporal View of NGC 2264 with Spitzer and CoRoT*

    Directory of Open Access Journals (Sweden)

    Cody Ann Marie

    2014-01-01

    Full Text Available Variability is a signature feature of young stars. Among the well known light curve phenomena are periodic variations attributed to surface spots and irregular changes associated with accretion or circumstellar disk material. While decades of photometric monitoring have provided a framework for classifying young star variability, we still know surprisingly little about its underlying mechanisms and connections to the surrounding disks. In the past few years, dedicated photometric monitoring campaigns from the ground and space have revolutionized our view of young stars in the time domain. We present a selection of optical and infrared time series from several recent campaigns, highlighting the Coordinated Synoptic Investigation of NGC 2264 (“CSI 2264”– a joint30-day effort with the Spitzer, CoRoT, and MOST telescopes. The extraordinary photometric precision, high cadence, and long time baseline of these observations is now enabling correlation of variability properties at very different wavelengths, corresponding to locations from the stellar surface to the inner 0.1 AU of the disk. We present some results of the CSI 2264 program, including new classes of optical/infrared behavior. Further efforts to tie observed variability features to physical models will provide insights into the inner disk environment at a time when planet formation may be underway.

  5. Dust in protoplanetary disks: observations*

    Directory of Open Access Journals (Sweden)

    Waters L.B.F.M.

    2015-01-01

    Full Text Available Solid particles, usually referred to as dust, are a crucial component of interstellar matter and of planet forming disks surrounding young stars. Despite the relatively small mass fraction of ≈1% (in the solar neighborhood of our galaxy; this number may differ substantially in other galaxies that interstellar grains represent of the total mass budget of interstellar matter, dust grains play an important role in the physics and chemistry of interstellar matter. This is because of the opacity dust grains at short (optical, UV wavelengths, and the surface they provide for chemical reactions. In addition, dust grains play a pivotal role in the planet formation process: in the core accretion model of planet formation, the growth of dust grains from the microscopic size range to large, cm-sized or larger grains is the first step in planet formation. Not only the grain size distribution is affected by planet formation. Chemical and physical processes alter the structure and chemical composition of dust grains as they enter the protoplanetary disk and move closer to the forming star. Therefore, a lot can be learned about the way stars and planets are formed by observations of dust in protoplanetary disks. Ideally, one would like to measure the dust mass, the grain size distribution, grain structure (porosity, fluffiness, the chemical composition, and all of these as a function of position in the disk. Fortunately, several observational diagnostics are available to derive constrains on these quantities. In combination with rapidly increasing quality of the data (spatial and spectral resolution, a lot of progress has been made in our understanding of dust evolution in protoplanetary disks. An excellent review of dust evolution in protoplanetary disks can be found in Testi et al. (2014.

  6. From Disks to Planets: The Making of Planets and Their Early Atmospheres. An Introduction

    Science.gov (United States)

    Lammer, Helmut; Blanc, Michel

    2018-03-01

    This paper is an introduction to volume 56 of the Space Science Series of ISSI, "From disks to planets—the making of planets and their proto-atmospheres", a key subject in our quest for the origins and evolutionary paths of planets, and for the causes of their diversity. Indeed, as exoplanet discoveries progressively accumulated and their characterization made spectacular progress, it became evident that the diversity of observed exoplanets can in no way be reduced to the two classes of planets that we are used to identify in the solar system, namely terrestrial planets and gas or ice giants: the exoplanet reality is just much broader. This fact is no doubt the result of the exceptional diversity of the evolutionary paths linking planetary systems as a whole as well as individual exoplanets and their proto-atmospheres to their parent circumstellar disks: this diversity and its causes are exactly what this paper explores. For each of the main phases of the formation and evolution of planetary systems and of individual planets, we summarize what we believe we understand and what are the important open questions needing further in-depth examination, and offer some suggestions on ways towards solutions. We start with the formation mechanisms of circumstellar disks, with their gas and disk components in which chemical composition plays a very important role in planet formation. We summarize how dust accretion within the disk generates planet cores, while gas accretion on these cores can lead to the diversity of their fluid envelopes. The temporal evolution of the parent disk itself, and its final dissipation, put strong constraints on how and how far planetary formation can proceed. The radiation output of the central star also plays an important role in this whole story. This early phase of planet evolution, from disk formation to dissipation, is characterized by a co-evolution of the disk and its daughter planets. During this co-evolution, planets and their

  7. Atomic and Molecular Isotope Ratios in Circumstellar Envelopes: Fractionation vs. Nucleosynthesis

    Science.gov (United States)

    Milam, Stefanie

    The long standing question of "What are the origin, evolution, and fate of our Universe and/or Galaxy?" has puzzled humankind for centuries. One approach to answering this question is to gain further understanding of stellar evolution, since stars are fundamental in galaxy development and evolution. A compilation of stellar composition can reveal the age, dynamics, and possibly the evolutionary state of a galaxy. Stars are the factories of heavy elements, including carbon, nitrogen, and oxygen, that are key to the chemical complexity associated with planetary systems. Primitive materials, such as meteorites and IDPs, have revealed a component of "atypical" isotopic signatures of these fundamental elements denoting a possible stellar origin. Understanding the processes by which these elements derive is essential for astrophysics on cosmochemical, galactic, stellar, and planetary scales. We propose to analyze data obtained from the Herschel Space Observatory of circumstellar envelopes to definitively measure C, N, and O isotope ratios and test current models of photo-selective isotope fractionation vs. nucleosynthetically determined values. This proposal augments completed programs from the Herschel Space Observatory, namely the the HIFISTARS program (PI: Bujarrabal), which at the time of proposal submission a significant portion of data will no longer be under proprietary regulations (https://nhscsci.ipac.caltech.edu/sc/).) The broader implications for this study include fundamental data necessary for furthering our current understanding of stellar nucleosynthesis, circumstellar chemistry, Galactic chemical evolution, and the origin of presolar grains found in primitive materials. We will focus on isotopologues of species formed in thermochemical equilibrium and trace their natal, nucleosynthetic isotope ratios. We will analyze Herschel data obtained for a survey of evolved stars with varying degrees of nuclear processing, evolutionary states, and envelope chemistry

  8. Herschel Studies of Circumstellar Volatile Isotopes: Supporting Observations from the Ground and SOFIA

    Science.gov (United States)

    Milam, Stefanie

    The long standing question of ''What are the origin, evolution, and fate of our Universe and/or Galaxy?" has puzzled humankind for centuries. One approach to answering this question is to gain further understanding of stellar evolution, since stars are fundamental in galaxy development and evolution. A compilation of stellar composition can reveal the age, dynamics, and possibly the evolution of a galaxy. Stars are the factories of heavy elements, including carbon, nitrogen, and oxygen, that are fundamental in chemical complexity associated with planetary systems. Primitive materials have revealed a component of “atypical” isotopic signatures of these fundamental elements denoting a possible stellar origin. Understanding the processes by which these elements derive are essential for astrophysics on cosmochemical, galactic, stellar, and planetary scales. We propose to perform a comprehensive program of radioastronomical and infrared observations in circumstellar envelopes to definitively measure C, N, and O isotope ratios and test current models of photo-selective isotope fractionation vs. nucleosynthetically determined values. These data augment current programs underway with the Herschel Space Observatory. The broad implications for this study include fundamental values necessary for furthering our current understanding of stellar nucleosynthesis, circumstellar chemistry, Galactic chemical evolution, and the origin of presolar grains found in primitive materials. We will focus on isotopologues of species formed in thermochemical equilibrium and trace the natal, nucleosynthetic isotope ratio. We will survey a sample of evolved stars with varying degrees of nuclear processing, evolutionary states, and envelope chemistry (e.g. oxygen-rich vs. carbon-rich). The isotope ratios of 12C/13C, 14N/15N, 16O/17O, and 16O/18O will be obtained and compared to previous studies conducted on species now considered to be affected by chemical effects in the circumstellar shell

  9. An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris

    Science.gov (United States)

    Hankins, M. J.; Herter, T. L.; Maercker, M.; Lau, R. M.; Sloan, G. C.

    2018-01-01

    The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the most extensively studied stars on the AGB. R Scl is a carbon star with a massive circumstellar shell (M shell ∼ 7.3 × 10‑3 M ⊙) that is thought to have been produced during a thermal pulse event ∼2200 years ago. To study the thermal dust emission associated with its circumstellar material, observations were taken with the Faint Object InfraRed CAMera for the SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 μm. Maps of the infrared emission at these wavelengths were used to study the morphology and temperature structure of the spatially extended dust emission. Using the radiative-transfer code DUSTY, and fitting the spatial profile of the emission, we find that a geometrically thin dust shell cannot reproduce the observed spatially resolved emission. Instead, a second dust component in addition to the shell is needed to reproduce the observed emission. This component, which lies interior to the dust shell, traces the circumstellar envelope of R Scl. It is best fit by a density profile with n ∝ r α , where α ={0.75}-0.25+0.45 and a dust mass of {M}d={9.0}-4.1+2.3× {10}-6 {M}ȯ . The strong departure from an r ‑2 law indicates that the mass-loss rate of R Scl has not been constant. This result is consistent with a slow decline in the post-pulse mass loss that has been inferred from observations of the molecular gas.

  10. Gas phase chemical kinetics at high temperature of carbonaceous molecules: application to circumstellar envelopes

    Science.gov (United States)

    Biennier, L.; Gardez, A.; Saidani, G.; Georges, R.; Rowe, B.; Reddy, K. P. J.

    2011-05-01

    Circumstellar shells of evolved stars are a theater of extremely rich physical and chemical processes. More than seventy molecules of varied nature have been identified in the envelopes through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals and a significant number are unique to the circumstellar medium. However, observational data remain scarce and more than half of the detected species have been observed in only one object, the nearby carbon star IRC + 10216. Chemical kinetic models are needed to describe the formation of molecules in evolved circumstellar outflows. Upcoming terrestrial telescopes such as ALMA will increase the spatial resolution by several orders of magnitude and provide a wealth of data. The determination of relevant laboratory kinetics data is critical to keep up with the development of the observations and of the refinement of chemical models. Today, the majority of reactions studied in the laboratory are the ones involved in combustion and concerning light hydrocarbons. Our objective is to provide the scientific community with rate coefficients of reactions between abundant species in these warm environments. Cyanopolyynes from HC_2N to HC_9N have all been detected in carbon rich circumstellar envelopes in up to 10 sources for HC_3N. Neutral-neutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures. Our approach aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high enthalpy source (Moudens et al. 2011) with a flow tube and a pulsed laser photolysis and laser induced fluorescence system to probe the undergoing chemical reactions. The high enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane, propene

  11. Three types of galaxy disks

    NARCIS (Netherlands)

    Pohlen, M.; Erwin, P.; Trujillo, I.; Beckman, J. E.; Knapen, JH; Mahoney, TJ; Vazdekis, A

    2008-01-01

    We present our new scheme for the classification of radial stellar surface brightness profiles for disk galaxies. We summarize the current theoretical attempts to understand their origin and give an example of an application by comparing local galaxies with their counterparts at high redshift (z

  12. Disk Operating System User's Guide

    Science.gov (United States)

    1972-05-01

    This document serves the purpose of bringing together in one place most of the information a user needs to use the DDP-516 Disk Operating System, (DOS). DOS is a core resident, one user, console-oriented operating system which allows the user to cont...

  13. Method and apparatus for bistable optical information storage for erasable optical disks

    Science.gov (United States)

    Land, Cecil E.; McKinney, Ira D.

    1990-01-01

    A method and an optical device for bistable storage of optical information, together with reading and erasure of the optical information, using a photoactivated shift in a field dependent phase transition between a metastable or a bias-stabilized ferroelectric (FE) phase and a stable antiferroelectric (AFE) phase in an lead lanthanum zirconate titanate (PLZT). An optical disk contains the PLZT. Writing and erasing of optical information can be accomplished by a light beam normal to the disk. Reading of optical information can be accomplished by a light beam at an incidence angle of 15 to 60 degrees to the normal of the disk.

  14. THE LONG-TERM DYNAMICAL EVOLUTION OF DISK-FRAGMENTED MULTIPLE SYSTEMS IN THE SOLAR NEIGHBORHOOD

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yun [Department of Astronomy, School of Physics, Peking University, Yiheyuan Lu 5, Haidian Qu, Beijing 100871 (China); Kouwenhoven, M. B. N. [Department of Mathematical Sciences, Xi’an Jiaotong-Liverpool University, 111 Ren’ai Road, Suzhou Dushu Lake Science and Education Innovation District, Suzhou Industrial Park, Suzhou 215123 (China); Stamatellos, D. [Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Goodwin, Simon P., E-mail: t.kouwenhoven@xjtlu.edu.cn [Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

    2016-11-10

    The origin of very low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) at the low-mass end of the initial mass function is not yet fully understood. Gravitational fragmentation of circumstellar disks provides a possible mechanism for the formation of such low-mass objects. The kinematic and binary properties of very low-mass objects formed through disk fragmentation at early times (<10 Myr) were discussed in our previous paper. In this paper we extend the analysis by following the long-term evolution of disk-fragmented systems up to an age of 10 Gyr, covering the ages of the stellar and substellar populations in the Galactic field. We find that the systems continue to decay, although the rates at which companions escape or collide with each other are substantially lower than during the first 10 Myr, and that dynamical evolution is limited beyond 1 Gyr. By t = 10 Gyr, about one third of the host stars are single, and more than half have only one companion left. Most of the other systems have two companions left that orbit their host star in widely separated orbits. A small fraction of companions have formed binaries that orbit the host star in a hierarchical triple configuration. The majority of such double-companion systems have internal orbits that are retrograde with respect to their orbits around their host stars. Our simulations allow a comparison between the predicted outcomes of disk fragmentation with the observed low-mass hydrogen-burning stars, BDs, and PMOs in the solar neighborhood. Imaging and radial velocity surveys for faint binary companions among nearby stars are necessary for verification or rejection of the formation mechanism proposed in this paper.

  15. Accretion disk viscosity and internal waves in disks

    Science.gov (United States)

    Huang, Min

    1992-01-01

    Recently, Vishniac, Jin and Diamond suggested that internal waves in accretion disks play a critical role in generating magnetic fields, and consequently are indirectly responsible for angular momentum transfer in thin, conducting, and non-self-gravitational disk systems. A project in which we will construct a quantitative model of the internal wave spectrum in accretion disks is started. It includes two aspects of work. The physical properties of the waves in a thin, non-self-gravitational, and non-magnetized accretion disk with realistic vertical structure is cataloged and examined. Besides the low frequency internal waves discovered by Vishniac and Diamond, it was found that sound waves with low frequency and low axisymmetry (with small absolute value of m) are capable of a driving dynamo because they are (1) well confined in a layer with thickness 2(absolute value of m)H where H is the disk scale height; (2) highly dispersive so they may survive the strong dissipation caused by the coherent nonlinear interaction their high frequency partners experience; and (3) elliptically polarized because they are confined in the z-direction. As a first step towards constructing a quantitative theory of this dynamo effect, a framework of calculating resonant nonlinear interaction among waves in disk is established. We are developing a numerical code which will compute the steady spectrum of the wave field in this framework. For simplicity, we only include the low frequency internal waves suggested by Vishniac and Diamond in the present stage. In the vicinity of the static state, the time step whose length is determined by the evolution of the modes with the largest amplitudes is too large for the modes with smaller amplitudes and overshooting occurs. Through nonlinear coupling, this overshooting is amplified and appears as a numerical instability affecting the evolution of the large amplitude modes. Shorter time steps may delay the appearance of the instability but not cure

  16. Toward Detection of Exoplanetary Rings via Transit Photometry: Methodology and a Possible Candidate

    Energy Technology Data Exchange (ETDEWEB)

    Aizawa, Masataka; Masuda, Kento; Suto, Yasushi [Department of Physics, The University of Tokyo, Tokyo, 113-0033 (Japan); Uehara, Sho [Department of Physics, Tokyo Metropolitan University, Tokyo 192-4397 (Japan); Kawahara, Hajime, E-mail: aizawa@utap.phys.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, The University of Tokyo, Tokyo 113-0033 (Japan)

    2017-04-01

    The detection of a planetary ring of exoplanets remains one of the most attractive, but challenging, goals in the field of exoplanetary science. We present a methodology that implements a systematic search for exoplanetary rings via transit photometry of long-period planets. This methodology relies on a precise integration scheme that we develop to compute a transit light curve of a ringed planet. We apply the methodology to 89 long-period planet candidates from the Kepler data so as to estimate, and/or set upper limits on, the parameters of possible rings. While the majority of our samples do not have sufficient signal-to-noise ratios (S/Ns) to place meaningful constraints on ring parameters, we find that six systems with higher S/Ns are inconsistent with the presence of a ring larger than 1.5 times the planetary radius, assuming a grazing orbit and a tilted ring. Furthermore, we identify five preliminary candidate systems whose light curves exhibit ring-like features. After removing four false positives due to the contamination from nearby stars, we identify KIC 10403228 as a reasonable candidate for a ringed planet. A systematic parameter fit of its light curve with a ringed planet model indicates two possible solutions corresponding to a Saturn-like planet with a tilted ring. There also remain two other possible scenarios accounting for the data; a circumstellar disk and a hierarchical triple. Due to large uncertain factors, we cannot choose one specific model among the three.

  17. Optimization of the Processing of Mo Disks

    Energy Technology Data Exchange (ETDEWEB)

    Tkac, Peter [Argonne National Lab. (ANL), Argonne, IL (United States); Rotsch, David A. [Argonne National Lab. (ANL), Argonne, IL (United States); Stepinski, Dominique [Argonne National Lab. (ANL), Argonne, IL (United States); Makarashvili, Vakhtang [Argonne National Lab. (ANL), Argonne, IL (United States); Harvey, James [NorthStar Medical Technologies, LLC, Madison, WI (United States); Vandegrift, George F. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2016-01-01

    The objective of this work is to decrease the processing time for irradiated disks of enriched Mo for the production of 99Mo. Results are given for the dissolution of nonirradiated Mo disks, optimization of the process for large-scale dissolution of sintered disks, optimization of the removal of the main side products (Zr and Nb) from dissolved targets, and dissolution of irradiated Mo disks.

