scholarly journals Multi-epoch monitoring of the AA Tauri-like star V 354 Mon

2018 ◽  
Vol 614 ◽  
pp. A108 ◽  
Author(s):  
P. C. Schneider ◽  
C. F. Manara ◽  
S. Facchini ◽  
H. M. Günther ◽  
G. J. Herczeg ◽  
...  
Keyword(s):  
Accretion Rate ◽  
Central Star ◽  
T Tauri Stars ◽  
Gas Absorption ◽  
Gas Content ◽  
Dust Extinction ◽  
T Tauri ◽  
Disk Material ◽  
A Minor ◽  
High Dust

Disk warps around classical T Tauri stars (CTTSs) can periodically obscure the central star for some viewing geometries. For these so- called AA Tau-like variables, the obscuring material is located in the inner disk and absorption spectroscopy allows one to characterize its dust and gas content. Since the observed emission from CTTSs consists of several components (photospheric, accretion, jet, and disk emission), which can all vary with time, it is generally challenging to disentangling disk features from emission variability. Multi- epoch, flux-calibrated, broadband spectra provide us with the necessary information to cleanly separate absorption from emission variability. We applied this method to three epochs of VLT/X-shooter spectra of the CTTS V 354 Mon (CSI Mon-660) located in NGC 2264 and find that: (a) the accretion emission remains virtually unchanged between the three epochs; (b) the broadband flux evolution is best described by disk material obscuring part of the star, and (c) the Na and K gas absorption lines show only a minor increase in equivalent width during phases of high dust extinction. The limits on the absorbing gas column densities indicate a low gas-to-dust ratio in the inner disk, less than a tenth of the ISM value. We speculate that the evolutionary state of V 354 Mon, rather old with a low accretion rate, is responsible for the dust excess through an evolution toward a dust dominated disk or through the fragmentation of larger bodies that drifted inward from larger radii in a still gas dominated disk.

scholarly journals Brown dwarf jets: Investigating the universality of jet launching mechanisms at the lowest masses

2010 ◽  
Vol 6 (S275) ◽  
pp. 396-399
Author(s):  
Emma Teresa Whelan ◽  
Francesca Bacciotti ◽  
Tom Ray ◽  
Catherine Dougados
Keyword(s):  
Accretion Rate ◽  
T Tauri Stars ◽  
Brown Dwarf ◽  
Central Mass ◽  
Mass Accretion Rate ◽  
T Tauri ◽  
Mass Outflow ◽  
The Common ◽  
Protostellar Objects

AbstractRecently it has become apparent that proto-stellar-like outflow activity extends to the brown dwarf (BD) mass regime. While the presence of accretion appears to be the common ingredient in all objects known to drive jets fundamental questions remain unanswered. The more prominent being the exact mechanism by which jets are launched, and whether this mechanism remains universal among such a diversity of sources and scales. To address these questions we have been investigating outflow activity in a sample of protostellar objects that differ considerably in mass and mass accretion rate. Central to this is our study of brown dwarf jets. To date Classical T Tauri stars (CTTS) have offered us the best touchstone for decoding the launching mechanism. Here we shall summarise what is understood so far of BD jets and the important constraints observations can place on models. We will focus on the comparison between jets driven by objects with central mass <0.1M⊙ and those driven by CTTSs. In particular we wish to understand how the the ratio of the mass outflow to accretion rate compares to what has been measured for CTTSs.

scholarly journals GIARPS High-resolution Observations of T Tauri stars (GHOsT)

2020 ◽  
Vol 643 ◽  
pp. A32
Author(s):  
M. Gangi ◽  
B. Nisini ◽  
S. Antoniucci ◽  
T. Giannini ◽  
K. Biazzo ◽  
...  
Keyword(s):  
High Resolution ◽  
Complex Structure ◽  
Central Star ◽  
T Tauri Stars ◽  
Resolving Power ◽  
High Resolution Spectroscopy ◽  
Young Stellar Objects ◽  
Clear Correlation ◽  
Low Velocity ◽  
T Tauri

