Abstract
Abstract A new grid of detailed atmosphere model spectra for hot and moderately cool subdwarf stars is presented. High-resolution spectra and synthetic photometry are calculated in the range from 1000–10,000 Å using non-LTE fully line-blanketed atmosphere structures. Our grid covers eight temperatures within 10,000 ≤ T eff [K] ≤ 65,000, three surface gravities in the range 4.5 ≤ log g [cgs] ≤ 6.5, two helium abundances matching two extreme helium-rich and helium-poor scenarios, and two limiting metallicity boundaries regarding both solar ([Fe/H] = 0) and Galactic halos ([Fe/H] = −1.5 and [α/Fe] = +0.4). Besides its application in the determination of fundamental parameters of subdwarfs in isolation and in binaries, the resulting database is also of interest for population synthesis procedures in a wide variety of stellar systems.
Highlights
The evolutionary scenario of subdwarfs is still emerging
Hot subdwarf stars evolve from low- to intermediate-mass progenitors and reach far beyond the main sequence, at the blue end of the horizontal branch (HB) or mixed with post-HB stars (Heber 2009)
The most accepted formation scenario is of an extreme HB star that lost its envelope after the He-burning phase, evolving directly to the white dwarf (WD)-cooling sequence by avoiding the asymptotic giant branch (AGB) (Wade et al 2005; Heber 2009; Fontaine et al 2012)
Summary
The evolutionary scenario of subdwarfs is still emerging. Hot subdwarf stars evolve from low- to intermediate-mass progenitors and reach far beyond the main sequence, at the blue end of the horizontal branch (HB) or mixed with post-HB stars (Heber 2009). Analysis by Lanz & Hubeny (1995) took H, C, and Fe into account for the opacity of hot and high-gravity NLTE atmosphere models They found critical differences in effective temperature determinations and line profiles arising from the inclusion of explicit atomic species (i.e. with the kinetic equilibrium equation solved) in the atmospheric structure. The subdwarfs’ atmospheres have more evident NLTE effects due to their lower surface gravities (when compared to WDs; Lanz et al 1997) They built spectra considering full line blanketing with H/He, CNO, Si, Fe, and Ni as implicit ions and concluded that this approach significantly improved the line profile analysis.
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