  18. Growing and moving planets in disks

    NARCIS (Netherlands)

    Paardekooper, Sijme-Jan

    2006-01-01

    Planets form in disks that are commonly found around young stars. The intimate relationship that exists between planet and disk can account for a lot of the exotic extrasolar planetary systems known today. In this thesis we explore disk-planet interaction using numerical hydrodynamical simulations.

  19. A COMMON SOURCE OF ACCRETION DISK TILT

    International Nuclear Information System (INIS)

    Montgomery, M. M.; Martin, E. L.

    2010-01-01

    Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source that causes and maintains disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through the disk's center of mass. The disk responds to lift by pitching around the disk's line of nodes. If the gas stream flow ebbs, then lift also ebbs and the disk attempts to return to its original orientation. To first approximation, lift does not depend on magnetic fields or radiation sources but does depend on the mass and the surface area of the disk. Also, for disk tilt to be initiated, a minimum mass transfer rate must be exceeded. For example, a 10 -11 M sun disk around a 0.8 M sun compact central object requires a mass transfer rate greater than ∼ 8 x 10 -11 M sun yr -1 , a value well below the known mass transfer rates in cataclysmic variable dwarf novae systems that retrogradely precess and exhibit negative superhumps in their light curves and a value well below mass transfer rates in protostellar-forming systems.

  20. Mapping Circumstellar Matter with Polarized Light: The Case of Supernova 2014J in M82

    Science.gov (United States)

    Yang, Yi; Wang, Lifan; Baade, Dietrich; Brown, Peter. J.; Cikota, Aleksandar; Cracraft, Misty; Höflich, Peter A.; Maund, Justyn R.; Patat, Ferdinando; Sparks, William B.; Spyromilio, Jason; Stevance, Heloise F.; Wang, Xiaofeng; Wheeler, J. Craig

    2018-02-01

    Optical polarimetry is an effective way of probing the environment of a supernova for dust. We acquired linear HST ACS/WFC polarimetry in bands F475W, F606W, and F775W of the supernova (SN) 2014J in M82 at six epochs from ∼277 days to ∼1181 days after the B-band maximum. The polarization measured at day 277 shows conspicuous deviations from other epochs. These differences can be attributed to at least ∼{10}-6 {M}ȯ of circumstellar dust located at a distance of ∼ 5× {10}17 {cm} from the SN. The scattering dust grains revealed by these observations seem to be aligned with the dust in the interstellar medium that is responsible for the large reddening toward the supernova. The presence of this circumstellar dust sets strong constraints on the progenitor system that led to the explosion of SN 2014J; however, it cannot discriminate between single- and double-degenerate models.

  1. Infrared spectrophotometry and radiative transfer in optically thick circumstellar dust envelopes

    International Nuclear Information System (INIS)

    Merrill, K.M.

    1976-01-01

    The Two-Micron Sky Survey of Neugebauer and Leighton and, more recently, the AFCRL Infrared Sky Survey of Walker and Price have detected numerous compact, isolated, bright infrared sources which are not identified with previously cataloged stars. Observations of many such objects suggest that extensive circumstellar dust envelopes modify the flux from a central source. The present investigations employ broad bandpass photometry at lambda lambda 1.65 μm to 12.5 μm and narrow bandpass spectrophotometry (Δ lambda/lambda approximately 0.015) at lambda lambda 2-4 μm and lambda lambda 8-13 μm to determine the properties of a large sample of such infrared sources. Infrared spectrophotometry can clearly differentiate between normal stars of spectral types M(''oxygen-rich'') and C (''carbon-rich'') on the basis of characteristic absorption bands arising in cool stellar atmospheres. Most of the 2 μ Sky Survey and many of the AFCRL Sky Survey sources appear to be stars of spectral types M and C which are differentiated from normal cool comparison stars only by the presence of extensive circumstellar dust envelopes. Due to the large optical depth of the envelopes, the flux from the star and from the dust cannot be simply separated. Hence solutions of radiative transfer through spherically symmetric envelopes of arbitrary optical depth were generated by a generalized computer code which employed opacities of real dust

  2. SN 2014C: VLBI images of a supernova interacting with a circumstellar shell

    Science.gov (United States)

    Bietenholz, Michael F.; Kamble, Atish; Margutti, Raffaella; Milisavljevic, Danny; Soderberg, Alicia

    2018-04-01

    We report on very long baseline interferometry (VLBI) measurements of supernova 2014C at several epochs between t = 384 and 1057 d after the explosion. SN 2014C was an unusual supernova that initially had Type Ib optical spectrum, but after t = 130 d it developed a Type IIn spectrum with prominent Hα lines, suggesting the onset of strong circumstellar interaction. Our first VLBI observation was at t = 384 d, and we find that the outer radius of SN 2014C was (6.40 ± 0.26) × 1016 cm (for a distance of 15.1 Mpc), implying an average expansion velocity of 19 300 ± 790 km s-1 up to that time. At our last epoch, SN 2014C was moderately resolved and shows an approximately circular outline but with an enhancement of the brightness on the W side. The outer radius of the radio emission at t = 1057 d is (14.9 ± 0.6) × 1016 cm. We find that the expansion between t = 384 and 1057 d is well described by a constant velocity expansion with v = 13 600 ± 650 km s-1. SN 2014C had clearly been substantially decelerated by t = 384 d. Our measurements are compatible with a scenario where the expanding shock impacted upon a shell of dense circumstellar material during the first year, as suggested by the observations at other wavelengths, but had progressed through the dense shell by the time of the VLBI observations.

  3. Enantiomeric separation of complex organic molecules produced from irradiation of interstellar/circumstellar ice analogs

    Science.gov (United States)

    Nuevo, M.; Meierhenrich, U. J.; D'Hendecourt, L.; Muñoz Caro, G. M.; Dartois, E.; Deboffle, D.; Thiemann, W. H.-P.; Bredehöft, J.-H.; Nahon, L.

    Irradiation of interstellar/circumstellar ice analogs by ultraviolet (UV) light followed by warm up in the laboratory leads to the formation of complex organic molecules, stable at room temperature. Hydrolysis of the room temperature residue releases amino acids, the building blocks of proteins. These amino acids exist in two different forms (L and D), but proteins encountered in living beings consist exclusively of L enantiomers. The origin of this property, called homochirality, is still unknown. Amino acids can be detected and quantified by chemical techniques such as chiral gas chromatography coupled with mass spectrometry (GC-MS). Enantiomers of chiral organics are also known to interact selectively with circularly polarized light (CPL), leading to a selective production or destruction of the final compounds. This paper describes how we settled an experiment where amino acids are formed by irradiation of interstellar/circumstellar ice analogs with ultraviolet (UV) CPL, produced by a synchrotron radiation beamline, which allowed us to quantify the effect of such polarized light on the production of amino acids. These results can be compared to the enantiomeric excesses measured in primitive meteorites such as Murchison.

  4. Models of bright nickel-free supernovae from stripped massive stars with circumstellar shells

    Science.gov (United States)

    Kleiser, Io K. W.; Kasen, Daniel; Duffell, Paul C.

    2018-04-01

    The nature of an emerging class of rapidly fading supernovae (RFSNe) - characterized by their short-lived light-curve duration, but varying widely in peak brightness - remains puzzling. Whether the RFSNe arise from low-mass thermonuclear eruptions on white dwarfs or from the core collapse of massive stars is still a matter of dispute. We explore the possibility that the explosion of hydrogen-free massive stars could produce bright but rapidly fading transients if the effective pre-supernova radii are large and if little or no radioactive nickel is ejected. The source of radiation is then purely due to shock cooling. We study this model of RFSNe using spherically symmetric hydrodynamics and radiation transport calculations of the explosion of stripped stars embedded in helium-dominated winds or shells of various masses and extent. We present a parameter study showing how the properties of the circumstellar envelopes affect the dynamics of the explosion and can lead to a diversity of light curves. We also explore the dynamics of the fallback of the innermost stellar layers, which might be able to remove radioactive nickel from the ejecta, making the rapid decline in the late-time light curve possible. We provide scaling relations that describe how the duration and luminosity of these events depend on the supernova kinetic energy and the mass and radius of the circumstellar material.

  5. When may unstable gravitating disk be considered an infinitely thin gravitating disk

    Energy Technology Data Exchange (ETDEWEB)

    Polyachenko, V.L.; Fridman, A.M. (AN SSSR, Irkutsk. Sibirskij Inst. Zemnogo Magnetizma Ionosfery i Rasprostraneniya Radiovoln; AN SSSR, Moscow. Astronomicheskij Sovet)

    1981-03-01

    It is shown that the model of an infinitely thin gravitating disk is valid for investigation of its stability only if a massive halo is present. Conditions for main parameters of the disk and halo are obtained when, firstly, most unstable wavelengths are much larger than the disk thickness (approximation of an infinitely thin disk) and, secondary, the contribution of a halo to the perturbed gravitational potential can be neglected. Density distributions of the disk and halo are obtained.

  6. Regression of lumbar disk herniation

    Directory of Open Access Journals (Sweden)

    G. Yu Evzikov

    2015-01-01

    Full Text Available Compression of the spinal nerve root, giving rise to pain and sensory and motor disorders in the area of its innervation is the most vivid manifestation of herniated intervertebral disk. Different treatment modalities, including neurosurgery, for evolving these conditions are discussed. There has been recent evidence that spontaneous regression of disk herniation can regress. The paper describes a female patient with large lateralized disc extrusion that has caused compression of the nerve root S1, leading to obvious myotonic and radicular syndrome. Magnetic resonance imaging has shown that the clinical manifestations of discogenic radiculopathy, as well myotonic syndrome and morphological changes completely regressed 8 months later. The likely mechanism is inflammation-induced resorption of a large herniated disk fragment, which agrees with the data available in the literature. A decision to perform neurosurgery for which the patient had indications was made during her first consultation. After regression of discogenic radiculopathy, there was only moderate pain caused by musculoskeletal diseases (facet syndrome, piriformis syndrome that were successfully eliminated by minimally invasive techniques. 

  7. Fullerenes and disk-fullerenes

    International Nuclear Information System (INIS)

    Deza, M; Dutour Sikirić, M; Shtogrin, M I

    2013-01-01

    A geometric fullerene, or simply a fullerene, is the surface of a simple closed convex 3-dimensional polyhedron with only 5- and 6-gonal faces. Fullerenes are geometric models for chemical fullerenes, which form an important class of organic molecules. These molecules have been studied intensively in chemistry, physics, crystallography, and so on, and their study has led to the appearance of a vast literature on fullerenes in mathematical chemistry and combinatorial and applied geometry. In particular, several generalizations of the notion of a fullerene have been given, aiming at various applications. Here a new generalization of this notion is proposed: an n-disk-fullerene. It is obtained from the surface of a closed convex 3-dimensional polyhedron which has one n-gonal face and all other faces 5- and 6-gonal, by removing the n-gonal face. Only 5- and 6-disk-fullerenes correspond to geometric fullerenes. The notion of a geometric fullerene is therefore generalized from spheres to compact simply connected two-dimensional manifolds with boundary. A two-dimensional surface is said to be unshrinkable if it does not contain belts, that is, simple cycles consisting of 6-gons each of which has two neighbours adjacent at a pair of opposite edges. Shrinkability of fullerenes and n-disk-fullerenes is investigated. Bibliography: 87 titles

  8. Grand canonical simulations of hard-disk systems by simulated tempering

    DEFF Research Database (Denmark)

    Döge, G.; Mecke, K.; Møller, Jesper

    2004-01-01

    The melting transition of hard disks in two dimensions is still an unsolved problem and improved simulation algorithms may be helpful for its investigation. We suggest the application of simulating tempering for grand canonical hard-disk systems as an efficient alternative to the commonly......-used Monte Carlo algorithms for canonical systems. This approach allows the direct study of the packing fraction as a function of the chemical potential even in the vicinity of the melting transition. Furthermore, estimates of several spatial characteristics including pair correlation function are studied...

  9. Foundations of Black Hole Accretion Disk Theory.

    Science.gov (United States)

    Abramowicz, Marek A; Fragile, P Chris

    2013-01-01

    This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin) disks, slim disks, and advection-dominated accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs).

  10. THE LATE STAGES OF PROTOPLANETARY DISK EVOLUTION: A MILLIMETER SURVEY OF UPPER SCORPIUS

    International Nuclear Information System (INIS)

    Mathews, Geoffrey S.; Williams, Jonathan P.; Ménard, Francois; Duchêne, Gaspard; Pinte, Christophe; Phillips, Neil

    2012-01-01

    We present deep 1.2 mm photometry of 37 stars in the young (5 Myr) Upper Scorpius OB association, sensitive to ∼4 × 10 –3 M Jup of cool millimeter dust. Disks around four low- and solar-mass stars are detected, as well as one debris disk around an intermediate-mass star, with dust masses ranging from 3.6 × 10 –3 to 1.0 × 10 –1 M Jup . The source with the most massive disk exhibits a transition-disk spectral energy distribution. Combining our results with previous studies, we find that the millimeter-detection fraction of Class II sources has significantly decreased from younger ages, and comparison with near-infrared and Hα measurements indicates that the present disks have undergone significant evolution in composition or structure at all radii. The disks of Upper Scorpius represent the tail-end of the depletion of primordial disks; while a few near-solar-mass stars may still sustain giant planet formation, this process has finished around higher mass stars.

  11. Curvature-driven stability of defects in nematic textures over spherical disks

    Science.gov (United States)

    Duan, Xiuqing; Yao, Zhenwei

    2017-06-01

    Stabilizing defects in liquid-crystal systems is crucial for many physical processes and applications ranging from functionalizing liquid-crystal textures to recently reported command of chaotic behaviors of active matters. In this work, we perform analytical calculations to study the curvature-driven stability mechanism of defects based on the isotropic nematic disk model that is free of any topological constraint. We show that in a growing spherical disk covering a sphere the accumulation of curvature effect can prevent typical +1 and +1/2 defects from forming boojum textures where the defects are repelled to the boundary of the disk. Our calculations reveal that the movement of the equilibrium position of the +1 defect from the boundary to the center of the spherical disk occurs in a very narrow window of the disk area, exhibiting the first-order phase-transition-like behavior. For the pair of +1/2 defects by splitting a +1 defect, we find the curvature-driven alternating repulsive and attractive interactions between the two defects. With the growth of the spherical disk these two defects tend to approach and finally recombine towards a +1 defect texture. The sensitive response of defects to curvature and the curvature-driven stability mechanism demonstrated in this work in nematic disk systems may have implications towards versatile control and engineering of liquid-crystal textures in various applications.

  12. Circumstellar Interaction in Supernovae in Dense Environments—An Observational Perspective

    Science.gov (United States)

    Chandra, Poonam

    2018-02-01

    In a supernova explosion, the ejecta interacting with the surrounding circumstellar medium (CSM) give rise to variety of radiation. Since CSM is created from the mass loss from the progenitor, it carries footprints of the late time evolution of the star. This is one of the unique ways to get a handle on the nature of the progenitor system. Here, I will focus mainly on the supernovae (SNe) exploding in dense environments, a.k.a. Type IIn SNe. Radio and X-ray emission from this class of SNe have revealed important modifications in their radiation properties, due to the presence of high density CSM. Forward shock dominance in the X-ray emission, internal free-free absorption of the radio emission, episodic or non-steady mass loss rate, and asymmetry in the explosion seem to be common properties of this class of SNe.

  13. The circumstellar envelopes of F and G type supergiants in the large magellanic cloud

    International Nuclear Information System (INIS)

    Hagen, W.; Humphreys, R.M.; Stencel, R.E.

    1981-01-01

    We have obtained high-dispersion echellograms at 2.5 and 5.1 A/mm of four F and G-type supergiants (Msub(V) approximately -9) in the large Magellanic Cloud for the purpose of studying their outer atmospheres as compared to their Milky Way counterparts. Line doubling at Na I D indicates extensive circumstellar envelopes and mass loss rates in excess of 10 -5 M . yr -1 with outflow velocities of 10-60 km s -1 . Deep exposures at Ca II H and K reveal new information about the chromospheres of extragalactic stars. The presence of H and K wing emission lines augments this, and also provides an independent way of estimating Msub(V). (author)

  14. Increased H2CO production in the outer disk around HD 163296

    Science.gov (United States)

    Carney, M. T.; Hogerheijde, M. R.; Loomis, R. A.; Salinas, V. N.; Öberg, K. I.; Qi, C.; Wilner, D. J.

    2017-09-01

    Context. The gas and dust in circumstellar disks provide the raw materials to form planets. The study of organic molecules and their building blocks in such disks offers insight into the origin of the prebiotic environment of terrestrial planets. Aims: We aim to determine the distribution of formaldehyde, H2CO, in the disk around HD 163296 to assess the contribution of gas- and solid-phase formation routes of this simple organic. Methods: Three formaldehyde lines were observed (H2CO 303-202, H2CO 322-221, and H2CO 321-220) in the protoplanetary disk around the Herbig Ae star HD 163296 with ALMA at 0.5″ (60 AU) spatial resolution. Different parameterizations of the H2CO abundance were compared to the observed visibilities, using either a characteristic temperature, a characteristic radius or a radial power law index to describe the H2CO chemistry. Similar models were applied to ALMA Science Verification data of C18O. In each scenario, χ2 minimization on the visibilities was used to determine the best-fit model in each scenario. Results: H2CO 303-202 was readily detected via imaging, while the weaker H2CO 322-221 and H2CO 321-220 lines required matched filter analysis to detect. H2CO is present throughout most of the gaseous disk, extending out to 550 AU. An apparent 50 AU inner radius of the H2CO emission is likely caused by an optically thick dust continuum. The H2CO radial intensity profile shows a peak at 100 AU and a secondary bump at 300 AU, suggesting increased production in the outer disk. In all modeling scenarios, fits to the H2CO data show an increased abundance in the outer disk. The overall best-fit H2CO model shows a factor of two enhancement beyond a radius of 270 ± 20 AU, with an inner abundance (relative to H2) of 2 - 5 × 10-12. The H2CO emitting region has a lower limit on the kinetic temperature of T> 20 K. The C18O modeling suggests an order of magnitude depletion of C18O in the outer disk and an abundance of 4 - 12 × 10-8 in the inner disk

  15. CONSTRAINTS ON THE LIFETIMES OF DISKS RESULTING FROM TIDALLY DESTROYED ROCKY PLANETARY BODIES

    International Nuclear Information System (INIS)

    Girven, J.; Gänsicke, B. T.; Marsh, T. R.; Brinkworth, C. S.; Hoard, D. W.; Farihi, J.; Koester, D.

