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Sample records for circumstellar disk envelope

  1. Vortices in circumstellar disks

    CERN Document Server

    Adams, F; Adams, Fred; Watkins, Richard

    1995-01-01

    We discuss the physics of vortices in the circumstellar disks associated with young stellar objects. We elucidate the basic physical properties of these localized storm systems. In particular, we consider point vortices, linear vortices, the effects of self-gravity, magnetic fields, and nonlinear aspects of the problem. We find that these vortices can exist in many different forms in the disks of young stellar objects and may play a role in the formation of binary companions and/or giant planets. Vortices may enhance giant planet formation via gravitational instability by allowing dust grains (heavy elements) to settle to the center on a short timescale; the gravitational instability itself is also enhanced because the vortices also create a larger local surface density in the disk. In addition, vortices can enhance energy dissipation in disks and thereby affect disk accretion. Finally, we consider the possibility that vortices of this type exist in molecular clouds and in the disk of the galaxy itself. On al...

  2. Bimodality of circumstellar disk evolution induced by Hall current

    CERN Document Server

    Tsukamoto, Y; Okuzumi, S; Machida, M N; Inutsuka, S

    2015-01-01

    The formation process of circumstellar disks is still controversial because of the interplay of complex physical processes that occurs during the gravitational collapse of prestellar cores. In this study, we investigate the effect of the Hall current term on the formation of circumstellar disk using three-dimensional simulations. In our simulations, all non-ideal effects as well as the radiation transfer are considered. We show that the size of the disk is significantly affected by a simple difference in the inherent properties of the prestellar core, namely whether the rotation vector and the magnetic field are parallel or anti-parallel. In the former case, only a very small disk ($20$ AU) disk is formed in the early phase of protostar formation. We also show that the anti-rotating envelopes against the disk-rotation appear with a size of $\\gtrsim 200$ AU. We predict that the anti-rotating envelope will be found in the future observations.

  3. Rapid disappearance of a warm, dusty circumstellar disk

    OpenAIRE

    Melis, Carl; Zuckerman, B.; Rhee, Joseph H.; Song, Inseok; Murphy, Simon J.; Bessell, Michael S.

    2012-01-01

    Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in...

  4. Processed and unprocessed ices in circumstellar disks

    CERN Document Server

    Pontoppidan, K; Thi, W F; Van Dishoeck, E F

    2004-01-01

    We present 3-5 micron VLT-ISAAC spectroscopy searching for evidence of methanol ices in edge-on disks of young embedded stars. Examples include the disks of L1489 IRS in Taurus and CRBR 2422.8-3423 in Ophiuchus, the last of which has the highest column density of solid CO known toward a YSO. We find no unambiguous evidence for abundant methanol in the observed disks, but give strict upper limits. Several additional low-mass sources in the Serpens and Chameleon molecular clouds exhibit abundant solid methanol, although it is not clear if the ice is associated with a disk or with the envelope. These are the first detections of solid methanol in the circumstellar environments of embedded young low-mass stars providing evidence that complex molecular species previously observed only in the solid state toward high-mass star forming regions are also present near solar-type young stars. The constraints on the formation mechanisms of methanol and the chemical evolution of ices as the material is incorporated into cir...

  5. SO2 and SO in circumstellar envelopes

    Science.gov (United States)

    Guilloteau, S.; Lucas, R.; Omont, A.; Nguyen-Q-Rieu

    1986-09-01

    After its first detection in circumstellar envelopes (Lucas et al. 1986) SO2 has been systematically searched for with the IRAM 30-m telescope. It has been found in 3 new stars, with very strong lines in OH 231.8+4.2 (TA* ≈ 0.7 - 1.4K, Trot ≈ 25K, Δv ≈ 80 km s-1, TA*(SO2) > TA*(CO) ) and relatively strong ones in OH 26.5+0.6. SO has been detected for the first time in a circumstellar shell, in OH 231.8+4.2. H13CN has been observed in the same star, suggesting a very large abundance of 13C.

  6. The circumstellar envelope of AFGL 4106

    CERN Document Server

    Van Loon, J T; Van Winckel, H; Waters, L B F M; Loon, Jacco Th. van; Winckel, Hans van

    1999-01-01

    We present new imaging and spectroscopy of the post-red supergiant binary AFGL 4106. Coronographic imaging in H-alpha reveals the shape and extent of the ionized region in the circumstellar envelope (CSE). Echelle spectroscopy with the slit covering almost the entire extent of the CSE is used to derive the physical conditions in the ionized region and the optical depth of the dust contained within the CSE. The dust shell around AFGL 4106 is clumpy and mixed with ionized gas. H-alpha and [N II] emission is brightest from a thin bow-shaped layer just outside of the detached dust shell. On-going mass loss is traced by [Ca II] emission and blue-shifted absorption in lines of low-ionization species. A simple model is used to interpret the spatial distribution of the circumstellar extinction and the dust emission in a consistent way.

  7. Gravitational Instabilities in Circumstellar Disks

    CERN Document Server

    Kratter, Kaitlin M

    2016-01-01

    [Abridged] Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability, and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability, supplemented with a survey of numerical simulations that aim to capture the non-linear evolution. We emphasize the role of thermodynamics and large scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analyt...

  8. Circumstellar Debris Disks: Diagnosing the Unseen Perturber

    CERN Document Server

    Nesvold, Erika R; Vican, Laura; Farr, Will M

    2016-01-01

    The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles' eccentricities and inclinations via the Kozai-Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. We demonstrate that a Kozai-Lidov excited disk can generate a dust disk via collisions and we compare t...

  9. Magnetic field and early evolution of circumstellar disks

    CERN Document Server

    Tsukamoto, Yusuke

    2016-01-01

    The magnetic field plays a central role in the formation and evolution of circumstellar disks. The magnetic field connects the rapidly rotating central region with the outer envelope and extracts angular momentum from the central region during gravitational collapse of the cloud core. This process is known as magnetic braking. Both analytical and multidimensional simulations have shown that disk formation is strongly suppressed by magnetic braking in moderately magnetized cloud cores in the ideal magnetohydrodynamic limit. On the other hand, recent observations have provided growing evidence of a relatively large disk several tens of astronomical units in size existing in some Class 0 young stellar objects. This introduces a serious discrepancy between the theoretical study and observations. Various physical mechanisms have been proposed to solve the problem of catastrophic magnetic braking, such as misalignment between the magnetic field and the rotation axis, turbulence, and non-ideal effect. In this paper,...

  10. Chemical history of molecules in circumstellar disks

    OpenAIRE

    Visser, Ruud; van Dishoeck, Ewine F.; Doty, Steven D.

    2011-01-01

    The chemical composition of a protoplanetary disk is determined not only by in situ chemical processes during the disk phase, but also by the history of the gas and dust before it accreted from the natal envelope. In order to understand the disk's chemical composition at the time of planet formation, especially in the midplane, one has to go back in time and retrace the chemistry to the molecular cloud that collapsed to form the disk and the central star. Here we present a new astrochemical m...

  11. Circumstellar disks around binary stars in Taurus

    International Nuclear Information System (INIS)

    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 Fmm∝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.

  12. 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.

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

    International Nuclear Information System (INIS)

    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

  14. An MCMC Circumstellar Disks Modeling Tool

    Science.gov (United States)

    Wolff, Schuyler; Perrin, Marshall D.; Mazoyer, Johan; Choquet, Elodie; Soummer, Remi; Ren, Bin; Pueyo, Laurent; Debes, John H.; Duchene, Gaspard; Pinte, Christophe; Menard, Francois

    2016-01-01

    We present an enhanced software framework for the Monte Carlo Markov Chain modeling of circumstellar disk observations, including spectral energy distributions and multi wavelength images from a variety of instruments (e.g. GPI, NICI, HST, WFIRST). The goal is 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 the derived properties. This modular code is designed to work with a collection of existing modeling tools, ranging from simple scripts to define the geometry for optically thin debris disks, to full radiative transfer modeling of complex grain structures in protoplanetary disks (using the MCFOST radiative transfer modeling code). The MCMC chain relies on direct chi squared comparison of model images/spectra to observations. We will include a discussion of how best to weight different observations in the modeling of a single disk and how to incorporate forward modeling from PCA PSF subtraction techniques. The code is open source, python, and available from github. Results for several disks at various evolutionary stages will be discussed.

  15. Studying Young Circumstellar Disks with ALMA

    Science.gov (United States)

    Ménard, F. C.

    2005-12-01

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material for stellar build-up, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve the mystery of the formation of our Solar System. This article focuses on observational studies of circumstellar disks associated with pre-main sequence solar-like stars and presents a few selected problems where ALMA will contribute in finding answers. At optical and near-infrared wavelengths, the direct measurement of disk parameters poses an obvious challenge: at the distance of typical star forming regions (e.g. ˜140 pc for Taurus), a planetary system like ours (with a diameter of ≃ 50 AU out to Pluto, but excluding the Kuiper belt) subtends only 0.35 arcsec. Moreover, its surface brightness is low in comparison to the bright central star. Hence, high angular resolution and high contrast imaging techniques are required if one hopes to resolve and measure such protoplanetary disks. Fortunately, potent imaging instruments have been available for about 10 years now. They cover a large part of the electromagnetic spectrum, from the UV/optical with HST, the near-infrared with ground-based adaptive optics systems to the millimeter range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of disks surrounding low-mass stars has made a gigantic leap forward in the last decade. However, the angular resolution of current millimeter interferometers will remain significantly poorer than the resolution that is available at shorter wavelengths (˜ 0.1 arcsec) until ALMA provides the necessary long baselines. At that time, astronomers will have access to data of comparable resolution over a very large wavelength range, with unprecedented sensitivity. As a direct consequence, our understanding of the disk structure and evolution should improve just as much

  16. Circumstellar envelopes and mass loss of red giant stars

    International Nuclear Information System (INIS)

    Mass loss from red giants is rediscussed on the basis of new observations of circumstellar absorption lines. The second ionization of Ca and the run of the expansion velocity with height above the stellar surface which are important for deriving mass loss rates of M giants have been determined. Deutsch's (1960) mass loss rates had to be revised considerably for early M giants. A review of the properties of expanding circumstellar envelopes of red giants as determined from optical, infrared, and microwave observations is given. (orig./BJ)

  17. Rapid disappearance of a warm, dusty circumstellar disk

    CERN Document Server

    Melis, Carl; Rhee, Joseph H; Song, Inseok; Murphy, Simon J; Bessell, Michael S

    2012-01-01

    Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in which post-collision ejecta evolution is typically ignored, although recent work has considered the fate of such material. Here we report observations of a young, Sun-like star (TYC 8241 2652 1) where infrared flux from post-collisional ejecta has decreased drastically, by a factor of about 30, over a period of less than two years. The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amoun...

  18. Erosion of circumstellar particle disks by interstellar dust

    Science.gov (United States)

    Lissauer, Jack J.; Griffith, Caitlin A.

    1989-01-01

    Circumstellar particle disks appear to be a common phenomenon; however, their properties vary greatly. Models of the evolution of such systems focus on internal mechanisms such as interparticle collisions and Poynting-Robertson drag. Herein it is shown that 'sandblasting' by interstellar dust can be an important and even dominant contributor to the evolution of circumstellar particle disks. Stars spend up to about 3 percent of their main-sequence lifetimes within atomic clouds. Among an IRAS sample of 21 nearby main-sequence A stars, beta Pictoris has the brightest disk; it also possesses the smallest random velocity and therefore the slowest predicted erosion rate.

  19. External Shaping of Circumstellar Envelopes of Evolved Stars

    Science.gov (United States)

    Cox, N. L. J.

    2015-08-01

    The circumstellar envelopes of asymptotic giant branch (AGB) stars and red supergiants (RSGs) are complex chemical and physical environments, and the specifics of their mass-loss history are important for both stellar and galactic evolution. One key aspect in this is to understand how the circumstellar medium of these stars can be shaped and affected by both internal and external mechanisms. These influences can skew our view on the (dust) chemistry and mass-loss history of these stars, and hence their role in the chemical enrichment of galaxies. This contribution focuses on the external mechanism related to the interaction between the slow dusty stellar wind and the local ambient medium. I will discuss what recent observations and hydrodynamical simulations have revealed and how these can help us learn more about AGB stars and RSGs, as well as the interstellar medium (ISM).

  20. Cepheids at high angular resolution: circumstellar envelope and pulsation

    Science.gov (United States)

    Gallenne, Alexandre

    2011-12-01

    In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out a statistical study of the speckle noise and inspect a possible asymmetry. Secondly, I analysed VISIR data to study the spectral energy distribution of a sample of Cepheids. These diffraction-limited images enabled me to carry out an accurate photometry in the N band and to detect an IR excess linked to the presence of a circumstellar component. On the other hand, applying a Fourier analysis I showed that some components are resolved. I then explored the K' band with the recombination instrument FLUOR for some bright Cepheids. Thanks to new set of data of Y Oph, I improved the study of its circumstellar envelope, using a ring-like model for the CSE. For two other Cepheids, U Vul and S Sge, I applied the interferometric Baade-Wesselink method in order to estimate their distance.

  1. Evidence for dust grain growth in young circumstellar disks

    CERN Document Server

    Throop, H B; Esposito, L W; McCaughrean, M J; Throop, Henry B.; Bally, John; Esposito, Larry W.; Caughrean, Mark J. Mc

    2001-01-01

    Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation -- the growth of dust grains into larger particles -- may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.

  2. Physical processes in circumstellar disks around young stars

    CERN Document Server

    2011-01-01

    Circumstellar disks are vast expanses of dust that form around new stars in the earliest stages of their birth. Predicted by astronomers as early as the eighteenth century, they weren't observed until the late twentieth century, when interstellar imaging technology enabled us to see nascent stars hundreds of light years away. Since then, circumstellar disks have become an area of intense study among astrophysicists, largely because they are thought to be the forerunners of planetary systems like our own-the possible birthplaces of planets.            This volume brings

  3. Circumplanetary disk or circumplanetary envelope?

    CERN Document Server

    Szulágyi, J; Lega, E; Crida, A; Morbidelli, A; Guillot, T

    2016-01-01

    We present three-dimensional simulations with nested meshes of the dynamics of the gas around a Jupiter mass planet with the JUPITER and FARGOCA codes. We implemented a radiative transfer module into the JUPITER code to account for realistic heating and cooling of the gas. We focus on the circumplanetary gas flow, determining its characteristics at very high resolution ($80\\%$ of Jupiter's diameter). In our nominal simulation where the temperature evolves freely by the radiative module and reaches 13000 K at the planet, a circumplanetary envelope was formed filling the entire Roche-lobe. Because of our equation of state is simplified and probably overestimates the temperature, we also performed simulations with limited maximal temperatures in the planet region (1000 K, 1500 K, and 2000 K). In these fixed temperature cases circumplanetary disks (CPDs) were formed. This suggests that the capability to form a circumplanetary disk is not simply linked to the mass of the planet and its ability to open a gap. Inste...

  4. Hot Molecular Circumstellar Disk around Massive Protostar Orion Source I

    CERN Document Server

    Hirota, Tomoya; Kurono, Yasutaka; Honma, Mareki

    2013-01-01

    We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidate. We detected two ortho-H$_{2}$O lines at 321 GHz ($10_{2,9}$-$9_{3,6}$) and 336 GHz ($\

  5. Growth of a Protostar and a Young Circumstellar Disk with High Mass Accretion Rate onto the Disk

    CERN Document Server

    Ohtani, Takuya

    2013-01-01

    The growing process of both a young protostar and a circumstellar disk is investigated. Viscous evolution of a disk around a single star is considered with a model where a disk increases its mass by dynamically accreting envelope and simultaneously loses its mass via viscous accretion onto the central star. We focus on the circumstellar disk with high mass accretion rate onto the disk $\\dot{M}=8.512c_{\\rm s}^3/G$ as a result of dynamical collapse of rotating molecular cloud core. We study the origin of the surface density distribution and the origin of the disk-to-star mass ratio by means of numerical calculations of unsteady viscous accretion disk in one-dimensional axisymmetric model. It is shown that the radial profiles of the surface density $\\Sigma$, azimuthal velocity $v_{\\phi}$, and mass accretion rate $\\dot{M}$ in the inner region approach to the quasi-steady state. Profile of the surface density distribution in the quasi-steady state is determined as a result of angular momentum transport rather than...

  6. Constraints on the Formation and Evolution of Circumstellar Disks in Rotating Magnetized Cloud Cores

    CERN Document Server

    Basu, S

    1998-01-01

    We use magnetic collapse models to place some constraints on the formation and angular momentum evolution of circumstellar disks which are embedded in magnetized cloud cores. Previous models have shown that the early evolution of a magnetized cloud core is governed by ambipolar diffusion and magnetic braking, and that the core takes the form of a nonequilibrium flattened envelope which ultimately collapses dynamically to form a protostar. In this paper, we focus on the inner centrifugally-supported disk, which is formed only after a central protostar exists, and grows by dynamical accretion from the flattened envelope. We estimate a centrifugal radius for the collapse of mass shells within a rotating, magnetized cloud core. The centrifugal radius of the inner disk is related to its mass through the two important parameters characterizing the background medium: the background rotation rate $\\Omb$ and the background magnetic field strength $\\Bref$. We also revisit the issue of how rapidly mass is deposited onto...

  7. Massive circumstellar envelope around type IIn supernova SN 1995G

    CERN Document Server

    Chugai, N N

    2003-01-01

    We model the interaction of the supernova SN 1995G with a dense circumstellar (CS) gas in a thin shell approximation. A model fit of the observed bolometric light curve combined with data on the supernova expansion velocity provides an estimate of the density of the CS shell, its mass ($approx 1 M_{odot}$), and age ($approx 8$ years). It is shown that the derived CS gas density does not depend on the assumed mass of the supernova ejecta. This results from the high CS density, which ensures that the forward shock wave is essentially radiative. The derived CS density is consistent with the H$alpha$ luminosity and with the presence of the apparent effect of Thomson scattering in the red wing of this line. The mass of the CS envelope together with its expansion velocity indicates that the CS envelope was ejected as a result of violent energy release ($sim 6times10^{48}$ erg) eight years before the supernova outburst.

  8. Cepheids at high angular resolution: circumstellar envelope and pulsation

    CERN Document Server

    Gallenne, Alexandre

    2011-01-01

    In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out ...

  9. The Circumstellar Disk of the Be Star $o$~Aquarii

    CERN Document Server

    Sigut, T A A; Jansen, B; Zavala, R T

    2015-01-01

    Omicron Aquarii is late-type, Be shell star with a stable and nearly symmetric H$\\alpha$ emission line. We combine H$\\alpha$ interferometric observations obtained with the Navy Precision Optical Interferometer (NPOI) covering 2007 through 2014 with H$\\alpha$ spectroscopic observations over the same period and a 2008 observation of the system's near-infrared spectral energy distribution to constrain the properties of $o$~Aqr's circumstellar disk. All observations are consistent with a circumstellar disk seen at an inclination of $75\\pm\\,3^{\\circ}$ with a position angle on the sky of $110\\pm\\,8^{\\circ}$ measured E from N. From the best-fit disk density model, we find that 90\\% of the H$\\alpha$ emission arises from within $9.5$ stellar radii, and the mass associated with this H$\\alpha$ disk is $\\sim 1.8\\times10^{-10}$ of the stellar mass and the associated angular momentum, assuming Keplerian rotation for the disk, is $\\sim 1.6\\times10^{-8}$ of the total stellar angular momentum. The occurrence of a central quas...

  10. Observations of Circumstellar Disks with Infrared Interferometry

    Science.gov (United States)

    Akeson, Rachel

    2008-01-01

    Star formation is arguably the area of astrophysics in which infrared interferometry has had the biggest impact. The optically thick portion of T Tauri and Herbig Ae/Be disks DO NOT extend to a few stellar radii of the stellar surface. Emission is coming from near the dust sublimation radius, but not all from a single radius. The Herbig Ae stars can be either flared or self-shadowed but very massive (early Be) stars are geometrically thin. The Herbig Ae stars can be either flared or self-shadowed but very massive (early Be) stars are geometrically thin. Observational prospects are rapidly improving: a) Higher spectral resolution will allow observations of the gas: jets, winds, accretion. b) Closure phase and imaging will help eliminate model uncertainties/dependencies.

  11. A Collisional Algorithm for Modeling Circumstellar Debris Disks

    Science.gov (United States)

    Nesvold, Erika; Kuchner, Marc

    2011-01-01

    Many planetary systems harbor circumstellar disks of dust and planetesimals thought to be debris left over from planet formation. These debris disks exhibit a range of morphological features which can arise from the gravitational perturbations of planets. Accurate models of these features, accounting for the interactions of the particles in a disk with each other and with whatever planets they contain, can act as signposts for planets in debris disks that otherwise could not be detected. Such models can also constrain the planet's mass and orbital parameters. Current models for many disks consider the gravitational and radiative effects of the star and planets on the disk, but neglect the morphological consequences of collisional interactions between the planetesimals. Many observed disk features are not satisfactorily explained by the current generation of models. I am developing a new kind of debris disk model that considers both the gravitational shaping of the disk by planets and the inelastic collisions between particles. I will use a hybrid N-body integrator to numerically solve the equations of motion for the particles and planets in the disk. To include the collisional effects, I begin with an algorithm that tests for collisions at each step of the orbit integration and readjusts the velocities of colliding particles. I am adapting this algorithm to the problem at hand by allowing each particle to represent a "swarm" of planetesimals with a range of masses. When the algorithm detects an encounter between swarms, two or three swarms are produced to approximate the range of possible trajectories of the daughter planetesimals. Here I present preliminary results from my collisional algorithm.

  12. Dust Migration and Morphology in Optically Thin Circumstellar Gas Disks

    CERN Document Server

    Takeuchi, T; Takeuchi, Taku; Artymowicz, Pawel

    2001-01-01

    We analyze the dynamics of gas-dust coupling in the presence of stellar radiation pressure in circumstellar gas disks, which are in a transitional stage between the gas-dominated, optically thick, primordial nebulae, and the dust-dominated, optically thin Vega-type disks. Dust undergo radial migration, seeking a stable equilibrium orbit in corotation with gas. The migration of dust gives rise to radial fractionation of dust and creates a variety of possible observed disk morphologies, which we compute by considering the equilibrium between the dust production and the dust-dust collisions removing particles from their equilibrium orbits. Sand-sized and larger grains are distributed throughout most of the gas disk, with concentration near the gas pressure maximum in the inner disk. Smaller grains (typically in the range of 10 to 200 micron) concentrate in a prominent ring structure in the outer region of the gas disk (presumably at radius 100 AU), where gas density is rapidly declining with radius. The width an...

  13. A Rotating Circumstellar Disk Around a High-Mass Protostar in IRAS 18162-2048

    Science.gov (United States)

    Fernández-López, M.; Girart, J. M.; Curiel, S.; Patel, N.; Gómez, Y.; Ho, P. T. P.

    2011-10-01

    Searching for molecular tracers of disks in massive star-formation regions is a complex task. There are molecules that show emission from the envelope and the disk simultaneously. Other molecules show optically thick emission, thus complicating the kinematic study of disks. On the other hand, S-bearing species (such as H2S, SO, SO2, CS, and OCS) could be intimately linked with the evaporation process of the disk surface becoming good tracers of the dynamics of the innermost parts of the high-mass protostars. Recently, several papers have been published on the detection of S-bearing species in disks and other warm gas structures of massive star-forming regions. In particular, SO2 transitions, ubiquitous within the (sub)millimeter range, show a very compact nature, suggesting their close association with circumstellar structures. We have carried out sub-arcsecond SMA observations towards the central region of the HH 80-81 system. The mm continuum emission shows two main sources, one of them located at the center of the extremely large (5.3 pc long) bipolar radio continuum jet observed in this region. The dust emission appears compact and coincides with a radio continuum source. Between the spectral lines detected (H2CO and SO), the SO2 line transitions show compact emission toward this source. These molecular lines clearly show a velocity gradient perpendicular to the radio jet axis. Both, the dust continuum and the molecular line emission suggest the existence of a rotating circumstellar disk around a massive protostar.

  14. ALMA Observations of HD141569's Circumstellar Disk

    CERN Document Server

    White, J A; Hughes, A M; Flaherty, K M; Ford, E; Wilner, D; Corder, S; Payne, M

    2016-01-01

    We present ALMA band 7 (345 GHz) continuum and $^{12}$CO(J = 3-2) observations of the circumstellar disk surrounding HD141569. 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 $870\\rm~\\mu m$ ALMA continuum observations resolve a dust disk out to approximately $ 56 ~\\rm au$ from the star (assuming a distance of 116 pc) with $0."38$ resolution and $0.07 ~ \\rm mJy~beam^{-1}$ sensitivity. We measure a continuum flux density for this inner material of $3.8 \\pm 0.4 ~ \\rm mJy$ (including calibration uncertainties). The $^{12}$CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated $^{12}$CO(3-2) line flux density is $15.7 \\pm 1.6~\\rm Jy~km~s^{-1}$. We estimate the mass of the millimeter debris and $^{12}$CO(3-2) gas to be $\\gtrsim0.04~\\rm M_{\\oplus}$ and $\\sim2\\times 10^{-3}~\\rm M_{\\oplus}$, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk ($&...

  15. The chemical history of molecules in circumstellar disks. I. Ices

    CERN Document Server

    Visser, R; Doty, S D; Dullemond, C P

    2009-01-01

    (Abridged) Aims & Methods. A two-dimensional, semi-analytical model is presented that follows, for the first time, the chemical evolution from a collapsing molecular cloud (a pre-stellar core) to a protostar and circumstellar disk. The model computes infall trajectories from any point in the cloud and tracks the radial and vertical motion of material in the viscously evolving disk. It includes a full time-dependent radiative transfer treatment of the dust temperature, which controls much of the chemistry. A small parameter grid is explored to understand the effects of the sound speed and the mass and rotation of the cloud. The freeze-out and evaporation of carbon monoxide (CO) and water (H2O), as well as the potential for forming complex organic molecules in ices, are considered as important first steps to illustrate the full chemistry. Results. Both species freeze out towards the centre before the collapse begins. Pure CO ice evaporates during the infall phase and re-adsorbs in those parts of the disk th...

  16. Beta Pic-like Circumstellar Gas Disk Around 2 And

    Science.gov (United States)

    Cheng, Patricia

    2003-01-01

    This grant was awarded to support the data analysis and publication of results from our project entitled P Pic-like Circumstellar Gas Disk Around 2 And . We proposed to obtain FUSE observations of 2 And and study the characteristics and origin of its circumstellar gas. We observed 2 Andromedae with FUSE on 3-4 July 2001 in 11 exposures with a total exposure time of 21,289 seconds through the LWRS aperture. Our data were calibrated with Version 1.8.7 of the CALFUSE pipeline processing software. We corrected the wavelength scale for the heliocentric velocity error in this version of the CALFUSE software. The relative accuracy of the calibrated wavelength scale is +/- 9 km/s . We produced a co-added spectrum in the LiF 1B and LiF 2A channels (covering the 1100 to 1180 A region) by cross-correlating the 11 individual exposures and doing an exposure-time weighted average flux. The final co-added spectra have a signal-to-noise ratio in the stellar continuum near 1150 A of about 20. To obtain an absolute wavelength calibration, we cross-correlated our observed spectra with a model spectrum to obtain the best fit for the photospheric C I lines. Because the photospheric lines are very broad, this yields an absolute accuracy for the wavelength scale of approx.+/- 15 km/s. We then rebinned 5 original pixels to yield the optimal sampling of .033 A for each new pixel, because the calibrated spectra oversample the spectral resolution for FUSE+LWRS (R = 20,000 +/- 2,000).

  17. Tracing the disk, envelope and outflow cavity of VLA1623 with ALMA

    Science.gov (United States)

    Murillo, N. M.; Walsh, C.; van Dishoeck, E. F.; Bruderer, S.; Harsono, D.; Lai, S.-P.

    2016-05-01

    Our ALMA Cycle 0 and 2 observations in Band 6 provide tracers of the disk (C18O, 13CO), the envelope (13CO, DCO+) and the outflow and its cavity (12CO, 13CO, c-C3H2) towards VLA1623, a triple non-coeval system in ρ Ophiuchus (d˜120 pc). The observations are combined with simple chemical and physical models. We find differing circumstellar envelope and outflows. VLA1623 appears to not be as chemically rich as other deeply embedded sources.

  18. Modeling transiting circumstellar disks: characterizing the newly discovered eclipsing disk system OGLE LMC-ECL-11893

    Energy Technology Data Exchange (ETDEWEB)

    Scott, Erin L.; Mamajek, Eric E.; Pecaut, Mark J.; Quillen, Alice C.; Moolekamp, Fred; Bell, Cameron P. M., E-mail: elscott@pas.rochester.edu [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627-0171 (United States)

    2014-12-10

    We investigate the nature of the unusual eclipsing star OGLE LMC-ECL-11893 (OGLE J05172127-6900558) in the Large Magellanic Cloud recently reported by Dong et al. The eclipse period for this star is 468 days, and the eclipses exhibit a minimum of ∼1.4 mag, preceded by a plateau of ∼0.8 mag. Spectra and optical/IR photometry are consistent with the eclipsed star being a lightly reddened B9III star of inferred age ∼150 Myr and mass ∼4 M {sub ☉}. The disk appears to have an outer radius of ∼0.2 AU with predicted temperatures of ∼1100-1400 K. We model the eclipses as being due to either a transiting geometrically thin dust disk or gaseous accretion disk around a secondary object; the debris disk produces a better fit. We speculate on the origin of such a dense circumstellar dust disk structure orbiting a relatively old low-mass companion, and on the similarities of this system to the previously discovered EE Cep.

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

    CERN Document Server

    Kuchner, Marc J; 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; Schawinski, Kevin; Thaller, Michelle L; Grady, Carol A; Biggs, Joseph; Bosch, Milton; Cernohous, Tadeás; Luca, Hugo A Durantini; Hyogo, Michiharu; Wah, Lily Lau Wan; Piipuu, Art; Piñeiro, Fernanda

    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 NASA's 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, background stars, 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 o...

  20. Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216

    CERN Document Server

    Agundez, M; Agundez, Marcelino; Cernicharo, Jose

    2006-01-01

    In this paper we study the oxygen chemistry in the C-rich circumstellar shells of IRC+10216. The recent discoveries of oxygen bearing species (water, hydroxyl radical and formaldehyde) toward this source challenge our current understanding of the chemistry in C-rich circumstellar envelopes. The presence of icy comets surrounding the star or catalysis on iron grain surfaces have been invoked to explain the presence of such unexpected species. This detailed study aims at evaluating the chances of producing O-bearing species in the C-rich circumstellar envelope only by gas phase chemical reactions. For the inner hot envelope, it is shown that although most of the oxygen is locked in CO near the photosphere (as expected for a C/O ratio greater than 1), some stellar radii far away species such as H2O and CO2 have large abundances under the assumption of thermochemical equilibrium. It is also shown how non-LTE chemistry makes very difficult the CO-->H2O,CO2 transformation predicted in LTE. Concerning the chemistry ...

  1. Atomic and molecular hydrogen in the circumstellar envelopes of late-type stars

    Science.gov (United States)

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

    1983-01-01

    The distribution of atomic and molecular hydrogen in the expanding circumstellar envelopes of cool evolved stars is discussed. The main concern is to evaluate the effects of photodestruction of H2 by galactic UV radiation, including shielding of the radiation by H2 itself and by dust in the envelope. One of the most important parameters is the H/H2 ratio which is frozen out in the upper atmosphere of the star. For stars with photospheric temperatures greater than about 2500 K, atmospheric models suggest that the outflowing hydrogen is mainly atomic, whereas cooler stars should be substantially molecular. In the latter case, photodissociation of H2 and heavy molecules contribute to the atomic hydrogen content of the outer envelope. The presented estimates indicate that atomic hydrogen is almost at the limit of detection in the C-rich star IRC + 10216, and may be detectable in warmer stars. Failure to detect it would have important implications for the general understanding of circumstellar envelopes.

  2. Chemistry and distribution of daughter species in the circumstellar envelopes of O-rich AGB stars

    Science.gov (United States)

    Li, Xiaohu; Millar, Tom J.; Heays, Alan N.; Walsh, Catherine; van Dishoeck, Ewine F.; Cherchneff, Isabelle

    2016-03-01

    Context. Thanks to the advent of Herschel and ALMA, new high-quality observations of molecules present in the circumstellar envelopes of asymptotic giant branch (AGB) stars are being reported that reveal large differences from the existing chemical models. New molecular data and more comprehensive models of the chemistry in circumstellar envelopes are now available. Aims: The aims are to determine and study the important formation and destruction pathways in the envelopes of O-rich AGB stars and to provide more reliable predictions of abundances, column densities, and radial distributions for potentially detectable species with physical conditions applicable to the envelope surrounding IK Tau. Methods: We use a large gas-phase chemical model of an AGB envelope including the effects of CO and N2 self-shielding in a spherical geometry and a newly compiled list of inner-circumstellar envelope parent species derived from detailed modeling and observations. We trace the dominant chemistry in the expanding envelope and investigate the chemistry as a probe for the physics of the AGB phase by studying variations of abundances with mass-loss rates and expansion velocities. Results: We find a pattern of daughter molecules forming from the photodissociation products of parent species with contributions from ion-neutral abstraction and dissociative recombination. The chemistry in the outer zones differs from that in traditional PDRs in that photoionization of daughter species plays a significant role. With the proper treatment of self-shielding, the N → N2 and C+→ CO transitions are shifted outward by factors of 7 and 2, respectively, compared with earlier models. An upper limit on the abundance of CH4 as a parent species of (≲2.5 × 10-6 with respect to H2) is found for IK Tau, and several potentially observable molecules with relatively simple chemical links to other parent species are determined. The assumed stellar mass-loss rate, in particular, has an impact on the

  3. The infrared spectral features of circumstellar envelope of evolved low- and intermediate-mass stars

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The circumstellar envelope of evolved stars of low- and intermediate-mass is an important site for dust formation. In comparison with the interstellar medium, they have more types of organics and different types of inorganics. Various infrared features in the circumstellar envelope can reveal the composition and abundance of dust, as well as the chemical and physical conditions of the circumstellar shell. Infrared features and their carriers are different in the C-rich or O-rich environment, and the mixed-environment where the C-rich and O-rich circumstellar materials co-exist. The C-rich sources exhibit a series of spectral features which are attrib- uted to organic molecules. They also show two prominent features at 21 μm and 30 μm which emit a large portion of infrared radiation. The O-rich sources exhibit the strong 9.7 μm and 18 μm features attributed to the Si-O bending and O-Si-O stretching modes of amorphous silicate dust. With the ISO/SWS spectrometer, about 50 narrow bands are identified with the crystalline silicate grains, mainly forsterite and enstatite. In addition, a series of features, at 13 μm, 16.8 μm, 19.5 μm and 31.8 μm, appearing to be correlated with each other, are attributed to oxides. Some objects simultaneously show the C-rich and O-rich features, e.g. some C-rich sources have silicate features. There is no well-accepted interpretation for such mixed appearance, though a binary model is suggested.

  4. The infrared spectral features of circumstellar envelope of evolved low-and intermediate-mass stars

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ke; JIANG BiWei

    2008-01-01

    The circumstellar envelope of evolved stars of low-and intermediate-mass is an important site for dust formation. In comparison with the interstellar medium, they have more types of organics and different types of inorganics. Various infrared features in the circumstellar envelope can reveal the composition and abundance of dust, as well as the chemical and physical conditions of the circumstellar shell. Infrared features and their carriers are different in the C-rich or O-rich environment, and the mixed-environment where the C-rich and O-rich circumstellar materials co-exist. The C-rich sources exhibit a series of spectral features which are attrib-uted to organic molecules. They also show two prominent features at 21 μm and 30 μm which emit a large portion of infrared radiation. The O-rich sources exhibit the strong 9.7 μm and 18 μm features attributed to the Si-O bending and O-Si-O stretching modes of amorphous silicate dust. With the ISO/SWS spectrometer, about 50 narrow bands are identified with the crystalline silicate grains, mainly forsterite and enstatite. In addition, a series of features, at 13 μm, 16.8 μm, 19.5 μm and 31.8 μm, appearing to be correlated with each other, are attributed to oxides. Some objects simultaneously show the C-rich and O-rich features, e.g. some C-rich sources have silicate features. There is no well-accepted interpretation for such mixed appearance, though a binary model is suggested.

  5. 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.

  6. Photoevaporation of Circumstellar Disks due to External FUV Radiation in Stellar Aggregates

    CERN Document Server

    Adams, F C; Laughlin, G; Gorti, U; Adams, Fred C.; Hollenbach, David; Laughlin, Gregory; Gorti, Uma

    2004-01-01

    When stars form in small groups (N = 100 - 500 members), their circumstellar disks are exposed to little EUV radiation but a great deal of FUV radiation from massive stars in the group. This paper calculates mass loss rates for circumstellar disks exposed to external FUV radiation. Previous work treated large disks and/or intense radiation fields in which the disk radius exceeds the critical radius (supercritical disks) where the sound speed in the FUV heated layer exceeds the escape speed. This paper shows that significant mass loss still takes place for subcritical systems. Some of the gas extends beyond the disk edge (above the disk surface) to larger distances where the temperature is higher, the escape speed is lower, and an outflow develops. The evaporation rate is a sensitive function of the stellar mass and disk radius, which determine the escape speed, and the external FUV flux, which determines the temperature structure of the flow. Disks around red dwarfs are readily evaporated and shrink to disk r...

  7. Sulphur molecules in the circumstellar envelopes of M-type AGB stars

    CERN Document Server

    Danilovich, Taissa; Black, J H; Olofsson, H; Justtanont, K

    2016-01-01

    The sulphur compounds SO and SO$_2$ have not been widely studied in the circumstellar envelopes of asymptotic giant branch (AGB) stars. By presenting and modelling a large number of SO and SO$_2$ lines in the low mass-loss rate M-type AGB star R Dor, and modelling the available lines of those molecules in a further four M-type AGB stars, we aim to determine their circumstellar abundances and distributions. We use a detailed radiative transfer analysis based on the accelerated lambda iteration method to model circumstellar SO and SO$_2$ line emission and molecular data files for both SO and SO$_2$ that are more extensive than those previously available. Using 17 SO lines and 98 SO2 lines to constrain our models for R Dor, we find an SO abundance of 6.7x10$^{-6}$ and an SO$_2$ abundance of 5x10$^{-6}$ with both species having high abundances close to the star. We also modelled $^{34}$SO and found an abundance of 3.1x10$^{-7}$, giving an $^{32}$SO/$^{34}$SO ratio of 21.6. We derive similar results for the circum...

  8. The warm circumstellar envelope and wind of the G9 IIb star HR 6902

    Science.gov (United States)

    Kirsch, T.; Baade, R.; Reimers, D.

    2001-12-01

    IUE observations of the eclipsing binary system HR 6902 obtained at various epochs spread over four years indicate the presence of warm circumstellar material enveloping the G9 IIb primary. The spectra show Si Iv and C Iv absorption up to a distance of 3.3 giant radii (Rg). Line ratio diagnostics yields an electron temperature of ~ 78 000 K which appears to be constant over the observed height range. Applying a least square fit absorption line analysis we derive column densities as a function of height. We find that the inner envelope (improved agreement with observations over the whole height regime including the emission line region is obtained with an outflow model. We demonstrate that the common β power-law as well as a P ∝ ρ wind yield appropriate fit models. Adopting a continuous mass outflow we obtain a mass-loss rate of M⊙=0.8 - 3.4 × 10-11 Msolar yr-1 depending on the particular wind model. The emission lines observed during total eclipse are attributed mostly to resonance scattering of B star photons in the extended envelope of the giant. By means of a multi-dimensional line formation study we show that the global envelope properties are consistent with the wind models derived from the absorption line analysis. We argue that future high resolution UV spectroscopy will resolve the large-scale velocity structure of the circumstellar shell. As an illustration we present theoretical Si Iv and C Iv emission profiles showing model-dependent line shifts and asymmetries.

  9. Observational Possibility of the "Snow Line" on the Surface of Circumstellar Disks with the Scattered Light

    CERN Document Server

    Inoue, Akio K; Nakamoto, Taishi; Oka, Akinori

    2008-01-01

    We discuss how we obtain the spatial distribution of ice on the surface of the circumstellar disk around young stars. Ice in the disks plays a very important role in various issues, for instance, on the disk structure, on the planet formation, on the isotopic anomaly in meteorites, and on the origin of the sea on the Earth. Therefore, the spatially resolved observation of the condensation/sublimation front of ice, so-called ``snow line'' is strongly required. Here, we propose a new method for obtaining the spatially resolved ``snow line'' on the circumstellar disks by observing 3 \\micron H$_2$O ice feature in the scattered light. Based on radiative transfer considerations, we show that the feature is clearly imprinted in the spectrum of the scattered light from both optically thick and thin circumstellar disks. We also show that the scattered light and the H$_2$O ice feature from protoplanetary disks are detectable and spatially resolvable with the current instruments through a $H_2O$ narrowband filter around...

  10. The Nature of Transition Circumstellar Disks II. Southern Molecular Clouds

    OpenAIRE

    Romero, Gisela A.; Schreiber, Matthias R.; Cieza, Lucas A.; Rebassa-Mansergas, Alberto; Merín, Bruno; Castelli, Analía V. Smith; Allen, Lori E.; Morrell, Nidia

    2012-01-01

    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 ...

  11. On the central symmetry of the circumstellar envelope of RS Cnc

    CERN Document Server

    Nhung, Pham Tuyet; Winters, Jan Martin; Darriulat, Pierre; Gérard, Eric; Bertre, Thibaut Le

    2014-01-01

    We present a phenomenological study of CO(1-0) and CO(2-1) emission from the circumstellar envelope (CSE) of the Asymptotic Giant Branch (AGB) star RS\\,Cnc. It reveals departures from central symmetry that turn out to be efficient tools for the exploration of some of the CSE properties. We use a wind model including a bipolar flow with a typical wind velocity of $\\sim$8 km\\,s$^{-1}$ decreasing to $\\sim$2 km\\,s$^{-1}$ near the equator to describe Doppler velocity spectral maps obtained by merging data collected at the IRAM Plateau de Bure Interferometer and Pico Veleta single dish radio telescope. Parameters describing the wind morphology and kinematics are obtained, together with the radial dependence of the gas temperature in the domain of the circumstellar envelope probed by the CO observations. Significant north-south central asymmetries are revealed by the analysis, which we quantify using a simple phenomenological description. The origin of such asymmetries is unclear.

  12. The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales

    CERN Document Server

    Leao, I C; Mekarnia, D; De Medeiros, J R; Vandame, B; Laverny, Patrick De; Vandame, Benoit

    2006-01-01

    Aims.Analysis of the innermost regions of the carbon-rich star IRC+10216 and of the outer layers of its circumstellar envelope have been performed in order to constrain its mass-loss history. Methods: .We analyzed the high dynamic range of near-infrared adaptive optics and the deep V-band images of the circumstellar envelope of IRC+10216 using high angular resolution, collected with the VLT/NACO and FORS1 instruments. Results: .From the near-infrared observations, we present maps of the sub-arcsecond structures, or clumps, in the innermost regions. The morphology of these clumps is found to strongly vary from J- to L-band. Their relative motion appears to be more complex than proposed in earlier works: they can be weakly accelerated, have a constant velocity, or even be motionless with respect to one another. From V-band imaging, we present a high spatial resolution map of the shell distribution in the outer layers of IRC+10216. Shells are resolved well up to a distance of about 90'' to the core of the nebula...

  13. The circumstellar envelope of the C-rich post-AGB star HD 56126

    CERN Document Server

    Hony, S; Waters, L B F M; De Koter, A

    2003-01-01

    We present a detailed study of the circumstellar envelope of the post-asymptotic giant branch ``21 micron object'' HD 56126. We build a detailed dust radiative transfer model of the circumstellar envelope in order to derive the dust composition and mass, and the mass-loss history of the star. To model the emission of the dust we use amorphous carbon, hydrogenated amorphous carbon, magnesium sulfide and titanium carbide. We present a detailed parametrisation of the optical properties of hydrogenated amorphous carbon as a function of H/C content. The mid-infrared imaging and spectroscopy is best reproduced by a single dust shell from 1.2 to 2.6 arcsec radius around the central star. This shell originates from a short period during which the mass-loss rate exceeded 10^(-4) M_sun/yr. We find that the strength of the ``21'' micron feature poses a problem for the TiC identification. The low abundance of Ti requires very high absorption cross-sections in the ultraviolet and visible wavelength range to explain the st...

  14. AGB stars in the LMC: evolution of dust in circumstellar envelopes

    CERN Document Server

    Dell'Agli, F; Schneider, R; Di Criscienzo, M; García-Hernández, D A; Rossi, C; Brocato, E

    2014-01-01

    We calculated theoretical evolutionary sequences of asymptotic giant branch (AGB) stars, including formation and evolution of dust grains in their circumstellar envelope. By considering stellar populations of the Large Magellanic Cloud (LMC), we calculate synthetic colour-colour and colour-magnitude diagrams, which are compared with those obtained by the Spitzer Space Telescope. The comparison between observations and theoretical predictions outlines that extremely obscured carbon-stars and oxygen-rich sources experiencing hot bottom burning (HBB) occupy well defined, distinct regions in the colour-colour ($[3.6]-[4.5]$, $[5.8]-[8.0]$) diagram. The C-rich stars are distributed along a diagonal strip that we interpret as an evolutionary sequence, becoming progressively more obscured as the stellar surface layers enrich in carbon. Their circumstellar envelopes host solid carbon dust grains with size in the range $0.05 2$, are the descendants of stars with initial mass $M_{in} \\sim 2.5 - 3 M_{\\odot}$ in the ver...

  15. Tracing planet-induced structures in circumstellar disks using molecular lines

    CERN Document Server

    Ober, F; Uribe, A L; Klahr, H H

    2015-01-01

    Circumstellar disks are considered to be the birthplace of planets. Specific structures like spiral arms, gaps, and cavities are characteristic indicators of planet-disk interaction. Investigating these structures can provide insights into the growth of protoplanets and the physical properties of the disk. We investigate the feasibility of using molecular lines to trace planet-induced structures in circumstellar disks. Based on 3D hydrodynamic simulations of planet-disk interactions, we perform self-consistent temperature calculations and produce N-LTE molecular line velocity-channel maps and spectra of these disks using our new N-LTE line radiative transfer code Mol3D. Subsequently, we simulate ALMA observations using the CASA simulator. We consider two nearly face-on inclinations, 5 disk masses, 7 disk radii, and 2 different typical pre-main-sequence host stars (T Tauri, Herbig Ae). We calculate up to 141 individual velocity-channel maps for five molecules/isotopoloques in a total of 32 rotational transitio...

  16. The Nature of Transition Circumstellar Disks II. Southern Molecular Clouds

    CERN Document Server

    Romero, Gisela A; Cieza, Lucas A; Rebassa-Mansergas, Alberto; Merín, Bruno; Castelli, Analía V Smith; Allen, Lori E; Morrell, Nidia; 10.1088/0004-637X/749/1/79

    2012-01-01

    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 lsim1 to 10 M JUP, and accretion rates ranging from lsim10-11 to 10-7.7 M \\odot yr-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, ph...

  17. Photoevaporation of Circumstellar Disks Revisited: The Dust-Free Case

    CERN Document Server

    Tanaka, Kei E I; Omukai, Kazuyuki

    2013-01-01

    Photoevaporation by stellar ionizing radiation is believed to play an important role in the dispersal of disks around young stars. The mass loss model for dust-free disks developed by Hollenbach et al. is currently regarded as a conventional one and has been used in a wide variety of studies. However, the rate in this model was derived by the crude so-called 1+1D approximation of ionizing radiation transfer, which assumes that diffuse radiation propagates in a direction vertical to the disk. In this study, we revisit the photoevaporation of dust-free disks by solving the 2D axisymmetric radiative transfer for steady-state disks. Unlike that solved by the conventional model, we determine that direct stellar radiation is more important than the diffuse field at the disk surface. The radial density distribution at the ionization boundary is represented by the single power-law with an index -3/2 in contrast to the conventional double power-law. For this distribution, the photoevaporation rate from the entire disk...

  18. A Survey for Circumstellar Disks Around Young Substellar Objects

    CERN Document Server

    Liu, M C; Tokunaga, A T; Liu, Michael C.; Najita, Joan; Tokunaga, Alan T.

    2003-01-01

    (Abridged) We have completed the first systematic survey for disks around spectroscopically identified young brown dwarfs and very low mass stars. We have obtained L'-band (3.8 um) imaging for 38 very cool objects in IC 348 and Taurus. Our targets span spectral types from M6 to M9.5 (~100 to ~15 Mjup). We find that most of our sample (77%+/-15%) possess intrinsic IR excesses, indicative of disks. Because the excesses are modest, conventional analyses using only IR colors would have missed most of the sources with excesses. The observed IR excesses are correlated with Halpha emission, consistent with a common accretion disk origin. The excesses can be explained by disk reprocessing of starlight alone; the implied accretion rates are at least an order of magnitude below typical values for classical T Tauri stars. The observed distribution of IR excesses suggests the presence of inner disk holes. The disk frequency appears to be independent of mass and age. In the same star-forming regions, disks around brown dw...

  19. Sulphur molecules in the circumstellar envelopes of M-type AGB stars

    Science.gov (United States)

    Danilovich, T.; De Beck, E.; Black, J. H.; Olofsson, H.; Justtanont, K.

    2016-04-01

    Aims: The sulphur compounds SO and SO2 have not been widely studied in the circumstellar envelopes of asymptotic giant branch (AGB) stars. By presenting and modelling a large number of SO and SO2 lines in the low mass-loss rate M-type AGB star R Dor, and modelling the available lines of those molecules in a further four M-type AGB stars, we aim to determine their circumstellar abundances and distributions. Methods: We use a detailed radiative transfer analysis based on the accelerated lambda iteration method to model circumstellar SO and SO2 line emission. We use molecular data files for both SO and SO2 that are more extensive than those previously available. Results: Using 17 SO lines and 98 SO2 lines to constrain our models for R Dor, we find an SO abundance of (6.7 ± 0.9) × 10-6 and an SO2 abundance of 5 × 10-6 with both species having high abundances close to the star. We also modelled 34SO and found an abundance of (3.1 ± 0.8) × 10-7, giving an 32SO/34SO ratio of 21.6 ± 8.5. We derive similar results for the circumstellar SO and SO2 abundances and their distributions for the low mass-loss rate object W Hya. For the higher mass-loss rate stars, we find shell-like SO distributions with peak abundances that decrease and peak abundance radii that increase with increasing mass-loss rate. The positions of the peak SO abundance agree very well with the photodissociation radii of H2O. We also modelled SO2 in two higher mass-loss rate stars but our models for these were less conclusive. Conclusions: We conclude that for the low mass-loss rate stars, the circumstellar SO and SO2 abundances are much higher than predicted by chemical models of the extended stellar atmosphere. These two species may also account for all the available sulphur. For the higher mass-loss rate stars we find evidence that SO is most efficiently formed in the circumstellar envelope, most likely through the photodissociation of H2O and the subsequent reaction between S and OH. The S

  20. Formation Process of the Circumstellar Disk: Long-term Simulations in the Main Accretion Phase of Star Formation

    Science.gov (United States)

    Machida, Masahiro N.; Inutsuka, Shu-ichiro; Matsumoto, Tomoaki

    2010-12-01

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of gsim3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of ~0.005-0.1 M sun, while the protostar has a mass of ~10-3 M sun. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for ~105 yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

  1. Detection of warm molecular hydrogen in the circumstellar disk around the Herbig Ae star HD97048

    OpenAIRE

    Martin-Zaidi, C.; Lagage, P-. O.; Pantin, E.; Habart, E.

    2007-01-01

    We present high resolution spectroscopic mid-infrared observations of the circumstellar disk around the Herbig Ae star HD97048 with the VLT Imager and Spectrometer for the mid-InfraRed (VISIR). We detect the S(1) pure rotational line of molecular hydrogen (H2) at 17.035 microns arising from the disk around the star. This detection reinforces the claim that HD97048 is a young object surrounded by a flared disk at an early stage of evolution. The emitting warm gas is located within the inner 35...

  2. Dust Distribution in the beta Pictoris Circumstellar Disks

    CERN Document Server

    Ahmic, Mirza; Artymowicz, Pawel

    2009-01-01

    We present 3-D models of dust distribution around beta Pictoris that produce the best fits to the Hubble Space Telescope Advanced Camera for Surveys' (HST/ACS) images obtained by Golimowski and co-workers. We allow for the presence of either one or two separate axisymmetric dust disks. The density models are analytical, radial two-power-laws joined smoothly at a cross-over radius with density exponentially decreasing away from the mid-plane of the disks. Two-disk models match the data best, yielding a reduced chi^2 of ~1.2. Our two-disk model reproduces many of the asymmetries reported in the literature and suggests that it is the secondary (tilted) disk which is largely responsible for them. Our model suggests that the secondary disk is not constrained to the inner regions of the system (extending out to at least 250 AU) and that it has a slightly larger total area of dust than the primary, as a result of slower fall-off of density with radius and height. This surprising result raises many questions about th...

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

    CERN Document Server

    Tanii, Ryoko; Kudo, Tomoyuki; Hioki, Tomonori; Oasa, Yumiko; Gupta, Ranjan; Sen, A K; Wisniewski, J P; Muto, T; Grady, C A; Hashimoto, J; Fukagawa, M; Mayama, S; Hornbeck, J; Sitko, M; Russell, R; Werren, C; Cure, M; Currie, T; Ohashi, N; Okamoto, Y; Momose, M; Honda, M; Inutsuka, S -I; Takeuchi, T; Dong, R; Abe, L; Brandner, W; Brandt, T; Carson, J; Egner, S; Feldt, M; Fukue, T; Goto, M; Guyon, O; Hayano, Y; Hayashi, M; Hayashi, S S; Henning, T; Hodapp, K W; Ishii, M; Iye, M; Janson, M; Kandori, R; Knapp, G P; Kusakabe, N; Kuzuhara, M; Matsuo, T; McElwain, M W; Miyama, S; Morino, J -I; Moro-Martin, A; Nishimura, T; Pyo, T -S; Serabyn, G; Suto, H; Suzuki, R; Takami, M; Takato, N; Terada, H; Thalmann, C; Tomono, D; Turner, E L; Watanabe, M; Yamada, T; Takami, H; Usuda, T; Tamura, M

    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 \\pm 2 degree 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 (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 w...

  4. Photodissociation and chemistry of N2 in the circumstellar envelope of carbon-rich AGB stars

    Science.gov (United States)

    Li, Xiaohu; Millar, Tom J.; Walsh, Catherine; Heays, Alan N.; van Dishoeck, Ewine F.

    2014-08-01

    Context. The envelopes of asymptotic giant branch (AGB) stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N2 and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N2 has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. Aims: For the first time, we use accurate N2 and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. Methods: We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N2 photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. Results: The transition of N2→ N (also, CO → C → C+) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, CnN (n = 1, 3, 5), CnN- (n = 1, 3, 5), HCnN (n = 1, 3, 5, 7, 9), H2CN and CH2CN. Conclusions: The chemistry of many species is directly or indirectly affected by the photodissociation of N2 and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N2 and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance.

  5. Circumstellar disks of the most vigorously accreting young stars.

    Science.gov (United States)

    Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer L; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-02-01

    Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood. PMID:26989772

  6. Apparent Stellar Wobble by a Planet in a Circumstellar Disk: Limitations on Planet Detection by Astrometry

    Science.gov (United States)

    Takeuchi, Taku; Velusamy, T.; Lin, D. N. C.

    2005-01-01

    Astrometric detection of a stellar wobble on the plane of the sky will provide us the next breakthrough in searching for extrasolar planets. The Space Interferometry Mission (SIM) is expected to achieve high-precision astrometry as accurate as 1 (mu)as, which is precise enough to discover a newborn Jupiter mass planet around a pre-main-sequence (PMS) star in the Taurus-Auriga star-forming region. PMS stars, however, have circumstellar disks that may be obstacles to the precise measurement of the stellar position.We present results on disk influences on the stellar wobble. The density waves excited by a planet move both the disk's mass center and the photocenter. The motion of the disk mass center induces an additional wobble of the stellar position, and the motion of the disk photocenter causes a contamination in the measurement of the stellar position. We show that the additional stellar motion dynamically caused by the disk's gravity is always negligible but that the contamination by the disk light can interfere with the precise measurement of the stellar position if the planet's mass is smaller than approximately 10MJ. The motion of the disk photocenter is sensitive to a slight change in the wave pattern and the disk properties. Measurements by interferometers are generally insensitive to extended sources such as disks. Because of this property, SIM will not suffer significant contamination by the disk light, even if the planet's mass is as small as 1M(sub J).

  7. Dynamics of Circumstellar Disks; 2, Heating and Cooling

    CERN Document Server

    Nelson, A F; Ruzmaikina, T; Nelson, Andrew F.; Benz, Willy; Ruzmaikina, Tamara

    1999-01-01

    We present a series of 2-d ($r,\\phi$) hydrodynamic simulations of marginally self gravitating disks around protostars using an SPH code. We implement simple dynamical heating and we cool each location as a black body, using a photosphere temperature obtained from the local vertical structure. We synthesize SEDs from our simulations and compare them to fiducial SEDs derived from observed systems. These simulations produce less distinct spiral structure than isothermally evolved systems, especially in the inner third of the disk. Pattern are similar further from the star but do not collapse into condensed objects. The photosphere temperature is well fit to a power law in radius with index $q\\sim1.1$, which is very steep. Far from the star, internal heating ($PdV$ work and shocks) are not responsible for generating a large fraction of the thermal energy contained in the disk matter. Gravitational torques responsible for such shocks cannot transport mass and angular momentum efficiently in the outer disk. Within ...

