scholarly journals Recent results on polarization of T Tauri stars and other young stellar objects

1990 ◽  
Vol 137 ◽  
pp. 179-184
Author(s):  
Pierre Bastien ◽  
François Ménard
Keyword(s):  
Rotation Period ◽  
T Tauri Stars ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Current Evidence ◽  
Line Of Sight ◽  
Stellar Objects ◽  
T Tauri ◽  
Thick Part ◽  
The Difference

Recent results on observations and models of polarization of T Tauri stars (TTS) and other young stellar objects (YSO's) are presented. In particular, the difference in polarization properties between the classical T Tauri stars (CTTS) and the weak-line T Tauri stars (WTTS) is made. A correlation between polarization and rotation period is searched for but not found. Observations of polarization maps for many young stars are considered. Two types of models have been proposed to explain these observations. Current evidence favors single and multiple scattering in flattened, optically thick, structures, i.e. disks, around many TTS. In particular, the size of the optically thick part of the disks, and their inclination to our line of sight can determined for published polarization maps.

scholarly journals The Infrared Companions of T Tauri Stars: Clues to the Formation and Early Evolution of Binaries

2001 ◽  
Vol 200 ◽  
pp. 265-274 ◽  
Author(s):  
Chris D. Koresko ◽  
Christoph Leinert
Keyword(s):  
T Tauri Stars ◽  
Young Stars ◽  
Early Evolution ◽  
Young Stellar Objects ◽  
Physical Status ◽  
Stellar Objects ◽  
T Tauri ◽  
Mode Of Development ◽  
Source Of Information

Infrared companions are young stellar objects with unusual properties gravitationally bound to more or less typical T Tauri stars. As such they promise to be the source of information on either a particular phase in the development of young stars or on a particular mode of development. We discuss the observed properties of infrared companions as well as attempts to explain their physical status with the aim to see how much of solid conclusion has been obtained so far.

scholarly journals The accretion disk paradigm for young stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 1-12 ◽  
Author(s):  
Claude Bertout
Keyword(s):  
Accretion Disk ◽  
Indirect Evidence ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Recent Attempt ◽  
Disk Model ◽  
Stellar Objects ◽  
T Tauri

AbstractAccretion and magnetic fields play major roles in several of the many models put forward to explain the properties of T Tauri stars since their discovery by Alfred Joy in the 1940s. Early investigators already recognized in the 1950s that a source of energy external to the star was needed to account for the emission properties of these stars in the optical range.The opening of new spectral windows from the infrared to the ultraviolet in the 1970s and 1980s showed that the excess emission of T Tauri stars and related objects extends into all wavelength domains, while evidence of outflow and/or infall in their circumstellar medium was accumulating.Although the disk hypothesis had been put forward by Merle Walker as early as 1972 to explain properties of YY Orionis stars and although Lynden-Bell and Pringle worked out the accretion disk model and applied it specifically to T Tauri stars in 1974, the prevailing model for young stellar objects until the mid-1980s assumed that they experienced extreme solar-type activity. It then took until the late 1980s before the indirect evidence of disks presented by several teams of researchers became so compelling that a paradigm shift occurred, leading to the current consensual picture.I briefly review the various models proposed for explaining the properties of young stellar objects, from their discovery to the direct observations of circumstellar disks that have so elegantly confirmed the nature of young stars. I will go on to discuss more modern issues concerning their accretion disk properties and conclude with some results obtained in a recent attempt to better understand the evolution of Taurus-Auriga young stellar objects.

scholarly journals The bipolar-flow phenomenon

1991 ◽  
Vol 147 ◽  
pp. 447-448
Author(s):  
Wolfgang Kundt
Keyword(s):  
Active Galactic Nucleus ◽  
Lorentz Factor ◽  
T Tauri Stars ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Radio Sources ◽  
Stellar Objects ◽  
Pair Plasma ◽  
T Tauri ◽  
Relativistic Pair

Very young stars, known as ‘pre-T-Tauri stars’ (PTTS) or ‘young stellar objects’ (YSO), tend to be surrounded by elongated outflow regions involving ‘Herbig-Haro objects’ (HH). Such ‘bipolar flows’ (BF) are reminiscent of the extragalactic radio sources for which a consensus has formed in 1986 that their jets consist of extremely relativistic pair plasma, of typical Lorentz factor 104±1, generated by an ‘active galactic nucleus’ (AGN); [refs 6,7]. Here I collect new circumstantial evidence for the relativistic nature of BFs.