    2012-01-01

    Spitzer IRAC observations of 15 metal-polluted white dwarfs reveal infrared excesses in the spectral energy distributions of HE 0110–5630, GD 61, and HE 1349–2305. All three of these stars have helium-dominated atmospheres, and their infrared emissions are consistent with warm dust produced by the tidal destruction of (minor) planetary bodies. This study brings the number of metal-polluted, helium and hydrogen atmosphere white dwarfs surveyed with IRAC to 53 and 38, respectively. It also nearly doubles the number of metal-polluted helium-rich white dwarfs found to have closely orbiting dust by Spitzer. From the increased statistics for both atmospheric types with circumstellar dust, we derive a typical disk lifetime of log [t disk (yr)] = 5.6 ± 1.1 (ranging from 3 × 10 4 to 5 × 10 6 yr). This assumes a relatively constant rate of accretion over the timescale where dust persists, which is uncertain. We find that the fraction of highly metal-polluted helium-rich white dwarfs that have an infrared excess detected by Spitzer is only 23%, compared to 48% for metal-polluted hydrogen-rich white dwarfs, and we conclude from this difference that the typical lifetime of dusty disks is somewhat shorter than the diffusion timescales of helium-rich white dwarf. We also find evidence for higher time-averaged accretion rates onto helium-rich stars compared to the instantaneous accretion rates onto hydrogen-rich stars; this is an indication that our picture of evolved star-planetary system interactions is incomplete. We discuss some speculative scenarios that can explain the observations.

  16. Erasing Data and Recycling of Optical Disks

    Directory of Open Access Journals (Sweden)

    T Fujita

    2007-03-01

    Full Text Available Optical disks, DVDs and CDs, are convenient recording media on which to safely store data for a long period of time. However, the complete data erasure from recorded media is also important for the security of the data. After erasure of data from optical disks, recycling the material is needed in order to recover the valuable components of the optical disks. Here, data erasure methods for optical disks are discussed in the view of material recycling. The main finding of the study is that the explosion of optical disks in water is a very suitable method for complete erasure of data on the disks as well as recycling of their materials.

  17. Astrophysical disks Collective and Stochastic Phenomena

    CERN Document Server

    Fridman, Alexei M; Kovalenko, Ilya G

    2006-01-01

    The book deals with collective and stochastic processes in astrophysical discs involving theory, observations, and the results of modelling. Among others, it examines the spiral-vortex structure in galactic and accretion disks , stochastic and ordered structures in the developed turbulence. It also describes sources of turbulence in the accretion disks, internal structure of disk in the vicinity of a black hole, numerical modelling of Be envelopes in binaries, gaseous disks in spiral galaxies with shock waves formation, observation of accretion disks in a binary system and mass distribution of luminous matter in disk galaxies. The editors adaptly brought together collective and stochastic phenomena in the modern field of astrophysical discs, their formation, structure, and evolution involving the methodology to deal with, the results of observation and modelling, thereby advancing the study in this important branch of astrophysics and benefiting Professional Researchers, Lecturers, and Graduate Students.

  18. MONOLITHIC DISK FOR THE FAST CHROMATOGRAPHIC SEPARATION

    Directory of Open Access Journals (Sweden)

    Nurul Hidayat Aprilita

    2010-06-01

    Full Text Available Poly(styrene/divinylbenzene (PS/DVB monolithic disk was prepared by in situ free-radical copolymerization of styrene and divinylbenzene in the presence of decanol and tetrahydrofuran as porogens. PS/DVB monolithic disks were produced in two different lengths 1.5 mm and 3 mm. The disks were used in reversed phase chromatography of proteins with 0.2 % trifuoroacetic acid (TFA and 0.2 % TFA in acetonitrile as mobile phase A and B, respectively. The effect of gradient rate, flow rate, temperature and disk length on the separation of proteins were also studied. PS/DVB monolithic disks allow the rapid separation of proteins in reversed phase chromatography. Keywords: monolithic disk, poly(styrene/divinylbenzene, proteins

  19. Grain surface chemistry in protoplanetary disks

    International Nuclear Information System (INIS)

    Reboussin, Laura

    2015-01-01

    Planetary formation occurs in the protoplanetary disks of gas and dust. Although dust represents only 1% of the total disk mass, it plays a fundamental role in disk chemical evolution since it acts as a catalyst for the formation of molecules. Understanding this chemistry is therefore essential to determine the initial conditions from which planets form. During my thesis, I studied grain-surface chemistry and its impact on the chemical evolution of molecular cloud, initial condition for disk formation, and protoplanetary disk. Thanks to numerical simulations, using the gas-grain code Nautilus, I showed the importance of diffusion reactions and gas-grain interactions for the abundances of gas-phase species. Model results combined with observations also showed the effects of the physical structure (in temperature, density, AV) on the molecular distribution in disks. (author)

  20. Wetting controlled phase transitions in two-dimensional systems of colloids

    DEFF Research Database (Denmark)

    Gil, Tamir; Ipsen, John Hjorth; Tejero, T.F.

    1998-01-01

    The phase behavior of disk colloids, embedded in a two-dimensional fluid matrix that undergoes a first-order phase transition, is studied in the complete wetting regime where the thermodynamically metastable fluid phase is stabilized at the surface of the disks. In dilute collections of disks......, the tendency to minimize the extent of the fluid-fluid interface and the extent of the unfavorable wetting phase in the system gives rise to aggregation phenomena and to separation of large domains of disks that have the characteristics of bulk colloidal phases. The conditions for phase transitions among...... cluster gas, liquid, and solid phases of the disk colloids are determined from the corresponding values of the disk chemical potential within an analytic representation of the grand partition function for the excess energy associated with a gas of disk clusters in the low-disk-density limit. The wetting...

  1. ON THE FORMATION OF GALACTIC THICK DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Minchev, I.; Streich, D.; Scannapieco, C.; De Jong, R. S.; Steinmetz, M. [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Martig, M. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)

    2015-05-01

    Recent spectroscopic observations in the Milky Way suggest that the chemically defined thick disk (stars that have high [α/Fe] ratios and are thus old) has a significantly smaller scale-length than the thin disk. This is in apparent contradiction with observations of external edge-on galaxies, where the thin and thick components have comparable scale-lengths. Moreover, while observed disks do not flare (scale-height does not increase with radius), numerical simulations suggest that disk flaring is unavoidable, resulting from both environmental effects and secular evolution. Here we address these problems by studying two different suites of simulated galactic disks formed in the cosmological context. We show that the scale-heights of coeval populations always increase with radius. However, the total population can be decomposed morphologically into thin and thick disks, which do not flare. We relate this to the disk inside-out formation, where younger populations have increasingly larger scale-lengths and flare at progressively larger radii. In this new picture, thick disks are composed of the imbedded flares of mono-age stellar populations. Assuming that disks form inside out, we predict that morphologically defined thick disks must show a decrease in age (or [α/Fe] ratios) with radius and that coeval populations should always flare. This also explains the observed inversion in the metallicity and [α/Fe] gradients for stars away from the disk midplane in the Milky Way. The results of this work are directly linked to, and can be seen as evidence of, inside-out disk growth.

  2. Theory of Disk Accretion onto Magnetic Stars

    Directory of Open Access Journals (Sweden)

    Lai Dong

    2014-01-01

    Full Text Available Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields, white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron star and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.

  3. Simple Analytic Collisional Rates for non-LTE Vibrational Populations in Astrophysical Environments: the Cases of Circumstellar SiO Masers and Shocked H2

    Science.gov (United States)

    Bieniek, Ronald

    2008-05-01

    Rates for collisionally induced transitions between molecular vibrational levels are important in modeling a variety of non-LTE processes in astrophysical environments. Two examples are SiO masering in circumstellar envelopes in certain late-type stars [1] and the vibrational populations of molecular hydrogen in shocked interstellar medium [cf 2]. A simple exponential-potential model of molecular collisions leads to a two-parameter analytic expression for state-to-state and thermally averaged rates for collisionally induced vibrational-translational (VT) transitions in diatomic molecules [3,4]. The thermally averaged rates predicted by this formula have been shown to be in excellent numerical agreement with absolute experimental and quantum mechanical rates over large temperature ranges and initial vibrational excitation levels in a variety of species, e.g., OH, O2, N2 [3] and even for the rate of H2(v=1)+H2, which changes by five orders of magnitude in the temperature range 50-2000 K [4]. Analogous analytic rates will be reported for vibrational transitions in SiO due to collisions with H2 and compared to the numerical fit of quantum-mechanical rates calculated by Bieniek and Green [5]. [1] Palov, A.P., Gray, M.D., Field, D., & Balint-Kurti, G.G. 2006, ApJ, 639, 204. [2] Flower, D. 2007, Molecular Collisions in the Interstellar Medium (Cambridge: Cambridge Univ. Press) [3] Bieniek, R.J. & Lipson, S.J. 1996, Chem. Phys. Lett. 263, 276. [4] Bieniek, R.J. 2006, Proc. NASA LAW (Lab. Astrophys. Workshop) 2006, 299; http://www.physics.unlv.edu/labastro/nasalaw2006proceedings.pdf. [5] Bieniek, R.J., & Green, S. 1983, ApJ, 265, L29 and 1983, ApJ, 270, L101.

  4. PLANET-PLANET SCATTERING IN PLANETESIMAL DISKS

    International Nuclear Information System (INIS)

    Raymond, Sean N.; Armitage, Philip J.; Gorelick, Noel

    2009-01-01

    We study the final architecture of planetary systems that evolve under the combined effects of planet-planet and planetesimal scattering. Using N-body simulations we investigate the dynamics of marginally unstable systems of gas and ice giants both in isolation and when the planets form interior to a planetesimal belt. The unstable isolated systems evolve under planet-planet scattering to yield an eccentricity distribution that matches that observed for extrasolar planets. When planetesimals are included the outcome depends upon the total mass of the planets. For M tot ∼> 1 M J the final eccentricity distribution remains broad, whereas for M tot ∼ J a combination of divergent orbital evolution and recircularization of scattered planets results in a preponderance of nearly circular final orbits. We also study the fate of marginally stable multiple planet systems in the presence of planetesimal disks, and find that for high planet masses the majority of such systems evolve into resonance. A significant fraction leads to resonant chains that are planetary analogs of Jupiter's Galilean satellites. We predict that a transition from eccentric to near-circular orbits will be observed once extrasolar planet surveys detect sub-Jovian mass planets at orbital radii of a ≅ 5-10 AU.

  5. Contribution to the pathogenesis of slipped disk

    International Nuclear Information System (INIS)

    Kohlbach, W.

    1981-01-01

    The article describes the various types of slipped disk, such as spondylolisthesis, pseudo-spondylolisthesis and retrolisthesis, and their widely different basic features of anatomic pathology. (orig.) [de

  6. Probing local density inhomogeneities in the circumstellar disk of a Be star using the new spectro-astrometry mode at the Keck interferometer

    OpenAIRE

    Pott, J. -U.; Woillez, J.; Ragland, S.; Wizinowich, P. L.; Eisner, J. A.; Monnier, J. D.; Akeson, R. L.; Ghez, A. M.; Graham, J. R.; Hillenbrand, L. A.; Millan-Gabet, R.; Appleby, E.; Berkey, B.; Colavita, M. M.; Cooper, A.

    2010-01-01

    We report on the successful science verification phase of a new observing mode at the Keck interferometer, which provides a line-spread function width and sampling of 150km/s at K'-band, at a current limiting magnitude of K'~7mag with spatial resolution of lam/2B ~2.7mas and a measured differential phase stability of unprecedented precision (3mrad at K=5mag, which represents 3uas on sky or a centroiding precision of 10^-3). The scientific potential of this mode is demonstrated by the presente...

  7. The Stability of Galaxy Disks

    Science.gov (United States)

    Westfall, K. B.; Andersen, D. R.; Bershady, M. A.; Martinsson, T. P. K.; Swaters, R. A.; Verheijen, M. A. W.

    2014-03-01

    We calculate the stellar surface mass density (Σ*) and two-component (gas+stars) disk stability (QRW) for 25 late-type galaxies from the DiskMass Survey. These calculations are based on fits of a dynamical model to our ionized-gas and stellar kinematic data performed using a Markov Chain Monte Carlo sampling of the Bayesian posterior. Marginalizing over all galaxies, we find a median value of QRW = 2.0±0.9 at 1.5 scale lengths. We also find that QRW is anti-correlated with the star-formation rate surface density (Σ*), which can be predicted using a closed set of empirical scaling relations. Finally, we find that the star-formation efficiency (Σ*/Σg) is correlated with Σ* and weakly anti-correlated with QRW. The former is consistent with an equilibrium prediction of Σ*/Σg ∝ Σ*1/2. Despite its order-of-magnitude range, we find no correlation of Σ*/ΣgΣ*1/2 with any other physical quantity derived by our study.

  8. Hard disks with SCSI interface

    CERN Document Server

    Denisov, O Yu

    1999-01-01

    The testing of 20 models of hard SCSI-disks is carried out: the Fujitsu MAE3091LP; the IBM DDRS-39130, DGHS-318220, DNES-318350, DRHS-36V and DRVS-18V; the Quantum Atlas VI 18.2; the Viking 11 9.1; the Seagate ST118202LW, ST118273LW, ST118273W, ST318203LW, ST318275LW, ST34520W, ST39140LW and ST39173W; and the Western Digital WDE9100-0007, WDE9100-AV0016, WDE9100-AV0030 and WDE9180-0048. All tests ran under the Windows NT 4.0 workstation operating system with Service Pack 4, under video mode with 1024*768 pixel resolution, 32- bit colour depth and V-frequency equal to 85 Hz. The detailed description and characteristics of SCSI stores are presented. Test results (ZD Winstone 99 and ZD WinBench 99 tests) are given in both table and diagram (disk transfer rate) forms. (0 refs).

  9. The VLA view of the HL Tau Disk - Disk Mass, Grain Evolution, and Early Planet Formation

    OpenAIRE

    Carrasco-Gonzalez, Carlos; Henning, Thomas; Chandler, Claire J.; Linz, Hendrik; Perez, Laura; Rodriguez, Luis F.; Galvan-Madrid, Roberto; Anglada, Guillem; Birnstiel, Til; van Boekel, Roy; Flock, Mario; Klahr, Hubert; Macias, Enrique; Menten, Karl; Osorio, Mayra

    2016-01-01

    The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk-planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expec...

  10. Nearby Supernova Factory Observations of SN 2005gj: Another TypeIa Supernova in a Massive Circumstellar Envelope

    Energy Technology Data Exchange (ETDEWEB)

    Aldering, G.; Antilogus, P.; Bailey, S.; Baltay, C.; Bauer, A.; Blanc, N.; Bongard, S.; Copin, Y.; Gangler, E.; Gilles, S.; Kessler, R.; Kocevski, D.; Lee, B.C.; Loken, S.; Nugent, P.; Pain, R.; Pecontal, E.; Pereira, R.; Perlmutter, S.; Rabinowitz, D.; Rigaudier, G.; Scalzo, R.; Smadja, G.; Thomas, R.C.; Wang, L.; Weaver, B.A.; Rabinowitz, D.; Bauer, A.

    2006-06-01

    We report the independent discovery and follow-up observations of supernova 2005gj by the Nearby Supernova Factory. This is the second confirmed case of a ''hybrid'' Type Ia/IIn supernova, which like the prototype SN 2002ic, we interpret as the explosion of a white dwarf interacting with a circumstellar medium. Our early-phase photometry of SN 2005gj shows that the strength of the interaction between the supernova ejecta and circumstellar material is much stronger than for SN 2002ic. Our .rst spectrum shows a hot continuum with broad and narrow H{alpha} emission. Later spectra, spanning over 4 months from outburst, show clear Type Ia features combined with broad and narrow H{gamma}, H{beta},H{alpha} and He I {lambda}{lambda}5876,7065 in emission. At higher resolution, P Cygni profiles are apparent. Surprisingly, we also observe an inverted P Cygni profile for [O III] {lambda}5007. We find that the lightcurve and measured velocity of the unshocked circumstellar material imply mass loss as recently as 8 years ago. This is in contrast to SN 2002ic, for which an inner cavity in the circumstellar material was inferred. Within the context of the thin-shell approximation, the early lightcurve is well-described by a flat radial density profile for the circumstellar material. However, our decomposition of the spectra into Type Ia and shock emission components allows for little obscuration of the supernova, suggesting an aspherical or clumpy distribution for the circumstellar material. We suggest that the emission line velocity profiles arise from electron scattering rather than the kinematics of the shock. This is supported by the inferred high densities, and the lack of evidence for evolution in the line widths. Ground- and space-based photometry, and Keck spectroscopy, of the host galaxy are used to ascertain that the host galaxy has low metallicity (Z/Z{sub {circle_dot}} < 0.3; 95% confidence) and that this galaxy is undergoing a significant star

  11. ExPo: A Sensitive Imaging Polarimeter for Observations of Scattered Light from Circumstellar Environments

    NARCIS (Netherlands)

    Rodenhuis, M.

