Scaled solar tracks and isochrones in a large region of theZ–Yplane

Abstract

We extend our theoretical computations for low-mass stars to intermediate-mass and massive stars, for which few databases exist in the literature. Evolutionary tracks and isochrones are computed for initial masses 2.50−20 M for a grid of 37 chemical compositions with metal content Z between 0.0001 and 0.070 and helium content Y between 0.23 and 0.40 to enable users to obtain isochrones for ages as young as about 10 7 years and to simulate stellar populations with different helium-to-metal enrichment laws. The Padova stellar evolution code is identical to that used in the first paper of this series. Synthetic TP-AGB models allow stellar tracks and isochrones to be extended until the end of the thermal pulses along the AGB. We provide software tools for the bidimensional interpolation (in Y and Z) of the isochrones from very old ages down to about 10 7 years. This lower limit depends on chemical composition. The extension of the blue loops and the instability strip of Cepheid stars are compared and the Cepheid mass-discrepancy is discussed. The location of red supergiants in the H-R diagram is in good agreement with the evolutionary tracks for masses from 10 to 20 M . Tracks and isochrones are available in tabular form for the adopted grid of chemical compositions in the extended plane Z − Y in three photometric systems. An interactive web interface allows users to obtain isochrones of any chemical composition inside the provided Z − Y range and also to simulate stellar populations with different Y(Z) helium-to-metal enrichment laws.

Star formation in the S233 region

“…To estimate the distance to the ionizing star we used the Kband magnitude K = 9.63 obtained from 2MASS, absolute magnitude MK = −2.512 (Bertelli et al 2009) and interstellar absorption AK = AV /8.8 = 0.35 according to the reddening law of Cardelli, Clayton, & Mathis (1989) and AV = 3.1 estimated by Dobashi et al (2005). The estimated distance 2.3 ± 0.4 kpc is in agreement with published distances to the S231-235 complex.…”

Lithium-rich giants in the Galactic thick disk

“…5 stellar evolutionary tracks (Bertelli et al 2008(Bertelli et al , 2009) of metallicity appropriate to our stars. While the arguments in Sect.…”

Spiral arm kinematics for Milky Way stellar populations

“…We will not review the physics of these stellar tracks here but we just mention that over the years, these models were calculated including semi-convection in massive stars (e.g., Chiosi & Summa 1970), ballistic-convective overshooting from the core (Bressan, Chiosi & Bertelli 1981), overshooting from the the bottom of the convective envelope (Alongi et al 1991), turbulent diffusion from the convective core and convective shells Deng, Bressan & Chiosi (1996a,b); Salasnich, Bressan & Chiosi (1999), plus several additional improvements and revisions (Alongi et al 1993; Fagotto et al 1994b;Bertelli et al 1994;Fagotto et al 1994a,a;Bertelli & Nasi 2001;Bertelli et al 2003Bertelli et al , 2008Bertelli et al , 2009. The stellar models in use are those by Bertelli et al (2008Bertelli et al ( , 2009), which cover a wide grid of helium Y , metallicity Z, and enrichment ratio ∆Y /∆Z. The associated isochrones include the effect of mass loss by stellar wind and the thermally pulsing AGB phase according to the models calculated by Marigo & Girardi (2007).…”

“…The code in use is the last version of YZVAR developed over the years by the Padova group and already used in many studies (for instance Chiosi & Greggio 1981;Chiosi et al 1986Chiosi et al , 1989Bertelli et al 1995;Ng et al 1995;Aparicio et al 1996;Bertelli & Nasi 2001;Bertelli et al 2003) and recently extended to obtain isochrones and SSPs in a large region of the Z−Y plane. The details on the interpolation scheme at given ∆Y /∆Z are given in Bertelli et al (2008Bertelli et al ( , 2009). The present isochrones and SSPs are in the Johnson-Cousins-Glass system as defined by Bessell (1990) and Bessell & Brett (1988).…”