scholarly journals Flares in T Tauri Stars

1995 ◽  
Vol 151 ◽  
pp. 202-211 ◽  
Author(s):  
Gösta F. Gahm
Keyword(s):  
Time Scales ◽  
T Tauri Stars ◽  
Light Curves ◽  
Rapid Variability ◽  
Strong Emission ◽  
T Tauri ◽  
New Concepts ◽  
Circumstellar Extinction ◽  
Higher Sensitivity

This review concerns rapid variability, on time-scales of a few hours or less, occurring on T Tauri stars (TTS). There are several recent reviews on observed properties of TTS (e.g. Appenzeller & Mundt 1989, Bertout 1989, Gahm 1990a, Kuhi & Cram 1989), some with more emphasis on “flare-like” activity (Feigelson et al. 1991, Gahm 1990b, Montmerle 1991, Montmerle et al. 1993), and the ambition below has been to summarize more recent work. We will also give a compilation of published works on observations of optical variability on these time-scales and a related statistical overview. Some early, very interesting and extensive studies of this kind were made here at the Sonneberg Observatory, where for instance Götz & Wenzel (1967) concluded that the light-curve of RW Aurigae contains several components: quasi-periodic fluctuations over days, ‘waves’ over several hours, rapid outbursts with symmetric light-curves, rapid outbursts with asymmetric (flare-like) light-curves (see also Fürtig & Wenzel 1964) and small fluctuations with very small amplitudes, which they postulated could be due to changes in the emission line fluxes. Modern photometric results of higher sensitivity and time-resolution confirm the existence of these different types of rapid variations in classical TTS (CTTS), having strong emission (lines and continuous, so called veiling) superimposed on the photospheric absorption line spectrum. As described in the subsequent chapters there are new concepts for the interpretation of the short-lived fluctuations. Concerning the long-term quasi-periodic variations we can now usually relate them to the stellar rotational period (bright or dark spots), let be that RW Aur still is an uncertain case. There are other slow changes most likely related to variable circumstellar extinction in circumstellar dust in the line-of-sight to the star. The long-term optical changes were most recently discussed by Herbst et al. (1994).

scholarly journals Dynamics of wind and the dusty environments in the accreting T Tauri stars RY Tauri and SU Aurigae

2018 ◽  
Vol 483 (1) ◽  
pp. 132-146 ◽  
Author(s):  
P P Petrov ◽  
K N Grankin ◽  
J F Gameiro ◽  
S A Artemenko ◽  
E V Babina ◽  
...  
Keyword(s):  
T Tauri Stars ◽  
Gas Flows ◽  
Photometric Variability ◽  
Outflow Velocity ◽  
T Tauri ◽  
Photometric Observations ◽  
Accretion Model ◽  
Circumstellar Extinction ◽  
Magnetospheric Accretion

Abstract Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars, RY Tauri and SU Aurigae, with the aim to quantify the accretion and outflow dynamics at time-scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau, we observed a new effect: during events of enhanced outflow, the circumstellar extinction becomes lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time-scale of years. Periods of quiescence in the variability of the Hα profile were observed during the 2015–2016 period in RY Tau and during the 2016–2017 period in SU Aur. We interpret these findings in the framework of the magnetospheric accretion model, and we discuss how the global stellar magnetic field can influence the long-term variations of the outflow activity.

scholarly journals Optical photometric variable stars towards Cygnus OB7

2019 ◽  
Vol 487 (2) ◽  
pp. 1765-1776 ◽  
Author(s):  
Somnath Dutta ◽  
Soumen Mondal ◽  
Santosh Joshi ◽  
Ramkrishna Das
Keyword(s):  
Variable Stars ◽  
T Tauri Stars ◽  
Light Curves ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Rotation Rates ◽  
T Tauri ◽  
Photometric Observations ◽  
Sky Survey ◽  
Magnitude Diagram

