The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was
NASA Technical Reports Server (NTRS)
Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks
accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...
NASA Website
With IXO, spectroscopy of accretion onto black holes will finally rival optical and IR spectroscopy of accreting young stars. ...
... accreting young star that ... 4. TITLE AND SUBTITLE An X-Ray Outburst From the Rapidly Accreting Young Star That Illuminates McNeil's Nebula 5a. ...
DTIC Science & Technology
... Accession Number : ADA426581. Title : An X-Ray Outburst from the Rapidly Accreting Young Star that Illuminates McNeil's Nebula. ...
... wTTS). This term defines PMS stars without obvious signs for disk accretion, while young stars, in which accretion from ...
The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster pres...
National Technical Information Service (NTIS)
Geometrically thin, optically thick, turbulent accretion disks are believed to surround many stars. Some of them are the compact components of close binaries, while the others are throught to be T Tauri stars. These accretion disks must be magnetized obje...
have been. : size and distribution of such flux tubes. We then apply the model to identified using numerical, nonlinear hydrodynamic techniques, accretion ...
M stars as targets for terrestrial exoplanet searches and biosignature detection. [Astrobiology. 2007] Review M stars as targets for terrestrial exoplanet searches and...
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young stars in the Taurus and Orion dark clouds with the echelle spectrograph on the 4�m telescope in the flow. The appropriate equation for stars at the distance of the Taurus dark is log 10 Mw = \\Gamma4ACCRETION AND OUTFLOW FROM YOUNG STARS Patrick Hartigan Department ...
E-print Network
Accretion disks around young stars produce excess infrared continuum associated with the disk and excess optical and ultraviolet continua associated with the boundary layer or 'hot spot' as material falls from the disk onto the stellar photosphere. When w...
A star acquires much of its mass by accreting material from a disk. Accretion is probably not continuous but episodic. We have developed a method to include the effects of episodic accretion in simulations of star formation. Episodic accretion results in bursts of radiative ...
NASA Astrophysics Data System (ADS)
High resolution infrared spectroscopy is a very valuable tool for the study of the formation of low mass and very low mass stars. At the stage in which these objects are already visible, they still undergo strong mass accretion and mass loss processes. Many of the features observed on these stars can be explained by the magnetospheric ...
Jul 20, 2009... protoplanetary disks, radiative transfer, T-TAURI DISKS, ACCRETION DISKS, YOUNG OBJECTS, CIRCUMSTELLAR DISKS, STARS, GROWTH, EARTH, DUST ...
We propose a generalized model for stellar spin-down, disk accretion, and truncation, and the origin
ACCRETION ONTO YOUNG STARS WITH IXO. Costanza Argiroffi1, 2. Costanza Argiroffi. IXO science meeting, Rome, March 2011. 1 Dip. di Fisica, Universita' degli ...
ionized dead zone containing a smooth field that drives a residual flow of gas toward the young star. http://www.jpl.nasa.gov/ ...
We aim to monitor T Tauri star disk emission features and jet outflow morphologies to determine how these features vary with disk accretion rate, and how and when the outflow responds to major accretion events. Young stars are surrounded by circumstellar disks through which they ...
A baseline model of the composition and abundances of grains and gases in molecular cloud cores and accretion disks around young stars is defined by employing: a wide range of astronomical data and theory; the composition of primitive bodies in the solar ...
Herbig Ae/Be stars(HAeBes) are young stellar objects of spectral class F2 through B0, with the central star often surrounded by a circumstellar disk of gas and dust. They are the higher mass analogs to T Tauri stars. The interaction between the star and the disk is not well understood, nor is ...
We present an analysis of the rotation of young stars in the associations Cepheus OB3b, NGC 2264, 2362 and the Orion Nebula Cluster (ONC). We discover a correlation between rotation rate and position in a colour-magnitude diagram (CMD) such that stars which lie above an empirically determined median pre-main sequence rotate more ...
stars via accretion. A necessary condition for accretion growth of a hy- ... via accretion for stars more massive than 1 M@. 1. Introduction ...
A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed
We have constructed models of stars which form by accretion from a disk. We have calculated accretion and pre-main-sequence evolutionary tracks for a range of initial parameters which spans the physically reasonable modes for accretion. We find that these models agree with the observed positions of T Tauri ...
Energy Citations Database
This project investigates the origin of giant planets, both in the Solar System and around other stars. It is assumed that the planets form by the core accretion process: small solid particles in a disk surrounding a young star gradually coagulate into ob...
The third yearbook of the Astronomische Gesellschaft (AG) contains 19 contributions dedicated to the topic "Accretion and Winds". Modern developments in accretion-disk theory are presented; accretion disks are considered in close binaries, cataclysmic variables, neutron stars, and galaxies. Stellar winds are ...
The Corot satellite observed the young stellar cluster NGC 2264 during 23 days in March 2008. This was the first time a group of young accreting stars, classical T Tauri stars (CTTS), were followed ininterruptedly with high photometric accuracy for such a long run. Before the Corot ...
Young stars can produce X-rays by different mechanisms: Coronal activity, accretion shocks and shocks in outflows. We propose to observe two targets within one field-of-view (FOV): SU Aur is accreting mass from a disk and shows violent coronal activity. We will study the time evolution of stellar flares on time ...