  8. CO and HI emission from the circumstellar envelopes of some evolved stars

    CERN Document Server

    Diep, P N; Nhung, P T; Tuan-Anh, P; Bertre, T Le; Winters, J M; Matthews, L D; Phuong, N T; Thao, N T; Darriulat, P

    2015-01-01

    Studies of the CO and HI radio emission of some evolved stars are presented using data collected by the IRAM Plateau de Bure interferometer and Pico Veleta telescope, the Nan\\c{c}ay Radio Telescope and the JVLA and ALMA arrays. Approximate axial symmetry of the physical and kinematic properties of the circumstellar envelope (CSE) are observed in CO emission, in particular, from RS Cnc, EP Aqr and the Red Rectangle. A common feature is the presence of a bipolar outflow causing an enhanced wind velocity in the polar directions. HI emission extends to larger radial distances than probed by CO emission and displays features related to the interaction between the stellar outflow and interstellar matter. With its unprecedented sensitivity, FAST will open a new window on such studies. Its potential in this domain is briefly illustrated.

  9. Effects of stellar flybys on planetary systems: 3D modeling of the circumstellar disks damping effects

    CERN Document Server

    Picogna, Giovanni

    2014-01-01

    Stellar flybys in star clusters are suspected to affect the orbital architecture of planetary systems causing eccentricity excitation and orbital misalignment between the planet orbit and the equatorial plane of the star. We explore whether the impulsive changes in the orbital elements of planets, caused by an hyperbolic stellar flyby, can be fully damped by the circumstellar disk surrounding the star. The time required to disperse stellar clusters is in fact comparable to circumstellar disk's lifetime. We have modelled in 3D a system made of a solar type star surrounded by a low density disk with a giant planet embedded in it approached on a hyperbolic encounter trajectory by a second star, of similar mass and with its own disk. We focus on extreme configurations where a very deep stellar flyby perturbs a Jovian planet on an external orbit. This allows to test in full the ability of the disk to erase the effects of the stellar encounter. We find that the amount of mass lost by the disk during the stellar fly...

  10. FIRST SCIENCE OBSERVATIONS WITH SOFIA/FORCAST: PROPERTIES OF INTERMEDIATE-LUMINOSITY PROTOSTARS AND CIRCUMSTELLAR DISKS IN OMC-2

    International Nuclear Information System (INIS)

    We examine eight young stellar objects in the OMC-2 star-forming region based on observations from the SOFIA/FORCAST early science phase, the Spitzer Space Telescope, the Herschel Space Observatory, Two Micron All Sky Survey, Atacama Pathfinder Experiment, and other results in the literature. We show the spectral energy distributions (SED) of these objects from near-infrared to millimeter wavelengths, and compare the SEDs with those of sheet collapse models of protostars and circumstellar disks. Four of the objects can be modeled as protostars with infalling envelopes, two as young stars surrounded by disks, and the remaining two objects have double-peaked SEDs. We model the double-peaked sources as binaries containing a young star with a disk and a protostar. The six most luminous sources are found in a dense group within a 0.15 × 0.25 pc region; these sources have luminosities ranging from 300 L☉ to 20 L☉. The most embedded source (OMC-2 FIR 4) can be fit by a class 0 protostar model having a luminosity of ∼50 L☉ and mass infall rate of ∼10–4 M☉ yr–1.

  11. FIRST SCIENCE OBSERVATIONS WITH SOFIA/FORCAST: PROPERTIES OF INTERMEDIATE-LUMINOSITY PROTOSTARS AND CIRCUMSTELLAR DISKS IN OMC-2

    Energy Technology Data Exchange (ETDEWEB)

    Adams, Joseph D.; Herter, Terry L.; Gull, George E.; Henderson, Charles P.; Schoenwald, Justin; Stacey, Gordon [Department of Astronomy, Cornell University, Space Sciences Bldg., Ithaca, NY 14853 (United States); Osorio, Mayra; Macias, Enrique [Instituto de Astrofisica de Andalucia, CSIC, Camino Bajo de Huetor 50, E-18008 Granada (Spain); Thomas Megeath, S.; Fischer, William J. [Department of Physics and Astronomy, University of Toledo, Mailstop 111, 2801 West Bancroft Street, Toledo, OH 43606 (United States); Ali, Babar [NHSC/IPAC/Caltech, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Calvet, Nuria [Department of Astronomy, University of Michigan, 825 Dennison Building, 500 Church St, Ann Arbor, MI 48109 (United States); D' Alessio, Paola [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, 58089 Morelia, Michoacan (Mexico); De Buizer, James M.; Shuping, Ralph Y. [SOFIA-University Space Research Association, NASA Ames Research Center, Mail Stop N211-3, Moffett Field, CA 94035 (United States); Keller, Luke D. [Ithaca College, Physics Department, 264 Ctr for Natural Sciences, Ithaca, NY 14850 (United States); Morris, Mark R. [Department of Physics and Astronomy, University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1547 (United States); Remming, Ian S. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Stanke, Thomas [ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Muenchen (Germany); Stutz, Amelia [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); and others

    2012-04-20

    We examine eight young stellar objects in the OMC-2 star-forming region based on observations from the SOFIA/FORCAST early science phase, the Spitzer Space Telescope, the Herschel Space Observatory, Two Micron All Sky Survey, Atacama Pathfinder Experiment, and other results in the literature. We show the spectral energy distributions (SED) of these objects from near-infrared to millimeter wavelengths, and compare the SEDs with those of sheet collapse models of protostars and circumstellar disks. Four of the objects can be modeled as protostars with infalling envelopes, two as young stars surrounded by disks, and the remaining two objects have double-peaked SEDs. We model the double-peaked sources as binaries containing a young star with a disk and a protostar. The six most luminous sources are found in a dense group within a 0.15 Multiplication-Sign 0.25 pc region; these sources have luminosities ranging from 300 L{sub Sun} to 20 L{sub Sun }. The most embedded source (OMC-2 FIR 4) can be fit by a class 0 protostar model having a luminosity of {approx}50 L{sub Sun} and mass infall rate of {approx}10{sup -4} M{sub Sun} yr{sup -1}.

  12. First Science Observations with SOFIA/FORCAST: Properties of Intermediate-Luminosity Protostars and Circumstellar Disks in OMC-2

    CERN Document Server

    Adams, Joseph D; Osorio, Mayra; Macias, Enrique; Megeath, S Thomas; Fischer, William J; Ali, Babar; Calvet, Nuria; D'Alessio, Paola; De Buizer, James M; Gull, George E; Henderson, Charles P; Keller, Luke D; Morris, Mark R; Remming, Ian S; Schoenwald, Justin; Shuping, Ralph Y; Stacey, Gordon; Stanke, Thomas; Stutz, Amelia; Vacca, William

    2012-01-01

    We examine eight young stellar objects in the OMC-2 star forming region based on observations from the SOFIA/FORCAST early science phase, the Spitzer Space Telescope, the Herschel Space Observatory, 2MASS, APEX, and other results in the literature. We show the spectral energy distributions of these objects from near-infrared to millimeter wavelengths, and compare the SEDs with those of sheet collapse models of protostars and circumstellar disks. Four of the objects can be modelled as protostars with infalling envelopes, two as young stars surrounded by disks, and the remaining two objects have double-peaked SEDs. We model the double-peaked sources as binaries containing a young star with a disk and a protostar. The six most luminous sources are found in a dense group within a 0.15 x 0.25 pc region; these sources have luminosities ranging from 300 L_sun to 20 L_sun. The most embedded source (OMC-2 FIR 4) can be fit by a class 0 protostar model having a luminosity of ~50 L_sun and mass infall rate of ~10^-4 sol...

  13. Circumstellar Disks of the Most Vigorously Accreting Young Stars

    CERN Document Server

    Liu, Hauyu Baobab; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-01-01

    Young stellar objects (YSOs) may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. We report our high angular resolution, coronagraphic near-infrared polarization imaging observations using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) of the Subaru 8.2 m Telescope, towards four YSOs which are undergoing luminous accretion outbursts. The obtained infrared images have verified the presence of several hundred AUs scale arms and arcs surrounding these YSOs. In addition, our hydrodynamics simulations and radiative transfer models further demonstrate that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation p...

  14. Planet--planet scattering in circumstellar gas disks

    OpenAIRE

    Marzari, F.; Baruteau, C.; Scholl, H.

    2010-01-01

    Hydrodynamical simulations of two giant planets embedded in a gaseous disk have shown that in case of a smooth convergent migration they end up trapped into a mean motion resonance. These findings have led to the conviction that the onset of dynamical instability causing close encounters between the planets can occur only after the dissipation of the gas when the eccentricity damping is over. We show that a system of three giant planets may undergo planet-planet scattering when the gaseous di...

  15. FORMATION PROCESS OF THE CIRCUMSTELLAR DISK: LONG-TERM SIMULATIONS IN THE MAIN ACCRETION PHASE OF STAR FORMATION

    International Nuclear Information System (INIS)

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of ∼>3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than sun, while the protostar has a mass of ∼10-3 Msun. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for ∼105 yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

  16. Planet--planet scattering in circumstellar gas disks

    CERN Document Server

    Marzari, F; Scholl, H

    2010-01-01

    Hydrodynamical simulations of two giant planets embedded in a gaseous disk have shown that in case of a smooth convergent migration they end up trapped into a mean motion resonance. These findings have led to the conviction that the onset of dynamical instability causing close encounters between the planets can occur only after the dissipation of the gas when the eccentricity damping is over. We show that a system of three giant planets may undergo planet-planet scattering when the gaseous disk, with density values comparable to that of the Minimum Mass Solar Nebula, is still interacting with the planets. The hydrodynamical code FARGO--2D--1D is used to model the evolution ofthe disk and planets, modified to properly handle close encounters between the massive bodies. Our simulations predict a variety of different outcomes of the scattering phase which includes orbital exchange, planet merging and scattering of a planet in a hyperbolic orbit. This implies thatthe final fate of a multiplanet system under the a...

  17. The PDS 66 Circumstellar Disk as seen in Polarized Light with the Gemini Planet Imager

    CERN Document Server

    Wolff, Schuyler G; Millar-Blanchaer, Maxwell A; Nielsen, Eric L; Wang, Jason; Cardwell, Andrew; Chilcote, Jeffrey; Dong, Ruobing; Draper, Zachary H; Duchene, Gaspard; Fitzgerald, Michael P; Goodsell, Stephen J; Grady, Carol A; Graham, James R; Greenbaum, Alexandra Z; Hartung, Markus; Hibon, Pascale; Hines, Dean C; Hung, Li-Wei; Kalas, Paul; Macintosh, Bruce; Marchis, Franck; Marois, Christian; Pueyo, Laurent; Rantakyro, Fredrik T; Schneider, Glenn; Sivaramakrishnan, Anand; Wiktorowicz, Sloane J

    2016-01-01

    We present H and K band imaging polarimetry for the PDS 66 circumstellar disk obtained during the commissioning of the Gemini Planet Imager (GPI). Polarization images reveal a clear detection of the disk in to the 0.12'' inner working angle (IWA) in H band, almost 3 times as close to the star as the previous HST observations with NICMOS and STIS (0.35'' effective IWA). The centro-symmetric polarization vectors confirm that the bright inner disk detection is due to circumstellar scattered light. A more diffuse disk extends to a bright outer ring centered at 80 AU. We discuss several physical mechanisms capable of producing the observed ring + gap structure. GPI data confirm enhanced scattering on the East side of the disk which is inferred to be nearer to us. We also detect a lateral asymmetry in the South possibly due to shadowing from material within the inner working angle. This likely corresponds to a temporally variable azimuthal asymmetry observed in HST/STIS coronagraphic imaging.

  18. The warm circumstellar envelope and wind of the G9 IIb star HR 6902

    CERN Document Server

    Kirsch, T; Reimers, D

    2001-01-01

    IUE observations of the eclipsing binary system HR 6902 obtained at various epochs spread over four years indicate the presence of warm circumstellar material enveloping the G9 IIb primary. The spectra show Si IV and C IV absorption up to a distance of 3.3 giant radii (R_g}. Line ratio diagnostics yields an electron temperature of ~ 78000 K which appears to be constant over the observed height range. Applying a least square fit absorption line analysis we derive column densities as a function of height. We find that the inner envelope (< 3 R_g) of the bright giant is consistent with a hydrostatic density distribution. The derived line broadening velocity of ~ 70 kms^{-1} is sufficient to provide turbulent pressure support for the required scale height. However, an improved agreement with observations over the whole height regime including the emission line region is obtained with an outflow model. We demonstrate that the common beta power-law as well as a P \\propto rho wind yield appropriate fit models. Ad...

  19. ALMA Observations of Circumstellar Disks in the Upper Scorpius OB Association

    CERN Document Server

    Barenfeld, Scott A; Ricci, Luca; Isella, Andrea

    2016-01-01

    We present ALMA observations of 106 G-, K-, and M-type stars in the Upper Scorpius OB Association hosting circumstellar disks. With these data, we measure the 0.88 mm continuum and $^{12}$CO $J = 3-2$ line fluxes of disks around low mass ($0.14-1.66$ $M_{\\odot}$) stars at an age of 5-11 Myr. Of the 75 primordial disks in the sample, 53 are detected in the dust continuum and 26 in CO. Of the 31 disks classified as debris/evolved transitional disks, 5 are detected in the continuum and none in CO. The lack of CO emission in approximately half of the disks with detected continuum emission can be explained if CO is optically thick but has a compact emitting area ($\\lesssim 40$ AU), or if the CO is heavily depleted by a factor of at least $\\sim1000$ relative to interstellar medium abundances and is optically thin. The continuum measurements are used to estimate the dust mass of the disks. We find a correlation between disk dust mass and stellar host mass consistent with a power-law relation of $M_{dust}\\propto M_*^...

  20. A CHARA ARRAY SURVEY OF CIRCUMSTELLAR DISKS AROUND NEARBY Be-TYPE STARS

    International Nuclear Information System (INIS)

    We report on a high angular resolution survey of circumstellar disks around 24 northern sky Be stars. The K-band continuum survey was made using the CHARA Array long baseline interferometer (baselines of 30-331 m). The interferometric visibilities were corrected for the flux contribution of stellar companions in those cases where the Be star is a member of a known binary or multiple system. For those targets with good (u, v) coverage, we used a four-parameter Gaussian elliptical disk model to fit the visibilities and to determine the axial ratio, position angle, K-band photospheric flux contribution, and angular diameter of the disk's major axis. For the other targets with relatively limited (u, v) coverage, we constrained the axial ratio, inclination angle, and/or disk position angle where necessary in order to resolve the degeneracy between possible model solutions. We also made fits of the ultraviolet and infrared spectral energy distributions (SEDs) to estimate the stellar angular diameter and infrared flux excess of each target. The mean ratio of the disk diameter (measured in K-band emission) to stellar diameter (from SED modeling) is 4.4 among the 14 cases where we reliably resolved the disk emission, a value which is generally lower than the disk size ratio measured in the higher opacity Hα emission line. We estimated the equatorial rotational velocity from the projected rotational velocity and disk inclination for 12 stars, and most of these stars rotate close to or at the critical rotational velocity.

  1. HST Imaging of New Edge-on Circumstellar Disks in Nearby Star-forming Regions

    Science.gov (United States)

    Stapelfeldt, Karl R.; Duchene, G.; Padgett, D.; Perrin, M. D.; Wolff, S.; Krist, J. E.; Menard, F.; Pinte, C.

    2014-01-01

    Edge-on, optically thick circumstellar disks have been previously imaged at subarcsecond resolution around about a dozen nearby young stellar objects. In these systems the central star is occulted from direct view, bright star image artifacts are absent, and the disk reflected light is clearly seen. Comparison of Hubble Space Telescope (HST) edge-on disk images with scattered light models has allowed key disk structural parameters and dust grain properties to be determined. Edge-on disks have been systematically undercounted to date: while 10% of young stars should statistically be occulted by their disk, the observed frequency is much less. Thus there is a significant potential for discovering and imaging new examples. Spitzer Space Telescope legacy science programs have provided the first good spectral energy distribution (SED) measurements for the previously known edge-on disks. We have used these as templates to identify new candidates in far-infrared survey datasets. We report on the results of our HST Cycle 19 program to image twenty-one edge-on disk candidates mostly selected from their SEDs. Eleven are well-resolved with radii ranging from 30-300 AU, nine for the first time and six showing highly collimated jets. Outstanding individual sources include one showing remarkably little dust lane chromaticity (consistent with evolved grains), a highly flattened disk with a small scale height (suggestive of dust settling), and an asymmetric disk with a misaligned jet which likely traces tidal perturbations in a binary system. Follow-up work to obtain ancillary data and perform scattered light modeling of the most symmetric disks is now being pursued. The results of this program will guide a new round of searches for these rare but important snapshots of protoplanetary disk evolution.

  2. Understanding the Chemical Complexity in Circumstellar Envelopes of C-rich AGB Stars: the Case of IRC +10216

    CERN Document Server

    Agundez, M; Pardo, J R; Exposito, J P F; Guélin, M; Tenenbaum, E D; Ziurys, L M; Apponi, A J

    2007-01-01

    The circumstellar envelopes of carbon-rich AGB stars show a chemical complexity that is exemplified by the prototypical object IRC +10216, in which about 60 different molecules have been detected to date. Most of these species are carbon chains of the type CnH, CnH2, CnN, HCnN. We present the detection of new species (CH2CHCN, CH2CN, H2CS, CH3CCH and C3O) achieved thanks to the systematic observation of the full 3 mm window with the IRAM 30m telescope plus some ARO 12m observations. All these species, known to exist in the interstellar medium, are detected for the first time in a circumstellar envelope around an AGB star. These five molecules are most likely formed in the outer expanding envelope rather than in the stellar photosphere. A pure gas phase chemical model of the circumstellar envelope is reasonably successful in explaining the derived abundances, and additionally allows to elucidate the chemical formation routes and to predict the spatial distribution of the detected species.

  3. From Protoplanetary Disks to Extrasolar Planets: Understanding the Life Cycle of Circumstellar Gas with Ultraviolet Spectroscopy

    CERN Document Server

    France, Kevin; Ardila, David R; Bergin, Edwin A; Brown, Alexander; Burgh, Eric B; Calvet, Nuria; Chiang, Eugene; Cook, Timothy A; Désert, Jean-Michel; Ebbets, Dennis; Froning, Cynthia S; Green, James C; Hillenbrand, Lynne A; Johns-Krull, Christopher M; Koskinen, Tommi T; Linsky, Jeffrey L; Redfield, Seth; Roberge, Aki; Schindhelm, Eric R; Scowen, Paul A; Stapelfeldt, Karl R; Tumlinson, Jason

    2012-01-01

    Few scientific discoveries have captured the public imagination like the explosion of exoplanetary science during the past two decades. This work has fundamentally changed our picture of Earth's place in the Universe and led NASA to make significant investments towards understanding the demographics of exoplanetary systems and the conditions that lead to their formation. The story of the formation and evolution of exoplanetary systems is essentially the story of the circumstellar gas and dust that are initially present in the protostellar environment; in order to understand the variety of planetary systems observed, we need to understand the life cycle of circumstellar gas from its initial conditions in protoplanetary disks to its endpoint as planets and their atmospheres. In this white paper response to NASA's Request for Information "Science Objectives and Requirements for the Next NASA UV/Visible Astrophysics Mission Concepts (NNH12ZDA008L)", we describe scientific programs that would use the unique capabi...

  4. VOLATILE-RICH CIRCUMSTELLAR GAS IN THE UNUSUAL 49 CETI DEBRIS DISK

    International Nuclear Information System (INIS)

    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 along the line-of-sight to the central star. We determined the line-of-sight C I column density, estimated the total carbon column density, and set limits on the O I column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of β Pictoris

  5. THE GAS/DUST RATIO OF CIRCUMSTELLAR DISKS: TESTING MODELS OF PLANETESIMAL FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Horne, David [New York Center for Astrobiology, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180-3590 (United States); Gibb, Erika [Department of Physics and Astronomy, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121 (United States); Rettig, Terrence W.; Tilley, David; Balsara, Dinshaw [Center for Astrophysics, University of Notre Dame, Notre Dame, IN 46556 (United States); Brittain, Sean [Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978 (United States)

    2012-07-20

    We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6-5b. {sup 12}CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.

  6. VOLATILE-RICH CIRCUMSTELLAR GAS IN THE UNUSUAL 49 CETI DEBRIS DISK

    Energy Technology Data Exchange (ETDEWEB)

    Roberge, Aki; Grady, Carol A. [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States); Welsh, Barry Y. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Kamp, Inga [Kapteyn Astronomical Institute, University of Groningen, 9700 AV Groningen (Netherlands); Weinberger, Alycia J., E-mail: Aki.Roberge@nasa.gov [Department of Terrestrial Magnitism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington, DC 20015 (United States)

    2014-11-20

    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 along the line-of-sight to the central star. We determined the line-of-sight C I column density, estimated the total carbon column density, and set limits on the O I column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of β Pictoris.

  7. Volatile-Rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk

    CERN Document Server

    Roberge, Aki; Kamp, Inga; Weinberger, Alycia J; Grady, Carol A

    2014-01-01

    We present Hubble Space Telescope STIS far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing sub-mm CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying along the line-of-sight to the central star. We determined the line-of-sight CI column density, estimated the total carbon column density, and set limits on the OI column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of Beta Pictoris.

  8. THE GAS/DUST RATIO OF CIRCUMSTELLAR DISKS: TESTING MODELS OF PLANETESIMAL FORMATION

    International Nuclear Information System (INIS)

    We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6-5b. 12CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.

  9. Line-driven ablation of circumstellar disks: I. Optically thin decretion disks of classical Oe/Be stars

    CERN Document Server

    Kee, N D; Sundqvist, J O

    2016-01-01

    The extreme luminosities of hot, massive stars drive strong stellar winds through UV line-scattering. For OB stars with an orbiting circumstellar disk, we explore the effect of such line-scattering in ablating disk material, initially focusing on the marginally optically thin decretion disks of classical Oe and Be stars. For this we apply a multi-dimensional radiation-hydrodynamics code, assuming optically thin ray tracing for the stellar continuum and a multi-ray Sobolev treatment of the line transfer. This accounts for desaturation of line-absorption by Keplerian shear in the disk, and associated driving by non-radial photons. Results show dense, intermediate-speed surface ablation, consistent with the strong, blue-shifted absorption seen in UV wind lines of Be shell stars. The asymptotic ablation rate is typically an order-unity factor times the stellar wind mass loss rate, leading to disk destruction times of order months to years for Be disks, consistent with observations. The much stronger radiative for...

  10. Tracing planet-induced structures in circumstellar disks using molecular lines

    Science.gov (United States)

    Ober, F.; Wolf, S.; Uribe, A. L.; Klahr, H. H.

    2015-07-01

    Context. Circumstellar disks are considered to be the birthplace of planets. Specific structures like spiral arms, gaps, and cavities are characteristic indicators of planet-disk interaction. Investigating these structures can provide insights into the growth of protoplanets and the physical properties of the disk. Aims: We investigate the feasibility of using molecular lines to trace planet-induced structures in circumstellar disks. Methods: Based on 3D hydrodynamic simulations of planet-disk interactions obtained with the PLUTO code, we perform self-consistent temperature calculations and produce N-LTE molecular line velocity-channel maps and spectra of these disks using our new N-LTE line radiative transfer code Mol3D. Subsequently, we simulate ALMA observations using the CASA simulator. We consider two nearly face-on inclinations, five disk masses, seven disk radii, and two different typical pre-main-sequence host stars (T Tauri, Herbig Ae) at a distance of 140 pc. We calculate up to 141 individual velocity-channel maps for five molecules/isotopoloques (12C16O, 12C18O, HCO+, HCN, and CS) in a total of 32 rotational transitions to investigate the frequency dependence of the structures indicated above. Results: We find that the majority of protoplanetary disks in our parameter space could be detected in the molecular lines considered. However, unlike the continuum case, gap detection is not straightforward in lines. For example, gaps are not seen in symmetric rings but are masked by the pattern caused by the global (Keplerian) velocity field. By comparison with simulated observations of undisturbed disks we identify specific regions in the velocity-channel maps that are characteristic of planet-induced structures. Conclusions: Simulations of high angular resolution molecular line observations demonstrate the potential of ALMA to provide complementary information about the planet-disk interaction as compared to continuum observations. In particular, the detection

  11. SN 2012ca: a stripped envelope core-collapse SN interacting with dense circumstellar medium

    CERN Document Server

    Inserra, C; Scalzo, R; Fraser, M; Pastorello, A; Childress, M; Pignata, G; Jerkstrand, A; Kotak, R; Benetti, S; Della Valle, M; Gal-Yam, A; Mazzali, P; Smith, K; Sullivan, M; Valenti, S; Yaron, O; Young, D

    2013-01-01

    We report optical and near-infrared observations of SN 2012ca with PESSTO, spread over one year since discovery. The SN bears many similarities to SN 1997cy and to other events classified as Type IIn but which have been suggested to have a thermonuclear origin with narrow hydrogen lines produced when the ejecta impact a hydrogen-rich circumstellar medium (CSM). Our analysis, especially in the nebular phase, reveals the presence of strong oxygen, magnesium and carbon features. The broad ejecta lines resemble those seen in Type Ic SNe. This suggests a core collapse explanation for this event, in contrast to the thermonuclear interpretation proposed for some members of this group. We suggest that the data can be explained with a hydrogen and helium deficient SN ejecta (Type I) interacting with a hydrogen-rich CSM, but that the explosion was more likely a Ic core-collapse explosion than a Type Ia thermonuclear explosion. This suggests two channels (both thermonuclear and stripped envelope core-collapse) are respo...

  12. CARMA CO(J = 2 - 1) Observations of the Circumstellar Envelope of Betelgeuse

    CERN Document Server

    O'Gorman, Eamon; Brown, Joanna M; Brown, Alexander; Redfield, Seth; Richter, Matthew J; Requena-Torres, Miguel A

    2012-01-01

    We report radio interferometric observations of the 12C16O 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 klambda) by combining data from all three configurations allowing us to trace spatial scales as small as 0.9\\arcsec over a 32\\arcsec 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-1 to +10.6 km s-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 w...

  13. COMPUTING THE CONTINUUM POLARIZATION FROM THOMSON SCATTERING IN GASEOUS CIRCUMSTELLAR DISKS

    International Nuclear Information System (INIS)

    We investigate the computation of the intrinsic continuum linear polarization from electron scattering in optically thin and thick circumstellar disks of gas. We present the use of a non-LTE radiative transfer code, along with two different computational methods for obtaining the Stokes parameters, to reproduce the polarization levels that arise from disks of classical Be stars. Since the pioneering work of Poeckert and Marlborough, numerous improvements and refinements have been incorporated into computational radiative transfer models of classical Be stars. We present an assessment of the effect of several improvements on Poeckert and Marlborough's technique for calculating the polarization levels of the classical Be star γ Cas. We find that improvements to the sampling of the disk density and the inclusion of a non-isothermal structure for the gas in the disk yield polarization levels that differ from the levels expected by Poeckert and Marlborough. Principally, the inclusion of the self-consistent calculation of the thermal structure of the disk has a significant impact on the resulting polarization. In addition, we assess the importance of the inclusion of multiple scattering calculations in predicting the continuum polarization in classical Be stars. We confirm that multiple scattering calculations are necessary for studying the linear polarization levels from optically thick gaseous disks around classical Be stars.

  14. Far-infrared and sub-millimetre imaging of HD 76582's circumstellar disk

    Science.gov (United States)

    Marshall, Jonathan P.; Booth, Mark; Holland, Wayne; Matthews, Brenda C.; Greaves, Jane S.; Zuckerman, Ben

    2016-04-01

    Debris disks, the tenuous rocky and icy remnants of planet formation, are believed to be evidence for planetary systems around other stars. The JCMT/SCUBA-2 debris disk legacy survey `SCUBA-2 Observations of Nearby Stars' (SONS) observed 100 nearby stars, amongst them HD 76582, for evidence of such material. Here we present imaging observations by JCMT/SCUBA-2 and Herschel/PACS at sub-millimetre and far-infrared wavelengths, respectively. We simultaneously model the ensemble of photometric and imaging data, spanning optical to sub-millimetre wavelengths, in a self-consistent manner. At far-infrared wavelengths, we find extended emission from the circumstellar disk providing a strong constraint on the dust spatial location in the outer system, although the angular resolution is too poor to constrain the interior of the system. In the sub-millimetre, photometry at 450 and 850 μm reveal a steep fall-off that we interpret as a disk dominated by moderately-sized dust grains (amin~ = ~36~μm), perhaps indicative of a non-steady-state collisional cascade within the disk. A disk architecture of three distinct annuli, comprising an unresolved component at 20 au and outer components at 80 and 270 au, along with a very steep particle size distribution (γ~ = ~5), is proposed to match the observations.

  15. Apparent Stellar Wobble by a Planet in a Circumstellar Disk: Limitations on Planet Detection by Astrometry

    OpenAIRE

    Takeuchi, Taku; Velusamy, T.; Lin, D.N.C.

    2004-01-01

    Astrometric detection of a stellar wobble on the plane of the sky will provide us a next breakthrough in searching extrasolar planets. The Space Interferometry Mission (SIM) is expected to achieve a high-precision astrometry as accurate as 1 micro-as, which is precise enough to discover a new-born Jupiter mass planet around a pre-main-sequence (PMS) star in the Taurus-Auriga star forming region. PMS stars, however, have circum-stellar disks that may be obstacles to the precise measurement of ...

  16. Dynamics of Circumstellar Disks. III. The Case of GG Tau A

    Science.gov (United States)

    Nelson, Andrew F.; Marzari, F.

    2016-08-01

    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

  17. Formation Process of the Circumstellar Disk: Long-term Simulations in the Main Accretion Phase of Star Formation

    CERN Document Server

    Machida, Masahiro N; Matsumoto, Tomoaki

    2010-01-01

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing clouds, the first (adiabatic) core with a size of ~10AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure, and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually, and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk. This indicates that the circumstellar disk is formed before the protostar formation with a size of ~10AU, which means that no protoplanetary disk smaller than <10AU exists. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the circumstellar disk has a mass of ~0.01-0.1 solar mass, while the protostar has a mass of ~10^-3 solar mass. Thus, jus...

  18. Structure and Composition of Two Transitional Circumstellar Disks in Corona Australis

    CERN Document Server

    Hughes, A M; Wilner, D J; Meyer, M R; Carpenter, J M; Qi, C; Hales, A S; Casassus, S; Hogerheijde, M R; Mamajek, E E; Wolf, S; Henning, T; Silverstone, M D

    2010-01-01

    The late stages of evolution of the primordial circumstellar disks surrounding young stars are poorly understood, yet vital to constrain theories of planet formation. We consider basic structural models for the disks around two ~10 Myr-old members of the nearby RCrA association, RX J1842.9-3532 and RX J1852.3-3700. We present new arcsecond-resolution maps of their 230 GHz continuum emission from the Submillimeter Array and unresolved CO(3-2) spectra from the Atacama Submillimeter Telescope Experiment. By combining these data with broadband fluxes from the literature and infrared fluxes and spectra from the catalog of the Formation and Evolution of Planetary Systems (FEPS) Legacy program on the Spitzer Space Telescope, we assemble a multiwavelength data set probing the gas and dust disks. Using the Monte Carlo radiative transfer code RADMC to model simultaneously the SED and millimeter continuum visibilities, we derive basic dust disk properties and identify an inner cavity of radius 16 AU in the disk around R...

  19. A HOT MOLECULAR CIRCUMSTELLAR DISK AROUND THE MASSIVE PROTOSTAR ORION SOURCE I

    Energy Technology Data Exchange (ETDEWEB)

    Hirota, Tomoya; Honma, Mareki [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Kim, Mi Kyoung [Korea Astronomy and Space Science Institute, Hwaam-dong 61-1, Yuseong-gu, Daejeon, 305-348 (Korea, Republic of); Kurono, Yasutaka, E-mail: tomoya.hirota@nao.ac.jp [Chile Observatory, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan)

    2014-02-20

    We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidates. We detected two ortho-H{sub 2}O lines at 321 GHz (10{sub 2,} {sub 9}-9{sub 3,} {sub 6}) and 336 GHz (ν{sub 2} = 1, 5{sub 2,} {sub 3}-6{sub 1,} {sub 6}) for the first time in Source I. The latter one is in a vibrationally excited state at the lower state energy of 2939 K, suggesting evidence of hot molecular gas close to Source I. The integrated intensity map of the 321 GHz line is elongated along the bipolar outflow while the 336 GHz line map is unresolved with a beam size of 0.''4. Both of these maps show velocity gradients perpendicular to the bipolar outflow. The velocity centroid map of the 321 GHz line implies a spatial and velocity structure similar to that of vibrationally excited SiO masers tracing the root of the outflow emanating from the disk surface. In contrast, the 336 GHz line is most likely emitting from the disk midplane with a diameter of 0.''2 (84 AU) as traced by radio continuum emission and a dark lane devoid of the vibrationally excited SiO maser emission. The observed velocity gradient and the spectral profile of the 336 GHz H{sub 2}O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of >7 M{sub ☉} and an excitation temperature of >3000 K. The present results provide further evidence of a hot and neutral circumstellar disk rotating around Source I with a diameter of ∼100 AU scale.

  20. A HOT MOLECULAR CIRCUMSTELLAR DISK AROUND THE MASSIVE PROTOSTAR ORION SOURCE I

    International Nuclear Information System (INIS)

    We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidates. We detected two ortho-H2O lines at 321 GHz (102, 9-93, 6) and 336 GHz (ν2 = 1, 52, 3-61, 6) for the first time in Source I. The latter one is in a vibrationally excited state at the lower state energy of 2939 K, suggesting evidence of hot molecular gas close to Source I. The integrated intensity map of the 321 GHz line is elongated along the bipolar outflow while the 336 GHz line map is unresolved with a beam size of 0.''4. Both of these maps show velocity gradients perpendicular to the bipolar outflow. The velocity centroid map of the 321 GHz line implies a spatial and velocity structure similar to that of vibrationally excited SiO masers tracing the root of the outflow emanating from the disk surface. In contrast, the 336 GHz line is most likely emitting from the disk midplane with a diameter of 0.''2 (84 AU) as traced by radio continuum emission and a dark lane devoid of the vibrationally excited SiO maser emission. The observed velocity gradient and the spectral profile of the 336 GHz H2O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of >7 M☉ and an excitation temperature of >3000 K. The present results provide further evidence of a hot and neutral circumstellar disk rotating around Source I with a diameter of ∼100 AU scale

  1. V409 Tau As Another AA Tau: Photometric Observations of Stellar Occultations by the Circumstellar Disk

    CERN Document Server

    Rodriguez, Joseph E; Stassun, Keivan G; Siverd, Robert J; Cargile, Phillip; Weintraub, David A; Beatty, Thomas G; Gaudi, B Scott; Mamajek, Eric E; Sanchez, Nicole

    2015-01-01

    AA Tau is a well studied young stellar object that presents many of the photometric characteristics of a Classical T Tauri star (CTTS), including short-timescale stochastic variability attributed to spots and/or accretion as well as long duration dimming events attributed to occultations by vertical features (e.g., warps) in its circumstellar disk. We present new photometric observations of AA Tau from the Kilodegree Extremely Little Telescope North (KELT-North) which reveal a deep, extended dimming event in 2011, which we show supports the interpretation by Bouvier et al. (2013) of an occultation by a high-density feature in the circumstellar disk located >8 AU from the star. We also present KELT-North observations of V409 Tau, a relatively unstudied young stellar object also in Taurus-Auriga, showing short timescale erratic variability, along with two separate long and deep dimming events, one from January 2009 through late October 2010, and the other from March 2012 until at least September 2013. We interp...

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

    CERN Document Server

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

    2016-01-01

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

  3. Investigations of the Circumstellar Disk Fraction as a Function of Mass in Young Embedded Clusters in Orion B

    Science.gov (United States)

    De Furio, Matthew; Lada, Elizabeth A.; Marinas, Naibi

    2016-01-01

    In the current paradigm of star formation, all stars form with circumstellar disks. However, recent studies of the young NGC 2264 clusters (age ~ 2Myr, Marinas et al 2013; 2015) have unexpectedly revealed that stars with masses less than 0.3 solar masses exhibit a lower circumstellar disk fraction than more massive stars in the clusters. Is it possible that a significant number of very low mass stars form without a disk? To answer this, we are studying three very young embedded clusters (ageOrion B Molecular Cloud. For these clusters, we are determining the disk fraction as a function of spectral type and inferred mass. Since the clusters are very young, the disk fractions should represent the initial frequency distribution of disks in these clusters. We are using FLAMINGOS NIR spectroscopy (Levine PhD UF 2006) and photometry to estimate the masses of the stars and FLAMINGOS JHK and Spitzer photometry to estimate the disk frequency of our spectroscopic sample. Our work should provide valuable insights toward understanding the formation and early evolution of circumstellar disks around low mass stars in embedded clusters.

  4. Spitzer Observations of G Dwarfs in the Pleiades: Circumstellar Debris Disks at 100 Myr Age

    CERN Document Server

    Stauffer, J R; Carpenter, J; Hillenbrand, L; Backman, D; Meyer, M R; Kim, J S; Silverstone, M D; Young, E; Hines, D C; Soderblom, D R; Mamajek, E E; Morris, P; Bouwman, J; Strom, S E

    2005-01-01

    Fluxes and upper limits in the wavelength range from 3.6 to 70 microns from the Spitzer Space Telescope are provided for twenty solar-mass Pleiades members. One of these stars shows a probable mid-IR excess and two others have possible excesses, presumably due to circumstellar debris disks. For the star with the largest, most secure excess flux at MIPS wavelengths, HII1101, we derive Log(L[dust]/L[Sun]) ~ -3.8 and an estimated debris disk mass of 4.2 x 10^-5 M(Earth) for an assumed uniform dust grain size of 10 microns If the stars with detected excesses are interpreted as stars with relatively recent, large collision events producing a transient excess of small dust particles, the frequency of such disk transients is about ~ 10 % for our ~ 100 Myr, Pleiades G dwarf sample. For the stars without detected 24-70 micron excesses, the upper limits to their fluxes correspond to approximate 3 sigma upper limits to their disk masses of 6 x 10^-6 M(Earth) using the MIPS 24 micron upper limit, or 2 x 10^-4 M(Earth) us...

  5. A Deep Spitzer Survey of Circumstellar Disks in the Young Double Cluster, h and chi Persei

    CERN Document Server

    Cloutier, Ryan; Rieke, George; Kenyon, Scott J; Balog, Zoltan; Jayawardhana, Ray

    2014-01-01

    We analyze very deep IRAC and MIPS photometry of $\\sim$ 12,500 members of the 14 Myr old Double Cluster, h and $\\chi$ Persei, building upon on our earlier, shallower Spitzer studies (Currie et al. 2007a, 2008a). Numerous likely members show infrared (IR) excesses at 8 {\\mu}m and 24 $\\mu$m indicative of circumstellar dust. The frequency of stars with 8 $\\mu$m 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 (SED) modeling of 18 sources with detections at optical wavelengths through MIPS 24 $\\mu m$ reveals a diverse set of disk evolutionary states, including a high fraction of transitional disks, although similar data for all disk-bearing members would provide better constraints. We combine our results with those for other young clusters to study the global evolution of dust/gas disks. For nomi...

  6. Far-infrared and sub-millimetre imaging of HD~76582's circumstellar disk

    CERN Document Server

    Marshall, J P; Holland, W S; Matthews, B C; Greaves, J S; Zuckerman, B

    2016-01-01

    Debris disks, the tenuous rocky and icy remnants of planet formation, are believed to be evidence for planetary systems around other stars. The JCMT/SCUBA-2 debris disk legacy survey 'SCUBA-2 Observations of Nearby Stars' (SONS) observed 100 nearby stars, amongst them HD~76582, for evidence of such material. Here we present imaging observations by JCMT/SCUBA-2 and \\textit{Herschel}/PACS at sub-millimetre and far-infrared wavelengths, respectively. We simultaneously model the ensemble of photometric and imaging data, spanning optical to sub-millimetre wavelengths, in a self-consistent manner. At far-infrared wavelengths, we find extended emission from the circumstellar disk providing a strong constraint on the dust spatial location in the outer system, although the angular resolution is too poor to constrain the interior of the system. In the sub-millimetre, photometry at 450 and 850~$\\mu$m reveal a steep fall-off that we interpret as a disk dominated by moderately-sized dust grains ($a_{\\rm min}~=~36~\\mu$m), ...

  7. A CHARA Array Survey of Circumstellar Disks around Nearby Be-type Stars

    CERN Document Server

    Touhami, Y; Schaefer, G H; McAlister, H A; Ridgway, S T; Richardson, N D; Matson, R; Grundstrom, E D; Brummelaar, T A ten; Goldfinger, P J; Sturmann, L; Sturmann, J; Turner, N H; Farrington, C

    2013-01-01

    We report on a high angular resolution survey of circumstellar disks around 24 northern sky Be stars. The K-band continuum survey was made using the CHARA Array long baseline interferometer (baselines of 30 to 331 m). The interferometric visibilities were corrected for the flux contribution of stellar companions in those cases where the Be star is a member of a known binary or multiple system. For those targets with good uv coverage, we used a four parameter Gaussian elliptical disk model to fit the visibilities and to determine the axial ratio, position angle, K-band photospheric flux contribution, and angular diameter of the disk major axis. For the other targets with relatively limited uv coverage, we constrained the axial ratio, inclination angle, and or disk position angle where necessary in order to resolve the degeneracy between possible model solutions. We also made fits of the ultraviolet and infrared spectral energy distributions to estimate the stellar angular diameter and infrared flux excess of e...

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

    International Nuclear Information System (INIS)

    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 (τ0) 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 ☉ stars appear lower than for 1-2.5 M ☉ stars in other 10-30 Myr old clusters.

  9. HST/STIS results on circumstellar disks and jets, future coronography and technology for IR multi-object spectroscopy

    Science.gov (United States)

    Woodgate, Bruce E.

    2002-01-01

    Results of studies of circumstellar disks and jets obtained by HST/STIS visible coronagraphy and UV spectroscopy, and by ground-based Fabry-Perot coronagraphy will be presented. Future improvements in coronagraphy will be discussed. The development of microshutter arrays as programmable multi-object selectors for the NGST near IR spectrograph will be described.

  10. Recurring Occultations of RW Aurigae by Coagulated Dust in the Tidally Disrupted Circumstellar Disk

    CERN Document Server

    Rodriguez, Joseph E; Siverd, Robert J; Pepper, Joshua; Stassun, Keivan G; Gaudi, B Scott; Weintraub, David A; Beatty, Thomas G; Lund, Michael B; Stevens, Daniel J

    2015-01-01

    We present photometric observations of RW Aurigae, a Classical T Tauri system, that reveal two remarkable dimming events. These events are similar to that which we observed in 2010-2011, which was the first such deep dimming observed in RW Aur in a century's worth of photometric monitoring. We suggested the 2010-2011 dimming was the result of an occultation of the star by its tidally disrupted circumstellar disk. In 2012-2013, the RW Aur system dimmed by ~0.7 mag for ~40 days and in 2014/2015 the system dimmed by ~2 mag for >250 days. The ingress/egress duration measurements of the more recent events agree well with those from the 2010-2011 event, providing strong evidence that the new dimmings are kinematically associated with the same occulting source. Therefore, we suggest that both the 2012-2013 and 2014-2015 dimming events, measured using data from the Kilodegree Extremely Little Telescope and the Kutztown University Observatory, are also occultations of RW Aur A by tidally disrupted circumstellar materi...

  11. The inner circumstellar disk of the UX Ori star V1026 Sco

    CERN Document Server

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

    2014-01-01

    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. 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. 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. 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 disk...

  12. Dynamics of Circumstellar Disks III: The case of GG Tau A

    CERN Document Server

    Nelson, Andrew F

    2016-01-01

    (abridged) We present 2-dimensional hydrodynamic simulations using the Smoothed Particle Hydrodynamic (SPH) code, VINE, to model a self-gravitating binary system similar to the GG Tau A system. We simulate systems configured with semi-major axes of either $a=62$~AU (`wide') or $a=32$~AU (`close'), and with eccentricity of either $e=0$ or $e=0.3$. Strong spiral structures are generated with large material streams extending inwards. A small fraction accretes onto the circumstellar disks, with most returning to the torus. Structures also propagate outwards, generating net outwards mass flow and eventually losing coherence at large distances. The torus becomes significantly eccentric in shape. Accretion onto the stars occurs at a rate of a few $\\times10^{-8}$\\msun/yr implying disk lifetimes shorter than $\\sim10^4$~yr, without replenishment. Only wide configurations retain disks by virtue of robust accretion. In eccentric configurations, accretion is episodic, occurs preferentially onto the secondary at wrates pea...

  13. Polarization morphology of SiO masers in the circumstellar envelope of the AGB star R Cassiopeiae

    CERN Document Server

    Assaf, K A; Richards, A M S; Gray, M D

    2013-01-01

    Silicon monoxide maser emission has been detected in the circumstellar envelopes of many evolved stars in various vibrationally-excited rotational transitions. It is considered a good tracer of the wind dynamics close to the photosphere of the star. We have investigated the polarization morphology in the circumstellar envelope of an AGB star, R Cas. We mapped the linear and circular polarization of SiO masers in the v=1, J=1-0 transition. The linear polarization is typically a few tens of percent while the circular polarization is a few percent. The fractional polarization tends to be higher for emission of lower total intensity. We found that, in some isolated features the fractional linear polarization appears to exceed 100%. We found the Faraday rotation is not negligible but is ~15 deg., which could produce small scale structure in polarized emission whilst total intensity is smoother and partly resolved out. The polarization angles vary considerably from feature to feature but there is a tendency to favo...

  14. The close circumstellar environment of Betelgeuse - III. SPHERE/ZIMPOL visible polarimetry of the inner envelope and photosphere

    CERN Document Server

    Kervella, P; 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 Halpha 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 pre...

  15. The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks

    CERN Document Server

    Visser, R; Black, J H

    2009-01-01

    Aims. Photodissociation by UV light is an important destruction mechanism for CO in many astrophysical environments, ranging from interstellar clouds to protoplanetary disks. The aim of this work is to gain a better understanding of the depth dependence and isotope-selective nature of this process. Methods. We present a photodissociation model based on recent spectroscopic data from the literature, which allows us to compute depth-dependent and isotope-selective photodissociation rates at higher accuracy than in previous work. The model includes self-shielding, mutual shielding and shielding by atomic and molecular hydrogen, and it is the first such model to include the rare isotopologues C17O and 13C17O. We couple it to a simple chemical network to analyse CO abundances in diffuse and translucent clouds, photon-dominated regions, and circumstellar disks. Results. The photodissociation rate in the unattenuated interstellar radiation field is 2.6e-10 s^-1, 30% higher than currently adopted values. Increasing t...

  16. High Resolution HST-STIS Spectra of CI and CO in the Beta Pictoris Circumstellar Disk

    CERN Document Server

    Roberge, A; Lagrange, A M; Vidal-Madjar, A; Ferlet, R; Jolly, A; Lemaire, J L; Rostas, F

    2000-01-01

    High resolution FUV echelle spectra showing absorption features arising from CI and CO gas in the Beta Pictoris circumstellar (CS) disk were obtained on 1997 December 6 and 19 using the Space Telescope Imaging Spectrograph (STIS). An unsaturated spin-forbidden line of CI at 1613.376 A not previously seen in spectra of Beta Pictoris was detected, allowing for an improved determination of the column density of CI at zero velocity relative to the star (the stable component), N = (2-4) x 10^{16} cm^{-2}. Variable components with multiple velocities, which are the signatures of infalling bodies in the Beta Pictoris CS disk, are observed in the CI 1561 A and 1657 A multiplets. Also seen for the first time were two lines arising from the metastable singlet D level of carbon, at 1931 A and 1463 A The results of analysis of the CO A-X (0-0), (1-0), and (2-0) bands are presented, including the bands arising from {13}^CO, with much better precision than has previously been possible, due to the very high resolution provi...

  17. OGLE-LMC-ECL-11893: The discovery of a long-period eclipsing binary with a circumstellar disk

    International Nuclear Information System (INIS)

    We report the serendipitous discovery of a disk-eclipse system OGLE-LMC-ECL-11893. The eclipse occurs with a period of 468 days, a duration of about 15 days, and a deep (up to ΔmI ≈ 1.5), peculiar, and asymmetric profile. A possible origin of such an eclipse profile involves a circumstellar disk. The presence of the disk is confirmed by the H-α line profile from the follow-up spectroscopic observations, and the star is identified as Be/Ae type. Unlike the previously known disk-eclipse candidates, the eclipses of OGLE-LMC-ECL-11893 retain the same shape throughout the span of ∼17 yr (13 orbital periods), indicating no measurable orbital precession of the disk.

  18. The Circumstellar Disk of the Be Star o Aquarii as Constrained by Simultaneous Spectroscopy and Optical Interferometry

    Science.gov (United States)

    Sigut, T. A. A.; Tycner, C.; Jansen, B.; Zavala, R. T.

    2015-12-01

    Omicron Aquarii is a late-type, Be shell star with a stable and nearly symmetric Hα emission line. We combine Hα interferometric observations obtained with the Navy Precision Optical Interferometer covering 2007 through 2014 with Hα spectroscopic observations over the same period and a 2008 observation of the system's near-infrared spectral energy distribution to constrain the properties of o Aqr's circumstellar disk. All observations are consistent with a circumstellar disk seen at an inclination of 75° ± 3° with a position angle on the sky of 110° ± 8° measured East from North. From the best-fit disk density model, we find that 90% of the Hα emission arises from within 9.5 stellar radii, and the mass associated with this Hα disk is ˜1.8 × 10-10 of the stellar mass, and that the associated angular momentum, assuming Keplerian rotation for the disk, is ˜1.6 × 10-8 of the total stellar angular momentum. The occurrence of a central quasi-emission feature in Mg ii λ4481 is also predicted by this best-fit disk model and the computed profile compares successfully with observations from 1999. To obtain consistency between the Hα line profile modeling and the other constraints, it was necessary in the profile fitting to weight the line core (emission peaks and central depression) more heavily than the line wings, which were not well reproduced by our models. This may reflect the limitation of assuming a single power law for the disk's variation in equatorial density. The best-fit disk density model for o Aqr predicts that Hα is near its maximum strength as a function of disk density, and hence the Hα equivalent width and line profile change only weakly in response to large (factor of ˜5) changes in the disk density. This may in part explain the remarkable observed stability of o Aqr's Hα emission line profile.

  19. Detailed Modelling of the Circumstellar Envelope of the S-type AGB Star W Aquilae

    Science.gov (United States)

    Danilovich, T.; Bergman, P.; Justtanont, K.; Lombaert, R.; Maercker, M.; Olofsson, H.; Ramstedt, S.; Royer, P.

    2015-08-01

    We present new Herschel HIFI (de Graauw et al. 2010) and PACS (Poglitsch et al. 2010) sub-millimeter and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances.

  20. A chemical route to the formation of water in circumstellar envelopes around carbon-rich asymptotic branch stars: Fischer-Tropsch catalysis

    Science.gov (United States)

    Willacy, K.

    2004-01-01

    Fischer-Tropsch catalysis has been suggested as a means of driving hydrocarbon chemistry in oxygen rich regions such as the protosolar nebula. In addition to producing hydrocarbons, Fischer-Tropsch catalysis also produces water, and it is therefore possible that such processes could account for the recent observations of water in the circumstellar envelope of asymptotic giant branch star IRC +10216.

  1. Pericenter precession induced by a circumstellar disk on the orbit of massive bodies: comparison between analytical predictions and numerical results

    Science.gov (United States)

    Fontana, A.; Marzari, F.

    2016-04-01

    Context. Planetesimals and planets embedded in a circumstellar disk are dynamically perturbed by the disk gravity. It causes an apsidal line precession at a rate that depends on the disk density profile and on the distance of the massive body from the star. Aims: Different analytical models are exploited to compute the precession rate of the perihelion ϖ˙. We compare them to verify their equivalence, in particular after analytical manipulations performed to derive handy formulas, and test their predictions against numerical models in some selected cases. Methods: The theoretical precession rates were computed with analytical algorithms found in the literature using the Mathematica symbolic code, while the numerical simulations were performed with the hydrodynamical code FARGO. Results: For low-mass bodies (planetesimals) the analytical approaches described in Binney & Tremaine (2008, Galactic Dynamics, p. 96), Ward (1981, Icarus, 47, 234), and Silsbee & Rafikov (2015a, ApJ, 798, 71) are equivalent under the same initial conditions for the disk in terms of mass, density profile, and inner and outer borders. They also match the numerical values computed with FARGO away from the outer border of the disk reasonably well. On the other hand, the predictions of the classical Mestel disk (Mestel 1963, MNRAS, 126, 553) for disks with p = 1 significantly depart from the numerical solution for radial distances beyond one-third of the disk extension because of the underlying assumption of the Mestel disk is that the outer disk border is equal to infinity. For massive bodies such as terrestrial and giant planets, the agreement of the analytical approaches is progressively poorer because of the changes in the disk structure that are induced by the planet gravity. For giant planets the precession rate changes sign and is higher than the modulus of the theoretical value by a factor ranging from 1.5 to 1.8. In this case, the correction of the formula proposed by Ward (1981) to

  2. A low-mass protostar's disk-envelope interface: disk-shadowing evidence from ALMA DCO+ observations of VLA1623

    CERN Document Server

    Murillo, Nadia M; van Dishoeck, Ewine F; Walsh, Catherine; Harsono, Daniel; Lai, Shih-Ping; Fuchs, Christian M

    2015-01-01

    Due to instrumental limitations and a lack of disk detections, the structure between the envelope and the rotationally supported disk has been poorly studied. This is now possible with ALMA through observations of CO isotopologs and tracers of freezeout. Class 0 sources are ideal for such studies given their almost intact envelope and young disk. The structure of the disk-envelope interface of the prototypical Class 0 source, VLA1623A which has a confirmed Keplerian disk, is constrained from ALMA observations of DCO+ 3-2 and C18O 2-1. The physical structure of VLA1623 is obtained from the large-scale SED and continuum radiative transfer. An analytic model using a simple network coupled with radial density and temperature profiles is used as input for a 2D line radiative transfer calculation for comparison with the ALMA Cycle 0 12m array and Cycle 2 ACA observations of VLA1623. DCO+ emission shows a clumpy structure bordering VLA1623A's Keplerian disk, suggesting a cold ring-like structure at the disk-envelope...

  3. Vertical settling and radial segregation of large dust grains in the circumstellar disk of the Butterfly Star

    CERN Document Server

    Gräfe, Christian; Guilloteau, Stephane; Dutrey, Anne; Stapelfeldt, Karl; Pontoppidan, Klaus; Sauter, Jürgen

    2013-01-01

    Context: Circumstellar disks are considered to be the environment for the formation of planets. The growth of dust grains in these disks is the first step in the core accretion-gas capture planet formation scenario. Indicators and evidence of disk evolution can be traced in spatially resolved images and the spectral energy distribution (SED) of these objects. Aims: We develop a model for the dust phase of the edge-on oriented circumstellar disk of the Butterfly Star which allows one to fit observed multi-wavelength images and the SED simultaneously. Methods: Our model is based on spatially resolved high angular resolution observations at 1.3 mm, 894 micron, 2.07 micron, 1.87 micron, 1.60 micron, and 1.13 micron and an extensively covered SED ranging from 12 micron to 2.7 mm, including a detailed spectrum obtained with the Spitzer Space Telescope in the range from 12 micron to 38 micron. A parameter study based on a grid search method involving the detailed analysis of every parameter was performed to constrai...

  4. Rapid Circumstellar Disk Evolution and an Accelerating Star Formation Rate in the Infrared Dark Cloud M17 SWex

    CERN Document Server

    Povich, Matthew S; Robitaille, Thomas P; Broos, Patrick S; Orbin, Wesley T; King, Robert R; Naylor, Tim; Whitney, Barbara A

    2016-01-01

    We present a catalog of 840 X-ray sources and first results from a 100 ks Chandra X-ray Observatory imaging study of the filamentary infrared dark cloud G014.225$-$00.506, which forms the central regions of a larger cloud complex known as the M17 southwest extension (M17 SWex). In addition to the rich population of protostars and young stellar objects with dusty circumstellar disks revealed by Spitzer Space Telescope archival data, we discover a population of X-ray-emitting, intermediate-mass pre--main-sequence stars (IMPS) that lack infrared excess emission from circumstellar disks. We model the infrared spectral energy distributions of this source population to measure its mass function and place new constraints on the inner dust disk destruction timescales for 2-8 $M_{\\odot}$ stars. We also place a lower limit on the star formation rate (SFR) and find that it is quite high ($\\dot{M}\\ge 0.007~M_{\\odot}$ yr$^{-1}$), equivalent to several Orion Nebula Clusters in G14.225$-$0.506 alone, and likely accelerating...

  5. The First Circumstellar Disk Imaged in Silhouette with Adaptive Optics: MagAO Imaging of Orion 218-354

    CERN Document Server

    Follette, Katherine B; Males, Jared R; Kopon, Derek; Wu, Ya-Lin; Morzinski, Katie M; Hinz, Philip; Rodigas, Timothy J; 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 (SDI) mode at H-alpha. This is the first image of a circumstellar disk seen in silhouette with adaptive optics and is among the first visible light adaptive optics 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 H-alpha. 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 sub-mm 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 1-1000micron SED with a ~2...

  6. The Ionized Circumstellar Envelopes of Orion Source I and the Becklin Neugebauer Object

    CERN Document Server

    Plambeck, R L; Carpenter, J M; Eisner, J A; Lamb, J W; Leitch, E M; Marrone, D P; Muchovej, S J; Perez, L M; Pound, M W; Teuben, P J; Volgenau, N H; Woody, D P; Wright, M C H; Zauderer, B A

    2012-01-01

    The 229 GHz (lambda 1.3mm) radio emission from Orion-KL was mapped with up to 0.14'' angular resolution with CARMA, allowing measurements of the flux densities of Source I ('SrcI') and the Becklin-Neugebauer Object (BN), the 2 most massive stars in this region. We find integrated flux densities of 310 +/- 45 mJy for SrcI and 240 +/- 35 mJy for BN. SrcI is optically thick even at 229 GHz. No trace of the H30alpha recombination line is seen in its spectrum, although the v_2=1, 5(5,0)-6(4,3) transition of H2O, 3450 K above the ground state, is prominent. SrcI is elongated at position angle 140 degrees, as in 43 GHz images. These results are most easily reconciled with models in which the radio emission from SrcI arises via the H- free-free opacity in a T < 4500 K disk, as considered by Reid et al. (2007). By contrast, the radio spectrum of BN is consistent with p+/e- free-free emission from a dense (n_e ~ 5x10^7 cm^{-3}), but otherwise conventional, hypercompact HII region. The source is becoming optically th...