Context. Disk winds play a fundamental role in the evolution of protoplanetary systems. The complex structure and dynamics can be investigated through the emission of atomic and molecular lines detected in high-resolution optical/IR spectra of young stellar objects. Despite their great importance, however, studies connecting the atomic and molecular components are lacking so far. Aims. In the framework of the GIARPS High-resolution Observations of T Tauri stars (GHOsT) project, we aim to characterize the atomic and molecular winds in a sample of classical T Tauri stars (CTTs) of the Taurus-Auriga region, focusing on a statistical analysis of the kinematic properties of the [O I] 630 nm and H2 2.12 μm lines and their mutual relationship. Methods. We analyzed the flux calibrated [O I] 630 nm and H2 2.12 μm lines in a sample of 36 CTTs observed at the Telescopio Nazionale Galileo with the HARPS-N spectrograph (resolving power of R = 115 000) and with the GIANO spectrograph (R = 50 000). We decomposed the line profiles into different kinematic Gaussian components and focused on the most frequently detected component, the narrow low-velocity (vp < 20 km s−1) component (NLVC). Results. We found that the H2 line is detected in 17 sources (~50% detection rate), and [O I] is detected in all sources but one. The NLV components of the H2 and [O I] emission are kinematically linked, with a strong correlation between the peak velocities and the full widths at half maximum of the two lines. Assuming that the line width is dominated by Keplerian broadening, we found that the [O I] NVLC originates from a disk region between 0.05 and 20 au and that of H2 in a region from 2 and 20 au. We also found that H2 is never detected in sources where [O I] originates in regions below 1 au, as well as in sources of early (~F-G) spectral type with a luminosity >1 L⊙. Moreover, in seven sources, both H2 and [O I] have clear blueshifted peaks and prominent [O I] high-velocity components. These components have also been detected in sources with no relevant centroid shift. Finally, we did not find any clear correlation between vp of the H2 and [O I] NVLC and the outer disk inclination. This result is in line with previous studies. Conclusions. Our results suggest that molecular and neutral atomic emission in disk winds originate from regions that might overlap, and that the survival of molecular winds in disks strongly depends on the gas exposure to the radiation from the central star. The presence of jets does not necessarily affect the kinematics of the low-velocity winds. Our results demonstrate the potential of wide-band high-resolution spectroscopy in linking tracers of different manifestations of the same phenomenon.

The Stellar Mass-Accretion Rate Relation in T Tauri Stars and Brown Dwarfs

2006 ◽  
Vol 639 (2) ◽  
pp. L83-L86 ◽  
Author(s):  
Richard D. Alexander ◽  
Philip J. Armitage
Keyword(s):  
Accretion Rate ◽  
Brown Dwarfs ◽  
Stellar Mass ◽  
T Tauri Stars ◽  
Mass Accretion Rate ◽  
T Tauri ◽  
Rate Relation

scholarly journals Line-dependent veiling in very active classical T Tauri stars

2018 ◽  
Vol 610 ◽  
pp. A40 ◽  
Author(s):  
A. C. S. Rei ◽  
P. P. Petrov ◽  
J. F. Gameiro
Keyword(s):  
Signal To Noise Ratio ◽  
Hot Spot ◽  
Stellar Atmosphere ◽  
T Tauri Stars ◽  
Stellar Atmospheres ◽  
T Tauri ◽  
Excitation Potential ◽  
Chromospheric Emission ◽  
Emission Line Spectrum ◽  
A Minor

Context. The T Tauri stars with active accretion disks show veiled photospheric spectra. This is supposedly due to non-photospheric continuum radiated by hot spots beneath the accretion shocks at stellar surface and/or chromospheric emission lines radiated by the post-shocked gas. The amount of veiling is often considered as a measure of the mass-accretion rate. Aim. We analysed high-resolution photospheric spectra of accreting T Tauri stars LkHα 321, V1331 Cyg, and AS 353A with the aim of clarifying the nature of the line-dependent veiling. Each of these objects shows a strong emission line spectrum and powerful wind features indicating high rates of accretion and mass loss. Methods. Equivalent widths of hundreds of weak photospheric lines were measured in the observed spectra of high quality and compared with those in synthetic spectra of appropriate models of stellar atmospheres. Results. The photospheric spectra of the three T Tauri stars are highly veiled. We found that the veiling is strongly line-dependent: larger in stronger photospheric lines and weak or absent in the weakest ones. No dependence of veiling on excitation potential within 0 to 5 eV was found. Different physical processes responsible for these unusual veiling effects are discussed in the framework of the magnetospheric accretion model. Conclusions. The observed veiling has two origins: (1) an abnormal structure of stellar atmosphere heated up by the accreting matter, and (2) a non-photospheric continuum radiated by a hot spot with temperature lower than 10 000 K. The true level of the veiling continuum can be derived by measuring the weakest photospheric lines with equivalent widths down to ≈10 mÅ. A limited spectral resolution and/or low signal-to-noise ratio results in overestimation of the veiling continuum. In the three very active stars, the veiling continuum is a minor contributor to the observed veiling, while the major contribution comes from the line-dependent veiling.