We present X-shooter observations of two brown dwarf candidates. We focus on the determination of stellar parameters and their errors. The targets, an accreting class II and a non-accreting class III objects, are members of the ? Orionis star-forming region. We derive the spectroscopic spectral types from the VIS spectrum and the ...
(� \\Gamma5 km s \\Gamma1 ), possibly associated with a disk wind or magnetic accretion columns. The velocity (Beckwith and Sargent, 1993; Strom et al. 1993). Evidence that these disks accrete onto the stellar surface protostellar disks form and evolve (Strom, Edwards and Skrutski, 1993; Walter et al. 1988). At ages � ? 10 Myr
The formation of low mass stars takes place with the assistance of an accretion disk that transports gas and dust from the envelope of the system to the star, and a jet that removes angular momentum and allows accretion to proceed. In the radio, these ionized jets can be studied very close to the ...
Young, low-mass stars are luminous X-ray sources whose powerful X-ray flares may exert a profound influence over the process of planet formation. The origin of the X-ray emission is uncertain. Although many (or perhaps most) recently formed, low-mass star...
Numerical studies of the early evolution of star clusters have traditionally been based on full hydrodynamic treatments or a purely gravitational N-body approach . I will discuss recent work that pushes the N-body techniques toward a more realistic gas treatment. In particular I will focus on the behavior of very young clusters as they ...
Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life grow by accreting gas from the surrounding material. But for stars approximately 10 times more massive than the Sun (approximately 10M(o)), the powerful stellar radiation is expected to inhibit accretion and thus limit ...
PubMed
formation of massive stars via accretion. A necessary condition for accre- ... constraints on the accretion rate necessary to produce high mass stars and ...
A general mechanism is presented for generating pressure-driven winds that are intrinsically bipolar from objects undergoing disk accretion. The energy librated in a boundary layer shock as the disk matter impacts the central object is shown to be sufficient to eject a fraction ..beta..approx.10/sup -2/ to 10/sup -3/ of the accreted mass. These winds are ...
The birth of stars involves not only accretion but also, counter-intuitively, the expulsion of matter in the form of highly supersonic outflows. Although this phenomenon has been seen in young stars, a fundamental question is whether it also occurs among newborn brown dwarfs: these are the so-called 'failed ...
Although massive stars (commonly defined as those in excess of about eight solar masses, or with initial luminosities of a thousand times the solar luminosity or more) have an enormous impact on the galactic environment, how they form has been a mystery. The solution probably involves the existence of accretion disks. Rotational motions have been found in ...
Classical T Tauri stars (CTTS) are young, accreting systems. The accretion is thought to cause a soft X-ray excess and unusual line ratios in the He-like triplets. The accretion spots can also be seen with optical Doppler-imaging; however, the final test to correlate these signatures - ...
. The former (1) is violated by accretion� and collapse flows, the latter (2) because a new born young star structure. Energy transfer is very efficient once convection has started. In my results the stars haveThe Formation of Binary Stars ASP Conference Series, Vol. IAU Symposium 200, 2000 ...
Young Sun-like stars at the beginning of the pre-main sequence (PMS) evolution are surrounded by accretion discs and remnant protostellar envelopes. Photometric and spectroscopic variations of these stars are driven by interactions of the star with the disc. Time scales and wavelength ...
Young Sun-like stars at the beginning of the pre-main-sequence (PMS) evolution are surrounded by accretion discs and remnant protostellar envelopes. Photometric and spectroscopic variations of these stars are driven by interactions of the star with the disc. Time-scales and wavelength ...
A simple model of gas accretion in young galaxy disks suggests that fast turbulent motions can be driven by accretion energy for a time t{sub acc} {approx} 2(epsilon{sup 0.5} GM {sup 2}/xiV {sup 3}){sup 0.5} where epsilon is the fraction of the accretion energy going into disk turbulence, M and V are the galaxy ...
Jun 21, 2006 ... In addition to accretion disks around black holes, magnetic fields may play an important role in disks detected around young sun-like stars ...
The main efforts were directed towards determining the frequency of disk occurrence and the timescales for disk evolution for solar-type and intermediate mass stars. The results of the investigation showed that optically thick disks are accretion disks. T...
Young T Tauri stars exhibit strong solar-type magnetic activity, with extremely high temperature coronae and energetic flares. In a few systems discovered with Chandra and XMM-Newton there is also evidence for X-ray emission produced by shocks associated with magnetically channeled accretion. A recent 489 ksec Chandra HETG/ACIS-S ...
Protostars are precursors to the nearly fully assembled T Tauri and Herbig Ae/Be type stars undergoing quasistatic contraction toward the zero-age main sequence; they are in the process of acquiring the majority of their stellar mass. Although numerous young stars with spatially extended envelope-like structures appear to fit this ...
Strong stellar magnetic fields are believed to truncate the inner accretion disks around young stars, redirecting the accreting material to the high latitude regions of the stellar surface. In the past few years, observations of strong stellar fields on T Tauri stars with field strengths in ...
Here we present a self-consistent, bimodal stationary solution for spherically symmetric flows driven by young massive stellar clusters with a central supermassive black hole (SMBH). We demonstrate that the hydrodynamic regime of the flow depends on the location of the cluster in the 3D (star cluster mechanical luminosity-BH mass-star ...