    2011-01-01

    In astronomy, high-contrast imaging is a rapidly developing field focussing on the observation of faint targets in close proximity to very bright ones. This can be applied to the direct observation of exoplanets, but also for observations of disks or dust shells surrounding stars. The brightness of

  12. Scaling Ratios and Triangles in Siegel Disks

    DEFF Research Database (Denmark)

    Buff, Xavier; Henriksen, Christian

    1999-01-01

    Let f(z)=e^{2i\\pi \\theta} + z^2, where \\theta is a quadratic irrational. McMullen proved that the Siegel disk for f is self-similar about the critical point, and we show that if \\theta = (\\sqrt{5}-1)/2 is the golden mean, then there exists a triangle contained in the Siegel disk, and with one...

  13. A PRIMER ON UNIFYING DEBRIS DISK MORPHOLOGIES

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Eve J.; Chiang, Eugene, E-mail: evelee@berkeley.edu, E-mail: echiang@astro.berkeley.edu [Department of Astronomy, University of California Berkeley, Berkeley, CA 94720-3411 (United States)

    2016-08-20

    A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

  14. A PRIMER ON UNIFYING DEBRIS DISK MORPHOLOGIES

    International Nuclear Information System (INIS)

    Lee, Eve J.; Chiang, Eugene

    2016-01-01

    A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

  15. A Primer on Unifying Debris Disk Morphologies

    Science.gov (United States)

    Lee, Eve J.; Chiang, Eugene

    2016-08-01

    A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

  16. Protoplanetary disks and exoplanets in scattered light

    NARCIS (Netherlands)

    Stolker, T.

    2017-01-01

    High-contrast imaging facilitates the direct detection of protoplanetary disks in scattered light and self-luminous exoplanets on long-period orbits. The combined power of extreme adaptive optics and differential imaging techniques delivers high spatial resolution images of disk morphologies down to

  17. 10 MB disk platter from CDC 7638

    CERN Multimedia

    1974-01-01

    This magnetic disk was one of three which interfaced with various Control Data machines. This single platter came from a Control Data 7638 Disk Storage Subsystem and could contain up to 10MB - about the size of a few MP4's on your iPod.

  18. Recent development of disk lasers at TRUMPF

    Science.gov (United States)

    Schad, Sven-Silvius; Gottwald, Tina; Kuhn, Vincent; Ackermann, Matthias; Bauer, Dominik; Scharun, Michael; Killi, Alexander

    2016-03-01

    The disk laser is one of the most important laser concepts for today's industrial laser market. Offering high brilliance at low cost, high optical efficiency and great application flexibility the disk laser paved the way for many industrial laser applications. Over the past years power and brightness increased and the disk laser turned out to be a very versatile laser source, not only for welding but also for cutting. Both, the quality and speed of cutting are superior to CO2-based lasers for a vast majority of metals, and, most important, in a broad thickness range. In addition, due to the insensitivity against back reflections the disk laser is well suited for cutting highly reflective metal such as brass or copper. These advantages facilitate versatile cutting machines and explain the high and growing demand for disk lasers for applications besides welding applications that can be observed today. From a today's perspective the disk principle has not reached any fundamental limits regarding output power per disk or beam quality, and offers numerous advantages over other high power resonator concepts, especially over fiber lasers or direct diode lasers. This paper will give insight in the latest progress in kilowatt class cw disk laser technology at TRUMPF and will discuss recent power scaling results as well.

  19. Critical state in disk-shaped superconductors

    Science.gov (United States)

    Däumling, M.; Larbalestier, D. C.

    1989-11-01

    We have calculated the magnetic fields and currents occurring in a disk-shaped superconductor (radius >>thickness) in the critical state in a self-consistent way using finite-element analysis. We find that the field shielded (or trapped) in the center of the disk is roughly equal to Jcd, where d is the thickness of the disk. The shielding currents also create radial fields which are or order Jcd/2 on the disk surface. For low applied fields Happltelsa applied field. The field dependence of the calculated magnetic moment in the self-field dominated regime is independent of whether Jc is weakly or strongly (~1/H) dependent on field. The calculations were validated by comparison to both magnetic and resistive measurements on a disk-shaped section in Nb3Sn tape.

  20. Time Domain Astrochemistry in Protoplanetary Disks

    Science.gov (United States)

    Cleeves, Lauren Ilsedore

    2018-01-01

    The chemistry of protoplanetary disks sets the initial composition of newly formed planets and may regulate the efficiency by which planets form. Disk chemical abundances typically evolve over timescales spanning thousands if not millions of years. Consequently, it was a surprise when ALMA observations taken over the course of a single year showed significantly variable emission in H13CO+ relative to the otherwise constant thermal dust emission in the IM Lup protoplanetary disk. HCO+ is a known X-ray sensitive molecule, and by using simple time-evolving chemical models including stellar activity, we demonstrate that stellar X-ray flares are a viable explanation for the observed H13CO+ variability. If this link between chemistry and stellar activity is confirmed, simultaneous observations can provide a new tool to measure (and potentially map) fundamental disk parameters, such as electron density, as the light from X-ray flares propagates across the disk.

  1. Observational constraints on black hole accretion disks

    Science.gov (United States)

    Liang, Edison P.

    1994-01-01

    We review the empirical constraints on accretion disk models of stellar-mass black holes based on recent multiwavelength observational results. In addition to time-averaged emission spectra, the time evolutions of the intensity and spectrum provide critical information about the structure, stability, and dynamics of the disk. Using the basic thermal Keplerian disk paradigm, we consider in particular generalizations of the standard optically thin disk models needed to accommodate the extremely rich variety of dynamical phenomena exhibited by black hole candidates ranging from flares of electron-positron annihilations and quasiperiodic oscillations in the X-ray intensity to X-ray novae activity. These in turn provide probes of the disk structure and global geometry. The goal is to construct a single unified framework to interpret a large variety of black hole phenomena. This paper will concentrate on the interface between basic theory and observational data modeling.

  2. Continuum Reverberation Mapping of AGN Accretion Disks

    Energy Technology Data Exchange (ETDEWEB)

    Fausnaugh, Michael M. [Department of Astronomy, Ohio State University, Columbus, OH (United States); MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA (United States); Peterson, Bradley M. [Department of Astronomy, Ohio State University, Columbus, OH (United States); Center for Cosmology and AstroParticle Physics, Ohio State University, Columbus, OH (United States); Space Telescope Science Institute, Baltimore, MD (United States); Starkey, David A. [SUPA Physics and Astronomy, University of St. Andrews, Scotland (United Kingdom); Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL (United States); Horne, Keith, E-mail: faus@mit.edu [SUPA Physics and Astronomy, University of St. Andrews, Scotland (United Kingdom); Collaboration: the AGN STORM Collaboration

    2017-12-05

    We show recent detections of inter-band continuum lags in three AGN (NGC 5548, NGC 2617, and MCG+08-11-011), which provide new constraints on the temperature profiles and absolute sizes of the accretion disks. We find lags larger than would be predicted for standard geometrically thin, optically thick accretion disks by factors of 2.3–3.3. For NGC 5548, the data span UV through optical/near-IR wavelengths, and we are able to discern a steeper temperature profile than the T ~ R{sup −3/4} expected for a standard thin disk. Using a physical model, we are also able to estimate the inclinations of the disks for two objects. These results are similar to those found from gravitational microlensing of strongly lensed quasars, and provide a complementary approach for investigating the accretion disk structure in local, low luminosity AGN.

  3. Disk Evolution and the Fate of Water

    Science.gov (United States)

    Hartmann, Lee; Ciesla, Fred; Gressel, Oliver; Alexander, Richard

    2017-10-01

    We review the general theoretical concepts and observational constraints on the distribution and evolution of water vapor and ice in protoplanetary disks, with a focus on the Solar System. Water is expected to freeze out at distances greater than 1-3 AU from solar-type central stars; more precise estimates are difficult to obtain due to uncertainties in the complex processes involved in disk evolution, including dust growth, settling, and radial drift, and the level of turbulence and viscous dissipation within disks. Interferometric observations are now providing constraints on the positions of CO snow lines, but extrapolation to the unresolved regions where water ice sublimates will require much better theoretical understanding of mass and angular momentum transport in disks as well as more refined comparison of observations with sophisticated disk models.

  4. Development of Powered Disk Type Sugar Cane Stubble Saver

    Directory of Open Access Journals (Sweden)

    Radite P.A.S.

    2009-04-01

    Full Text Available The objective of this research was to design, fabricate and test a prototype of sugar cane stubble saver based on powered disk mechanism. In this research, a heavy duty disk plow or disk harrow was used as a rotating knife to cut the sugarcane stubble. The parabolic disk was chosen because it is proven reliable as soil working tools and it is available in the market as spare part of disk plow or disk harrow unit. The prototype was mounted on the four wheel tractor’s three point hitch, and powered by PTO of the tractor. Two kinds of disks were used in these experiments, those were disk with regular edge or plain disk and disk with scalloped edge or scalloped disk. Both disks had diameter of 28 inch. Results of field test showed that powered disk mechanism could satisfy cut sugar cane’s stubble. However, scalloped disk type gave smoother stubble cuts compared to that of plain disk. Plain disk type gave broken stubble cut. Higher rotation (1000 rpm resulted better cuts as compared to lower rotation (500 rpm both either on plain disk and scalloped disk. The developed prototype could work below the soil surface at depth of 5 to 10 cm. With tilt angle setting 20O and disk angle 45O the width of cut was about 25 cm.

  5. THE DARK DISK OF THE MILKY WAY

    International Nuclear Information System (INIS)

    Purcell, Chris W.; Bullock, James S.; Kaplinghat, Manoj

    2009-01-01

    Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter in disk-like configurations that co-rotate with the galaxy. This phenomenon has potentially dramatic consequences for dark matter detection experiments. We utilize focused, high-resolution simulations of accretion events onto disks designed to be Galaxy analogues, and compare the resultant disks to the morphological and kinematic properties of the Milky Way's thick disk in order to bracket the range of co-rotating accreted dark matter. In agreement with previous results, we find that the Milky Way's merger history must have been unusually quiescent compared to median Λ cold dark matter expectations and, therefore, its dark disk must be relatively small: the fraction of accreted dark disk material near the Sun is about 20% of the host halo density or smaller and the co-rotating dark matter fraction near the Sun, defined as particles moving with a rotational velocity lag less than 50 km s -1 , is enhanced by about 30% or less compared to a standard halo model. Such a dark disk could contribute dominantly to the low energy (of order keV for a dark matter particle with mass 100 GeV) nuclear recoil event rate of direct detection experiments, but it will not change the likelihood of detection significantly. These dark disks provide testable predictions of weakly interacting massive particle dark matter models and should be considered in detailed comparisons to experimental data. Our findings suggest that the dark disk of the Milky Way may provide a detectable signal for indirect detection experiments, contributing up to about 25% of the dark matter self-annihilation signal in the direction of the center of the Galaxy, lending the signal a noticeably oblate morphology.

  6. Improving the Friction Durability of Magnetic Head-Disk Interfaces by Thin Lubricant Films

    Directory of Open Access Journals (Sweden)

    Shojiro Miyake

    2016-01-01

    Full Text Available Nanowear and viscoelasticity were evaluated to study the nanotribological properties of lubricant films of Z-tetraol, D-4OH, and A20H, including their retention and replenishment properties. For A20H and thick Z-tetraol-coated disks, the disk surface partially protrudes, and the phase lag (tan⁡δ increases with friction. This result is consistent with replenishment of the lubricant upon tip sliding. For the D-4OH-coated disk, the tan⁡δ value decreases with tip sliding, similar to the case for the unlubricated disk. The durability of the lubricant-coated magnetic disks was then evaluated by load increase and decrease friction tests. The friction force of the unlubricated disk rapidly increases after approximately 30 reciprocating cycles, regardless of the load. The lubrication state can be estimated by mapping the dependence of friction coefficient on the reciprocating cycle number and load. The friction coefficient can be classified into one of four areas. The lowest friction area constitutes fluid lubrication. The second area constitutes the transition to mixed lubrication. The third area constitutes boundary lubrication. The highest friction of the fourth area results from surface fracture. The boundary lubricating area of the A20H lubricant was wide, because of its good retention and replenishment properties.

  7. Gas Cavities inside Dust Cavities in Disks Inferred from ALMA Observations

    Science.gov (United States)

    van der Marel, Nienke; van Dishoeck, Ewine F.; Bruderer, Simon; Pinilla, Paola; van Kempen, Tim; Perez, Laura; Isella, Andrea

    2016-01-01

    Protoplanetary disks with cavities in their dust distribution, also named transitional disks, are expected to be in the middle of active evolution and possibly planet formation. In recent years, millimeter-dust rings observed by ALMA have been suggested to have their origin in dust traps, caused by pressure bumps. One of the ways to generate these is by the presence of planets, which lower the gas density along their orbit and create pressure bumps at the edge. We present spatially resolved ALMA Cycle 0 and Cycle 1 observations of CO and CO isotopologues of several famous transitional disks. Gas is found to be present inside the dust cavities, but at a reduced level compared with the gas surface density profile of the outer disk. The dust and gas emission are quantified using the physical-chemical modeling code DALI. In the majority of these disks we find clear evidence for a drop in gas density of at least a factor of 10 inside the cavity, whereas the dust density drops by at least a factor 1000. The CO isotopologue observations reveal that the gas cavities are significantly smaller than the dust cavities. These gas structures suggest clearing by one or more planetary-mass companions.

  8. The Taurus Boundary of Stellar/Substellar (TBOSS) Survey. II. Disk Masses from ALMA Continuum Observations

    Science.gov (United States)

    Ward-Duong, K.; Patience, J.; Bulger, J.; van der Plas, G.; Ménard, F.; Pinte, C.; Jackson, A. P.; Bryden, G.; Turner, N. J.; Harvey, P.; Hales, A.; De Rosa, R. J.

    2018-02-01

    We report 885 μm ALMA continuum flux densities for 24 Taurus members spanning the stellar/substellar boundary with spectral types from M4 to M7.75. Of the 24 systems, 22 are detected at levels ranging from 1.0 to 55.7 mJy. The two nondetections are transition disks, though other transition disks in the sample are detected. Converting ALMA continuum measurements to masses using standard scaling laws and radiative transfer modeling yields dust mass estimates ranging from ∼0.3 to 20 M ⊕. The dust mass shows a declining trend with central object mass when combined with results from submillimeter surveys of more massive Taurus members. The substellar disks appear as part of a continuous sequence and not a distinct population. Compared to older Upper Sco members with similar masses across the substellar limit, the Taurus disks are brighter and more massive. Both Taurus and Upper Sco populations are consistent with an approximately linear relationship in M dust to M star, although derived power-law slopes depend strongly upon choices of stellar evolutionary model and dust temperature relation. The median disk around early-M stars in Taurus contains a comparable amount of mass in small solids as the average amount of heavy elements in Kepler planetary systems on short-period orbits around M-dwarf stars, with an order of magnitude spread in disk dust mass about the median value. Assuming a gas-to-dust ratio of 100:1, only a small number of low-mass stars and brown dwarfs have a total disk mass amenable to giant planet formation, consistent with the low frequency of giant planets orbiting M dwarfs.

  9. Disk Masses around Solar-mass Stars are Underestimated by CO Observations

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Mo; Evans II, Neal J. [Astronomy Department, University of Texas, 2515 Speedway, Stop C1400, Austin, TX 78712 (United States); Dodson-Robinson, Sarah E. [University of Delaware, Department of Physics and Astronomy, 217 Sharp Lab, Newark, DE 19716 (United States); Willacy, Karen; Turner, Neal J. [Mail Stop 169-506, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

    2017-05-20

    Gas in protostellar disks provides the raw material for giant planet formation and controls the dynamics of the planetesimal-building dust grains. Accurate gas mass measurements help map the observed properties of planet-forming disks onto the formation environments of known exoplanets. Rare isotopologues of carbon monoxide (CO) have been used as gas mass tracers for disks in the Lupus star-forming region, with an assumed interstellar CO/H{sub 2} abundance ratio. Unfortunately, observations of T-Tauri disks show that CO abundance is not interstellar, a finding reproduced by models that show CO abundance decreasing both with distance from the star and as a function of time. Here, we present radiative transfer simulations that assess the accuracy of CO-based disk mass measurements. We find that the combination of CO chemical depletion in the outer disk and optically thick emission from the inner disk leads observers to underestimate gas mass by more than an order of magnitude if they use the standard assumptions of interstellar CO/H{sub 2} ratio and optically thin emission. Furthermore, CO abundance changes on million-year timescales, introducing an age/mass degeneracy into observations. To reach a factor of a few accuracy for CO-based disk mass measurements, we suggest that observers and modelers adopt the following strategies: (1) select low- J transitions; (2) observe multiple CO isotopologues and use either intensity ratios or normalized line profiles to diagnose CO chemical depletion; and (3) use spatially resolved observations to measure the CO-abundance distribution.

  10. SUPERNOVA PTF 09UJ: A POSSIBLE SHOCK BREAKOUT FROM A DENSE CIRCUMSTELLAR WIND

    International Nuclear Information System (INIS)

    Ofek, E. O.; Neill, J. D.; Kulkarni, S. R.; Forster, K.; Kasliwal, M. M.; Law, N.; Martin, C.; Quimby, R. M.; Rabinak, I.; Arcavi, I.; Waxman, E.; Gal-Yam, A.; Cenko, S. B.; Bloom, J. S.; Filippenko, A. V.; Poznanski, D.; Nugent, P. E.; Jacobsen, J.; Bildsten, L.; Howell, D. A.

    2010-01-01

    Type-IIn supernovae (SNe IIn), which are characterized by strong interaction of their ejecta with the surrounding circumstellar matter (CSM), provide a unique opportunity to study the mass-loss history of massive stars shortly before their explosive death. We present the discovery and follow-up observations of an SN IIn, PTF 09uj, detected by the Palomar Transient Factory (PTF). Serendipitous observations by Galaxy Evolution Explorer (GALEX) at ultraviolet (UV) wavelengths detected the rise of the SN light curve prior to the PTF discovery. The UV light curve of the SN rose fast, with a timescale of a few days, to a UV absolute AB magnitude of about -19.5. Modeling our observations, we suggest that the fast rise of the UV light curve is due to the breakout of the SN shock through the dense CSM (n ∼ 10 10 cm -3 ). Furthermore, we find that prior to the explosion the progenitor went through a phase of high mass-loss rate (∼0.1 M sun yr -1 ) that lasted for a few years. The decay rate of this SN was fast relative to that of other SNe IIn.

