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 échelle 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 \pm 0.26 { M } _ { \odot } , R _ { A } = 4.93 \pm 0.15 { R } _ { \odot } and T _ { eff,A } = 21 600 \pm 220 K. For the secondary ( the mass-losing star ) we find M _ { B } = 2.79 \pm 0.12 { M } _ { \odot } , R _ { B } = 4.26 \pm 0.06 { R } _ { \odot } and T _ { eff,B } = 12 600 \pm 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 .