We present the results of a near IR spectroscopic survey of the LkH?233 group, which are some of the youngest stars in the Lacerta OB association. The sample was selected by choosing stars in the region that had signatures of substantial H? emission. Spectral types were then determined by comparing our spectra to optically classified ...
We present preliminary results of the first spectroscopic study of individual pre-main sequence (PMS) stars in the Large Magellanic Cloud. The observations, at intermediate spectral resolution, cover young stellar objects in NGC1850 and R136 (30 Dor) and were obtained at optical and near-infrared wavelengths with GIRAFFE and SINFONI on the VLT, ...
Young stellar systems orbiting in the potential of their birth cluster can accrete from the dense molecular interstellar medium during the period between the star's birth and the dispersal of the cluster's gas. Over this time, which may span several Myr, the amount of material accreted can rival ...
Young low-mass stars are characterized by ejection of collimated outflows and by circumstellar discs which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn remove the excess ...
The circumstellar disks around young stellar objects play a key role in the formation process of stars and provide the stage for planet formation. Since recently, infrared interferometry provides the spatial resolution required to directly study the distribution of the gas and dust in the innermost AU around the forming star. We ...
Far Ultraviolet Spectroscopic Explorer (FUSE) far-UV (FUV) spectra provide an unique view of accretion and stellar activity in nearby, minimally reddened pre-main sequence stars. We present first results of the FUSE Legacy study of young, intermediate-mass stars. The FUSE data show that over 1--10 Myr, Herbig Ae ...
A range of important astrophysical systems consist of a strongly magnetic star accreting material from a surrounding disc. These include young stars in T Tauri systems, magnetic neutron stars in X-ray binaries and strongly magnetic white dwarfs in some cataclysmic variables. In all these ...
The ubiquity of accretion disks around pre-main sequence and young main sequence stars having the potential to form planetary systems is now well established. However, unknown is an accurate estimate of the fraction of single stars with disks that have pr...
Recent Spitzer IRAC observations of young stars in Orion and NGC 2264 have shown a strong link between primordial circumstellar disks and stellar rotation. Slow rotators show a larger percentage of stars with excess infrared emission than fast rotators. If stars with massive primordial disks evolve into massive ...
High resolution X-ray spectroscopy of accreting young stars is providing new insights into the physical conditions of the shocked plasma. While young stars exhibit exceedingly active coronae (>10 MK) with highly energetic flares, the relatively low temperature ( 3 MK), high density (>1012 ...
We propose to obtain a Chandra/HETGS spectrum of IM Lup with an exposure of 150 ks. IM Lup is the only known X-ray bright transition object between the classical T Tauri star phase and the weak-lined T Tauri phase. IM Lup shows an IR excess, but its Halpha equivalent width is small, indicating very low accretion rates. The Chandra spectrum will provide ...
We outline recent progress in understanding the accretion of plasma to rotating magnetized stars obtained from global axisymmetric (2D) and 3D magnetohydrodynamic (MHD) simulations in three main areas: (1.) Formation of jets from disk accretion onto rotating magnetized stars: From simulations where the viscosity ...
The possible existence of the radio and X-ray star SS433 as a young binary neutron star is examined. The huge red- and blueshifts of the moving emission lines are thought to be a result of stimulated emission from the inner edge of an accretion disk around a rapidly spinning neutron star, ...
Studies of evolved massive stars indicate that they form in a clustered mode. During the earliest evolutionary stages, these regions are embedded within their natal cores. Here we present high-spatial-resolution interferometric dust continuum observations disentangling the cluster-like structure of a young massive star-forming region. ...
A series of simplified evolutionary calculations are used to show that deuterium burning acts as an effective thermostat in low-mass protostars over a plausible range of initial conditions and mass accretion rates. The thermostat keeps the central temperature of the accreting hydrostatic core close to 10 to the 6th K, and thereby tightly constrains the ...
We review recent theoretical progress aimed at understanding the formation and the early stages of evolution of giant planets, low-mass stars, and brown dwarfs. Calculations coupling giant planet formation, within a modern version of the core accretion model that includes planet migration and disk evolution, and subsequent evolution yield consistent ...
We present virial models for the global evolution of giant molecular clouds (GMCs). Focusing on the presence of an accretion flow and accounting for the amount of mass, momentum, and energy supplied by accretion and star formation feedback, we are able to follow the growth, evolution, and dispersal of individual GMCs. Our model clouds ...
We report on the discovery of the young, nearby, brown dwarf 2MASS J0041353-562112. The object has a spectral type of M7.5; it shows Li absorption and signatures of accretion, which implies that it still has a disk and suggests an age below 10 Myr. The space motion vector and position on the sky indicate that the brown dwarf is probably a member of the ~20 ...
Although massive stars play a critical role in the production of turbulent energy in the ISM, in the
Context: Accretion and ejection are complex and related processes that vary on various timescales in young stars. Aims: We intend to investigate the accretion and outflow dynamics and their interaction from observations of the classical T Tauri star AA Tau. Methods: From a long time series of ...
They could see details as fine as the neutron star's accretion disk, a ring of gas swirling around and flowing onto the neutron star, as the disk buckled ...
