scholarly journals Red and Near Infrared Spectra* of Pre-Main Sequence Stars I. A Preliminary Investigation of T Tauri Stars

1977 ◽  
Vol 42 ◽  
pp. 100-105 ◽  
Author(s):  
Y. Andrillat
Keyword(s):  
Color Index ◽  
Main Sequence ◽  
Near Infrared ◽  
Preliminary Investigation ◽  
Visible Spectrum ◽  
T Tauri Stars ◽  
Main Sequence Stars ◽  
Type K ◽  
T Tauri ◽  
Near Infrared Spectra

230 Å mm-1 spectra of 30 stars of T Tauri or related type were obtained in the 8000-11000 Å region using a grating spectrograph equipped with an S-1 photocathode image-tube. In addition a few T Tauri stars were observed at the same dispersion in the 6200-8800 Å region on IN plate. A preliminary qualitative analysis of the observations leads to possible correlations between the intensities of emissions of the Ca II triplet, Paschen series and He I 10830 Å, and the spectral type, K-L color index of the star, or the [0 I] and Fe II intensities in the visible spectrum.

scholarly journals Variability of young stellar objects in the star-forming region Pelican Nebula

2019 ◽  
Vol 627 ◽  
pp. A135 ◽  
Author(s):  
A. Bhardwaj ◽  
N. Panwar ◽  
G. J. Herczeg ◽  
W. P. Chen ◽  
H. P. Singh
Keyword(s):  
Main Sequence ◽  
T Tauri Stars ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Physical Parameters ◽  
Main Sequence Stars ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri ◽  
Optical Wavelengths

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.

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

1981 ◽  
Vol 251 ◽  
pp. 113 ◽  
Author(s):  
M. S. Giampapa ◽  
N. Calvet ◽  
C. L. Imhoff ◽  
L. V. Kuhi
Keyword(s):  
Resonance Line ◽  
Main Sequence ◽  
T Tauri Stars ◽  
Main Sequence Stars ◽  
T Tauri

scholarly journals Non thermal emission from T Tauri stars

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.

scholarly journals Anomalous Spectral Types and Intrinsic Colors of Young Stars

2015 ◽  
Vol 10 (S314) ◽  
pp. 85-90 ◽  
Author(s):  
Mark J. Pecaut
Keyword(s):  
Infrared Spectra ◽  
Spectral Type ◽  
Main Sequence ◽  
Near Infrared ◽  
Systematic Errors ◽  
Optical Spectra ◽  
Young Stars ◽  
Main Sequence Stars ◽  
Near Infrared Spectra ◽  
Dynamical Masses

AbstractWe highlight differences in spectral types and intrinsic colors observed in pre-main sequence (pre-MS) stars. Spectral types of pre-MS stars are wavelength-dependent, with near-infrared spectra being 3-5 spectral sub-classes later than the spectral types determined from optical spectra. In addition, the intrinsic colors of young stars differ from that of main-sequence stars at a given spectral type. We caution observers to adopt optical spectral types over near-infrared types, since Hertzsprung-Russell (H-R) diagram positions derived from optical spectral types provide consistency between dynamical masses and theoretical evolutionary tracks. We also urge observers to deredden pre-MS stars with tabulations of intrinsic colors specifically constructed for young stars, since their unreddened colors differ from that of main sequence dwarfs. Otherwise, V-band extinctions as much as ~0.6 mag erroneously higher than the true extinction may result, which would introduce systematic errors in the H-R diagram positions and thus bias the inferred ages.

scholarly journals The Occurrence of Lithium in Stars

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.

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

2020 ◽  
Vol 642 ◽  
pp. A99 ◽  
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.

scholarly journals T Tauri Disk Lifetime in the Lupus Association

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.

scholarly journals Magnetic Fields of T Tauri Stars

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.

scholarly journals A Comparative Anatomy of Dusty Disks Imaged by NICMOS

2004 ◽  
Vol 202 ◽  
pp. 308-315
Author(s):  
Glenn Schneider ◽  
Dean C. Hines ◽  
Murray Silverstone ◽  
Alycia J. Weinberger ◽  
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Hubble Space Telescope ◽  
Comparative Anatomy ◽  
Scattered Light ◽  
Infrared Camera ◽  
Main Sequence Stars ◽  
Spatially Resolved ◽  
T Tauri ◽  
Dusty Disks

Using the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope we have conducted a coronagraphic imaging survey of 18 main sequence stars with large infrared excesses, searching for circumstellar dust (debris) in scattered light. Dusty disks with radial and hemispheric brightness anisotropies and complex morphologies, both possibly indicative of dynamical interactions with unseen planetary mass companions, were spatially resolved and imaged around three young (≲ 10Myr old) stars. From these observations we describe the debris systems around: a) HR 4796A (A0V), a 70 AU radius ring less than 14 AU wide with unequal ansal flux densities; b) HD 141569A (Herbig Ae/Be), a 400 AU radius disk with a 40 AU wide gap; and c) TW Hya (K7 T-Tauri), a pole-on circularly symmetric disk with a radial break in its surface density of scattering particles. Additionally, our non-detection of scattered light and high precision photometry of a fourth system of similar age, HD 98800 A/B, coupled with mid and thermal IR measurements, greatly constrain a likely model for the debris about the B component.

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