scholarly journals New view of the corona of classical T Tauri stars: Effects of flaring activity in circumstellar disks

2019 ◽  
Vol 624 ◽  
pp. A50 ◽  
Author(s):  
S. Colombo ◽  
S. Orlando ◽  
G. Peres ◽  
F. Reale ◽  
C. Argiroffi ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Circumstellar Disks ◽  
Central Star ◽  
Field Configuration ◽  
T Tauri Stars ◽  
Stellar Objects ◽  
X Ray ◽  
T Tauri ◽  
Coronal Activity ◽  
Accretion Rates

Context. Classical T Tauri stars (CTTSs) are young low-mass stellar objects that accrete mass from their circumstellar disks. They are characterized by high levels of coronal activity, as revealed by X-ray observations. This activity may affect the disk stability and the circumstellar environment. Aims. Here we investigate if an intense coronal activity due to flares that occur close to the accretion disk may perturb the stability of the inner disk, disrupt the inner part of the disk, and might even trigger accretion phenomena with rates comparable with those observed. Methods. We modeled a magnetized protostar surrounded by an accretion disk through 3D magnetohydrodinamic simulations. The model takes into account the gravity from the central star, the effects of viscosity in the disk, the thermal conduction (including the effects of heat flux saturation), the radiative losses from optically thin plasma, and a parameterized heating function to trigger the flares. We explored cases characterized by a dipole plus an octupole stellar magnetic field configuration and different density of the disk or by different levels of flaring activity. Results. As a result of the simulated intense flaring activity, we observe the formation of several loops that link the star to the disk; all these loops build up a hot extended corona with an X-ray luminosity comparable with typical values observed in CTTSs. The intense flaring activity close to the disk can strongly perturb the disk stability. The flares trigger overpressure waves that travel through the disk and modify its configuration. Accretion funnels may be triggered by the flaring activity and thus contribute to the mass accretion rate of the star. Accretion rates synthesized from the simulations are in a range between 10−10 and 10−9 M⊙ yr−1. The accretion columns can be perturbed by the flares, and they can interact with each other; they might merge into larger streams. As a result, the accretion pattern can be rather complex: the streams are highly inhomogeneous, with a complex density structure, and clumped.

scholarly journals SpS1-Measuring magnetic fields on young stars

2009 ◽  
Vol 5 (H15) ◽  
pp. 524-524
Author(s):  
Christopher M. Johns-Krull ◽  
Jeff A. Valenti
Keyword(s):  
Magnetic Field ◽  
Accretion Rate ◽  
Critical Role ◽  
Circumstellar Disk ◽  
Stellar Rotation ◽  
T Tauri ◽  
Disk Material ◽  
Optical Wavelengths ◽  
The Magnetic Field ◽  
Cloud Material

T Tauri stars (TTSs) are young (~few Myr) late type stars that have only recently emerged from their natal molecular cloud material to become visible at optical wavelengths. It is now generally accepted that accretion of circumstellar disk material onto the surface of a TTS is controlled by a strong stellar magnetic field (e.g. see review by Bouvier et al. 2007). The stellar field appears critical for explaining the rotational properties of TTSs (Bouvier et al. 2007, Herbst et al. 2007) and may also play a critical role in driving the outflows seen from many of these sources (e.g. Shang et al. 2007, Mohanty & Shu 2008). As a result, there is a great deal of interest in measuring the magnetic field properties of TTSs (e.g. Johns–Krull 2007, Donati et al. 2008). In particular, disk locking theories predict that an equilibrium is established where the disk is trunctated at or close to corotation and the stellar rotation rate depends only on the (assumed) dipolar magnetic field strength, the stellar mass, radius, and the mass accretion rate in the disk (see Bouvier et al. 2007).

