Grids of stellar models with rotation

Abstract

Aims. We study the impact of a subsolar metallicity on various properties of non-rotating and rotating stars, such as surface velocities and abundances, lifetimes, evolutionary tracks, and evolutionary scenarios. Methods. We provide a grid of single star models covering a mass range of 0.8 to 120 M with an initial metallicity Z = 0.002 with and without rotation. We discuss the impact of a change in the metallicity by comparing the current tracks with models computed with exactly the same physical ingredients but with a metallicity Z = 0.014 (solar). Results. We show that the width of the main-sequence (MS) band in the upper part of the Hertzsprung-Russell diagram (HRD), for luminosity above log (L/L ) > 5.5, is very sensitive to rotational mixing. Strong mixing significantly reduces the MS width. Here for the first time over the whole mass range, we confirm that surface enrichments are stronger at low metallicity provided that comparisons are made for equivalent initial mass, rotation, and evolutionary stage. We show that the enhancement factor due to a lowering of the metallicity (all other factors kept constant) increases when the initial mass decreases. Present models predict an upper luminosity for the red supergiants (RSG) of log (L/L ) around 5.5 at Z = 0.002 in agreement with the observed upper limit of RSG in the Small Magellanic Cloud. We show that models using shear diffusion coefficient, which is calibrated to reproduce the surface enrichments observed for MS B-type stars at Z = 0.014, can also reproduce the stronger enrichments observed at low metallicity. In the framework of the present models, we discuss the factors governing the timescale of the first crossing of the Hertzsprung gap after the MS phase. We show that any process favouring a deep localisation of the H-burning shell (steep gradient at the border of the H-burning convective core, low CNO content), and/or the low opacity of the H-rich envelope favour a blue position in the HRD for the whole, or at least a significant fraction, of the core He-burning phase.

Evolution and Nucleosynthesis of Massive Stars

“…Also the minimum mass of single star entering a Wolf-Rayet stage is decreased by rotation. Many grids of rotating stellar models have appeared in the last decade [4,11,16,20,51]. Although these grids are all presented under the generic name of rotating stellar models, they are computed sometimes with very different physics.…”

“…The general theoretical framework of these models has been given by [59]. These models have the following characteristics [11,16,20]:…”

“…The upper labels indicate the type of the core collapse progenitors. Models of [16] and of [20] have been used.…”

“…Models of massive stars with Z=0 and an initial rotation velocity equal to about half the critical value have been calculated by [14,52]. Other models have been calculated with Z=10 −8 , 10 −5 [24,36], 2 10 −3 [20].…”

The Solar-Stellar Connection

“…Such models are sometimes coupled with approximations of magnetic effects, such as the Taylor-Spruit mechanism (Spruit 2002). This approach has been used to model massive rotating stars over secular time scales (Palacios et al 2003;Meibom et al 2013) and to generate grids of stellar models used for isochrones and chemical evolution studies Georgy et al 2013;Lagarde et al 2012). Some attempts have also been made to model in 2-D the secular evolution of internal angular momentum by considering the role of large scale magnetic field in the radiative interior (see Charbonneau and MacGregor 1993;Ruediger and Kitchatinov 1996;Spada et al 2010, and references therein).…”