Tracing CNO exposed layers in the Algol-type binary system u Her

Abstract

The chemical composition of stellar photospheres in mass-transferring binary systems is a precious diagnostic of the nucleosynthesis processes that occur deep within stars, and preserves information on the components' history. The binary system u Her belongs to a group of hot Algols with both components being B-stars. We have isolated the individual spectra of the two components by the technique of spectral disentangling of a new series of 43 high-resolutioń echelle spectra. Augmenting these with an analysis of the Hipparcos photometry of the system yields revised stellar quantities for the components of u Her. For the primary component (the mass-gaining star) we find M A = 7.88 ± 0.26 M ⊙ , R A = 4.93 ± 0.15 R ⊙ and T eff,A = 21 600 ± 220 K. For the secondary (the mass-losing star) we find M B = 2.79 ± 0.12 M ⊙ , R B = 4.26 ± 0.06 R ⊙ and T eff,B = 12 600 ± 550 K. A non-LTE analysis of the primary star's atmosphere reveals deviations in the abundances of nitrogen and carbon from the standard cosmic abundance pattern in accord with theoretical expectations for CNO nucleosynthesis processing. From a grid of calculated evolutionary models the best match to the observed properties of the stars in u Her enabled tracing the initial properties and history of this binary system. We confirm that it has evolved according to case A mass transfer. A detailed abundance analysis of the primary star gives C/N = 0.9, which supports the evolutionary calculations and indicates strong mixing in the early evolution of the secondary component, which was originally the more massive of the two. The composition of the secondary component would be a further important constraint on the initial properties of u Her system, but requires spectra of a higher signal to noise ratio.

The Dynamical Mass and Evolutionary Status of the Type II Cepheid in the Eclipsing Binary System OGLE-LMC-T2CEP-211 with a Double-ring Disk* †

“…To determine the evolutionary status of OGLE-LMC-T2CEP-211, we first calculated sets of initial parameters consistent with the current total mass and AM of the system. The calculations followed the method and conventions presented in Kolbas et al (2014). The input parameters were: the final masses of the donor and accretor (M f d , M f a ), the final mass ratio (q f = M f a /M f d ), and the final orbital period (P f ).…”

Absolute Dimensions of the Metallic-Line Eclipsing Binary V501 Monocerotis

“…For this we used a precalculated grid of theoretical spectra in local thermodynamical equilibrium (for details, see Kolbas et al 2014Kolbas et al , 2015. The metal lines superimposed on the wings were masked out.…”

Evidence for conservative mass transfer in the classical Algol system δ Librae from its surface carbon-to-nitrogen abundance ratio

“…The second approach calculates a series of models for a given system by guessing all possible initial configurations with angular momentum and mass loss assumptions and building binary evolution grids to find the best match. Nowadays this CPU-intensive method is possible thanks to modern computing power (Kolbas et al 2014).…”

“…Thus, disentangled components' spectra in turn make possible a precise determination of the atmospheric parameters, and chemical composition (Hensberge et al 2000;Pavlovski & Hensberge 2005). The spectral disentangling technique has previously been used to constrain the initial parameters for the system and components of the hot Algol-type system u Her (Kolbas et al 2014) and to obtain a complete optical spectrum of the faint subgiant component in Algol itself (Kolbas et al 2015).…”