  7. Constraints on the Radial Variation of Grain Growth in the AS 209 Circumstellar Disk

    CERN Document Server

    Pérez, Laura M; Chandler, Claire J; Isella, Andrea; Andrews, Sean M; Ricci, Luca; Calvet, Nuria; Corder, Stuartt A; Deller, Adam T; Dullemond, Cornelis P; Greaves, Jane S; Harris, Robert J; Henning, Thomas; Kwon, Woojin; Lazio, Joseph; Linz, Hendrik; Mundy, Lee G; Sargent, Anneila I; Storm, Shaye; Testi, Leonardo; Wilner, David J

    2012-01-01

    We present dust continuum observations of the protoplanetary disk surrounding the pre-main sequence star AS 209, spanning more than an order of magnitude in wavelength from 0.88 to 9.8 mm. The disk was observed with sub-arcsecond angular resolution (0.2"-0.5") to investigate radial variations in its dust properties. At longer wavelengths, the disk emission structure is notably more compact, providing model-independent evidence for changes in the grain properties across the disk. We find that physical models which reproduce the disk emission require a radial dependence of the dust opacity \\kappa_{\

  8. The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks. IV. Simulations with Envelope Irradiation

    CERN Document Server

    Cai, Kai; Boley, Aaron C; Pickett, Megan K; Mejia, Annie C

    2007-01-01

    It is generally thought that protoplanetary disks embedded in envelopes are more massive and thus more susceptible to gravitational instabilities (GIs) than exposed disks. We present three-dimensional radiative hydrodynamics simulations of protoplanetary disks with the presence of envelope irradiation. For a disk with a radius of 40 AU and a mass of 0.07 Msun around a young star of 0.5 Msun, envelope irradiation tends to weaken and even suppress GIs as the irradiating flux is increased. The global mass transport induced by GIs is dominated by lower-order modes, and irradiation preferentially suppresses higher-order modes. As a result, gravitational torques and mass inflow rates are actually increased by mild irradiation. None of the simulations produce dense clumps or rapid cooling by convection, arguing against direct formation of giant planets by disk instability, at least in irradiated disks. However, dense gas rings and radial mass concentrations are produced, and these might be conducive to accelerated p...

  9. Investigating the Nature of the Dust Emission around Massive Protostar NGC 7538 IRS 1: Circumstellar Disk and Outflow?

    CERN Document Server

    De Buizer, J M; Buizer, James M. De; Minier, Vincent

    2005-01-01

    We have obtained high resolution mid-infrared images of the high mass protostar NGC 7538 IRS 1 using Michelle on Gemini North and find that the circumstellar dust associated with this source is extended on both large and small scales. The large-scale mid-infrared emission is asymmetric about the peak of IRS 1, being more extended to the northwest than the southeast. The position angle of the mid-infrared emission is similar to the position angle of the linearly distributed methanol masers at this location which are thought to trace a circumstellar disk. However, this position angle is also very similar to that of the CO outflow in this region which appears to be centered on IRS 1. We suggest that the large-scale extended mid-infrared emission is coming from dust heated on the walls of the outflow cavities near the source. IRS 1 is also elongated in the mid-infrared on a smaller scale, and this elongation is near PERPENDICULAR to the axis of the CO outflow (and the linearly distributed methanol masers). Becaus...

  10. An alternative model for the origin of gaps in circumstellar disks

    CERN Document Server

    Vorobyov, Eduard I; Guedel, Manuel; Lin, D N C

    2016-01-01

    Motivated by recent observational and numerical studies suggesting that collapsing protostellar cores may be replenished from the local environment, we explore the evolution of protostellar cores submerged in the external counter-rotating environment. These models predict the formation of counter-rotating disks with a deep gap in the gas surface density separating the inner disk (corotating with the star) and the outer counter-rotating disk. The properties of these gaps are compared to those of planet-bearing gaps that form in disks hosting giant planets. We employ numerical hydrodynamics simulations of collapsing cores that are replenished from the local counter-rotating environment, as well as numerical hydrodynamic simulations of isolated disks hosting giant planets, to derive the properties of the gaps that form in both cases. Our numerical simulations demonstrate that counter-rotating disks can form for a wide range of mass and angular momentum available in the local environment. The gap that separates b...

  11. The JCMT Gould Belt Survey: SCUBA-2 observations of circumstellar disks in L 1495

    CERN Document Server

    Buckle, J V; Greaves, J; Richer, J S; Matthews, B C; Johnstone, D; Kirk, H; Beaulieu, S F; Berry, D S; Broekhoven-Fiene, H; Currie, M J; Fich, M; Hatchell, J; Jenness, T; Mottram, J C; Nutter, D; Pattle, K; Pineda, J E; Salji, C; Tisi, S; Di Francesco, J; Hogerheijde, M R; Ward-Thompson, D; Bastien, P; Butner, H; Chen, M; Chrysostomou, A; Coude, S; Davis, C J; Duarte-Cabral, A; Friberg, P; Friesen, R; Fuller, G A; Graves, S; Gregson, J; Holland, W; Joncas, G; Kirk, J M; Knee, L B G; Mairs, S; Marsh, K; Moriarty-Schieven, G; Rawlings, J; Rosolowsky, E; Rumble, D; Sadavoy, S; Thomas, H; Tothill, N; Viti, S; White, G J; Wilson, C D; Wouterloot, J; Yates, J; Zhu, M

    2015-01-01

    We present 850$\\mu$m and 450$\\mu$m data from the JCMT Gould Belt Survey obtained with SCUBA-2 and characterise the dust attributes of Class I, Class II and Class III disk sources in L1495. We detect 23% of the sample at both wavelengths, with the detection rate decreasing through the Classes from I--III. The median disk mask is 1.6$\\times 10^{-3}$M$_{\\odot}$, and only 7% of Class II sources have disk masses larger than 20 Jupiter masses. We detect a higher proportion of disks towards sources with stellar hosts of spectral type K than spectral type M. Class II disks with single stellar hosts of spectral type K have higher masses than those of spectral type M, supporting the hypothesis that higher mass stars have more massive disks. Variations in disk masses calculated at the two wavelengths suggests there may be differences in dust opacity and/or dust temperature between disks with hosts of spectral types K to those with spectral type M.

  12. An alternative model for the origin of gaps in circumstellar disks

    Science.gov (United States)

    Vorobyov, Eduard I.; Regaly, Zsolt; Guedel, Manuel; Lin, Doug N. C.

    2016-03-01

    Aims: Motivated by recent observational and numerical studies suggesting that collapsing protostellar cores may be replenished from the local environment, we explore the evolution of protostellar cores submerged in the external counter-rotating environment. These models predict the formation of counter-rotating disks with a deep gap in the gas surface density separating the inner disk (corotating with the star) and the outer counter-rotating disk. The properties of these gaps are compared to those of planet-bearing gaps that form in disks hosting giant planets. Methods: We employ numerical hydrodynamics simulations of collapsing cores that are replenished from the local counter-rotating environment and numerical hydrodynamics simulations of isolated disks hosting giant planets to derive the properties of the gaps that form in both cases. Results: Our numerical simulations demonstrate that counter-rotating disks can form for a wide range of mass and angular momentum available in the local environment. The gap that separates both disks has a substantial depletion factor, can be located at a distance from ten to over a hundred AU from the star, and can propagate inward with velocity ranging from 1 AU Myr-1 to >100 AU Myr-1. Unlike our previous conclusion, the gap can therefore be a long-lived phenomenon that is, in some case, comparable to the lifetime of the disk itself. For a proper choice of the planetary mass, the viscous α-parameter and disk mass, the planet-bearing gaps and gaps in counter-rotating disks may show a remarkable similarity in the gas density profile and depletion factor, which may complicate their observational differentiation.

  13. The Effect of Multiple Scattering on the Polarization from Binary Star Envelopes. I. Self- and Externally Illuminated Disks

    CERN Document Server

    Hoffman, J L; Nordsieck, K H; Hoffman, Jennifer L.; Whitney, Barbara A.; Nordsieck, Kenneth H.

    2003-01-01

    We present the results of a Monte Carlo radiative transfer code that calculates the polarization produced by multiple Thomson scattering and variable absorptive opacity in a circumstellar disk around one component of a close detached binary system. We consider in detail the polarization variations over the binary cycle that result from the disk's illumination by the external star and by its own volume emission. We identify key features of these polarization phase curves and investigate their behavior as functions of optical depth, albedo, and inclination for geometrically thin and thick disks. The polarization due to disk self-illumination is sensitive to the internal optical characteristics of the disk, while the polarization arising from external illumination is mainly sensitive to the disk's geometrical thickness. With appropriate flux weighting, these results, combined with those for an internally illuminated disk, allow simulation of the polarization signature from an arbitrary binary-disk system.

  14. Modeling Circumstellar Disks of B-Type Stars with Observations from the Palomar Testbed Interferometer

    Science.gov (United States)

    Grzenia, B. J.; Tycner, C.; Jones, C. E.; Rinehart, S. A.; vanBelle, G. T.; Sigut, T. A. A.

    2013-01-01

    Geometrical (uniform disk) and numerical models were calculated for a set of B-emission (Be) stars observed with the Palomar Testbed Interferometer (PTI). Physical extents have been estimated for the disks of a total of15 stars via uniform disk models. Our numerical non-LTE models used parameters for the B0, B2, B5, and B8spectral classes and following the framework laid by previous studies, we have compared them to infrared K-band interferometric observations taken at PTI. This is the first time such an extensive set of Be stars observed with long-baseline interferometry has been analyzed with self-consistent non-LTE numerical disk models.

  15. Detection of Strong Millimeter Emission from the Circumstellar Dust Disk Around V1094 Sco: Cold and Massive Disk around a T Tauri Star in a Quiescent Accretion Phase?

    CERN Document Server

    Tsukagoshi, Takashi; Kitamura, Yoshimi; Momose, Munetake; Shimajiri, Yoshito; Hiramatsu, Masaaki; Ikeda, Norio; Kamegai, Kazuhisa; Wilson, Grant; Yun, Min S; Scott, Kimberly; Austermann, Jay; Perera, Thushara; Hughes, David; Aretxaga, Itziar; Mauskopf, Philip; Ezawa, Hajime; Kohno, Kotaro; Kawabe, Ryohei

    2010-01-01

    We present the discovery of a cold massive dust disk around the T Tauri star V1094 Sco in the Lupus molecular cloud from the 1.1 millimeter continuum observations with AzTEC on ASTE. A compact ($r\\lesssim$320 AU) continuum emission coincides with the stellar position having a flux density of 272 mJy which is largest among T Tauri stars in Lupus. We also present the detection of molecular gas associated with the star in the five-point observations in $^{12}$CO J=3--2 and $^{13}$CO J=3--2. Since our $^{12}$CO and $^{13}$CO observations did not show any signature of a large-scale outflow or a massive envelope, the compact dust emission is likely to come from a disk around the star. The observed SED of V1094 Sco shows no distinct turnover from near infrared to millimeter wavelengths, which can be well described by a flattened disk for the dust component, and no clear dip feature around 10 $\\micron$ suggestive of absence of an inner hole in the disk. We fit a simple power-law disk model to the observed SED. The es...

  16. Transition from the infalling envelope to the Keplerian disk around L1551 IRS 5

    Energy Technology Data Exchange (ETDEWEB)

    Chou, Ti-Lin [Department of Physics, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 106, Taiwan (China); Takakuwa, Shigehisa; Yen, Hsi-Wei; Ohashi, Nagayoshi; Ho, Paul T. P., E-mail: tlchou@asiaa.sinica.edu.tw [Academia Sinica Institute of Astronomy and Astrophysics, P. O. Box 23-141, Taipei 10617, Taiwan (China)

    2014-11-20

    We present combined Submillimeter Array (SMA) +Atacama Submillimeter Telescope Experiment (ASTE) images of the Class I protobinary L1551 IRS 5 in the CS (J = 7-6) line, the submillimeter images of L1551 IRS 5 with the most complete spatial sampling ever achieved (0.''9-36''). The SMA image of L1551 IRS 5 in the 343 GHz dust-continuum emission is also presented, which shows an elongated feature along the northwest to southeast direction (∼160 AU × 80 AU), perpendicular to the associated radio jets. The combined SMA+ASTE images show that the high-velocity (≳1.5 km s{sup –1}) CS emission traces the structure of the dust component and shows a velocity gradient along the major axis, which is reproduced by a geometrically thin Keplerian-disk model with a central stellar mass of ∼0.5 M {sub ☉}. The low-velocity (≲1.3 km s{sup –1}) CS emission shows an extended (∼1000 AU) feature that exhibits slight south (blueshifted) to north (redshifted) emission offsets, which is modeled with a rotating and infalling envelope with a conserved angular momentum. The rotational motion of the envelope connects smoothly to the inner Keplerian rotation at a radius of ∼64 AU. The infalling velocity of the envelope is ∼three times lower than the free-fall velocity toward the central stellar mass of 0.5 M {sub ☉}. These results demonstrate transition from the infalling envelope to the Keplerian disk, consistent with the latest theoretical studies of disk formation. We suggest that sizable (r ∼ 50-200 AU) Keplerian disks are already formed when the protostars are still deeply embedded in the envelopes.

  17. Transition from the infalling envelope to the Keplerian disk around L1551 IRS 5

    International Nuclear Information System (INIS)

    We present combined Submillimeter Array (SMA) +Atacama Submillimeter Telescope Experiment (ASTE) images of the Class I protobinary L1551 IRS 5 in the CS (J = 7-6) line, the submillimeter images of L1551 IRS 5 with the most complete spatial sampling ever achieved (0.''9-36''). The SMA image of L1551 IRS 5 in the 343 GHz dust-continuum emission is also presented, which shows an elongated feature along the northwest to southeast direction (∼160 AU × 80 AU), perpendicular to the associated radio jets. The combined SMA+ASTE images show that the high-velocity (≳1.5 km s–1) CS emission traces the structure of the dust component and shows a velocity gradient along the major axis, which is reproduced by a geometrically thin Keplerian-disk model with a central stellar mass of ∼0.5 M ☉. The low-velocity (≲1.3 km s–1) CS emission shows an extended (∼1000 AU) feature that exhibits slight south (blueshifted) to north (redshifted) emission offsets, which is modeled with a rotating and infalling envelope with a conserved angular momentum. The rotational motion of the envelope connects smoothly to the inner Keplerian rotation at a radius of ∼64 AU. The infalling velocity of the envelope is ∼three times lower than the free-fall velocity toward the central stellar mass of 0.5 M ☉. These results demonstrate transition from the infalling envelope to the Keplerian disk, consistent with the latest theoretical studies of disk formation. We suggest that sizable (r ∼ 50-200 AU) Keplerian disks are already formed when the protostars are still deeply embedded in the envelopes.

  18. INTERACTION OF A GIANT PLANET IN AN INCLINED ORBIT WITH A CIRCUMSTELLAR DISK

    International Nuclear Information System (INIS)

    We investigate the dynamical evolution of a Jovian-mass planet injected into an orbit highly inclined with respect to its nesting gaseous disk. Planet-planet scattering induced by convergent planetary migration and mean motion resonances may push a planet into such an out-of-plane configuration with inclinations as large as 200-300. In this scenario, the tidal interaction of the planet with the disk is more complex and, in addition to the usual Lindblad and corotation resonances, it also involves inclination resonances responsible for bending waves. We have performed three-dimensional hydrodynamic simulations of the disk and of its interactions with the planet with a smoothed particle hydrodynamics code. A main result is that the initial large eccentricity and inclination of the planetary orbit are rapidly damped on a timescale of the order of 103 yr, almost independently of the initial semimajor axis and eccentricity of the planet. The disk is warped in response to the planet perturbations and it precesses. Inward migration also occurs when the planet is inclined, and it has a drift rate that is intermediate between type I and type II migration. The planet is not able to open a gap until its inclination becomes lower than ∼100, when it also begins to accrete a significant amount of mass from the disk.

  19. Investigating the Circumstellar Disk of the Be Shell Star 48 Librae

    CERN Document Server

    Silaj, J; Carciofi, A C; Escolano, C; Okazaki, A T; Tycner, C; Rivinius, T; Klement, R; Bednarski, D

    2016-01-01

    A global disk oscillation implemented in the viscous decretion disk (VDD) model has been used to reproduce most of the observed properties of the well known Be star $\\zeta$ Tau. 48 Librae shares several similarities with $\\zeta$ Tau -- they are both early-type Be stars, they display shell characteristics in their spectra, and they exhibit cyclic $V/R$ variations -- but has some marked differences as well, such as a much denser and more extended disk, a much longer $V/R$ cycle, and the absence of the so-called triple-peak features. We aim to reproduce the photometric, polarimetric, and spectroscopic observables of 48 Librae with a self-consistent model, and to test the global oscillation scenario for this target. Our calculations are carried out with the three-dimensional NLTE radiative transfer code HDUST. We employ a rotationally deformed, gravity-darkened central star, surrounded by a disk whose unperturbed state is given by the VDD model. A two-dimensional global oscillation code is then used to calculate ...

  20. Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope

    International Nuclear Information System (INIS)

    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 Hα emission. Later spectra, spanning over 4 months from outburst, show clear Type Ia features combined with broad and narrow Hγ, Hβ,Hα and He I λλ5876,7065 in emission. At higher resolution, P Cygni profiles are apparent. Surprisingly, we also observe an inverted P Cygni profile for [O III] λ5007. 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#circledot# < 0.3; 95% confidence) and that this galaxy is undergoing a significant star formation event that began roughly 200 ± 70 Myr ago. We discuss the

  1. SXP 214: An X-Ray Pulsar in the Small Magellanic Cloud, Crossing the Circumstellar Disk of the Companion

    Science.gov (United States)

    Hong, JaeSub; Antoniou, Vallia; Zezas, Andreas; Haberl, Frank; Drake, Jeremy J.; Plucinsky, Paul P.; Gaetz, Terrance; Sasaki, Manami; Williams, Benjamin; Long, Knox S.; Blair, William P.; Winkler, P. Frank; Wright, Nicholas J.; Laycock, Silas; Udalski, Andrzej

    2016-07-01

    Located in the Small Magellanic Cloud (SMC), SXP 214 is an X-ray pulsar in a high mass X-ray binary system with a Be-star companion. A recent survey of the SMC under a Chandra X-ray Visionary program found that the source was in a transition when the X-ray flux was on a steady rise. The Lomb–Scargle periodogram revealed a pulse period of 211.49 ± 0.42 s, which is significantly (>5σ) shorter than the previous measurements made with XMM-Newton and RXTE. This implies that the system has gone through sudden spin-up episodes recently. The pulse profile shows a sharp eclipse-like feature with a modulation amplitude of >95%. The linear rise of the observed X-ray luminosity from ≲2× to 7× {10}35 erg s‑1 is correlated with a steady softening of the X-ray spectrum, which can be described by the changes in the local absorption from N H ∼ 1024 to ≲1020 cm‑2 for an absorbed power-law model. The soft X-ray emission below 2 keV was absent in the early part of the observation when only the pulsating hard X-ray component was observed, whereas at later times, both soft and hard X-ray components were observed to be pulsating. A likely explanation is that the neutron star was initially hidden in the circumstellar disk of the companion, and later came out of the disk with the accreted material that continued fueling the observed pulsation.

  2. Detection of a large Be circumstellar disk during X-ray quiescence of XTE J1946+274

    CERN Document Server

    Arabaci, M Ozbey; Gutierrez-Soto, J; Zurita, C; Nespoli, E; Suso, J; Kiaeerad, F; Garcia-Rojas, J; Kiziloglu, U

    2014-01-01

    We present a multiwavelength study of the Be/X-ray binary system XTE J1946+274 with the main goal of better characterizing its behavior during X-ray quiescence. We aim to shed light on the mechanism which triggers the X-ray activity for this source. XTE J1946+274 was observed by Chandra-ACIS during quiescence in 2013 March 12. In addition, this source has been monitored from the ground-based astronomical observatories of El Teide (Tenerife, Spain), Roque de los Muchachos (La Palma, Spain) and Sierra Nevada (Granada, Spain) since 2011 September, and from the TUBITAK National Observatory (Antalya, Turkey) since 2005 April. We have performed spectral and photometric temporal analyses in order to investigate the quiescent state and transient behavior of this binary system. In 2006, a long mass ejection event took place from the Be star, lasting for about seven years. We also found that a large Be circumstellar disk was present during quiescence, although major X-ray activity was not observed. We made an attempt t...

  3. The Role of Evolutionary Age and Metallicity in the Formation of Classical BE Circumstellar Disks II. Assessing the True Nature of Candidate Disk Systems

    Science.gov (United States)

    Wisniewski, J. P.; Bjorkman, K. S.; Magalhaes, A. M.; Bjorkman, J. E.; Meade, M. R.; Pereyra, Antonio

    2007-01-01

    Photometric 2-color diagram (2-CD) surveys of young cluster populations have been used to identify populations of B-type stars exhibiting excess Ha emission. The prevalence of these excess emitters, assumed to be "Be stars". has led to the establishment of links between the onset of disk formation in classical Be stars and cluster age and/or metallicity. We have obtained imaging polarization observations of six SMC and six LMC clusters whose candidate Be populations had been previously identified via 2-CDs. The interstellar polarization (ISP) associated with these data has been identified to facilitate an examination of the circumstellar environments of these candidate Be stars via their intrinsic polarization signatures, hence determine the true nature of these objects. We determined that the ISP associated with the SMC cluster NGC 330 was characterized by a modified Serkowski law with a lambda(sub max) of approx. 4500Angstroms, indicating the presence of smaller than average dust grains. The morphology of the ISP associated with the LMC cluster NGC 2100 suggests that its interstellar environment is characterized by a complex magnetic field. Our intrinsic polarization results confirm the suggestion of Wisniewski et al. that a substantial number of bona-fide classical Be stars are present in clusters of age 5-8 Myr. Hence, our data contradict recent assertions that the Be phenomenon develops in the second half of a B star's main sequence lifetime, i.e. no earlier than 10 Myr. These data imply that a significant number of B-type stars must emerge onto the zero-age-main-sequence rotating at near-critical rotation rates, although we can not rule out the possibility that these data instead reveal the presence of a sub-group of the Be phenomenon characterized by sub-critically rotating objects. Comparing the polarimetric properties of our dataset to a similar survey of Galactic classical Be stars, we find that the prevalence of polarimetric Balmer jump signatures

  4. Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes -- I. The case of hydrogen cyanide

    CERN Document Server

    Marigo, Paola; Nanni, Ambra; Bressan, Alessandro; Girardi, Leo

    2015-01-01

    We investigate the formation of hydrogen cyanide (HCN) in the inner circumstellar envelopes of thermally pulsing asymptotic giant branch (TP-AGB) stars. A dynamic model for periodically shocked atmospheres, which includes an extended chemo-kinetic network, is for the first time coupled to detailed evolutionary tracks for the TP-AGB phase computed with the COLIBRI code. We carried out a calibration of the main shock parameters (the shock formation radius and the effective adiabatic index) using the circumstellar HCN abundances recently measured for a populous sample of pulsating TP-AGB stars. Our models recover the range of the observed HCN concentrations as a function of the mass-loss rates, and successfully reproduce the systematic increase of HCN moving along the M-S-C chemical sequence of TP-AGB stars, that traces the increase of the surface C/O ratio. The chemical calibration brings along two important implications: i) the first shock should emerge very close to the photosphere, and ii) shocks are expecte...

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

    International Nuclear Information System (INIS)

    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

  6. 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.

  7. Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope

    CERN Document Server

    Aldering, G; 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; Pécontal, E; Pereira, R; Perlmutter, S; Rabinowitz, D; Rigaudier, G; Scalzo, R; Smadja, G; Thomas, R C; Wang, L; Weaver, B A

    2006-01-01

    We report Nearby Supernova Factory observations of SN 2005gj, the second confirmed case of a "hybrid" Type Ia/IIn supernova. Our early-phase photometry of SN 2005gj shows that the interaction is much stronger than for the prototype, SN 2002ic. Our first 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 HeI 5876,7065 in emission. At higher resolution, P Cygni profiles are apparent. Surprisingly, we also observe an inverted P Cygni profile for [OIII] 5007. We find that the lightcurve and measured velocity of the unshocked circumstellar material imply mass loss as recently as 8 years ago. 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 clum...

  8. Two families of exocomets in the circumstellar disk of Beta Pictoris

    Science.gov (United States)

    Kiefer, F.

    2014-09-01

    The young planetary system surrounding Beta Pictoris harbors active minor bodies. These asteroids and comets produce a large amount of dust and gas through collisions and evaporation, as in the early ages of the Solar System. Spectroscopic observations of Beta Pictoris reveal a high rate of transits of small evaporating bodies, i.e. exo-comets. Here we report the analysis of more than thousand spectra gathered between 2003 and 2011, providing a sample of about 6000 variable absorption signatures due to transiting exocomets. Statistical analysis of the observed properties of these exocomets reveals that they belong to two distinct populations with highly different physical properties. A first family, with low evaporation efficiency, can be attributed to old exhausted comets, possibly trapped in a mean motion resonance with a massive planet; while a second family, with high evaporation efficiency, is possibly related to the recent fragmentation of a few parent bodies. Our results strengthen the analogy of nature of the evaporating bodies observed for decades transiting Beta Pictoris with the bodies so-called comets in the Solar System. Recently, we discovered that the Beta Pic-like system of HD172555 also harbors exocomets (Kiefer et al. 2014). The analysis of the Ca II doublet of about a hundred HARPS spectra of HD172555 collected between 2004 and 2011 revealed typical variable absorption signatures of exocomets transiting the star. It is the second example after Beta Pictoris of a young planetary system with a debris disk in which exocomets are detected and characterized thanks to the simultaneous observation of the Ca II-K and Ca II-H lines.

  9. Detection of a large Be circumstellar disk during X-ray quiescence of XTE J1946+274

    Science.gov (United States)

    Özbey Arabacı, M.; Camero-Arranz, A.; Zurita, C.; Gutiérrez-Soto, J.; Nespoli, E.; Suso, J.; Kiaeerad, F.; García-Rojas, J.; Kızıloǧlu, Ü.

    2015-10-01

    Aims: We present a multiwavelength study of the Be/X-ray binary system XTE J1946+274 with the main goal of better characterizing its behavior during X-ray quiescence. We also aim to shed light on the possible mechanisms which trigger the X-ray activity for this source. Methods: XTE J1946+274 was observed by Chandra-ACIS during quiescence in 2013 March 12. In addition, this source has been monitored from the ground-based astronomical observatories of El Teide (Tenerife, Spain), Roque de los Muchachos (La Palma, Spain) and Sierra Nevada (Granada, Spain) since 2011 September, and from the TÜBİTAK National Observatory (Antalya, Turkey) since 2005 April. We have performed spectral and photometric temporal analyses in order to investigate the quiescent state and transient behavior of this binary system. Results: Our optical study revealed that a long mass ejection event from the Be star took place in 2006, lasting for about seven years, and another one is currently ongoing. We also found that a large Be circumstellar disk is present during quiescence, although major X-ray activity is not observed. We made an attempt to explain this by assuming the permanently presence of a tilted (sometimes warped) Be decretion disk. The 0.3-10 keV X-ray spectrum of the neutron star during quiescence was well fitted with either an absorbed black-body or an absorbed power-law models. The main parameters obtained for these models were kT = 1.43 ± 0.17 and Γ = 0.9 ± 0.4 (with NH ~ 2-7 × 1022 cm-2). The 0.3-10 keV flux of the source was ~0.8-1 × 10-12 erg-1 cm-2 s-1. Pulsations were found with Ppulse = 15.757(1) s (epoch MJD 56 363.115) and an rms pulse fraction of 32.1(3)%. The observed X-ray luminosity during quiescent periods was close to that of expected in supersonic propeller regimen.

  10. Constraining dust properties in Circumstellar Envelopes of C-stars in the Small Magellanic Cloud: optical constants and grain size of Carbon dust

    CERN Document Server

    Nanni, Ambra; Groenewegen, Martin A T; Aringer, Bernhard; Girardi, Léo; Pastorelli, Giada; Bressan, Alessandro; Bladh, Sara

    2016-01-01

    We present a new approach aimed at constraining the typical size and optical properties of carbon dust grains in Circumstellar envelopes (CSEs) of carbon-rich stars (C-stars) in the Small Magellanic Cloud (SMC). To achieve this goal, we apply our recent dust growth description, coupled with a radiative transfer code to the CSEs of C-stars evolving along the TP-AGB, for which we compute spectra and colors. Then we compare our modeled colors in the near- and mid-infrared (NIR and MIR) bands with the observed ones, testing different assumptions in our dust scheme and employing several data sets of optical constants for carbon dust available in the literature. Different assumptions adopted in our dust scheme change the typical size of the carbon grains produced. We constrain carbon dust properties by selecting the combination of grain size and optical constants which best reproduces several colors in the NIR and MIR at the same time. The different choices of optical properties and grain size lead to differences i...

  11. Detection of FeCN (X^4Δ_i) in the Circumstellar Envelope of IRC+10216

    Science.gov (United States)

    Zack, L. N.; Halfen, D. T.; Ziurys, L. M.

    2011-06-01

    A new interstellar molecule, FeCN (X^4Δ_i), has been detected in the envelope of the carbon-rich AGB star, IRC+10216. This work is the first definitive detection of an iron-bearing molecule in the interstellar medium, and is based on newly-measured rest frequencies. Eight successive rotational transitions of this linear free radical in the lowest spin ladder, Ω = 7/2, were observed at 2 and 3 mm using the Arizona Radio Observatory (ARO) 12 m telescope. Three transitions appear as single, unblended features at the 1-2 mK level and exhibit characteristic IRC+10216 line profiles; one had previously been observed with the IRAM 30 m telescope. Two other transitions are partially blended, but exhibit distinct emission at the FeCN frequencies. The remaining transitions are either completely contaminated, or are too high in energy. Comparison of the ARO and IRAM data suggests a source size for FeCN in IRC+10216 of 30'', indicating an outer shell distribution, as expected for a free radical. The column density derived for FeCN in this object is NTot = 4.0x1011 Cm-2 with a rotational temperature of TRot = 21 K The fractional abundance of this molecule is [FeCN]/[H_2] = 3x10-10, comparable to that of AlNC and KCN in the outer envelope. FeCN is likely formed by gas-phase reactions of Fe^+ or neutral iron, which has a significant gas-phase abundance in the outer shell. The detection of FeCN is further evidence that, aside from silicon, metal cyanides/isocyanides dominate the chemistry of refractory elements in IRC+10216.

  12. Three-dimensional radiation-hydrodynamics calculations of the envelopes of young planets embedded in protoplanetary disks

    International Nuclear Information System (INIS)

    We perform global three-dimensional (3D) radiation-hydrodynamics calculations of the envelopes surrounding young planetary cores of 5, 10, and 15 Earth masses, located in a protoplanetary disk at 5 and 10 AU from a solar-mass star. We apply a nested-grid technique to resolve the thermodynamics of the disk at the orbital-radius length scale and that of the envelope at the core-radius length scale. The gas is modeled as a solar mixture of molecular and atomic hydrogen, helium, and their ions. The equation of state accounts for both gas and radiation, and gas energy includes contributions from rotational and vibrational states of molecular hydrogen and from ionization of atomic species. Dust opacities are computed from first principles, applying the full Mie theory. One-dimensional (1D) calculations of planet formation are used to supplement the 3D calculations by providing energy deposition rates in the envelope due to solids accretion. We compare 1D and 3D envelopes and find that masses and gas accretion rates agree within factors of 2, and so do envelope temperatures. The trajectories of passive tracers are used to define the size of 3D envelopes, resulting in radii much smaller than the Hill radius and smaller than the Bondi radius. The moments of inertia and angular momentum of the envelopes are determined and the rotation rates are derived from the rigid-body approximation, resulting in slow bulk rotation. We find that the polar flattening is ≲ 0.05. The dynamics of the accretion flow are examined by tracking the motion of tracers that move into the envelope. The anisotropy of this flow is characterized in terms of both its origin and impact site at the envelope surface. Gas merges with the envelope preferentially at mid- to high latitudes.

  13. Effect of Photodesorption on Snow Line at the Surface of Optically Thick Circumstellar Disks around Herbig Ae/Be Stars

    OpenAIRE

    Oka, Akinori; Inoue, Akio K.; Nakamoto, Taishi; Honda, Mitsuhito

    2012-01-01

    We investigate the effect of photodesorption on the snow line position at the surface of a protoplanetary disk around a Herbig Ae/Be star, motivated by the detection of water ice particles at the surface of the disk around HD142527 by Honda et al. For this aim, we obtain the density and temperature structure in the disk with a 1+1D radiative transfer and determine the distribution of water ice particles in the disk by the balance between condensation, sublimation, and photodesorption. We find...

  14. Grain Growth in the Circumstellar Disks of the Young Stars CY Tau and DoAr 25

    CERN Document Server

    Pérez, Laura M; Isella, Andrea; Carpenter, John M; Andrews, Sean M; Calvet, Nuria; Corder, Stuartt A; Deller, Adam T; Dullemond, Cornelis P; Greaves, Jane S; Harris, Robert J; Henning, Thomas; Kwon, Woojin; Lazio, Joseph; Linz, Hendrik; Mundy, Lee G; Ricci, Luca; Sargent, Anneila I; Storm, Shaye; Tazzari, Marco; Testi, Leonardo; Wilner, David J

    2015-01-01

    We present new results from the Disks@EVLA program for two young stars: CY Tau and DoAr 25. We trace continuum emission arising from their circusmtellar disks from spatially resolved observations, down to tens of AU scales, at {\\lambda} = 0.9, 2.8, 8.0, and 9.8 mm for DoAr25 and at {\\lambda} = 1.3, 2.8, and 7.1 mm for CY Tau. Additionally, we constrain the amount of emission whose origin is different from thermal dust emission from 5 cm observations. Directly from interferometric data, we find that observations at 7 mm and 1 cm trace emission from a compact disk while millimeter-wave observations trace an extended disk structure. From a physical disk model, where we characterize the disk structure of CY Tau and DoAr 25 at wavelengths shorter than 5 cm, we find that (1) dust continuum emission is optically thin at the observed wavelengths and over the spatial scales studied, (2) a constant value of the dust opacity is not warranted by our observations, and (3) a high-significance radial gradient of the dust op...

  15. Angular momentum loss in the envelope-disk transition region of HH 111 protostellar system: evidence for magnetic braking?

    CERN Document Server

    Lee, Chin-Fei; Li, Zhi-Yun

    2016-01-01

    HH 111 is a Class I protostellar system at a distance of ~ 400 pc, with the central source VLA 1 associated with a rotating disk deeply embedded in a flattened envelope. Here we present the observations of this system at ~ 0.6" (240 AU) resolution in C18O (J=2-1) and 230 GHz continuum obtained with Atacama Large Millimeter/Submillimeter Array, and in SO obtained with Submillimeter Array. The observations show for the first time how a Keplerian rotating disk can be formed inside a flattened envelope. The flattened envelope is detected in C18O, extending out to >~ 2400 AU from the VLA 1 source. It has a differential rotation, with the outer part (>~ 2000 AU) better described by a rotation that has constant specific angular momentum and the innermost part (<~ 160 AU) by a Keplerian rotation. The rotationally supported disk is therefore relatively compact in this system, which is consistent with the dust continuum observations. Most interestingly, if the flow is in steady state, there is a substantial drop in ...

  16. Three-Dimensional Radiation-Hydrodynamics Calculations of the Envelopes of Young Planets Embedded in Protoplanetary Disks

    CERN Document Server

    D'Angelo, Gennaro

    2013-01-01

    We perform global three-dimensional (3-D) radiation-hydrodynamics calculations of the envelopes surrounding young planetary cores of 5, 10, and 15 Earth masses, located in a protoplanetary disk at 5 and 10 AU from a solar-mass star. We apply a nested-grid technique to resolve the thermodynamics of the disk at the orbital-radius length scale and that of the envelope at the core-radius length scale. The gas is modeled as a solar mixture of molecular and atomic hydrogen, helium, and their ions. The equation of state accounts for both gas and radiation, and gas energy includes contributions from rotational and vibrational states of molecular hydrogen and from ionization of atomic species. Dust opacities are computed from first principles, applying the full Mie theory. One-dimensional (1-D) calculations of planet formation are used to supplement the 3-D calculations by providing energy deposition rates in the envelope due to solids accretion. We compare 1-D and 3-D envelopes and find that masses and gas accretion ...

  17. Dispersing Envelope around the Keplerian Circumbinary Disk in L1551 NE and its Implications for the Binary Growth

    CERN Document Server

    Takakuwa, Shigehisa; Saigo, Kazuya; Saito, Masao

    2015-01-01

    We performed mapping observations of the Class I protostellar binary system L1551 NE in the C$^{18}$O ($J$=3-2), $^{13}$CO ($J$=3-2), CS ($J$=7-6), and SO ($J_N$=7$_8$-6$_7$) lines with Atacama Submillimeter Telescope Experiment (ASTE). The ASTE C$^{18}$O data are combined with our previous SMA C$^{18}$O data, which show a $r \\sim$300-AU scale Keplerian disk around the protostellar binary system. The C$^{18}$O maps show a $\\sim$20000-AU scale protostellar envelope surrounding the central Keplerian circumbinary disk. The envelope exhibits a northeast (blue) - southwest (red) velocity gradient along the minor axis, which can be interpreted as a dispersing gas motion with an outward velocity of 0.3 km s$^{-1}$, while no rotational motion in the envelope is seen. In addition to the envelope, two $\\lesssim$4000 AU scale, high-velocity ($\\gtrsim$1.3 km s$^{-1}$) redshifted $^{13}$CO and CS emission components are found to $\\sim$40$^{\\prime\\prime}$ southwest and $\\sim$20$^{\\prime\\prime}$ west of the protostellar bin...

  18. Formation of a Keplerian disk in the infalling envelope around L1527 IRS: transformation from infalling motions to Kepler motions

    Energy Technology Data Exchange (ETDEWEB)

    Ohashi, Nagayoshi [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Saigo, Kazuya [Chile Observatory, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Aso, Yusuke; Koyamatsu, Shin [Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Aikawa, Yuri [Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501 (Japan); Machida, Masahiro N. [Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, Fukuoka 812-8581 (Japan); Saito, Masao [Joint ALMA Observatory, Ave. Alonso de Cordova 3107, Vitacura, Santiago (Chile); Takahashi, Sanemichi Z. [Department of Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan); Takakuwa, Shigehisa; Yen, Hsi-Wei [Academia Sinica Institute of Astronomy and Astrophysics, PO Box 23-141, Taipei 10617, Taiwan (China); Tomida, Kengo [Department of Astronomical Science, Princeton University, Princeton, NJ 08544 (United States); Tomisaka, Kohji, E-mail: nohashi@naoj.org [National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan)

    2014-12-01

    We report Atacama Large Millimeter/submillimeter Array (ALMA) cycle 0 observations of the C{sup 18}O (J = 2-1), SO (J{sub N} = 6{sub 5}-5{sub 4}), and the 1.3 mm dust continuum toward L1527 IRS, a class 0 solar-type protostar surrounded by an infalling and rotating envelope. C{sup 18}O emission shows strong redshifted absorption against the bright continuum emission associated with L1527 IRS, strongly suggesting infall motions in the C{sup 18}O envelope. The C{sup 18}O envelope also rotates with a velocity mostly proportional to r {sup –1}, where r is the radius, whereas the rotation profile at the innermost radius (∼54 AU) may be shallower than r {sup –1}, suggestive of formation of a Keplerian disk around the central protostar of ∼0.3 M {sub ☉} in dynamical mass. SO emission arising from the inner part of the C{sup 18}O envelope also shows rotation in the same direction as the C{sup 18}O envelope. The rotation is, however, rigid-body-like, which is very different from the differential rotation shown by C{sup 18}O. In order to explain the line profiles and the position-velocity (PV) diagrams of C{sup 18}O and SO observed, simple models composed of an infalling envelope surrounding a Keplerian disk of 54 AU in radius orbiting a star of 0.3 M {sub ☉} are examined. It is found that in order to reproduce characteristic features of the observed line profiles and PV diagrams, the infall velocity in the model has to be smaller than the free-fall velocity yielded by a star of 0.3 M {sub ☉}. Possible reasons for the reduced infall velocities are discussed.

  19. Effect of Photodesorption on Snow Line at the Surface of Optically Thick Circumstellar Disks around Herbig Ae/Be Stars

    CERN Document Server

    Oka, Akinori; Nakamoto, Taishi; Honda, Mitsuhito

    2012-01-01

    We investigate the effect of photodesorption on the snow line position at the surface of a protoplanetary disk around a Herbig Ae/Be star, motivated by the detection of water ice particles at the surface of the disk around HD142527 by Honda et al. For this aim, we obtain the density and temperature structure in the disk with a 1+1D radiative transfer and determine the distribution of water ice particles in the disk by the balance between condensation, sublimation, and photodesorption. We find that photodesorption induced by the far-ultraviolet radiation from the central star depresses the ice-condensation front toward the mid-plane and pushes the surface snow line outward significantly when the stellar effective temperature exceeds a certain critical value. This critical effective temperature depends on the stellar luminosity and mass, the water abundance in the disk, and the yield of photodesorption. We present an approximate analytic formula for the critical temperature. We separate Herbig Ae/Be stars into ...

  20. Radio Imaging of the NGC 1333 IRAS 4A Region: Envelope, Disks, and Outflows of a Protostellar Binary System

    CERN Document Server

    Choi, Minho; Tatematsu, Ken'ichi; Lee, Jeong-Eun; Park, Geumsook

    2011-01-01

    The NGC 1333 IRAS 4A protobinary was observed in the 1.3 cm and 6.9 mm continuum and the ammonia and SiO lines, with an angular resolution of about 0.4 arcseconds. The continuum maps show the circumstellar structures of the two protostars, A1 and A2. The A1 system is brighter and more massive than the A2 system. The ratio of mass, including dense gas and protostar, is about 6. The properties of the circumstellar disks and outflows suggest that A1 may be younger than A2. The deflected part of the northeastern jet of A2 is bright in the SiO line, and the distance between the brightest peak and deflection point suggests that the enhancement of SiO takes about 100 yr after the collision with a dense core. The ammonia maps show a small structure that seems to be a part of the obstructing core. The outflow properties were studied by comparing interferometric maps of SiO, ammonia, formaldehyde, and HCN lines. Their overall structures agree well, suggesting that these species are excited by the same mechanism. Howeve...

  1. Radiation Magnetohydrodynamic Simulations of Protostellar Collapse: Non-Ideal Magnetohydrodynamic Effects and Early Formation of Circumstellar Disks

    CERN Document Server

    Tomida, Kengo; Machida, Masahiro N

    2015-01-01

    The transport of angular momentum by magnetic fields is a crucial physical process in formation and evolution of stars and disks. Because the ionization degree in star forming clouds is extremely low, non-ideal magnetohydrodynamic (MHD) effects such as ambipolar diffusion and Ohmic dissipation work strongly during protostellar collapse. These effects have significant impacts in the early phase of star formation as they redistribute magnetic flux and suppress angular momentum transport by magnetic fields. We perform three-dimensional nested-grid radiation magnetohydrodynamic (RMHD) simulations including Ohmic dissipation and ambipolar diffusion. Without these effects, magnetic fields transport angular momentum so efficiently that no rotationally supported disk is formed even after the second collapse. Ohmic dissipation works only in a relatively high density region within the first core and suppresses angular momentum transport, enabling formation of a very small rotationally supported disk after the second co...

  2. Formation of a Keplerian disk in the infalling envelope around L1527 IRS: transformation from infalling motions to Kepler motions

    CERN Document Server

    Ohashi, Nagayoshi; Aso, Yusuke; Aikawa, Yuri; Koyamatsu, Shin; Machida, Masahiro N; Saito, Masao; Takahashi, Sanemichi Z; Takakuwa, Shigehisa; Tomida, Kengo; Tomisaka, Kohji; Yen, Hsi-Wei

    2014-01-01

    We report Atacama Large Millimeter/submillimeter Array (ALMA) cycle 0 observations of C$^{18}$O ($J=2-1$), SO ($J_N= 6_5-5_4$) and 1.3mm dust continuum toward L1527 IRS, a class 0 solar-type protostar surrounded by an infalling and rotating envelope. C$^{18}$O emission shows strong redshifted absorption against the bright continuum emission associated with L1527 IRS, strongly suggesting infall motions in the C$^{18}$O envelope. The C$^{18}$O envelope also rotates with a velocity mostly proportional to $r^{-1}$, where $r$ is the radius, while the rotation profile at the innermost radius (54 AU) may be shallower than $r^{-1}$, suggestive of formation of a Keplerian disk around the central protostar of 0.3 Mo in dynamical mass. SO emission arising from the inner part of the C$^{18}$O envelope also shows rotation in the same direction as the C$^{18}$O envelope. The rotation is, however, rigid-body like which is very different from the differential rotation shown by C$^{18}$O. In order to explain the line profiles...

  3. H2 and CO Emission from Disks around T Tauri and Herbig Ae Pre-Main-Sequence Stars and from Debris Disks around Young Stars: Warm and Cold Circumstellar Gas

    Science.gov (United States)

    Thi, W. F.; van Dishoeck, E. F.; Blake, G. A.; van Zadelhoff, G. J.; Horn, J.; Becklin, E. E.; Mannings, V.; Sargent, A. I.; van den Ancker, M. E.; Natta, A.; Kessler, J.

    2001-11-01

    We present ISO Short-Wavelength Spectrometer observations of H2 pure-rotational line emission from the disks around low- and intermediate-mass pre-main-sequence stars as well as from young stars thought to be surrounded by debris disks. The pre-main-sequence sources have been selected to be isolated from molecular clouds and to have circumstellar disks revealed by millimeter interferometry. We detect ``warm'' (T~100-200 K) H2 gas around many sources, including tentatively the debris-disk objects. The mass of this warm gas ranges from ~10-4 Msolar up to 8×10-3 Msolar and can constitute a nonnegligible fraction of the total disk mass. Complementary single-dish 12CO 3-2, 13CO 3-2, and 12CO 6-5 observations have been obtained as well. These transitions probe cooler gas at T~20-80 K. Most objects show a double-peaked CO emission profile characteristic of a disk in Keplerian rotation, consistent with interferometer data on the lower J lines. The ratios of the 12CO 3-2/13CO 3-2 integrated fluxes indicate that 12CO 3-2 is optically thick but that 13CO 3-2 is optically thin or at most moderately thick. The 13CO 3-2 lines have been used to estimate the cold gas mass. If a H2/CO conversion factor of 1×104 is adopted, the derived cold gas masses are factors of 10-200 lower than those deduced from 1.3 millimeter dust emission assuming a gas/dust ratio of 100, in accordance with previous studies. These findings confirm that CO is not a good tracer of the total gas content in disks since it can be photodissociated in the outer layers and frozen onto grains in the cold dense part of disks, but that it is a robust tracer of the disk velocity field. In contrast, H2 can shield itself from photodissociation even in low-mass ``optically thin'' debris disks and can therefore survive longer. The warm gas is typically 1%-10% of the total mass deduced from millimeter continuum emission, but it can increase up to 100% or more for the debris-disk objects. Thus, residual molecular gas may

  4. SXP 5.05 = IGR J00569-7226 : using X-rays to explore the structure of a Be stars circumstellar disk

    CERN Document Server

    Coe, M J; Bird, A J; Haberl, F; Kennea, J A; McBride, V A; Townsend, L J; Udalski, A

    2014-01-01

    On MJD 56590-1 (2013 Oct 25-26) observations of the Magellanic Clouds by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) observatory discovered a previously-unreported bright, flaring X-ray source. This source was initially given the identification IGR J00569-7226. Subsequent multi-wavelength observations identified the system as new Be/X-ray binary system in the Small Magellanic Cloud. Follow-up X-ray observations by Swift and XMM-Newton revealed an X-ray pulse period of 5.05s and that the system underwent regular occulation/eclipse behaviour every 17d. This is the first reported eclipsing Be/X-ray binary system in the SMC, and only the second such system known to date. Furthermore, the nature of the occultation makes it possible to use the neutron star to X-ray the circumstellar disk, thereby, for the first time, revealing direct observational evidence for its size and clumpy structure. Swift timing measurements allowed for the binary solution to be calculated from the Doppler shifted X-ray p...

  5. The Role of Evolutionary Age and Metallicity in the Formation of Classical Be Circumstellar Disks II. Assessing the Evolutionary Nature of Candidate Disk Systems

    CERN Document Server

    Wisniewski, John P; Magalhaes, Antonio M; Bjorkman, Jon E; Meade, Marilyn R; Pereyra, Antonio

    2007-01-01

    (Abridged version) We present the first detailed imaging polarization observations of six SMC and six LMC clusters, known to have large populations of B-type stars which exhibit excess H-alpha emission, to constrain the evolutionary status of these stars and hence better establish links between the onset of disk formation in classical Be stars and cluster age and/or metallicity. The wavelength dependence of our intrinsic polarization data provides a diagnostic of the dominant and any secondary polarigenic agents present, enabling us to discriminate pure gas disk systems, i.e. classical Be stars, from composite gas plus dust disk systems, i.e. Herbig Ae/Be or B[e] stars. Our intrinsic polarization results, along with available near-IR color information, strongly supports the suggestion of Wisniewski et al. that classical Be stars are present in clusters of age 5-8 Myr, and contradict assertions that the Be phenomenon only develops in the second half of a B star's main sequence lifetime, i.e. no earlier than 10...

  6. Mid - infrared interferometry of massive young stellar objects II Evidence for a circumstellar disk surrounding the Kleinmann - Wright object

    CERN Document Server

    Follert, R; Stecklum, B; van Boekel, R; Henning, Th; Feldt, M; Herbst, T M; Leinert, Ch

    2010-01-01

    The formation scenario for massive stars is still under discussion. To further constrain current theories, it is vital to spatially resolve the structures from which material accretes onto massive young stellar objects (MYSOs). Due to the small angular extent of MYSOs, one needs to overcome the limitations of conventional thermal infrared imaging, regarding spatial resolution, in order to get observational access to the inner structure of these objects.We employed mid - infrared interferometry, using the MIDI instrument on the ESO /VLTI, to investigate the Kleinmann - Wright Object, a massive young stellar object previously identified as a Herbig Be star precursor. Dispersed visibility curves in the N- band (8 - 13 {\\mu}m) have been obtained at 5 interferometric baselines. We show that the mid - infrared emission region is resolved. A qualitative analysis of the data indicates a non - rotationally symmetric structure, e.g. the projection of an inclined disk. We employed extensive radiative transfer simulation...

  7. HST/WFPC2 Study of the Trapezium Cluster: the Influence of Circumstellar Disks on the Initial Mass Function

    CERN Document Server

    Robberto, M; Carrillo, G M; Beckwith, S V W; Makidon, R B; Panagia, N

    2004-01-01

    We have performed the first measures of mass accretion rates in the core of the Orion Nebula Cluster. Four adjacent fields centered on the Trapezium stars have been imaged in the U- and B-bands using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. In this paper we focus our attention on a group of 40 stars with known spectral types and complete UBVI WFPC2 photometry. Approximately three quarters of the sources show excess luminosity in the U-band, that we attribute to mass accretion. The known correlation between the U-band excess and the total accretion luminosity allows us to estimate the accretion rates. Overall, mass accretion rates appear lower than those measured by other authors in the Orion flanking fields or in Taurus-Auriga. Mass accretion rates remain low even in the vicinity of the birth line of Palla & Stahler, suggesting that in the core of the Trapezium cluster disk accretion has been recently depressed by an external mechanism. We suggest that the UV radiation genera...

  8. 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.; Hogerheijde, M. R.; Hill, T.

    2007-01-01

    -2 line with a resolution of about 1". At this resolution a protoplanetary disk with a radius of a few hundred AUs should be detectable, if present. Radiative transfer tools are used to model the emission from both continuum and line data. Results. We find that these data are consistent with theoretical...... models of a collapsing envelope and Keplerian circumstellar disk. Models reproducing both the spectral energy distribution and the interferometric continuum observations reveal that the disk is inclined by 40°, which is significantly different to the surrounding envelope (74°). Conclusions. This...

  9. Modelling Molecular Emission from Young Embedded Disks

    Science.gov (United States)

    Harsono, D.; Visser, R.; van Dishoeck, E. F.; Kristensen, L.; Bruderer, S.; Brinch, C. Hogerheijde, M.

    2011-05-01

    Circumstellar disks play an important role in the formation of stars and planets. Recent observations and models have placed strong constraints on the later stages of their evolution (the T Tauri or Herbig Ae/Be phase), when an envelope is no longer present. However, little is known of the disk structure and evolution during the embedded phase of star formation. With Herschel and the VLT, and soon ALMA, we will be able to detect and characterize the early stages of disk formation. Sophisticated modeling including both physical and chemical structure of the system would be needed to interpret the high quality of data. We present a two-dimensional, semi-analytical model of disk formation as also used in Visser et al. (2009) and Visser and Dullemond (2010). The dust temperature is determined using a three-dimensional dust continuum radiative transfer code (RADMC-3D). Molecular abundances are calculated by following freeze-out and evaporation from the pre-stellar core up to the formation of the circumstellar disk. Synthetic spectra of CO and H2O within the wavelength ranges observable with Herschel and VLT-CRIRES are then produced at a series of time steps, tracing the different stages of disk formation. We also present simulated ALMA images. We discuss the evolution of the molecular emission and the possibility of identifying the presence of embedded disks.

  10. Spectroscopic studies of the classical Cepheid ζ Gem: Analysis of the velocity field in the atmosphere and manifestation of the presence of a circumstellar envelope

    Science.gov (United States)

    Usenko, I. A.

    2016-06-01

    with those for the B component of the Hα line, they are all formed in the Cepheid's atmosphere. The formation and passage of a shock wave due to the κ-mechanism at work can be responsible for the stronger scatter of the B1 and B2 components in their velocities at phases after the Cepheid's minimum radius. The averaged velocities of the R1 components also change with pulsation phase and differ only slightly from the remaining ones. On the other hand, the mean velocity estimate for the R component of the Hα line at all phases is +32.72 ± 2.50 km s-1 and differs significantly from the bulk of the velocities, suggesting the formation of this component in the envelope around the Cepheid. The unusual behavior of the mean velocities for the R2 components of the metal absorption lines can also point to their formation in the envelope and can be yet another indicator of its presence around ζ Gem.

  11. Confirmation of Circumstellar Phosphine

    Science.gov (United States)

    Agúndez, M.; Cernicharo, J.; Decin, L.; Encrenaz, P.; Teyssier, D.

    2014-08-01

    Phosphine (PH3) was tentatively identified a few years ago in the carbon star envelopes IRC +10216 and CRL 2688 from observations of an emission line at 266.9 GHz attributable to the J = 1-0 rotational transition. We report the detection of the J = 2-1 rotational transition of PH3 in IRC +10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH3. Radiative transfer calculations indicate that infrared pumping in excited vibrational states plays an important role in the excitation of PH3 in the envelope of IRC +10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R * from the star, with an abundance of 10-8 relative to H2. The detection of PH3 challenges chemical models, none of which offer a satisfactory formation scenario. Although PH3 holds just 2% of the total available phosphorus in IRC +10216, it is, together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggesting that it could also be an important phosphorus species in other astronomical environments. This is the first unambiguous detection of PH3 outside the solar system, and is a further step toward a better understanding of the chemistry of phosphorus in space.

  12. CONFIRMATION OF CIRCUMSTELLAR PHOSPHINE

    Energy Technology Data Exchange (ETDEWEB)

    Agúndez, M.; Cernicharo, J. [Instituto de Ciencia de Materiales de Madrid, CSIC, C/ Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco (Spain); Decin, L. [Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, NL-1098 Amsterdam (Netherlands); Encrenaz, P. [LERMA, Observatoire de Paris, 61 Av. de l' Observatoire, F-75014 Paris (France); Teyssier, D. [European Space Astronomy Centre, Urb. Villafranca del Castillo, P.O. Box 50727, E-28080 Madrid (Spain)

    2014-08-01

    Phosphine (PH{sub 3}) was tentatively identified a few years ago in the carbon star envelopes IRC +10216 and CRL 2688 from observations of an emission line at 266.9 GHz attributable to the J = 1-0 rotational transition. We report the detection of the J = 2-1 rotational transition of PH{sub 3} in IRC +10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH{sub 3}. Radiative transfer calculations indicate that infrared pumping in excited vibrational states plays an important role in the excitation of PH{sub 3} in the envelope of IRC +10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R {sub *} from the star, with an abundance of 10{sup –8} relative to H{sub 2}. The detection of PH{sub 3} challenges chemical models, none of which offer a satisfactory formation scenario. Although PH{sub 3} holds just 2% of the total available phosphorus in IRC +10216, it is, together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggesting that it could also be an important phosphorus species in other astronomical environments. This is the first unambiguous detection of PH{sub 3} outside the solar system, and is a further step toward a better understanding of the chemistry of phosphorus in space.

  13. Confirmation of circumstellar phosphine

    CERN Document Server

    Agundez, M; Decin, L; Encrenaz, P; Teyssier, D

    2014-01-01

    Phosphine (PH3) was tentatively identified a few years ago in the carbon star envelopes IRC+10216 and CRL2688 from observations of an emission line at 266.9 GHz attributable to the J=1-0 rotational transition. We report the detection of the J=2-1 rotational transition of PH3 in IRC+10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH3. Radiative transfer calculations indicate that infrared pumping to excited vibrational states plays an important role in the excitation of PH3 in the envelope of IRC+10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R* from the star, with an abundance of 1e-8 relative to H2. The detection of PH3 challenges chemical models, none of which offers a satisfactory formation scenario. Although PH3 locks just 2 % of the total available phosphorus in IRC+10216, it is together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggest...