The rotation period of classical T Tauri stars (CTTS) represents a longstanding puzzle. While young low-mass stars show a wide range of rotation periods, many CTTS are slow rotators, spinning at a small fraction of breakup, and their rotation period does not seem to shorten, despite the fact that they are actively ...
The Herbig Ae/Be stars are intermediate mass pre-main sequence stars that bridge the gap between the low mass T Tauri stars and the Massive Young Stellar Objects. In this mass range, the acting star forming mechanism switches from magnetically controlled accretion to an as ...
The surface of hot neutron stars is covered by a thin atmosphere. If there is accretion after neutron-star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, heavy elements (for example, Fe) ...
We present multi-epoch medium-resolution observations of two M4.5 candidate members in the halo of the �8 Myr ? Chamaeleontis open cluster. During six months of observations, both stars exhibited variations in their H? line profiles on time-scales of days to months, with at least one episode of substantial activity attributable to accretion from a ...
This volume contains the edited lecture notes of the First JETSET School on Jets from Young Stars: Models and Constraints, held by the Marie Curie Research and Training Network on JET Simulations, Experiments and Theory. At this school the lecturers gave an introduction to observational properties and basic models describing the launching and collimation ...
It is fairly common consensus that circumstellar disks are near-ubiquitously present around stars at birth. These disks are the sites of planetary formation, and with detection of exo-solar planets now occurring routinely, understanding of the evolutionary link between young circumstellar disks and planets is more critical than ever. Dimunition of ...
Lupus 3 subgroup (van den Ancker et al. 1998; Tjin A Djie et al. 1989). It is thought to have an accretion disk (e.g. Th� et al. 1996), which might cause ...
My talk will focus on the early evolution of low mass objects. I will discuss the main uncertainties on current evolutionary models and the effects of rotation, magnetic field and early accretion history on young object's structure. I will also present possible solutions to the well known spread in HRD observed in star formation ...
Topics covered include young rapidly spinning pulsars; static gaps in outer magnetospheres; dynamic gaps in pulsar outer magnetospheres; pulse structure of energetic radiation sustained by outer gap pair production; outer gap radiation, Crab pulsar; outer gap radiation, the Vela pulsar; radioemission; and high energy radiation during the accretion spin-up ...
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We present mapping observations of molecular lines 12CO (2-1), 12CO (3-2), 13CO (2-1), and 13CO (3-2) toward the massive star-forming region IRAS 04000+5052 that suggest kinematics consistent with cloud-cloud collision and a possible unusual abundance ratio of carbon isotopes. Together with the previous spectroscopic study that shows an extreme deficiency in heavy elements in ...
The dynamics and structure of accretion disks, which accumulate a vertical magnetic field in their centers, are investigated using two- and three-dimensional MHD simulations. The central field can be built up to the equipartition level, where it disrupts a nearly axisymmetric outer accretion disk inside a magnetospheric radius, forming a magnetically ...
A deep (489 ks) Chandra High Energy Transmission Grating spectrum of the classical T Tauri star TW Hydrae shows a new type of coronal structure that is produced by the accretion process. In the standard model for a stellar dipole, the magnetic field truncates the disk and channels the accreting material onto the ...
Nov 9, 2003 ... Consequently accretion disks have fundamental roles in the formation of planets, stars and compact objects, and are the engines driving the ...
Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding
Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons,
High spectral resolution observations of the massive young star cluster in the filaments of NGC 1275 reveal that the associated H-alpha emission line has a velocity width comparable to, or somewhat less than, that of H-alpha in typical giant H II regions of similar emission-line luminosity. If this linewidth reflects virial motions of matter within the ...
Classical T Tauri stars (CTTS) are young, accreting systems. The accretion causes a variable soft X-ray excess and unusual line ratios in the He-like triplets. Accretion signatures can also be seen in optical Doppler images. However, the true correlation of these different signatures only ...
The third yearbook of the Astronomische Gesellschaft (AG) contains 19 contributions, presented during the spring meeting of the AG, Berlin (Germany), Mar 1990, dedicated to the topic "accretion and winds". Modern developments in accreption-disk theory are presented; accretion disks are considered in close binaries, cataclysmic variables, neutron ...
do not have accretion disks. Optical spectra are the only way that we can .... inner accretion disks) confirms the asymmetrical distribution of such stars ...
I review the X-ray observations of galactic accreting black holes and neutron stars and interpretations of these in terms of solutions of the accretion flow equations. PMID:12804240
Nov 6, 2000 ... "accretion" means collecting of additional material. Two major places where astronomers see accretion disks are in binary star systems (two ...
MAGNETOHYDRODYNAMIC SIMULATIONS OF ACCRETION ONTO A STAR IN THE `` PROPELLER '' REGIME M. M ABSTRACT This work investigates spherical accretion onto a rotating magnetized star in the `` propeller-called `` propeller '' stage of evolution (Davidson & Ostriker 1973; Illarionov & Sunyaev 1975). The propeller ...
We use direct N-body simulations of gas embedded star clusters to study the importance of stellar collisions for the formation and mass accretion history of high-mass stars. Our clusters start in virial equilibrium as a mix of gas and protostars. Protostars then accrete matter using different mass ...
