scholarly journals Measuring the Masses of Young Stars

2001 ◽  
Vol 200 ◽  
pp. 454-463
Author(s):  
Michal Simon
Keyword(s):  
Main Sequence ◽  
Circumstellar Disks ◽  
Theoretical Models ◽  
Young Stars ◽  
Sequence Evolution ◽  
The Masses

This paper presents the masses of young stars measured by the rotation of their circumstellar disks (Simon, Dutrey, and Guilloteau 2000). Their precision is good enough to enable meaningful tests of theoretical models of pre-main sequence evolution. The tests are however limited by the imprecision with which the distances to the stars are known. The astrometric instruments now being developed have the potential to remove this limitation.

The Infancy of Solar-Type Stars and its Relevance for the Origin of Life

1997 ◽  
Vol 161 ◽  
pp. 267-282 ◽  
Author(s):  
Thierry Montmerle
Keyword(s):  
Main Sequence ◽  
Solar Nebula ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Necessary Condition ◽  
Sequence Evolution ◽  
T Tauri ◽  
Solar Type ◽  
Optical Domain ◽  
The Origin Of Life

AbstractFor life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.

scholarly journals Probing AU-scale Structure using Spectro-astrometry

2004 ◽  
Vol 221 ◽  
pp. 417-424 ◽  
Author(s):  
Michihiro Takami ◽  
Jeremy Bailey ◽  
Antonio Chrysostomou ◽  
Motohide Tamura ◽  
Hiroshi Terada
Keyword(s):  
Adaptive Optics ◽  
Main Sequence ◽  
Planet Formation ◽  
Hubble Space Telescope ◽  
Circumstellar Disks ◽  
Scale Structure ◽  
Young Stars ◽  
Space Telescope ◽  
Powerful Technique ◽  
Circumstellar Environment

The circumstellar environment within 10 AU of young stars are of particular interest for star and planet formation. Unfortunately, present imaging facilities such as the Hubble Space Telescope or adaptive optics on 10-m telescopes cannot resolve this region. We have proved that “spectro-astrometry” is a powerful technique for discovering pre-main-sequence binaries, determining kinematics of outflows and providing evidence for gaps in circumstellar disks — all down to AU scales. In this paper, we summarise our progress to date.

scholarly journals Circumstellar Disks and Star Formation

1992 ◽  
Vol 9 ◽  
pp. 377-380
Author(s):  
L. Hartmann ◽  
M. Gomez ◽  
S.J. Kenyon
Keyword(s):  
Star Formation ◽  
Spectral Region ◽  
Main Sequence ◽  
Circumstellar Disks ◽  
Central Star ◽  
Disk Accretion ◽  
Main Sequence Stars ◽  
Excess Emission ◽  
Infrared Spectral ◽  
The Masses

Results from the IRAS satellite showed that many pre-main sequence stars exhibited unexpectedly large fluxes in the infrared spectral region. Several studies have shown that the simplest and most satisfying explanation of this excess emission is that it arises in optically-thick, dusty, circumstellar disks (Rucinski 1985; Adams, Lada, and Shu 1987, 1988; Kenyon and Hartmann 1987; Bertout, Basri, and Bouvier 1988; Basri and Bertout 1989). The masses of these disks are estimated to range between 10-3M⊙ to 1M⊙ (Beckwith et al. 1990; Adams et al. 1990), large enough that disk accretion may have a significant effect on the evolution of the central star. Indeed, Mercer-Smith, Cameron, and Epstein (1984) suggested that stars are essentially completely accreted from disks, rather than formed from quasi-spherical accretion (Stabler 1983, 1988).

scholarly journals The rotational evolution of young low mass stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 231-240 ◽  
Author(s):  
Jérôme Bouvier
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Main Sequence ◽  
Young Stars ◽  
Sequence Evolution ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Rotational Evolution ◽  
Low Mass

AbstractStar-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed.

scholarly journals A Dialogue on Dynamical Pre-Main Sequence Tracks

2001 ◽  
Vol 200 ◽  
pp. 492-495 ◽  
Author(s):  
Günther Wuchterl
Keyword(s):  
Main Sequence ◽  
Thermal Structure ◽  
Brown Dwarfs ◽  
Young Star ◽  
Hydrostatic Equilibrium ◽  
Young Stars ◽  
Stellar Atmospheres ◽  
Stellar Structure ◽  
Sequence Evolution ◽  
Stellar Matter

Based on the theory of stellar structure and evolution combined with the theory of stellar atmospheres theoretical properties of young stars can be calculated. These calculations of pre-main sequence evolution have been refined over the last decades and do now provide theoretical spectra and colours even for very cool objects like young stars brown dwarfs and planets. Two of their key assumptions must become invalid towards the formation phases: (1) the hydrostatic equilibrium of pressure forces and gravity that assumes stellar matter to be at rest and (2) the non-dependence on the initial thermal structure. The former (1) is violated by accretion- and collapse flows, the latter (2) because a new born young star is observed with the specific thermal structure produced by the cloud collapse. I discuss changes in the theoretical properties of young stars that follow from calculating the pre-main sequence evolution as the consequence of the collapse of Bonnor-Ebert spheres.