ABSTRACT We present optical I-band light curves of the stars towards a star-forming region Cygnus OB7 from 17-night photometric observations. The light curves are generated from a total of 381 image frames with very good photometric precision. From the light curves of 1900 stars and their periodogram analyses, we detect 31 candidate variables including five previously identified. 14 out of 31 objects are periodic and exhibit the rotation rates in the range of 0.15–11.60 d. We characterize those candidate variables using optical/infrared colour–colour diagram and colour–magnitude diagram (CMD). From spectral indices of the candidate variables, it turns out that four are probably Classical T-Tauri stars (CTTSs), rest remain unclassified from present data, they are possibly field stars or discless pre-main-sequence stars towards the region. Based on their location on the various CMDs, the ages of two T Tauri Stars were estimated to be ∼5 Myr. The light curves indicate at least five of the periodic variables are eclipsing systems. The spatial distribution of young variable candidates on Planck 857 GHz (350 $\mu$m) and 2MASS (Two Micron All Sky Survey) Ks images suggest that at least two of the CTTSs are part of the active star-forming cloud Lynds 1003.

scholarly journals Properties of CVSO 30 from TESS measurements: probably a binary T Tauri star with complex light curves and no obvious planets

2020 ◽  
Vol 494 (3) ◽  
pp. 4349-4356
Author(s):  
C Koen
Keyword(s):  
Light Curve ◽  
Small Group ◽  
T Tauri Stars ◽  
Light Curves ◽  
Tauri Star ◽  
Curve Shape ◽  
T Tauri

ABSTRACT ‘Transiting Exoplanet Survey Satellite’ (TESS) photometry of CVSO 30 spanned 21.8 d, with a single large gap of 1.1 d. This allows alias-free determination of the two periodicities in the data. It is confirmed that both of these are non-sinusoidal: the dominant P1 = 0.4990 d has two detectable harmonics and P2 = 0.4486 d has seven. The large number of harmonics in the second periodicity characterizes a very complex light curve shape. One of the features in the light curve is a sharp dip of duration ∼2 h: this is probably the source of the previously claimed planetary transit signature. The star is a member of a small group of T Tauri stars with complex light curves, which have recently been exhaustively studied using Kepler and TESS observations. The two non-commensurate periods are most simply interpreted as being from two stars, i.e. CVSO 30 is probably a binary.

scholarly journals Long-term variability of T Tauri stars using WASP

2016 ◽  
Vol 465 (4) ◽  
pp. 3889-3901 ◽  
Author(s):  
Laura Rigon ◽  
Alexander Scholz ◽  
David Anderson ◽  
Richard West
Keyword(s):  
T Tauri Stars ◽  
T Tauri

scholarly journals A search for rapid variability in T Tauri stars

1996 ◽  
Vol 282 (1) ◽  
pp. 167-174 ◽  
Author(s):  
K. W. Smith ◽  
D. H. P. Jones ◽  
C. J. Clarke
Keyword(s):  
T Tauri Stars ◽  
Rapid Variability ◽  
T Tauri

scholarly journals A survey for variable young stars with small telescopes: II – mapping a protoplanetary disc with stable structures at 0.15 au

2020 ◽  
Vol 493 (1) ◽  
pp. 184-198 ◽  
Author(s):  
Jack J Evitts ◽  
Dirk Froebrich ◽  
Aleks Scholz ◽  
Jochen Eislöffel ◽  
Justyn Campbell-White ◽  
...  
Keyword(s):  
Time Scales ◽  
Broad Band ◽  
T Tauri ◽  
Low Levels ◽  
Short Time ◽  
Citizen Science Project ◽  
The Hill ◽  
Colour Terms ◽  
High Cadence

