A spectroscopic study of the close eclipsing binary HS Herculis

Abstract

Aims. New high-resolution spectroscopic observations of the eclipsing binary HS Herculis are presented. The main aims were to determine the stellar parameters of the two components, their evolutionary stage, and to search for spectroscopic evidence for a possible third body. Methods. Using the cross-correlation technique, we detect spectroscopically the faint secondary component of HS Herculis, and for the firts time measure its radial velocity. The primary and secondary radial velocity curves are analyzed simultaneously and the results of the orbital solution are combined with those derived from multiband light curve analysis to derive orbital and stellar parameters. Results. We find the masses to be M 1 = 4.49± 0.16 and M 2 = 1.75± 0.09 M , the radii to be R 1 = 2.83± 0.04 and R 2 = 1.61± 0.02 R , and the effective temperatures to be T 1 = 15 200 ± 750 K and T 2 = 7600 ± 400 K for the primary and secondary stars, respectively. We also derive projected rotational velocities of the components as v 1 sin i = 81 ± 3 and v 2 sin i = 24 ± 6. Conclusions. While a synchronous rotation for the primary star is indicated by the broadening of the spectral lines, the secondary component appears to rotate more slowly, nearly one half the synchronous rotation velocity. This discrepancy indicates that the less massive secondary component could have not yet attained tidal synchronization. Although the presence of a third body physically bound to the eclipsing pair has been suggested by many investigators, we find no sign of its presence in our CCD spectra. The evolutionary stage of the system's components is briefly discussed by comparing their physical parameters with those of theoretical models. We find that the two components are located near the zero-age main sequence, with an age of about 32 Myr.

Eccentric orbits and apsidal motion in the eclipsing binaries EK Cep and HS Her

“…The errors reported here are estimated by assuming that the errors in the adopted primary temperatures correspond to half a spectral class. This results in an error of about 200 K for the primary of EK Cep and about 1000 K for the primary of HS Her (fairly close to the estimate given by Çakırlı, Ö. and Ibanoǧlu, C. and Frasca, A. 2007).…”

“…The most recent study of HS Her was done by Çakırlı, Ö. and Ibanoǧlu, C. and Frasca, A. (2007), who measured, for the first time, the radial velocities of the faint secondary.…”

“…In addition to these new measurements, we use the radial velocities measured by Çakırlı, Ö. and Ibanoǧlu, C. and Frasca, A. (2007) for the orbital solution of HS Her.…”

“…EK Cep was the first known eclipsing binary with a pre-main-sequence (PMS) component, apsidal motion and metallicity measurements (see e.g., Claret et al 1995). HS Her was the subject of a long debate surrounding its relatively short apsidal motion period (of the order of 100 years) and the possibility of having a third component (Colak & Muyesseroglu 2005); there are also indications of primordial protostellar matter lingering inside the Roche lobe of the secondary star (Çakırlı, Ö. and Ibanoǧlu, C. and Frasca, A. 2007).…”

A Magnetic Snapshot Survey of F-Type Stars

“…The star is sharp-lined, with an overabundance of rare-earth elements (Rice & Hill 1988), while containing overall abundances less than solar (Adelman et al 1991). The sharp spectral lines has enabled the star to be used as a radial velocity standard star (Cakirli,İbanoglu & Frasca 2007). We obtained fourteen polarized spectra for ι Psc over a 2.0 h interval on 2016 August 16, corresponding to 1.2 per cent of the estimated rotational period of 10.5 d. The mean LSD profile combined 7502 lines, and did not show a magnetic detection.…”