  11. EXTINCTION LAWS TOWARD STELLAR SOURCES WITHIN A DUSTY CIRCUMSTELLAR MEDIUM AND IMPLICATIONS FOR TYPE IA SUPERNOVAE

    International Nuclear Information System (INIS)

    Nagao, Takashi; Maeda, Keiichi; Nozawa, Takaya

    2016-01-01

    Many astronomical objects are surrounded by dusty environments. In such dusty objects, multiple scattering processes of photons by circumstellar (CS) dust grains can effectively alter extinction properties. In this paper, we systematically investigate the effects of multiple scattering on extinction laws for steady-emission sources surrounded by the dusty CS medium using a radiation transfer simulation based on the Monte Carlo technique. In particular, we focus on whether and how the extinction properties are affected by properties of CS dust grains by adopting various dust grain models. We confirm that behaviors of the (effective) extinction laws are highly dependent on the properties of CS grains, especially the total-to-selective extinction ratio R V , which characterizes the extinction law and can be either increased or decreased and compared with the case without multiple scattering. We find that the criterion for this behavior is given by a ratio of albedos in the B and V bands. We also find that either small silicate grains or polycyclic aromatic hydrocarbons are necessary for realizing a low value of R V as often measured toward SNe Ia if the multiple scattering by CS dust is responsible for their non-standard extinction laws. Using the derived relations between the properties of dust grains and the resulting effective extinction laws, we propose that the extinction laws toward dusty objects could be used to constrain the properties of dust grains in CS environments.

  12. EXTINCTION LAWS TOWARD STELLAR SOURCES WITHIN A DUSTY CIRCUMSTELLAR MEDIUM AND IMPLICATIONS FOR TYPE IA SUPERNOVAE

    Energy Technology Data Exchange (ETDEWEB)

    Nagao, Takashi; Maeda, Keiichi [Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Nozawa, Takaya, E-mail: nagao@kusastro.kyoto-u.ac.jp [National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2016-06-01

    Many astronomical objects are surrounded by dusty environments. In such dusty objects, multiple scattering processes of photons by circumstellar (CS) dust grains can effectively alter extinction properties. In this paper, we systematically investigate the effects of multiple scattering on extinction laws for steady-emission sources surrounded by the dusty CS medium using a radiation transfer simulation based on the Monte Carlo technique. In particular, we focus on whether and how the extinction properties are affected by properties of CS dust grains by adopting various dust grain models. We confirm that behaviors of the (effective) extinction laws are highly dependent on the properties of CS grains, especially the total-to-selective extinction ratio R{sub V}, which characterizes the extinction law and can be either increased or decreased and compared with the case without multiple scattering. We find that the criterion for this behavior is given by a ratio of albedos in the B and V bands. We also find that either small silicate grains or polycyclic aromatic hydrocarbons are necessary for realizing a low value of R{sub V} as often measured toward SNe Ia if the multiple scattering by CS dust is responsible for their non-standard extinction laws. Using the derived relations between the properties of dust grains and the resulting effective extinction laws, we propose that the extinction laws toward dusty objects could be used to constrain the properties of dust grains in CS environments.

  13. The close circumstellar environment of Betelgeuse. III. SPHERE/ZIMPOL imaging polarimetry in the visible

    Science.gov (United States)

    Kervella, P.; Lagadec, E.; Montargès, M.; Ridgway, S. T.; Chiavassa, A.; Haubois, X.; Schmid, H.-M.; Langlois, M.; Gallenne, A.; Perrin, G.

    2016-01-01

    The physical mechanism through which the outgoing material of massive red supergiants is accelerated above the escape velocity is unclear. Thanks to the transparency of its circumstellar envelope, the nearby red supergiant Betelgeuse gives the opportunity to probe the innermost layers of the envelope of a typical red supergiant down to the photosphere, I.e. where the acceleration of the wind is expected to occur. We took advantage of the SPHERE/ZIMPOL adaptive optics imaging polarimeter to resolve the visible photosphere and close envelope of Betelgeuse. We detect an asymmetric gaseous envelope inside a radius of 2 to 3 times the near-infrared photospheric radius of the star (R⋆), and a significant Hα emission mostly contained within 3 R⋆. From the polarimetric signal, we also identify the signature of dust scattering in an asymmetric and incomplete dust shell located at a similar radius. The presence of dust so close to the star may have a significant impact on the wind acceleration through radiative pressure on the grains. The 3 R⋆ radius emerges as a major interface between the hot gaseous and dusty envelopes. The detected asymmetries strengthen previous indications that the mass loss of Betelgeuse is likely tied to the vigorous convective motions in its atmosphere. Based on observations made with ESO telescopes at Paranal Observatory, under ESO program 095.D-0309(E).

  14. The circumstellar shells and mass loss rates of four M supergiants

    Energy Technology Data Exchange (ETDEWEB)

    Bernat, A.P.

    1977-05-01

    A reanalysis of the physical structure of the circumstellar gas shells of four bright M supergiants, Betelgeuse, Antares, ..cap alpha.. Herculis, and ..mu.. Cephei, has been undertaken. The observational data include old Hale Observatories plates, recent McDonald Struve telescope plates, and McDonald 2.7 m photoelectric scans. These data are analyzed in the full expanding spherical geometry formulation of the radiative transfer equation.The results of the present analysis indicate that column densities in the gas shells must be revised downward compared with the previous plane-parallel results. However, the physical extents of the shells are considerably larger than previously assumed. These extents are inferred through ionization modeling, Weymann's Ca II technique, and direct observation. Also inferred are schematic wavelength-dependent chromospheric color temperatures. These results lead to much larger mass loss rates (in the range 6.7 x 10/sup -7/ to 4.2 x 10/sup -4/ M/sub sun/ yr/sup -2/) than previously inferred. The influence of these large rates of mass loss on the evolution of both stars and the Galaxy is briefly discussed.

  15. Pyrene synthesis in circumstellar envelopes and its role in the formation of 2D nanostructures

    Science.gov (United States)

    Zhao, Long; Kaiser, Ralf I.; Xu, Bo; Ablikim, Utuq; Ahmed, Musahid; Joshi, Dharati; Veber, Gregory; Fischer, Felix R.; Mebel, Alexander M.

    2018-03-01

    For the past decades, the hydrogen-abstraction/acetylene-addition (HACA) mechanism has been instrumental in attempting to untangle the origin of polycyclic aromatic hydrocarbons (PAHs) as identified in carbonaceous meteorites such as Allende and Murchison. However, the fundamental reaction mechanisms leading to the synthesis of PAHs beyond phenanthrene (C14H10) are still unknown. By exploring the reaction of the 4-phenanthrenyl radical (C14H9•) with acetylene (C2H2) under conditions prevalent in carbon-rich circumstellar environments, we show evidence of a facile, isomer-selective formation of pyrene (C16H10). Along with the hydrogen-abstraction/vinylacetylene-addition (HAVA) mechanism, molecular mass growth processes from pyrene may lead through systematic ring expansions not only to more complex PAHs, but ultimately to 2D graphene-type structures. These fundamental reaction mechanisms are crucial to facilitate an understanding of the origin and evolution of the molecular universe and, in particular, of carbon in our Galaxy.

  16. Strong late-time circumstellar interaction in the peculiar supernova iPTF14hls

    Science.gov (United States)

    Andrews, Jennifer E.; Smith, Nathan

    2018-03-01

    We present a moderate-resolution spectrum of the peculiar Type II supernova iPTF14hls taken on day 1153 after discovery. This spectrum reveals the clear signature of shock interaction with dense circumstellar material (CSM). We suggest that this CSM interaction may be an important clue for understanding the extremely unusual photometric and spectroscopic evolution seen over the first 600 days of iPTF14hls. The late-time spectrum shows a double-peaked intermediate-width Hα line indicative of expansion speeds around 1000 km s-1, with the double-peaked shape hinting at a disc-like geometry in the CSM. If the CSM was highly asymmetric, perhaps in a disc or torus that was ejected from the star 3-6 years prior to explosion, then the CSM interaction could have been overrun and hidden below the SN ejecta photosphere from a wide range of viewing angles. In that case, CSM interaction luminosity would have been thermalized well below the photosphere, potentially sustaining the high luminosity without exhibiting the traditional observational signatures of strong CSM interaction (narrow Hα emission and X-rays). Variations in density structure of the CSM could account for the multiple rebrightenings of the lightcurve. We propose that a canonical 1× 1051 erg explosion energy with enveloped CSM interaction as seen in some recent SNe, rather than an entirely new explosion mechanism, may be adequate to explain the peculiar evolution of iPTF14hls.

  17. Chondrules and the Protoplanetary Disk

    Science.gov (United States)

    Hewins, R. H.; Jones, Rhian; Scott, Ed

    2011-03-01

    Part I. Introduction: 1. Chondrules and the protoplanetary disk: An overview R. H. Hewins; Part. II. Chonrules, Ca-Al-Rich Inclusions and Protoplanetary Disks: 2. Astronomical observations of phenomena in protostellar disks L. Hartmann; 3. Overview of models of the solar nebula: potential chondrule-forming environments P. Cassen; 4. Large scale processes in the solar nebula A. P. Boss; 5. Turbulence, chondrules and planetisimals J. N. Cuzzi, A. R. Dobrovolskis and R. C. Hogan; 6. Chondrule formation: energetics and length scales J. T. Wasson; 7. Unresolved issues in the formation of chondrules and chondrites J. A. Wood; 8. Thermal processing in the solar nebula: constraints from refractory inclusions A. M. Davis and G. J. MacPherson; 9. Formation times of chondrules and Ca-Al-Rich inclusions: constraints from short-lived radionuclides T. D. Swindle, A. M. Davis, C. M. Hohenberg, G. J. MacPherson and L. E. Nyquist; 10. Formation of chondrules and chondrites in the protoplanetary nebula E. R. D. Scott, S. G. Love and A. N. Krot; Part III. Chondrule precursors and multiple melting: 11. Origin of refractory precursor components of chondrules K. Misawa and N. Nakamura; 12. Mass-independent isotopic effects in chondrites: the role of chemical processes M. H. Thiemens; 13. Agglomeratic chondrules: implications for the nature of chondrule precursors and formation by incomplete melting M. K. Weisberg and M. Prinz; 14. Constraints on chondrule precursors from experimental Data H. C. Connolly Jr. and R. H. Hewins; 15. Nature of matrix in unequilibrated chondrites and its possible relationship to chondrules A. J. Brearly; 16. Constraints on chondrite agglomeration from fine-grained chondrule Rims K. Metzler and A. Bischoff; 17. Relict grains in chondrules: evidence for chondrule recycling R. H. Jones; 18. Multiple heating of chondrules A. E. Rubin and A. N. Krot; 19. Microchondrule-bearing chondrule rims: constraints on chondrule formation A. N. Krot and A. E. Rubin; Part IV

  18. Hot Molecular Gas in the Circumnuclear Disk

    Science.gov (United States)

    Mills, Elisabeth A. C.; Togi, Aditya; Kaufman, Michael

    2017-12-01

    We present an analysis of archival Infrared Space Observatory observations of H2 for three 14\\prime\\prime × 20\\prime\\prime pointings in the central 3 pc of the Galaxy: toward the southwest region and northeast region of the Galactic center circumnuclear disk (CND), and toward the supermassive black hole Sgr A*. We detect pure rotational lines from 0-0 S(0) to S(13), as well as a number of rovibrationally excited transitions. Using the pure rotational lines, we perform both fits to a discrete temperature distribution (measuring up to three temperature components with T = 500-600 K, T = 1250-1350 K, and T > 2600 K) and fits to a continuous temperature distribution, assuming a power-law distribution of temperatures. We measure power-law indices of n = 3.22 for the northeast region and n = 2.83 for the southwest region. These indices are lower than those measured for other galaxies or other Galactic center clouds, indicating a larger fraction of gas at high temperatures. We also test whether extrapolating this temperature distribution can yield a reasonable estimate of the total molecular mass, as has been recently done for H2 observations in other galaxies. Extrapolating to a cutoff temperature of 50 K in the southwest (northeast) region, we would measure 32% (140%) of the total molecular gas mass inferred from the dust emission, and 26% (125%) of the total molecular gas mass inferred from the CO emission. Ultimately, the inconsistency of the masses inferred in this way suggests that a simple application of this method cannot yield a reliable estimate of the mass of the CND.

  19. Lunar and Meteorite Sample Disk for Educators

    Science.gov (United States)

    Foxworth, Suzanne; Luckey, M.; McInturff, B.; Allen, J.; Kascak, A.

    2015-01-01

    NASA Johnson Space Center (JSC) has the unique responsibility to curate NASA's extraterrestrial samples from past and future missions. Curation includes documentation, preservation, preparation and distribution of samples for research, education and public outreach. Between 1969 and 1972 six Apollo missions brought back 382 kilograms of lunar rocks, core and regolith samples, from the lunar surface. JSC also curates meteorites collected from a US cooperative effort among NASA, the National Science Foundation (NSF) and the Smithsonian Institution that funds expeditions to Antarctica. The meteorites that are collected include rocks from Moon, Mars, and many asteroids including Vesta. The sample disks for educational use include these different samples. Active relevant learning has always been important to teachers and the Lunar and Meteorite Sample Disk Program provides this active style of learning for students and the general public. The Lunar and Meteorite Sample Disks permit students to conduct investigations comparable to actual scientists. The Lunar Sample Disk contains 6 samples; Basalt, Breccia, Highland Regolith, Anorthosite, Mare Regolith and Orange Soil. The Meteorite Sample Disk contains 6 samples; Chondrite L3, Chondrite H5, Carbonaceous Chondrite, Basaltic Achondrite, Iron and Stony-Iron. Teachers are given different activities that adhere to their standards with the disks. During a Sample Disk Certification Workshop, teachers participate in the activities as students gain insight into the history, formation and geologic processes of the moon, asteroids and meteorites.

  20. Time-Dependent Variations of Accretion Disk

    Directory of Open Access Journals (Sweden)

    Hye-Weon Na

    1987-06-01

    Full Text Available In dward nova we assume the primary star as a white dwarf and the secondary as the late type star which filled Roche lobe. Mass flow from the secondary star leads to the formation of thin accretion disk around the white dwarf. We use the α parameter as viscosity to maintain the disk form and propose that the outburst in dwarf nova cause the steep increase of source term. With these assumptions we solve the basic equations of stellar structure using Newton-Raphson method. We show the physical parameters like temperature, density, pressure, opacity, surface density, height and flux to the radius of disk. Changing the value of α, we compare several parameters when mass flow rate is constant with those of when luminosity of disk is brightest. At the same time, we obtain time-dependent variations of luminosity and mass of disk. We propose the suitable range of α is 0.15-0.18 to the difference of luminosity. We compare several parameters of disk with those of the normal late type stars which have the same molecular weight of disk is lower. Maybe the outburst in dwarf nova is due to the variation of the α value instead of increment of mass flow from the secondary star.

  1. The CDF Run II disk inventory manager

    International Nuclear Information System (INIS)

    Hubbard, Paul; Lammel, Stephan

    2001-01-01

    The Collider Detector at Fermilab (CDF) experiment records and analyses proton-antiproton interactions at a center-of-mass energy of 2 TeV. Run II of the Fermilab Tevatron started in April of this year. The duration of the run is expected to be over two years. One of the main data handling strategies of CDF for Run II is to hide all tape access from the user and to facilitate sharing of data and thus disk space. A disk inventory manager was designed and developed over the past years to keep track of the data on disk, to coordinate user access to the data, and to stage data back from tape to disk as needed. The CDF Run II disk inventory manager consists of a server process, a user and administrator command line interfaces, and a library with the routines of the client API. Data are managed in filesets which are groups of one or more files. The system keeps track of user access to the filesets and attempts to keep frequently accessed data on disk. Data that are not on disk are automatically staged back from tape as needed. For CDF the main staging method is based on the mt-tools package as tapes are written according to the ANSI standard

  2. Latest advances in high brightness disk lasers

    Science.gov (United States)

    Kuhn, Vincent; Gottwald, Tina; Stolzenburg, Christian; Schad, Sven-Silvius; Killi, Alexander; Ryba, Tracey

    2015-02-01

    In the last decade diode pumped solid state lasers have become an important tool for many industrial materials processing applications. They combine ease of operation with efficiency, robustness and low cost. This paper will give insight in latest progress in disk laser technology ranging from kW-class CW-Lasers over frequency converted lasers to ultra-short pulsed lasers. The disk laser enables high beam quality at high average power and at high peak power at the same time. The power from a single disk was scaled from 1 kW around the year 2000 up to more than 10 kW nowadays. Recently was demonstrated more than 4 kW of average power from a single disk close to fundamental mode beam quality (M²=1.38). Coupling of multiple disks in a common resonator results in even higher power. As an example we show 20 kW extracted from two disks of a common resonator. The disk also reduces optical nonlinearities making it ideally suited for short and ultrashort pulsed lasers. In a joint project between TRUMPF and IFSW Stuttgart more than 1.3 kW of average power at ps pulse duration and exceptionally good beam quality was recently demonstrated. The extremely low saturated gain makes the disk laser ideal for internal frequency conversion. We show >1 kW average power and >6 kW peak power in multi ms pulsed regime from an internally frequency doubled disk laser emitting at 515 nm (green). Also external frequency conversion can be done efficiently with ns pulses. >500 W of average UV power was demonstrated.

