IUE observations of pre-main-sequence stars. I - MG II and CA II resonance line fluxes for T Tauri stars

Context. Pre-main-sequence variability characteristics can be used to probe the physical processes leading to the formation and initial evolution of both stars and planets. Aims. The photometric variability of pre-main-sequence stars is studied at optical wavelengths to explore star–disk interactions, accretion, spots, and other physical mechanisms associated with young stellar objects. Methods. We observed a field of 16′ × 16′ in the star-forming region Pelican Nebula (IC 5070) at BVRI wavelengths for 90 nights spread over one year in 2012−2013. More than 250 epochs in the VRI bands are used to identify and classify variables up to V ∼ 21 mag. Their physical association with the cluster IC 5070 is established based on the parallaxes and proper motions from the Gaia second data release (DR2). Multiwavelength photometric data are used to estimate physical parameters based on the isochrone fitting and spectral energy distributions. Results. We present a catalog of optical time-series photometry with periods, mean magnitudes, and classifications for 95 variable stars including 67 pre-main-sequence variables towards star-forming region IC 5070. The pre-main-sequence variables are further classified as candidate classical T Tauri and weak-line T Tauri stars based on their light curve variations and the locations on the color-color and color-magnitude diagrams using optical and infrared data together with Gaia DR2 astrometry. Classical T Tauri stars display variability amplitudes up to three times the maximum fluctuation in disk-free weak-line T Tauri stars, which show strong periodic variations. Short-term variability is missed in our photometry within single nights. Several classical T Tauri stars display long-lasting (≥10 days) single or multiple fading and brightening events of up to two magnitudes at optical wavelengths. The typical mass and age of the pre-main-sequence variables from the isochrone fitting and spectral energy distributions are estimated to be ≤1 M⊙ and ∼2 Myr, respectively. We do not find any correlation between the optical amplitudes or periods with the physical parameters (mass and age) of pre-main-sequence stars. Conclusions. The low-mass pre-main-sequence stars in the Pelican Nebula region display distinct variability and color trends and nearly 30% of the variables exhibit strong periodic signatures attributed to cold spot modulations. In the case of accretion bursts and extinction events, the average amplitudes are larger than one magnitude at optical wavelengths. These optical magnitude fluctuations are stable on a timescale of one year.

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Non thermal emission from T Tauri stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310016492 ◽

2010 ◽

Vol 6 (S275) ◽

pp. 404-405

Author(s):

María V. del Valle ◽

Gustavo E. Romero

Keyword(s):

Main Sequence ◽

Thermal Emission ◽

High Energy ◽

Magnetic Activity ◽

T Tauri Stars ◽

Main Sequence Stars ◽

High Energy Radiation ◽

X Ray ◽

T Tauri ◽

Low Mass

AbstractT Tauri stars are low mass, pre-main sequence stars. These objects are surrounded by an accretion disk and present strong magnetic activity. T Tauri stars are copious emitters of X-ray emission which belong to powerful magnetic reconnection events. Strong magnetospheric shocks are likely outcome of massive reconnection. Such shocks can accelerate particles up to relativistic energies through Fermi mechanism. We present a model for the high-energy radiation produced in the environment of T Tauri stars. We aim at determining whether this emission is detectable. If so, the T Tauri stars should be very nearby.

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The Occurrence of Lithium in Stars

Highlights of Astronomy ◽

10.1017/s1539299600001192 ◽

1968 ◽

Vol 1 ◽

pp. 230-232

Author(s):

G. H. Herbig

Keyword(s):

Main Sequence ◽

Solar Nebula ◽

T Tauri Stars ◽

Stellar Atmospheres ◽

Limited Time ◽

Main Sequence Stars ◽

Solar Abundance ◽

T Tauri ◽

Observational Knowledge ◽

Li Content

My task is to outline our present observational knowledge of the occurrence of lithium in stellar atmospheres. On account of the limited time, I shall not attempt to include a description of the situation in post-main sequence stars. Also for shortness of time, forgive me if I do not stop at each point to give due credit to the astronomers who have contributed to that topic.The youngest stars we know which are cool enough to exhibit neutral Li are the T Tauri stars, which are in the early stages of contraction toward the main sequence. All these objects that have been adequately observed are very abundant in Li: the range is between 50 and 400 times the so-called ‘solar abundance’, a convenient unit which corresponds to a H/Li ratio by number of atoms of about 1011. It is significant that the average Li content of chondritic meteorites, which are often considered to be samples of the non-volatile, unprocessed material of the original solar nebula, is about 150 on this system, within the range observed in the TTauri stars.