  14. Protoplanetary and Debris Disk Morphologies

    Science.gov (United States)

    Lomax, Jamie R.; Wisniewski, John P.; Grady, Carol A.; McElwain, Michael W.; Hashimoto, Jun; Donaldson, Jessica; Debes, John H.; Malumuth, Eliot; Roberge, Aki; Weinberger, Alycia J.; SEEDS Team

    2016-01-01

    The types of planets that form around other stars are highly dependent on their natal disk conditions. Therefore, the composition, morphology, and distribution of material in protoplanetary and debris disks are important for planet formation. Here we present the results of studies of two disk systems: AB Aur and AU Mic.The circumstellar disk around the Herbig Ae star AB Aur has many interesting features, including spirals, asymmetries, and non-uniformities. However, comparatively little is known about the envelope surrounding the system. Recent work by Tang et al (2012) has suggested that the observed spiral armss may not in fact be in the disk, but instead are due to areas of increased density in the envelope and projection effects. Using Monte Carlo modeling, we find that it is unlikely that the envelope holds enough material to be responsible for such features and that it is more plausible that they form from disk material. Given the likelihood that gravitational perturbations from planets cause the observed spiral morphology, we use archival H band observations of AB Aur with a baseline of 5.5 years to determine the locations of possible planets.The AU Mic debris disk also has many interesting morphological features. Because its disk is edge on, the system is an ideal candidate for color studies using coronagraphic spectroscopy. Spectra of the system were taken by placing a HST/STIS long slit parallel to and overlapping the disk while blocking out the central star with an occulting fiducial bar. Color gradients may reveal the chemical processing that is occuring within the disk. In addition, it may trace the potential composition and architecture of any planetary bodies in the system because collisional break up of planetesimals produces the observed dust in the system. We present the resulting optical reflected spectra (5200 to 10,200 angstroms) from this procedure at several disk locations. We find that the disk is bluest at the innermost locations of the

  15. EFFECT OF PHOTODESORPTION ON THE SNOW LINES AT THE SURFACE OF OPTICALLY THICK CIRCUMSTELLAR DISKS AROUND HERBIG Ae/Be STARS

    International Nuclear Information System (INIS)

    We investigate the effect of photodesorption on the snow line position at the surface of a protoplanetary disk around a Herbig Ae/Be star, motivated by the detection of water ice particles at the surface of the disk around HD142527 by Honda et al. For this aim, we obtain the density and temperature structure in the disk with a 1+1D radiative transfer and determine the distribution of water ice particles in the disk by the balance between condensation, sublimation, and photodesorption. We find that photodesorption induced by far-ultraviolet radiation from the central star depresses the ice-condensation front toward the mid-plane and pushes the surface snow line significantly outward when the stellar effective temperature exceeds a certain critical value. This critical effective temperature depends on the stellar luminosity and mass, the water abundance in the disk, and the yield of photodesorption. We present an approximate analytic formula for the critical temperature. We separate Herbig Ae/Be stars into two groups on the HR diagram according to the critical temperature: one is the disks where photodesorption is effective and from which we may not find ice particles at the surface, and the other is the disks where photodesorption is not effective. We estimate the snow line position at the surface of the disk around HD142527 to be 100-300 AU, which is consistent with the water ice detection at >140 AU in the disk. All the results depend on the dust grain size in a complex way, and this point requires more work in the future.

  16. Embryos grown in the dead zone: Assembling the first protoplanetary cores in low mass self-gravitating circumstellar disks of gas and solids

    OpenAIRE

    Lyra, W.; Johansen, A; Klahr, H.; Piskunov, N.

    2008-01-01

    In the borders of the dead zones of protoplanetary disks, the inflow of gas produces a local density maximum that triggers the Rossby wave instability. The vortices that form are efficient in trapping solids. We aim to assess the possibility of gravitational collapse of the solids within the Rossby vortices. We perform global simulations of the dynamics of gas and solids in a low mass non-magnetized self-gravitating thin protoplanetary disk with the Pencil code. We use multiple particle speci...

  17. The circumstellar disk of FS Tau B - A self-consistent model based on observations in the mid-infrared with NACO -

    CERN Document Server

    Kirchschlager, Florian; Madlener, David

    2016-01-01

    Protoplanetary disks are a byproduct of the star formation process. In the dense mid-plane of these disks, planetesimals and planets are expected to form. The first step in planet formation is the growth of dust particles from submicrometer-sized grains to macroscopic mm-sized aggregates. The grain growth is accompanied by radial drift and vertical segregation of the particles within the disk. To understand this essential evolutionary step, spatially resolved multi-wavelength observations as well as photometric data are necessary which reflect the properties of both disk and dust. We present the first spatially resolved image obtained with NACO at the VLT in the L$_\\text{p}$ band of the near edge-on protoplanetary disk FS Tau B. Based on this new image, a previously published Hubble image in H band and the spectral energy distribution from optical to millimeter wavelengths, we derive constraints on the spatial dust distribution and the progress of grain growth. For this purpose we perform a disk modeling usin...

  18. Dynamics of extended AGB star envelopes

    CERN Document Server

    Dreyer, C; Sedlmayr, E

    2010-01-01

    The dust formed in extended circumstellar envelopes of long-period variables and Miras has a strong influence on the envelope dynamics. A radiatively driven instability caused by the formation of dust leads to the development of an autonomous dynamics characterised by a set of distinct frequencies. We study the interplay between the envelope's internal dynamics and an external excitation by a pulsating star.

  19. On the Intrinsic Continuum Linear Polarization of Classical Be Stars during Disk Growth and Dissipation

    CERN Document Server

    Halonen, Robbie J

    2013-01-01

    We investigate the intrinsic continuum linear polarization from axisymmetric density distributions of gas surrounding classical Be stars during the formation and dissipation of their circumstellar disks. We implement a Monte Carlo calculation of the Stokes parameters with the use of the non-LTE radiative transfer code of Sigut & Jones (2007) to reproduce the continuous polarimetric spectra of classical Be stars. The scattering of light in the nonspherical circumstellar envelopes of classical Be stars produces a distinct polarization signature that can be used to study the physical nature of the scattering environment. In this paper, we highlight the utility of polarimetric measurements as important diagnostics in the modeling of these systems. We illustrate the effects of using self-consistent calculation of the thermal structure of the circumstellar gas on the characteristic wavelength-dependence of the polarization spectrum. In showing that the principal features of the polarization spectrum originate f...

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

    CERN Document Server

    Takami, Michihiro; Hashimoto, Jun; Kim, Hyosun; Wisnewski, John; Henning, Thomas; Grady, Carol A; Kandori, Ryo; Hodapp, Klaus W; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Chou, Mei-Yin; Itoh, Yoichi; Momose, Munetake; Mayama, Satoshi; Currie, Thayne; Follette, Katherine B; Kwon, Jungmi; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D; Carson, Joseph; Egner, Sebastian E; Feldt, Markus; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko; Ishii, Miki; Iye, Masanori; Janson, Markus; Knapp, Gillian R; Kuzuhara, Masayuki; McElwain, Michael W; Matsuo, Taro; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suto, Hiroshi; Suzuki, Ryuji; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L; Watanabe, Makoto; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    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 (~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, S...

  1. On the Intrinsic Continuum Linear Polarization of Classical Be Stars during Disk Growth and Dissipation

    Science.gov (United States)

    Halonen, Robbie J.; Jones, Carol E.

    2013-03-01

    We investigate the intrinsic continuum linear polarization from axisymmetric density distributions of gas surrounding classical Be stars during the formation and dissipation of their circumstellar disks. We implement a Monte Carlo calculation of the Stokes parameters with the use of the non-LTE radiative transfer code of Sigut & Jones to reproduce the continuous polarimetric spectra of classical Be stars. The scattering of light in the nonspherical circumstellar envelopes of classical Be stars produces a distinct polarization signature that can be used to study the physical nature of the scattering environment. In this paper, we highlight the utility of polarimetric measurements as important diagnostics in the modeling of these systems. We illustrate the effects of using self-consistent calculation of the thermal structure of the circumstellar gas on the characteristic wavelength-dependence of the polarization spectrum. In showing that the principal features of the polarization spectrum originate from different parts of the disk, we emphasize the capability of polarimetric observations to trace the evolution of the disk on critical scales. We produce models that approximate the disk formation and dissipation periods and illustrate how the polarimetric properties of these systems can have a pivotal role in determining the mechanism for mass decretion from the central star.

  2. Binary Stellar Mergers with Marginally-Bound Ejecta: Excretion Disks, Inflated Envelopes, Outflows, and their Luminous Transients

    CERN Document Server

    Pejcha, Ondrej; Tomida, Kengo

    2016-01-01

    We study mass loss from the outer Lagrange point (L2) in binary stellar mergers and their luminous transients by means of radiative hydrodynamical simulations. Previously, we showed that for binary mass ratios 0.06 0.15. By contrast, for cold L2 mass-loss (\\epsilon 0.8, the equatorial outflow instead remains marginally-bound and falls back to the binary over tens to hundreds of binary orbits, where it experiences additional tidal torqueing and shocking. As the bound gas becomes virialized with the binary, the luminosity of the system increases slowly at approximately constant photosphere radius, causing the temperature to rise. Subsequent evolution depends on the efficiency of radiative cooling. If the bound atmosphere is able to cool efficiently, as quantified by radiative diffusion time being shorter than the advection time (t_diff/t_adv 10 an isotropic wind is formed. Between these two extremes, an inflated envelope transports the heat generated near the binary to the surface by meridional flows. In all...

  3. The Migrating Embryo Model for Disk Evolution

    CERN Document Server

    Basu, Shantanu

    2012-01-01

    A new view of disk evolution is emerging from self-consistent numerical simulation modeling of the formation of circumstellar disks from the direct collapse of prestellar cloud cores. This has implications for many aspects of star and planet formation, including the growth of dust and high-temperature processing of materials. A defining result is that the early evolution of a disk is crucially affected by the continuing mass loading from the core envelope, and is driven into recurrent phases of gravitational instability. Nonlinear spiral arms formed during these episodes fragment to form gaseous clumps in the disk. These clumps generally migrate inward due to gravitational torques arising from their interaction with a trailing spiral arm. Occasionally, a clump can open up a gap in the disk and settle into a stable orbit, revealing a direct pathway to the formation of companion stars, brown dwarfs, or giant planets. At other times, when multiple clumps are present, a low mass clump may even be ejected from the...

  4. The complex circumstellar environment of HD142527

    CERN Document Server

    Verhoeff, A P; Pantin, E; Waters, L B F M; Tielens, A G G M; Honda, M; Fujiwara, H; Bouwman, J; van Boekel, R; Dougherty, S M; de Koter, A; Dominik, C; Mulders, G D

    2011-01-01

    The recent findings of gas giant planets around young A-type stars suggest that disks surrounding Herbig Ae/Be stars will develop planetary systems. An interesting case is HD142527, for which previous observations revealed a complex circumstellar environment and an unusually high ratio of infrared to stellar luminosity. Its properties differ considerably from other Herbig Ae/Be stars. This suggests that the disk surrounding HD142527 is in an uncommon evolutionary stage. We aim for a better understanding of the geometry and evolutionary status of the circumstellar material around the Herbig Ae/Be star HD142527. We map the composition and spatial distribution of the dust around HD142527. We analyze SEST and ATCA millimeter data, VISIR N and Q-band imaging and spectroscopy. We gather additional relevant data from the literature. We use the radiative transfer code MCMax to construct a model of the geometry and density structure of the circumstellar matter, which fits all of the observables satisfactorily. We find...

  5. Composite Circumstellar Dust Grains

    CERN Document Server

    Gupta, Ranjan; Dutta, Rajeshwari

    2016-01-01

    We calculate the absorption efficiencies of composite silicate grains with inclusions of graphite and silicon carbide in the spectral range 5--25$\\rm \\mu m$. We study the variation in absorption profiles with volume fractions of inclusions. In particular we study the variation in the wavelength of peak absorption at 10 and 18$\\rm \\mu m$. We also study the variation of the absorption of porous silicate grains. We use the absorption efficiencies to calculate the infrared flux at various dust temperatures and compare with the observed infrared emission flux from the circumstellar dust around some M-Type \\& AGB stars obtained from IRAS and a few stars from Spitzer satellite. We interpret the observed data in terms of the circumstellar dust grain sizes; shape; composition and dust temperature.

  6. The Rich Circumstellar Chemistry of SMP LMC 11

    CERN Document Server

    Malek, Sarah E; Bernard-Salas, Jeronimo

    2011-01-01

    Carbon-rich evolved stars from the asymptotic giant branch to the planetary nebula phase are characterized by a rich and complex carbon chemistry in their circumstellar envelopes. A peculiar object is the preplanetary nebula SMP LMC 11, whose Spitzer-IRS spectrum shows remarkable and diverse molecular absorption bands. To study how the molecular composition in this object compares to our current understanding of circumstellar carbon chemistry, we modeled this molecular absorption. We find high abundances for a number of molecules, perhaps most notably benzene. We also confirm the presence of propyne (CH3C2H) in this spectrum. Of all the cyanopolyynes, only HC3N is evident; we can detect at best a marginal presence of HCN. From comparisons to various chemical models, we can conclude that SMP LMC 11 must have an unusual circumstellar environment (a torus rather than an outflow).

  7. HIGH-CONTRAST NEAR-INFRARED IMAGING POLARIMETRY OF THE PROTOPLANETARY DISK AROUND RY TAU

    International Nuclear Information System (INIS)

    We present near-infrared coronagraphic imaging polarimetry of RY Tau. The scattered light in the circumstellar environment was imaged at the H band at a high resolution (∼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

  8. Millimeter Continuum Measurements of Circumstellar Dust Around Very Young Low Mass Stars

    Science.gov (United States)

    Terebey, S.; Chandler, C. J.; Andre, P.

    1992-01-01

    We investigate the question of disk formation during the protostar phase. We build on the results of Keene and Masson (1990) who analysis of L1551 showed themillimeter continuum emission comes from both an unresolved circumstellar conponent i.e. disk and an extended cloud core.

  9. The progenitor of SN 2011ja: Clues from circumstellar interaction

    OpenAIRE

    Chakraborti, Sayan; Ray, Alak; Smith, Randall; Ryder, Stuart; Yadav, Naveen; Sutaria, Firoza; Dwarkadas, Vikram V; Chandra, Poonam; Pooley, David; Roy, Rupak

    2013-01-01

    Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II Plateau (IIP) supernovae. The ejecta from these explosions shock the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical pho...

  10. High-resolution near-infrared imaging of the Orion 114-426 silhouette disk

    CERN Document Server

    McCaughrean, M J; Bally, J; Erickson, E; Thompson, R; Rieke, M J; Schneider, G; Stolovy, S; Young, E; Caughrean, Mark J. Mc; Chen, Hua; Bally, John; Erickson, Ed; Thompson, Rodger; Rieke, Marcia; Schneider, Glenn; Stolovy, Susan; Young, Erick

    1997-01-01

    We present the first high-resolution near-infrared images of the edge-on silhouette circumstellar disk, Orion 114-426, made using NICMOS on the Hubble Space Telescope. Images taken against the bright nebular background of the ionized hydrogen Pa$\\alpha$ line at 1.87 micron show the major axis of the disk to be approximately 20% smaller than at 0.6 micron, from which we deduce the structure of the edge of the disk. Continuum images of diffuse polar lobes above and below the plane of the disk show a morphology and evolution with wavelength consistent with predictions for reflection nebulae in a diffuse envelope with large polar cavities, surrounding a thin, massless, Keplerian disk, centered on an otherwise hidden central star. We make use of our observations and reasonable assumptions about the underlying disk structure to show that the disk mass is at least 10 earth masses and plausibly $\\geq 5\\times 10^{-4}$ solar masses.

  11. Interstellar and circumstellar fullerenes

    CERN Document Server

    Bernard-Salas, J; Jones, A P; Peeters, E; Micelotta, E R; Otsuka, M; Sloan, G C; Kemper, F; Groenewegen, M

    2014-01-01

    Fullerenes are a particularly stable class of carbon molecules in the shape of a hollow sphere or ellipsoid that might be formed in the outflows of carbon stars. Once injected into the interstellar medium (ISM), these stable species survive and are thus likely to be widespread in the Galaxy where they contribute to interstellar extinction, heating processes, and complex chemical reactions. In recent years, the fullerene species C60 (and to a lesser extent C70) have been detected in a wide variety of circumstellar and interstellar environments showing that when conditions are favourable, fullerenes are formed efficiently. Fullerenes are the first and only large aromatics firmly identified in space. The detection of fullerenes is thus crucial to provide clues as to the key chemical pathways leading to the formation of large complex organic molecules in space, and offers a great diagnostic tool to describe the environment in which they reside. Since fullerenes share many physical properties with PAHs, understand...

  12. X-raying circumstellar material around young stars

    CERN Document Server

    Schneider, P C

    2015-01-01

    Young stars are surrounded by copious amounts of circumstellar material. Its composition, in particular its gas-to-dust ratio, is an important parameter. However, measuring this ratio is challenging, because gas mass estimates are often model dependent. X-ray absorption is sensitive to the gas along the line-of-sight while optical/near-IR extinction depends on the dust content. Therefore, the gas-to-dust ratio of an absorber is given by the ratio between X-ray and optical/near-IR extinction. We present three systems where we used X-ray and optical/near-IR data to constrain the gas-to-dust ratio of circumstellar material; from a dust-rich debris disk to gaseous protoplanetary disks.

  13. CPD–52 9243: Circumstellar Dust and Gas Properties Derived from Interferometric and Spectroscopic Data/footnotemark

    Czech Academy of Sciences Publication Activity Database

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

    San Francisco: Astronomical Society of the Pacific, 2012 - (Carciofi, A.), s. 323-328. (ASP Conference Series. 464). ISBN 9781583818107. [Circumstellar Dynamics at High Resolution. Foz do Iguaçu (BR), 27.02.2012-02.03.2012] R&D Projects: GA ČR(CZ) GAP209/11/1198 Institutional research plan: CEZ:AV0Z10030501 Keywords : circumstellar dust * disk structure * kinematics Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  14. The circumstellar structure around supernovae

    International Nuclear Information System (INIS)

    The time dependent ionization and temperature structure of the circumstellar medium around supernovae has been calculated, in order to interpret recent supernova radio observations. For a stellar wind origin of the circumstellar medium, the authors relate the time of radio turn-on to the progenitor mass loss rate. They also show that large column densities for the UV resonance lines are expected. The results are applied to SN 1979c, SN 1980K and SN 1987A

  15. Morphology and kinematics of the gas envelope of the variable AGB star $\\pi^1$ Gruis

    CERN Document Server

    Nhung, P T; Diep, P N; Phuong, N T; Thao, N T; Tuan-Anh, P; Darriulat, P

    2016-01-01

    Observations of the $^{12}$CO(3-2) emission of the circumstellar envelope (CSE) of the variable star $\\pi^1$ Gru using the compact array (ACA) of the ALMA observatory have been recently made accessible to the public. An analysis of the morphology and kinematics of the CSE is presented with a result very similar to that obtained earlier for $^{12}$CO(2-1) emission by Chiu et al. (2006) using the Sub-Millimeter Array. A quantitative comparison is made using their flared disk model. A new model is presented that provides a significantly better description of the data, using radial winds and smooth evolutions of the radio emission and wind velocity from the stellar equator to the poles.

  16. Morphology and kinematics of the gas envelope of the variable AGB star π1 Gruis

    Science.gov (United States)

    Tuyet Nhung, Pham; Thi Hoai, Do; Diep, Pham Ngoc; Thi Phuong, Nguyen; Thi Thao, Nguyen; Anh, Pham Tuan; Darriulat, Pierre

    2016-07-01

    Observations of the 12CO(3–2) emission from the circumstellar envelope (CSE) of the variable star π1 Gru using the compact array of the ALMA observatory have been recently made accessible to the public. An analysis of the morphology and kinematics of the CSE is presented with a result very similar to that obtained earlier for 12CO(2–1) emission using the Submillimeter Array. A quantitative comparison is made using their flared disk model. A new model is presented that provides a significantly better description of the data, using radial winds and smooth evolutions of the radio emission and wind velocity from the stellar equator to the poles. ) operated by the NAOJ.

  17. The Magnetic Field in the Class 0 Protostellar Disk of L1527

    CERN Document Server

    Segura-Cox, Dominique M; Stephens, Ian W; Fernandez-Lopez, Manuel; Kwon, Woojin; Tobin, John J; Li, Zhi-Yun; Crutcher, Richard

    2014-01-01

    We present subarcsecond (~0.35") resolved observations of the 1.3 mm dust polarization from the edge-on circumstellar disk around the Class 0 protostar L1527. The inferred magnetic field is consistent with a dominantly toroidal morphology; there is no significantly detected vertical poloidal component to which observations of an edge-on disk are most sensitive. This suggests that angular momentum transport in Class 0 protostars (when large amounts of material are fed down to the disk from the envelope and accreted onto the protostar) is driven mainly by magnetorotational instability rather than magnetocentrifugal winds at 50 AU scales. In addition, with the data to date there is an early, tentative trend that R>30 AU disks have so far been found in Class 0 systems with average magnetic fields on the 1000 AU scale strongly misaligned with the rotation axis. The absence of such a disk in the aligned case could be due to efficient magnetic braking that disrupts disk formation. If this is the case, this implies t...

  18. Young Planetary disks

    Science.gov (United States)

    Lecavelier Des Etangs, A.

    2007-07-01

    The present review focuses on UV observations of young planetary disks and consequently mostly on the gaseous content of those disks. Few examples are taken to illustrate the capability of the UV observatories to scrutinize in detail the gas content of low density circumstellar disks if they are seen edge-on or nearly edge-on. For instance, in the case of HD100546, FUSE observations re- vealed signatures of outflow and infall in the disk caused by interaction of the stellar magnetosphere with the circumstellar disk. Observations of numerous absorption lines from H2 around young stars give constrains on the gas temper- ature and density, and physical size of the absorbing layer. In the case of T-Tauri stars and one brown dwarf, emissions from exited H2 have been detected. In the case of Beta Pictoris, the observation of CO in the UV and search for H2 with FUSE demonstrated that the evaporation of frozen bodies like comets must produce the CO seen in the disk. Extensive observations of spectral variability of Beta Pictoris are now interpreted by extrasolar comets evaporating in the vicinity of the central star of this young planetary system.

  19. Isotopes in the interstellar medium and circumstellar envelopes

    International Nuclear Information System (INIS)

    Measurements of the present-day abundances of elements and isotopes, combined with model calculations, allow us to trace the history of nucleosynthesis in the universe. Throughout this review, emphasis will be placed on descriptions of the measurement processes and the interpretations needed to obtain actual isotope and element abundances from measurements. Comparisons of the abundances of isotopomers of a given element are less affected by systematic effects than are comparisons of the abundances of different elements. Thus ratios of isotopomers should be given a greater weight when data and models are compared. As is generally accepted, the universe began with an explosive event, the Big Bang. The nucleosynthesis associated with this event produced 'primordial' abundances of the 'light elements', deuterium, 3He, 4He, and 7Li. Subsequent stellar processing of the light elements has altered the relative abundances, and also produced heavier elements such as carbon, nitrogen and oxygen. Stellar nucleosynthesis products from solar and larger mass stars are expelled into the interstellar medium (ISM). The goal of studies of the abundances of the light elements is to estimate the primordial abundances, that is, the abundances produced in the Big Bang. It is believed that D is always net destroyed in stars; 3He and 7Li may be net produced, 4He is certainly net produced. In the Solar System itself, results are obtained from in situ measurements with space probes to Jupiter, measurements of solar wind constituents, the analysis of the content of meteorites, and spectral line measurements of the solar photosphere. For sources outside the Solar System, these data are based on spectral line measurements of gas-phase species. The ratio of gas-phase abundances of elements, such as carbon to lithium may be affected by differing amounts of condensation onto dust grains; however such a process will not affect the ratio of isotopes such as 6Li/7Li. The most reliable measurements of D to H ratios are based on spectroscopic measurements of Lyman series ultraviolet absorption lines from foreground interstellar gas. Measurements of clouds in our galaxy have been obtained with satellites such as the International Ultraviolet Observatory, Copernicus, and the Hubble Space Telescope. The most interesting new development is the measurement of distant clouds with large redshifted velocities. Such data can be taken with Earth-bound optical telescopes. In the near future the Far Ultra Violet Explorer will refine and extend measurements of D/H ratios in relatively nearby regions. Abundances of 3He in the ISM have been measured using the hyperfine transition of 3He+, in galactic H II regions which are ionized by high-mass stars. 4He is the most abundant of the light elements. The primordial abundance must be very accurately determined if one wishes to use this quantity to estimate the baryon density in the early universe. Recently 4He/H ratios have been measured in a number of metal-poor compact blue galaxies. These sources seem to have had little stellar evolution, so the ratio should be close to the primordial value. Estimates of the primordial abundance of 7Li are made for a population of old stars found far from the plane of our galaxy. A refinement of Li abundance estimates requires a more detailed understanding of the Li destruction processes in stars. (author)

  20. Planet formation in transition disks: Modeling, spectroscopy, and theory

    Science.gov (United States)

    Liskowsky, Joseph Paul

    An important field of modern astronomy is the study of planets. Literally for millennia, careful observers of the night sky have tracked these 'wanderers', with their peculiar motions initiating avenues of inquiry not able to elucidated by a study of the stars alone: we have discovered that the planets (as well as Earth) orbit the sun and that the stars are so far away, even their relative positions do not seem to shift perceptibly when Earth's position moves hundreds of millions of miles. With the advent of the telescope, and subsequent improvements upon it over the course of centuries, accelerating to the dramatically immense telescopes available today and those on the horizon, we have been able to continuously probe farther and in more detail than the previous generation of scientists and telescopes allowed. Now, we are just entering the time when detection of planets outside of our own solar system has become possible, and we have found that planets are extraordinarily common in the galaxy (and by extrapolation, the universe). At the time of this document's composition, there are several thousand such examples of planets around other stars (being dubbed 'exoplanets'). We have discovered that planets are plentiful, but multiple open questions remain which are relevant to this work: How do planets form and, when a planet does form from its circumstellar envelope, what are the important processes that influence its formation? This work adds to the understanding of circumstellar disks, the intermediate stage between a cold collapsing cloud (of gas and dust) and a mature planetary system. Specifically, we study circumstellar disks in an evolved state termed 'transition disks'. This state corresponds to a time period where the dust in the disk has either undergone grain growth—where the microscopic grains have clumped together to form far fewer dust particles of much higher mass, or the inner portion (or an inner annulus) of the disk has lost a large amount of gas

  1. Carbon stars with oxygen-rich circumstellar material

    Science.gov (United States)

    Jura, Michael; Hawkins, I.

    1991-01-01

    The IUE satellite was used to search for companions to two carbon-rich stars with oxygen-rich circumstellar envelopes, EU And and V778 Cyg. Depending upon the amount of interstellar extinction and distances (probably between 1 and 2 kpc from the Sun) to these two stars, upper limits were placed between approx. 1.5 and 6 solar mass to the mass of any main sequence companions. For the 'near' distance of 1 kpc, it seems unlikely that there are white dwarf companions because the detection would be expected of ultraviolet emission from accretion of red giant wind material onto the white dwarf. A new model is proposed to explain the oxygen-rich envelopes. If these stars have a high nitrogen abundance, the carbon that is in excess of the oxygen may be carried in the circumstellar envelopes in HCN rather than C2H2 which is a likely key seed molecule for the formation of carbon grains. Consequently, carbon particles may not form; instead, oxygen-rich silicate dust may nucleate from the SiO present in the outflow.

  2. Archival Legacy Investigations of Circumstellar Environments: Overview and First Results

    CERN Document Server

    Choquet, Élodie; Hagan, J Brendan; Gofas-Salas, Elena; Rajan, Abhijith; Chen, Christine; Perrin, Marshall D; Debes, John; Golimowski, David; Hines, Dean C; N'Diaye, Mamadou; Schneider, Glenn; Mawet, Dimitri; Marois, Christian; Soummer, Rémi

    2014-01-01

    We are currently conducting a comprehensive and consistent re-processing of archival HST-NICMOS coronagraphic surveys using advanced PSF subtraction methods, entitled the Archival Legacy Investigations of Circumstellar Environments program (ALICE, HST/AR 12652). This virtual campaign of about 400 targets has already produced numerous new detections of previously unidentified point sources and circumstellar structures. We present five newly spatially resolved debris disks revealed in scattered light by our analysis of the archival data. These images provide new views of material around young solar-type stars at ages corresponding to the period of terrestrial planet formation in our solar system. We have also detected several new candidate substellar companions, for which there are ongoing followup campaigns (HST/WFC3 and VLT/SINFONI in ADI mode). Since the methods developed as part of ALICE are directly applicable to future missions (JWST, AFTA coronagraph) we emphasize the importance of devising optimal PSF s...

  3. Circumstellar debris and pollution at white dwarf stars

    Science.gov (United States)

    Farihi, J.

    2016-04-01

    Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

  4. Circumstellar Debris and Pollution at White Dwarf Stars

    CERN Document Server

    Farihi, J

    2016-01-01

    Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

  5. Low-Mass Star Formation: From Molecular Cloud Cores to Protostars and Protoplanetary Disks

    Science.gov (United States)

    Inutsuka, S.-I.; Machida, M.; Matsumoto, T.; Tsukamoto, Y.; Iwasaki, K.

    2016-05-01

    This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (˜103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.

  6. An interferometric view of hot star disks

    CERN Document Server

    Faes, Daniel Moser

    2015-01-01

    Optical long baseline interferometry was recently established as a technique capable of resolving stars and their circumstellar environments at the milliarcsecond (mas) resolution level. This high-resolution opens an entire new window to the study of astrophysical systems, providing information inaccessible by other techniques. Astrophysical disks are observed in a wide variety of systems, from galaxies up to planetary rings, commonly sharing similar physical processes. Two particular disk like systems are studied in the thesis: (i) B He-rich stars that exhibits magnetic fields in order of kG and that trap their winds in structures called magnetospheres; and (ii) Be stars, fast rotating stars that create circumstellar viscous disks. This study uses the interferometric technique to investigate both the photosphere proper and the circumstellar environment of these stars. The objective is to combine interferometry with other observational techniques (such as spectroscopy and polarimetry) to perform a complete an...

  7. Debris disks and the search for life in the universe

    CERN Document Server

    Cataldi, Gianni

    2016-01-01

    Circumstellar debris disks are the extrasolar analogues of the asteroid belt and the Kuiper belt. They consist of comets and leftover planetesimals that continuously collide and produce 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. This thesis presents observational studies of secondary gas in debris disks. It also discusses the astrobiological potential of debris disks created during impact events onto exoplanets.

  8. Detection of circumstellar gas associated with GG Tauri

    Science.gov (United States)

    Skrutskie, M. F.; Snell, R. L.; Strom, K. M.; Strom, S. E.; Edwards, S.; Fukui, Y.; Mizuno, A.; Hayashi, M.; Ohashi, N.

    1993-01-01

    Double-peaked (C-12)O (1-0) emission centered on the young T Tauri star GG Tau possesses a line profile which may be modeled on the assumption that CO emission arises in an extended circumstellar disk. While bounds on the observed gas mass can be estimated on this basis, it is suggested that a large amount of mass could lie within a small and optically thick region, escaping detection due to beam-dilution effects. In addition, CO may no longer accurately trace the gas mass due to its dissociation, or freezing into grains, or due to the locking-up of carbon into more complex molecules.

  9. Light-scattering models applied to circumstellar dust properties

    International Nuclear Information System (INIS)

    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

  10. Imaging the circumstellar environment of the young T Tauri star SU Aurigae

    CERN Document Server

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

    2013-01-01

    The circumstellar environments of classical T Tauri stars are challenging to directly image because of their high star-to-disk contrast ratio. One method to overcome this is by using imaging polarimetry where scattered and consequently polarised starlight from the star's circumstellar disk can be separated from the unpolarised light of the central star. We present images of the circumstellar environment of SU Aur, a classical T Tauri star at the transition of T Tauri to Herbig stars. The images directly show that the disk extends out to ~500 au with an inclination angle of $\\sim$ 50$^\\circ$. Using interpretive models, we derived very small grains in the surface layers of its disk, with a very steep size- and surface-density distribution. Additionally, we resolved a large and extended nebulosity in our images that is most likely a remnant of the prenatal molecular cloud. The position angle of the disk, determined directly from our images, rules out a polar outflow or jet as the cause of this large-scale nebulo...

  11. Wind Dynamics and Circumstellar Extinction Variations in the T Tauri Star RY Tau

    CERN Document Server

    Babina, Elena V; Petrov, Peter P

    2016-01-01

    The wind interaction with the dusty environment of the classical T Tauri star RY Tau has been investigated. During two seasons of 2013-2015 we carried out a spectroscopic and photometric (BVR) monitoring of the star. A correlation between the stellar brightness and the radial velocity of the wind determined from the H-alpha and Na D line profiles has been found for the first time. The irregular stellar brightness variations are shown to be caused by extinction in a dusty disk wind at a distance of about 0.2 AU from the star. We suppose, that variations of the circumstellar extinction results from cyclic rearrangements of the stellar magnetosphere and coronal mass ejections, which affect the dusty disk wind near the inner boundary of the circumstellar disk.

  12. Silica in Protoplanetary Disks

    CERN Document Server

    Sargent, B A; Tayrien, C; McClure, M K; Li, A; Basu, A R; Manoj, P; Watson, D M; Bohac, C J; Furlan, E; Kim, K H; Green, J D; Sloan, G C

    2008-01-01

    Mid-infrared spectra of a few T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope show prominent narrow emission features indicating silica (crystalline silicon dioxide). Silica is not a major constituent of the interstellar medium; therefore, any silica present in the circumstellar protoplanetary disks of TTS must be largely the result of processing of primitive dust material in the disks surrouding these stars. We model the silica emission features in our spectra using the opacities of various polymorphs of silica and their amorphous versions computed from earth-based laboratory measurements. This modeling indicates that the two polymorphs of silica, tridymite and cristobalite, which form at successively higher temperatures and low pressures, are the dominant forms of silica in the TTS of our sample. These high temperature, low pressure polymorphs of silica present in protoplanetary disks are consistent with a grain composed mostly of tridymite named Ada found...

  13. Disks around stars and the growth of planetary systems.

    Science.gov (United States)

    Greaves, Jane S

    2005-01-01

    Circumstellar disks play a vital evolutionary role, providing a way to move gas inward and onto a young star. The outward transfer of angular momentum allows the star to contract without breaking up, and the remnant disk of gas and particles is the reservoir for forming planets. High-resolution spectroscopy is uncovering planetary dynamics and motion within the remnant disk, and imaging at infrared to millimeter wavelengths resolves disk structure over billions of years of evolution. Most stars are born with a disk, and models of planet formation need to form such bodies from the disk material within the disk's 10-million-year life-span. PMID:15637266

  14. Circumstellar Nebulae in Young Supernova Remnants

    OpenAIRE

    Chu, Y.-H.

    2000-01-01

    Supernovae descendent from massive stars explode in media that have been modified by their progenitors' mass loss and UV radiation. The supernova ejecta will first interact with the circumstellar material shed by the progenitors at late evolutionary stages, and then interact with the interstellar material. Circumstellar nebulae in supernova remnants can be diagnosed by their small expansion velocities and high [N II]/H$\\alpha$ ratios. The presence of circumstellar nebulae appears ubiquitous a...

  15. Herniated disk

    Science.gov (United States)

    ... the disk. This may place pressure on nearby nerves or the spinal cord. ... Lumbar radiculopathy; Cervical radiculopathy; Herniated intervertebral disk; Prolapsed intervertebral disk; Slipped disk; Ruptured disk; Herniated nucleus pulposus

  16. Protostellar Disk Formation Enabled by Removal of Small Dust Grains

    CERN Document Server

    Zhao, Bo; Li, Zhi-Yun; Krasnopolsky, Ruben; Shang, Hsien; Nakamura, Fumitaka

    2016-01-01

    It has been shown that a realistic level of magnetization of dense molecular cloud cores can suppress the formation of a rotationally supported disk (RSD) through catastrophic magnetic braking in the axisymmetric ideal MHD limit. In this study, we present conditions for the formation of RSDs through non-ideal MHD effects computed self-consistently from an equilibrium chemical network. We find that removing from the standard MRN distribution the large population of very small grains (VSGs) of ~10 $\\AA$ to few 100 $\\AA$ that dominate the coupling of the bulk neutral matter to the magnetic field increases the ambipolar diffusivity by ~1--2 orders of magnitude at densities below 10$^{10}$ cm$^{-3}$. The enhanced ambipolar diffusion (AD) in the envelope reduces the amount of magnetic flux dragged by the collapse into the circumstellar disk-forming region. Therefore, magnetic braking is weakened and more angular momentum can be retained. With continuous high angular momentum inflow, RSDs of tens of AU are able to f...

  17. Biomimetic Envelopes

    Directory of Open Access Journals (Sweden)

    Ilaria Mazzoleni

    2010-06-01

    Full Text Available How to translate the lessons learned from the analysis and observation of the animal world is the design learning experience presented in this article. Skin is a complex and incredibly sophisticated organ that performs various functions, including protection, sensation and heat and water regulation. In a similar way building envelopes serve multiple roles, as they are the interface between the building inhabitants and environmental elements. The resulting architectural building envelopes proto-architectural research and design projects here presented, inspired by the study of animal skins, perform and respond; they take into consideration various dynamic local environmental conditions, enhancing and supporting them rather than exploiting them, creating a more sustainable way of building and living.

  18. Enveloping algebras

    International Nuclear Information System (INIS)

    Since the works of Gelfand, Harish-Chandra, Kostant and Duflo, a new theory has earned its place in the field of mathematics, due to the abundance of its results and the coherence of its methods: the theory of enveloping algebras. This study is the first to present the whole subject in textbook form. The most recent results are included, as well as complete proofs, starting from the elementary theory of Lie algebras. (Auth.)

  19. INTERNAL ENVELOPES

    CERN Multimedia

    Mail Office

    2001-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unused stock could deposit them in their mail box, after attaching them together with an elastic band or piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration.

  20. ROTATIONAL LINE EMISSION FROM WATER IN PROTOPLANETARY DISKS

    NARCIS (Netherlands)

    Meijerink, R.; Poelman, D. R.; Spaans, M.; Tielens, A. G. G. M.; Glassgold, A. E.

    2008-01-01

    Circumstellar disks provide the material reservoir for the growth of young stars and for planet formation. We combine a high-level radiative transfer program with a thermal-chemical model of a typical T Tauri star disk to investigate the diagnostic potential of the far-infrared lines of water for pr

  1. Polarimetry with the Gemini Planet Imager: Methods, Performance at First Light, and the Circumstellar Ring around HR 4796A

    CERN Document Server

    Perrin, Marshall D; Millar-Blanchaer, Max; Fitzgerald, Michael P; Graham, James R; Wiktorowicz, Sloane J; Kalas, Paul G; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; Chilcote, Jeffrey; De Rosa, Robert J; Dillon, Daren; Doyon, René; Dunn, Jennifer; Gavel, Donald; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale; Ingraham, Patrick; Kerley, Daniel; Konapacky, Quinn; Larkin, James E; Maire, Jérôme; Marchis, Franck; Marois, Christian; Mittal, Tushar; Morzinski, Katie M; Oppenheimer, B R; Palmer, David W; Patience, Jennifer; Poyneer, Lisa; Pueyo, Laurent; Rantakyrö, Fredrik T; Sadakuni, Naru; Saddlemyer, Leslie; Savransky, Dmitry; Soummer, Rémi; Sivaramakrishnan, Anand; Song, Inseok; Thomas, Sandrine; Wallace, J Kent; Wang, Jason J; Wolff, Schuyler G

    2014-01-01

    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 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. Ba...

  2. Studies of Gas Disks in Binary Systems

    OpenAIRE

    de Val Borro, Miguel

    2008-01-01

    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 ...

  3. A Circumstellar Disk Observed around a Massive Star

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    @@ Although the formation process of low-mass stars like our Sun has been well understood, the birth of high-mass stars with more than eight solar masses still remains a mystery. A recent study by CAS astronomers and their collaborators from Japan and UK offered direct observational evidence for demystifying the puzzle. The work was published in the Sept. 1 issue of Nature.

  4. CIRCUMSTELLAR AND CIRCUMBINARY DISKS IN ECCENTRIC STELLAR BINARIES

    Directory of Open Access Journals (Sweden)

    L. A. Aguilar

    2008-01-01

    Full Text Available Investigamos la existencia de trayectorias estables, donde el gas puede acumularse y formar discos de acreción, alrededor de estrellas que forman parte de sistemas binarios de órbitas excéntricas. Dado que el potencial depende del tiempo, no existen órbitas fijas, cerradas y periódicas. En su lugar, buscamos lazos invariantes: curvas cerradas cuya forma varía en sincronía con la fase orbital del sistema binario. Los lazos invariantes que no se auto-intersectan, pueden formar el armazón sobre el que se puede tener discos circunestelares y circumbinarios en estos sistemas. Estudiamos la extensión de las regiones en espacio fase donde estos lazos invariantes sin intersección existen y encontramos que ésta depende de la razón de masa de las estrellas y la excentricidad orbital, con una fuerte dependencia del segundo factor. El descubrimiento reciente de planetas en sistemas binarios de separación pequeña hace que el presente trabajo tenga una gran relevancia.

  5. WISE Circumstellar Disks in the Young Sco-Cen Association

    CERN Document Server

    Rizzuto, Aaron C; Zucker, Daniel B

    2011-01-01

    We present an analysis of the WISE photometric data for 829 stars in the Sco-Cen OB2 association, using the latest high-mass membership probabilities. We detect infrared excesses associated with 135 BAF-type stars, 99 of which are secure Sco-Cen members. There is a clear increase in excess fraction with membership probability, which can be fitted linearly. We infer that 41+-5% of Sco-Cen OB2 BAF stars to have excesses, while the field star excess fraction is consistent with zero. This is the first time that the probability of non-membership has been used in the calculation of excess fractions for young stars. We do not observe any significant change in excess fraction between the three subgroups. Within our sample, we have observed that B-type association members have a significantly smaller excess fraction than A and F-type association members.

  6. Circumstellar molecular composition of the oxygen-rich AGB star IK Tau: I. Observations and LTE chemical abundance analysis

    CERN Document Server

    Kim, Hyunjoo; Menten, Karl M; Decin, Leen

    2010-01-01

    The aim of this paper is to study the molecular composition in the circumstellar envelope around the oxygen-rich star IK Tau. We observed IK Tau in several (sub)millimeter bands using the APEX telescope during three observing periods. To determine the spatial distribution of the $\\mathrm{^{12}CO(3-2)}$ emission, mapping observations were performed. To constrain the physical conditions in the circumstellar envelope, multiple rotational CO emission lines were modeled using a non local thermodynamic equilibrium radiative transfer code. The rotational temperatures and the abundances of the other molecules were obtained assuming local thermodynamic equilibrium. An oxygen-rich Asymptotic Giant Branch star has been surveyed in the submillimeter wavelength range. Thirty four transitions of twelve molecular species, including maser lines, were detected. The kinetic temperature of the envelope was determined and the molecular abundance fractions of the molecules were estimated. The deduced molecular abundances were com...

  7. THE PROGENITOR OF SN 2011ja: CLUES FROM CIRCUMSTELLAR INTERACTION

    International Nuclear Information System (INIS)

    Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II plateau (IIP) supernovae. The ejecta from these explosions shocks the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray parts of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work, we use X-rays observations from the Chandra and radio observations from the Australia Telescope Compact Array to study the relative importance of processes which accelerate particles and those which amplify magnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the explosion date. Multiple Chandra observations allow us to probe the history of variable mass loss from the progenitor. The ejecta expands into a low-density bubble followed by interaction with a higher density wind from a red supergiant consistent with MZAMS ∼> 12 M☉. Our results suggest that a fraction of Type IIP supernovae may interact with circumstellar media set up by non-steady winds

  8. The interaction of supernovae and pulsars with circumstellar environment

    International Nuclear Information System (INIS)

    In Chapter One, self-similar solutions for the time-dependent behavior of a shocked, spherically, symmetric, relativistic fluid with tangential magnetic field in the case where the boundaries of the shocked fluid move at a constant velocity are found. These solutions can be applied to the evolution of the shocked-relativistic pulsar winds which are probably observed as Crab-like supernova remnants. Since the models include time evolution, they can be applied to young objects and may be relevant to a possible pulsar nebular in SN1987a. In Chapter Two, the development of models for the infrared echo from Type II supernovae arising from the heating of circumstellar dust is discussed. In these models, ellipsoidial dust distributions are considered (previous models considered only spherically symmetric dust distributions) since some red supergiants, the likely progenitors of most Type II supernovae, are known to have asymmetric circumstellar envelopes. The models show that an asymmetric dust distribution can have a substantial effect on the time evolution of the echo. In Chapter Three, the properties to be expected of the infrared and scattered light echoes from SN1987A are derived. These echoes are expected to arise from the dust formed within the wind given off by the progenitor during a previous red supergiant phase. The models take into account the emission and scattering properties of the dust grains, in particular silicate dust grains, and the observed supernova light curve. The predictions of the models are compared with the available observations

  9. DiskJockey: Protoplanetary disk modeling for dynamical mass derivation

    Science.gov (United States)

    Czekala, Ian

    2016-03-01

    DiskJockey derives dynamical masses for T Tauri stars using the Keplerian motion of their circumstellar disks, applied to radio interferometric data from the Atacama Large Millimeter Array (ALMA) and the Submillimeter Array (SMA). The package relies on RADMC-3D (ascl:1202.015) to perform the radiative transfer of the disk model. DiskJockey is designed to work in a parallel environment where the calculations for each frequency channel can be distributed to independent processors. Due to the computationally expensive nature of the radiative synthesis, fitting sizable datasets (e.g., SMA and ALMA) will require a substantial amount of CPU cores to explore a posterior distribution in a reasonable timeframe.

  10. The progenitor of SN 2011ja: Clues from circumstellar interaction

    CERN Document Server

    Chakraborti, Sayan; Smith, Randall; Ryder, Stuart; Yadav, Naveen; Sutaria, Firoza; Dwarkadas, Vikram V; Chandra, Poonam; Pooley, David; Roy, Rupak

    2013-01-01

    Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until the time of core collapse produce Type IIP (Plateau) supernovae. The ejecta from these explosions shock the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray part of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work we use X-rays observations from the Chandra and radio observations from the ATCA to study the relative importance of particle acceleration and magnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the ...

  11. Polytype distribution in circumstellar silicon carbide.

    Science.gov (United States)

    Daulton, T L; Bernatowicz, T J; Lewis, R S; Messenger, S; Stadermann, F J; Amari, S

    2002-06-01

    The inferred crystallographic class of circumstellar silicon carbide based on astronomical infrared spectra is controversial. We have directly determined the polytype distribution of circumstellar SiC from transmission electron microscopy of presolar silicon carbide from the Murchison carbonaceous meteorite. Only two polytypes (of a possible several hundred) were observed: cubic 3C and hexagonal 2H silicon carbide and their intergrowths. We conclude that this structural simplicity is a direct consequence of the low pressures in circumstellar outflows and the corresponding low silicon carbide condensation temperatures. PMID:12052956

  12. Infrared Variability of Protoplanetary Disks: Signs of Complex Disk Structure

    Science.gov (United States)

    Flaherty, Kevin M.; Muzerolle, J.; Rieke, G.; Gutermuth, R.; Balog, Z.; Herbst, W.; Megeath, S.; Kun, M.

    2012-01-01

    Circumstellar disks around newly formed stars are the sites of planet formation, and their structure can have a large influence on the formation and early evolution of planets. We have obtained multi-wavelength multi-epoch infrared observations of the IC348 cluster, focusing on six transition disks, to look for rapid changes in the structure of these systems. These measurements include optical, near-infrared and mid-infrared spectra, along with intensive mid-infrared photometry covering timescales of days to years. We find that 70% of the stars with disks are variable, with infrared fluctuations up to a few tenths of a magnitude on timescales of days to weeks. The transition disks, characterized by an SED that indicates clearing of the inner disk, display a 'seesaw' behavior in which the short-wavelength (8μm) flux vary in opposite directions by as much as 60% in as little as one week. Our observations show that this can be explained by varying the scale height of the inner disk. We can rule out accretion and disk winds, leaving an embedded planet or a dynamic magnetic field as the likely physical source of the disk perturbation.

  13. Shadows Cast by a Warp in the HD 142527 Protoplanetary Disk

    Science.gov (United States)

    Marino, S.; Perez, S.; Casassus, S.

    2015-01-01

    Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in the H band, so that the shape and orientation of the shadows inform on the three-dimensional structure of the system. Radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70° ± 5°. This finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions.

  14. SHADOWS CAST BY A WARP IN THE HD 142527 PROTOPLANETARY DISK

    Energy Technology Data Exchange (ETDEWEB)

    Marino, S.; Perez, S.; Casassus, S., E-mail: smarino@das.uchile.cl [Departamento de Astronomía, Universidad de Chile, Casilla 36-D Santiago (Chile)

    2015-01-10

    Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in the H band, so that the shape and orientation of the shadows inform on the three-dimensional structure of the system. Radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70° ± 5°. This finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions.

  15. SHADOWS CAST BY A WARP IN THE HD 142527 PROTOPLANETARY DISK

    International Nuclear Information System (INIS)

    Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in the H band, so that the shape and orientation of the shadows inform on the three-dimensional structure of the system. Radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70° ± 5°. This finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions

  16. Shadows cast by a warp in the HD 142527 protoplanetary disk

    CERN Document Server

    Marino, Sebastian; Casassus, Simon

    2014-01-01

    Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in H-band, so that the shape and orientation of the shadows inform on the three-dimmensional structure of the system. Radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70+-5 deg. This finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions.

  17. Circumstellar Molecular Spectra towards Evolved Stars

    CERN Document Server

    Bakker, E J

    1997-01-01

    In this paper we discuss the relevance of, and possible scientific gains which can be acquired from studying circumstellar molecular spectra toward evolved stars. Where can we expect circumstellar molecular spectra, why would we want to study these spectra, which molecules might be present, and what can we learn from these studies? We present an overview of reported detections, and discuss some of the results.

  18. 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

  19. Molecular gas in young debris disks

    CERN Document Server

    Moór, A; Juhász, A; Kiss, Cs; Pascucci, I; Kóspál, Á; Apai, D; Henning, Th; Csengeri, T; Grady, C

    2011-01-01

    Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas, and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J=3-2 survey with Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities...

  20. Herschel Observations of Dusty Debris Disks

    CERN Document Server

    Vican, Laura; Bryden, Geoff; Melis, Carl; Zuckerman, B; Rhee, Joseph; Song, Inseok

    2016-01-01

    We present results from two Herschel observing programs using the Photodetector Array Camera and Spectrometer. During three separate campaigns, we obtained Herschel data for 24 stars at 70, 100, and 160 microns. We chose stars that were already known or suspected to have circumstellar dust based on excess infrared emission previously measured with IRAS or Spitzer, and used Herschel to examine long-wavelength properties of the dust. Fifteen stars were found to be uncontaminated by background sources, and possess infrared emission most likely due to a circumstellar debris disk. We analyzed the properties of these debris disks to better understand the physical mechanisms responsible for dust production and removal. Seven targets were spatially resolved in the Herschel images. Based on fits to their spectral energy distributions, nine disks appear to have two temperature components. Of these nine, in three cases, the warmer dust component is likely the result of a transient process rather than a steady state coll...

  1. Non-isothermal effects on Be disks

    CERN Document Server

    Vieira, Rodrigo G; Bjorkman, Jon E

    2016-01-01

    In the last decade, the viscous decretion disk model has emerged as the new paradigm for Be star disks. In this contribution, we propose a simple analytical model to estimate the continuum infrared excess arising from these circumstellar disks, in the light of the currently accepted scenario. We demonstrate that the disk can be satisfactorily described by a two component system: an inner optically thick region, which we call the pseudo-photosphere, and a diffuse outer part. In particular, a direct connexion between the disk brightness profile and the thermal structure is derived, and then confronted to realistic numerical simulations. This result quantifies how the non-isothermality of the disk ultimately affects both infrared measured fluxes and visibilities.

  2. Dust amorphization in protoplanetary disks

    CERN Document Server

    Glauser, Adrian M; Watson, Dan M; Henning, Thomas; Schegerer, Alexander A; Wolf, Sebastian; Audard, Marc; Baldovin-Saavedra, Carla

    2009-01-01

    High-energy irradiation of the circumstellar material might impact the structure and the composition of a protoplanetary disk and hence the process of planet formation. In this paper, we present a study on the possible influence of the stellar irradiation, indicated by X-ray emission, on the crystalline structure of the circumstellar dust. The dust crystallinity is measured for 42 class II T Tauri stars in the Taurus star-forming region using a decomposition fit of the 10 micron silicate feature, measured with the Spitzer IRS instrument. Since the sample includes objects with disks of various evolutionary stages, we further confine the target selection, using the age of the objects as a selection parameter. We correlate the X-ray luminosity and the X-ray hardness of the central object with the crystalline mass fraction of the circumstellar dust and find a significant anti-correlation for 20 objects within an age range of approx. 1 to 4.5 Myr. We postulate that X-rays represent the stellar activity and consequ...

  3. Modeling water emission from low-mass protostellar envelopes

    OpenAIRE

    van Kempen, T. A.; Doty, S. D.; van Dishoeck, E. F.; Hogerheijde, M.R.; Joergensen, J. K.

    2008-01-01

    Within low-mass star formation, water vapor plays a key role in the chemistry and energy balance of the circumstellar material. The Herschel Space Observatory will open up the possibility to observe water lines originating from a wide range of excitation energies.Our aim is to simulate the emission of rotational water lines from envelopes characteristic of embedded low-mass protostars. A large number of parameters that influence the water line emission are explored: luminosity, density,densit...

  4. Molecular Gas in Young Debris Disks

    Science.gov (United States)

    Moor, A.; Abraham, P.; Juhasz, A.; Kiss, Cs.; Pascucci, I.; Kospal, A.; Apai, D.; Henning, T.; Csengeri, T.; Grady, C.

    2011-01-01

    Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J = 3-2 survey with the Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities of HD21997 and 49 Ceti are not particularly high, these objects seem to harbor the most extended disks within our sample. The double-peaked profiles of HD21997 were reproduced by a Keplerian disk model combined with the LIME radiative transfer code. Based on their similarities, 49 Ceti and HD21997 may be the first representatives of a so far undefined new class of relatively old > or approx.8 Myr), gaseous dust disks. From our results, neither primordia1 origin nor steady secondary production from icy planetesima1s can unequivocally explain the presence of CO gas in the disk ofHD21997.

  5. MOLECULAR GAS IN YOUNG DEBRIS DISKS

    International Nuclear Information System (INIS)

    Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J = 3-2 survey with the Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities of HD21997 and 49 Ceti are not particularly high, these objects seem to harbor the most extended disks within our sample. The double-peaked profiles of HD21997 were reproduced by a Keplerian disk model combined with the LIME radiative transfer code. Based on their similarities, 49 Ceti and HD21997 may be the first representatives of a so far undefined new class of relatively old (∼>8 Myr), gaseous dust disks. From our results, neither primordial origin nor steady secondary production from icy planetesimals can unequivocally explain the presence of CO gas in the disk of HD21997.

  6. Stellar Multiplicity and Debris Disks: An Unbiased Sample

    CERN Document Server

    Rodriguez, David R; Tom, Henry; Kennedy, Grant; Matthews, Brenda; Greaves, Jane; Butner, Harold

    2015-01-01

    Circumstellar dust disks have been observed around many nearby stars. However, many stars are part of binary or multiple stellar systems. A natural question arises regarding the presence and properties of such disks in systems with more than one star. To address this, we consider a sample of 449 systems (spectral types A-M) observed with the Herschel Space Observatory as part of the DEBRIS program. We have examined the stellar multiplicity of this sample by gathering information from the literature and performing an adaptive optics imaging survey at Lick Observatory. Five new companions were revealed with our program. In total, we identify 188 (42%) binary or multiple star systems. The multiplicity of the sample is examined with regards to the detection of circumstellar disks for stars of spectral types AFGK. In general, disks are less commonly detected around binaries than single stars, though the disk frequency is comparable among A stars regardless of multiplicity. However, this sample reveals the period d...

  7. Observations of Protostellar Disks

    Science.gov (United States)

    Ménard, F.

    2004-12-01

    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 the mystery of the formation of our Solar System. This chapter focuses on observational studies 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 typical star forming regions (e.g., ˜140pc for Taurus), a planetary system like ours (with diameter ≃ 50AU out to Pluto, but excluding the Kuiper belt) 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 I will attempt to give an overview of the structural and physical parameters of protoplanetary disks that can be estimated today from direct observations.

  8. Evolution of Disk Accretion

    OpenAIRE

    Calvet, Nuria; Hartmann, Lee; Strom, Stephen E.

    1999-01-01

    We review the present knowledge of disk accretion in young low mass stars, and in particular, the mass accretion rate and its evolution with time. The methods used to obtain mass accretion rates from ultraviolet excesses and emission lines are described, and the current best estimates of mass accretion rate for Classical T Tauri stars and for objects still surrounded by infalling envelopes are given. We argue that the low mass accretion rates of the latter objects require episodes of high mas...

  9. Properties of the H-alpha-emitting Circumstellar Regions of Be Stars

    CERN Document Server

    Tycner, C; Hajian, A R; Armstrong, J T; Benson, J A; Gilbreath, G C; Hutter, D J; Pauls, T A; White, N M; Tycner, Christopher; Lester, John B.; Hajian, Arsen R.