  3. Magnetically Induced Disk Winds and Transport in the HL Tau Disk

    Energy Technology Data Exchange (ETDEWEB)

    Hasegawa, Yasuhiro; Flock, Mario; Turner, Neal J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Okuzumi, Satoshi, E-mail: yasuhiro@caltech.edu [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan)

    2017-08-10

    The mechanism of angular momentum transport in protoplanetary disks is fundamental to understanding the distributions of gas and dust in the disks. The unprecedented ALMA observations taken toward HL Tau at high spatial resolution and subsequent radiative transfer modeling reveal that a high degree of dust settling is currently achieved in the outer part of the HL Tau disk. Previous observations, however, suggest a high disk accretion rate onto the central star. This configuration is not necessarily intuitive in the framework of the conventional viscous disk model, since efficient accretion generally requires a high level of turbulence, which can suppress dust settling considerably. We develop a simplified, semi-analytical disk model to examine under what condition these two properties can be realized in a single model. Recent, non-ideal MHD simulations are utilized to realistically model the angular momentum transport both radially via MHD turbulence and vertically via magnetically induced disk winds. We find that the HL Tau disk configuration can be reproduced well when disk winds are properly taken into account. While the resulting disk properties are likely consistent with other observational results, such an ideal situation can be established only if the plasma β at the disk midplane is β {sub 0} ≃ 2 × 10{sup 4} under the assumption of steady accretion. Equivalently, the vertical magnetic flux at 100 au is about 0.2 mG. More detailed modeling is needed to fully identify the origin of the disk accretion and quantitatively examine plausible mechanisms behind the observed gap structures in the HL Tau disk.

  4. Patterns In Debris Disks: No Planets Required?

    Science.gov (United States)

    Kuchner, Marc

    2012-01-01

    Debris disks like those around Fomalhaut and Beta Pictoris show striking dust patterns often attributed to hidden exoplanets. These patterns have been crucial for constraining the masses and orbits of these planets. But adding a bit of gas to our models of debris disks--too little gas to detect--seems to alter this interpretation. Small amounts of gas lead to new dynamical instabilities that may mimic the narrow eccentric rings and other structures planets would create in a gas-free disk. Can we still use dust patterns to find hidden exoplanets?

  5. Growth of dust rims around chondrules in MHD-turbulent protoplanetary disks

    Science.gov (United States)

    Carballido, A.

    2009-12-01

    The accretion of dust onto chondrule-sized particles is modeled through magnetohydrodynamic (MHD) simulations of a protoplanetary disk. The observed dust rims around chondrules in meteorites, such as CM carbonaceous chondrites, have been suggested to form on the parent body by a combination of compaction and aqueous alteration of a generic enveloping matrix. However, a nebular origin of these rims seems to be favored in semi-analytical models, where turbulence drives the dynamics of dust sweep-up by chondrules. To assess the feasibility of this scenario, we model a small patch of a gaseous circumstellar disk. The patch is assumed to be located at an orbital radius of 3 AU , and is represented by a Cartesian box in which the equations of ideal MHD are solved. Turbulence is self-consistently generated by the action of the so-called magnetorotational instability, which is triggered by the effect of the disk differential rotation on magnetic field lines threading the disk. Fine-grained dust is modeled as a passive contaminant, with initial densities f0 equal to the gas density, and half this value. Turbulence quickly disperses the initial dust concentration, which acquires different equilibrium values depending on f0. These values can vary by as much as a factor of ˜100. Chondrules are modeled as Lagrangian particles that are subject to gas drag. An equation for the growth rate of the radius of a chondrule-dust compound is integrated whenever a chondrule enters a region permeated by dust, and perfect sticking is assumed. The rate of growth of the radius depends on the local dust density and on the relative velocity between the chondrule and the dust component. The variation of the equilibrium dust density has an effect on the final distribution of compound radii, with most compounds growing by factors ranging from less than ˜1.5 up to ˜8. Growth times are typically of the order of 10 years, roughly consistent with previous analytical results for the level of

  6. Spontaneous rotation of a melting ice disk

    Science.gov (United States)

    Dorbolo, Stephane; Vandewalle, Nicolas; Darbois-Texier, Baptiste; Grasp Team

    Ice disks were released at the surface of a thermalised aluminium plate. The fusion of the ice creates a lubrication film between the ice disk and the plate. The situation is similar to the Leidenfrost effect reported for liquid droplet evaporating at the surface of a plate which temperature is above the boiling temperature of the liquid. An analogy is depicted between the Leidenfrost phenomenon and the rapid fusion of a solid at the contact of a hot plate. Similarly to Leidenfrost droplet, we observe that, while the ice disks were melting, the disks were very mobile: translation and rotation. SD acknowledges support from FNRS as Senior Research Associate. This research has been funded by the Interuniversity Attraction Pole Programme (IAP 7/38 MicroMAST) initiated by the Belgian Science Policy Office.

  7. Exact Relativistic Magnetized Haloes around Rotating Disks

    Directory of Open Access Journals (Sweden)

    Antonio C. Gutiérrez-Piñeres

    2015-01-01

    Full Text Available The study of the dynamics of magnetic fields in galaxies is one of important problems in formation and evolution of galaxies. In this paper, we present the exact relativistic treatment of a rotating disk surrounded by a magnetized material halo. The features of the halo and disk are described by the distributional energy-momentum tensor of a general fluid in canonical form. All the relevant quantities and the metric and electromagnetic potentials are exactly determined by an arbitrary harmonic function only. For instance, the generalized Kuzmin-disk potential is used. The particular class of solutions obtained is asymptotically flat and satisfies all the energy conditions. Moreover, the motion of a charged particle on the halo is described. As far as we know, this is the first relativistic model describing analytically the magnetized halo of a rotating disk.

  8. High-Speed Bullet Ejections during the AGB to Planetary Nebula Transition: A Study of the Carbon Star V Hydrae

    Science.gov (United States)

    Sahai, Raghvendra

    2017-08-01

    The carbon star V Hya is experiencing heavy mass loss as it undergoes the transition from an AGB star to a planetary nebula (PN). This is possibly the earliest object known in this brief phase, which is so short that few nearby stars are likely to be caught in the act. Molecular observations reveal that a bipolar nebula has been established even at this early stage. Using STIS, we obtained high spatial-resolution long-slit optical spectra of V Hya spanning 3 epochs spaced apart by a year during each of two periods (2002-2004, 2011-2013). These data reveal high-velocity emission in [SII] lines from compact blobs located both on- and off-source, with the ejection axis executing a flip-flop, both in, and perpendicular to, the sky-plane. We have proposed a detailed model in which V Hya ejects high-speed (200-250 km/s) bullets once every 8.5 yr associated with periastron passage of a binary companion in an eccentric orbit with an 8.5 yr period. We suggest that the jet driver is an accretion disk (produced by gravitational capture of material from the primary) that is warped and precessing. Our model predicts the locations of previously ejected bullets in V Hya and future epochs at which new bullets will emerge. We now propose new STIS observations of these remarkable bullet ejections over two new epochs well separated from previous ones, to robustly test our model. The proposed observations will provide us with an unprecedented opportunity to look on as V Hya's circumstellar envelope is sculpted by these bullets. Our study will help solve the long-standing puzzle of how the spherical mass-loss envelopes of AGB stars evolve into bipolar and multipolar PNe.

  9. EARTH, MOON, SUN, AND CV ACCRETION DISKS

    International Nuclear Information System (INIS)

    Montgomery, M. M.

    2009-01-01

    Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar, and black hole systems. We find that spinning, tilted CV DN systems cannot be described by a precessing ring or by a precessing rigid disk. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our analysis indicates that the best description of a retrogradely precessing spinning, tilted, CV DN accretion disk is a differentially rotating, tilted disk with an attached rotating, tilted ring located near the innermost disk annuli. In agreement with the observations and numerical simulations by others, we find that our numerically simulated CV DN accretion disks retrogradely precess as a unit. Our final, reduced expression for retrograde precession agrees well with our numerical simulation results and with selective observational systems that seem to have main-sequence secondaries. Our results suggest that a major source to retrograde precession is tidal torques like that by the Moon and the Sun on the Earth. In addition, these tidal torques should be common to a variety of systems where one member is spinning and tilted, regardless if

  10. THE RISE AND FALL OF PASSIVE DISK GALAXIES: MORPHOLOGICAL EVOLUTION ALONG THE RED SEQUENCE REVEALED BY COSMOS

    International Nuclear Information System (INIS)

    Bundy, Kevin; Hopkins, Philip; Ma, Chung-Pei; Scarlata, Claudia; Capak, Peter; Carollo, C. M.; Oesch, Pascal; Ellis, Richard S.; Salvato, Mara; Scoville, Nick; Drory, Niv; Leauthaud, Alexie; Koekemoer, Anton M.; Murray, Norman; Ilbert, Olivier; Pozzetti, Lucia

    2010-01-01

    The increasing abundance of passive 'red-sequence' galaxies since z ∼ 1-2 is mirrored by a coincident rise in the number of galaxies with spheroidal morphologies. In this paper, however, we show in detail, that, the correspondence between galaxy morphology and color is not perfect, providing insight into the physical origin of this evolution. Using the COSMOS survey, we study a significant population of red-sequence galaxies with disk-like morphologies. These passive disks typically have Sa-Sb morphological types with large bulges, but they are not confined to dense environments. They represent nearly one-half of all red-sequence galaxies and dominate at lower masses (∼ 10 M sun ) where they are increasingly disk-dominated. As a function of time, the abundance of passive disks with M * ∼ 11 M sun increases, but not as fast as red-sequence spheroidals in the same mass range. At higher mass, the passive disk population has declined since z ∼ 1, likely because they transform into spheroidals. Based on these trends, we estimate that as much as 60% of galaxies transitioning onto the red sequence evolve through a passive disk phase. The origin of passive disks therefore has broad implications for our understanding of how star formation shuts down. Because passive disks tend to be more bulge-dominated than their star-forming counterparts, a simple fading of blue disks does not fully explain their origin. We explore the strengths and weaknesses of several more sophisticated explanations, including environmental effects, internal stabilization, and disk regrowth during gas-rich mergers. While previous work has sought to explain color and morphological transformations with a single process, these observations open the way to new insight by highlighting the fact that galaxy evolution may actually proceed through several separate stages.

  11. DISCOVERY OF MOLECULAR GAS AROUND HD 131835 IN AN APEX MOLECULAR LINE SURVEY OF BRIGHT DEBRIS DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Moór, A.; Ábrahám, P.; Kóspál, Á.; Szabó, Gy. M.; Kiss, Cs. [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 67, H-1525 Budapest (Hungary); Henning, Th.; Balog, Z. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Juhász, A. [Institute of Astronomy, Madingley Road, Cambridge CB3, OHA (United Kingdom); Pascucci, I. [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States); Vavrek, R. [Herschel Science Centre, ESA/ESAC, P.O. Box 78, Villanueva de la Cañada, E-28691, Madrid (Spain); Curé, M. [Instituto de Física y Astronomía, Universidad de Valparaíso (Chile); Csengeri, T.; Güsten, R. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Grady, C., E-mail: moor@konkoly.hu [NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States)

    2015-11-20

    Debris disks are considered to be gas-poor, but recent observations revealed molecular or atomic gas in several 10–40 Myr old systems. We used the APEX and IRAM 30 m radio telescopes to search for CO gas in 20 bright debris disks. In one case, around the 16 Myr old A-type star HD 131835, we discovered a new gas-bearing debris disk, where the CO 3–2 transition was successfully detected. No other individual system exhibited a measurable CO signal. Our Herschel Space Observatory far-infrared images of HD 131835 marginally resolved the disk at both 70 and 100 μm, with a characteristic radius of ∼170 AU. While in stellar properties HD 131835 resembles β Pic, its dust disk properties are similar to those of the most massive young debris disks. With the detection of gas in HD 131835 the number of known debris disks with CO content has increased to four, all of them encircling young (≤40 Myr) A-type stars. Based on statistics within 125 pc, we suggest that the presence of a detectable amount of gas in the most massive debris disks around young A-type stars is a common phenomenon. Our current data cannot conclude on the origin of gas in HD 131835. If the gas is secondary, arising from the disruption of planetesimals, then HD 131835 is a comparably young, and in terms of its disk, more massive analog of the β Pic system. However, it is also possible that this system, similar to HD 21997, possesses a hybrid disk, where the gas material is predominantly primordial, while the dust grains are mostly derived from planetesimals.

  12. Ocular ultrasound findings in optic disk melanocytoma

    OpenAIRE

    Andrés Lisker-Cervantes; David Arturo Ancona-Lezama; Luis Javier Arroyo-Garza; Jaime D. Martinez; Roberta Gomez Diaz Barreiro; Victor Daniel Valdepeña-López-Velarde; Virgilio Morales-Canton; Eduardo Moragrega-Adame

    2017-01-01

    Purpose: To describe the echographic characteristics of optic disk melanocytoma using a high resolution 10–20 MHz ophthalmic ultrasound. Methods: We conducted a 10-year retrospective review finding 9 cases with optic disk melanocytoma. The echographic studies were performed by the same experienced ophthalmologist. The form and density of the tumors were evaluated with B-scan ultrasound. Internal reflectivity and vascularity of the tumors were assessed with a standardized A-scan. Base (vert...

  13. CLUSTER DYNAMICS LARGELY SHAPES PROTOPLANETARY DISK SIZES

    Energy Technology Data Exchange (ETDEWEB)

    Vincke, Kirsten; Pfalzner, Susanne, E-mail: kvincke@mpifr-bonn.mpg.de [Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, D-53121 Bonn (Germany)

    2016-09-01

    To what degree the cluster environment influences the sizes of protoplanetary disks surrounding young stars is still an open question. This is particularly true for the short-lived clusters typical for the solar neighborhood, in which the stellar density and therefore the influence of the cluster environment change considerably over the first 10 Myr. In previous studies, the effect of the gas on the cluster dynamics has often been neglected; this is remedied here. Using the code NBody6++, we study the stellar dynamics in different developmental phases—embedded, expulsion, and expansion—including the gas, and quantify the effect of fly-bys on the disk size. We concentrate on massive clusters (M {sub cl} ≥ 10{sup 3}–6 ∗ 10{sup 4} M {sub Sun}), which are representative for clusters like the Orion Nebula Cluster (ONC) or NGC 6611. We find that not only the stellar density but also the duration of the embedded phase matters. The densest clusters react fastest to the gas expulsion and drop quickly in density, here 98% of relevant encounters happen before gas expulsion. By contrast, disks in sparser clusters are initially less affected, but because these clusters expand more slowly, 13% of disks are truncated after gas expulsion. For ONC-like clusters, we find that disks larger than 500 au are usually affected by the environment, which corresponds to the observation that 200 au-sized disks are common. For NGC 6611-like clusters, disk sizes are cut-down on average to roughly 100 au. A testable hypothesis would be that the disks in the center of NGC 6611 should be on average ≈20 au and therefore considerably smaller than those in the ONC.

  14. Scaling Ratios and Triangles in Siegel Disks

    DEFF Research Database (Denmark)

    Buff, Xavier; Henriksen, Christian

    1999-01-01

    Let f(z)=e^{2i\\pi \\theta} + z^2, where \\theta is a quadratic irrational. McMullen proved that the Siegel disk for f is self-similar about the critical point, and we show that if \\theta = (\\sqrt{5}-1)/2 is the golden mean, then there exists a triangle contained in the Siegel disk, and with one ver...

  15. Synthesis of disk-on-rod antennas

    Science.gov (United States)

    Dubrovka, F. F.; Lenivenko, V. A.

    1993-05-01

    The analysis and synthesis of disk-on-rod antennas (DORAs) with canonical and stepwise disk shapes are considered. A comparison of theoretical and experimental results shows that mathematical models and software developed by solving the appropriate boundary value problems can be used for the design of optimal DORAs. A broadband centimeter-wave DORA is considered as an example of the application of the proposed method for the constructive synthesis of DORAs using multicriterial optimization.

  16. Variational thermodynamics of relativistic thin disks

    Science.gov (United States)

    Gutiérrez-Piñeres, Antonio C.; Lopez-Monsalvo, Cesar S.; Quevedo, Hernando

    2015-12-01

    We present a relativistic model describing a thin disk system composed of two fluids. The system is surrounded by a halo in the presence of a non-trivial electromagnetic field. We show that the model is compatible with the variational multifluid thermodynamics formalism, allowing us to determine all the thermodynamic variables associated with the matter content of the disk. The asymptotic behavior of these quantities indicates that the single fluid interpretation should be abandoned in favor of a two-fluid model.

  17. A New M Dwarf Debris Disk Candidate in a Young Moving Group Discovered with Disk Detective

    Science.gov (United States)

    Silverberg, Steven M.; Kuchner, Marc J.; Wisniewski, John P.; Gagne, Jonathan; Bans, Alissa S.; Bhattacharjee, Shambo; Currie, Thayne R.; Debes, John R.; Biggs, Joseph R; Bosch, Milton

    2016-01-01

    We used the Disk Detective citizen science project and the BANYAN II Bayesian analysis tool to identify a new candidate member of a nearby young association with infrared excess. WISE J080822.18-644357.3, an M5.5-type debris disk system with significant excess at both 12 and 22 microns, is a likely member (approx.90% BANYAN II probability) of the approx.45 Myr old Carina association. Since this would be the oldest M dwarf debris disk detected in a moving group, this discovery could be an important constraint on our understanding of M dwarf debris disk evolution.

  18. YottaYotta announces new world record set for TCP disk-to-disk bulk transfer

    CERN Document Server

    2002-01-01

    The Yottabyte NetStorage(TM) Company, today announced a new world record for TCP disk-to-disk data transfer using the company's NetStorager(R) System. The record-breaking demonstration transferred 5 terabytes of data between Chicago, Il. to Vancouver, BC and Ottawa, ON, at a sustained average throughput of 11.1 gigabits per second. Peak throughput exceeded 11.6 gigabits per second, more than 15-times faster than previous records for TCP transfer from disk-to-disk (1 page).

  19. Instability of counter-rotating stellar disks

    Science.gov (United States)

    Hohlfeld, R. G.; Lovelace, R. V. E.