scholarly journals Lifetimes of Circumstellar Disks in Lynds 1641

1997 ◽  
Vol 163 ◽  
pp. 683-684
Author(s):  
Lori E. Allen ◽  
Karen M. Strom
Keyword(s):  
Molecular Cloud ◽  
Main Sequence ◽  
Circumstellar Disks ◽  
Young Stars ◽  
Knowing How ◽  
Giant Molecular Cloud ◽  
Cloud Complex

AbstractIt is by now evident that most young stars have associated disks and/or envelopes, which may be active (accreting) or passive (reprocessing stellar photons), or both. Knowing how such disks evolve is crucial to our understanding of how stars form, and may be relevant to other questions, such as the time available for the formation of planets in solar nebulae. In this poster we discuss the properties of pre-main sequence circumstellar disks in Lynds 1641 in Orion, the nearest giant molecular cloud complex.

scholarly journals Spectroscopic Hα and Hγ survey of field Be stars: 2004–2009

2010 ◽  
Vol 6 (S272) ◽  
pp. 290-291
Author(s):  
Erika D. Grundstrom ◽  
Douglas R. Gies ◽  
Christina Aragona ◽  
Tabetha S. Boyajian ◽  
E. Victor Garcia ◽  
...  
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Line Emission ◽  
Circumstellar Disks ◽  
Circumstellar Disk ◽  
Sequence Evolution ◽  
Be Stars ◽  
B Stars ◽  
Significant Variability ◽  
The Universe

AbstractMassive O- and B-type stars are “cosmic engines” in the Universe and can be the dominant source of luminosity in a galaxy. The class of Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity. We find that 90% of the observed stars show some variability with 8% showing significant variability over the 5-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while ~20% of the sample consists of known binaries, we find that another 15–30% of the sample shows indications of binarity.

scholarly journals Constraints on stellar evolution theory from precise eclipsing binary data

1984 ◽  
Vol 105 ◽  
pp. 391-394
Author(s):  
J. Andersen ◽  
J.V. Clausen ◽  
H.E. J⊘rgensen ◽  
B. Nordström
Keyword(s):  
Stellar Evolution ◽  
Binary Data ◽  
Main Sequence ◽  
Theoretical Models ◽  
Stellar Structure ◽  
Sequence Evolution ◽  
Evolution Theory ◽  
Eclipsing Binary ◽  
Standard Models ◽  
Structure Calculations

Previous attempts at a detailed confrontation of eclipsing binary data with theoretical models of main-sequence evolution were faced with the choice between data of inhomogeneous (mostly low) quality for many systems (Kriz, 1969; Lacy, 1979) or accurate values of mass, radius, and temperature (or luminosity) for very few systems only (Popper et al., 1970). In addition, more detailed and homogeneous stellar structure calculations for several compositions were needed. Since 1972, a coordinated photometric and spectroscopic programme at our institute contributes to building a sufficient observational basis for such a test. Among published standard models for the range 1–10 M⊙, Hejlesen's (1980) are the most extensive, agree well with other standard models, and are presented in a format suitable for comparison with binary data. Here we can only outline a few salient new results from this study.

scholarly journals Towards a precise white dwarf cooling age of a globular cluster

2008 ◽  
Vol 4 (S258) ◽  
pp. 315-316
Author(s):  
Harvey B. Richer ◽  
Saul Davis ◽  
Jason Kalirai ◽  
Aaron Dotter ◽  
R. Michael Rich
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Velocity Dispersion ◽  
Theoretical Models ◽  
Age Dating ◽  
Main Sequence Stars ◽  
Final Mass ◽  
Geometric Technique ◽  
The Masses

AbstractThe white dwarf cooling age of a globular star cluster provides a potentially precise method of determining the ages of these ancient systems. This age-dating technique should be viewed as one distinct from that of turn-off ages, with a largely different set of input physics and problems. As such the ages produced by these two methods are complimentary and we seek convergent to the same value. In addition to deep photometry and astrometry of cluster stars, precise distances to the clusters and their reddenings are required. Theoretical models of both main sequence stars and cooling white dwarfs are also needed as well as the masses of the white dwarfs and an initial-final mass relationship. In this contribution I discuss a potentially precise approach to cluster distances via a geometric technique (comparing the internal proper motion dispersion of cluster stars with their radial velocity dispersion) and spectroscopically determined masses of M4 white dwarfs at the top of the cooling sequence. These latter data extend the initial-final mass relationship down to the lowest mass stars that are currently forming white dwarfs.

scholarly journals Spectroscopic Hα and Hγ survey of field Be stars: 2004-2008

2009 ◽  
Vol 5 (S262) ◽  
pp. 343-344
Author(s):  
Erika Grundstrom ◽  
Christina Aragona ◽  
Tabetha Boyajian ◽  
Douglas Gies ◽  
Amber ◽  
...  
Keyword(s):  
Main Sequence ◽  
Line Emission ◽  
Circumstellar Disks ◽  
Circumstellar Disk ◽  
Sequence Evolution ◽  
Be Stars ◽  
B Stars ◽  
Significant Variability ◽  
Vanderbilt University ◽  
The Universe

AbstractMassive O- and B-type stars are “cosmic engines” in the Universe and can be the dominant source of luminosity in a galaxy. Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity.We find that 90% of the observed stars show some variability with only 4% showing significant variability over the 4-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while 20% of the sample consists of known binaries, we find that another 15-30% of the sample shows indications of binarity.This work has been supported in part by a grant from the Vanderbilt University Learning Sciences Institute, NASA grant # NNX08AV70G, and NSF Career grant AST-0349075.

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