    2005-01-01

    Long-baseline interferometric observations obtained with the Navy Prototype Optical Interferometer of the H-alpha-emitting envelopes of the Be stars eta Tauri and beta Canis Minoris are presented. For compatibility with the previously published interferometric results in the literature of other Be stars, circularly symmetric and elliptical Gaussian models were fitted to the calibrated H-alpha observations. The models are sufficient in characterizing the angular distribution of the H-alpha-emitting circumstellar material associated with these Be stars. To study the correlations between the various model parameters and the stellar properties, the model parameters for eta Tau and beta CMi were combined with data for other Be stars from the literature. After accounting for the different distances to the sources and stellar continuum flux levels, it was possible to study the relationship between the net H-alpha emission and the physical extent of the H-alpha-emitting circumstellar region. A clear dependence of the...

  10. Circumstellar CO in OH/IR stars close to the Galactic Centre

    International Nuclear Information System (INIS)

    A pilot project is carried out to measure circumstellar CO emission from three OH/IR, stars close to the GC using the Nobeyama Millimeter Array at 115 GHz and the Sub-Millimeter Array at 230 GHz. An interferometer is necessary as a 'spatial filter' in this region of space because of the confusion with interstellar CO emission. The intention is to find out whether it is possible to later conduct a large-scale survey for mass-loss rates using, for example, ALMA. Thus an important parameter would be added to our understanding of the evolution of the Galactic Bulge. Sources have been detected towards two of the stars with 'correct' positions and radial velocities. However, for one of the stars the line profile is not what one expects for expanding circumstellar envelopes. This surprising result is discussed and our plans for future observations are presented

  11. Millimeter continuum measurements of circumstellar dust around very young low-mass stars

    Science.gov (United States)

    Terebey, S.; Chandler, C. J.; Andre, P.

    1994-01-01

    We investigate the question of disk formation during the protostar phase. We build on the results of Keene and Masson (1990) whose analysis of L1551 showed the millimeter continuum emission comes from both an unresolved circumstellar component, i.e., a disk and an extended cloud core. We model the dust continuum emission from the cloud core and show how it is important at 1.3 mm but negligible at 2.7 mm. Combining new 2.7 mm Owens Valley Interferometer data of IRAS-Dense cores with data from the literature we conclude that massive disks are also seen toward a number of other sources. However, 1.3 mm data from the IRAM 30 m telescope for a larger sample shows that massive disks are relatively rare, occurring around perhaps 5% of young embedded stars. This implies that either massive disks occur briefly during the embedded phase or that relatively few young stars form massive disks. At 1.3 mm the median flux of IRAS-Dense cores is nearly the same as T Tauri stars in the sample of Beckwith et al. (1990). We conclude that the typical disk mass during the embedded phase is nearly the same or less than the typical disk mass during the T Tauri phase.

  12. Detailed modelling of the circumstellar molecular line emission of the S-type AGB star W Aquilae

    CERN Document Server

    Danilovich, T; Justtanont, K; Lombaert, R; Maercker, M; Olofsson, H; Ramstedt, S; Royer, P

    2014-01-01

    S-type AGB stars have a C/O ratio which suggests that they are transition objects between oxygen-rich M-type stars and carbon-rich C-type stars. As such, their circumstellar compositions of gas and dust are thought to be sensitive to their precise C/O ratio, and it is therefore of particular interest to examine their circumstellar properties. We present new Herschel HIFI and PACS sub-millimetre and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances. We used radiative transfer codes to model the circumstellar dust and molecular line emission to determine circumstellar properties and molecular abundances. We assumed a spherically symmetric envelope formed by a constant mass-loss rate driven by an accelerating wind. Our model includes fully integrated H2O line cooling as part of the solution of th...

  13. 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

  14. Identification of transitional disks in Chamaeleon with Herschel

    CERN Document Server

    Ribas, Á; Bouy, H; de Oliveira, C Alves; Ardila, D R; Puga, E; Kóspál, Á; Spezzi, L; Cox, N L J; Prusti, T; Pilbratt, G L; André, Ph; Matrà, L; Vavrek, R

    2013-01-01

    Transitional disks are circumstellar disks with inner holes that in some cases are produced by planets and/or substellar companions in these systems. For this reason, these disks are extremely important for the study of planetary system formation. The Herschel Space Observatory provides an unique opportunity for studying the outer regions of protoplanetary disks. In this work we update previous knowledge on the transitional disks in the Chamaeleon I and II regions with data from the Herschel Gould Belt Survey. We propose a new method for transitional disk classification based on the WISE 12 micron-PACS 70 micron color, together with inspection of the Herschel images. We applied this method to the population of Class II sources in the Chamaeleon region and studied the spectral energy distributions of the transitional disks in the sample. We also built the median spectral energy distribution of Class II objects in these regions for comparison with transitional disks. The proposed method allows a clear separatio...

  15. THE EVOLUTION OF PROTOPLANETARY DISKS IN THE ARCHES CLUSTER

    International Nuclear Information System (INIS)

    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.

  16. A Short Guide to Debris Disk Spectroscopy

    OpenAIRE

    Chen, Christine H.

    2009-01-01

    Multi-wavelength spectroscopy can be used to constrain the dust and gas properties in debris disks. Circumstellar dust absorbs and scatters incident stellar light. The scattered light is sometimes resolved spatially at visual and near-infrared wavelengths using high contrast imaging techniques that suppress light from the central star. The thermal emission is inferred from infrared through submillimeter excess emission that may be 1-2 orders of magnitude brighter than the stellar photosphere ...

  17. An interferometric view of hot star disks

    Science.gov (United States)

    Faes, Daniel Moser

    2015-08-01

    Optical long baseline interferometry was recently established as a technique capable of resolving stars and their circumstellar environments at the milliarcsecond (mas) resolution level. This high-resolution opens an entire new window to the study of astrophysical systems, providing information inaccessible by other techniques. Astrophysical disks are observed in a wide variety of systems, from galaxies up to planetary rings, commonly sharing similar physical processes. Two particular disk like systems are studied in the thesis: (i) B He-rich stars that exhibits magnetic fields in order of kG and that trap their winds in structures called magnetospheres; and (ii) Be stars, fast rotating stars that create circumstellar viscous disks. This study uses the interferometric technique to investigate both the photosphere proper and the circumstellar environment of these stars. The objective is to combine interferometry with other observational techniques (such as spectroscopy and polarimetry) to perform a complete and well-constrained physical description of these systems. This description is accompanied by radiative transfer models performed by the HDUST code.

  18. HIFISTARS Herschel/HIFI observations of VY Canis Majoris. Molecular-line inventory of the envelope around the largest known star

    OpenAIRE

    Alcolea, J.; Bujarrabal, V.; Planesas, P.; Teyssier, D.; Cernicharo, J; De Beck, E.; Decin, L.; Dominik, C.; Justtanont, K.; Koter, de, A.; Marston, A.P.; Melnick, G.; Menten, K. M.; Neufeld, D A; Olofsson, H

    2013-01-01

    Aims. The study of the molecular gas in the circumstellar envelopes of evolved stars is normally undertaken by observing lines of CO (and other species) in the millimetre-wave domain. In general, the excitation requirements of the observed lines are low at these wavelengths, and therefore these observations predominantly probe the cold outer envelope while studying the warm inner regions of the envelopes normally requires sub-millimetre (sub-mm) and far-infrared (FIR) observational data. ...

  19. Spectroscopic Evolution of Disintegrating Planetesimals: Minutes to Months Variability in the Circumstellar Gas Associated with WD 1145+017

    CERN Document Server

    Redfield, Seth; Cauley, P Wilson; Parsons, Steven G; Gaensicke, Boris T; Duvvuri, Girish

    2016-01-01

    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 ten different elements associated with planetary composition, e.g., O, Mg, Ca, Ti, Cr, Mn, Fe, Ni. Broad circumstellar gas absorption with a velocity spread of 225 km/s is detected, but over the course of a year blue shifted 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 tau approximately 2). We discuss simple models of an eccentric disk couple...

  20. The formation of polycyclic aromatic hydrocarbons in evolved circumstellar environments

    CERN Document Server

    Cherchneff, Isabelle

    2010-01-01

    The formation of Polycyclic Aromatic Hydrocarbons in the circumstellar outflows of evolved stars is reviewed, with an emphasis on carbon stars on the Asymptotic Giant Branch. Evidence for PAHs present in their winds is provided by meteoritic studies and recent observations of the Unidentified Infrared bands. We detail the chemical processes leading to the closure of the first aromatic ring as well as the growth mechanisms leading to amorphous carbon grains. Existing studies on PAH formation in evolved stellar envelopes are reviewed and new results for the modelling of the inner wind of the archetype carbon star IRC+10216 are presented. Benzene, C6H6, forms close to the star, as well as water, H2O, as a result of non-equilibrium chemistry induced by the periodic passage of shocks. The growth process of aromatic rings may thus resemble that active in sooting flames due to the presence of radicals like hydroxyl, OH. Finally, we discuss possible formation processes for PAHs and aromatic compounds in the hydrogen-...

  1. The circumstellar environment of pre-SN Ia systems

    CERN Document Server

    Harvey, E; Boumis, P; Kopsacheili, M; Akras, S; Sabin, L; Jurkic, T

    2016-01-01

    Here we explore the possible preexisting circumstellar debris of supernova type Ia systems. Classical, symbiotic and recurrent novae all accrete onto roughly solar mass white dwarfs from main sequence or Mira type companions and result in thermonuclear runaways and expulsion of the accreted material at high velocity. The expelled material forms a fast moving shell that eventually slows to planetary nebula expansion velocities within several hundred years. All such systems are recurrent and thousands of shells (each of about 0.001 Mo) snow plough into the environment. As these systems involve common envelope binaries the material is distributed in a non-spherical shell. These systems could be progenitors of some SN Ia and thus explode into environments with large amounts of accumulated gas and dust distributed in thin non-spherical shells. Such shells should be observable around 100 years after a SN Ia event in a radio flash as the SN Ia debris meets that of the ejected material of the systems previous incarna...

  2. Spectral Energy Distributions of Young Stars in IC 348: The Role of Disks in Angular Momentum Evolution of Young, Low-Mass Stars

    OpenAIRE

    Blanc, Thompson S. Le; Covey, Kevin R.; Stassun, Keivan G.

    2011-01-01

    Theoretical work suggests that a young star's angular momentum and rotation rate may be strongly influenced by magnetic interactions with its circumstellar disk. A generic prediction of these 'disk-locking' (DL) theories is that a disk-locked star will be forced to co-rotate with the Keplerian angular velocity of the inner edge of the disk. These theories have also been interpreted to suggest a correlation between young stars' rotation periods and the structural properties of their disks, suc...

  3. Stability of Magnetized Disks and Implications for Planet Formation

    CERN Document Server

    Lizano, Susana; Cai, Mike J; Adams, Fred C

    2010-01-01

    This paper considers gravitational perturbations in geometrically thin disks with rotation curves dominated by a central object, but with substantial contributions from magnetic pressure and tension. The treatment is general, but the application is to the circumstellar disks that arise during the gravitational collapse phase of star formation. We find the dispersion relation for spiral density waves in these generalized disks and derive the stability criterion for axisymmetric $(m=0)$ disturbances (the analog of the Toomre parameter $Q_T$) for any radial distribution of the mass-to-flux ratio $\\lambda$. The magnetic effects work in two opposing directions: on one hand, magnetic tension and pressure stabilize the disk against gravitational collapse and fragmentation; on the other hand, they also lower the rotation rate making the disk more unstable. For disks around young stars the first effect generally dominates, so that magnetic fields allow disks to be stable for higher surface densities and larger total m...

  4. Dipper disks not inclined towards edge-on orbits

    CERN Document Server

    Ansdell, M; Williams, J P; Kennedy, G; Wyatt, M C; LaCourse, D M; Jacobs, T L; Mann, A W

    2016-01-01

    The so-called "dipper" stars host circumstellar disks and have optical and infrared light curves that exhibit quasi-periodic or aperiodic dimming events consistent with extinction by transiting dusty structures orbiting in the inner disk. Most of the proposed mechanisms explaining the dips---i.e., occulting disk warps, vortices, and forming planetesimals---assume nearly edge-on viewing geometries. However, our analysis of the three known dippers with publicly available resolved sub-mm data reveals disks with a range of inclinations, most notably the face-on transition disk J1604-2130 (EPIC 204638512). This suggests that nearly edge-on viewing geometries are not a defining characteristic of the dippers and that additional models should be explored. If confirmed by further observations of more dippers, this would point to inner disk processes that regularly produce dusty structures far above the outer disk midplane in regions relevant to planet formation.

  5. Insights into planet formation from debris disks: I. The solar system as an archetype for planetesimal evolution

    OpenAIRE

    Matthews, Brenda C.; Kavelaars, JJ

    2016-01-01

    Circumstellar disks have long been regarded as windows into planetary systems. The advent of high sensitivity, high resolution imaging in the submillimetre where both the solid and gas components of disks can be detected opens up new possibilities for understanding the dynamical histories of these systems and therefore, a better ability to place our own solar system, which hosts a highly evolved debris disk, in context. Comparisons of dust masses from protoplanetary and debris disks have reve...

  6. Observations of Solids in Protoplanetary Disks

    CERN Document Server

    Andrews, Sean M

    2015-01-01

    This review addresses the state of research that employs astronomical (remote sensing) observations of solids ("dust") in young circumstellar disks to learn about planet formation. The intention is for it to serve as an accessible, introductory, pedagogical resource for junior scientists interested in the subject. After some historical background and a basic observational primer, the focus is shifted to the three fundamental topics that broadly define the field: (1) demographics -- the relationships between disk properties and the characteristics of their environments and hosts; (2) structure -- the spatial distribution of disk material and its associated physical conditions and composition; and (3) evolution -- the signposts of key changes in disk properties, including the growth and migration of solids and the impact of dynamical interactions with young planetary systems. Based on the state of the art results in these areas, suggestions are made for potentially fruitful lines of work in the near future.

  7. Ionization and Dust Charging in Protoplanetary Disks

    CERN Document Server

    Ivlev, A V; Caselli, P

    2016-01-01

    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 the development of magnetorotational instability in protoplanetary disks. We present a self-consistent analytical model which allows us to exactly calculate abundances of charged species in dusty gas, in the regime where the dust-phase recombination dominates over the gas-phase recombination. The model is employed to verify applicability of a conventional approximation of low dust charges in protoplanetary disks, and to discuss the implications for the dust coagulation and the development of the "dead zone" in the disk. Furthermore, the importance of mutually consistent models for the ionization and dust evolution is addressed: These processes are coupled via several mechanisms operating in the disk, and therefore their interplay can be crucial for the ultimate ...

  8. Observations of Solids in Protoplanetary Disks

    Science.gov (United States)

    Andrews, Sean M.

    2015-10-01

    This review addresses the state of research that employs astronomical (remote sensing) observations of solids ("dust") in young circumstellar disks to learn about planet formation. The intention is for it to serve as an accessible, introductory, pedagogical resource for junior scientists interested in the subject. After some historical background and a basic observational primer, the focus is shifted to the three fundamental topics that broadly define the field: (1) demographics—the relationships between disk properties and the characteristics of their environments and hosts; (2) structure—the spatial distribution of disk material and its associated physical conditions and composition; and (3) evolution—the signposts of key changes in disk properties, including the growth and migration of solids and the impact of dynamical interactions with young planetary systems. Based on the state-of-the-art results in these areas, suggestions are made for potentially fruitful lines of work in the near future.

  9. A symmetric inner cavity in the HD~141569A transitional disk

    CERN Document Server

    Mazoyer, J; Choquet, E; Perrin, M D; Pueyo, L; Augereau, J -C; Lagrange, A -M; Debes, J; Wolff, S G

    2016-01-01

    Some circumstellar disks, called transitional or hybrid disks, present characteristics of both protoplanetary disks (significant amount of gas) and debris disks (evolved structures around young main-sequence stars, composed of second generation dust, from collisions between planetesimals). Therefore, they are an ideal astrophysical laboratory to witness the last stages of planet formation. The circumstellar disk around HD~141569A was intensively observed and resolved in the past from space but also from the ground but the recent implementation of high contrast imaging systems opens new opportunities to re-analyze this object. We analyzed Gemini archival data from the Near-Infrared Coronagraphic Imager (NICI) obtained in 2011 in the H band, using several angular differential imaging techniques (classical ADI, LOCI, KLIP). These images reveal the complex structures of this disk with an unprecedented resolution. We also include archival Hubble Space Telescope (HST) images as an independent dataset to confirm the...

  10. A Pulsar and a Disk

    Science.gov (United States)

    Kohler, Susanna

    2016-07-01

    Recent, unusual X-ray observations from our galactic neighbor, the Small Magellanic Cloud, have led to an interesting model for SXP 214, a pulsar in a binary star system.Artists illustration of the magnetic field lines of a pulsar, a highly magnetized, rotating neutron star. [NASA]An Intriguing BinaryAn X-ray pulsar is a magnetized, rotating neutron star in a binary system with a stellar companion. Material is fed from the companion onto the neutron star, channeled by the objects magnetic fields onto a hotspot thats millions of degrees. This hotspot rotating past our line of sight is what produces the pulsations that we observe from X-ray pulsars.Located in the Small Magellanic Cloud, SXP 214 is a transient X-ray pulsar in a binary with a Be-type star. This star is spinning so quickly that material is thrown off of it to form a circumstellar disk.Recently, a team of authors led by JaeSub Hong (Harvard-Smithsonian Center for Astrophysics) have presented new Chandra X-ray observations of SXP 214, tracking it for 50 ks (~14 hours) in January 2013. These observations reveal some very unexpected behavior for this pulsar.X-ray PuzzleThe energy distribution of the X-ray emission from SXP 214 over time. Dark shades or blue colors indicate high counts, and light shades or yellow colors indicate low counts. Lower-energy X-ray emission appeared only later, after about 20 ks. [Hong et al. 2016]Three interesting pieces of information came from the Chandra observations:SXP 214s rotation period was measured to be 211.5 s an increase in the spin rate since the discovery measurement of a 214-second period. Pulsars usually spin down as they lose angular momentum over time so what caused this one to spin up?Its overall X-ray luminosity steadily increased over the 50 ks of observations.Its spectrum became gradually softer (lower energy) over time; in the first 20 ks, the spectrum only consisted of hard X-ray photons above 3 keV, but after 20 ks, softer X-ray photons below 2 ke

  11. The Effects on Supernova Shock Breakout and Swift Light Curves Due to the Mass of the Hydrogen-Rich Envelope

    CERN Document Server

    Bayless, Amanda J; Frey, Lucille H; Fryer, Chris L; Roming, Peter W A; Young, Patrick A

    2014-01-01

    Mass loss remains one of the primary uncertainties in stellar evolution. In the most massive stars, mass loss dictates the circumstellar medium and can significantly alter the fate of the star. Mass loss is caused by a variety of wind mechanisms and also through binary interactions. Supernovae are excellent probes of this mass loss, both the circumstellar material and the reduced mass of the hydrogen-rich envelope. In this paper, we focus on the effects of reducing the hydrogen-envelope mass on the supernova light curve, studying both the shock breakout and peak light curve emission for a wide variety of mass loss scenarios. Even though the trends of this mass loss will be masked somewhat by variations caused by different progenitors, explosion energies, and circumstellar media, these trends have significant effects on the supernova light-curves that should be seen in supernova surveys. We conclude with a comparison of our results to a few key observations.

  12. Indirect Detection of Forming Protoplanets via Chemical Asymmetries in Disks

    CERN Document Server

    Cleeves, L Ilsedore; Harries, Tim J

    2015-01-01

    We examine changes in the molecular abundances resulting from increased heating due to a self-luminous planetary companion embedded within a narrow circumstellar disk gap. Using 3D models that include stellar and planetary irradiation, we find that luminous young planets locally heat up the parent circumstellar disk by many tens of Kelvin, resulting in efficient thermal desorption of molecular species that are otherwise locally frozen out. Furthermore, the heating is deposited over large regions of the disk, $\\pm5$ AU radially and spanning $\\lesssim60^\\circ$ azimuthally. From the 3D chemical models, we compute rotational line emission models and full ALMA simulations, and find that the chemical signatures of the young planet are detectable as chemical asymmetries in $\\sim10h$ observations. HCN and its isotopologues are particularly clear tracers of planetary heating for the models considered here, and emission from multiple transitions of the same species is detectable, which encodes temperature information i...

  13. Polarization of thermal molecular lines in the envelope of IK Tau

    CERN Document Server

    Vlemmings, W H T; Rao, R; Maercker, M

    2012-01-01

    Molecular line polarization is a unique source of information about the magnetic fields and anisotropies in the circumstellar envelopes of evolved stars. Here we present the first detection of thermal CO(J=2-1) and SiO(J=5-4, v=0) polarization, in the envelope of the asymptotic giant branch star IK Tau. The observed polarization direction does not match predictions for circumstellar envelope polarization induced only by an anisotropic radiation field. Assuming that the polarization is purely due to the Goldreich-Kylafis effect, the linear polarization direction is defined by the magnetic field as even the small Zeeman splitting of CO and SiO dominates the molecular collisional and spontaneous emission rates. The polarization was mapped using the Submillimeter Array (SMA) and is predominantly north-south. There is close agreement between the CO and SiO observations, even though the CO polarization arises in the circumstellar envelope at ~800 AU and the SiO polarization at <250 AU. If the polarization indeed...

  14. THE HERSCHEL DIGIT SURVEY OF WEAK-LINE T TAURI STARS: IMPLICATIONS FOR DISK EVOLUTION AND DISSIPATION

    International Nuclear Information System (INIS)

    As part of the 'Dust, Ice, and Gas In Time (DIGIT)' Herschel Open Time Key Program, we present Herschel photometry (at 70, 160, 250, 350, and 500 μm) of 31 weak-line T Tauri star (WTTS) candidates in order to investigate the evolutionary status of their circumstellar disks. Of the stars in our sample, 13 had circumstellar disks previously known from infrared observations at shorter wavelengths, while 18 of them had no previous evidence for a disk. We detect a total of 15 disks as all previously known disks are detected at one or more Herschel wavelengths and two additional disks are identified for the first time. The spectral energy distributions (SEDs) of our targets seem to trace the dissipation of the primordial disk and the transition to the debris disk regime. Of the 15 disks, 7 appear to be optically thick primordial disks, including 2 objects with SEDs indistinguishable from those of typical Classical T Tauri stars, 4 objects that have significant deficit of excess emission at all IR wavelengths, and 1 'pre-transitional' object with a known gap in the disk. Despite their previous WTTS classification, we find that the seven targets in our sample with optically thick disks show evidence for accretion. The remaining eight disks have weaker IR excesses similar to those of optically thin debris disks. Six of them are warm and show significant 24 μm Spitzer excesses, while the last two are newly identified cold debris-like disks with photospheric 24 μm fluxes, but significant excess emission at longer wavelengths. The Herschel photometry also places strong constraints on the non-detections, where systems with F 70/F 70,* ∼> 5-15 and L disk/L * ∼> 10–3 to 10–4 can be ruled out. We present preliminary models for both the optically thick and optically thin disks and discuss our results in the context of the evolution and dissipation of circumstellar disks.

  15. Shadows cast by a warp in the HD 142527 protoplanetary disk

    OpenAIRE

    Marino, Sebastian; Perez, Sebastian; Casassus, Simon

    2014-01-01

    Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in H-band, so that the shape and orientation of the shadows infor...

  16. Disk Chemistry*

    OpenAIRE

    Thi Wing-Fai

    2015-01-01

    The chemical species in protoplanetary disks react with each other. The chemical species control part of the thermal balance in those disks. How the chemistry proceeds in the varied conditions encountered in disks relies on detailed microscopic understanding of the reactions through experiments or theoretical studies. This chapter strives to summarize and explain in simple terms the different types of chemical reactions that can lead to complex species. The first part of the chapter deals wit...

  17. Carrier-envelope-phase stabilization via dual wavelength pumping.

    Science.gov (United States)

    Seidel, Marcus; Brons, Jonathan; Lücking, Fabian; Pervak, Vladimir; Apolonski, Alexander; Udem, Thomas; Pronin, Oleg

    2016-04-15

    A power-scalable concept for carrier-envelope-phase stabilization is presented. It takes advantage of simultaneous pumping of the zero- and first-phonon absorption line of Yb:YAG at 969 and 940 nm. The concept was implemented to lock the carrier-envelope-offset frequency of a 45 W average power Kerr-lens mode-locked thin-disk oscillator. The lock performance is compared to previous experiments where carrier-envelope-stabilization was realized by means of cavity loss modulation. PMID:27082362

  18. 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.

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

    International Nuclear Information System (INIS)

    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

  20. 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.; Duchene, Gaspard; Millar-Blanchaer, Max; Fitzgerald, Michael P.; Graham, James R.; Wiktorowicz, Sloane J.; Kalas, Paul G.; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; Chilcote, Jeffrey; De Rosa, Robert J.; Dillon, Daren; Doyon, René; Dunn, Jennifer; Erikson, Darren; Gavel, Donald; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale; Ingraham, Patrick; Kerley, Daniel; Konapacky, Quinn; Larkin, James E.; Maire, Jérôme; Marchis, Franck; Marois, Christian; Mittal, Tushar; Morzinski, Katie M.; Oppenheimer, B. R.; Palmer, David W.; Patience, Jennifer; Poyneer, Lisa; Pueyo, Laurent; Rantakyrö, Fredrik T.; Sadakuni, Naru; Saddlemyer, Leslie; Savransky, Dmitry; Soummer, Rémi; Sivaramakrishnan, Anand; Song, Inseok; Thomas, Sandrine; Wallace, J. Kent; Wang, Jason J.; Wolff, Schuyler G.

    2015-01-28

    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 subtraction via di erential 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.

  1. UV Spectroscopy of Star-Grazing Comets within the 49 Ceti Debris Disk

    OpenAIRE

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

    2015-01-01

    We present analysis of time-variable, 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 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 C II and C IV, but not for any of the other circumstellar absorption lines. Similar variable fe...

  2. ALMA CONTINUUM OBSERVATIONS OF A 30 Myr OLD GASEOUS DEBRIS DISK AROUND HD 21997

    International Nuclear Information System (INIS)

    Circumstellar disks around stars older than 10 Myr are expected to be gas-poor. There are, however, two examples of old (30-40 Myr) debris-like disks containing a detectable amount of cold CO gas. Here we present Atacama Large Millimeter/Submillimeter Array (ALMA) and Herschel Space Observatory observations of one of these disks, around HD 21997, and study the distribution and origin of the dust and its connection to the gas. Our ALMA continuum images at 886 μm clearly resolve a broad ring of emission within a diameter of ∼4.''5, adding HD 21997 to the dozen debris disks resolved at (sub)millimeter wavelengths. Modeling the morphology of the ALMA image with a radiative transfer code suggests inner and outer radii of ∼55 and ∼150 AU, and a dust mass of 0.09 M ⊕. Our data and modeling hints at an extended cold outskirt of the ring. Comparison with the morphology of the CO gas in the disk reveals an inner dust-free hole where gas nevertheless can be detected. Based on dust grain lifetimes, we propose that the dust content of this gaseous disk is of secondary origin and is produced by planetesimals. Since the gas component is probably primordial, HD 21997 is one of the first known examples of a hybrid circumstellar disk, a thus-far little studied late phase of circumstellar disk evolution

  3. Storage envelopes or sleeves

    International Nuclear Information System (INIS)

    A storage envelope or sleeve particularly for processed X-ray films is described. It consists of front and back panels joined together at a hinge line and connected along the intermediate sides by connecting flaps. An inner pocket is formed from a third flap which is folded to lie against the inner face of the back panel. The panels may have additional score lines parallel to the closed sides of the envelope and the inner pocket so that the envelope and the inner pocket can accommodate bulky contents. The free edge of the pocket is inset from the open side of the envelope, and finger cut-outs may be provided to facilitate access to the contents of the envelope and the pocket. (author)

  4. The effects of viscosity on circumplanetary disks

    Institute of Scientific and Technical Information of China (English)

    De-Fu Bu; Hsien Shang; Feng Yuan

    2013-01-01

    The effects of viscosity on the circumplanetary disks residing in the vicinity of protoplanets are investigated through two-dimensional hydrodynamical simulations with the shearing sheet model.We find that viscosity can considerably affect properties of the circumplanetary disk when the mass of the protoplanet Mp (<) 33 M(⊙),where M(⊙) is the Earth's mass.However,effects of viscosity on the circumplanetary disk are negligibly small when the mass of the protoplanet Mp(>) 33 M(⊙).We find that when Mp(<) 33 M(⊙),viscosity can markedly disrupt the spiral structure of the gas around the planet and smoothly distribute the gas,which weakens the torques exerted on the protoplanet.Thus,viscosity can slow the migration speed of a protoplanet.After including viscosity,the size of the circumplanetary disk can be decreased by a factor of (>) 20%.Viscosity helps to transport gas into the circumplanetary disk from the differentially rotating circumstellar disk.The mass of the circumplanetary disk can be increased by a factor of 50% after viscosity is taken into account when Mp(<) 33 M(⊙).Effects of viscosity on the formation of planets and satellites are briefly discussed.

  5. The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO2 emission

    Science.gov (United States)

    Podio, L.; Codella, C.; Gueth, F.; Cabrit, S.; Bachiller, R.; Gusdorf, A.; Lee, C.-F.; Lefloch, B.; Leurini, S.; Nisini, B.; Tafalla, M.

    2015-09-01

    Context. The investigation of the disk formation and jet launching mechanism in protostars is crucial to understanding the earliest stages of star and planet formation. Aims: We aim to constrain the physical and dynamical properties of the molecular jet and disk of the HH 212 protostellar system at unprecedented angular scales, exploiting the capabilities of the Atacama Large Millimeter Array (ALMA). Methods: The ALMA observations of HH 212 in emission lines from sulfur-bearing molecules, SO 98-87, SO 1011-1010, SO282,6-71,7, are compared with simultaneous CO 3-2, SiO 8-7 data. The molecules column density and abundance are estimated using simple radiative transfer models. Results: SO 98-87 and SO282,6-71,7 show broad velocity profiles. At systemic velocity, they probe the circumstellar gas and the cavity walls. Going from low to high blue- and red-shifted velocities the emission traces the wide-angle outflow and the fast (~100-200 km s-1), collimated (~90 AU) molecular jet revealing the inner knots with timescales ≤50 yr. The jet transports a mass-loss rate ≥ 0.2-2 × 10-6 M⊙ yr-1, implying high ejection efficiency (≥ 0.03-0.3). The SO and SO2 abundances in the jet are ~ 10-7-10-6. SO 1011-1010 emission is compact and shows small-scale velocity gradients, indicating that it originates partly from the rotating disk previously seen in HCO+ and C17O, and partly from the base of the jet. The disk mass is ≥ 0.002-0.013 M⊙ and the SO abundance in the disk is ~ 10-8-10-7. Conclusions: SO and SO2 are effective tracers of the molecular jet in the inner few hundreds AU from the protostar. Their abundances indicate that 1-40% of sulfur is in SO and SO2 due to shocks in the jet/outflow and/or to ambipolar diffusion at the wind base. The SO abundance in the disk is 3-4 orders of magnitude larger than in evolved protoplanetary disks. This may be due to an SO enhancement in the accretion shock at the envelope-disk interface or in spiral shocks if the disk is partly

  6. Detailed modelling of the circumstellar molecular line emission of the S-type AGB star W Aquilae

    Science.gov (United States)

    Danilovich, T.; Bergman, P.; Justtanont, K.; Lombaert, R.; Maercker, M.; Olofsson, H.; Ramstedt, S.; Royer, P.

    2014-09-01

    Context. S-type AGB stars have a C/O ratio which suggests that they are transition objects between oxygen-rich M-type stars and carbon-rich C-type stars. As such, their circumstellar compositions of gas and dust are thought to be sensitive to their precise C/O ratio, and it is therefore of particular interest to examine their circumstellar properties. Aims: We present new Herschel HIFI and PACS sub-millimetre and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances. Methods: We used radiative transfer codes to model the circumstellar dust and molecular line emission to determine circumstellar properties and molecular abundances. We assumed a spherically symmetric envelope formed by a constant mass-loss rate driven by an accelerating wind. Our model includes fully integrated H2O line cooling as part of the solution of the energy balance. Results: We detect circumstellar molecular lines from CO, H2O, SiO, HCN, and, for the first time in an S-type AGB star, NH3. The radiative transfer calculations result in an estimated mass-loss rate for W Aql of 4.0 × 10-6 M⊙ yr-1 based on the 12CO lines. The estimated 12CO/13CO ratio is 29, which is in line with ratios previously derived for S-type AGB stars. We find an H2O abundance of 1.5 × 10-5, which is intermediate to the abundances expected for M and C stars, and an ortho/para ratio for H2O that is consistent with formation at warm temperatures. We find an HCN abundance of 3 × 10-6, and, although no CN lines are detected using HIFI, we are able to put some constraints on the abundance, 6 × 10-6, and distribution of CN in W Aql's circumstellar envelopeusing ground-based data. We find an SiO abundance of 3 × 10-6, and an NH3 abundance of 1.7 × 10-5, confined to a small envelope. If we include uncertainties

  7. Envelopes of Commutative Rings

    Institute of Scientific and Technical Information of China (English)

    Rafael PARRA; Manuel SAOR(I)N

    2012-01-01

    Given a significative class F of commutative rings,we study the precise conditions under which a commutative ring R has an F-envelope.A full answer is obtained when.F is the class of fields,semisimple commutative rings or integral domains.When F is the class of Noetherian rings,we give a full answer when the Krull dimension of R is zero and when the envelope is required to be epimorphic.The general problem is reduced to identifying the class of non-Noetherian rings having a monomorphic Noetherian envelope,which we conjecture is the empty class.

  8. A young massive planet in a star-disk system.

    Science.gov (United States)

    Setiawan, J; Henning, Th; Launhardt, R; Müller, A; Weise, P; Kürster, M

    2008-01-01

    There is a general consensus that planets form within disks of dust and gas around newly born stars. Details of their formation process, however, are still a matter of ongoing debate. The timescale of planet formation remains unclear, so the detection of planets around young stars with protoplanetary disks is potentially of great interest. Hitherto, no such planet has been found. Here we report the detection of a planet of mass (9.8+/-3.3)M(Jupiter) around TW Hydrae (TW Hya), a nearby young star with an age of only 8-10 Myr that is surrounded by a well-studied circumstellar disk. It orbits the star with a period of 3.56 days at 0.04 au, inside the inner rim of the disk. This demonstrates that planets can form within 10 Myr, before the disk has been dissipated by stellar winds and radiation. PMID:18172492

  9. Observational Constraints on Dust Disk Lifetimes: Implications for Planet Formation

    CERN Document Server

    Hillenbrand, L A

    2005-01-01

    (abridged) Thus far our impressions regarding the evolutionary time scales for young circumstellar disks have been based on small number statistics. Over the past decade, however, in addition to precision study of individual star/disk systems, substantial observational effort has been invested in obtaining less detailed data on large numbers of objects in young star clusters. This has resulted in a plethora of information now enabling statistical studies of disk evolutionary diagnostics. Along an ordinate one can measure disk presence or strength through indicators such as ultraviolet/blue excess or spectroscopic emission lines tracing accretion, infrared excess tracing dust, or millimeter flux measuring mass. Along an abscissa one can track stellar age. While bulk trends in disk indicators versus age are evident, observational errors affecting both axes, combined with systematic errors in our understanding of stellar ages, both cloud and bias any such trends Thus detailed understanding of the physical proces...

  10. Detection of Weak Circumstellar Gas around the DAZ White Dwarf WD 1124-293: Evidence for the Accretion of Multiple Asteroids

    CERN Document Server

    Debes, J H; Faedi, F; Shkolnik, E L; Lopez-Morales, M; Weinberger, A J; Slesnick, C; West, R G

    2012-01-01

    Single metal polluted white dwarfs with no dusty disks are believed to be actively accreting metals from a circumstellar disk of gas caused by the destruction of asteroids perturbed by planetary systems. We report, for the first time, the detection of circumstellar Ca~II gas in absorption around the DAZ WD~1124-293, which lacks an infrared excess. We constrain the gas to $>$7 $R_{\\rm WD}$ and $$ R$_{\\rm \\oplus}$ using the WASP survey. The presence of gas in orbit around WD~1124-293 implies that most DAZs could harbor planetary systems. Since 25-30\\% of white dwarfs show metal line absorption, the dynamical process for perturbing small bodies must be robust.

  11. The Nuclear Envelope

    OpenAIRE

    Watson, Michael L.

    2010-01-01

    An electron microscope study of thin sections of interphase cells has revealed the following:— Circular pores are formed in the double nuclear envelope by continuities between the inner and outer membranes which permit contact between the nucleoplasm and the cytoplasm unmediated by a well defined membrane. The pores, seen in sections normal to the nuclear envelope, are profiles of the ring-shaped structures described by others and seen in tangential section. The inner and outer nuclear membra...

  12. Detection Of Exocomets Within Edge-on Debris Disks

    Science.gov (United States)

    Montgomery, Sharon Lynn; Welsh, B.

    2011-01-01

    The youngest circumstellar debris disks in orbit around main sequence stars are thought to represent the last stage in the formation of a planetary system. Dust and gas continues to be replenished in these systems when planetesimals reach sizes of around 2000 km. Dynamical instabilities can "stir" the population of smaller planetesimals such that they undergo violent dust-generating collisions with each other. The same instabilities may send comets on highly eccentric orbits toward the star in these debris disk systems. Four stars, including the protypical debris disk star Beta Pic, have already been shown to exhibit short-term (i.e., night-to-night) variability in Ca II, which is widely believed to be due to infalling evaporating bodies (FEBs or exocomets). We have collected moderately high-resolution spectra of ten young, A-type, rapidly-rotating stars with excess infrared continuum emission using the Cassegrain-Echelle spectrograph of the 2.1m Otto Struve Telescope. Here, we report the detection of two new gas disk systems with short-term variability in CaII: 5 Vul and 49 Cet. While the circumstellar disks of both stars have been previously described in the literature, this is the first report of night-to-night variability within the debris disk gas. Velocity arguments have allowed us to place some constraints on the dynamics of the absorbing gas.

  13. Signatures of Planet Formation in Gravitationally Unstable Disks

    CERN Document Server

    Boss, H J C A P

    2007-01-01

    In this paper, we calculate simulated scattered light images of a circumstellar disk in which a planet is forming by gravitational instability. The simulated images bear no correlation to the vertically integrated surface density of the disk, but rather trace the density structure in the tenuous upper layers of the disk. Although the density at high altitudes does not bear a direct relation to activity at the midplane, the very existence of structure at high altitudes along with high time variability is an indicator of gravitational instability within the disk. The timescale for variations is much shorter than the orbital period of the planet, which facilitates observation of the phenomenon. Scattered light images may not necessarily be able to tell us where exactly a planet might be forming in a disk, but can still be a useful probe of active planet formation within a circumstellar disk. Although these phenomena are unlikely to be observable by current telescopes, future large telescopes, such as the Giant M...

  14. Circumstellar water vapour in M-type AGB stars: Radiative transfer models, abundances and predictions for HIFI

    CERN Document Server

    Maercker, Matthias; Olofsson, Hans; Bergman, Per; Ramstedt, Sofia

    2008-01-01

    Aims: By performing a detailed radiative transfer analysis, we determine fractional abundances of circumstellar H2O in the envelopes around six M-type asymptotic giant branch stars. The models are also used to predict H2O spectral line emission for the upcoming Herschel/HIFI mission. Methods: We use Infrared space observatory long wavelength spectrometer spectra to constrain the circumstellar fractional abundance distribution of ortho-H2O, using a non-local thermal equilibrium, and non-local, radiative transfer code based on the accelerated lambda iteration formalism. The mass-loss rates and kinetic temperature structures for the sample stars are determined through radiative transfer modelling of CO line emission based on the Monte-Carlo method. The density and temperature profiles of the circumstellar dust grains are determined through spectral energy distribution modelling using the publicly available code Dusty. Results: The determined ortho-H2O abundances lie between 1e-4 and 1.5e-3 relative to H2, with t...

  15. High-resolution near-infrared imaging of the Orion 114-426 silhouette disk

    OpenAIRE

    McCaughrean, Mark J.; Chen, Hua; Bally, John; Erickson, Ed; Thompson, Rodger; Rieke, Marcia; Schneider, Glenn; Stolovy, Susan; Young, Erick

    1997-01-01

    We present the first high-resolution near-infrared images of the edge-on silhouette circumstellar disk, Orion 114-426, made using NICMOS on the Hubble Space Telescope. Images taken against the bright nebular background of the ionized hydrogen Pa$\\alpha$ line at 1.87 micron show the major axis of the disk to be approximately 20% smaller than at 0.6 micron, from which we deduce the structure of the edge of the disk. Continuum images of diffuse polar lobes above and below the plane of the disk s...

  16. The Structure and Evolution of Protoplanetary Disks: an Infrared and Submillimeter View

    Science.gov (United States)

    Cieza, Lucas A.

    2016-01-01

    Circumstellar disks are the sites of planet formation, and the very high incidence of extrasolar planets implies that most of them actually form planetary systems. Studying the structure and evolution of protoplanetary disks can thus place important constraints on the conditions, timescales, and mechanisms associated with the planet formation process. In this review, we discuss observational results from infrared and submillimeter wavelength studies. We review disk lifetimes, transition objects, disk demographics, and highlight a few remarkable results from ALMA Early Science observations. We finish with a brief discussion of ALMA's potential to transform the field in near future.

  17. The Structure and Evolution of Protoplanetary Disks: an infrared and submillimeter view

    CERN Document Server

    Cieza, Lucas A

    2015-01-01

    Circumstellar disks are the sites of planet formation, and the very high incidence of extrasolar planets implies that most of them actually form planetary systems. Studying the structure and evolution of protoplanetary disks can thus place important constraints on the conditions, timescales, and mechanisms associated with the planet formation process. In this review, we discuss observational results from infrared and submillimeter wavelength studies. We review disk lifetimes, transition objects, disk demographics, and highlight a few remarkable results from ALMA Early Science observations. We finish with a brief discussion of ALMA's potential to transform the field in near future.

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

    CERN Document Server

    Hoard, D W; 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....

  19. c2d Spitzer IRS spectra of disks around T Tauri stars. III. [Ne II], [Fe I], and H-2 gas-phase lines

    NARCIS (Netherlands)

    Lahuis, Fred; van Dishoeck, Ewine F.; Blake, Geoffrey A.; Evans, Neal J.; Kessler-Silacci, Jacqueline E.; Pontoppidan, Klaus M.

    2007-01-01

    We present a survey of mid-infrared gas-phase lines toward a sample of 76 circumstellar disks around low-mass pre-main-sequence stars from the Spitzer "Cores to Disks" legacy program. We report the first detections of [ Ne II] and [ Fe I] toward classical T Tauri stars in similar to 20% and similar

  20. Disk-dispersal and planet-formation timescales

    International Nuclear Information System (INIS)

    Well before the existence of exo-solar systems was confirmed, it was accepted knowledge that most-if not all-stars possess circumstellar material during the first one-to-several million years of their pre-main sequence lives, and thus that these systems commonly have the potential to form planets. Here, I summarize current understanding regarding the evolution of protoplanetary disks

  1. Spitzer SAGE-Spec: Near Infrared Spectroscopy, Dust Shells, and Cool Envelopes in Extreme Large Magellanic Cloud Asymptotic Giant Branch Stars

    Science.gov (United States)

    Blum, R. D.; Srinivasan, S.; Kemper, F.; Ling, B.; Volk, K.

    2014-11-01

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ``tip" of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ``stellar" cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  2. Erratum: “Spitzer SAGE-Spec: Near Infrared Spectroscopy, Dust Shells, and Cool Envelopes in Extreme Large Magellanic Cloud Asymptotic Giant Branch Stars” (2014, AJ, 148, 86)

    Science.gov (United States)

    Blum, R. D.; Srinivasan, S.; Kemper, F.; Ling, B.; Volk, K.

    2015-02-01

    K-band spectra are presented for a sample of 39 Spitzer IRS SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near infrared - Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars were chosen from the luminous and red extreme "tip" of the color magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich "stellar" cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near infrared and mid infrared colors. One object in our sample, HV 915, a known post asymptotic giant branch star of the RV Tau type exhibits CO 2.3 micron band head emission consistent with previous work that demonstrates the object has a circumstellar disk.

  3. Spitzer SAGE-Spec: Near infrared spectroscopy, dust shells, and cool envelopes in extreme Large Magellanic Cloud asymptotic giant branch stars

    International Nuclear Information System (INIS)

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

  4. Spitzer SAGE-Spec: Near infrared spectroscopy, dust shells, and cool envelopes in extreme Large Magellanic Cloud asymptotic giant branch stars

    Energy Technology Data Exchange (ETDEWEB)

    Blum, R. D. [NOAO, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Srinivasan, S.; Kemper, F.; Ling, B. [Academia Sinica, Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, NTU/AS, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (China); Volk, K. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2014-11-01

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

  5. The Peculiar Balmer Decrement of SN 2009ip: Constraints on Circumstellar Geometry

    CERN Document Server

    Levesque, Emily M; Ginsburg, Adam G; Bally, John; Keeney, Brian A

    2012-01-01

    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 lightcurve, 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(H-alpha)/I(H-beta) ratio (~1.5) in the 2012-B spectra. Such a ratio implies either a rare Case B recombination scenario where H-alpha, but not H-beta, is optically thick, or an extremely high density for the circumstellar material of n_e > 10^(13) cm^(-3). The H-alpha line intensity yields a minimum radiating surface area of >~20,000 AU^2 in H-alpha 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...

  6. Two-dimensional Distributions and Column Densities of Gaseous Molecules in Protoplanetary Disks II

    OpenAIRE

    Y. Aikawa; Herbst, E.

    2002-01-01

    We have investigated the two-dimensional (R,Z) distribution of deuterated molecular species in circumstellar disks around young stellar objects. The abundance ratios between singly deuterated and normal molecules (``D/H ratios'') in disks evolve in a similar way as in molecular clouds. Fractionation is caused by rapid exchange reactions that are exothermic because of energy differences between deuterated and normal species. In the midplane region, where molecules are heavily depleted onto gra...

  7. Analysis of the circumstellar environment of the B[e] star HD 45677 (FS CMa)

    CERN Document Server

    Muratorio, G; Friedjung, M; Rossi, Corinne; Friedjung, Michael

    2006-01-01

    We studied the circumstellar environment of the B[e] star HD 45677 through the analysis of the emission lines from ionized metals. We used the statistical approach of the self absorption curve method (SAC) to derive physical parameters of the line emitting region. The Fe II and Cr II double-peaked emission line structure is explained by the presence of a thin absorption component red shifted by ~3 km/s. This absorption component can be interpreted geometricaly as being due to infalling material perpendicularly to the disk seen nearly pole-on, as indicated by the emission line structure. The Cr II and Fe II emission lines have a complex structure with two (narrow and broad) components, of 45 and 180 km/s FWHM for the permitted lines and 25 and 100 km/s FWHM for the forbidden ones, respectively. We argue that the narrow components are principaly emitted by an optically thin disk seen nearly pole-on, in a region whose minimum radius is estimated to be 4 10^12 cm, while the broad ones are formed in a disk-linked ...

  8. Synthetic Spectra and Light Curves of Interacting Binaries and Exoplanets with Circumstellar Material: SHELLSPEC

    Science.gov (United States)

    Budaj, Ján

    2012-04-01

    Program SHELLSPEC is designed to calculate light-curves, spectra and images of interacting binaries and extrasolar planets immersed in a moving circumstellar environment which is optically thin. It solves simple radiative transfer along the line of sight in moving media. The assumptions include LTE and optional known state quantities and velocity fields in 3D. Optional (non)transparent objects such as a spot, disc, stream, jet, shell or stars may be defined (embedded) in 3D and their composite synthetic spectrum calculated. The Roche model can be used as a boundary condition for the radiative transfer. Recently, a new model of the reflection effect, dust and Mie scattering were incorporated into the code. ɛ Aurigae is one of the most mysterious objects on the sky. Prior modeling of its light-curve assumed a dark, inclined, disk of dust with a central hole to explain the light-curve with a sharp mid-eclipse brightening. Our model consists of two geometrically thick flared disks: an internal optically thick disk and an external optically thin disk which absorbs and scatters radiation. Shallow mid-eclipse brightening may result from eclipses by nearly edge-on flared (dusty or gaseous) disks. Mid-eclipse brightening may also be due to strong forward scattering and optical properties of the dust which can have an important effect on the light-curves. There are many similarities between interacting binary stars and transiting extrasolar planets. The reflection effect which is briefly reviewed is one of them. The exact Roche shape and temperature distributions over the surface of all currently known transiting extrasolar planets have been determined. In some cases (HAT-P-32b, WASP-12b, WASP-19b), departures from the spherical shape can reach 7-15%.

  9. ALMA imaging of the CO snowline of the HD 163296 disk with DCO

    NARCIS (Netherlands)

    Mathews, G. S.; Klaassen, P. D.; Juhasz, A.; Harsono, D.; Chapillon, E.; van Dishoeck, E. F.; Espada, D.; de Gregorio-Monsalvo, I.; Hales, A.; Hogerheijde, M. R.; Mottram, J. C.; Rawlings, M. G.; Takahashi, S.; Testi, L.

    2013-01-01

    Context. The high spatial resolution and line sensitivity of the Atacama Large Millimeter/submillimeter Array (ALMA) opens the possibility of resolving emission from molecules in large samples of circumstellar disks. With an understanding of the conditions under which these molecules can have high a

  10. FRACTIONAL CRYSTALLIZATION FEED ENVELOPE

    International Nuclear Information System (INIS)

    Laboratory work was completed on a set of evaporation tests designed to establish a feed envelope for the fractional crystallization process. The feed envelope defines chemical concentration limits within which the process can be operated successfully. All 38 runs in the half-factorial design matrix were completed successfully, based on the qualitative definition of success. There is no feed composition likely to be derived from saltcake dissolution that would cause the fractional crystallization process to not meet acceptable performance requirements. However, some compositions clearly would provide more successful operation than other compositions

  11. A database of circumstellar OH masers

    CERN Document Server

    Engels, D

    2015-01-01

    We present a new database of circumstellar OH masers at 1612, 1665, and 1667 MHz in the Milky Way galaxy. The database (version 2.4) contains 13655 observations and 2341 different stars detected in at least one transition. Detections at 1612\\,MHz are considered to be complete until the end of 2014 as long as they were published in refereed papers. Detections of the main lines (1665 and 1667 MHz) and non-detections in all transitions are included only if published after 1983. The database contains flux densities and velocities of the two strongest maser peaks, the expansion velocity of the shell, and the radial velocity of the star. Links are provided for about 100 stars ($<$5\\% of all stars with OH masers) to interferometric observations and monitoring programs of the maser emission published since their beginnings in the 1970s. Access to the database is possible over the Web (www.hs.uni-hamburg.de/maserdb), allowing cone searches for individual sources and lists of sources. A general search is possible in...

  12. Radiative Transfer on Perturbations in Protoplanetary Disks

    CERN Document Server

    Jang-Condell, H; Jang-Condell, Hannah; Sasselov, Dimitar D.

    2003-01-01

    We present a method for calculating the radiative tranfer on a protoplanetary disk perturbed by a protoplanet. We apply this method to determine the effect on the temperature structure within the photosphere of a passive circumstellar disk in the vicinity of a small protoplanet of up to 20 Earth masses. The gravitational potential of a protoplanet induces a compression of the disk material near it, resulting in a decrement in the density at the disk's surface. Thus, an isodensity contour at the height of the photosphere takes on the shape of a well. When such a well is illuminated by stellar irradiation at grazing incidence, it results in cooling in a shadowed region and heating in an exposed region. For typical stellar and disk parameters relevant to the epoch of planet formation, we find that the temperature variation due to a protoplanet at 1 AU separation from its parent star is about 4% (5 K) for a planet of 1 Earth mass, about 14% (19 K) for planet of 10 Earth masses, and about 18% (25 K) for planet of ...

  13. Radiative Ablation of Disks Around Massive Stars

    CERN Document Server

    Kee, N D

    2015-01-01

    Hot, massive stars (spectral types O and B) have extreme luminosities ($10^4 -10^6 L_\\odot$) that drive strong stellar winds through UV line-scattering. Some massive stars also have disks, formed by either decretion from the star (as in the rapidly rotating "Classical Be stars"), or accretion during the star's formation. This dissertation examines the role of stellar radiation in driving (ablating) material away from these circumstellar disks. A key result is that the observed month to year decay of Classical Be disks can be explained by line-driven ablation without, as previously done, appealing to anomalously strong viscous diffusion. Moreover, the higher luminosity of O stars leads to ablation of optically thin disks on dynamical timescales of order a day, providing a natural explanation for the lack of observed Oe stars. In addition to the destruction of Be disks, this dissertation also introduces a model for their formation by coupling observationally inferred non-radial pulsation modes and rapid stellar...

  14. Accretion disks in luminous young stellar objects

    CERN Document Server

    Beltran, M T

    2015-01-01

    An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and therefore predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates.

  15. Accretion Disks

    OpenAIRE

    Spruit, H.C.

    1995-01-01

    This is an introduction to accretion disk theory, with emphasis on aspects relevant for X-ray Binaries and Cataclysmic Variables. The text corrects some mistakes in an earlier version, which appeared in 'Lives of Neutron Stars', A. Alpar, \\"U. Kizilo\\u glu and J. van Paradijs (eds.), Kluwer, Dordrecht (NATO ASI series, 1994).

  16. The circumstellar matter of supernova 2014J and the core-degenerate scenario

    CERN Document Server

    Soker, Noam

    2015-01-01

    I show that the circumstellar matter (CSM) of the type Ia supernova 2014J is too massive and its momentum too large to be accounted for by any but the core-degenerate (CD) scenario for type Ia supernovae. Assuming the absorbing gas is of CSM origin, the several shells responsible of the absorption potassium lines are accounted for by a mass loss episode from a massive asymptotic giant branch star during a common envelope phase with a white dwarf companion. The time-varying potassium lines can be accounted for by ionization of neutral potassium and the Na-from-dust absorption (NaDA) model. Before explosion some of the potassium resides in the gas phase and some in dust. Weakening in absorption strength is caused by potassium-ionizing radiation of the supernova, while release of atomic potassium from dust increases the absorption. I conclude that if the absorbing gas originated from the progenitor of SN 2014J, then a common envelope phase took place about 15,000 years ago, leading to the merging of the core wit...

  17. Elliptic stable envelope

    CERN Document Server

    Aganagic, Mina

    2016-01-01

    We construct stable envelopes in equivariant elliptic cohomology of Nakajima quiver varieties. In particular, this gives an elliptic generalization of the results of arXiv:1211.1287. We apply them to the computation of the monodromy of $q$-difference equations arising the enumerative K-theory of rational curves in Nakajima varieties, including the quantum Knizhnik-Zamolodchikov equations.

  18. (Quasi-)Poisson enveloping algebras

    OpenAIRE

    Yang, Yan-Hong; Yuan YAO; Ye, Yu

    2010-01-01

    We introduce the quasi-Poisson enveloping algebra and Poisson enveloping algebra for a non-commutative Poisson algebra. We prove that for a non-commutative Poisson algebra, the category of quasi-Poisson modules is equivalent to the category of left modules over its quasi-Poisson enveloping algebra, and the category of Poisson modules is equivalent to the category of left modules over its Poisson enveloping algebra.

  19. 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.

  20. HOPS 136: An edge-on orion protostar near the end of envelope infall

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, William J.; Megeath, S. Thomas [Department of Physics and Astronomy, University of Toledo, Toledo, OH (United States); Tobin, John J. [National Radio Astronomy Observatory, Charlottesville, VA (United States); Hartmann, Lee; Kounkel, Marina [Department of Astronomy, University of Michigan, Ann Arbor, MI (United States); Stutz, Amelia M. [Max-Planck-Institut für Astronomie, Heidelberg (Germany); Poteet, Charles A. [New York Center for Astrobiology, Rensselaer Polytechnic Institute, Troy, NY (United States); Ali, Babar [NHSC/IPAC/Caltech, Pasadena, CA (United States); Osorio, Mayra [Instituto de Astrofísica de Andalucía, CSIC, Granada (Spain); Manoj, P. [Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Mumbai (India); Remming, Ian [Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL (United States); Stanke, Thomas [ESO, Garching bei München (Germany); Watson, Dan M., E-mail: wjfischer@gmail.com [Department of Physics and Astronomy, University of Rochester, Rochester, NY (United States)

    2014-02-01

    Edge-on protostars are valuable for understanding the disk and envelope properties of embedded young stellar objects, since the disk, envelope, and envelope cavities are all distinctly visible in resolved images and well constrained in modeling. Comparing Two Micron All Sky Survey, Wide-field Infrared Survey Explorer, Spitzer, Herschel, and APEX photometry and an IRAM limit from 1.2 to 1200 μm, Spitzer spectroscopy from 5 to 40 μm, and high-resolution Hubble imaging at 1.60 and 2.05 μm to radiative transfer modeling, we determine envelope and disk properties for the Class I protostar HOPS 136, an edge-on source in Orion's Lynds 1641 region. The source has a bolometric luminosity of 0.8 L {sub ☉}, a bolometric temperature of 170 K, and a ratio of submillimeter to bolometric luminosity of 0.8%. Via modeling, we find a total luminosity of 4.7 L {sub ☉} (larger than the observed luminosity due to extinction by the disk), an envelope mass of 0.06 M {sub ☉}, and a disk radius and mass of 450 AU and 0.002 M {sub ☉}. The stellar mass is highly uncertain but is estimated to fall between 0.4 and 0.5 M {sub ☉}. To reproduce the flux and wavelength of the near-infrared scattered-light peak in the spectral energy distribution, we require 5.4 × 10{sup –5} M {sub ☉} of gas and dust in each cavity. The disk has a large radius and a mass typical of more evolved T Tauri disks in spite of the significant remaining envelope. HOPS 136 appears to be a key link between the protostellar and optically revealed stages of star formation.