ABSTRACT The HOYS citizen science project conducts long-term, multifilter, high-cadence monitoring of large YSO samples with a wide variety of professional and amateur telescopes. We present the analysis of the light curve of V1490 Cyg in the Pelican Nebula. We show that colour terms in the diverse photometric data can be calibrated out to achieve a median photometric accuracy of 0.02 mag in broad-band filters, allowing detailed investigations into a variety of variability amplitudes over time-scales from hours to several years. Using Gaia DR2, we estimate the distance to the Pelican Nebula to be 870 $^{+70}_{-55}$ pc. V1490 Cyg is a quasi-periodic dipper with a period of 31.447 ± 0.011 d. The obscuring dust has homogeneous properties, and grains larger than those typical in the ISM. Larger variability on short time-scales is observed in U and Rc−H α, with U amplitudes reaching 3 mag on time-scales of hours, indicating that the source is accreting. The H α equivalent width and NIR/MIR colours place V1490 Cyg between CTTS/WTTS and transition disc objects. The material responsible for the dipping is located in a warped inner disc, about 0.15 au from the star. This mass reservoir can be filled and emptied on time-scales shorter than the period at a rate of up to 10−10 M⊙ yr−1, consistent with low levels of accretion in other T Tauri stars. Most likely, the warp at this separation from the star is induced by a protoplanet in the inner accretion disc. However, we cannot fully rule out the possibility of an AA Tau-like warp, or occultations by the Hill sphere around a forming planet.

scholarly journals Magnetospheric Accretion in T Tauri Stars

1997 ◽  
Vol 163 ◽  
pp. 515-519
Author(s):  
Philip J. Armitage
Keyword(s):  
T Tauri Stars ◽  
Stellar Surface ◽  
Photometric Variability ◽  
Accretion Flows ◽  
Rotation Rates ◽  
T Tauri ◽  
Show Evidence ◽  
Magnetospheric Accretion

AbstractMany, perhaps most, accreting T Tauri stars show evidence for magnetically dominated accretion flows near the stellar surface. I discuss the implications of this for the rotation rates and long-term photometric variability of T Tauri stars.

scholarly journals Dense Cores and Young Stars in Dark Clouds

1987 ◽  
Vol 115 ◽  
pp. 33-43
Author(s):  
Philip C. Myers
Keyword(s):  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Low Mass Stars ◽  
Iras Source ◽  
Dark Clouds ◽  
Dense Cores ◽  
T Tauri ◽  
Circumstellar Extinction ◽  
Molecular Lines ◽  
Low Mass

Dark clouds within a few hundred pc of the Sun contain hundreds of condensations with typical size 0.1 pc, density 104 molecules per cubic cm, mass 1 M⊙, and temperature 10 K. These “dense cores” are defined by maps of molecular lines, such as the (J,K)=(1,1) line of ammonia at 1.3 cm wavelength. They are associated with regions of opaque visual obscuration, groups of T Tauri stars, and other cores. They are closely correlated with steep-spectrum, low-luminosity (1-10 L⊙) IRAS sources! of about 60 cores with ammonia maps, half have an IRAS source within one map diameter. Thus cores form low-mass stars, which are probably precursors of T Tauri stars. Simple models indicate that time for a core to wait before collapsing, to collapse and form a star, and to disperse are each of order 105 yr. Cores with stars have broader lines and bigger velocity gradients than cores without stars, suggesting interaction between the star and the core due to gravity and/or outflow. Stars in cores have about 30 mag greater circumstellar extinction, and greater likelihood of CO outflow, than stars near, but not in, cores. Models of the 1-100 μm spectra of stars in cores suggest that inside of ∼100 A.U., the typical star suffers relatively little line-of-sight extinction but is accompanied by a source of significant luminosity at 5-25 μm. Models involving circumstellar disks provide good fits to the observed spectra.

scholarly journals Synthetic Light Curves of Accretion Variability in T Tauri Stars

2021 ◽  
Vol 908 (1) ◽  
pp. 16
Author(s):  
Connor E. Robinson ◽  
Catherine C. Espaillat ◽  
James E. Owen
Keyword(s):  
T Tauri Stars ◽  
Light Curves ◽  
T Tauri
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