scholarly journals The VLTi/PIONIER survey of southern TTauri disks

2013 ◽  
Vol 8 (S299) ◽  
pp. 94-98
Author(s):  
Fabien Anthonioz ◽  
F. Ménard ◽  
C. Pinte ◽  
W-F. Thi ◽  
J.-B. Lebouquin ◽  
...  
Keyword(s):  
Integrated Optics ◽  
Significant Contribution ◽  
Protoplanetary Disks ◽  
Central Star ◽  
T Tauri Stars ◽  
Near Ir ◽  
Accretion Process ◽  
T Tauri ◽  
Extended Component ◽  
Expected Position

AbstractStudying the inner regions of protoplanetary disks (1-10 AU) is of importance to understand the formation of planets and the accretion process feeding the forming central star. Herbig AeBe stars are bright enough to be routinely observed by Near IR interferometers. The data for the fainter T Tauri stars is much more sparse. In this contribution we present the results of our ongoing survey at the VLTI. We used the PIONIER combiner that allows the simultaneous use of 4 telescopes, yielding 6 baselines and 3 independent closure phases at once. PIONIER's integrated optics technology makes it a sensitive instrument. We have observed 22 T Tauri stars so far, the largest survey for T Tauri stars to this date.Our results demonstrate the very significant contribution of an extended component to the interferometric signal. The extended component is different from source to source and the data, with several baselines, offer a way to improve our knowledge of the disk geometry and/or composition. These results validate an earlier study by Pinte et al. 2008 and show that the dust inner radii of T Tauri disks now appear to be in better agreement with the expected position of the dust sublimation radius, contrary to previous claims.

scholarly journals Envelope-to-disk mass transport in the FUor-type young eruptive star V346 Normae

2018 ◽  
Vol 14 (S345) ◽  
pp. 320-321
Author(s):  
Á. Kóspál ◽  
P. Ábrahám ◽  
O. Fehér ◽  
F. Cruz-Sáenz de Miera ◽  
M. Takami
Keyword(s):  
Mass Transport ◽  
Velocity Structure ◽  
Accretion Rate ◽  
Central Star ◽  
Type Star ◽  
Disk Mass ◽  
Disk Material ◽  
Accretion Rates

AbstractHaving disk-to-star accretion rates on the order of 10-4M&odot;/yr, FU Orionis-type stars (FUors) are thought to be the visible examples for episodic accretion. FUors are often surrounded by massive envelopes, which replenish the disk material and enable the disk to produce accretion outbursts. We observed the FUor-type star V346 Nor with ALMA at 1.3 mm continuum and in different CO rotational lines. We mapped the density and velocity structure of its envelope and analyzed the results using channel maps, position-velocity diagrams, and spectro-astrometric methods. We discovered a pseudo-disk and a Keplerian disk around a 0.1 M&odot; central star. We determined an infall rate from the envelope onto the disk of 6&times;10-6M&odot;/yr, a factor of few higher than the quiescent accretion rate from the disk onto the star. This hints for a mismatch between the infall and accretion rates as the cause of the eruption.

scholarly journals Classical T Tauri stars: accretion, wind, dust

2021 ◽  
Vol 2 (1) ◽  
pp. 1-8
Author(s):  
Petr Petrov
Keyword(s):  
Accretion Disks ◽  
Accretion Rate ◽  
T Tauri Stars ◽  
Evolutionary Stage ◽  
Gas Flows ◽  
Spectroscopic Monitoring ◽  
T Tauri ◽  
Dynamical Parameters ◽  
Wind Flows ◽  
Magnetospheric Accretion

Classical T Tauri stars (CTTS) are at the early evolutionary stage when the processes of planet formation take place in the surrounding accretion disks. Most of the observed activity in CTTS is due to magnetospheric accretion and wind flows. Observations of the accreting gas flows and appearance of the line-dependent veiling of the photospheric spectrum in CTTS are considered. Evidence for the dusty wind causing the observed irregular variability of CTTS is presented. Photometric and spectroscopic monitoring of two CTTS, RY Tau and SU Aur, has been carried out atthe Crimean Astrophysical Observatory since 2013 aimed at studying the dynamics of accretion and wind flows on time scales from days to years. The observed variations in the dynamical parameters may be caused by changes in the accretion rate and in the global magnetic fields of CTTS.

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