  1. Cooling Requirements for the Vertical Shear Instability in Protoplanetary Disks

    CERN Document Server

    Lin, Min-Kai

    2015-01-01

    It is difficult to understand how cold circumstellar disks accrete onto their central stars. A hydrodynamic mechanism, the vertical shear instability (VSI), offers a means to drive angular momentum transport in cold accretion disks such as protoplanetary disks (PPDs). The VSI is driven by a weak vertical gradient in the disk's orbital motion. In order to grow, the VSI must overcome vertical buoyancy, a strongly stabilizing influence in cold disks, where heating is dominated by external irradiation. Rapid cooling, via radiative losses, reduces the effective buoyancy and allows the VSI to operate. In this paper, we quantify the cooling timescale, $t_c$, needed for growth of the VSI. We perform a linear analysis of the VSI with cooling in vertically global and radially local disk models. For irradiated disks, we find that the VSI is most vigorous for rapid cooling with $t_c < \\Omega_\\mathrm{K}^{-1} h |q| / (\\gamma -1)$ in terms of the Keplerian orbital frequency, $\\Omega_\\mathrm{K}$, the disk's aspect ratio, ...

  2. MASSIVE PROTOPLANETARY DISKS IN ORION BEYOND THE TRAPEZIUM CLUSTER

    International Nuclear Information System (INIS)

    We present Submillimeter Array1The 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.

  3. Thermal Activated Envelope

    DEFF Research Database (Denmark)

    Foged, Isak Worre; Pasold, Anke

    2015-01-01

    search procedure, the combination of materials and their bonding temperature is found in relation to the envelope effect on a thermal environment inside a defined space. This allows the designer to articulate dynamic composites with time-based thermal functionality, related to the material dynamics......, environmental dynamics and occupancy dynamics. Lastly, a physical prototype is created, which illustrates the physical expression of the bi-materials and the problems related to manufacturing of these composite structures.......The research studies the making of a responsive architectural envelope based on bi-materials. The bi-materials are organized according to a method that combines different isotropic metals and plastic into an active composite structure that reacts to temperature variations. Through an evolutionary...

  4. Thermal Responsive Envelope

    DEFF Research Database (Denmark)

    Foged, Isak Worre; Pasold, Anke

    2015-01-01

    includes the calculation of bending behaviour, the calculation of perceived temperatures inside the envelope and the evolutionary module, which in a design process advance the composite structure in relation to the thermal environment desired. The research presents the methods used and developed, the way...... composite layers and their relative layer lengths thereby embedding the merged material effect to create a responsive behavioural architectural envelope. Copper and polypropylene are used as base materials for the composite structure due to their high differences in thermal expansion, surface emissivity...... alterations, their respective durability and copper’s architectural (visual and transformative) aesthetic qualities. Through the use of an evolutionary solver, the composite structure of the elements are organised to find the bending behaviour specified by and for the thermal environments. The entire model...

  5. A disk asymmetry in motion around the B[e] star MWC158

    CERN Document Server

    Kluska, J; Soulez, F; Berger, J -P; Bouquin, J -B Le; Malbet, F; Lazareff, B; Thiébaut, E

    2016-01-01

    MWC158 is a star with the B[e] phenomenon that shows strong spectrophotometric variability (in lines and in UV and visible continuum) attributed to phases of shell ejection. The evolutionary stage of this star was never clearly determined. Previous interferometric, spectropolarimetric and spectro-interferometric studies suggest a disk morphology for its environment. We investigate the origin of the variability within the inner astronomical unit of the central star using near-infrared interferometric observations with PIONIER at the VLTI over a two-year period. We performed an image reconstruction of the circumstellar environment using the SPARCO method. We discovered that the morphology of the circumstellar environment could vary on timescales of weeks or days. We carried out a parametric fit of the data with a model consisting of a star, a disk and a bright spot that represents a brighter emission in the disk. We detect strong morphological changes in the first astronomical unit around the star, that happen ...

  6. On isogeometric yield envelopes.

    OpenAIRE

    Coombs, W.M.

    2015-01-01

    In numerical analysis the failure of engineering materials is controlled through specifying yield envelopes (or surfaces) that bound the allowable stress in the material. Simple examples include the prismatic von Mises (circle) and Tresca (hexagon) yield surfaces. However, each surface is distinct and requires a specific equation describing the shape of the surface to be formulated in each case. These equations impact on the numerical implementation (specifically relating to st...

  7. Data envelopment analysis

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This review introduces the history and present status of data envelopment analysis (DEA) research, particularly the evaluation process. And extensions of some DEA models are also described. It is pointed out that mathematics, economics and management science are the main forces in the DEA development, optimization provides the fundamental method for the DEA research, and the wide range of applications enforces the rapid development of DEA.

  8. INTERNAL MAIL ENVELOPES

    CERN Multimedia

    Mail Office

    2001-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unused stock could deposit them in their mail box, after attaching them together with an elastic band or piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration.

  9. INTERNAL MAIL ENVELOPES

    CERN Multimedia

    Mail Office

    2002-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unused stock could deposit them in their mail box, after attaching them together with an elastic band or piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration. Mail Office

  10. INTERNAL MAIL ENVELOPES

    CERN Multimedia

    Mail Office

    2002-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unused stock could deposit them in their mail box, after attaching them together with an elastic band or piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration.   Mail Office

  11. INTERNAL MAIL ENVELOPES

    CERN Multimedia

    Mail Office

    2002-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unused stock could deposit them in their mail box, after attaching them together with an elastic band or piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration.

  12. URGENT - Internal Mail Envelopes

    CERN Multimedia

    2007-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unused stock could deposit them in their mail box, after attaching them together with an elastic band or piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration. Mail Office

  13. INTERNAL CIRCULATION ENVELOPES

    CERN Multimedia

    Mail Office

    2001-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unused stock could deposit them in their mail box, after attaching them together with an elastic band or a piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration.

  14. URGENT - Internal Mail Envelopes

    CERN Multimedia

    Mail Office

    2004-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unused stock could deposit them in their mail box, after attaching them together with an elastic band or piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration. Mail Office

  15. Internal mail envelopes

    CERN Multimedia

    2003-01-01

    Internal mail envelopes often finish up in large piles in certain offices, thus creating a shortage for other users of the mail service, who would be grateful if everyone with an unusual stock could deposit them in their mail box, after attaching them together with an elastic band or piece of string. The messengers will then collect them so that the Mail Office can put them back in circulation. Thank you for your understanding and collaboration. Mail Office

  16. Gaps, rings, and non-axisymmetric structures in protoplanetary disks: Emission from large grains

    Science.gov (United States)

    Ruge, J. P.; Flock, M.; Wolf, S.; Dzyurkevich, N.; Fromang, S.; Henning, Th.; Klahr, H.; Meheut, H.

    2016-04-01

    Aims: Dust grains with sizes around (sub)mm are expected to couple only weakly to the gas motion in regions beyond 10 au of circumstellar disks. In this work, we investigate the influence of the spatial distribution of these grains on the (sub)mm appearance of magnetized protoplanetary disks. Methods: We perform non-ideal global 3D magneto-hydrodynamic (MHD) stratified disk simulations, including particles of different sizes (50 μm to 1 cm), using a Lagrangian particle solver. Subsequently, we calculate the spatial dust temperature distribution, including the dynamically coupled submicron-sized dust grains, and derive ideal continuum re-emission maps of the disk through radiative transfer simulations. Finally, we investigate the feasibility of observing specific structures in the thermal re-emission maps with the Atacama Large Millimeter/submillimeter Array (ALMA). Results: Depending on the level of turbulence, the radial pressure gradient of the gas, and the grain size, particles settle to the midplane and/or drift radially inward. The pressure bump close to the outer edge of the dead-zone leads to particle-trapping in ring structures. More specifically, vortices in the disk concentrate the dust and create an inhomogeneous distribution of solid material in the azimuthal direction. The large-scale disk perturbations are preserved in the (sub)mm re-emission maps. The observable structures are very similar to those expected from planet-disk interaction. Additionally, the larger dust particles increase the brightness contrast between the gap and ring structures. We find that rings, gaps, and the dust accumulation in the vortex could be traced with ALMA down to a scale of a few astronomical units in circumstellar disks located in nearby star-forming regions. Finally, we present a brief comparison of these structures with those recently found with ALMA in the young circumstellar disks of HL Tau and Oph IRS 48.

  17. 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

  18. Synthetic Spectra and Light Curves of Interacting Binaries and Exoplanets with Circumstellar Material: SHELLSPEC

    CERN Document Server

    Budaj, Jan

    2011-01-01

    Program SHELLSPEC is designed to calculate light-curves, spectra and images of interacting binaries and extrasolar planets immersed in a moving circumstellar environment which is optically thin. It solves simple radiative transfer along the line of sight in moving media. The assumptions include LTE and optional known state quantities and velocity fields in 3D. Optional (non)transparent objects such as a spot, disc, stream, jet, ufo, shell or stars may be defined (embedded) in 3D and their composite synthetic spectrum calculated. Roche model can be used as a boundary condition for the radiative transfer. Recently a new model of the reflection effect, dust and Mie scattering were incorporated into the code. $\\epsilon$ Aurigae is one of the most mysterious objects on the sky. Prior modeling of its light-curve assumed dark, inclined, disk of dust with the central hole to explain the light-curve with a sharp mid-eclipse brightening. Our model consists of two geometrically thick flared disks. Internal optically thi...

  19. Chemistry in disks. X. The molecular content of protoplanetary disks in Taurus

    Science.gov (United States)

    Guilloteau, S.; Reboussin, L.; Dutrey, A.; Chapillon, E.; Wakelam, V.; Piétu, V.; Di Folco, E.; Semenov, D.; Henning, Th.

    2016-08-01

    Aims: We attempt to determine the molecular composition of disks around young low-mass stars. Methods: We used the IRAM 30 m radio telescope to perform a sensitive wideband survey of 30 stars in the Taurus Auriga region known to be surrounded by gaseous circumstellar disks. We simultaneously observed HCO+(3-2), HCN(3-2), C2H(3-2), CS(5-4), and two transitions of SO. We combined the results with a previous survey that observed 13CO (2-1), CN(2-1), two o-H2CO lines, and another transition of SO. We used available interferometric data to derive excitation temperatures of CN and C2H in several sources. We determined characteristic sizes of the gas disks and column densities of all molecules using a parametric power-law disk model. Our study is mostly sensitive to molecules at 200-400 au from the stars. We compared the derived column densities to the predictions of an extensive gas-grain chemical disk model under conditions representative of T Tauri disks. Results: This survey provides 20 new detections of HCO+ in disks, 18 in HCN, 11 in C2H, 8 in CS, and 4 in SO. HCO+ is detected in almost all sources and its J = 3-2 line is essentially optically thick, providing good estimates of the disk radii. The other transitions are (at least partially) optically thin. Large variations of the column density ratios are observed, but do not correlate with any specific property of the star or disk. Disks around Herbig Ae stars appear less rich in molecules than those around T Tauri stars, although the sample remains small. SO is only found in the (presumably younger) embedded objects, perhaps reflecting an evolution of the S chemistry due to increasing depletion with time. Overall, the molecular column densities, and in particular the CN/HCN and CN/C2H ratios, are well reproduced by gas-grain chemistry in cold disks. Conclusions: This study provides a comprehensive census of simple molecules in disks of radii >200-300 au. Extending that to smaller disks, or searching for less

  20. Intermediate luminosity optical transients during the grazing envelope evolution (GEE)

    CERN Document Server

    Soker, Noam

    2016-01-01

    By comparing photon diffusion time with gas outflow time, I argue that a large fraction of the energy carried by the jets during the grazing envelope evolution (GEE) might end in radiation, hence leading to an intermediate luminosity optical transient (ILOT). In the GEE a companion orbiting near the outskirts of the larger primary star accretes mass through an accretion disk, and launches jets that efficiently remove the envelope gas in the vicinity of the secondary star. In cases of high mass accretion rates onto the stellar companion the energy carried by the jets surpass the recombination energy from the ejected mass, and when the primary star is a giant this energy surpasses also the gravitational energy of the binary system. Some future ILOTs of giant stars might be better explained by the GEE than by merger and common envelope evolution without jets.

  1. Intermediate luminosity optical transients during the grazing envelope evolution (GEE)

    Science.gov (United States)

    Soker, Noam

    2016-08-01

    By comparing photon diffusion time with gas outflow time, I argue that a large fraction of the energy carried by the jets during the grazing envelope evolution (GEE) might end in radiation, hence leading to an intermediate luminosity optical transient (ILOT). In the GEE a companion orbiting near the outskirts of the larger primary star accretes mass through an accretion disk, and launches jets that efficiently remove the envelope gas from the vicinity of the secondary star. In cases of high mass accretion rates onto the stellar companion the energy carried by the jets surpass the recombination energy from the ejected mass, and when the primary star is a giant this energy surpasses also the gravitational binding energy of the binary system. Some future ILOTs of giant stars might be better explained by the GEE than by merger and common envelope evolution without jets.

  2. CO gas inside the protoplanetary disk cavity in HD 142527: disk structure from ALMA

    CERN Document Server

    Perez, Sebastian; Ménard, F; Roman, P; van der Plas, G; Cieza, L; Pinte, C; Christiaens, V; Hales, A S

    2014-01-01

    Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends up to 140 au from the central star, as seen in continuum images at infrared and millimeter wavelengths. Estimates of the survival of gas inside disk cavities are needed to discriminate between clearing scenarios. We present a spatially and spectrally resolved carbon monoxide isotopologue observations of the gas-rich disk HD 142527, in the J=2-1 line of 12CO, 13CO and C18O, obtained with the Atacama Large Millimeter Array (ALMA). We detect emission coming from inside the dust-depleted cavity in all three isotopologues. Based on our analysis of the gas in the dust cavity, the 12CO emission is optically thick, while 13CO and C18O emission are both optically thin. The total mass of residual gas inside the cavity is about 1.5-2 Jupiter masses. We model the gas with an axisymmetric disk model. Our best fit model shows t...

  3. Secure Disk Mixed System

    Directory of Open Access Journals (Sweden)

    Myongchol Ri

    2013-01-01

    Full Text Available 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 limitations of existing disk encryption methods and to control security performance flexibly according to the security requirement of system.

  4. Observations of ``Gas-Rich'' Disks

    Science.gov (United States)

    Ménard, François

    2004-06-01

    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 the mystery of the formation of our Solar System. This chapter focuses on observational studies 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 typical star forming regions (e.g., ~140pc for Taurus), a planetary system like ours (with diameter ~= 50AU out to Pluto, but excluding the Kuiper belt) 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 I will attempt to give an overview of the structural and physical parameters of protoplanetary disks that can be estimated today from direct observations.

  5. Uncertain data envelopment analysis

    CERN Document Server

    Wen, Meilin

    2014-01-01

    This book is intended to present the milestones in the progression of uncertain Data envelopment analysis (DEA). Chapter 1 gives some basic introduction to uncertain theories, including probability theory, credibility theory, uncertainty theory and chance theory. Chapter 2 presents a comprehensive review and discussion of basic DEA models. The stochastic DEA is introduced in Chapter 3, in which the inputs and outputs are assumed to be random variables. To obtain the probability distribution of a random variable, a lot of samples are needed to apply the statistics inference approach. Chapter 4

  6. THE LONG-TERM EVOLUTION OF PHOTOEVAPORATING PROTOPLANETARY DISKS

    International Nuclear Information System (INIS)

    We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting for ∼wall plane, which possibly explains the different observed properties between the two populations. However, we further find that scaling the photoevaporation rates downward by a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of the photoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii of the order of 10 AU

  7. Chemical evolution of circumstellar matter around young stellar objects

    Science.gov (United States)

    van Dishoeck, E. F.; Blake, G. A.

    1995-01-01

    Recent observational studies of the chemical composition of circumstellar matter around both high- and low-mass young stellar objects are reviewed. The molecular abundances are found to be a strong function of evolutionary state, but not of system mass or luminosity. The data are discussed with reference to recent theoretical models.

  8. Circumstellar and explosion properties of Type Ibn supernovae

    CERN Document Server

    Moriya, Takashi J

    2016-01-01

    We investigate circumstellar and explosion properties of Type Ibn supernovae (SNe) by analyzing their bolometric light curves. Bolometric light curves of Type Ibn SNe generally have a large contrast between peak luminosity and late-phase luminosity, which is much larger than those of 56Ni-powered SNe. Thus, most of them are likely powered by the interaction between SN ejecta and dense circumstellar media. In addition, Type Ibn SNe decline much faster than Type IIn SNe, and this indicates that the interaction in Type Ibn SNe ceases earlier than in Type IIn SNe. Thus, we argue that Type Ibn SN progenitors experience high mass-loss rates in a short period just before explosion, while Type IIn SN progenitors have high mass-loss rates sustained for a long time. Furthermore, we show that rise time and peak luminosity of Type Ibn and Type IIn SNe are similar and thus, they have similar explosion properties and circumstellar density. The similar circumstellar density in the two kinds of SNe may indicate that mass-los...

  9. Physical properties of Be star envelopes from Balmer and Fe II emission lines

    Science.gov (United States)

    Slettebak, Arne; Collins, George W., II; Truax, Ryland

    1992-07-01

    The study obtains H-alpha, B-beta, H-gamma, and Fe II 6516 line profiles with resolution 0.45 A for 41 bright Be stars with a CCD detonator during two observing periods in 1989. Analysis of the structure of the emission profiles indicates that the Be star emitting envelope is most likely axially symmetric, consistent with a rotating, equatorial disk. A number of Be stars show either a 'wine bottle' structure or inflection points on one side of their H-alpha emission profiles, suggesting a two-component structure for the emitting envelope: an inner disk, possibly turbulent, and an outer extended disk. Differentially rotating disks producing weak H-alpha emission are closer to the central star where rotation broadens the line more strongly, relative to stars with extended envelopes which emit strongly but rotate more slowly. From the Balmer emission decrements it is found that Be star envelopes with Te near 10,000 K have electron densities in the range 10 exp 11 to 10 exp 13/cu cm. Be stars with weak Balmer emission have, on average, somewhat flatter Balmer decrements than stars with strong emission, suggesting envelopes with higher electron densities.

  10. Dippers and Dusty Disks Edges: A Unified Model

    CERN Document Server

    Bodman, Eva H L; Ansdell, Megan; Hippke, Michael; Boyajian, Tabetha S; Mamajek, Eric E; Blackman, Eric G; Rizzuto, Aaron; Kastner, Joel H

    2016-01-01

    A search for dips in observed stellar flux in the Upper Scorpius and $\\rho$ Ophiuchus star formation regions with the Kepler mission by Ansdell et al. primarily identified young, low mass stars (dippers) with low accretion rates and hosting moderately evolved dusty circumstellar disks. These young stars likely exhibit rotating star spots that cause quasi-periodic photometric variations. However, a separate period associated with the dips is not evident in spectrograms constructed from the light curves. The material causing the dips in most of these light curves must be approximately corotating with the star. We find that disk temperatures computed at the disk corotation radius are cool enough that dust should not sublimate. Dippers are preferentially associated with young, low mass stars as they have low enough luminosities to allow dust to survive within a few stellar radii. Crude estimates for stellar magnetic field strengths and accretion rates are consistent with magnetospheric truncation near the corotat...

  11. Metamorphosis of SN 2014C: Delayed Interaction Between a Hydrogen Poor Core-collapse Supernova and a Nearby Circumstellar Shell

    CERN Document Server

    Milisavljevic, D; Kamble, A; Patnaude, D; Raymond, J; Eldridge, J; Fong, W; Bietenholz, M; Challis, P; Chornock, R; Drout, M; Fransson, C; Fesen, R; Grindlay, J; Kirshner, R; Lunnan, R; Mackey, J; Miller, G; Parrent, J; Sanders, N; Soderberg, A; Zauderer, B

    2015-01-01

    We present optical observations of supernova SN 2014C, which underwent an unprecedented slow metamorphosis from H-poor type Ib to H-rich type IIn over the course of one year. The observed spectroscopic evolution is consistent with the supernova having exploded in a cavity before encountering a massive shell of the progenitor star's stripped hydrogen envelope. Possible origins for the circumstellar shell include a brief Wolf-Rayet fast wind phase that overtook a slower red supergiant wind, eruptive ejection, or confinement of circumstellar material by external influences of neighboring stars. An extended high velocity Halpha absorption feature seen in near-maximum light spectra implies that the progenitor star was not completely stripped of hydrogen at the time of core collapse. Archival pre-explosion Subaru Telescope Suprime-Cam and Hubble Space Telescope Wide Field Planetary Camera 2 images of the region obtained in 2009 show a coincident source that is most likely a compact massive star cluster in NGC 7331 ...

  12. 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).

  13. 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)

  14. A cavity and further radial substructures in the disk around HD~97048

    CERN Document Server

    van der Plas, G; Ménard, F; Casassus, S; Canovas, H; Pinte, C; Maddison, S T; Maaskant, K; Avenhaus, H; Cieza, L; Perez, S; Ubach, C

    2016-01-01

    Context: Gaps, cavities and rings in circumstellar disks are signposts of disk evolution and planet-disk interactions. We follow the recent suggestion that Herbig Ae/Be disks with a flared disk harbour a cavity, and investigate the disk around HD~97048. Aims: We aim to resolve the 34$\\pm$ 4 au central cavity predicted by Maaskant et al. (2013) and to investigate the structure of the disk. Methods: We image the disk around HD~97048 using ALMA at 0.85~mm and 2.94~mm, and ATCA (multiple frequencies) observations. Our observations also include the 12CO J=1-0, 12CO J=3-2 and HCO+ J=4-3 emission lines. Results: A central cavity in the disk around HD~97048 is resolved with a 40-46 au radius. Additional radial structure present in the surface brightness profile can be accounted for either by an opacity gap at ~90 au or by an extra emitting ring at ~150 au. The continuum emission tracing the dust in the disk is detected out to 355 au. The 12CO J=3-2 disk is detected 2.4 times farther out. The 12CO emission can be trac...

  15. Morphology and kinematics of the gas envelope of the Mira binary W Aquilae

    OpenAIRE

    Hoai, D. T.; Nhung, P. T.; Diep, P. N.; Phuong, N. T.; Tuan-Anh, P.; Thao, N. T.; Darriulat, P.

    2016-01-01

    We analyse ALMA observations of the 12CO(3-2) emission of the circumstellar envelope (CSE) of the Mira variable binary star W Aql. These provide, for the first time, spatially resolved Doppler velocity spectra of the CSE up to angular distances to the central star of ~ 5" (meaning some 2000 AU). The exploratory nature of the observations (only five minutes in each of two different configurations) does not allow for a detailed modelling of the properties of the CSE but provides important quali...

  16. 41Ca in Circumstellar Graphite from Supernovae

    Science.gov (United States)

    Amari, S.; Zinner, E.; Lewis, R. S.

    1995-09-01

    anomalies (Fig. 1), with patterns that are consistent with that predicted for the O-rich zones of a 25 (sub)Solar Mass supernova [4] (shown as broad lines in the figure). Thus, ^41Ca in these two grains is likely to have been produced by neutron capture in these zones. One grain (KE3c-242) has a ^44Ca excess due to the decay of ^44Ti (T(sub)1/2=52a), with an inferred ^44Ti/^48Ti ratio of (3.6+/-1.4) x 10^-2. The presence of ^41Ca together with Ca isotopic anomalies in circumstellar graphite grains is evidence for mixing between the C-rich and O-rich zones. Furthermore, evidence for ^44Ti in a few low density graphite grains [6] strongly suggests contributions from the innermost zone to the ejecta from which the grains formed. Observations of SN 1987A [e.g., 7] and hydrodynamic calculations [e.g., 8] indicate the existence of clumps of variable compositions in SN ejecta. The large variety of isotopic compositions in low density graphite grains is evidence for extensive and heterogeneous mixing of SN ejecta, confirming the astronomical observations and the theoretical calculations. References: [1] Amari S. et al. (1994) LPS XXV, 27-28. [2] Zinner E. et al. (1995) LPS XXVI, 1561-1562. [3] Travaglio C. et al. (1995) in preparation. [4] Meyer B. S. et al. (1995) Meteoritics, 30, 319-324. [5] Woosley S. E. and Weaver T. A. (1995) Astrophys. J. Suppl., in press. [6] Amari S. et al. (1995) LPS XXVI, 37-38. [7] Hass M. R. et al. (1990) Astrophys. J., 360, 257-266. [8] Herant M. and Benz W. (1992) Astrophys. J., 387, 294-308.

  17. The Circumstellar Environment of R Coronae Borealis: White Dwarf Merger or Final Helium Shell Flash?

    CERN Document Server

    Clayton, Geoffrey C; Stanford, S Adam; Whitney, B A; Honor, J; Babler, B; Barlow, M J; Gordon, K D; Andrews, J E; Geballe, T R; Bond, Howard E; De Marco, O; Lawson, W A; Sibthorpe, B; Olofsson, G; Polehampton, E; Gomez, H L; Matsuura, M; Hargrave, P C; Ivison, R J; Wesson, R; Leeks, S J; Swinyard, B M; Lim, T L

    2011-01-01

    In 2007, R Coronae Borealis (R CrB) went into an 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 micron with Gemini/GMOS, HST/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 micron. The SED of R CrB can be well fit 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^-4 and 10^2 M(Sun), respectively, assuming a gas-to-dust ratio ...

  18. Circumstellar Dust Shells: Clues to the Evolution of R Coronae Borealis Stars

    Science.gov (United States)

    Montiel, Edward J.; Clayton, Geoffrey C.

    2016-06-01

    R Coronae Borealis (RCB) stars are an exotic group of extremely hydrogen- deficient, carbon-rich supergiants that are known for their spectacular declines in brightness (up to 8 mags) at irregular intervals. Two scenarios are currently competing to explain the origins of these stars. One suggests that RCB stars are the products after a binary white dwarf (WD) system merges. The other takes a single, evolved star and has it undergo a final, helium-shell flash (FF) and becoming a cool giant. Recently, observations of elemental abundances in RCB stars have strongly swung the argument in favor of the WD merger model. The FF scenario has maintained its relevancy by seemingly being the only model able to offer a suitable explanation for one RCB feature that merger model has historically struggled with explaining: the presence of cold, circumstellar dust envelopes which might be fossil planetary nebulae (PNe). In reality, the shells could actually be fossil PNe, material left over from the WD merger, or mass lost during the RCB phase, itself. I will present the results of my dissertation, which is to try and discern the nature and history of the far-IR dust shells around RCB stars to help understand the origin of these enigmatic stars. I will discuss our efforts to determine the mass, size, temperature, and morphology of these diffuse structures surrounding a sample of RCB stars using multi-wavelength observations ranging from the ultraviolet to the submillimeter. These observations have provided unprecedented wavelength coverage for both the central stars and their CSM. They have been examined by eye for morphology and have been used in the construction of maximum-light spectral energy distributions (SEDs). I will present the results of our Monte Carlo radiative transfer of the maximum-light SEDs. Finally, I will highlight our work investigating the HI abundance of the envelope of R Coronae Borealis, itself, using archival 21—cm observations from the Arecibo

  19. Adaptive Architectural Envelope

    DEFF Research Database (Denmark)

    Foged, Isak Worre; Kirkegaard, Poul Henning

    2010-01-01

    Recent years have seen an increasing variety of applications of adaptive architectural structures for improvement of structural performance by recognizing changes in their environments and loads, adapting to meet goals, and using past events to improve future performance or maintain serviceability....... The general scopes of this paper are to develop a new adaptive kinetic architectural structure, particularly a reconfigurable architectural structure which can transform body shape from planar geometries to hyper-surfaces using different control strategies, i.e. a transformation into more than one or...... two different shape alternatives. The adaptive structure is a proposal for a responsive building envelope which is an idea of a first level operational framework for present and future investigations towards performance based responsive architectures through a set of responsive typologies. A mock- up...

  20. Formation of Jupiter's Core and Early Stages of Envelope Accretion

    Science.gov (United States)

    D'Angelo, G.; Weidenschilling, S.; Lissauer, J. J.; Bodenheimer, P.; Hubickyj, O.

    2012-12-01

    We are performing calculations of the formation of Jupiter via core nucleated accretion and gas capture. The core starts as a seed body of a few hundred kilometers in radius and orbits within a swarm of planetesimals whose initial size distribution ranges from ~10 m to ~100 km. The planetesimals are immersed in a gaseous disk, representative of an early solar nebula. The evolution of the swarm of planetesimals accounts for collisions and gravitational stirring due to mutual interactions among bodies, and for migration and velocity damping due to interactions with the nebula gas. Collisions among planetesimals lead to growth and/or fragmentation, altering the size distribution of the swarm over time. Collisions of planetesimals with the seed body lead to its growth, resulting in the formation of a planetary core. Gas capture by the core leads to the accumulation of a tenuous atmosphere, which later becomes a massive envelope, increasing the size-dependent effective cross-section of the planet for planetesimals' accretion. Planetesimals that travel through the core's envelope release energy, affecting the thermal budget of the envelope, and deliver mass, affecting the opacity of the envelope. The calculation of dust opacity, which is especially important for envelope contraction, is performed self-consistently, accounting for coagulation and sedimentation of dust and small particles that are released in the envelope as passing planetesimals are ablated. We find that, in a disk of planetesimals with a surface density of about 10 g/cm2 at 5.2 AU, a one Earth mass core accumulates in less than 1e5 years, and that it takes over 1.5e6 years to accumulate a core of 3 Earth masses, when the core's geometrical cross-section is used for the accretion of planetesimals. Gas drag in the core's envelope increases the ability of the planet to accrete planetesimals. Smaller planetesimals are affected to a greater extent than are larger planetesimals. We find that the effective

  1. Categories with envelopes and imprints

    CERN Document Server

    Akbarov, Sergei

    2011-01-01

    An envelope in a category is a construction generalizing operations of "exterior completion", like completion of a locally convex space. Dually, an imprint generalizes operations of "interior enrichment", like saturation of a locally convex space. We give abstract definition for envelopes and imprints, prove existence of these objects in the categories of stereotype spaces and of stereotype algebras, and give some examples.

  2. First Results from the Disk Eclipse Search with KELT (DESK) Survey

    CERN Document Server

    Rodriguez, Joseph E; Stassun, Keivan G

    2015-01-01

    Using time-series photometry from the Kilodegree Extremely Little Telescope (KELT) exoplanet survey, we are looking for eclipses of stars by their protoplanetary disks, specifically in young stellar associations. To date, we have discovered two previously unknown, large dimming events around the young stars RW Aurigae and V409 Tau. We attribute the dimming of RW Aurigae to an occultation by its tidally disrupted disk, with the disruption perhaps resulting from a recent flyby of its binary companion. Even with the dynamical environment of RW Aurigae, the distorted disk material remains very compact and presumably capable of forming planets. This system also shows that strong binary interactions with disks can also influence planet and core composition by stirring up and mixing materials during planet formation. We interpret the dimming of V409 Tau to be due to a feature, possibly a warp or perturbation, lying at least 10 AU from the host star in its nearly edge-on circumstellar disk.

  3. Rings of C2H in the Molecular Disks Orbiting TW Hya and V4046 Sgr

    CERN Document Server

    Kastner, J H; Gorti, U; Hily-Blant, P; Oberg, K; Forveille, T; Andrews, S; Wilner, D

    2015-01-01

    We have used the Submillimeter Array to image, at ~1" resolution, C2H(3-2) emission from the molecule-rich circumstellar disks orbiting the nearby, classical T Tauri star systems TW Hya and V4046 Sgr. The SMA imaging reveals that the C2H emission exhibits a ring-like morphology within each disk, the inner hole radius of the C2H ring within the V4046 Sgr disk (~70 AU) is somewhat larger than than of its counterpart within the TW Hya disk (~45 AU). We suggest that, in each case, the C2H emission likely traces irradiation of the tenuous surface layers of the outer disks by high-energy photons from the central stars.

  4. Cold CO gas in the disk of the young eruptive star EX Lup

    CERN Document Server

    Kóspál, Ágnes; Csengeri, Timea; Gorti, Uma; Henning, Thomas; Moór, Attila; Semenov, Dmitry A; Szűcs, László; Güsten, Rolf

    2016-01-01

    EX Lupi-type objects (EXors) form a sub-class of T Tauri stars, defined by sudden sporadic flare-ups of 1-5 magnitudes at optical wavelengths. These eruptions are attributed to enhanced mass accretion from the circumstellar disk to the star, and may constitute important events in shaping the structure of the inner disk and the forming planetary system. Although disk properties must play a fundamental role in driving the outbursts, they are surprisingly poorly known. In order to characterize the dust and gas components of EXor disks, here we report on observations of the $^{12}$CO J=3-2 and 4-3 lines, and the $^{13}$CO 3-2 line in EX Lup, the prototype of the EXor class. We reproduce the observed line fluxes and profiles with a line radiative transfer model, and compare the obtained parameters with corresponding ones of other T Tauri disks.

  5. Cold CO Gas in the Disk of the Young Eruptive Star EX Lup

    Science.gov (United States)

    Kóspál, Á.; Ábrahám, P.; Csengeri, T.; Gorti, U.; Henning, Th.; Moór, A.; Semenov, D. A.; Szűcs, L.; Güsten, R.

    2016-04-01

    EX Lupi-type objects (EXors) form a sub-class of T Tauri stars, defined by sudden sporadic flare-ups of 1–5 mag at optical wavelengths. These eruptions are attributed to enhanced mass accretion from the circumstellar disk to the star, and may constitute important events in shaping the structure of the inner disk and the forming planetary system. Although disk properties must play a fundamental role in driving the outbursts, they are surprisingly poorly known. In order to characterize the dust and gas components of EXor disks, here we report on observations of the 12CO J = 3‑2 and 4–3 lines, and the 13CO 3–2 line in EX Lup, the prototype of the EXor class. We reproduce the observed line fluxes and profiles with a line radiative transfer model and compare the obtained parameters with corresponding ones of other T Tauri disks.

  6. Observations, Modeling and Theory of Debris Disks

    CERN Document Server

    Matthews, Brenda C; Wyatt, Mark C; Bryden, Geoff; Eiroa, Carlos

    2014-01-01

    Main sequence stars, like the Sun, are often found to be orbited by circumstellar material that can be categorized into two groups, planets and debris. The latter is made up of asteroids and comets, as well as the dust and gas derived from them, which makes debris disks observable in thermal emission or scattered light. These disks may persist over Gyrs through steady-state evolution and/or may also experience sporadic stirring and major collisional breakups, rendering them atypically bright for brief periods of time. Most interestingly, they provide direct evidence that the physical processes (whatever they may be) that act to build large oligarchs from micron-sized dust grains in protoplanetary disks have been successful in a given system, at least to the extent of building up a significant planetesimal population comparable to that seen in the Solar System's asteroid and Kuiper belts. Such systems are prime candidates to host even larger planetary bodies as well. The recent growth in interest in debris dis...

  7. LABORATORY INVESTIGATIONS OF POLYCYCLIC AROMATIC HYDROCARBON FORMATION AND DESTRUCTION IN THE CIRCUMSTELLAR OUTFLOWS OF CARBON STARS

    International Nuclear Information System (INIS)

    The formation and destruction mechanisms of interstellar dust analogs formed from a variety of polycyclic aromatic hydrocarbon (PAH) and hydrocarbon molecular precursors are studied in the laboratory. We used the newly developed facility COSmIC, which simulates interstellar and circumstellar environments, to investigate both PAHs and species that include the cosmically abundant atoms O, N, and S. The species generated in a discharge plasma are detected, monitored, and characterized in situ using highly sensitive techniques that provide both spectral and ion mass information. We report here the first series of measurements obtained in these experiments which focus on the characterization of the most efficient molecular precursors in the chemical pathways that eventually lead to the formation of carbonaceous grains in the stellar envelopes of carbon stars. We compare and discuss the relative efficiencies of the various molecular precursors that lead to the formation of the building blocks of carbon grains. We discuss the most probable molecular precursors in terms of size and structure and the implications for the expected growth and destruction processes of interstellar carbonaceous dust

  8. LABORATORY INVESTIGATIONS OF POLYCYCLIC AROMATIC HYDROCARBON FORMATION AND DESTRUCTION IN THE CIRCUMSTELLAR OUTFLOWS OF CARBON STARS

    Energy Technology Data Exchange (ETDEWEB)

    Contreras, Cesar S.; Salama, Farid, E-mail: cesar.contreras@nasa.gov, E-mail: Farid.Salama@nasa.gov [Space Science and Astrobiology Division, NASA-Ames Research Center, Moffett Field, CA 94035 (United States)

    2013-09-15

    The formation and destruction mechanisms of interstellar dust analogs formed from a variety of polycyclic aromatic hydrocarbon (PAH) and hydrocarbon molecular precursors are studied in the laboratory. We used the newly developed facility COSmIC, which simulates interstellar and circumstellar environments, to investigate both PAHs and species that include the cosmically abundant atoms O, N, and S. The species generated in a discharge plasma are detected, monitored, and characterized in situ using highly sensitive techniques that provide both spectral and ion mass information. We report here the first series of measurements obtained in these experiments which focus on the characterization of the most efficient molecular precursors in the chemical pathways that eventually lead to the formation of carbonaceous grains in the stellar envelopes of carbon stars. We compare and discuss the relative efficiencies of the various molecular precursors that lead to the formation of the building blocks of carbon grains. We discuss the most probable molecular precursors in terms of size and structure and the implications for the expected growth and destruction processes of interstellar carbonaceous dust.

  9. Diffraction-limited ten micron imaging of circumstellar dust with a detector array

    International Nuclear Information System (INIS)

    An imaging system was constructed that achieves diffraction-limited spatial resolution (about 0.6'') at a wavelength of 10 μm on large telescopes. The system uses an array of 25 photovoltaic detectors in the focal plane, arranged along two crossed arms. The very small physical size of individual detectors, and the use of drift scans with a stationary telescope, permit reliable imaging on a spatial scale not easily probed before. Several broad-band interference filters (with Δlambda/lambda approx. = 0.1) permit imaging on and off the 9.7 μm spectral feature due to silicate dust particles. The array system was used to map the circumstellar dust envelopes of several late-type stars, including α Scorpii, α Orionis, and IRC + 10216. The first two objects, oxygen-rich type M supergiants, show faint extended emission around an unresolved stellar photosphere which dominates the surface brightness. Particularly accurate east-west profiles of the brightness distributions are obtained, and in the case of α Orionis a distinct east-west asymmetry was observed in February 1983. This asymmetry, to which previous interferometric imaging techniques would not have been sensitive, apparently indicated the presence of a bright discrete cloud about 0.9'' to the west of the photosphere, superimposed on fainter, more extended thermal radiation from dust. Observation of this source one year later revealed a substantial decline in the flux from the discrete cloud, by a factor of at least two

  10. Sculpting the disk around T Cha: an interferometric view

    CERN Document Server

    Olofsson, Johan; Bouquin, Jean-Baptiste Le; Berger, Jean-Philippe; Lacour, Sylvestre; Ménard, François; Henning, Thomas; Crida, Aurélien; Burtscher, Leonard; Meeus, Gwendolyn; Ratzka, Thorsten; Pinte, Christophe; Augereau, Jean-Charles; Malbet, Fabien; Lazareff, Bernard; Traub, Wesley A

    2013-01-01

    (Abridged) Circumstellar disks are believed to be the birthplace of planets and are expected to dissipate on a timescale of a few Myr. The processes responsible for the removal of the dust and gas will strongly modify the radial distribution of the dust and consequently the SED. In particular, a young planet will open a gap, resulting in an inner disk dominating the near-IR emission and an outer disk emitting mostly in the far-IR. We analyze a full set of data (including VLTI/Pionier, VLTI/Midi, and VLT/NaCo/Sam) to constrain the structure of the transition disk around TCha. We used the Mcfost radiative transfer code to simultaneously model the SED and the interferometric observations. We find that the dust responsible for the emission in excess in the near-IR must have a narrow temperature distribution with a maximum close to the silicate sublimation temperature. This translates into a narrow inner dusty disk (0.07-0.11 AU). We find that the outer disk starts at about 12 AU and is partially resolved by the P...

  11. VLT imaging of the {\\beta} Pictoris gas disk

    CERN Document Server

    Nilsson, R; Olofsson, G; Fathi, K; Thébault, Ph; Liseau, R

    2012-01-01

    Circumstellar debris disks older than a few Myr should be largely devoid of primordial gas remaining from the protoplanetary disk phase. Tracing the origin of observed atomic gas in Keplerian rotation in the edge-on debris disk surrounding the ~12 Myr old star {\\beta} Pictoris requires more detailed information about its spatial distribution than has previously been acquired by limited slit spectroscopy. Especially indications of asymmetries and presence of Ca II gas at high disk latitudes call for additional investigation. We set out to recover a complete image of the Fe I and Ca II gas emission around {\\beta} Pic by spatially resolved, high-resolution spectroscopic observations to better understand the morphology and origin of the gaseous disk component. The multiple fiber facility FLAMES/GIRAFFE at the VLT, with the large IFU ARGUS, was used to obtain spatially resolved optical spectra in four regions covering the northeast and southwest side of the disk. Emission lines from Fe I and Ca II were mapped and ...

  12. Debris disks: seeing dust, thinking of planetesimals and planets

    Institute of Scientific and Technical Information of China (English)

    Alexander V.Krivov

    2010-01-01

    Debris disks are optically thin, almost gas-free dusty disks observed around a significant fraction of main-sequence stars older than about 10Myr. Since the circumstellar dust is short-lived, the very existence of these disks is considered as evidence that dust-producing planetesimals are still present in mature systems, in which planets have formed-or failed to form-a long time ago. It is inferred that these planetesimals orbit their host stars at asteroid to Kuiper-belt distances and continually supply fresh dust through mutual collisions. This review outlines observational techniques and results on debris disks, summarizes their essential physics and theoretical models, and then places them into the general context of planetary systems, uncovering interrelations between the disks, dust parent bodies, and planets. It is shown that debris disks can serve as tracers of planetesimals and planets and shed light on the planetesimal and planet formation processes that operated in these systems in the past.

  13. Discovery of an Inner Disk Component around HD 141569 A

    Science.gov (United States)

    Konishi, Mihoko; Grady, Carol A.; Schneider, Glenn; Shibai, Hiroshi; McElwain, Michael W.; Nesvold, Erika R.; Kuchner, Marc J.; Carson, Joseph; Debes, John. H.; Gaspar, Andras; Henning, Thomas K.; Hines, Dean C.; Hinz, Philip M.; Jang-Condell, Hannah; Moro-Martín, Amaya; Perrin, Marshall; Rodigas, Timothy J.; Serabyn, Eugene; Silverstone, Murray D.; Stark, Christopher C.; Tamura, Motohide; Weinberger, Alycia J.; Wisniewski, John. P.

    2016-02-01

    We report the discovery of a scattering component around the HD 141569 A circumstellar debris system, interior to the previously known inner ring. The discovered inner disk component, obtained in broadband optical light with Hubble Space Telescope/Space Telescope Imaging Spectrograph coronagraphy, was imaged with an inner working angle of 0.″25, and can be traced from 0.″4 (∼46 AU) to 1.″0 (∼116 AU) after deprojection using i = 55°. The inner disk component is seen to forward scatter in a manner similar to the previously known rings, has a pericenter offset of ∼6 AU, and break points where the slope of the surface brightness changes. It also has a spiral arm trailing in the same sense as other spiral arms and arcs seen at larger stellocentric distances. The inner disk spatially overlaps with the previously reported warm gas disk seen in thermal emission. We detect no point sources within 2″ (∼232 AU), in particular in the gap between the inner disk component and the inner ring. Our upper limit of 9 ± 3 MJ is augmented by a new dynamical limit on single planetary mass bodies in the gap between the inner disk component and the inner ring of 1 MJ, which is broadly consistent with previous estimates. Based on data collected by the Hubble Space Telescope, operated by the Space Telescope Science Institute.

  14. Discovery of an Inner Disk Component Around HD 141569 A

    Science.gov (United States)

    Konishi, Mihoko; Grady, Carol A.; Schneider, Glenn; Shibai, Hiroshi; McElwain, Michael W.; Nesvold, Erika R.; Kuchner, Marc J.; Carson, Joseph; Debes, John H.; Gaspar, Andras; Serabyn, Eugene

    2016-01-01

    We report the discovery of a scattering component around the HD 141569 A circumstellar debris system, interior to the previously known inner ring. The discovered inner disk component, obtained in broadband optical light with Hubble Space Telescope/Space Telescope Imaging Spectrograph coronagraphy, was imaged with an inner working angle of 0 25 arcseconds, and can be traced from 0 4 seconds (approximately 46 atomic units) to 1.0 arcseconds (approximately 116 atomic units) after deprojection using inclination = 55 degrees. The inner disk component is seen to forward scatter in a manner similar to the previously known rings, has a pericenter offset of approximately 6 atomic units, and break points where the slope of the surface brightness changes. It also has a spiral arm trailing in the same sense as other spiral arms and arcs seen at larger stellocentric distances. The inner disk spatially overlaps with the previously reported warm gas disk seen in thermal emission. We detect no point sources within 2 arcseconds (approximately 232 atomic units), in particular in the gap between the inner disk component and the inner ring. Our upper limit of 9 plus or minus 3 mass Jupiter (M (sub J)) is augmented by a new dynamical limit on single planetary mass bodies in the gap between the inner disk component and the inner ring of 1 mass Jupiter, which is broadly consistent with previous estimates.

  15. The Importance of Disk Structure in Stalling Type I Migration

    CERN Document Server

    Kretke, Katherine A

    2012-01-01

    As planets form they tidally interact with their natal disks. Though the tidal perturbation induced by Earth and super-Earth mass planets is generally too weak to significantly modify the structure of the disk, the interaction is potentially strong enough to cause the planets to undergo rapid type I migration. This physical process may provide a source of short-period super-Earths, though it may also pose a challenge to the emergence and retention of cores on long-period orbits with sufficient mass to evolve into gas giants. Previous numerical simulations have shown that the type I migration rate sensitively depends upon the circumstellar disk's properties, particularly the temperature and surface density gradients. Here, we derive these structure parameters for 1) a self-consistent viscous-disk model based on a constant \\alpha-prescription, 2) an irradiated disk model that takes into account heating due to the absorption of stellar photons, and 3) a layered-accretion disk model with variable \\alpha-parameter...

  16. A Spitzer view of protoplanetary disks in the gamma Velorum cluster

    CERN Document Server

    Hernandez, Jesus; Calvet, Nuria; Jeffries, R D; Gutermuth, R; Muzerolle, J; Stauffer, J

    2008-01-01

    We present new Spitzer Space Telescope observations of stars in the young ~5 Myr gamma Velorum stellar cluster. Combining optical and 2MASS photometry, we have selected 579 stars as candidate members of the cluster. With the addition of the Spitzer mid-infrared data, we have identified 5 debris disks around A-type stars, and 5-6 debris disks around solar-type stars, indicating that the strong radiation field in the cluster does not completely suppress the production of planetesimals in the disks of cluster members. However, we find some evidence that the frequency of circumstellar primordial disks is lower, and the IR flux excesses are smaller than for disks around stellar populations with similar ages. This could be evidence for a relatively fast dissipation of circumstellar dust by the strong radiation field from the highest mass star(s) in the cluster. Another possibility is that gamma Velorum stellar cluster is slightly older than reported ages and the the low frequency of primordial disks reflects the fa...

  17. Direct detection of scattered light gaps in the transitional disk around HD 97048 with VLT/SPHERE

    CERN Document Server

    Ginski, C; Pinilla, P; Dominik, C; Boccaletti, A; de Boer, J; Benisty, M; Biller, B; Feldt, M; Garufi, A; Keller, C U; Kenworthy, M; Maire, A L; Ménard, F; Mesa, D; Milli, J; Min, M; Pinte, C; Quanz, S P; van Boekel, R; Bonnefoy, M; Chauvin, G; Desidera, S; Gratton, R; Girard, J H V; Keppler, M; Kopytova, T; Lagrange, A -M; Langlois, M; Rouan, D; Vigan, A

    2016-01-01

    We studied the well known circumstellar disk around the Herbig Ae/Be star HD 97048 with high angular resolution to reveal undetected structures in the disk, which may be indicative of disk evolutionary processes such as planet formation. We used the IRDIS near-IR subsystem of the extreme adaptive optics imager SPHERE at the ESO/VLT to study the scattered light from the circumstellar disk via high resolution polarimetry and angular differential imaging. We imaged the disk in unprecedented detail and revealed four ring-like brightness enhancements and corresponding gaps in the scattered light from the disk surface with radii between 39 au and 341 au. We derived the inclination and position angle as well as the height of the scattering surface of the disk from our observational data. We found that the surface height profile can be described by a single power law up to a separation ~270 au. Using the surface height profile we measured the scattering phase function of the disk and found that it is well consistent ...

  18. The conducting disk, revisited

    DEFF Research Database (Denmark)

    Karlsson, Per W.

    1999-01-01

    The classical formula for the charge distribution on a conducting circular disk is proved by establishing the constancy of the potential on the disk, utilizing known properties of hypergeometric functions......The classical formula for the charge distribution on a conducting circular disk is proved by establishing the constancy of the potential on the disk, utilizing known properties of hypergeometric functions...

  19. The conducting disk, revisited

    DEFF Research Database (Denmark)

    Karlsson, Per W.

    2000-01-01

    The classical formula for the charge distribution on a conducting disk is proved by establishing the constancy of the potential on the disk, utilizing known properties of hypergeometric functions.......The classical formula for the charge distribution on a conducting disk is proved by establishing the constancy of the potential on the disk, utilizing known properties of hypergeometric functions....

  20. A CO survey in planet-forming disks: characterizing the gas content in the epoch of planet formation

    CERN Document Server

    Hales, A S; Montesinos, B; Casassus, S; Dent, W F R; Dougados, C; Eiroa, C; Hughes, A M; Garay, G; Mardones, D; Ménard, F; Palau, Aina; Pérez, S; Phillips, N; Torrelles, J M; Wilner, D

    2014-01-01

    We carried out a 12CO(3-2) survey of 52 southern stars with a wide range of IR excesses (LIR/L*) using the single dish telescopes APEX and ASTE. The main aims were (1) to characterize the evolution of molecular gas in circumstellar disks using LIR/L* values as a proxy of disk dust evolution, and (2) to identify new gas-rich disk systems suitable for detailed study with ALMA. About 60% of the sample (31 systems) have LIR/L* > 0.01 typical of T-Tauri or Herbig AeBe stars, and the rest (21 systems) have LIR/L* 0.01. However, the spectra of only four of the newly detected systems appear free of contamination from background or foreground emission from molecular clouds. These include the early-type stars HD 104237 (A4/5V, 116 pc) and HD 98922 (A2 III, 507 pc, as determined in this work), where our observations reveal the presence of CO-rich circumstellar disks for the first time. Of the other detected sources, many could harbor gaseous circumstellar disks, but our data are inconclusive. For these two newly discov...

  1. A HIFI view on circumstellar H2O in M-type AGB stars: radiative transfer, velocity profiles, and H2O line cooling

    CERN Document Server

    Maercker, M; Olofsson, H; De Beck, E; Justtanont, K; Lombaert, R; Royer, P

    2016-01-01

    We aim to constrain the temperature and velocity structures, and H2O abundances in the winds of a sample of M-type AGB stars. We further aim to determine the effect of H2O line cooling on the energy balance in the inner circumstellar envelope. We use two radiative-transfer codes to model molecular emission lines of CO and H2O towards four M-type AGB stars. We focus on spectrally resolved observations of CO and H2O from HIFI. The observations are complemented by ground-based CO observations, and spectrally unresolved CO and H2O observations with PAC. The observed line profiles constrain the velocity structure throughout the circumstellar envelopes (CSEs), while the CO intensities constrain the temperature structure in the CSEs. The H2O observations constrain the o-H2O and p-H2O abundances relative to H2. Finally, the radiative-transfer modelling allows to solve the energy balance in the CSE, in principle including also H2O line cooling. The fits to the line profiles only set moderate constraints on the velocit...

  2. A CO survey in planet-forming disks: Characterizing the gas content in the epoch of planet formation

    International Nuclear Information System (INIS)

    We carried out a 12CO(3-2) survey of 52 southern stars with a wide range of IR excesses (L IR/L *) using the single-dish telescopes APEX and ASTE. The main aims were (1) to characterize the evolution of molecular gas in circumstellar disks using L IR/L * values as a proxy of disk dust evolution, and (2) to identify new gas-rich disk systems suitable for detailed study with ALMA. About 60% of the sample (31 systems) have L IR/L * > 0.01, typical of T Tauri or Herbig AeBe stars, and the rest (21 systems) have L IR/L * < 0.01, typical of debris disks. We detect CO(3-2) emission from 20 systems, and 18 (90%) of these have L IR/L * > 0.01. However, the spectra of only four of the newly detected systems appear free of contamination from background or foreground emission from molecular clouds. These include the early-type stars HD 104237 (A4/5V, 116 pc) and HD 98922 (A2 III, 507 pc, as determined in this work), where our observations reveal the presence of CO-rich circumstellar disks for the first time. Of the other detected sources, many could harbor gaseous circumstellar disks, but our data are inconclusive. For these two newly discovered gas-rich disks, we present radiative transfer models that simultaneously reproduce their spectral energy distributions and the 12CO(3-2) line profiles. For both of these systems, the data are fit well by geometrically flat disks, placing them in the small class of non-flaring disks with significant molecular gas reservoirs.

  3. A CO survey in planet-forming disks: Characterizing the gas content in the epoch of planet formation

    Energy Technology Data Exchange (ETDEWEB)

    Hales, A. S.; De Gregorio-Monsalvo, I.; Dent, W. F. R.; Phillips, N. [Atacama Large Millimeter/Submillimeter Array, Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura 763-0355 Santiago (Chile); Montesinos, B. [Department of Astrophysics, Centre for Astrobiology (CAB, CSIC-INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Casassus, S.; Garay, G.; Mardones, D.; Pérez, S. [Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago (Chile); Dougados, C.; Ménard, F. [UMI-FCA, CNRS/INSU, France (UMI 3386) (France); Eiroa, C. [Departamento de Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Hughes, A. M. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Palau, Aina [Institut de Ciéncies de l' Espai (CSIC-IEEC), Campus UAB-Facultat de Ciéncies, Torre C5-parell 2, E-08193 Bellaterra, Catalunya (Spain); Torrelles, J. M. [Institut de Ciències de l' Espai (CSIC-IEEC) and Institut de Ciències del Cosmos (UB-IEEC), Martí i Franquès 1, E-08028 Barcelona (Spain); Wilner, D., E-mail: ahales@alma.cl [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

    2014-09-01

    We carried out a {sup 12}CO(3-2) survey of 52 southern stars with a wide range of IR excesses (L {sub IR}/L {sub *}) using the single-dish telescopes APEX and ASTE. The main aims were (1) to characterize the evolution of molecular gas in circumstellar disks using L {sub IR}/L {sub *} values as a proxy of disk dust evolution, and (2) to identify new gas-rich disk systems suitable for detailed study with ALMA. About 60% of the sample (31 systems) have L {sub IR}/L {sub *} > 0.01, typical of T Tauri or Herbig AeBe stars, and the rest (21 systems) have L {sub IR}/L {sub *} < 0.01, typical of debris disks. We detect CO(3-2) emission from 20 systems, and 18 (90%) of these have L {sub IR}/L {sub *} > 0.01. However, the spectra of only four of the newly detected systems appear free of contamination from background or foreground emission from molecular clouds. These include the early-type stars HD 104237 (A4/5V, 116 pc) and HD 98922 (A2 III, 507 pc, as determined in this work), where our observations reveal the presence of CO-rich circumstellar disks for the first time. Of the other detected sources, many could harbor gaseous circumstellar disks, but our data are inconclusive. For these two newly discovered gas-rich disks, we present radiative transfer models that simultaneously reproduce their spectral energy distributions and the {sup 12}CO(3-2) line profiles. For both of these systems, the data are fit well by geometrically flat disks, placing them in the small class of non-flaring disks with significant molecular gas reservoirs.

  4. Circumstellar absorption in double detonation Type Ia supernovae

    CERN Document Server

    Shen, Ken J; Foley, Ryan J

    2013-01-01

    Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He-C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

  5. CIRCUMSTELLAR ABSORPTION IN DOUBLE DETONATION TYPE Ia SUPERNOVAE

    International Nuclear Information System (INIS)

    Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He+C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

  6. The 0.5-2.22-micron Scattered Light Spectrum of the Disk Around TW Hya: Detection of a Partially Filled Disk Gap at 80 AU

    CERN Document Server

    Debes, J H; Weinberger, A J; Roberge, A; Schneider, G

    2013-01-01

    We present a 0.5-2.2 micron scattered light spectrum of the circumstellar disk around TW Hya from a combination of spatially resolved HST STIS spectroscopy and NICMOS coronagraphic images of the disk. We investigate the morphology of the disk at distances > 40 AU over this wide range of wavelengths, and identify the presence of a depression in surface brightness at ~80 AU that could be caused by a gap in the disk. Additionally, we quantify the surface brightness, azimuthal symmetry, and spectral character of the disk as a function of radius. Our analysis shows that the scattering efficiency of the dust is largely neutral to blue over the observed wavelengths. We model the disk as a steady alpha-disk with an ad hoc gap structure. The thermal properties of the disk are self-consistently calculated using a three-dimensional radiative transfer code that uses ray-tracing to model the heating of the disk interior and scattered light images. We find a good fit to the data over a wide range of distances from the star...

  7. Effects of Turbulence on Cosmic Ray Propagation in Protostars and Young Star/Disk Systems

    CERN Document Server

    Fatuzzo, Marco

    2014-01-01

    The magnetic fields associated with young stellar objects are expected to have an hour-glass geometry, i.e., the magnetic field lines are pinched as they thread the equatorial plane surrounding the forming star but merge smoothly onto a background field at large distances. With this field configuration, incoming cosmic rays experience both a funneling effect that acts to enhance the flux impinging on the circumstellar disk and a magnetic mirroring effect that acts to reduce that flux. To leading order, these effects nearly cancel out for simple underlying magnetic field structures. However, the environments surrounding young stellar objects are expected to be highly turbulent. This paper shows how the presence of magnetic field fluctuations affects the process of magnetic mirroring, and thereby changes the flux of cosmic rays striking circumstellar disks. Turbulence has two principle effects: 1) The (single) location of the magnetic mirror point found in the absence of turbulence is replaced with a wide distr...