We conducted a long-term optical photometric and spectroscopic monitoring of the strongly variable, accreting young sun-like star [KOS94] HA11, associated with the dark cloud Lynds 1340 that exhibited large amplitude (5-6 mag in the I C band) brightness variations on 2-3 years timescales, flat spectral energy distribution (SED), and ...
Located at the centre of our Galaxy is Sgr A*, a 3 million Msun super-massive black hole (SMBH). Sgr A* is hundreds of times closer than any other known SMBH, and as such it is an ideal object to study accretion physics. Recent observations have revealed the presence of dozens of young mass-losing stars. The winds from these ...
We present a model for the rotational evolution of a young, solar mass star interacting with an accretion disk. The model incorporates a description of the angular momentum transfer between the star and the disk due to a magnetic connection, and includes changes in the star's mass and radius ...
We present a model for the rotational evolution of a young, solar mass star interacting with an accretion disk. The model incorporates a description of the angular momentum transfer between the star and the disk due to a magnetic connection, and includes changes in the star's mass and ...
This article summarizes the processes of high-energy emission in young stellar objects. Stars of spectral type A and B are called Herbig Ae/Be (HAeBe) stars in this stage, all later spectral types are termed classical T Tauri stars (CTTS). Both types are studied by high-resolution X-ray and UV spectroscopy and ...
The birth process and (early) evolution of massive stars is still poorly understood. Massive stars are rare, their birthplaces are hidden from view and their formation timescale is short. So far, our physical knowledge of these young massive stars has been derived from near-IR imaging and spectroscopy, revealing ...
X-ray flashes from accreting neutron stars are considered. A number of possible explanations for the phenomenon are reviewed. A physical picture is drawn, and numerical models are discussed. 3 figures. (RWR)
Jan 22, 2010 ... Many astrophysical objects, including neutron stars and accretion disks, are powered by a combination of very strong magnetic fields and ...
CAN MASSIVE STARS BE FORMED BY ACCRETION? Harold W. Yorke. Jet Propulsion Laboratory, California Insitute of Technology, Pasadena, CA email: Harold. ...
There is currently no accepted theoretical framework for the formation of the most massive stars, and the manner in which protostars continue to accrete and grow in mass beyond �10 M? is still a controversial topic. In this study we use several prescriptions of stellar accretion and a description of the Galactic gas distribution to ...
There is currently no accepted theoretical framework for the formation of the most massive stars, and the manner in which protostars continue to accrete and grow in mass beyond �10 M&sun; is still a controversial topic. In this study we use several prescriptions of stellar accretion and a description of the Galactic gas ...
The understanding of accretion processes and specifically of massive accretion disks is considered the holy grail in high-mass star formation. We propose to study the recently identified massive accretion disk candidate IRAS18089-1732 at high angular resolution (<0.7'') in the highly excited NH3(4,4) and (5,5) ...
The Mira AB system is a nearby (~107 pc) example of a wind accreting binary star system. In this class of system, the wind from a mass-losing red giant star (Mira A) is accreted onto a companion (Mira B), as indicated by an accretion shock signature in spectra at ultraviolet and X-ray ...
Magnetospheric accretion is an important process for a wide range of astrophysical systems and may play a role in the formation of gas giant planets. Extending the formalism describing stellar magnetospheric accretion into the planetary regime, we demonstrate that magnetospheric processes may govern accretion onto ...
We modify a stellar structure code to estimate the effect upon the main sequence of the accretion of weakly-interacting dark matter onto stars and its subsequent annihilation. The effect upon the stars depends upon whether the energy generation rate from dark matter annihilation is large enough to shut off the nuclear burning in the ...
This study examines the solar wind energy flux, from 17 years of Ulysses measurements at different heliolatitudes, completed by multi-instrument observations. The solar wind energy flux is almost constant, nearly independant on wind speed and solar activity. We then compare the energy flux of the Sun to the stellar wind fluxes, in addition to the luminosity fluxes, from young ...
Young stellar objects of both high and low luminosity emit energetic jets or winds of material that are often highly collimated and often bipolar. Near the stars, turbulent swept-up gas is observed in the emission of interstellar molecules such as carbon monoxide, and small, bright regions of water maser emission and the nebulous bright patches known as ...
We present one-dimensional numerical simulations, which consider the effects of radiative cooling and gravity on the hydrodynamics of the matter reinserted by stellar winds and supernovae within young nuclear starbursts (NSBs) with a central supermassive black hole (SMBH). The simulations confirm our previous semi-analytic results for low-energetic starbursts, evolving in a ...
We present X-ray spectral analysis of the accreting young star TW Hydrae from a 489 ks observation using the Chandra High Energy Transmission Grating. The spectrum provides a rich set of diagnostics for electron temperature Te , electron density Ne , hydrogen column density NH , relative elemental abundances, and velocities, and ...
We present X-ray spectral analysis of the accreting young star TW Hydrae from a 489 ks observation using the Chandra High Energy Transmission Grating. The spectrum provides a rich set of diagnostics for electron temperature T{sub e} , electron density N{sub e} , hydrogen column density N{sub H} , relative elemental abundances, and ...