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Magnetospheric accretion in the intermediate-mass T Tauri star HQ Tauri

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038086 ◽

2020 ◽

Vol 642 ◽

pp. A99 ◽

Cited By ~ 1

Author(s):

K. Pouilly ◽

J. Bouvier ◽

E. Alecian ◽

S. H. P. Alencar ◽

A.-M. Cody ◽

...

Keyword(s):

Magnetic Field ◽

Strong Magnetic Field ◽

Main Sequence ◽

T Tauri Stars ◽

Line Profiles ◽

Main Sequence Stars ◽

Intermediate Mass ◽

Accretion Process ◽

T Tauri ◽

Magnetospheric Accretion

Context. Classical T Tauri stars are pre-main sequence stars surrounded by an accretion disk. They host a strong magnetic field, and both magnetospheric accretion and ejection processes develop as the young magnetic star interacts with its disk. Studying this interaction is a major goal toward understanding the properties of young stars and their evolution. Aims. The goal of this study is to investigate the accretion process in the young stellar system HQ Tau, an intermediate-mass T Tauri star (1.9 M⊙). Methods. The time variability of the system is investigated both photometrically, using Kepler-K2 and complementary light curves, and from a high-resolution spectropolarimetric time series obtained with ESPaDOnS at CFHT. Results. The quasi-sinusoidal Kepler-K2 light curve exhibits a period of 2.424 d, which we ascribe to the rotational period of the star. The radial velocity of the system shows the same periodicity, as expected from the modulation of the photospheric line profiles by surface spots. A similar period is found in the red wing of several emission lines (e.g., HI, CaII, NaI), due to the appearance of inverse P Cygni components, indicative of accretion funnel flows. Signatures of outflows are also seen in the line profiles, some being periodic, others transient. The polarimetric analysis indicates a complex, moderately strong magnetic field which is possibly sufficient to truncate the inner disk close to the corotation radius, rcor ∼ 3.5 R⋆. Additionally, we report HQ Tau to be a spectroscopic binary candidate whose orbit remains to be determined. Conclusions. The results of this study expand upon those previously reported for low-mass T Tauri stars, as they indicate that the magnetospheric accretion process may still operate in intermediate-mass pre-main sequence stars, such as HQ Tauri.

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T Tauri Disk Lifetime in the Lupus Association

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315006262 ◽

2015 ◽

Vol 10 (S314) ◽

pp. 191-192

Author(s):

P. A. B. Galli ◽

C. Bertout ◽

R. Teixeira ◽

C. Ducourant

Keyword(s):

Main Sequence ◽

T Tauri Stars ◽

Young Stars ◽

Main Sequence Stars ◽

Disk Model ◽

Star Forming ◽

T Tauri

AbstractIn a recent study, we derived individual distances for a sample of pre-main sequence stars that define the comoving association of young stars in the Lupus star-forming region. Here, we use these new distances to investigate the mass and age distributions of Lupus T Tauri stars and derive the average disk lifetime in the Lupus association based on an empirical disk model.

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Magnetic Fields of T Tauri Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900061866 ◽

1997 ◽

Vol 182 ◽

pp. 465-474

Author(s):

Eike W. Guenther

Keyword(s):

Magnetic Field ◽

Main Sequence ◽

T Tauri Stars ◽

Main Sequence Stars ◽

Emission Component ◽

Upper Limit ◽

T Tauri ◽

Late Type Star ◽

T Tau ◽

The Magnetic Field

The magnetic field strengths of several T Tauri stars are derived by measuring the width of unblended Fe I lines of high and low values of geff·λ2 using the autocorrelation function. The T Tauri stars were selected for their low values of v · sin i, and large strengths of the Ca II emission component. The derived magnetic field strength are 2.0 ± 0.6 kG and 2.6 ± 0.8 kG for the classical T Tauri stars Lk Ca 15 and T Tau, respectively. An upper limit of 0.6 ± 0.8 kG is found for the weak-line T Tauri star Lk Ca 16. The method is tested by analysing two non-magnetic main sequence stars, and a late-type star that is known to have a strong magnetic field.