  8. Fine Structure in the Circumstellar Environment of a Young, Solar-like Star the Unique Eclipses of KH 15D

    CERN Document Server

    Herbst, W; Vrba, F J; Ibrahimov, M A; Bailer-Jones, C A L; Mundt, R; Lamm, M J; Mazeh, T; Webster, Z T; Haisch, K E; Williams, E C; Rhodes, A H; Balonek, T J; Riffeser, A; Herbst, William; Hamilton, Catrina M.; Vrba, Frederick J.; Ibrahimov, Mansur A.; Bailer-Jones, Coryn A.L.; Mundt, Reinhard; Lamm, Markus; Mazeh, Tsevi; Webster, Zodiac T.; Haisch, Karl E.; Williams, Eric C.; Rhodes, Andrew H.; Balonek, Thomas J.; Riffeser, Alexander Scholz and Arno

    2002-01-01

    Results of an international campaign to photometrically monitor the unique pre-main sequence eclipsing object KH 15D are reported. An updated ephemeris for the eclipse is derived that incorporates a slightly revised period of 48.36 d. There is some evidence that the orbital period is actually twice that value, with two eclipses occurring per cycle. The extraordinary depth (~3.5 mag) and duration (~18 days) of the eclipse indicate that it is caused by circumstellar matter, presumably the inner portion of a disk. The eclipse has continued to lengthen with time and the central brightness reversals are not as extreme as they once were. V-R and V-I colors indicate that the system is slightly bluer near minimum light. Ingress and egress are remarkably well modeled by the passage of a knife-edge across a limb-darkened star. Possible models for the system are briefly discussed.

  9. On the excitation and formation of circumstellar fullerenes

    OpenAIRE

    Bernard-Salas, J.; Cami, J.; E. Peeters; Jones, A.P.; Micelotta, E. R.; Groenewegen, M. A. T.

    2012-01-01

    We compare and analyze the Spitzer mid-infrared spectrum of three fullerene-rich planetary nebulae in the Milky Way and the Magellanic Clouds; Tc1, SMP SMC 16, and SMP LMC 56. The three planetary nebulae share many spectroscopic similarities. The strongest circumstellar emission bands correspond to the infrared active vibrational modes of the fullerene species C60 and little or no emission is present from Polycyclic Aromatic Hydrocarbons (PAHs). The strength of the fullerene bands in the thre...

  10. Sculpting the disk around T Chamaeleontis: an interferometric view

    Science.gov (United States)

    Olofsson, J.; Benisty, M.; Le Bouquin, J.-B.; Berger, J.-P.; Lacour, S.; Ménard, F.; Henning, Th.; Crida, A.; Burtscher, L.; Meeus, G.; Ratzka, T.; Pinte, C.; Augereau, J.-C.; Malbet, F.; Lazareff, B.; Traub, W.

    2013-04-01

    Context. Circumstellar disks are believed to be the birthplace of planets and are expected to dissipate on a timescale of a few Myr. The processes responsible for the removal of the dust and gas will strongly modify the radial distribution of the circumstellar matter and consequently the spectral energy distribution. In particular, a young planet will open a gap, resulting in an inner disk dominating the near-IR emission and an outer disk emitting mostly in the far-infrared. Aims: We analyze a full set of data involving new near-infrared data obtained with the 4-telescope combiner (VLTI/PIONIER), new mid-infrared interferometric VLTI/MIDI data, literature photometric and archival data from VLT/NaCo/SAM to constrain the structure of the transition disk around T Cha. Methods: After a preliminary analysis with a simple geometric model, we used the MCFOST radiative transfer code to simultaneously model the SED and the interferometric observables from raytraced images in the H-, L'-, and N-bands. Results: We find that the dust responsible for the strong emission in excess in the near-IR must have a narrow temperature distribution with a maximum close to the silicate sublimation temperature. This translates into a narrow inner dusty disk (0.07-0.11 AU), with a significant height (H/r ~ 0.2) to increase the geometric surface illuminated by the central star. We find that the outer disk starts at about 12 AU and is partially resolved by the PIONIER, SAM, and MIDI instruments. We discuss the possibility of a self-shadowed inner disk, which can extend to distances of several AU. Finally, we show that the SAM closure phases, interpreted as the signature of a candidate companion, may actually trace the asymmetry generated by forward scattering by dust grains in the upper layers of the outer disk. These observations help constrain the inclination and position angle of the disk to about + 58° and - 70°, respectively. Conclusions: The circumstellar environment of T Cha appears

  11. XMM-NEWTON MONITORING OF THE CLOSE PRE-MAIN-SEQUENCE BINARY AK SCO. EVIDENCE OF TIDE-DRIVEN FILLING OF THE INNER GAP IN THE CIRCUMBINARY DISK

    International Nuclear Information System (INIS)

    AK Sco stands out among pre-main-sequence binaries because of its prominent ultraviolet excess, the high eccentricity of its orbit, and the strong tides driven by it. AK Sco consists of two F5-type stars that get as close as 11 R* at periastron passage. The presence of a dense (ne ∼ 1011 cm–3) extended envelope has been unveiled recently. In this article, we report the results from an XMM-Newton-based monitoring of the system. We show that at periastron, X-ray and UV fluxes are enhanced by a factor of ∼3 with respect to the apastron values. The X-ray radiation is produced in an optically thin plasma with T ∼ 6.4 × 106 K and it is found that the NH column density rises from 0.35 × 1021 cm–2 at periastron to 1.11 × 1021 cm–2 at apastron, in good agreement with previous polarimetric observations. The UV emission detected in the Optical Monitor band seems to be caused by the reprocessing of the high-energy magnetospheric radiation on the circumstellar material. Further evidence of the strong magnetospheric disturbances is provided by the detection of line broadening of 278.7 km s–1 in the N V line with Hubble Space Telescope/Space Telescope Imaging Spectrograph. Numerical simulations of the mass flow from the circumbinary disk to the components have been carried out. They provide a consistent scenario with which to interpret AK Sco observations. We show that the eccentric orbit acts like a gravitational piston. At apastron, matter is dragged efficiently from the inner disk border, filling the inner gap and producing accretion streams that end as ring-like structures around each component of the system. At periastron, the ring-like structures come into contact, leading to angular momentum loss, and thus producing an accretion outburst.

  12. Coronagraphic Imaging of Debris Disks from a High Altitude Balloon Platform

    Science.gov (United States)

    Unwin, Stephen; Traub, Wesley; Bryden, Geoffrey; Brugarolas, Paul; Chen, Pin; Guyon, Olivier; Hillenbrand, Lynne; Kasdin, Jeremy; Krist, John; Macintosh, Bruce; Mawet, Dimitri; Mennesson, Bertrand; Moody, Dwight; Roberts, Lewis C. Jr; Stapelfeldt, Karl; Stuchlik, David; Trauger, John; Vasisht, Gautam

    2012-01-01

    Debris disks around nearby stars are tracers of the planet formation process, and they are a key element of our understanding of the formation and evolution of extrasolar planetary systems. With multi-color images of a significant number of disks, we can probe important questions: can we learn about planetary system evolution; what materials are the disks made of; and can they reveal the presence of planets? Most disks are known to exist only through their infrared flux excesses as measured by the Spitzer Space Telescope, and through images measured by Herschel. The brightest, most extended disks have been imaged with HST, and a few, such as Fomalhaut, can be observed using ground-based telescopes. But the number of good images is still very small, and there are none of disks with densities as low as the disk associated with the asteroid belt and Edgeworth-Kuiper belt in our own Solar System. Direct imaging of disks is a major observational challenge, demanding high angular resolution and extremely high dynamic range close to the parent star. The ultimate experiment requires a space-based platform, but demonstrating much of the needed technology, mitigating the technical risks of a space-based coronagrap, and performing valuable measurements of circumstellar debris disks, can be done from a high-altitude balloon platform. In this paper we present a balloon-borne telescope experiment based on the Zodiac II design that would undertake compelling studies of a sample of debris disks.

  13. Multifamily Envelope Leakage Model

    Energy Technology Data Exchange (ETDEWEB)

    Faakye, Omari [Consortium for Advanced Residential Buildings, Norwalk, CT (United States); Griffiths, Dianne [Consortium for Advanced Residential Buildings, Norwalk, CT (United States)

    2015-05-08

    “The cost for blower testing is high, because it is labor intensive, and it may disrupt occupants in multiple units. This high cost and disruption deter program participants, and dissuade them from pursuing energy improvements that would trigger air leakage testing, such as improvements to the building envelope.” This statement found in a 2012 report by Heschong Mahone Group for several California interests emphasizes the importance of reducing the cost and complexity of blower testing in multifamily buildings. Energy efficiency opportunities are being bypassed. The cost of single blower testing is on the order of $300. The cost for guarded blower door testing—the more appropriate test for assessing energy savings opportunities—could easily be six times that, and that’s only if you have the equipment and simultaneous access to multiple apartments. Thus, the proper test is simply not performed. This research seeks to provide an algorithm for predicting the guarded blower door test result based upon a single, total blower door test.

  14. Signatures of Gravitational Instability in Resolved Images of Protostellar Disks

    CERN Document Server

    Dong, Ruobing; Pavlyuchenkov, Yaroslav; Chiang, Eugene; Liu, Hauyu Baobab

    2016-01-01

    Protostellar (class 0/I) disks, having masses comparable to those of their nascent host stars, and fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and mm-wave interferometry, we explore the observational signatures of GI in disks, using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and mm dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of AUs, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane, arms therefore scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. By contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes, such fragment...

  15. Multitechnique testing of the viscous decretion disk model I. The stable and tenuous disk of the late-type Be star $\\beta$ CMi

    CERN Document Server

    Klement, R; Rivinius, T; Panoglou, D; Vieira, R G; Bjorkman, J E; Štefl, S; Tycner, C; Faes, D M; Korčáková, D; Müller, A; Zavala, R T; Curé, M

    2015-01-01

    The viscous decretion disk (VDD) model is able to explain most of the currently observable properties of the circumstellar disks of Be stars. However, more stringent tests, focusing on reproducing multitechnique observations of individual targets via physical modeling, are needed to study the predictions of the VDD model under specific circumstances. In the case of nearby, bright Be star $\\beta$ CMi, these circumstances are a very stable low-density disk and a late-type (B8Ve) central star. The aim is to test the VDD model thoroughly, exploiting the full diagnostic potential of individual types of observations, in particular, to constrain the poorly known structure of the outer disk if possible, and to test truncation effects caused by a possible binary companion using radio observations. We use the Monte Carlo radiative transfer code HDUST to produce model observables, which we compare with a very large set of multitechnique and multiwavelength observations that include ultraviolet and optical spectra, photo...

  16. Circumstellar Structure around Evolved Stars in the Cygnus-X Star Formation Region

    CERN Document Server

    Kraemer, Kathleen E; Egan, Michael P; Adams, Joseph; Allen, Lori E; Bontemps, Sylvain; Carey, Sean J; Fazio, Giovanni G; Gutermuth, Robert; Keto, Eric; Koenig, Xavier P; Megeath, S Thomas; Mizuno, Donald R; Motte, Frederique; Price, Stephan D; Schneider, Nicola; Simon, Robert; Smith, Howard

    2010-01-01

    We present observations of newly discovered 24 micron circumstellar structures detected with the Multiband Imaging Photometer for Spitzer (MIPS) around three evolved stars in the Cygnus-X star forming region. One of the objects, BD+43 3710, has a bipolar nebula, possibly due to an outflow or a torus of material. A second, HBHA 4202-22, a Wolf-Rayet candidate, shows a circular shell of 24 micron emission suggestive of either a limb-brightened shell or disk seen face-on. No diffuse emission was detected around either of these two objects in the Spitzer 3.6-8 micron Infrared Array Camera (IRAC) bands. The third object is the luminous blue variable candidate G79.29+0.46. We resolved the previously known inner ring in all four IRAC bands. The 24 micron emission from the inner ring extends ~1.2 arcmin beyond the shorter wavelength emission, well beyond what can be attributed to the difference in resolutions between MIPS and IRAC. Additionally, we have discovered an outer ring of 24 micron emission, possibly due to ...

  17. 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.; Silverstone, Murray D.; Jang-Condell, Hannah; Henning, Thomas; Bruce E. Woodgate; Serabyn, Eugene; Moro-Martin, Amaya; Tamura, Motohide; Hinz, Phillip M.; Rodigas, Timothy J.

    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

  18. 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

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

    International Nuclear Information System (INIS)

    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 disk/F star = 5 × 10–5), 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 temporal variability in

  20. G5.89-0.39: A compact H II region with a very dense circumstellar dust torus

    Science.gov (United States)

    Harvey, Paul M.; Lester, Daniel F.; Colome, Cecilia; Smith, Beverly; Monin, Jean-Louis; Vauglin, Isabelle

    1994-01-01

    We present the results of high angular resolution infrared observations of the compact H II region G5.89-0.39. Subarcsecond imaging at 1.65, 2.2, 3.6, and 4.8 microns and diffraction-limited scans at 50 and 100 microns have been obtained at NASA's Infrared Telescope Facility and Kupier Airborne Observatory and the Canada-France-Hawaii Telescope. We find a bipolar source morphology at the shortest infrared wavelengths, a compact single source at 4-5 microns, similar to that seen at 10 microns, and a very high optical depth, barely resolved far-infrared source. Spherical radiative transfer models have been used to estimate dust envelope properties; in spite of the obvious nonspherical geometry at short wavelengths, these models provide strong constraints on the overall properties of the circumnebular envelope. We find that the bulk of the circumstellar dust must be relatively close to the H II region, with a relatively steep gradient. The high column densities and steep density gradient imply densities at the inner edge of the cloud of order 10(exp 7)-10(exp 8)/cc. These results suggest that the compact H II region is surrounded by a very dense dust torus.

  1. Safe operating envelope

    International Nuclear Information System (INIS)

    This is a slide-based oral presentation given to the COG/IAEA: Fifth technical committee meeting on 'Exchange of operating experience of pressurized heavy water reactors' held in Mangalia, Romania on 7-10 September 1998. The plant states and operating conditions are defined as resulting from the consequences of a Licensing Basis Event occurrence. Three categories of important plant parameters are considered: A - directly associated with either the mechanical or instrumentation and control aspects of the Special Safety Systems; B - process conditions related to trip parameters; C - other parameters that effect outcome of an accident. In A category the following aspects were addressed: Instrument loop uncertainties and time lags and delays; Tank levels, pressures and chemistry; Valve operating times and characteristics; Pump performance; The number of redundant pieces of equipment. Relating to category B the process conditions implied in trip initiation parameters as they effect margin to trip are discussed and illustrated by the cases of pressurizer level, RB pressure, etc. Finally, in the last category, the parameters effecting accident outcome are considered, i.e. either process variables, or equipment associated with safety related or safety support systems. The following cases are analysed PHTS Isotopic/temperatures/flows, moderator outlet temperature, RCW/RSW temperature, number of available aux. boiler feedpumps. In connection with the plant states the following matters are analyzed: fueling; boiler tube leak; defect fuel; non-equilibrium core; shutdown and reduced power operation; two pump operation. Concerning the Safety Operating Envelope (SOE) the following issues are presented: OP and P (high level overview), supported by OM tests and surveillance, by taking into account the use Tech Specs for the future, the role of safety analysis, historical perspective at PLGS. Finally, the DOA (Design/Operation/Analysis) Program at PLGS is described and the following

  2. Structure and Evolution of the Envelopes of Deeply Embedded Massive Young Stars

    Science.gov (United States)

    van der Tak, Floris F. S.; van Dishoeck, Ewine F.; Evans, Neal J., II; Blake, Geoffrey A.

    2000-07-01

    The physical structure of the envelopes around a sample of 14 massive young stars is investigated using maps and spectra in submillimeter continuum and lines of C17O, CS, C34S, and H2CO. Nine of the sources are highly embedded luminous (103-105 Lsolar) young stellar objects that are bright near-infrared sources but weak in radio continuum; the other objects are similar but not bright in the near-infrared and contain ``hot-core''-type objects and/or ultracompact H II regions. The data are used to constrain the temperature and density structure of the circumstellar envelopes on 102-105 AU scales, to investigate the relation between the different objects, and to search for evolutionary effects. The total column densities and the temperature profiles are obtained by fitting self-consistent dust models to submillimeter photometry. The calculated temperatures range from 300 to 1000 K at ~102 AU and from 10 to 30 K at ~105 AU from the star. Visual extinctions are a few hundred to a few thousand magnitudes, assuming a grain opacity at 1300 μm of ~1 cm-2 g-1 of dust, as derived earlier for one of our sources. The mid-infrared data are consistent with a 30% decrease of the opacity at higher temperatures, caused by the evaporation of the ice mantles. The CS, C34S, and H2CO data as well as the submillimeter dust emission maps indicate density gradients n~r-α. Assuming a constant CS abundance throughout the envelope, values of α=1.0-1.5 are found, which is significantly flatter than the α=2.0+/-0.3 generally found for low-mass objects. This flattening may indicate that in massive young stellar objects, nonthermal pressure is more important for the support against gravitational collapse, while thermal pressure dominates for low-mass sources. We find α=2 for two hot-core-type sources but regard this as an upper limit since, in these objects, the CS abundance may be enhanced in the warm gas close to the star. The assumption of spherical symmetry is tested by modeling infrared

  3. Warped accretion disks and the unification of Active Galactic Nuclei

    CERN Document Server

    Nayakshin, S

    2004-01-01

    Orientation of parsec-scale accretion disks in AGN is likely to be nearly random for different black hole feeding episodes. Since AGN accretion disks are unstable to self-gravity on parsec scales, star formation in these disks will create young stellar disks, similar to those recently discovered in our Galactic Center. The disks blend into the quasi-spherical star cluster enveloping the AGN on time scales much longer than a likely AGN lifetime. Therefore, the gravitational potential within the radius of the black hole influence is at best axi-symmetric rather than spherically symmetric. Here we show that as a result, a newly formed accretion disk will be warped. For the simplest case of a potential resulting from a thin stellar ring, we calculate the disk precession rates, and the time dependent shape. We find that, for a realistic parameter range, the disk becomes strongly warped in few hundred orbital times. We suggest that this, and possibly other mechanisms of accretion disk warping, have a direct relevan...

  4. HERSCHEL OBSERVATIONS OF GAS AND DUST IN THE UNUSUAL 49 Ceti DEBRIS DISK

    International Nuclear Information System (INIS)

    We present far-IR/sub-mm imaging and spectroscopy of 49 Ceti, an unusual circumstellar disk around a nearby young A1V star. The system is famous for showing the dust properties of a debris disk, but the gas properties of a low-mass protoplanetary disk. The data were acquired with the Herschel Space Observatory PACS and SPIRE instruments, largely as part of the ''Gas in Protoplanetary Systems'' (GASPS) Open Time Key Programme. Disk dust emission is detected in images at 70, 160, 250, 350, and 500 μm; 49 Cet is significantly extended in the 70 μm image, spatially resolving the outer dust disk for the first time. Spectra covering small wavelength ranges centered on eight atomic and molecular emission lines were obtained, including [O I] 63 μm and [C II] 158 μm. The C II line was detected at the 5σ level—the first detection of atomic emission from the disk. No other emission lines were seen, despite the fact that the O I line is the brightest one observed in Herschel protoplanetary disk spectra. We present an estimate of the amount of circumstellar atomic gas implied by the C II emission. The new far-IR/sub-mm data fills in a large gap in the previous spectral energy distribution (SED) of 49 Cet. A simple model of the new SED confirms the two-component structure of the disk: warm inner dust and cold outer dust that produces most of the observed excess. Finally, we discuss preliminary thermochemical modeling of the 49 Cet gas/dust disk and our attempts to match several observational results simultaneously. Although we are not yet successful in doing so, our investigations shed light on the evolutionary status of the 49 Cet gas, which might not be primordial gas but rather secondary gas coming from comets.

  5. The LHC in an envelope

    CERN Multimedia

    2007-01-01

    The series of envelopes featuring CERN issued this summer was a huge success. The French postal services of the Pays de Gex will shortly be launching the second set of pre-paid envelopes issued in collaboration with the Laboratory this year, this time highlighting the LHC. Five thousand envelopes describing the accelerator’s capabilities will go on sale on 12 November, and some of the packs will even contain a small sample of the cables from the heart of the LHC magnets. The sets of ten pre-paid envelopes will tell you everything about CERN’s flagship accelerator, from its astounding technical capabilities to its spin-offs in the fields of technology and human resources. Each envelope will feature a different attribute or spin-off of the LHC. People will be invited to consult CERN’s public website for more detailed explanations if they want to know more. The new envelopes will be available from five post offices in the Pays de Gex (Ferney-Voltaire, Prévessin...

  6. The LHC on an envelope

    CERN Multimedia

    2007-01-01

    The series of envelopes featuring CERN issued this summer was a huge success. The French postal services of the Pays de Gex will shortly be launching the second set of pre-paid envelopes issued in collaboration with the Laboratory this year, this time highlighting the LHC. Five thousand envelopes describing the accelerator’s capabilities will go on sale on 12 November, and some of the packs will even contain a small sample of the cables from the heart of the LHC magnets. The sets of ten pre-paid envelopes will tell you everything about CERN’s flagship accelerator, from its astounding technical capabilities to its spin-offs in the fields of technology and human resources. Each envelope will feature a different attribute or spin-off of the LHC. People will be invited to consult CERN’s public website for more detailed explanations if they want to know more. The new envelopes will be available from five post offices in the Pays ...

  7. A resolved debris disk around the candidate planet-hosting star HD95086

    OpenAIRE

    Moór, A.; Ábrahám, P.; Kóspál, Á.; Szabó, Gy. M.; Apai, D.; Balog, Z.; Csengeri, T.; Grady, C; Henning, Th.; Juhász, A.; Kiss, Cs; Pascucci, I.; Szulágyi, J.; Vavrek, R.

    2013-01-01

    Recently, a new planet candidate was discovered on direct images around the young (10-17 Myr) A-type star HD95086. The strong infrared excess of the system indicates that, similarly to HR8799, {\\ss} Pic, and Fomalhaut, the star harbors a circumstellar disk. Aiming to study the structure and gas content of the HD95086 disk, and to investigate its possible interaction with the newly discovered planet, here we present new optical, infrared and millimeter observations. We detected no CO emission,...

  8. Magnetic Braking and Protostellar Disk Formation: The Ideal MHD Limit

    Science.gov (United States)

    Mellon, Richard R.; Li, Zhi-Yun

    2008-07-01

    Magnetic fields are usually considered dynamically important in star formation when the dimensionless mass-to-flux ratio is close to, or less than, unity (λ lesssim 1). We show that, in disk formation, the requirement is far less stringent. This conclusion is drawn from a set of 2D (axisymmetric) simulations of the collapse of rotating, singular isothermal cores magnetized to different degrees. We find that a weak field corresponding to λ ~ 100 can begin to disrupt the rotationally supported disk through magnetic braking, by creating regions of rapid, supersonic collapse in the disk. These regions are separated by one or more centrifugal barriers, where the rapid infall is temporarily halted. The number of centrifugal barriers increases with the mass-to-flux ratio λ. When λ gtrsim 100, they merge together to form a more or less contiguous, rotationally supported disk. Even though the magnetic field in such a case is extremely weak on the scale of dense cores, it is amplified by collapse and differential rotation, to the extent that its pressure dominates the thermal pressure in both the disk and its surrounding region. For relatively strongly magnetized cores with λ lesssim 10, the disk formation is suppressed completely, as found previously. A new feature is that the mass accretion is highly episodic, due to reconnection of the magnetic field lines accumulated near the center. For rotationally supported disks to appear during the protostellar mass accretion phase of star formation in dense cores with realistic field strengths, the powerful magnetic brake must be weakened, perhaps through nonideal MHD effects. Another possibility is to remove, through protostellar winds, the material that acts to brake the disk rotation. We discuss the possibility of observing a generic product of the magnetic braking, an extended circumstellar region that is supported by a combination of toroidal magnetic field and rotation—a "magnetogyrosphere"—interferometrically.

  9. First Images of Debris Disks around TWA 7, TWA 25, HD 35650, and HD 377

    Science.gov (United States)

    Choquet, Élodie; Perrin, Marshall D.; Chen, Christine H.; Soummer, Rémi; Pueyo, Laurent; Hagan, James B.; Gofas-Salas, Elena; Rajan, Abhijith; Golimowski, David A.; Hines, Dean C.; Schneider, Glenn; Mazoyer, Johan; Augereau, Jean-Charles; Debes, John; Stark, Christopher C.; Wolff, Schuyler; N'Diaye, Mamadou; Hsiao, Kevin

    2016-01-01

    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.

  10. First images of debris disks around TWA 7, TWA 25, HD 35650, and HD 377

    CERN Document Server

    Choquet, Élodie; Chen, Christine H; Soummer, Rémi; Pueyo, Laurent; Hagan, James B; Gofas-Salas, Elena; Rajan, Abhijith; Golimowski, David A; Hines, Dean C; Schneider, Glenn; Mazoyer, Johan; Augereau, Jean-Charles; Debes, John; Stark, Christopher C; Wolff, Schuyler; N'Diaye, Mamadou; Hsiao, Kevin

    2015-01-01

    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 (ALICE) 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.

  11. Is the HD 15115 inner disk really asymmetrical ?

    CERN Document Server

    Mazoyer, J; Augereau, J -C; Lagrange, A -M; Galicher, R; Baudoz, P

    2014-01-01

    Context. Debris disks are intrinsically connected to the planetary system's formation and evolution. The development of high-contrast imaging techniques in the past 20 years is now allowing the detection of faint material around bright stars with high angular resolution, hence opening an avenue to study in detail the structures of circumstellar disks and their relation to planetary formation. Aims. The purpose of this paper is to revisit the morphology of the almost edge-on debris disk around HD 15115. Methods. We analyzed data from the Gemini science archive obtained in 2009 and 2011 with the Near-Infrared Coronagraphic Imager instrument in the H and Ks bands using coronagraphy and angular differential imaging tech- niques. Results. We resolved the disk in both the H and Ks bands. We confirmed the position angles inferred by previous authors, as well as the brightness asymmetry, which is the origin of the object's nickname, the blue needle. We were able to detect the bow-like shape of the disk suspected from...

  12. Discovery of an Inner Disk Component around HD 141569 A

    CERN Document Server

    Konishi, Mihoko; Schneider, Glenn; Shibai, Hiroshi; McElwain, Michael W; Nesvold, Erika R; Kuchner, Marc J; Carson, Joseph; Debes, John H; Gaspar, Andras; Henning, Thomas K; Hines, Dean C; Hinz, Philip M; Jang-Condell, Hannah; Moro-Martin, Amaya; Perrin, Marshall; Rodigas, Timothy J; Serabyn, Eugene; Silverstone, Murray D; Stark, Christopher C; Tamura, Motohide; Weinberger, Alycia J; Wisniewski, John P

    2016-01-01

    We report the discovery of a scattering component around the HD 141569 A circumstellar debris system, interior to the previously known inner ring. The discovered inner disk component, obtained in broadband optical light with HST/STIS coronagraphy, was imaged with an inner working angle of 0".25, and can be traced from 0".4 (~46 AU) to 1".0 (~116 AU) after deprojection using i=55deg. The inner disk component is seen to forward scatter in a manner similar to the previously known rings, has a pericenter offset of ~6 AU, and break points where the slope of the surface brightness changes. It also has a spiral arm trailing in the same sense as other spiral arms and arcs seen at larger stellocentric distances. The inner disk spatially overlaps with the previously reported warm gas disk seen in thermal emission. We detect no point sources within 2" (~232 AU), in particular in the gap between the inner disk component and the inner ring. Our upper limit of 9+/-3 M_J is augmented by a new dynamical limit on single plane...

  13. Detection of N$_2$D$^+$ in a protoplanetary disk

    CERN Document Server

    Huang, Jane

    2015-01-01

    Observations of deuterium fractionation in the solar system, and in interstellar and circumstellar material, are commonly used to constrain the formation environment of volatiles. Toward protoplanetary disks, this approach has been limited by the small number of detected deuterated molecules, i.e. DCO$^+$ and DCN. Based on ALMA Cycle 2 observations toward the disk around the T Tauri star AS 209, we report the first detection of N$_2$D$^+$ (J=3-2) in a protoplanetary disk. These data are used together with previous Submillimeter Array observations of N$_2$H$^+$ (J=3-2) to estimate a disk-averaged D/H ratio of 0.3--0.5, an order of magnitude higher than disk-averaged ratios previously derived for DCN/HCN and DCO$^+$/HCO$^+$ around other young stars. The high fractionation in N$_2$H$^+$ is consistent with model predictions. The presence of abundant N$_2$D$^+$ toward AS 209 also suggests that N$_2$D$^+$ and the N$_2$D$^+$/N$_2$H$^+$ ratio can be developed into effective probes of deuterium chemistry, kinematics, ...

  14. Morphology of the very inclined debris disk around HD 32297

    CERN Document Server

    Boccaletti, Anthony; Lagrange, Anne-Marie; Milli, Julien; Baudoz, Pierre; Mawet, Dimitri; Mouillet, David; Lebreton, Jeremy; Maire, Anne-Lise

    2012-01-01

    Direct imaging of circumstellar disks at high angular resolution is mandatory to provide morphological information that bring constraints on their properties, in particular the spatial distribution of dust. New techniques combining observing strategy and data processing now allow very high contrast imaging with 8-m class ground-based telescopes (10^-4 to 10^-5 at ~1") and complement space telescopes while improving angular resolution at near infrared wavelengths. We carried out a program at the VLT with NACO to image known debris disks with higher angular resolution in the near IR than ever before in order to study morphological properties and ultimately to detect signpost of planets. The observing method makes use of advanced techniques: Adaptive Optics, Coronagraphy and Differential Imaging, a combination designed to directly image exoplanets with the upcoming generation of "planet finders" like GPI (Gemini Planet Imager) and SPHERE (Spectro-Polarimetric High contrast Exoplanet REsearch). Applied to extende...

  15. CO GAS INSIDE THE PROTOPLANETARY DISK CAVITY IN HD 142527: DISK STRUCTURE FROM ALMA

    Energy Technology Data Exchange (ETDEWEB)

    Perez, S.; Casassus, S.; Van der Plas, G.; Christiaens, V. [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Ménard, F.; Roman, P.; Cieza, L.; Hales, A. S. [Millenium Nucleus " Protoplanetary Disks in ALMA Early Science," Universidad de Chile, Casilla 36-D, Santiago (Chile); Pinte, C. [UMI-FCA 3386, CNRS/INSU, Casilla 36-D, Santiago (Chile)

    2015-01-10

    Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends up to 140 AU from the central star, as seen in continuum images at infrared and millimeter wavelengths. Estimates of the survival of gas inside disk cavities are needed to discriminate between clearing scenarios. We present a spatially and spectrally resolved carbon monoxide isotopologue observations of the gas-rich disk HD 142527, in the J = 2-1 line of {sup 12}CO, {sup 13}CO, and C{sup 18}O obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). We detect emission coming from inside the dust-depleted cavity in all three isotopologues. Based on our analysis of the gas in the dust cavity, the {sup 12}CO emission is optically thick, while {sup 13}CO and C{sup 18}O emissions are both optically thin. The total mass of residual gas inside the cavity is ∼1.5-2 M {sub Jup}. We model the gas with an axisymmetric disk model. Our best-fit model shows that the cavity radius is much smaller in CO than it is in millimeter continuum and scattered light observations, with a gas cavity that does not extend beyond 105 AU (at 3σ). The gap wall at its outer edge is diffuse and smooth in the gas distribution, while in dust continuum it is manifestly sharper. The inclination angle, as estimated from the high velocity channel maps, is 28 ± 0.5 deg, higher than in previous estimates, assuming a fix central star mass of 2.2 M {sub ☉}.

  16. Mid-IR Observations of T Tauri stars: Probing the Star-Disk Connection in Rotational Evolution

    CERN Document Server

    Kundurthy, P; Robberto, M; Beckwith, S V W; Herbst, T; Kundurthy, Praveen; Meyer, Michael R.; Robberto, Massimo; Beckwith, Steven V.W.; Herbst, Tom

    2006-01-01

    We present mid-IR N-band $(\\lambda_{eff} = 10.2\\micron)$ photometry of a carefully selected sample of T Tauri stars thought to be single from the Taurus-Auriga molecular cloud. Infrared excesses in these stars are generally attributed to circumstellar dust-disks. Combining observations at 2.16$\\micron$ (K$_{s}$-band) and 10.2$\\micron$ (N-band) we probe a region in the circumstellar dust-disk from a few stellar radii through the terrestrial planet zone (0.02-1.0AU). By analyzing the distribution of the $(K_{s}-N)$ color index with respect to previously measured photometric rotation periods we investigate what role circumstellar disks play in the rotational evolution of the central star. The resulting positive correlation between these two variables is consistent with the notion that a star-disk interaction facilitates the regulation of angular momentum during the T Tauri stage. We also demonstrate, how including non-single stars in such an analysis will \\textit{weaken} any correlation in the relation between $...

  17. Debris Disks in Nearby Young Moving Groups in the ALMA Era

    CERN Document Server

    Kóspál, Á

    2015-01-01

    Many members of nearby young moving groups exhibit infrared excess attributed to circumstellar debris dust, formed via erosion of planetesimals. With their proximity and well-dated ages, these groups are excellent laboratories for studying the early evolution of debris dust and of planetesimal belts. ALMA can spatially resolve the disk emission, revealing the location and extent of these belts, putting constraints on planetesimal evolution models, and allowing us to study planet-disk interactions. While the main trends of dust evolution in debris disks are well-known, there is almost no information on the evolution of gas. During the transition from protoplanetary to debris state, even the origin of gas is dubious. Here we review the exciting new results ALMA provided by observing young debris disks, and discuss possible future research directions.

  18. Debris Disks in Nearby Young Moving Groups in the ALMA Era

    Science.gov (United States)

    Kóspál, Á.; Moór, A.

    2016-01-01

    Many members of nearby young moving groups exhibit infrared excess attributed to circumstellar debris dust, formed via erosion of planetesimals. With their proximity and well-dated ages, these groups are excellent laboratories for studying the early evolution of debris dust and of planetesimal belts. ALMA can spatially resolve the disk emission, revealing the location and extent of these belts, putting constraints on planetesimal evolution models, and allowing us to study planet-disk interactions. While the main trends of dust evolution in debris disks are well-known, there is almost no information on the evolution of gas. During the transition from protoplanetary to debris state, even the origin of gas is dubious. Here we review the exciting new results ALMA provided by observing young debris disks, and discuss possible future research directions.

  19. ALMA observations of the Th 28 protostellar disk - A new exemple of counter-rotation between disk and optical jet

    CERN Document Server

    Louvet, F; Cabrit, S; Hales, A; Pinte, C; Menard, F; Bacciotti, F; Coffey, D; Mardones, D; Bronfman, L; Gueth, F

    2016-01-01

    Differences in Doppler shifts across the base of four close classical T-Tauri star jets have been detected with the HST in optical and NUV emission lines, and interpreted as rotation signatures under the assumption of steady state flow. To support this interpretation, it is necessary that the underlying disks rotate in the same sense. Agreement between disk rotation and jet rotation determined from optical lines has been verified in two cases and rejected in one. We propose here to perform this test on the fourth system, Th 28. We present ALMA high angular resolution Band 7 continuum, 12CO(2-1) and 13CO(2-1) observations of the circumstellar disk around the T-Tauri star Th 28. The sub-arcsecond angular resolution (0.46"x0.37") and high-sensitivity reached enable us to detect in CO and continuum clear signatures of a disk in Keplerian rotation around Th28. The 12CO emission allows us to derive estimates of disk position angle and inclination. The large velocity separation of the peaks in 12CO combined with the...

  20. POLARIMETRIC IMAGING OF LARGE CAVITY STRUCTURES IN THE PRE-TRANSITIONAL PROTOPLANETARY DISK AROUND PDS 70: OBSERVATIONS OF THE DISK

    International Nuclear Information System (INIS)

    We present high-resolution H-band polarized intensity (FWHM = 0.''1: 14 AU) 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 ∼70 AU. Our data show that the geometric center of the disk shifts by ∼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 ∼30 to ∼50 MJ 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.

  1. Accretion disk electrodynamics

    Science.gov (United States)

    Coroniti, F. V.

    1985-01-01

    Accretion disk electrodynamic phenomena are separable into two classes: (1) disks and coronas with turbulent magnetic fields; (2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an alpha-omega dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.

  2. Chemistry in Protoplanetary Disks

    OpenAIRE

    Henning, Thomas; Semenov, Dmitry

    2013-01-01

    This comprehensive review summarizes our current understanding of the evolution of gas, solids and molecular ices in protoplanetary disks. Key findings related to disk physics and chemistry, both observationally and theoretically, are highlighted. We discuss which molecular probes are used to derive gas temperature, density, ionization state, kinematics, deuterium fractionation, and study organic matter in protoplanetary disks.

  3. Understanding Floppy Disks.

    Science.gov (United States)

    Valentine, Pamela

    1980-01-01

    The author describes the floppy disk with an analogy to the phonograph record, and discusses the advantages, disadvantages, and capabilities of hard-sectored and soft-sectored floppy disks. She concludes that, at present, the floppy disk will continue to be the primary choice of personal computer manufacturers and their customers. (KC)

  4. An interferometric study of the post-AGB binary 89 Herculis I Spatially resolving the continuum circumstellar environment at optical and near-IR wavelengths with the VLTI, NPOI, IOTA, PTI, and the CHARA Array

    CERN Document Server

    Hillen, M; Van Winckel, H; Chesneau, O; Hummel, C A; Monnier, J D; Farrington, C; Tycner, C; Mourard, D; Brummelaar, T ten; Banerjee, D P K; Zavala, R T

    2013-01-01

    Binary post-AGB stars are interesting laboratories to study both the evolution of binaries as well as the structure of circumstellar disks. A multiwavelength high angular resolution study of the prototypical object 89 Herculis is performed with the aim of identifying and locating the different emission components seen in the SED. A large interferometric data set, collected over the past decade and covering optical and near-IR wavelengths, is analyzed with simple geometric models. Combining the interferometric constraints with the photometry and the optical spectra, we reassess the energy budget of the post-AGB star and its circumstellar environment. We report the first (direct) detection of a large (35-40%) optical circumstellar flux contribution and spatially resolve its emission region. Given this large amount of reprocessed and/or redistributed optical light, the fitted size of the emission region is rather compact and fits with(in) the inner rim of the circumbinary dust disk. This rim dominates our K band...

  5. Disks and Outflows Around Young Stars

    Science.gov (United States)

    Beckwith, Steven; Staude, Jakob; Quetz, Axel; Natta, Antonella

    The subject of the book, the ubiquitous circumstellar disks around very young stars and the corresponding jets of outflowing matter, has recently become one of the hottest areas in astrophysics. The disks are thought to be precursors to planetary systems, and the outflows are thought to be a necessary phase in the formation of a young star, helping the star to get rid of angular momentum and energy as it makes its way onto the main sequence. The possible connections to planetary systems and stellar astrophysics makes these topics especially broad, appealing to generalists and specialists alike. The CD not only contains papers that could not be printed in the book but allows the authors to include a fair amount of data, often displayed as color images. The CD-ROM contains all the contributions printed in the corresponding book (Lecture Notes in Physics Vol. 465) and, in addition, those presented exclusively in digital form. Each contribution consists of a file in portable document format (PDF). The electronic version allows full-text searching within each file using Adobe's Acrobat Reader providing instructions for installation on Unix (Sun), PC and Macintosh computers, respectively. All contributions can be printed out; the color diagrams and color frames, which are printed in black and white in the book, can be viewed in color on screen.

  6. 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.

  7. ON THE EFFECTS OF OPTICALLY THICK GAS (DISKS) AROUND MASSIVE STARS

    International Nuclear Information System (INIS)

    Numerical simulations have shown that the often cited radiation pressure barrier to accretion onto massive stars can be circumvented, when the radiation field is highly anisotropic in the presence of a circumstellar accretion disk with high optical depth. Here, these studies of the so-called flashlight effect are expanded by including the opacity of the innermost dust-free but potentially optically thick gas regions around forming massive stars. In addition to frequency-dependent opacities for the dust grains, we use temperature- and density-dependent Planck and Rosseland mean opacities for the gas. The simulations show that the innermost dust-free parts of the accretion disks are optically thick to the stellar radiation over a substantial fraction of the solid angle above and below the disk's midplane. The temperature in the shielded disk region decreases faster with radius than in a comparison simulation with a lower constant gas opacity, and the dust sublimation front is shifted to smaller radii. The shielding by the dust-free gas in the inner disk thus contributes to an enhanced flashlight effect, which ultimately results in a smaller opening angle of the radiation pressure driven outflow and in a much longer timescale of sustained feeding of the circumstellar disk by the molecular cloud core. We conclude that it is necessary to properly account for the opacity of the inner dust-free disk regions around forming massive stars in order to correctly assess the effectiveness of the flashlight effect, the opening angle of radiation pressure driven outflows, and the lifetime and morphological evolution of the accretion disk.

  8. Metamorphosis of SN 2014C: Delayed Interaction between a Hydrogen Poor Core-collapse Supernova and a Nearby Circumstellar Shell

    Science.gov (United States)

    Milisavljevic, D.; Margutti, R.; Kamble, A.; Patnaude, D. J.; Raymond, J. C.; Eldridge, J. J.; Fong, W.; Bietenholz, M.; Challis, P.; Chornock, R.; Drout, M. R.; Fransson, C.; Fesen, R. A.; Grindlay, J. E.; Kirshner, R. P.; Lunnan, R.; Mackey, J.; Miller, G. F.; Parrent, J. T.; Sanders, N. E.; Soderberg, A. M.; Zauderer, B. A.

    2015-12-01

    We present optical observations of supernova SN 2014C, which underwent an unprecedented slow metamorphosis from H-poor type Ib to H-rich type IIn over the course of one year. The observed spectroscopic evolution is consistent with the supernova having exploded in a cavity before encountering a massive shell of the progenitor star's stripped hydrogen envelope. Possible origins for the circumstellar shell include a brief Wolf-Rayet fast wind phase that overtook a slower red supergiant wind, eruptive ejection, or confinement of circumstellar material by external influences of neighboring stars. An extended high velocity Hα absorption feature seen in near-maximum light spectra implies that the progenitor star was not completely stripped of hydrogen at the time of core collapse. Archival pre-explosion Subaru Telescope Suprime-Cam and Hubble Space Telescope Wide Field Planetary Camera 2 images of the region obtained in 2009 show a coincident source that is most likely a compact massive star cluster in NGC 7331 that hosted the progenitor system. By comparing the emission properties of the source with stellar population models that incorporate interacting binary stars we estimate the age of the host cluster to be 30-300 Myr, and favor ages closer to 30 Myr in light of relatively strong Hα emission. SN 2014C is the best observed member of a class of core-collapse supernovae that fill the gap between events that interact strongly with dense, nearby environments immediately after explosion and those that never show signs of interaction. Better understanding of the frequency and nature of this intermediate population can contribute valuable information about the poorly understood final stages of stellar evolution.

  9. The Earliest Stages of Star and Planet Formation: Core Collapse, and the Formation of Disks and Outflows

    CERN Document Server

    Li, Zhi-Yun; Pudritz, Ralph E; Jørgensen, Jes K; Shang, Hsien; Krasnopolsky, Ruben; Maury, Anaëlle

    2014-01-01

    (Abridged) In this review we focus on the observations and theory of the formation of early disks and outflows, and their connections with the first phases of planet formation. Large rotationally supported circumstellar disks, although common around more evolved young stellar objects, are rarely detected during the earliest, "Class 0" phase; however, a few excellent candidates have been discovered recently around both low and high mass protostars. In this early phase, prominent outflows are ubiquitously observed; they are expected to be associated with at least small magnetized disks. Disk formation - once thought to be a simple consequence of the conservation of angular momentum during hydrodynamic core collapse - is far more subtle in magnetized gas. In this case, the rotation can be strongly magnetically braked. Indeed, both analytic arguments and numerical simulations have shown that disk formation is suppressed in the strict ideal magnetohydrodynamic (MHD) limit for the observed level of core magnetizati...

  10. Stellar orbit evolution in close circumstellar disc encounters

    CERN Document Server

    Muñoz, Diego J; Vogelsberger, Mark; Hernquist, Lars; Springel, Volker

    2014-01-01

    The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3-D, focusing on disc-disc interactions that result from stellar fly-bys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3-D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericenter separation r_p, disc orientation and disc-star mass ratio (M_d/M_*) on the orbital evolution of the host stars. Close encounters (2r_p<~ disc radius) can truncate discs on very short time scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that ...

  11. Modelling circumstellar discs with 3D radiation hydrodynamics

    CERN Document Server

    Acreman, David M; Rundle, David A

    2009-01-01

    We present results from combining a grid-based radiative transfer code with a Smoothed Particle Hydrodynamics code to produce a flexible system for modelling radiation hydrodynamics. We use a benchmark model of a circumstellar disc to determine a robust method for constructing a gridded density distribution from SPH particles. The benchmark disc is then used to determine the accuracy of the radiative transfer results. We find that the SED and the temperature distribution within the disc are sensitive to the representation of the disc inner edge, which depends critically on both the grid and SPH resolution. The code is then used to model a circumstellar disc around a T-Tauri star. As the disc adjusts towards equilibrium vertical motions in the disc are induced resulting in scale height enhancements which intercept radiation from the central star. Vertical transport of radiation enables these perturbations to influence the mid-plane temperature of the disc. The vertical motions decay over time and the disc ulti...

  12. Herschel/HIFI observations of the circumstellar ammonia lines in IRC+10216

    Science.gov (United States)

    Schmidt, M. R.; He, J. H.; Szczerba, R.; Bujarrabal, V.; Alcolea, J.; Cernicharo, J.; Decin, L.; Justtanont, K.; Teyssier, D.; Menten, K. M.; Neufeld, D. A.; Olofsson, H.; Planesas, P.; Marston, A. P.; Sobolev, A. M.; de Koter, A.; Schöier, F. L.

    2016-08-01

    Context. A discrepancy exists between the abundance of ammonia (NH3) derived previously for the circumstellar envelope (CSE) of IRC+10216 from far-IR submillimeter rotational lines and that inferred from radio inversion or mid-infrared (MIR) absorption transitions. Aims: To address the discrepancy described above, new high-resolution far-infrared (FIR) observations of both ortho- and para-NH3 transitions toward IRC+10216 were obtained with Herschel, with the goal of determining the ammonia abundance and constraining the distribution of NH3 in the envelope of IRC+10216. Methods: We used the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel to observe all rotational transitions up to the J = 3 level (three ortho- and six para-NH3 lines). We conducted non-LTE multilevel radiative transfer modelling, including the effects of near-infrared (NIR) radiative pumping through vibrational transitions. The computed emission line profiles are compared with the new HIFI data, the radio inversion transitions, and the MIR absorption lines in the ν2 band taken from the literature. Results: We found that NIR pumping is of key importance for understanding the excitation of rotational levels of NH3. The derived NH3 abundances relative to molecular hydrogen were (2.8 ± 0.5) × 10-8 for ortho-NH3 and for para-NH3, consistent with an ortho/para ratio of 1. These values are in a rough agreement with abundances derived from the inversion transitions, as well as with the total abundance of NH3 inferred from the MIR absorption lines. To explain the observed rotational transitions, ammonia must be formed near to the central star at a radius close to the end of the wind acceleration region, but no larger than about 20 stellar radii (1σ confidence level). Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. HIFI is the Herschel Heterodyne Instrument for the Far

  13. THE 0.5-2.22 {mu}m SCATTERED LIGHT SPECTRUM OF THE DISK AROUND TW Hya: DETECTION OF A PARTIALLY FILLED DISK GAP AT 80 AU

    Energy Technology Data Exchange (ETDEWEB)

    Debes, John H. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Jang-Condell, Hannah [University of Wyoming, Laramie, WY 82071 (United States); Weinberger, Alycia J. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 (United States); Roberge, Aki [Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Schneider, Glenn [Steward Observatory, University of Arizona, Tuscon, AZ 85721 (United States)

    2013-07-01

    We present a 0.5-2.2 {mu}m scattered light spectrum of the circumstellar disk around TW Hya from a combination of spatially resolved Hubble Space Telescope STIS spectroscopy and NICMOS coronagraphic images of the disk. We investigate the morphology of the disk at distances >40 AU over this wide range of wavelengths, and identify the presence of a depression in surface brightness at {approx}80 AU that could be caused by a gap in the disk. Additionally, we quantify the surface brightness, azimuthal symmetry, and spectral character of the disk as a function of radius. Our analysis shows that the scattering efficiency of the dust is largely neutral to blue over the observed wavelengths. We model the disk as a steady {alpha}-disk with an ad hoc gap structure. The thermal properties of the disk are self-consistently calculated using a three-dimensional radiative transfer code that uses ray tracing to model the heating of the disk interior and scattered light images. We find a good fit to the data over a wide range of distances from the star if we use a model disk with a partially filled gap of 30% depth at 80 AU and with a self-similar truncation knee at 100 AU. The origin of the gap is unclear, but it could arise from a transition in the nature of the disk's dust composition or the presence of a planetary companion. Based on scalings to previous hydrodynamic simulations of gap-opening criteria for embedded proto-planets, we estimate that a planetary companion forming the gap could have a mass between 6 and 28 M{sub Circled-Plus }.

  14. 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

  15. Moisture Dynamics in Building Envelopes

    DEFF Research Database (Denmark)

    Peuhkuri, Ruut Hannele

    2003-01-01

    moisture conditions in the exterior weather and indoor climate the materials dynamically absorb and release moisture. The complexity of the impact of these conditions on the resulting moisture transport and content of the materials has been studied in this Thesis with controlled laboratory tests. The first......The overall scope of this Thesis "Moisture dynamics in building envelopes" has been to characterise how the various porous insulation materials investigated performed hygrothermally under conditions similar to those in a typical building envelope. As a result of the changing temperature and...

  16. Moisture dynamics in building envelopes

    Energy Technology Data Exchange (ETDEWEB)

    Peuhkuri, R.

    2003-07-01

    The overall scope of this Thesis 'Moisture dynamics in building envelopes' has been to characterise how the various porous insulation materials investigated performed hygro thermally under conditions similar to those in a typical building envelope. As a result of the changing temperature and moisture conditions in the exterior weather and indoor climate the materials dynamically absorb and release moisture. The complexity of the impact of these conditions on the resulting moisture transport and content of the materials has been studied in this Thesis with controlled laboratory tests. (au)

  17. Envelope Inflation or Stellar Wind?

    Science.gov (United States)

    Ro, S.; Matzner, C. D.

    We an optically-thick, transonic, steady wind model for a H-free Wolf-Rayet star. A bifurcation is found across a critical mass loss rate Mb. Slower winds M < Mb extend by several hydrostatic stellar radii, reproduce features of envelope in ation from Petrovic et al. (2006) and Gräfener et al. (2012), and are energetically unbound. This work is of particular interest for extended envelopes and winds, radiative hydrodynamic instabilities (eg. wind stagnation, clumping, etc.), and NLTE atmospheric models.

  18. Integrability of motion around galactic razor-thin disks

    CERN Document Server

    Vieira, Ronaldo S S

    2016-01-01

    We consider the three-dimensional bounded motion of a test particle around razor-thin disk configurations, by focusing on the adiabatic invariance of the vertical action associated with disk-crossing orbits. We find that it leads to an approximate third integral of motion predicting envelopes of the form $Z(R)\\propto[\\Sigma(R)]^{-1/3}$, where $R$ is the radial galactocentric coordinate, $Z$ is the z-amplitude (vertical amplitude) of the orbit and $\\Sigma$ represents the surface mass density of the thin disk. This third integral, which was previously formulated for the case of flattened 3D configurations, is tested for a variety of trajectories in different thin-disk models.

  19. Spirals in protoplanetary disks from photon travel time

    CERN Document Server

    Kama, M; Heays, A N

    2016-01-01

    Spiral structures are a common feature in scattered-light images of protoplanetary disks, and of great interest as possible tracers of the presence of planets. However, other mechanisms have been put foward to explain them, including self-gravity, disk-envelope interactions, and dead zone boundaries. These mechanisms explain many spirals very well, but are unable to easily account for very loosely wound spirals and single spiral arms. We study the effect of light travel time on the shape of a shadow cast by a clump orbiting close (within ${\\sim}1\\,$au) of the central star, where there can be significant orbital motion during the light travel time from the clump to the outer disk and then to the sky plane. This delay in light rays reaching the sky plane gives rise to a variety of spiral- and arc-shaped shadows, which we describe with a general fitting formula for a flared, inclined disk.

  20. A photospheric metal line profile analysis of hot DA white dwarfs with circumstellar material

    CERN Document Server

    Dickinson, Nathan J; Welsh, Barry Y

    2012-01-01

    Some hot DA white dwarfs have circumstellar high ion absorption features in their spectra, in addition to those originating in the photosphere. In many cases, the line profiles of these absorbing components are unresolved. Given the importance of the atmospheric composition of white dwarfs to studies of stellar evolution, extra-solar planetary systems and the interstellar medium, we examine the effect of including circumstellar line profiles in the abundance estimates of photospheric metals in six DA stars. The photospheric C and Si abundances are reduced in five cases where the circumstellar contamination is strong, though the relative weakness of the circumstellar Si IV absorption introduces minimal contamination, resulting in a small change in abundance. The inability of previous, approximate models to reproduce the photospheric line profiles here demonstrates the need for a technique that accounts for the physical line profiles of both the circumstellar and photospheric lines when modelling these blended ...

  1. The HST/ACS Atlas of Protoplanetary Disks in the Great Orion Nebula

    CERN Document Server

    Ricci, Luca; Soderblom, David R

    2008-01-01

    We present the atlas of protoplanetary disks in the Orion Nebula based on the ACS/WFC images obtained for the HST Treasury Program on the Orion Nebula Cluster. The observations have been carried out in 5 photometric filters nearly equivalent to the standard B, V, Halpha, I, and z passbands. Our master catalog lists 178 externally ionized proto-planetary disks (proplyds), 28 disks seen only in absorption against the bright nebular background (silhouette disks), 8 disks seen only as dark lanes at the midplane of extended polar emission (bipolar nebulae or reflection nebulae) and 5 sources showing jet emission with no evidence of neither external ionized gas emission nor dark silhouette disks. Many of these disks are associated with jets seen in Halpha and circumstellar material detected through reflection emission in our broad-band filters; approximately 2/3 have identified counterparts in x-rays. A total of 47 objects (29 proplyds, 7 silhouette disks, 6 bipolar nebulae, 5 jets with no evidence of proplyd emiss...

  2. Possible Molecular Spiral Arms in the Protoplanetary Disk of AB Aur

    CERN Document Server

    Lin, S Y; Ho, P T P; Lim, J; Ohashi, N; Tamura, M; Fukagawa, Misato; Ho, Paul T.P.; Lim, Jeremy; Lin, Shin-Yi; Ohashi, Nagayoshi; Tamura, Motohide

    2006-01-01

    The circumstellar dust disk of the Herbig Ae star AB Aur has been found to exhibit complex spiral-like structures in the near-IR image obtained with the Subaru Telescope. We present maps of the disk in both 12CO (3-2) and dust continuum at 345 GHz with the SMA at an angular resolution of 1.0"x0.7" (144AU x 100AU). The continuum emission traces a dust disk with a central depression and a maximum overall dimension of 450AU (FWHM). This dust disk exhibits several distinct peaks that appear to coincide with bright features in the near-IR image, in particular the brightest inner spiral arm. The CO emission traces a rotating gas disk of size 530AU x 330AU with a deprojected maximum velocity of 2.8km/s at 450AU. In contrast to the dust disk, the gas disk exhibits an intensity peak at the stellar position. Furthermore, the CO emission in several velocity channels traces the innermost spiral arm seen in the near-IR. We compare the observed spatial-kinematic structure of the CO emission to a simple model of a disk in K...

  3. The Hubble space telescope/advanced camera for surveys atlas of protoplanetary disks in the great Orion Nebula

    International Nuclear Information System (INIS)

    We present the atlas of protoplanetary disks in the Orion Nebula based on the Wide Field Channel of the Advanced Camera for Surveys (ACS/WFC) images obtained for the Hubble Space Telescope (HST) Treasury Program on the Orion Nebula Cluster. The observations have been carried out in five photometric filters nearly equivalent to the standard B, V, Hα, I, and z passbands. Our master catalog lists 178 externally ionized protoplanetary disks (proplyds), 28 disks seen only in absorption against the bright nebular background (silhouette disks), eight disks seen only as dark lanes at the midplane of extended polar emission (bipolar nebulae or reflection nebulae), and five sources showing jet emission with no evidence of either external ionized gas emission or dark silhouette disks. Many of these disks are associated with jets seen in Hα and circumstellar material detected through reflection emission in our broadband filters; approximately two-thirds have identified counterparts in X-rays. A total of 47 objects (29 proplyds, seven silhouette disks, six bipolar nebulae, five jets with no evidence of proplyd emission or silhouette disk) are new detections with HST. We include in our list four objects previously reported as circumstellar disks, which have not been detected in our HST/ACS images either because they are hidden by the bleeding trails of a nearby saturated bright star or because of their location out of the HST/ACS Treasury Program field. The other 31 sources previously reported as extended objects do not harbor a stellar source in our HST/ACS images. We also report on the detection of 16 red, elongated sources. Their location at the edges of the field, far from the Trapezium cluster core (≳10'), suggests that these are probably background galaxies observed through low-extinction regions of the Orion Molecular Cloud (OMC-1).