The observational consequences of the merger scenario for massive star formation are explored and contrasted with the gradual accumulation of mass by accretion. In high-density protostar clusters, envelopes and disks provide a viscous medium that can dissipate the kinetic energy of passing stars, greatly enhancing the probability of ...
in the CTTS V2129 Oph Investigators Institute EMAIL J. Bouvier Laboratoire d'Astrophysique de Grenoble+VIS+NIR spectra of the young star V2129 Oph over 2 ro- tational periods (Prot=6.53 days) in order to determine multi-wavelength campaign to map the magnetic field, accretion and X-ray emission in the CTTS V2129 Oph
Aims: We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1-10 Myr) clusters ? Ori and ? Ori. Methods: We observed 98 and 49 low-mass (0.2-1.0 M?) stars in ? Ori and ? Ori respectively, using the multi-object optical ...
Magnetic fields are present in a wide variety of stars throughout the HR diagram and play a role at basically all evolutionary stages, from very-low-mass dwarfs to very massive stars, and from young star-forming molecular clouds and protostellar accretion discs to evolved giants/supergiants and ...
A neutron star high mass X-ray binary (HMXB) is a system consisting of a neutron star and a massive O- or B-type companion star. OB stars, which are young giant stars, have powerful stellar winds and are spreading a fraction of their mass continuously. As the neutron ...
We propose to obtain multi-epoch observations of two fields in the Cygnus-X massive star-forming complex to determine the variability characteristics of intermediate- to high-mass young stellar objects (YSOs). This program is complementary to the YSOVAR exploration science program which obtained lightcurves for a sample of low- mass YSOs in nearby ...
A large, perhaps dominant fraction, of the Milky Way's halo is thought to be built up by the accretion of smaller galaxies and their globular cluster (GC) systems. Here, we examine the Milky Way's GC system to estimate the fraction of accreted versus in situ formed GCs. We first assemble a high-quality data base of ages and metallicities for 93 Milky Way ...
The loss of angular momentum owing to unstable r-modes in hot young neutron stars has been proposed as a mechanism for achieving the spin rates inferred for young pulsars. One factor that could have a significant effect on the action of the r-mode instability is fallback of supernova remnant material. The associated ...
Program Hae2BPIC resulted in usable ISO spectra of three young, Herbig Ae stars: HR 5999 (A7e, t=0.6 Myr), SV Cep (al-2e, t=1-3 Myr), and MW Vul (Al-2e, t=1-3 Myr). While too small a sample to pursue our original goal of surveying the silicate emission in these young, protoplanetary disk systems, comparison of these data with ...
One possible mechanism for giant planet formation is disk instability in which the planet is formed as a result of gravitational instability in the protoplanetary disk surrounding the young star. The final composition and core mass of the planet will depend on the planet's mass, environment, and the planetesimal accretion efficiency. ...
Using the largest high-resolution spectroscopic sample to date of young, very low mass stars and brown dwarfs, we investigate disk accretion in objects ranging from just above the hydrogen-burning limit all the way to nearly planetary masses. Our 82 targets span spectral types from M5 to M9.5, or masses from 0.15 Msolar down to about ...
Abstract. The accretion process onto a magnetized isolated neutron star, which captures material from the interstellar medium, is discussed. The evolutionary track of such a star can be presented as a sequence of four states: ejector, supersonic propeller, subsonic propeller, andsteady accretor. Ishowthatsubsonic propeller ? accretor ...
We present low-resolution Keck I/LRIS spectra spanning from 3200 to 9000 A of nine young brown dwarfs and three low-mass stars in the TW Hya Association and in Upper Sco. The optical spectral types of the brown dwarfs range from M5.5 to M8.75, though two have near-IR spectral types of early L dwarfs. We report new accretion rates ...
Context. Accretion is a fundamental process in star formation. Although the time evolution of accretion remains a matter of debate, observations and modelling studies suggest that episodic outbursts of strong accretion may dominate the formation of the central protostar. Observing young stellar ...
We present Hubble Space Telescope photometry of young stars in NGC 5102, a nearby gas-rich post-starburst S0 galaxy with a bright young stellar nucleus. We use the IAC-pop/MinnIAC algorithm to derive the recent star formation history in three fields in the bulge and disk of NGC 5102. In the disk fields, the recent ...
Turbulence is ubiquitous in astrophysics, ranging from cosmology, interstellar medium to stars, supernovae, accretion disks, etc. ...
A large number of neutron stars (NSs), approximately 10(exp 9), populate the Galaxy, but only a tiny
The explosion of a star supernova occurs at the end of its evolution when the nuclear fuel in its core is almost, or completely, consumed. The star may explode due to a small residual thermonuclear detonation, type I SN or it may collapse, type I and type II SN leaving a neutron star remnant. The type I progenitor should be thought to ...
Properties of non-rotating and rapidly rotating protoneutron stars and neutron stars are investigated. Protoneutron stars are hot, lepton rich neutron stars which are formed in Type-II supernovae. The hot dense matter is described by a realistic equation of state which is obtained by extending a recent approach of ...
Context. Stellar rotation is a crucial parameter driving stellar magnetism, activity and mixing of chemical elements. Measuring rotational velocities of young stars can give additional insight in the initial conditions of the star formation process. Furthermore, the evolution of stellar rotation is coupled to the evolution of ...