    2015-09-01

    We use an N-body simulation, constructed using GADGET-2, to investigate an accretion flow onto an astrophysical disk that is in the opposite sense to the disk's rotation. In order to separate dynamics intrinsic to the counter-rotating flow from the impact of the flow onto the disk, we consider an initial condition in which the counter-rotating flow is in an annular region immediately exterior the main portion of the astrophysical disk. Such counter-rotating flows are seen in systems such as NGC 4826 (known as the "Evil Eye Galaxy"). Interaction between the rotating and counter-rotating components is due to two-stream instability in the boundary region. A multi-armed spiral density wave is excited in the astrophysical disk and a density distribution with high azimuthal mode number is excited in the counter-rotating flow. Density fluctuations in the counter-rotating flow aggregate into larger clumps and some of the material in the counter-rotating flow is scattered to large radii. Accretion flow processes such as this are increasingly seen to be of importance in the evolution of multi-component galactic disks.

  20. Empirical Temperature Measurement in Protoplanetary Disks

    Science.gov (United States)

    Weaver, Erik; Isella, Andrea; Boehler, Yann

    2018-02-01

    The accurate measurement of temperature in protoplanetary disks is critical to understanding many key features of disk evolution and planet formation, from disk chemistry and dynamics, to planetesimal formation. This paper explores the techniques available to determine temperatures from observations of single, optically thick molecular emission lines. Specific attention is given to issues such as the inclusion of optically thin emission, problems resulting from continuum subtraction, and complications of real observations. Effort is also made to detail the exact nature and morphology of the region emitting a given line. To properly study and quantify these effects, this paper considers a range of disk models, from simple pedagogical models to very detailed models including full radiative transfer. Finally, we show how the use of the wrong methods can lead to potentially severe misinterpretations of data, leading to incorrect measurements of disk temperature profiles. We show that the best way to estimate the temperature of emitting gas is to analyze the line peak emission map without subtracting continuum emission. Continuum subtraction, which is commonly applied to observations of line emission, systematically leads to underestimation of the gas temperature. We further show that once observational effects such as beam dilution and noise are accounted for, the line brightness temperature derived from the peak emission is reliably within 10%–15% of the physical temperature of the emitting region, assuming optically thick emission. The methodology described in this paper will be applied in future works to constrain the temperature, and related physical quantities, in protoplanetary disks observed with ALMA.

  1. Multi-epoch spectropolarimetry of SN 2009ip: direct evidence for aspherical circumstellar material

    Science.gov (United States)

    Mauerhan, Jon; Williams, G. Grant; Smith, Nathan; Smith, Paul S.; Filippenko, Alexei V.; Hoffman, Jennifer L.; Milne, Peter; Leonard, Douglas C.; Clubb, Kelsey I.; Fox, Ori D.; Kelly, Patrick L.

    2014-08-01

    We present spectropolarimetry of SN 2009ip throughout the evolution of its 2012 explosion. During the 2012a phase, when the spectrum exhibits broad P-Cygni lines, we measure a V-band polarization of P ≈ 0.9 per cent at a position angle of θ ≈ 166°, indicating substantial asphericity for the 2012a outflow. Near the subsequent peak of the 2012b phase, when the spectrum shows signs of intense interaction with circumstellar material (CSM), we measure P ≈ 1.7 per cent and θ ≈ 72°, indicating a separate component of polarization during 2012b, which exhibits a higher degree of asphericity than 2012a and an orthogonal axis of symmetry on the sky. Around 30 d past peak, coincident with a substantial bump in the declining light curve, we measure P ≈ 0.7 per cent and another significant shift in θ. At this point, broad photospheric lines have again become prominent and exhibit significant variations in P relative to the continuum, particularly He I/Na ID. By 60 d past peak, the continuum polarization has dropped below 0.2 per cent, probably declining towards a low value of interstellar polarization. The results are consistent with a scenario in which a prolate (possibly bipolar) explosion launched during the 2012a phase impacts an oblate (toroidal) distribution of CSM in 2012b. Previous calculations that assumed spherical symmetry for the CSM have substantially underestimated the required explosion energy, since only a small fraction of the SN ejecta appears to have participated in strong CSM interaction. A kinetic energy of ˜1051 erg is difficult to avoid, supporting the interpretation that the 2012 outburst of SN 2009ip was the result of a core-collapse explosion.

  2. No Evidence of Circumstellar Gas Surrounding Type Ia Supernova SN 2017cbv

    Science.gov (United States)

    Ferretti, Raphael; Amanullah, Rahman; Bulla, Mattia; Goobar, Ariel; Johansson, Joel; Lundqvist, Peter

    2017-12-01

    Nearby type Ia supernovae (SNe Ia), such as SN 2017cbv, are useful events to address the question of what the elusive progenitor systems of the explosions are. Hosseinzadeh et al. suggested that the early blue excess of the light curve of SN 2017cbv could be due to the supernova ejecta interacting with a non-degenerate companion star. Some SN Ia progenitor models suggest the existence of circumstellar (CS) environments in which strong outflows create low-density cavities of different radii. Matter deposited at the edges of the cavities should be at distances at which photoionization due to early ultraviolet (UV) radiation of SNe Ia causes detectable changes to the observable Na I D and Ca II H&K absorption lines. To study possible narrow absorption lines from such material, we obtained a time series of high-resolution spectra of SN 2017cbv at phases between ‑14.8 and +83 days with respect to B-band maximum, covering the time at which photoionization is predicted to occur. Both narrow Na I D and Ca II H&K are detected in all spectra, with no measurable changes between the epochs. We use photoionization models to rule out the presence of Na I and Ca II gas clouds along the line of sight of SN 2017cbv between ∼8 × 1016–2 × 1019 cm and ∼1015–1017 cm, respectively. Assuming typical abundances, the mass of a homogeneous spherical CS gas shell with radius R must be limited to {M}{{H} {{I}}}{CSM}< 3× {10}-4× {(R/{10}17[{cm}])}2 {M}ȯ . The bounds point to progenitor models that deposit little gas in their CS environment.

  3. Power Spectrum Density of Stochastic Oscillating Accretion Disk GB ...

    Indian Academy of Sciences (India)

    radius in the disk, Rout is the outer radius of the disk, and the surface density index η is either 3/5 or 3/4 (Shakura & Sunyaev 1973). We assume that the restoring force of the disk oscillation is caused by gravitational attraction of the central compact object. We can deduce the characteristic frequency of the disk using ...

  4. Debris Disk Structure and Morphology as Revealed by Aggressive STIS Multi-Roll Coronagraphy: A New Look at Some Old Friends

    Science.gov (United States)

    Grady, Carol A; Kuchner, Marc; Woodgate, Bruce E.

    2012-01-01

    We present new imaging results from a well-selected sample of II circumstellar debris disks, all with HST pedigree, using STIS visible-light 6-roll PSF-template subtracted coronagraphy (PSFTSC). These new observations, pushing HST to its highest levels of coronagraphic performance, simultaneously probe both the interior regions of these debris systems, with inner working distances morphologies strongly suggestive of ISM wind interactions), HD 181327 & HDI07146 (close to face-on with respectively narrow and broad debris rings), and MP Mus (a "mature" proto-planetary disk hosted by a cTTS). All of our objects were previously observed in the near-IR with inferior spatial resolution and imaging efficacy, but with NICMOS r = 0.3" inner working angle (IWA) comparable to STIS multi-roll coronagraphy. The combination of new optical and existing near-IR imaging can strongly constrain the dust properties, thus enabling an assessment of grain processing and planetesimal populations. These results will directly inform upon the posited planet formation mechanisms that occur after the approximately 10 My epoch of gas depletion, a time in our solar system when giant planets were migrating and terrestrial planets were forming, and directly test theoretical models of these processes. These observations lmiquely probe both into the interior regions of these systems and are sensitive to and spatially resolve low surface-brightness (SB) material at large stellocentric distances with spatial resolution comparable to ACS and with augmenting NICMOS near-IR disk photometry in hand.

  5. Head-Disk Interface Technology: Challenges and Approaches

    Science.gov (United States)

    Liu, Bo

    Magnetic hard disk drive (HDD) technology is believed to be one of the most successful examples of modern mechatronics systems. The mechanical beauty of magnetic HDD includes simple but super high accuracy positioning head, positioning technology, high speed and stability spindle motor technology, and head-disk interface technology which keeps the millimeter sized slider flying over a disk surface at nanometer level slider-disk spacing. This paper addresses the challenges and possible approaches on how to further reduce the slider disk spacing whilst retaining the stability and robustness level of head-disk systems for future advanced magnetic disk drives.

  6. Can accretion disk properties distinguish gravastars from black holes?

    International Nuclear Information System (INIS)

    Harko, Tiberiu; Kovacs, Zoltan; Lobo, Francisco S N

    2009-01-01

    Gravastars, hypothetic astrophysical objects, consisting of a dark energy condensate surrounded by a strongly correlated thin shell of anisotropic matter, have been proposed as an alternative to the standard black hole picture of general relativity. Observationally distinguishing between astrophysical black holes and gravastars is a major challenge for this latter theoretical model. This is due to the fact that in static gravastars large stability regions (of the transition layer of these configurations) exist that are sufficiently close to the expected position of the event horizon, so that it would be difficult to distinguish the exterior geometry of gravastars from an astrophysical black hole. However, in the context of stationary and axially symmetrical geometries, a possibility of distinguishing gravastars from black holes is through the comparative study of thin accretion disks around rotating gravastars and Kerr-type black holes, respectively. In the present paper, we consider accretion disks around slowly rotating gravastars, with all the metric tensor components estimated up to the second order in the angular velocity. Due to the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution and equilibrium radiation spectrum) are different for these two classes of compact objects, consequently giving clear observational signatures. In addition to this, it is also shown that the conversion efficiency of the accreting mass into radiation is always smaller than the conversion efficiency for black holes, i.e. gravastars provide a less efficient mechanism for converting mass to radiation than black holes. Thus, these observational signatures provide the possibility of clearly distinguishing rotating gravastars from Kerr-type black holes.

  7. Fast vortex oscillations in a ferrimagnetic disk near the angular momentum compensation point

    Science.gov (United States)

    Kim, Se Kwon; Tserkovnyak, Yaroslav

    2017-07-01

    We theoretically study the oscillatory dynamics of a vortex core in a ferrimagnetic disk near its angular momentum compensation point, where the spin density vanishes but the magnetization is finite. Due to the finite magnetostatic energy, a ferrimagnetic disk of suitable geometry can support a vortex as a ground state similar to a ferromagnetic disk. In the vicinity of the angular momentum compensation point, the dynamics of the vortex resemble those of an antiferromagnetic vortex, which is described by equations of motion analogous to Newton's second law for the motion of particles. Owing to the antiferromagnetic nature of the dynamics, the vortex oscillation frequency can be an order of magnitude larger than the frequency of a ferromagnetic vortex, amounting to tens of GHz in common transition-metal based alloys. We show that the frequency can be controlled either by applying an external field or by changing the temperature. In particular, the latter property allows us to detect the angular momentum compensation temperature, at which the lowest eigenfrequency attains its maximum, by performing ferromagnetic resonance measurements on the vortex disk. Our work proposes a ferrimagnetic vortex disk as a tunable source of fast magnetic oscillations and a useful platform to study the properties of ferrimagnets.

  8. The Lack of Chemical Equilibrium does not Preclude the Use of the Classical Nucleation Theory in Circumstellar Outflows

    Science.gov (United States)

    Paquette, John A.; Nuth, Joseph A., III

    2011-01-01

    Classical nucleation theory has been used in models of dust nucleation in circumstellar outflows around oxygen-rich asymptotic giant branch stars. One objection to the application of classical nucleation theory (CNT) to astrophysical systems of this sort is that an equilibrium distribution of clusters (assumed by CNT) is unlikely to exist in such conditions due to a low collision rate of condensable species. A model of silicate grain nucleation and growth was modified to evaluate the effect of a nucleation flux orders of magnitUde below the equilibrium value. The results show that a lack of chemical equilibrium has only a small effect on the ultimate grain distribution.

  9. THE LACK OF CHEMICAL EQUILIBRIUM DOES NOT PRECLUDE THE USE OF CLASSICAL NUCLEATION THEORY IN CIRCUMSTELLAR OUTFLOWS

    International Nuclear Information System (INIS)

    Paquette, John A.; Nuth, Joseph A.

    2011-01-01

    Classical nucleation theory (CNT) has been used in models of dust nucleation in circumstellar outflows around oxygen-rich asymptotic giant branch stars. One objection to the application of CNT to astrophysical systems of this sort is that an equilibrium distribution of clusters (assumed by CNT) is unlikely to exist in such conditions due to a low collision rate of condensable species. A model of silicate grain nucleation and growth was modified to evaluate the effect of a nucleation flux orders of magnitude below the equilibrium value. The results show that a lack of chemical equilibrium has only a small effect on the ultimate grain distribution.

  10. Equilibrium configuration of a stratus floating above accretion disks: Full-disk calculation

    Science.gov (United States)

    Itanishi, Yusuke; Fukue, Jun

    2017-06-01

    We examine floating strati above a luminous accretion disk, supported by the radiative force from the entire disk, and calculate the equilibrium locus, which depends on the disk luminosity and the optical depth of the stratus. Due to the radiative transfer effect (albedo effect), the floating height of the stratus with a finite optical depth generally becomes high, compared with the particle case. In contrast to the case of the near-disk approximation, moreover, the floating height becomes yet higher in the present full-disk calculation, since the intense radiation from the inner disk is taken into account. As a result, when the disk luminosity normalized by the Eddington luminosity is ˜0.3 and the stratus optical depth is around unity, the stable configuration disappears at around r ˜ 50 rg, rg being the Schwarzschild radius, and the stratus would be blown off as a cloudy wind consisting of many strati with appropriate conditions. This luminosity is sufficiently smaller than the Eddington one, and the present results suggest that the radiation-driven cloudy wind can be easily blown off from the sub-Eddington disk, and this can explain various outflows observed in ultra-fast outflow objects as well as in broad-absorption-line quasars.

  11. A novel rotating disk electrode cell design; The inverted rotating disk electrode

    Energy Technology Data Exchange (ETDEWEB)

    Zdunek, A.D.; Selman, J.R. (Illinois Inst. of Tech., Chicago, IL (United States). Dept. of Chemical Engineering)

    1992-09-01

    In this paper a new cell configuration for use with the rotating disk electrode (RDE), the inverted rotating disk electrode (IRDE), is outlined. The IRDE faces upwards in solution and rotates without electrolyte leakage, even in highly corrosive solutions. This facilitates gas evolution and free convection studies. Mass transfer characteristics obtained by limiting current measurements agree well with literature for the RDE.

  12. Structural properties of hard disks in a narrow tube

    International Nuclear Information System (INIS)

    Varga, S; Gurin, P; Balló, G

    2011-01-01

    Positional ordering of a two-dimensional fluid of hard disks is examined in tubes so narrow that only nearest neighbor interactions take place. Using the exact transfer-matrix method the transverse and longitudinal pressure components and the correlation function are determined numerically. Fluid–solid phase transition does not occur even in the widest tube, where the method just loses its exactness, but the appearance of a dramatic change in the equation of state and the longitudinal correlation function shows that the system undergoes a structural change from a fluid to a solid-like order. The pressure components show that the collisions are dominantly longitudinal at low densities, while they are transverse in the vicinity of the close packing density. The transverse correlation function shows that the size of solid-like domains grows exponentially with increasing pressure and the correlation length diverges at close packing. It is possible to find an analytically solvable model by expanding the contact distance up to first order. The approximate model, which corresponds to a system of hard parallel rhombuses, behaves very similarly to the system of hard disks

  13. Evolution of silicate dust in interstellar, circumstellar and cometary environments: the role of irradiation and temperature

    International Nuclear Information System (INIS)

    Davoisne, Carine

    2006-01-01

    Due to the development of observational and analytical tools, our knowledge of the silicate dust has considerably increased these last years. Dust is formed around evolved stars and injected in the interstellar medium (ISM) in which it travels. Dust is then incorporated in the proto-planetary disks around young stars. During its life cycle, the silicate dust is subjected by numerous processes. The aim of this PhD work is firstly to study the chemical and morphological modifications of silicate dust in supernovae shock waves then to indicate its evolution when it is incorporated around young stars. We have developed low energy ion irradiations in situ in a photoelectron spectrometer (XPS). The chemical and morphological changes have been measured respectively by XPS and atomic force microscopy. We have also carried out thermal annealing under controlled atmosphere of amorphous silicates. The structural and chemical modifications have been observed by analytical transmission electron microscopy. We have shown that ion irradiation induces chemical and morphological changes in silicate. In the ISM, supernovae shock waves are thus a major process which could affect the silicate dust evolution. The microstructure obtained after thermal annealing strongly depends on oxygen fugacity. They often offer a good comparison with those observed in primitive materials present in our solar system. The recrystallization of amorphous interstellar precursors in the inner accretion disk is thus an efficient process to form crystalline silicates which are furthermore incorporated in small parent bodies (asteroids or comets). (author) [fr

  14. Probing Protoplanetary Disks: From Birth to Planets

    Science.gov (United States)

    Cox, Erin Guilfoil

    2018-01-01

    Disks are very important in the evolution of protostars and their subsequent planets. How early disks can form has implications for early planet formation. In the youngest protostars (i.e., Class 0 sources) magnetic fields can control disk growth. When the field is parallel to the collapsing core’s rotation axis, infalling material loses angular momentum and disks form in later stages. Sub-/millimeter polarization continuum observations of Class 0 sources at ~1000 au resolution support this idea. However, in the inner (~100 au), denser regions, it is unknown if the polarization only traces aligned dust grains. Recent theoretical studies have shown that self-scattering of thermal emission in the disk may contribute significantly to the polarization. Determining the scattering contribution in these sources is important to disentangle the magnetic field. At older times (the Class II phase), the disk structure can both act as a modulator and signpost of planet formation, if there is enough of a mass reservoir. In my dissertation talk, I will present results that bear on disk evolution at both young and late ages. I will present 8 mm polarization results of two Class 0 protostars (IRAS 4A and IC348 MMS) from the VLA at ~50 au resolution. The inferred magnetic field of IRAS 4A has a circular morphology, reminiscent of material being dragged into a rotating structure. I will show results from SOFIA polarization data of the area surrounding IRAS 4A at ~4000 au. I will also present ALMA 850 micron polarization data of ten protostars in the Perseus Molecular Cloud. Most of these sources show very ordered patterns and low (~0.5%) polarization in their inner regions, while having very disordered patterns and high polarization patterns in their extended emission that may suggest different mechanisms in the inner/outer regions. Finally, I will present results from our ALMA dust continuum survey of protoplanetary disks in Rho Ophiuchus; we measured both the sizes and fluxes of

  15. Effects of inclined star-disk encounter on protoplanetary disk size

    Science.gov (United States)

    Bhandare, Asmita; Breslau, Andreas; Pfalzner, Susanne

    2016-10-01

    Most, if not all, young stars are initially surrounded by protoplanetary disks. Owing to the preferential formation of stars in stellar clusters, the protoplanetary disks around these stars may potentially be affected by the cluster environment. Various works have investigated the influence of stellar fly-bys on disks, although many of them consider only the effects due to parabolic, coplanar encounters often for equal-mass stars, which is only a very special case. We perform numerical simulations to study the fate of protoplanetary disks after the impact of parabolic star-disk encounter for the less investigated case of inclined up to coplanar, retrograde encounters, which is a much more common case. Here, we concentrate on the disk size after such encounters because this limits the size of the potentially forming planetary systems. In addition, with the possibilities that ALMA offers, now a direct comparison to observations is possible. Covering a wide range of periastron distances and mass ratios between the mass of the perturber and central star, we find that despite the prograde, coplanar encounters having the strongest effect on the disk size, inclined and even the least destructive retrograde encounters mostly also have a considerable effect, especially for close periastron passages. Interestingly, we find a nearly linear dependence of the disk size on the orbital inclination for the prograde encounters, but not for the retrograde case. We also determine the final orbital parameters of the particles in the disk such as eccentricities, inclinations, and semi-major axes. Using this information the presented study can be used to describe the fate of disks and also that of planetary systems after inclined encounters.