scholarly journals The bipolar-flow phenomenon

1991 ◽  
Vol 147 ◽  
pp. 447-448
Author(s):  
Wolfgang Kundt
Keyword(s):  
Active Galactic Nucleus ◽  
Lorentz Factor ◽  
T Tauri Stars ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Radio Sources ◽  
Stellar Objects ◽  
Pair Plasma ◽  
T Tauri ◽  
Relativistic Pair

Very young stars, known as ‘pre-T-Tauri stars’ (PTTS) or ‘young stellar objects’ (YSO), tend to be surrounded by elongated outflow regions involving ‘Herbig-Haro objects’ (HH). Such ‘bipolar flows’ (BF) are reminiscent of the extragalactic radio sources for which a consensus has formed in 1986 that their jets consist of extremely relativistic pair plasma, of typical Lorentz factor 104±1, generated by an ‘active galactic nucleus’ (AGN); [refs 6,7]. Here I collect new circumstantial evidence for the relativistic nature of BFs.

scholarly journals The Observational Evidence for Accretion

1997 ◽  
Vol 182 ◽  
pp. 391-405 ◽  
Author(s):  
Lee Hartmann
Keyword(s):  
Large Range ◽  
Observational Evidence ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
T Tauri ◽  
Accretion Rates ◽  
Low Mass ◽  
Stellar Magnetospheres ◽  
Mass Ejection

Outflows from low-mass young stellar objects are thought to draw upon the energy released by accretion onto T Tauri stars. I briefly summarize the evidence for this accretion and outline present estimates of mass accretion rates. Young stars show a very large range of accretion rates, and this has important implications for both mass ejection and for the structure of stellar magnetospheres which may truncate T Tauri disks.

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.

scholarly journals The circumstellar environment of chromospherically active T Tauri stars

1987 ◽  
Vol 122 ◽  
pp. 103-104
Author(s):  
U. Finkenzeller ◽  
G. Basri
Keyword(s):  
Interstellar Extinction ◽  
T Tauri Stars ◽  
Activity Level ◽  
Young Stellar Objects ◽  
Balmer Line ◽  
Stellar Envelope ◽  
Stellar Objects ◽  
T Tauri ◽  
Type 3 ◽  
Circumstellar Environment

We discuss new spectroscopic material on 7 T Tauri stars of low to intermediate activity level which have envelopes of low optical thickness and small circumstellar/interstellar extinction. We show that difference plots between the target star and appropriate standards are a powerful tool to probe the stellar envelope structure. In our sample we find 1 object with a P Cyg type, 3 with inverse P Cyg type, and 3 with symmetrical Balmer line profiles. We conclude that the physical processes in these T Tauri stars do not differ qualitatively from the ones found in extremely active ones. In particular, the inverse P Cyg type profiles are not restricted to stars with very opaque envelopes and are possibly a much more common attribute of young stellar objects.

scholarly journals Star Formation at High Galactic Latitude: A Case for Extensions to the Hα Survey

1998 ◽  
Vol 15 (1) ◽  
pp. 155-156 ◽  
Author(s):  
Kristen A. Larson
Keyword(s):  
Star Formation ◽  
High Latitude ◽  
T Tauri Stars ◽  
Young Stellar Objects ◽  
Galactic Latitude ◽  
Stellar Objects ◽  
High Galactic Latitude ◽  
T Tauri

AbstractThe AAO/UKST Hα Survey should be extended to high Galactic latitude (∣b∣ > 25°) to search for T Tauri stars. The Hα Survey can contribute to a complete inventory of young stellar objects in high-latitude clouds, which will help define the limits of conditions and processes that lead to star formation.

Two New T Tauri stars and a Candidate FU Orionis Star associated with Bok Globules

1997 ◽  
Vol 163 ◽  
pp. 839-839
Author(s):  
J. L. Yun ◽  
M. Moreira
Keyword(s):  
Infrared Emission ◽  
T Tauri Stars ◽  
Emission Lines ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Energy Distributions ◽  
Stellar Objects ◽  
T Tauri ◽  
Bok Globules ◽  
Reflection Nebulae

AbstractWe present photometric and spectroscopic evidence of two new T Tauri stars formed in the conditions of isolated small Bok globules. The spectral energy distributions of these objects display excess infrared emission, they are associated with optical reflection nebulae, and their optical spectra reveal Balmer emission lines and the Li I λ6707 Å absorption line. Additionnally, we report the discovery of what is likely to be a new FU Orionis star seen towards Bok globule CB34. The star is about 4 magnitudes brighter than it appears on the Palomar plates and is associated with the aggregate of young stellar objects forming in Bok globule CB34.

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