The star formation properties as traced by CCD H? images are discussed for 65 Virgo Cluster spiral galaxies and a control sample of 35 isolated spirals. We present analyses of surface brightness profiles, asymmetries in the distribution of star formation, and star formation along bars. Virgo Cluster Sc spirals display a larger scatter ...
Young Stellar Objects are the builders of worlds. During its infancy, a star transforms ordinary interstellar dust particles into astronomical gold: planets! These planets may be host to life elsewhere in the universe. Needless to say the process is complex, and largely unknown to date. Yet, violent and spectacular events of mass ejection are witnessed, ...
The Orion Molecular Cloud contains many known star-forming regions mostly located in the southern parts of the constellation. However, northern Orion is largely unsurveyed outside of a few well-established clusters meaning there could be more sites of ongoing star formation. We have conducted a search for young ...
T Tauri stars (TTS) are low-mass pre-main-sequence stars that are accreting mass from the surrounding disc. The hotspots detected in some of them are probably heated by the release of gravitational energy in the accretion of the disc material on to the star. In this work we study the UV ...
The rate of accretion of the interstellar medium onto a star is discussed. It is shown that this is a complex, fractionated process. The relative abundances of heavy elements accreting onto the star are very different from the abundances in the ambient medium. These accretion rates are ...
The magnetospheres of accreting compact stars (neutron stars and white dwarfs) are examined. It is assumed that the compact star possesses a multipole magnetic field. The shape of the magnetosphere for the two-dimensional analog of spherically symmetric accretion and the magnetic-field ...
accreting star. Roughly half the known X�ray novae contain BH candidates and the rest contain NSs. X of the accreting star. As discussed in the Introduction, the accretion rate in a typical X�ray nova spans a wide in which the compact accreting primary ...
Young stars (such as T Tauri and Herbig Ae/Be sources) exhibit photometric variability across the electromagnetic spectrum, including in the visible and infrared regions. Time-variable mass accretion rates may cause some of the observed variability, although other mechanisms such as starspots or structural changes in the circumstellar ...
building for lower LX from young stars with strong accretion indicators (H#11; or Ca ii: Preibisch & Zinnecker, R., & Adams, M. T. 2000, AJ, 119, 3026 Stassun, K. G., Mathieu, R. D., Mazeh, T., & Vrba, F. J. 1999
The birth of a solar system is enshrouded in gas and dust. A collapsing rotating cloud increases in density until a critical point is reached and a YOUNG STELLAR OBJECT begins its rapid accretion at the center, still surrounded by a disk of gas and dust (figure 1). As stars evolve through a T-Tauri phase, much of this primordial dust ...
We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and accretion ...
Young stellar objects radiate large numbers of keV-photons that are able to penetrate significant columns of gas and thus ionize and heat circumstellar material, including the accretion disks and outflows of very young stars. The unshielded ionization rates are high. At a distance of 1 AU from a ...
The exact processes by which interstellar matter condenses to form young stars are of great interest, in part because they bear on the formation of planets like our own from the material that fails to become part of the star. Theoretical models suggest that ejection of gas during early phases of stellar evolution is a key mechanism for ...
We have studied the properties of the stellar populations in the field of the NGC 346 cluster in the Small Magellanic Cloud, using a novel self-consistent method that allows us to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with ...
Fermi-LAT has recently detected two gamma-ray bubbles disposed symmetrically with respect to the Galactic plane. The bubbles have been suggested to be in a quasi-steady state, inflated by ongoing star formation over the age of the Galaxy. Here we propose an alternative picture where the bubbles are the remnants of a large-scale wide-angle outflow from Sgr A*, the supermassive ...
{\\it Fermi}-LAT has recently detected two gamma ray bubbles disposed symmetrically with respect to the Galactic plane. The bubbles have been suggested to be in a quasi-steady state, inflated by ongoing star formation over the age of the Galaxy. Here we propose an alternative picture where the bubbles are the remnants of a large-scale wide-angle outflow from \\sgra, the SMBH ...
The Mira AB system is a nearby ( 107 pc) example of a wind accreting binary star system. In this class of system, the wind from a mass-losing red giant star is accreted onto a companion, as indicated by emission related to an accretion shock at ultraviolet and X-ray wavelengths. Imaging the ...
We present Chandra HETGS observations of the Herbig Ae star HD 104237 and the associated young stars comprising lower mass stars, in the 0.15-1.75 Msolar mass range, in their pre-main-sequence phase. The brightest X-ray source in the association is the central system harboring the Herbig Ae primary and a K3 ...
Here we examine the Milky Way's GC system to estimate the fraction of accreted versus in situ formed GCs. We first assemble a high quality database of ages and metallicities for 93 Milky Way GCs from literature deep colour-magnitude data. The age-metallicity relation for the Milky Way's GCs reveals two distinct tracks -- one with near constant old age of ~12.8 Gyr and the ...
We present high-cadence (1-10 hr�1) time-series photometry of the eruptive young variable star V1647 Orionis during its 2003-2004 and 2008-2009 outbursts. The 2003 light curve was obtained mid-outburst at the phase of steepest luminosity increase of the system, during which time the accretion rate of the system was presumably ...
The Ceph C star forming region will be monitored in Sept. 2010 by both the Chandra X-ray Observatory and Spitzer Space Telescope. These observations will link stellar X-ray flares with mid-IR disk afterglows, indicating how coronal emission affects the temperature or structure of circumstellar disks. We propose to use the MOIRCS and TripleSpec spectrographs at the Subuaru and ...