  16. CARMA CO(J = 2 - 1) OBSERVATIONS OF THE CIRCUMSTELLAR ENVELOPE OF BETELGEUSE

    Energy Technology Data Exchange (ETDEWEB)

    O' Gorman, Eamon; Harper, Graham M. [School of Physics, Trinity College Dublin, Dublin 2 (Ireland); Brown, Joanna M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Brown, Alexander [Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389 (United States); Redfield, Seth [Astronomy Department, Van Vleck Observatory, Wesleyan University, Middletown, CT 06459 (United States); Richter, Matthew J. [Physics Department, UC Davis, 1 Shields Avenue, Davis, CA 95616 (United States); Requena-Torres, Miguel A. [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany)

    2012-08-15

    We report radio interferometric observations of the {sup 12}C{sup 16}O 1.3 mm J = 2 - 1 emission line in the circumstellar envelope of the M supergiant {alpha} Ori and have detected and separated both the S1 and S2 flow components for the first time. Observations were made with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) interferometer in the C, D, and E antenna configurations. We obtain good u - v coverage (5-280 k{lambda}) by combining data from all three configurations allowing us to trace spatial scales as small as 0.''9 over a 32'' field of view. The high spectral and spatial resolution C configuration line profile shows that the inner S1 flow has slightly asymmetric outflow velocities ranging from -9.0 km s{sup -1} to +10.6 km s{sup -1} with respect to the stellar rest frame. We find little evidence for the outer S2 flow in this configuration because the majority of this emission has been spatially filtered (resolved out) by the array. We also report a SOFIA-GREAT CO(J = 12 - 11) emission line profile, which we associate with this inner higher excitation S1 flow. The outer S2 flow appears in the D and E configuration maps and its outflow velocity is found to be in good agreement with high-resolution optical spectroscopy of K I obtained at the McDonald Observatory. We image both S1 and S2 in the multi-configuration maps and see a gradual change in the angular size of the emission in the high absolute velocity maps. We assign an outer radius of 4'' to S1 and propose that S2 extends beyond CARMA's field of view (32'' at 1.3 mm) out to a radius of 17'', which is larger than recent single-dish observations have indicated. When azimuthally averaged, the intensity falloff for both flows is found to be proportional to R{sup -1}, where R is the projected radius, indicating optically thin winds with {rho}{proportional_to}R{sup -2}.

  17. SN 2017dio: A Type-Ic Supernova Exploding in a Hydrogen-rich Circumstellar Medium

    Science.gov (United States)

    Kuncarayakti, Hanindyo; Maeda, Keiichi; Ashall, Christopher J.; Prentice, Simon J.; Mattila, Seppo; Kankare, Erkki; Fransson, Claes; Lundqvist, Peter; Pastorello, Andrea; Leloudas, Giorgos; Anderson, Joseph P.; Benetti, Stefano; Bersten, Melina C.; Cappellaro, Enrico; Cartier, Régis; Denneau, Larry; Della Valle, Massimo; Elias-Rosa, Nancy; Folatelli, Gastón; Fraser, Morgan; Galbany, Lluís; Gall, Christa; Gal-Yam, Avishay; Gutiérrez, Claudia P.; Hamanowicz, Aleksandra; Heinze, Ari; Inserra, Cosimo; Kangas, Tuomas; Mazzali, Paolo; Melandri, Andrea; Pignata, Giuliano; Rest, Armin; Reynolds, Thomas; Roy, Rupak; Smartt, Stephen J.; Smith, Ken W.; Sollerman, Jesper; Somero, Auni; Stalder, Brian; Stritzinger, Maximilian; Taddia, Francesco; Tomasella, Lina; Tonry, John; Weiland, Henry; Young, David R.

    2018-02-01

    SN 2017dio shows both spectral characteristics of a type-Ic supernova (SN) and signs of a hydrogen-rich circumstellar medium (CSM). Prominent, narrow emission lines of H and He are superposed on the continuum. Subsequent evolution revealed that the SN ejecta are interacting with the CSM. The initial SN Ic identification was confirmed by removing the CSM interaction component from the spectrum and comparing with known SNe Ic and, reversely, adding a CSM interaction component to the spectra of known SNe Ic and comparing them to SN 2017dio. Excellent agreement was obtained with both procedures, reinforcing the SN Ic classification. The light curve constrains the pre-interaction SN Ic peak absolute magnitude to be around {M}g=-17.6 mag. No evidence of significant extinction is found, ruling out a brighter luminosity required by an SN Ia classification. These pieces of evidence support the view that SN 2017dio is an SN Ic, and therefore the first firm case of an SN Ic with signatures of hydrogen-rich CSM in the early spectrum. The CSM is unlikely to have been shaped by steady-state stellar winds. The mass loss of the progenitor star must have been intense, \\dot{M}∼ 0.02{({ε }{{H}α }/0.01)}-1 ({v}{wind}/500 km s‑1) ({v}{shock}/10,000 km s‑1)‑3 M ⊙ yr‑1, peaking at a few decades before the SN. Such a high mass-loss rate might have been experienced by the progenitor through eruptions or binary stripping. Based on observations made with the NOT, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. This work is based (in part) on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile as part of PESSTO, (the Public ESO Spectroscopic Survey for Transient Objects Survey) ESO program 188.D-3003, 191.D-0935, 197.D-1075. Based on observations made with the Liverpool Telescope operated on the

  18. Formulas for Radial Transport in Protoplanetary Disks

    Science.gov (United States)

    Desch, Steven J.; Estrada, Paul R.; Kalyaan, Anusha; Cuzzi, Jeffrey N.

    2017-05-01

    The quantification of the radial transport of gaseous species and solid particles is important to many applications in protoplanetary disk evolution. An especially important example is determining the location of the water snow lines in a disk, which requires computing the rates of outward radial diffusion of water vapor and the inward radial drift of icy particles; however, the application is generalized to evaporation fronts of all volatiles. We review the relevant formulas using a uniform formalism. This uniform treatment is necessary because the literature currently contains at least six mutually exclusive treatments of radial diffusion of gas, only one of which is correct. We derive the radial diffusion equations from first principles using Fick's law. For completeness, we also present the equations for radial transport of particles. These equations may be applied to studies of diffusion of gases and particles in protoplanetary and other accretion disks.

  19. Intelligent multi-unit disk controller

    International Nuclear Information System (INIS)

    Poirot, Lucien

    1982-01-01

    This controller has been designed as a link between a 16 bits minicomputer and two types of disks units interface: the SMD interface and an equivalent to the DRI unit interface. Four units of each type can be handled by the controller. A bit slice microprocessor controls the interface with the disks units. The maximum exchange rate is 8 megabits per second. A CRC feature has been provided for error detection. A 16 bits microprocessor implements the interface to the computer, assuring head positioning, the management of bad tracks, as well as the supervision of each transfer. A internal buffer memory allows an asynchronous dialogue with the computer. The implementation of the controller makes easy the adaptation to disks units of various types, and though it has been initially intended for a minicomputer of the MITRA type, its microprocessor based design makes it fitted to any minicomputer. (author) [fr

  20. Industrial application of high power disk lasers

    Science.gov (United States)

    Brockmann, Rüdiger; Havrilla, David

    2008-02-01

    Laser welding has become one of the fastest growing areas for industrial laser applications. The increasing cost effectiveness of the laser process is enabled by the development of new highly efficient laser sources, such as the Disk laser, coupled with decreasing cost per Watt. TRUMPF introduced the Disk laser several years ago, and today it has become the most reliable laser tool on the market. The excellent beam quality and output powers of up to 10 kW enable its application in the automotive industry as well as in the range of thick plate welding, such as heavy construction and ship building. This serves as an overview of the most recent developments on the TRUMPF Disk laser and its industrial applications like cutting, welding, remote welding and hybrid welding, too. The future prospects regarding increased power and even further improved productivity and economics are presented.

  1. Seeded inert gas driven disk generator

    International Nuclear Information System (INIS)

    Joshi, N.K.; Venkatramani, N.; Rohatgi, V.K.

    1987-01-01

    This report outlines the present status of work being carried out in closed cycle MHD and disk generators. It gives the basic principles and discusses a proposal for setting up an experimental facility to study nonequilibrium plasmas using an inert gas driven disk generator. Disk geometry is a near ideal geometry for plasma studies since it has single or few pair electrodes combined with near perfect insulating walls. The proposed outlay of facility with components and subsystem is given. The facility may also be used to study the concept of fully ionized seed and to develop advanced diagnostic techniques. The absic equation describing the working parameters of such a system is also given in the Appendix. (author). 57 refs

  2. Permeable disks at low Reynolds numbers

    Science.gov (United States)

    Viola, Ignazio Maria; Cummins, Cathal; Mastropaolo, Enrico; Nakayama, Naomi

    2017-11-01

    The wake of a permeable disk can be rather exceptional: a toroidal vortex can form and remains stably at a fixed distance from the disk. The streamwise length of the vortex depends on the Reynolds and Darcy numbers. We investigate this fascinating flow for Reynolds numbers from 10 to 130 and Darcy numbers (Da) from 10-9 to 1. Direct numerical simulations are performed on a 2D grid with axisymmetric boundary conditions. Three flow regimes are observed: for low Da (effectively impervious), the wake is characterized by the presence of a toroidal vortex whose length is approximately equal to that of an impervious disk. For 10-6 RPG-2015-255].

  3. Destruction of Refractory Carbon in Protoplanetary Disks

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Dana E.; Blake, Geoffrey A. [Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Bergin, Edwin A. [Department of Astronomy, University of Michigan, 1085 S. University, Ann Arbor, MI 48109-1107 (United States); Ciesla, Fred J. [Department of Geophysical Sciences, The University of Chicago, 5734 South Ellis Ave., Chicago, IL 60637 (United States); Visser, Ruud [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748, Garching (Germany); Lee, Jeong-Eun [School of Space Research, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104 (Korea, Republic of)

    2017-08-10

    The Earth and other rocky bodies in the inner solar system contain significantly less carbon than the primordial materials that seeded their formation. These carbon-poor objects include the parent bodies of primitive meteorites, suggesting that at least one process responsible for solid-phase carbon depletion was active prior to the early stages of planet formation. Potential mechanisms include the erosion of carbonaceous materials by photons or atomic oxygen in the surface layers of the protoplanetary disk. Under photochemically generated favorable conditions, these reactions can deplete the near-surface abundance of carbon grains and polycyclic aromatic hydrocarbons by several orders of magnitude on short timescales relative to the lifetime of the disk out to radii of ∼20–100+ au from the central star depending on the form of refractory carbon present. Due to the reliance of destruction mechanisms on a high influx of photons, the extent of refractory carbon depletion is quite sensitive to the disk’s internal radiation field. Dust transport within the disk is required to affect the composition of the midplane. In our current model of a passive, constant- α disk, where α = 0.01, carbon grains can be turbulently lofted into the destructive surface layers and depleted out to radii of ∼3–10 au for 0.1–1 μ m grains. Smaller grains can be cleared out of the planet-forming region completely. Destruction may be more effective in an actively accreting disk or when considering individual grain trajectories in non-idealized disks.

  4. Cosmological Accretion Disks via External Radiation Drag

    OpenAIRE

    FUKUE, Jun; UMEMURA, Masayuki

    1994-01-01

    Accretion disks as well as disk accretion driven by external radiation drag are presented under a steady approximation in the cases of the point-mass potential and of the dark-matter potential. We assume that the external drag force can be expressed as -beta_v, where (beta) is a constant coefficient and v the velocity vector. When the gravitational potential is given by a central point-mass M, we find, in a cold regime where the pressure force is neglected, steady solutions such that the infa...

  5. The Rossby wave instability in protoplanetary disks

    Directory of Open Access Journals (Sweden)

    Meheut H.

    2013-04-01

    Full Text Available The Rossby wave instability has been proposed as a mechanism to transport angular momentum in the dead zone of protoplanetary disks and to form vortices. These vortices are of particular interest to concentrate solids in their centres and eventually to form planetesimals. Here we summarize some recent results concerning the growth and structure of this instability in radially and vertically stratified disks, its saturation and non-linear evolution. We also discuss the concentration of solids in the Rossby vortices including vertical settling.

  6. Decreasing turbulent helium flow in hard disk drive

    Science.gov (United States)

    Tawinprai, Supitcha; Suriyawanakul, Jarupol; Tangchaichit, Kiatfa

    2018-02-01

    A spoiler installed in a hard disk drive is helpful for reducing the flow which strikes the Head Gimbals Assembly (HGA) causing positioning errors and vibration. Filling a hard disk drive, with an installed spoiler, with helium gas was simulated by ANSYS Fluent software by using a realizable k – ε model to carry out the turbulence calculation of helium flow. The results show that the pressure fluctuation in a hard disk drive with a spoiler installed is lower than in a hard disk drive without, and accordingly the lower pressure fluctuation can reduce the force caused by pressure on the platter disks and reduce vibration in the hard disk drive.

  7. Experimental and Observational Studies of Molecular Hydrogen in Interstellar and Circumstellar Environments

    Science.gov (United States)

    Hoadley, Keri

    2017-08-01

    Understanding the evolution of gas over the lifetime of protoplanetary disks provides us with important clues about how planet formation mechanisms drive the diversity of exoplanetary systems observed to date. In the first part of my thesis, I discuss how I use fluorescent emission observations of molecular hydrogen (H2) in the far-ultraviolet (far-UV) with the Hubble Space Telescope to study the warm molecular regions (a rocket experiment designed to probe the warm and cool atoms and molecules near sites of recent star formation in the local interstellar medium. I present the science goals, design, research and development components, and calibration of the CHESS instrument. I provide results on observations taken during both launches of CHESS, with detailed analysis of the epsilon Per sightline, as inferred from the flight data. I conclude by providing future works and simple estimates of the performance of an instrument like CHESS on LUVOIR to study planet-forming environments.

  8. THE CIRCUMSTELLAR ENVIRONMENT OF R CORONAE BOREALIS: WHITE DWARF MERGER OR FINAL-HELIUM-SHELL FLASH?

    Energy Technology Data Exchange (ETDEWEB)

    Clayton, Geoffrey C.; Andrews, J. E. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Sugerman, Ben E. K. [Department of Physics and Astronomy, Goucher College, 1021 Dulaney Valley Rd., Baltimore, MD 21204 (United States); Adam Stanford, S. [IGPP, Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States); Whitney, B. A. [Space Science Institute, 4750 Walnut St. Suite 205, Boulder, CO 80301 (United States); Honor, J.; Babler, B. [Department of Astronomy, 475 North Charter St., University of Wisconsin, Madison, WI 53706 (United States); Barlow, M. J. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Gordon, K. D.; Bond, Howard E.; Matsuura, M. [STScI, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Geballe, T. R. [Gemini Observatory, 670 N. A' ohoku Place, Hilo, HI 96720 (United States); De Marco, O. [Department of Physics, Macquarie University, Sydney, NSW 2109 (Australia); Lawson, W. A. [School of PEMS, University of New South Wales, ADFA, P.O. Box 7916, Canberra, ACT 2610 (Australia); Sibthorpe, B. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Olofsson, G. [Department of Astronomy, Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, SE-10691 Stockholm (Sweden); Polehampton, E. [Space Science and Technology Department, Rutherford Appleton Laboratory, Didcot OX11 0QX (United Kingdom); Gomez, H. L.; Hargrave, P. C. [School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff, Wales CF24 3YB (United Kingdom); Ivison, R. J., E-mail: gclayton@phys.lsu.edu, E-mail: jandrews@phys.lsu.edu, E-mail: ben.sugerman@goucher.edu, E-mail: stanford@physics.ucdavis.edu, E-mail: bwhitney@spacescience.org, E-mail: jhonor@astro.wisc.edu, E-mail: brian@astro.wisc.edu, E-mail: mjb@star.ucl.ac.uk [UK Astronomy Technology Centre, ROE, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); and others

    2011-12-10

    In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 {mu}m with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 {mu}m. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10{sup -4} and 2 M{sub Sun }, respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger.

  9. STELLAR TRANSITS IN ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Béky, Bence; Kocsis, Bence

    2013-01-01

    Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, U