Chemical evolution of high-mass stars in close binaries ��� II. The evolved component of the eclipsing binary V380���Cygni

Abstract

The eclipsing and double-lined spectroscopic binary V380 Cyg is an extremely important probe of stellar evolution: its primary component is a high-mass star at the brink of leaving the main sequence whereas the secondary star is still in the early part of its main sequence lifetime. We present extensive high-resolutionéchelle and grating spectroscopy from Ondřejov, Calar Alto, Victoria and La Palma. We apply spectral disentangling to unveil the individual spectra of the two stars and obtain new spectroscopic elements. The secondary star contributes only about 6 per cent of the total light, which remains the main limitation to measuring the system's characteristics. We determine improved physical properties, finding masses 13.1 ± 0.3 and 7.8 ± 0.1 M , radii 16.2 ± 0.3 and 4.06 ± 0.08 R , and effective temperatures 21 750 ± 280 and 21 600 ± 550 K, for the primary and secondary components, respectively. We perform a detailed abundance analysis by fitting non-local thermodynamic equilibrium (LTE) theoretical line profiles to the disentangled spectrum of the evolved primary star, and reveal an elemental abundance pattern reminiscent of a typical nearby B star. Contrary to the predictions of recent theoretical evolution models with rotational mixing, no trace of abundance modifications due to the CNO cycle are detected. No match can be found between the predictions of these models and the properties of the primary star: a mass discrepancy of 1.5 M exists and remains unexplained.

Fundamental properties of nearby single early B-type stars

“…This is in agreement with results on a sample of massive DEBs (Pavlovski & Hensberge 2005;Pavlovski & Southworth 2009Pavlovski et al , 2011Mayer et al 2013;Tkachenko et al 2014, with typical v rot sin i 100 km s −1 ), which also show no signs of mixing with CN-cycled matter. Mixing signatures are found in the remaining 1/3 of our sample stars.…”

“…The most accurate and precise fundamental parameters for massive stars available at present can be found in the compilation by Torres et al (2010, henceforth abbreviated TAG10), mainly for the most common among them, the early B-type stars of spectral types B0 to B3. Data on abundances of individual chemical elements in massive DEBs are scarce, though ongoing projects promise to alleviate the situation (Pavlovski & Hensberge 2005;Pavlovski & Southworth 2009Pavlovski et al , 2011Mayer et al 2013;Tkachenko et al 2014). …”

The two components of the evolved massive binary LZ Cephei

“…This evolved system is thus particularly interesting because it provides observational constraints of theoretical binary evolutionary models. Similar analyses have been performed for B stars (e.g., see Pavlovski et al 2009) but studies of systems composed of two evolved early-type stars are scarce (e.g., Plaskett's star by Linder et al 2008). We have emphasized the need for theoretical binary system evolutionary models because our comparison of the stellar properties of the components of evolved binary systems with those of single-star theoretical predictions has revealed discrepancies.…”

The solar-type eclipsing binary system LL Aquarii

“…This is because e and ω can be strongly correlated (e.g. Pavlovski et al 2009), compromising their utility as fitted parameters. Light curves of eccentric dEBs typically allow the quantity e cos ω to be determined precisely, as it primarily affects the time difference between primary and secondary eclipse (e.g.…”