We present preliminary results of our X-shooter survey in star forming regions. In this contribution we focus on sub-samples of young stellar and sub-stellar objects (YSOs) in the Lupus star forming region and in the TW Hya association. We show that the X-shooter spectra are suitable for conducting several parallel studies such as YSO ...
The extent to which the continuum spectral energy distributions of T Tauri stars from 0.2 to 10 microns can be explained by a simple model consisting of an active PMS star and active accretion disk is considered. The disk contributes both an IR excess due to accretion energy dissipation and stellar light ...
Very-long-baseline interferometry observations have revealed a bright, compact radio component near the center of the expanding shell of supernova 1986J. The component, not present in earlier images, has an inverted radio spectrum different from that of the shell. Such an inversion has not been seen in the spectrum of any other supernova. The new component is likely radio emission associated ...
I will discuss results of 2D and 3D MHD simulations of disk accretion onto young rotating magnetized stars. The disk magnetosphere interaction leads to formation of funnel streams and hot spots on the stellar surface. The energy distribution in the spots is such that the highest energy photons are expected to radiate from the central ...
Recent Kepler observations revealed an abundance of 'hot' Earth-size to Neptune-size planets in the inner 0.02-0.2 au from their parent stars. We propose that at least some of these smaller planets are the remnants of massive giant planets that migrated inwards quicker than they could contract. We show that such disruptions occur if the young giant planet ...
Young stars are thought to accumulate most of their mass through an accretion disk, which channels the gas and dust of a collapsing cloud onto the central protostellar object. The rotational and magnetic forces in the star-disk system often produce high-velocity jets of outflowing gas. These jets can in principle ...
opportunity to study rapid variations in stars that are very compact, like white dwarfs and neutron stars exotic neutron stars. How does accretion occur in binary stars? Two stars in orbit around each other up like compact stars (black holes, neutron ...
The variable star V1735 Cyg (=Elias 1-12) lies in the IC 5146 dark cloud and is a member of the class of FU Orionis objects whose dramatic optical brightenings are thought to be linked to episodic accretion. We report the first X-ray detections of V1735 Cyg and a deeply embedded class I protostar lying 24'' to its northeast. X-ray spectra ...
The only high-resolution X-ray spectrum of a low-mass, pre-main sequence Classical T Tauri star, TW Hya, showed dramatic differences from all other stellar coronal spectra: very cool, sharply peaked temperature distribution, and high density. Abundances were similar to, but more extreme, than other coronae: very weak iron, and very strong neon. We attributed the X-ray emission ...
Recent detections of disks around young high-mass stars indicate their formation through accretion rather than coalescence, but the physical properties of these disks are poorly known. In this study, we used Plateau de Bure interferometric images to probe the environment of the nearby (�1 kpc) and luminous (�20000 L_?) high-mass ...
The discovery of hundreds of young, bright stars within a parsec from the massive black hole at the center of the Galaxy presents a challenge to star formation theories. The requisite Roche densities for gravitational collapse of gas clouds are most naturally achieved in accretion disks. The water maser sources in ...
Models in which gamma-ray bursters are young neutron stars may be difficult to reconcile with the apparently isotropic distribution of observed bursts. To justify this statement, the distribution of old neutron stars in the Galaxy was calculated by integrating numerically some 90,000 orbits in the Galactic gravitational potential for ...
Important aspects of the theory of accretion are reviewed and the theory of the spherical accretion of a polytropic gas is presented. The effect of the termination of the flow at the surface of a neutron star or white dwarf is studied with consideration given to the interaction with a magnetic field anchored to the ...
Young low-mass stars host intense magnetic fields that play an important role in regulating the mass and angular momentum transfer between the star and its circumstellar disk, and at the same time heat and confine hot stellar coronae. The X-ray emission from the coronal plasma in turn heats and ionizes the circumstellar disk, affecting ...
We have identified several young stars located in the Small Magellanic Cloud (SMC), a nearby dwarf galaxy, that have spectral signatures of proto-planetary disks. Infrared spectra taken with the Spitzer Space Telescope reveal strong emission that indicates the presence of silicate dust, molecular and atomic gas, and hydrocarbon molecules orbiting close ...
During mass exchange in binary systems the star which is receiving mass increases its volume. This effect is estimated by evolutionary calculations for different (constant) accretion rates. It is shown the chance that the two stars do not come in contact ...
The basic ideas of accretion onto magnetized neutron stars are outlined. These are applied to a simple model of the structure of the plasma mound sitting at the magnetic poles of such a star, in which upward diffusion of photons is balanced by their downw...
Dec 31, 2008 ... The line widths are influenced by rotation of the star via the Doppler effect. Since the spin rates of many of these accreting neutron stars ...
APOD: 1999 December 19 Accretion Disk Binary System Explanation: Our Sun is unusual in that it is alone - most stars occur in multiple or binary systems. ...
Young nearby associations provide a crucial sample of stars for studying the local star formation history, investigating the early phases of planet formation, and searching for exoplanets through direct imaging. While numerous new associations have been identified in the last decade, their members are mostly restricted to relatively ...
