The Angular Momentum Evolution of Very Low Mass Stars

By A. Sills, M. Pinsonneault, D. Terndrup. 2000

161 citations recorded by the source corpus.

We present theoretical models of the angular momentum evolution of very low mass stars (0.1-0.5 M☉). We also present models of solar analogs (0.6-1.1 M☉) for comparison with previous work. We investigate the effect of rotation on the effective temperature and luminosity of these stars. Rotation lowers the effective temperature and luminosity of the models relative to standard models of the same mass and composition. We find that the decrease in Teff and L can be significant at the higher end of our mass range but becomes small below 0.4 M☉. The effects of different assumptions about internal angular momentum transport are discussed. Formulae for relating Teff to mass and vrot are presented. We demonstrate that the kinetic energy of rotation is not a significant contribution to the luminosity of low-mass stars. Previous studies of the angular momentum evolution of low-mass stars concentrated on solar analogs and were complicated by uncertainties related to the internal transport of angular momentum. In this paper we extend our theoretical models for the angular momentum evolution of stars down to 0.1 M☉. We compare our models to rotational data from young open clusters of different ages to infer the rotational history of low-mass stars and the dependence of initial conditions and rotational evolution on mass. We find that the qualitative conclusions for stars below 0.6 M☉ do not depend on the assumptions about internal angular momentum transport with the exception of a zero-point shift in the angular momentum loss saturation threshold. We argue that this makes these low-mass stars ideal candidates for the study of the angular momentum loss law and distribution of initial conditions. For stars with masses between 0.6 and 1.1 M☉, scaling the saturation threshold by the Rossby number can reproduce the observed mass dependence of the stellar angular momentum evolution. We find that neither models with solid-body rotation nor differentially rotating models can simultaneously reproduce the observed stellar spin-down in the 0.6-1.1 M☉ range and for stars between 0.1 and 0.6 M☉. We argue that the most likely explanation is that the saturation threshold drops more steeply at low masses than would be predicted with a simple Rossby scaling. In young clusters there is a systematic increase in the mean rotation rate with decreased temperature below 3500 K (0.4 M☉). This suggests either inefficient angular momentum loss or mass-dependent initial conditions for stars near the fully convective boundary.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8e354598ec8c3699dde8df8f9447a8df43ea6fc1

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In Astronomy and Astrophysics

1. A. Reiners
2. D. Charbonneau
3. G. Basri
4. G. Chabrier
5. K. Luhman
6. J. Irwin
7. Isabelle Baraffe
8. C. Knigge

Citations in the corpus

• THE EVOLUTION OF CATACLYSMIC VARIABLES AS REVEALED BY THEIR DONOR STARS (2011, background): “In order to explain these observations, Sills et al. (2000) modified the K88 prescription in a way that makes the dependence of J̇ on Ω much shallower at high rotation rates.”
• Are Magnetically Active Low-Mass M Dwarfs Completely Convective? (2001, methodology): “ÏÏ Sills et al. (2000) Ðnd that, in the clusters they have examined, there is no evidence for a ““ sharp break at the fully convective boundary.”
• On the Rotational Evolution of Solar- and Late-Type Stars, Its Magnetic Origins, and the Possibility of Stellar Gyrochronology (2003, background): “However, this model, or the Yale models that inherited that behavior (Pinsonneault et al. 1989, 1990; Chaboyer et al. 1995; Barnes & Sofia 1996; Sills et al. 2000), or indeed any model that relies on hydrodynamic means to transport angular momentum within stars decouples, but cannot re-attach the…”
• Chromospheric Activity, Rotation, and Rotational Braking in M and L Dwarfs (2008, methodology): “For the form of the braking law, we follow the models of Chaboyer et al. (1995) and Sills et al. (2000).”
• Large-scale alpha^2-dynamo in low-mass stars and brown dwarfs (2005, background): “Observations indicate that the loss of angular momentum in very-low-mass stars is smaller than that expected from a direct relation between the angular momentum loss rate and the Rossby number (Sills et al 2000).”
• RINGS AND RADIAL WAVES IN THE DISK OF THE MILKY WAY (2015, methodology): “In this paper, ugriz isochrones were generated from the Yale Rotating Evolutionary Code (Sills et al. 2000;Delahaye & Pinsonneault 2006), using MARCS (Gustafsson et al. 2008) model atmospheres.”
• The age, life expectancy, and space density of Post Common Envelope Binaries (2003, methodology): “Sills et al. (2000) and Pinsonneault et al. (2002) presented theoretical models of the angular momentum evolution of low mass stars (0.1−0.5 M ) and compared their models to rotational data from open clusters of different ages to infer the rotational history of low-mass stars and the dependence of…”
• STELLAR ROTATION IN M35: MASS–PERIOD RELATIONS, SPIN-DOWN RATES, AND GYROCHRONOLOGY (2008, background): “…by introducing “magnetic saturation” of the angular momentum loss via stellar winds (Stauffer & Hartmann 1987; MacGregor & Brenner 1991; Barnes & Sofia 1996; Bouvier et al. 1997; Krishnamurthi et al. 1997; Sills et al. 2000), and by allowing the saturation threshold to depend on the stellar mass.”
• ON THE ANGULAR MOMENTUM EVOLUTION OF FULLY CONVECTIVE STARS: ROTATION PERIODS FOR FIELD M-DWARFS FROM THE MEarth TRANSIT SURVEY (2010, background): “It may therefore be necessary to invoke a more complete treatment of stellar evolution, incorporating rotation, to reproduce the behavior of these objects, for example the treatment used by Sills et al. (2000) and Denissenkov et al. (2010).”
• RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I (2011, methodology): “Moreover, the data also require that this exponent change at some critical rotation velocity (the “saturation” velocity), such that the loss rate increases more slowly with rotation above this threshold (Chaboyer et al. 1995; Sills et al. 2000).”