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-resolution 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_sun, R_A = 4.93 +/- 0.15 R_sun and T_eff_A = 21600 +/- 220 K. For the secondary (the mass-losing star) we find M_B = 2.79 +/- 0.12 M_sun, R_B = 4.26 +/- 0.06 R_sun and T_eff_B = 12600 +/- 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.

Accepted for publication in MNRAS

References in corpus (14)

• The chemical composition of the Sun
• Evolution of binary stars and the effect of tides on binary populations
• A Computational Guide to Physics of Eclipsing Binaries. Paper I. Demonstrations and Perspectives
• Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models
• A Complete Survey of Case A Binary Evolution with Comparison to Observed Algol-Type Systems
• Efficiency of mass transfer in massive close binaries, Tests from double-lined eclipsing binaries in the SMC
• Modelling the binary progenitor of supernova 1993J
• Hydrogen and helium line formation in OB dwarfs and giants. A hybrid non-LTE approach
• The chemical composition of the Orion star-forming region. III. C, N, Ne, Mg and Fe abundances in B-type stars revisited
• The chemical composition of the Orion star forming region: I. Homogeneity of O and Si abundances in B-type stars
• Temperature, gravity and bolometric correction scales for non-supergiant OB stars
• Chemical evolution of high-mass stars in close binaries. II. The evolved component of the eclipsing binary V380 Cygni
• Constrained fitting of disentangled binary spectra: application to V615 Per in the open cluster h Persei
• Carbon deficiencies in the primaries of some classical Algols

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