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Magnetic Activity of Pre-main Sequence Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900182130 ◽

2004 ◽

Vol 219 ◽

pp. 211-222

Author(s):

Eric D. Feigelson

Keyword(s):

Main Sequence ◽

Magnetic Activity ◽

T Tauri Stars ◽

X Rays ◽

Orion Nebula ◽

Main Sequence Stars ◽

Nearby Star ◽

X Ray ◽

T Tauri ◽

Pms Stars

I review here recent advances in our understanding of magnetic activity in pre-main sequence (PMS) protostars and T Tauri stars. Results are based on recent imaging, spectroscopic and temporal studies of nearby star forming regions from the Chandra X — ray Observatory and XMM — Newton, including a first look at an ultradeep Chandra exposure of the Orion Nebula Cluster.Pre-main sequence stars exhibit a high level of X-ray emission dominated by a bewildering variety of magnetic reconnection flares. Activity is linked to bulk stellar properties — Lbol, mass, surface area or volume — rather than rotation. This suggests that dynamo processes in deeply convective PMS stars may fundamentally differ from the tachocline dynamo operating in main sequence stars.X-rays and MeV particles from magnetic flares will affect the circumstellar environment in PMS systems, particularly the protoplanetary disk. X-ray emission may influence: disk ionization, turbulence and viscosity; Jovian planet formation and migration; the production of meteoritic isotopes and melting of meteoritic chondrules; the heating and chemistry of the disk. X-ray surveys are also effective in locating post-T Tauri stars for disk evolution studies.

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Evidences of protoplanetary disks in a selected sample of weak T Tauri stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900218172 ◽

2004 ◽

Vol 202 ◽

pp. 335-337

Author(s):

Jane Gregorio-Hetem ◽

Annibal Hetem

Keyword(s):

Main Sequence ◽

Planetary System ◽

Protoplanetary Disks ◽

T Tauri Stars ◽

Evolutionary Sequence ◽

Main Sequence Stars ◽

T Tauri ◽

Dust Distribution

A model with two dust components is used do explain the circumstellar structure of weak-T Tauri stars. The IR-excess was calculated and compared to spectroscopic criteria in order to classify the objects according an evolutionary sequence. About 46% of the sample correspond to young main sequence stars showing dust distribution consistent with a disrupted disk, that could be possibly caused by the formation of a planetary system.

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A Radio Survey of Older T Tauri Stars in the η Chamaeleontis Cluster

Publications of the Astronomical Society of Australia ◽

10.1071/as99257 ◽

1999 ◽

Vol 16 (3) ◽

pp. 257-261 ◽

Cited By ~ 12

Author(s):

Eric E. Mamajek ◽

Warrick A. Lawson ◽

Eric D. Feigelson

Keyword(s):

Radio Emission ◽

Main Sequence ◽

T Tauri Stars ◽

Young Stars ◽

Radio Continuum ◽

Rotating Stars ◽

Main Sequence Stars ◽

X Ray ◽

Rotation Periods ◽

T Tauri

AbstractA radio continuum survey of X-ray-identified weak-lined T Tauri stars (WTTs) in the newly-discovered η Chamaeleontis cluster has been completed using the Australia Telescope Compact Array (ATCA). The 10 known WTTs in the cluster form a unique sample of codistant late-type pre-main-sequence stars with ages of ~8 Myr and masses ranging from 0·1–1·0 M⊙. Our survey detected none of the 10 X-ray-emitting WTTs with 3σ sensitivity limits at 4·8 and 8·6 GHz (6·2 and 3·5 cm) of typically 0·4 mJy, corresponding to a radio luminosity of 4·5 ×1015 erg Hz−1 s−1. Rotation periods for these stars indicate that they are not, as a group, fast-rotating stars. The non-detection in the radio bands supports the findings of other radio surveys of inhomogeneous samples of young stars, where radio emission is fairly common (10–30%) among very young T Tauri stars across all late spectral types, but confined to rapidly-rotating F-G-K stars amongst older zero-age main sequence stars. Rotation, more than youth, appears to be the key to radio emission in young stars.

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Sodium Ionization in T-Tauri Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100023952 ◽

1989 ◽

Vol 120 ◽

pp. 304-304

Author(s):

A. Natta ◽

C. Giovanardi

Keyword(s):

Mass Loss ◽

Main Sequence ◽

T Tauri Stars ◽

Line Profiles ◽

Main Sequence Stars ◽

T Tauri

We present the results of a study of the sodium ionization and excitation in the winds of low-luminosity, pre-main-sequence stars. Line profiles for the Nal doublet at 5990,5986 Åare discussed and compared with the observations for those T Tauri stars with P-Cygni profiles. We find that the observed shape of the lines put significative constraints on the rate of mass-loss (M ≥ 3 x 10-8M⊙/yr).

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