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

    CERN Document Server

    Schneider, Glenn; Hines, Dean C; Stark, Christopher C; Debes, John H; Carson, Joe; Kuchner, Mark J; Perrin, Marshall D; Weinberger, Alycia J; Wisniewski, John P; Silverstone, Murray D; Jang-Condell, Hannah; Henning, Thomas; Woodgate, Bruce E; Serabyn, Eugene; Moro-Martin, Amaya; Tamura, Motohide; Hinz, Phillip M; Rodigas, Timothy J

    2014-01-01

    Spatially resolved scattered-light images of circumstellar (CS) 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, systemic architectures, and forces perturbing starlight-scattering CS material. Using HST/STIS optical coronagraphy, we have completed the observational phase of a program to study the spatial distribution of dust in ten CS debris systems, and one "mature" protoplanetrary disk all with HST pedigree, using PSF-subtracted multi-roll coronagraphy. These observations probe stellocentric distances > 5 AU for the nearest stars, and simultaneously resolve disk substructures well beyond, corresponding to the giant planet and Kuiper belt regions in our Solar System. They also disclose diffuse very low-surface brightness dust at larger stellocentric distances. We present new results inclusive of fainter disks such as HD92945 confirming, and better revealing, the existence of a narrow inner...

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

    International Nuclear Information System (INIS)

    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.

  6. New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme

    Science.gov (United States)

    Danilovich, T.; Teyssier, D.; Justtanont, K.; Olofsson, H.; Cerrigone, L.; Bujarrabal, V.; Alcolea, J.; Cernicharo, J.; Castro-Carrizo, A.; García-Lario, P.; Marston, A.

    2015-09-01

    Context. Asymptotic giant branch (AGB) stars are in one of the latest evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss has a significant effect on the stellar evolution, and is a significant source of heavy elements and dust grains for the interstellar medium. The mass-loss rate can be well traced by carbon monoxide (CO) line emission. Aims: We present new Herschel/HIFI and IRAM 30 m telescope CO line data for a sample of 53 galactic AGB stars. The lines cover a fairly large range of excitation energy from the J = 1 → 0 line to the J = 9 → 8 line, and even the J = 14 → 13 line in a few cases. We perform radiative transfer modelling for 38 of these sources to estimate their mass-loss rates. Methods: We used a radiative transfer code based on the Monte Carlo method to model the CO line emission. We assume spherically symmetric circumstellar envelopes that are formed by a constant mass-loss rate through a smoothly accelerating wind. Results: We find models that are consistent across a broad range of CO lines for most of the stars in our sample, i.e., a large number of the circumstellar envelopes can be described with a constant mass-loss rate. We also find that an accelerating wind is required to fit, in particular, the higher-J lines and that a velocity law will have a significant effect on the model line intensities. The results cover a wide range of mass-loss rates (~10-8 to 2 × 10-5 M⊙ yr-1) and gas expansion velocities (2 to 21.5 km s-1) , and include M-, S-, and C-type AGB stars. Our results generally agree with those of earlier studies, although we tend to find slightly lower mass-loss rates by about 40%, on average. We also present "bonus" lines detected during our CO observations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Based on observations carried out with the IRAM 30 m Telescope. IRAM is

  7. Galaxy Disks are Submaximal

    CERN Document Server

    Bershady, Matthew A; Verheijen, Marc A W; Westfall, Kyle B; Andersen, David R; Swaters, Rob A

    2011-01-01

    We measure the contribution of galaxy disks to the overall gravitational potential of 30 nearly face-on intermediate-to-late-type spirals from the DiskMass Survey. The central vertical velocity dispersion of the disk stars, sigma(z,R=0), is related to the maximum rotation speed (Vmax) as sigma(z,R=0) ~ 0.26 Vmax, consistent with previous measurements for edge-on disk galaxies and a mean stellar velocity ellipsoid axial ratio sigma(z) / sigma(R) = 0.6. For reasonable values of disk oblateness, this relation implies these galaxy disks are submaximal. We find disks in our sample contribute only 15% to 30% of the dynamical mass within 2.2 disk scale-lengths (hR), with percentages increasing systematically with luminosity, rotation speed and redder color. These trends indicate the mass ratio of disk-to-total matter remains at or below 50% at 2.2 hR even for the most extreme, fast-rotating disks (Vmax > 300 km/s), of the reddest rest-frame, face-on color (B-K ~ 4 mag), and highest luminosity (M(K)<-26.5 mag). Th...

  8. Energy efficiency of building envelope

    OpenAIRE

    V.M. Yakubson

    2014-01-01

    November, 12-13th, in Saint-Petersburg the 7th International congress "Energy efficiency. XXI century" took place. The reports were done in breakuo groups according to the various aspects of energy efficiency challenge: HVAC systems, water supply and sewerage systems, gas supply, energy metering. One of the grourps was devoted to thermophysics of buildings and energy effective design of building envelope.

  9. Outliers In Data Envelopment Analysis

    Directory of Open Access Journals (Sweden)

    Shaik Khaleel Ahamed

    2015-06-01

    Full Text Available Data Envelopment Analysis is a linear programming technique that assigns efficiency scores to firms engaged in producing similar outputs employing similar inputs. Extremely efficient firms are potential Outliers. The method developed detects Outliers, implementing Stochastic Threshold Value, with computational ease. It is useful in data filtering in BIG DATA problems.

  10. New debris disks in nearby young moving groups

    CERN Document Server

    Moór, A; Ábrahám, P; Balog, Z; Csengeri, T; Henning, Th; Juhász, A; Kiss, Cs

    2016-01-01

    A significant fraction of nearby young moving group members harbor circumstellar debris dust disks. Due to their proximity and youth, these disks are attractive targets for studying the early evolution of debris dust and planetesimal belts. Here we present 70 and 160$\\mu$m observations of 31 systems in the $\\beta$ Pic moving group, and in the Tucana-Horologium, Columba, Carina and Argus associations, using the Herschel Space Observatory. None of these stars were observed at far-infrared wavelengths before. Our Herschel measurements were complemented by photometry from the WISE satellite for the whole sample, and by submillimeter/millimeter continuum data for one source, HD 48370. We identified six stars with infrared excess, four of them are new discoveries. By combining our new findings with results from the literature, we examined the incidence and general characteristics of debris disks around Sun-like members of the selected groups. With their dust temperatures of <45 K the newly identified disks aroun...

  11. New Debris Disks in Nearby Young Moving Groups

    Science.gov (United States)

    Moór, A.; Kóspál, Á.; Ábrahám, P.; Balog, Z.; Csengeri, T.; Henning, Th.; Juhász, A.; Kiss, Cs.

    2016-08-01

    A significant fraction of nearby young moving group members harbor circumstellar debris dust disks. Due to their proximity and youth, these disks are attractive targets for studying the early evolution of debris dust and planetesimal belts. Here we present 70 and 160 μm observations of 31 systems in the β Pic moving group, and in the Tucana–Horologium, Columba, Carina, and Argus associations, using the Herschel Space Observatory. None of these stars were observed at far-infrared wavelengths before. Our Herschel measurements were complemented by photometry from the WISE satellite for the whole sample, and by submillimeter/millimeter continuum data for one source, HD 48370. We identified six stars with infrared excess, four of them are new discoveries. By combining our new findings with results from the literature, we examined the incidence and general characteristics of debris disks around Sun-like members of the selected groups. With their dust temperatures of groups. In terms of dust content, they resemble the hypothesized debris disk of the ancient solar system.

  12. An azimuthal asymmetry in the LkHa 330 disk

    CERN Document Server

    Isella, Andrea; Carpenter, John M; Ricci, Luca; Andrews, Sean; Rosenfeld, Katherine

    2013-01-01

    Theory predicts that giant planets and low mass stellar companions shape circumstellar disks by opening annular gaps in the gas and dust spatial distribution. For more than a decade it has been debated whether this is the dominant process that leads to the formation of transitional disks. In this paper, we present millimeter-wave interferometric observations of the transitional disk around the young intermediate mass star LkHa330. These observations reveal a lopsided ring in the 1.3 mm dust thermal emission characterized by a radius of about 100 AU and an azimuthal intensity variation of a factor of 2. By comparing the observations with a Gaussian parametric model, we find that the observed asymmetry is consistent with a circular arc, that extends azimuthally by about 90 deg and emits about 1/3 of the total continuum flux at 1.3 mm. Hydrodynamic simulations show that this structure is similar to the azimuthal asymmetries in the disk surface density that might be produced by the dynamical interaction with unse...

  13. Resolved Millimeter Emission from the HD 15115 Debris Disk

    CERN Document Server

    MacGregor, Meredith A; Andrews, Sean M; Hughes, A Meredith

    2015-01-01

    We have used the Submillimeter Array (SMA) to make 1.3 millimeter observations of the debris disk surrounding HD 15115, an F-type star with a putative membership in the beta Pictoris moving group. This nearly edge-on debris disk shows an extreme asymmetry in optical scattered light, with an extent almost two times larger to the west of the star than to the east (originally dubbed the "Blue Needle"). The SMA observations reveal resolved emission that we model as a circumstellar belt of thermal dust emission. This belt extends to a radius of ~110 AU, coincident with the break in the scattered light profile convincingly seen on the western side of the disk. This outer edge location is consistent with the presence of an underlying population of dust-producing planetesimals undergoing a collisional cascade, as hypothesized in "birth ring" theory. In addition, the millimeter emission shows a ~3 sigma feature aligned with the asymmetric western extension of the scattered light disk. If this millimeter extension is r...

  14. Searching for circumplanetary disks around LkCa 15

    CERN Document Server

    Isella, Andrea; Carpenter, John M; Pe'rez, Laura M; Ricci, Luca

    2014-01-01

    We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm continuum emission from the disk surrounding the young star LkCa 15. The observations achieve an angular resolution of 70 mas and spatially resolve the circumstellar emission on a spatial scale of 9 AU. The continuum emission traces a dusty annulus of 45 AU in radius that is consistent with the dust morphology observed at shorter wavelengths. The VLA observations also reveal a compact source at the center of the disk, possibly due to thermal emission from hot dust or ionized gas located within a few AU from the central star. No emission is observed between the star and the dusty ring, and, in particular, at the position of the candidate protoplanet LkCa 15 b. By comparing the observations with theoretical models for circumplanetary disk emission, we find that if LkCa~15~b is a massive planet (>5 M_J) accreting at a rate greater than 1.e-6 M_J yr^{-1}, then its circumplanetary disk is less massive than 0.1 M_J, or smaller than 0.4 Hill r...

  15. The reliability of approximate radiation transport methods for irradiated disk studies

    CERN Document Server

    Kuiper, Rolf

    2013-01-01

    Context: Dynamical studies of irradiated circumstellar disks require an accurate treatment of radiation transport to, for example, properly determine cooling and fragmentation properties. The radiation transport algorithm should be as fast as the (magneto-) hydrodynamics to allow for an efficient usage of computing resources. Methods: We use a setup of a central star and a slightly flared circumstellar disk. We perform simulations for a wide range of optical depths of the disk's midplane from tau(550nm) = 0.1 up to tau(810nm) = 1 million. We check the accuracy of the gray flux-limited diffusion (FLD) approximation and a gray and frequency-dependent ray-tracing plus FLD approximation. Results: 1. For moderate optical depths, a gray approximation of the stellar irradiation yields a slightly hotter inner rim and a slightly cooler midplane of the disk at larger radii, but is otherwise in agreement with the frequency-dependent treatment. 2. The gray FLD approximation fails to compute an appropriate temperature pro...

  16. Modeling water emission from low-mass protostellar envelopes

    CERN Document Server

    van Kempen, T A; Van Dishoeck, E F; Hogerheijde, M R; Jørgensen, J K

    2008-01-01

    Within low-mass star formation, water vapor plays a key role in the chemistry and energy balance of the circumstellar material. The Herschel Space Observatory will open up the possibility to observe water lines originating from a wide range of excitation energies.Our aim is to simulate the emission of rotational water lines from envelopes characteristic of embedded low-mass protostars. A large number of parameters that influence the water line emission are explored: luminosity, density,density slope and water abundances.Both dust and water emission are modelled using full radiative transfer in spherical symmetry. The temperature profile is calculated for a given density profile. The H2O level populations and emission profiles are in turn computed with a non-LTE line code. The results are analyzed to determine the diagnostic value of different lines, and are compared with existing observations. Lines can be categorized in: (i) optically thick lines, including ground-state lines, mostly sensitive to the cold ou...

  17. On the formation and abundance of CO in AGB envelopes

    CERN Document Server

    Papoular, Renaud

    2008-01-01

    It is generally considered, as a rule of thumb, that carbon monoxide forms very early in envelopes of AGB stars, and that it consumes most of the carbon, or most of the oxygen, depending on whether the photosphere is oxygen-rich or carbon-rich, respectively. \\rm This work focuses on the latter case, with the purpose of quantifying the remaining fraction of gaseous carbon which is then available for forming carbonaceous grains. Since AGB stars are (probably) the main providers of cosmic carbon grains, this residual fraction is essential in establishing the validity of current grain models. Here, we use a kinetic treatment to follow the chemical evolution of circumstellar shells towards steady state. It is shown that the residual fraction depends essentially on the atomic ratio of pristine gaseous carbon and oxygen, and on the cross-section for CH formation by collision of C and H atoms. It lies between 55 and 144 C atoms per million H atoms, depending on the values adopted for unknown reaction rates and cosmic...

  18. The Mineralogy of Circumstellar Silicates Preserved in Cometary Dust

    Science.gov (United States)

    Keller, L. P.; Messenger, S.

    2010-01-01

    Interplanetary dust particles (IDPs) contain a record of the building blocks of the solar system including presolar grains, molecular cloud material, and materials formed in the early solar nebula. Cometary IDPs have remained relatively unaltered since their accretion because of the lack of parent body thermal and aqueous alteration. We are using coordinated transmission electron microscope (TEM) and ion microprobe studies to establish the origins of the various components within cometary IDPs. Of particular interest is the nature and abundance of presolar silicates in these particles because astronomical observations suggest that crystalline and amorphous silicates are the dominant grain types produced in young main sequence stars and evolved O-rich stars. Five circumstellar grains have been identified including three amorphous silicate grains and two polycrystalline aggregates. All of these grains are between 0.2 and 0.5 micrometers in size. The isotopic compositions of all five presolar silicate grains fall within the range of presolar oxides and silicates, having large (17)O-enrichments and normal (18)O/(16)O ratios (Group 1 grains from AGB and RG stars). The amorphous silicates are chemically heterogeneous and contain nanophase FeNi metal and FeS grains in a Mg-silicate matrix. Two of the amorphous silicate grains are aggregates with subgrains showing variable Mg/Si ratios in chemical maps. The polycrystalline grains show annealed textures (equilibrium grains boundaries, uniform Mg/Fe ratios), and consist of 50-100 nm enstatite and pyrrhotite grains with lesser forsterite. One of the polycrystalline aggregates contains a subgrain of diopside. The polycrystalline aggregates form by subsolidus annealing of amorphous precursors. The bulk compositions of the five grains span a wide range in Mg/Si ratios from 0.4 to 1.2 (avg. 0.86). The average Fe/Si (0.40) and S/Si (0.21) ratios show a much narrower range of values and are approximately 50% of their solar

  19. Recycling of Neutron Stars in Common Envelopes and Hypernova Explosions

    CERN Document Server

    Barkov, Maxim V

    2010-01-01

    In this paper we propose a new plausable mechanism of supernova explosions specific to close binary systems. The starting point is the common envelope phase in the evolution of a binary consisting of a red super giant and a neutron star. As the neutron star spirals towards the center of its companion it spins up via disk accretion. Depending on the specific angular momentum of gas captured by the neutron star via the Bondi-Hoyle mechanism, it may reach millisecond periods either when it is still inside the common envelope or after it has merged with the companion core. Then it can generate magnetar strength magnetic field via becoming unstable to emission of gravitational waves and developing strong differential rotation, as this has been recently proposed by H.Spruit. The magnetar wind can blow away the common envelope if its magnetic field is as strong as $10^{15}\\,$G, and can destroy the entire companion if it is as strong as $10^{16}\\,$G. The total explosion energy can be comparable to the rotational ener...

  20. 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.

  1. REMARKS ON JOHN DISKS

    Institute of Scientific and Technical Information of China (English)

    Chu Yuming; Cheng Jinfa; Wang Gendi

    2009-01-01

    Let D R2 be a Jordan domain, D* = -R2 \\ -D, the exterior of D. In this article, the authors obtained the following results: (1) If D is a John disk, then D is an outer linearly locally connected domain; (2) If D* is a John disk, then D is an inner linearly locally connected domain; (3) A homeomorphism f: R2→R2 is a quasiconformal mapping if and only if f(D) is a John disk for any John disk D(∈)R2; and (4) If D is a bounded quasidisk, then D is a John disk, and there exists an unbounded quasidisk which is not a John disk.

  2. Percutaneous laser disk decompression

    International Nuclear Information System (INIS)

    Experimental data show that a small change in volume is associated with a disproportionately large change in intradiskal pressure. The authors of this paper conducted a clinical study toe valuate a new method of treating lumbar disk disease by vaporizing a small volume of the protruding disk with a Nd:YAG laser applied percutaneously. Patients with symptoms of disk herniation were selected after failure of conservative therapy. A complete neurologic examination was performed in all patients before and after therapy. Disk disease was confirmed with CT or MR imaging. Sixty-three treatments of 56 disks in 47 patients have been performed to date, all on an outpatient basis. Under fluoroscopic control, ND:YAG laser energy (600-1,200 J) is delivered into the disk through a 3-F fiber passed through the needle

  3. The close circumstellar environment of Betelgeuse - II. Diffraction-limited spectro-imaging from 7.76 to 19.50 microns with VLT/VISIR

    CERN Document Server

    Kervella, Pierre; Chiavassa, Andrea; Ridgway, Stephen T; Cami, Jan; Haubois, Xavier; Verhoelst, Tijl; 10.1051/0004-6361/201116962

    2011-01-01

    Context: Mass-loss occurring in red supergiants (RSGs) is a major contributor to the enrichment of the interstellar medium in dust and molecules. The physical mechanism of this mass loss is however relatively poorly known. Betelgeuse is the nearest RSG, and as such a prime object for high angular resolution observations of its surface (by interferometry) and close circumstellar environment. Aims: The goal of our program is to understand how the material expelled from Betelgeuse is transported from its surface to the interstellar medium, and how it evolves chemically in this process. Methods: We obtained diffraction-limited images of Betelgeuse and a PSF calibrator (Aldebaran) in six filters in the N band (7.76 to 12.81 mic) and two filters in the Q band (17.65 and 19.50 mic), using the VLT/VISIR instrument. Results: Our images show a bright, extended and complex circumstellar envelope at all wavelengths. It is particularly prominent longwards of 9-10 mic, pointing at the presence of O-rich dust, such as silic...

  4. Comparative Spectra of Oxygen-Rich vs. Carbon-Rich Circumstellar Shells: VY Canis Majoris and IRC+10216 at 215-285 GHz

    CERN Document Server

    Tenenbaum, E D; Milam, S N; Woolf, N J; Ziurys, L M

    2010-01-01

    A sensitive (1{\\sigma} rms at 1 MHz resolution ~3 mK) 1 mm spectral line survey (214.5-285.5 GHz) of VY Canis Majoris (VY CMa) and IRC+10216 has been conducted to compare the chemistries of oxygen and carbon-rich circumstellar envelopes. This study was carried out using the Submillimeter Telescope (SMT) of the Arizona Radio Observatory (ARO) with a new ALMA-type receiver. This survey is the first to chemically characterize an O-rich circumstellar shell at millimeter wavelengths. In VY CMa, 128 emission features were detected arising from 18 different molecules, and in IRC+10216, 720 lines were observed, assigned to 32 different species. The 1 mm spectrum of VY CMa is dominated by SO2 and SiS; in IRC +10216, C4H and SiC2 are the most recurrent species. Ten molecules were common to both sources: CO, SiS, SiO, CS, CN, HCN, HNC, NaCl, PN, and HCO+. Sulfur plays an important role in VY CMa, but saturated/unsaturated carbon dominates the molecular content of IRC+10216, producing CH2NH, for example. Although the mol...

  5. Isolated unilateral disk edema

    OpenAIRE

    Varner P

    2011-01-01

    Paul VarnerJohn J Pershing VAMC, Poplar Bluff, MO, USAAbstract: Isolated unilateral disk edema is a familiar clinical presentation with myriad associations. Related, non-consensus terminology is a barrier to understanding a common pathogenesis. Mechanisms for the development of disk edema are reviewed, and a new framework for clinical differentiation of medical associations is presented.Keywords: disk edema, axoplasmic flow, clinical multiplier, optic neuritis, ischemic optic neuropathy, papi...

  6. Review: Accretion Disk Theory

    OpenAIRE

    Montesinos, Matias

    2012-01-01

    In this paper I review and discuss the basic concepts of accretion disks, focused especially on the case of accretion disks around black holes. The well known alpha-model is revisited, showing the strengths and weaknesses of the model. Other turbulent viscosity prescription, based on the Reynolds number, that may improve our understanding of the accretion paradigm is discussed. A simple but efficient mathematical model of a self-gravitating accretion disk, as well as observational evidence of...

  7. Exploring the circumstellar environment of the young eruptive star V2492 Cygni

    Science.gov (United States)

    Kóspál, Á.; Ábrahám, P.; Acosta-Pulido, J. A.; Arévalo Morales, M. J.; Balog, Z.; Carnerero, M. I.; Szegedi-Elek, E.; Farkas, A.; Henning, Th.; Kelemen, J.; Kovács, T.; Kun, M.; Marton, G.; Mészáros, Sz.; Moór, A.; Pál, A.; Sárneczky, K.; Szakáts, R.; Szalai, N.; Szing, A.; Tóth, I.; Turner, N. J.; Vida, K.

    2013-03-01

    Context. V2492 Cyg is a young eruptive star that went into outburst in 2010. The near-infrared color changes observed since the outburst peak suggest that the source belongs to a newly defined sub-class of young eruptive stars, where time-dependent accretion and variable line-of-sight extinction play a combined role in the flux changes. Aims: In order to learn about the origin of the light variations and to explore the circumstellar and interstellar environment of V2492 Cyg, we monitored the source at ten different wavelengths, between 0.55 μm and 2.2 μm from the ground and between 3.6 μm and 160 μm from space. Methods: We analyze the light curves and study the color-color diagrams via comparison with the standard reddening path. We examine the structure of the molecular cloud hosting V2492 Cyg by computing temperature and optical depth maps from the far-infrared data. Results: We find that the shapes of the light curves at different wavelengths are strictly self-similar and that the observed variability is related to a single physical process, most likely variable extinction. We suggest that the central source is episodically occulted by a dense dust cloud in the inner disk and, based on the invariability of the far-infrared fluxes, we propose that it is a long-lived rather than a transient structure. In some respects, V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars. Conclusions: The example of V2492 Cyg demonstrates that the light variations of young eruptive stars are not exclusively related to changing accretion. The variability provided information on an azimuthally asymmetric structural element in the inner disk. Such an asymmetric density distribution in the terrestrial zone may also have consequences for the initial conditions of planet formation. This work is based on observations made with the Herschel Space Observatory and with the Spitzer Space Telescope. Herschel is an ESA space observatory with science instruments

  8. Resolved images of self-gravitating circumstellar discs with ALMA

    CERN Document Server

    Cossins, P; Testi, L

    2010-01-01

    In this paper we present simulated observations of massive self-gravitating circumstellar discs using the Atacama Large Millimetre/sub-millimetre Array (ALMA). Using a smoothed particle hydrodynamics model of a $0.2M_{\\odot}$ disc orbiting a $1M_{\\odot}$ protostar, with a cooling model appropriate for discs at temperatures below $\\sim 160$K and representative dust opacities, we have constructed maps of the expected emission at sub-mm wavelengths. We have then used the CASA ALMA simulator to generate simulated images and visibilities with various array configurations and observation frequencies, taking into account the expected thermal noise and atmospheric opacities. We find that at 345 GHz (870 $\\mu$m) spiral structures at a resolution of a few AU should be readily detectable in approximately face-on discs out to distances of the Taurus-Auriga star-forming complex.

  9. Flash-Heating of Circumstellar Clouds by $\\gamma$ Ray Bursts

    CERN Document Server

    Dermer, C D; Dermer, Charles D.; Boettcher, Markus

    2000-01-01

    The blast-wave model for gamma-ray bursts (GRBs) has been called intoquestion by observations of spectra from GRBs that are harder than can beproduced through optically thin synchrotron emission. If GRBs originate fromthe collapse of massive stars, then circumstellar clouds near burst sourceswill be illuminated by intense gamma radiation, and the electrons in theseclouds will be rapidly scattered to energies as large as several hundred keV.Low-energy photons that subsequently pass through the hot plasma will bescattered to higher energies, hardening the intrisic spectrum. This effectresolves the "line-of-death" objection to the synchrotron shock model.Illuminated clouds near GRBs will form relativistic plasmas containing largenumbers of electron-positron pairs that can be detected within ~ 1-2 days ofthe explosion before expanding and dissipating. Localized regions of pairannihilation radiation in the Galaxy would reveal past GRB explosions.

  10. Archival Legacy Investigation of Circumstellar Environments (ALICE). Survey results

    Science.gov (United States)

    Soummer, Remi; Choquet, Elodie; Pueyo, Laurent; Brendan Hagan, J.; Gofas-Salas, Elena; Rajan, Abhijith; Chen, Christine; Perrin, Marshall D.; Debes, John H.; Golimowski, David A.; Hines, Dean C.; N'Diaye, Mamadou; Schneider, Glenn; Mawet, Dimitri; Marois, Christian

    2016-01-01

    We report on the status of the ALICE project (Archival Legacy Investigation of Circumstellar Environments. HST/AR-12652), which consists in a consistent reanalysis of the entire HST-NICMOS coronagraphic archive with advanced post-processing techniques. Over the last two years, we have developed a sophisticated pipeline able to handle the data of the 400 stars of the archive. We present the results of the overall reduction campaign and discuss the first statistical analysis of the candidate detections. As we will deliver high-level science products to the STScI MAST archive, we are defining a new standard format for high-contrast science products, which will be compatible with every new high-contrast imaging instrument and used by the JWST coronagraphs. We present here an update and overview of the specifications of this standard.

  11. Water vapor in the protoplanetary disk of DG Tau

    CERN Document Server

    Podio, L; Codella, C; Cabrit, S; Nisini, B; Dougados, C; Sandell, G; Williams, J P; Testi, L; Thi, W -F; Woitke, P; Meijerink, R; Spaans, M; Aresu, G; Menard, F; Pinte, C

    2013-01-01

    Water is key in the evolution of protoplanetary disks and the formation of comets and icy/water planets. While high excitation water lines originating in the hot inner disk have been detected in several T Tauri stars (TTSs), water vapor from the outer disk, where most of water ice reservoir is stored, was only reported in the closeby TTS TW Hya. We present spectrally resolved Herschel/HIFI observations of the young TTS DG Tau in the ortho- and para- water ground-state transitions at 557, 1113 GHz. The lines show a narrow double-peaked profile, consistent with an origin in the outer disk, and are ~19-26 times brighter than in TW Hya. In contrast, CO and [C II] lines are dominated by emission from the envelope/outflow, which makes H2O lines a unique tracer of the disk of DG Tau. Disk modeling with the thermo-chemical code ProDiMo indicates that the strong UV field, due to the young age and strong accretion of DG Tau, irradiates a disk upper layer at 10-90 AU from the star, heating it up to temperatures of 600 K...

  12. 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.; Bryden, G.; Danchi, W.; Ertel, S.; Lebreton, J.; Liseau, R.; Mora, A.; Mustill, A. J.; Mutschke, H.; Neuhaeuser, R.; Pilbratt, G. L.; Roberge, A.; Schmidt, T. O. B.; Stapelfeldt, K. R.; Thebault, Ph.; Vitense, Ch.; White, G. J.; Wolf, S.

    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

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

    International Nuclear Information System (INIS)

    Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around ∼100 μm 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 μm, which is larger than the 100 μm 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 ∼100 μm, 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 than a few

  14. HNC in Protoplanetary Disks

    CERN Document Server

    Graninger, Dawn; Qi, Chunhua; Kastner, Joel

    2015-01-01

    The distributions and abundances of small organics in protoplanetary disks are potentially powerful probes of disk physics and chemistry. HNC is a common probe of dense interstellar regions and the target of this study. We use the Submillimeter Array (SMA) to observe HNC 3--2 towards the protoplanetary disks around the T Tauri star TW Hya and the Herbig Ae star HD 163296. HNC is detected toward both disks, constituting the first spatially resolved observations of HNC in disks. We also present SMA observations of HCN 3--2, and IRAM 30m observations of HCN and HNC 1--0 toward HD 163296. The disk-averaged HNC/HCN emission ratio is 0.1--0.2 toward both disks. Toward TW Hya, the HNC emission is confined to a ring. The varying HNC abundance in the TW Hya disk demonstrates that HNC chemistry is strongly linked to the disk physical structure. In particular, the inner rim of the HNC ring can be explained by efficient destruction of HNC at elevated temperatures, similar to what is observed in the ISM. To realize the fu...

  15. Sintering-induced Dust Ring Formation in Protoplanetary Disks: Application to the HL Tau Disk

    CERN Document Server

    Okuzumi, Satoshi; Sirono, Sin-iti; Kobayashi, Hiroshi; Tanaka, Hidekazu

    2015-01-01

    The latest observation of HL Tau by ALMA revealed spectacular concentric dust rings in its circumstellar disk. We attempt to explain the multiple ring structure as a consequence of aggregate sintering. Sintering is a process that reduces the sticking efficiency of dust aggregates, and takes place where the temperature is slightly below the sublimation point of some constituent material. We here present a dust growth model that incorporates sintering, and use it to simulate global dust evolution in a modeled HL Tau disk taking into account coagulation, fragmentation, and radial inward drift. We show that the aggregates collisionally disrupt and pile up at multiple locations where different volatiles cause sintering. At wavelengths of 0.87--1.3 mm, these "sintering zones" appear as bright, optically thick rings with spectral slope $\\approx$ 2, whereas the non-sintering zones as darker, optically thinner rings of spectral slope $\\approx$ 2.3--2.5, consistent with major bright and dark rings found in the HL Tau d...

  16. Searching for circumplanetary disks around LkCa 15

    Energy Technology Data Exchange (ETDEWEB)

    Isella, Andrea; Carpenter, John M.; Ricci, Luca [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Chandler, Claire J.; Pérez, Laura M., E-mail: isella@astro.caltech.edu [National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801 (United States)

    2014-06-20

    We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm continuum emission from the disk surrounding the young star LkCa 15. The observations achieve an angular resolution of 70 mas and spatially resolve the circumstellar emission on a spatial scale of 9 AU. The continuum emission traces a dusty annulus of 45 AU in radius that is consistent with the dust morphology observed at shorter wavelengths. The VLA observations also reveal a compact source at the center of the disk, possibly due to thermal emission from hot dust or ionized gas located within a few AU from the central star. No emission is observed between the star and the dusty ring and, in particular, at the position of the candidate protoplanet LkCa 15 b. By comparing the observations with theoretical models for circumplanetary disk emission, we find that if LkCa 15 b is a massive planet (>5 M{sub J} ) accreting at a rate greater than 10{sup –6} M{sub J} yr{sup –1}, then its circumplanetary disk is less massive than 0.1 M{sub J} , or smaller than 0.4 Hill radii. Similar constraints are derived for any possible circumplanetary disk orbiting within 45 AU from the central star. The mass estimates are uncertain by at least one order of magnitude due to the uncertainties on the mass opacity. Future ALMA observations of this system might be able to detect circumplanetary disks down to a mass of 5 × 10{sup –4} M{sub J} and as small as 0.2 AU, providing crucial constraints on the presence of giant planets in the act of forming around this young star.

  17. The SPHERE view of the planet-forming disk around HD 100546

    Science.gov (United States)

    Garufi, A.; Quanz, S. P.; Schmid, H. M.; Mulders, G. D.; Avenhaus, H.; Boccaletti, A.; Ginski, C.; Langlois, M.; Stolker, T.; Augereau, J.-C.; Benisty, M.; Lopez, B.; Dominik, C.; Gratton, R.; Henning, T.; Janson, M.; Ménard, F.; Meyer, M. R.; Pinte, C.; Sissa, E.; Vigan, A.; Zurlo, A.; Bazzon, A.; Buenzli, E.; Bonnefoy, M.; Brandner, W.; Chauvin, G.; Cheetham, A.; Cudel, M.; Desidera, S.; Feldt, M.; Galicher, R.; Kasper, M.; Lagrange, A.-M.; Lannier, J.; Maire, A. L.; Mesa, D.; Mouillet, D.; Peretti, S.; Perrot, C.; Salter, G.; Wildi, F.

    2016-04-01

    Context. The mechanisms governing planet formation are not fully understood. A new era of high-resolution imaging of protoplanetary disks has recently started, thanks to new instruments such as SPHERE, GPI, and ALMA. The planet formation process can now be directly studied by imaging both planetary companions embedded in disks and their effect on disk morphology. Aims: We image disk features that could be potential signs of planet-disk interaction with unprecedented spatial resolution and sensitivity. Two companion candidates have been claimed in the disk around the young Herbig Ae/Be star HD 100546. Thus, this object serves as an excellent target for our investigation of the natal environment of giant planets. Methods: We exploit the power of extreme adaptive optics operating in conjunction with the new high-contrast imager SPHERE to image HD 100546 in scattered light. We obtained the first polarized light observations of this source in the visible (with resolution as fine as 2 AU) and new H and K band total intensity images that we analyzed with the pynpoint package. Results: The disk shows a complex azimuthal morphology, where multiple scattering of photons most likely plays an important role. High brightness contrasts and arm-like structures are ubiquitous in the disk. A double-wing structure (partly due to angular differential imaging processing) resembles a morphology newly observed in inclined disks. Given the cavity size in the visible (11 AU), the CO emission associated to the planet candidate c might arise from within the circumstellar disk. We find an extended emission in the K band at the expected location of b. The surrounding large-scale region is the brightest in scattered light. There is no sign of any disk gap associated to b. Based on data collected at the European Southern Observatory, Chile (ESO Programs 095.C-0273(A) and 095.C-0298(A)).

  18. Apparent disk-mass reduction and planetesimal formation in gravitationally unstable disks in Class 0/I YSOs

    CERN Document Server

    Tsukamoto, Y; Kataoka, A

    2016-01-01

    We investigate the dust structure of gravitationally unstable gas disks undergoing mass accretion from the envelope, envisioning application to Class 0/I YSOs. We compute evolution of the surface density and dust size by taking into account dust collisional growth and radial drift. We find that the dust disk quickly settles into the steady state and the dust mass in the steady-state disk decreases by a factor of 1/2 to 1/3, while the radiative flux of the dust thermal emission also decreases by a factor of 1/3 to 1/5, both compared to that for a disk with ISM dust-to-gas mass ratio and micron-sized dust. We suggest that the disk mass in the Class 0/I YSOs is underestimated by factor of 1/3 to 1/5 when it is calculated from the dust thermal emission assuming an ISM dust-to-gas mass ratio and micron-sized dust opacity, and that a larger fraction of the disks in Class 0/I YSOs is gravitationally unstable than previously considered. We derive an empirical formula for the disk-mass reduction rate, which can be use...

  19. Chemical Models of Collapsing Envelopes

    CERN Document Server

    Bergin, E A

    1999-01-01

    We discuss recent models of chemical evolution in the developing and collapsing protostellar envelopes associated with low-mass star formation. In particular, the effects of depletion of gas-phase molecules onto grain surfaces is considered. We show that during the middle to late evolutionary stages, prior to the formation of a protostar, various species selectively deplete from the gas phase. The principal pattern of selective depletions is the depletion of sulfur-bearing molecules relative to nitrogen-bearing species: NH3 and N2H+. This pattern is shown to be insensitive to the details of the dynamics and marginally sensitive to whether the grain mantle is dominated by polar or non-polar molecules. Based on these results we suggest that molecular ions are good tracers of collapsing envelopes. The effects of coupling chemistry and dynamics on the resulting physical evolution are also examined. Particular attention is paid to comparisons between models and observations.

  20. FORMING AN O STAR VIA DISK ACCRETION?

    International Nuclear Information System (INIS)

    We present a study of outflow, infall, and rotation in a ∼105 L☉ star-forming region, IRAS 18360-0537, with Submillimeter Array and IRAM 30 m observations. The 1.3 mm continuum map shows a 0.5 pc dust ridge, of which the central compact part has a mass of ∼80 M☉ and harbors two condensations, MM1 and MM2. The CO (2-1) and SiO (5-4) maps reveal a biconical outflow centered at MM1, which is a hot molecular core (HMC) with a gas temperature of 320 ± 50 K and a mass of ∼13 M☉. The outflow has a gas mass of 54 M☉ and a dynamical timescale of 8 × 103 yr. The kinematics of the HMC are probed by high-excitation CH3OH and CH3CN lines, which are detected at subarcsecond resolution and unveil a velocity gradient perpendicular to the outflow axis, suggesting a disk-like rotation of the HMC. An infalling envelope around the HMC is evidenced by CN lines exhibiting a profound inverse P Cygni profile, and the estimated mass infall rate, 1.5 × 10–3 M☉ yr–1, is well comparable to that inferred from the mass outflow rate. A more detailed investigation of the kinematics of the dense gas around the HMC is obtained from the 13CO and C18O (2-1) lines; the position-velocity diagrams of the two lines are consistent with the model of a free-falling and Keplerian-like rotating envelope. The observations suggest that the protostar of a current mass ∼10 M☉ embedded within MM1 will develop into an O star via disk accretion and envelope infall.

  1. A NEW DIAGNOSTIC OF THE RADIAL DENSITY STRUCTURE OF Be DISKS

    International Nuclear Information System (INIS)

    We analyze the intrinsic polarization of two classical Be stars in the process of losing their circumstellar disks via a Be to normal B star transition originally reported by Wisniewski et al. During each of five polarimetric outbursts which interrupt these disk-loss events, we find that the ratio of the polarization across the Balmer jump (BJ+/BJ-) versus the V-band polarization traces a distinct loop structure as a function of time. Since the polarization change across the Balmer jump is a tracer of the innermost disk density whereas the V-band polarization is a tracer of the total scattering mass of the disk, we suggest that such correlated loop structures in Balmer jump-V-band polarization diagrams (BJV diagrams) provide a unique diagnostic of the radial distribution of mass within Be disks. We use the three-dimensional Monte Carlo radiation transfer code HDUST to reproduce the observed clockwise loops simply by turning 'on/off' the mass decretion from the disk. We speculate that counterclockwise loop structures we observe in BJV diagrams might be caused by the mass decretion rate changing between subsequent 'on/off' sequences. Applying this new diagnostic to a larger sample of Be disk systems will provide insight into the time-dependent nature of each system's stellar decretion rate.

  2. Deep Spitzer spectroscopy of the `Flying Saucer' edge-on disk: Large grains beyond 50 AU

    CERN Document Server

    Pontoppidan, K M; Blake, G A; Van Dishoeck, E F; Dullemond, C P; Pontoppidan, Klaus M.; Stapelfeldt, Karl R.; Blake, Geoffrey A.; Dishoeck, Ewine F. van; Dullemond, Cornelis P.

    2007-01-01

    We present deep Spitzer-IRS low-resolution (lambda/Delta lambda ~ 100) 5-35 micron spectroscopy of the edge-on disk ``the Flying Saucer'' (2MASS J16281370-2431391) in the Ophiuchus molecular cloud. The spectral energy distribution exhibits the characteristic two-peak shape predicted for a circumstellar disk viewed very close to edge-on. The short-wavelength peak is entirely due to photons scattered off the surface of the disk, while the long-wavelength peak is due to thermal emission from the disk itself. The Spitzer spectrum represents the first spectroscopic detection of scattered light out to 15 micron from a bona-fide, isolated edge-on disk around a T Tauri star. The depth and the wavelength of the mid-infrared "valley" of the SED give direct constraints on the size distribution of large grains in the disk. Using a 2D continuum radiative transfer model, we find that a significant amount of 5-10 micron-sized grains is required in the surface layers of the disk at radii of 50-300 AU. The detection of relati...

  3. Planet-disk interactions in non-isothermal disks

    OpenAIRE

    Lobo Gomes, Aiara

    2015-01-01

    Protoplanetary disks control the formation and evolution of planets, in reaction the planets also influence the disk structure. Disk gas and dust are the building materials of planets. Tidal forces between planet and disk determine the radial movement of the planet (migration); the planets simultaneously influence the disk, possibly carving out a gap. The interplay between planets and disks is important to understand the variety of exoplanets observed and constrain planet formation theories....

  4. Data Envelopment Analysis: An Overview

    OpenAIRE

    Subhash C. Ray

    2014-01-01

    Over the past decades Data Envelopment Analysis (DEA) has emerged as an important nonparametric method of evaluating performance of decision making units through benchmarking. Although developed primarily for measuring technical efficiency, DEA is now applied extensively for measuring scale efficiency, cost efficiency, and profit efficiency as well. This paper integrates the different DEA models commonly applied in empirical research with their underlying theoretical foundations in neoclassic...

  5. Origin of apparent period variations in eclipsing post-common-envelope binaries

    CERN Document Server

    Zorotovic, M

    2012-01-01

    Apparent period variations detected in several eclipsing, close-compact binaries are frequently interpreted as being caused by circumbinary giant planets. This interpretation raises the question of the origin of the potential planets that must have either formed in the primordial circumbinary disk, together with the host binary star, and survived its evolution into a close-compact binary or formed in a post-common-envelope circumbinary disk that remained bound to the post-common-envelope binary (PCEB). Here we combine current knowledge of planet formation and the statistics of giant planets around primordial and evolved binary stars with the theory of close-compact binary star evolution aiming to derive new constraints on possible formation scenarios. We compiled a comprehensive list of observed eclipsing PCEBs, estimated the fraction of systems showing apparent period variations, reconstructed the evolutionary history of the PCEBs, and performed binary population models of PCEBs to characterize their main se...

  6. The Milky Way disk

    Science.gov (United States)

    Carraro, G.

    2015-08-01

    This review summarises the invited presentation I gave on the Milky Way disc. The idea underneath was to touch those topics that can be considered hot nowadays in the Galactic disk research: the reality of the thick disk, the spiral structure of the Milky Way, and the properties of the outer Galactic disk. A lot of work has been done in recent years on these topics, but a coherent and clear picture is still missing. Detailed studies with high quality spectroscopic data seem to support a dual Galactic disk, with a clear separation into a thin and a thick component. Much confusion and very discrepant ideas still exist concerning the spiral structure of the Milky Way. Our location in the disk makes it impossible to observe it, and we can only infer it. This process of inference is still far from being mature, and depends a lot on the selected tracers, the adopted models and their limitations, which in many cases are neither properly accounted for, nor pondered enough. Finally, there are very different opinions on the size (scale length, truncation radius) of the Galactic disk, and on the interpretation of the observed outer disk stellar populations in terms either of external entities (Monoceros, Triangulus-Andromeda, Canis Major), or as manifestations of genuine disk properties (e.g., warp and flare).

  7. Gluing pseudoholomorphic quilted disks

    CERN Document Server

    Ma'u, Sikimeti

    2009-01-01

    We construct families of quilted surfaces parametrized by the multiplihedra, and define moduli spaces of pseudoholomorphic quilted disks using the theory of pseudoholomorphic quilts of Wehrheim and Woodward. We prove a gluing theorem for regular, isolated pseudoholomorphic quilted disks. This analytical result is a fundamental ingredient for the construction of A-infinity functors associated to Lagrangian correspondences.

  8. THE EVOLUTION OF CIRCUMPLANETARY DISKS AROUND PLANETS IN WIDE ORBITS: IMPLICATIONS FOR FORMATION THEORY, OBSERVATIONS, AND MOON SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Shabram, Megan; Boley, Aaron C. [Department of Astronomy, University of Florida, 211 Bryant Space Center, Gainesville, FL 32611 (United States)

    2013-04-10

    Using radiation hydrodynamics simulations, we explore the evolution of circumplanetary disks around wide-orbit proto-gas giants. At large distances from the star ({approx}100 AU), gravitational instability followed by disk fragmentation can form low-mass substellar companions (massive gas giants and/or brown dwarfs) that are likely to host large disks. We examine the initial evolution of these subdisks and their role in regulating the growth of their substellar companions, as well as explore consequences of their interactions with circumstellar material. We find that subdisks that form in the context of GIs evolve quickly from a very massive state. Long-term accretion rates from the subdisk onto the proto-gas giant reach {approx}0.3 Jupiter masses kyr{sup -1}. We also find consistency with previous simulations, demonstrating that subdisks are truncated at {approx}1/3 of the companion's Hill radius and are thick, with (h/r) of {approx}> 0.2. The thickness of subdisks draws to question the use of thin-disk approximations for understanding the behavior of subdisks, and the morphology of subdisks has implications for the formation and extent of satellite systems. These subdisks create heating events in otherwise cold regions of the circumstellar disk and serve as planet formation beacons that can be detected by instruments such as ALMA.

  9. New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme

    CERN Document Server

    Danilovich, Taissa; Justtanont, K; Olofsson, H; Cerrigone, L; Bujarrabal, V; Alcolea, J; Cernicharo, J; Castro-Carrizo, A; Garcia-Lario, P; Marston, A

    2015-01-01

    CONTEXT: Asymptotic giant branch (AGB) stars are in one of the latest evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss has a significant effect on the stellar evolution, and is a significant source of heavy elements and dust grains for the interstellar medium. The mass-loss rate can be well traced by carbon monoxide (CO) line emission. AIMS: We present new Herschel HIFI and IRAM 30m telescope CO line data for a sample of 53 galactic AGB stars. The lines cover a fairly large range of excitation energy from the $J=1\\to0$ line to the $J=9\\to8$ line, and even the $J=14\\to13$ line in a few cases. We perform radiative transfer modelling for 38 of these sources to estimate their mass-loss rates. METHODS: We used a radiative transfer code based on the Monte Carlo method to model the CO line emission. We assume spherically symmetric circumstellar envelopes that are formed by a constant mass-loss rate through a smoothly accelerating wind. RESULTS: We find models that are consistent across...

  10. Setting the Stage for Circumstellar Interaction in Core-Collapse Supernovae II: Wave-Driven Mass Loss in Supernova Progenitors

    CERN Document Server

    Shiode, Joshua H

    2013-01-01

    Supernovae (SNe) powered by interaction with circumstellar material provide evidence for intense stellar mass loss during the final years leading up to core collapse. We have argued that during and after core neon burning, internal gravity waves excited by core convection can tap into the core fusion power and transport a super-Eddington energy flux out to the stellar envelope, potentially unbinding up to ~ 1 solar mass of material. In this work, we explore the internal conditions of SN progenitors using the MESA 1-D stellar evolution code, in search of those most susceptible to wave-driven mass loss. We focus on simple, order of magnitude considerations applicable to a wide range of progenitors. Wave-driven mass loss during core neon and oxygen fusion happens preferentially in either lower mass (<~ 20 solar mass ZAMS) stars or massive, sub-solar metallicity stars. Roughly 20 per cent of the SN progenitors we survey can excite ~ 10^46 - 10^48 erg of energy in waves that can potentially drive mass loss with...

  11. Planetesimals in Debris Disks

    CERN Document Server

    Youdin, Andrew N

    2015-01-01

    Planetesimals form in gas-rich protoplanetary disks around young stars. However, protoplanetary disks fade in about 10 Myr. The planetesimals (and also many of the planets) left behind are too dim to study directly. Fortunately, collisions between planetesimals produce dusty debris disks. These debris disks trace the processes of terrestrial planet formation for 100 Myr and of exoplanetary system evolution out to 10 Gyr. This chapter begins with a summary of planetesimal formation as a prelude to the epoch of planetesimal destruction. Our review of debris disks covers the key issues, including dust production and dynamics, needed to understand the observations. Our discussion of extrasolar debris keeps an eye on similarities to and differences from Solar System dust.

  12. Radio pulsar disk electrodynamics

    Science.gov (United States)

    Michel, F. C.

    1983-01-01

    Macroscopic physics are discussed for the case of a disk close to an isolated, magnetized, rotating neutron star that acts as a Faraday disk dynamo, while the disk acts as both a load and a neutral sheet. This sheet allows the polar cap current to return to the neutron star, splitting a dipolar field into two monopolar halves. The dominant energy loss is from the stellar wind torque, and the next contribution is dissipation in the auroral zones, where the current returns to the star in a 5 cm-thick sheet. The disk itself may be a source of visible radiation comparable to that in pulsed radio frequency emission. As the pulsar ages, the disk expands and narrows into a ring which, it is suggested, may lead to a cessation of pulsed emission at periods of a few sec.

  13. Magnetohydrodynamics of accretion disks

    International Nuclear Information System (INIS)

    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

  14. M Stars in the TW Hya Association: Stellar X-Rays and Disk Dissipation

    Science.gov (United States)

    Kastner, Joel H.; Principe, David A.; Punzi, Kristina; Stelzer, Beate; Gorti, Uma; Pascucci, Ilaria; Argiroffi, Costanza

    2016-07-01

    To investigate the potential connection between the intense X-ray emission from young low-mass stars and the lifetimes of their circumstellar planet-forming disks, we have compiled the X-ray luminosities (L X ) of M stars in the ∼8 Myr old TW Hya Association (TWA) for which X-ray data are presently available. Our investigation includes analysis of archival Chandra data for the TWA binary systems TWA 8, 9, and 13. Although our study suffers from poor statistics for stars later than M3, we find a trend of decreasing {L}X/{L}{bol} with decreasing T eff for TWA M stars, wherein the earliest-type (M0–M2) stars cluster near {log}({L}X/{L}{bol})≈ -3.0 and then {log}({L}X/{L}{bol}) decreases, and its distribution broadens, for types M4 and later. The fraction of TWA stars that display evidence for residual primordial disk material also sharply increases in this same (mid-M) spectral type regime. This apparent anticorrelation between the relative X-ray luminosities of low-mass TWA stars and the longevities of their circumstellar disks suggests that primordial disks orbiting early-type M stars in the TWA have dispersed rapidly as a consequence of their persistent large X-ray fluxes. Conversely, the disks orbiting the very lowest-mass pre-MS stars and pre-MS brown dwarfs in the Association may have survived because their X-ray luminosities and, hence, disk photoevaporation rates are very low to begin with, and then further decline relatively early in their pre-MS evolution.

  15. WATER VAPOR IN THE PROTOPLANETARY DISK OF DG Tau

    Energy Technology Data Exchange (ETDEWEB)

    Podio, L.; Dougados, C.; Thi, W.-F.; Menard, F.; Pinte, C. [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d' Astrophysique de Grenoble (IPAG) UMR 5274, F-38041 Grenoble (France); Kamp, I.; Meijerink, R.; Spaans, M.; Aresu, G. [Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen (Netherlands); Codella, C. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Florence (Italy); Cabrit, S. [LERMA, UMR 8112 du CNRS, Observatoire de Paris, Ecole Normale Superieure, Universite Pierre et Marie Curie, Universite de Cergy-Pontoise, 61 Av. de l' Observatoire, F-75014 Paris (France); Nisini, B. [INAF-Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monte Porzio Catone (Italy); Sandell, G. [SOFIA-USRA, NASA Ames Research Center, MS 232-12, Building N232, Rm. 146, P.O. Box 1, Moffett Field, CA 94035-0001 (United States); Williams, J. P. [Institute for Astronomy (IfA), University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822 (United States); Testi, L. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Woitke, P. [SUPA, School of Physics and Astronomy, University of St. Andrews, KY16 9SS (United Kingdom)

    2013-03-20

    Water is key in the evolution of protoplanetary disks and the formation of comets and icy/water planets. While high-excitation water lines originating in the hot inner disk have been detected in several T Tauri stars (TTSs), water vapor from the outer disk, where most water ice reservoirs are stored, was only reported in the nearby TTS TW Hya. We present spectrally resolved Herschel/HIFI observations of the young TTS DG Tau in the ortho- and para-water ground-state transitions at 557 and 1113 GHz. The lines show a narrow double-peaked profile, consistent with an origin in the outer disk, and are {approx}19-26 times brighter than in TW Hya. In contrast, CO and [C II] lines are dominated by emission from the envelope/outflow, which makes H{sub 2}O lines a unique tracer of the disk of DG Tau. Disk modeling with the thermo-chemical code ProDiMo indicates that the strong UV field, due to the young age and strong accretion of DG Tau, irradiates a disk upper layer at 10-90 AU from the star, heating it up to temperatures of 600 K and producing the observed bright water lines. The models suggest a disk mass of 0.015-0.1 M{sub Sun }, consistent with the estimated minimum mass of the solar nebula before planet formation, and a water reservoir of {approx}10{sup 2}-10{sup 3} Earth oceans in vapor and {approx}100 times larger in the form of ice. Hence, this detection supports the scenario of ocean delivery on terrestrial planets by the impact of icy bodies forming in the outer disk.

  16. Water emission in NGC1333-IRAS4 Probing its surrounding envelope

    CERN Document Server

    Maret, S; Caux, E; Tielens, A G G M; Castets, A

    2002-01-01

    Sun like stars are born from the collapse of fragment of molecular clouds. During the first embedded phase (the so called class 0/1), the protostar is surrounded by a collapsing envelope, whose physical and chemical structure would set up the initial conditions of the proto-stellar disk which may eventually form planets. In this contribution, we show how spectroscopic far infrared to millimeter observations can be a powerful diagnostic to derive the chemical and physical structure of the innermost regions of envelopes collapsing around solar type protostars, where disk are believe to form. Our claim is based on the simultaneous modeling of the dynamics, chemistry and radiative transfer in a protostellar envelope. Here we present a study of a class 0 protostar NGC1333-IRAS4, obtained using ISO-LWS observations of water far-infrared lines. We show the derived physical and chemical structure of the protostar, namely the density and temperature profiles, as well as the water abundance across the envelope. Besides...

  17. Water emission in NGC1333-IRAS4 Probing its surrounding envelope

    CERN Document Server

    Maret, S; Caux, E; Tielens, A G G M; Castets, A

    2003-01-01

    Sun like stars are born from the collapse of fragment of molecular clouds. During the first embedded phase (the so called class 0/1), the protostar is surrounded by a collapsing envelope, whose physical and chemical structure would set up the initial conditions of the proto-stellar disk which may eventually form planets. In this contribution, we show how spectroscopic far infrared to millimeter observations can be a powerful diagnostic to derive the chemical and physical structure of the innermost regions of envelopes collapsing around solar type protostars, where disk are believe to form. Our claim is based on the simultaneous modeling of the dynamics, chemistry and radiative transfer in a protostellar envelope. Here we present a study of a class 0 protostar NGC1333-IRAS4, obtained using ISO-LWS observations of water far-infrared lines. We show the derived physical and chemical structure of the protostar, namely the density and temperature profiles, as well as the water abundance across the envelope. Besides...

  18. Ionization Driven Chemistry in Protoplanetary Disks and Observational Signatures of Ionization Suppression

    Science.gov (United States)

    Cleeves, Lauren Ilsedore; Bergin, Edwin A.

    2015-01-01

    Circumstellar disks around young stars set the stage for the formation of planetary systems. The ionization fraction of the disk fundamentally regulates turbulence, which drives accretion onto the star and plays a role in the formation of planetesimals. Ionization is also central to the chemistry of the coldest disk gas, where comets and other icy bodies are assembled. During my PhD I studied the expected levels --- including possible severe suppression --- of the primary ionizing agents in disks, including cosmic rays, X-rays and the decay of short-lived radionuclides. Within this framework, I examined how each of these sources impacts turbulence-free "dead zones," and I identified submillimeter molecular emission tracers that can be used to spatially map-out ionization in disks with ALMA. I applied these theoretical results to SMA and ALMA observations of the extensively studied TW Hya protoplanetary disk, and I measured a disk-averaged upper limit to the cosmic ray ionization rate ~100 times below the canonical rate of 10-17 s-1 per H2. These results point to extensive CR deflection by either natal winds or twisted magnetic fields from the background environment or within the disk itself. One of the important implications of this work is that cold disk chemistry is inefficient without sufficient ionization, and as a direct result, deuterated water (HDO) is not significantly produced in disks. Given the elevated levels of HDO/H2O present throughout Solar System bodies, these results point to a substantial interstellar inheritance of deuterium-enriched ices during the formation of our own planetary system.

  19. Truncations in stellar disks

    CERN Document Server

    Van der Kruit, P C

    2000-01-01

    The presence of radial truncations in stellar disks is reviewed. There is ample evidence that many disk galaxies have relatively shaprt truncations in their disks. These often are symmetric and independent of the wavelength band of the observations. The ratio of the truncation radius R_{max} to the disk scalelength h appears often less then 4.5, as expected on a simple model for the disk collapse. Current samples of galaxies observed may however not be representative and heavily biased towards sisks witht he largest scalelengths. Many spiral galaxies also have HI warps and these generally start at the truncation radius of the stellar disk. The HI surface density suddenly becomes much flatter with radius. In some galaxies the start of the warp and the position of the disk truncation radius is accompanied by a drop in the rotation velocity. In the regiosn beyond the dis truncation in the HI layer some star formation does occur, but the heavy element abundance and the dust content are very low. All evidence is c...

  20. The Disk and Extraplanar Regions of NGC 55

    CERN Document Server

    Davidge, T J

    2005-01-01

    The stellar content of the nearby SB(s)m galaxy NGC 55 is investigated using images covering the visible and near-infrared wavelength regions. A well-defined plume, which stellar evolution models suggest contains stars with masses near the RSG - AGB transition, is detected in CMDs of the disk, and it is concluded that star formation in the thin disk of NGC 55 has ocurred at a significant rate for at least the past 0.1 - 0.2 Gyr. The disk also contains a large population of old (log(t_yr) ~ 10) stars, and it is argued that a stable disk has been in place in NGC 55 for a significant fraction of the age of the Universe. At projected distances in excess of 2 kpc off of the disk plane the brightest AGB stars have ages 10(+3)(-2) Gyr. Thus, despite indications that dust and gas are present in the envelope surrounding the NGC 55 disk, the AGB content suggests that recently formed stars do not occur in large numbers in the extraplanar region. The mean metallicity of extraplanar RGB stars is in excellent agreement wit...