Astronomy and Astrophysics – Astronomy
Scientific paper
May 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998arep...42..312l&link_type=abstract
Astronomy Reports, Volume 42, Issue 3, May 1998, pp.312-321
Astronomy and Astrophysics
Astronomy
3
Scientific paper
CCD spectra with high resolution and large signal-to-noise ratio are used to study the binary system V373 Cas, which includes two early B stars, and is apparently undergoing a very early phase of mass exchange between the components. The new radial velocity measurements made it possible to improve the system's orbital elements and to refine the mass estimates for the components: M_orb = 18.6 +/- 2.4 M for the primary (star A) and 14.2 +/- 1.9M_solar for the secondary (star B). A self-consistent method for estimation of the effective temperature and gravitational acceleration yields T_eff = 23,200 +/- 600 K and lg g= 3.0 +/- 0.2 for component A and T_eff = 26,800 +/- 1500 K and lg g = 3.5 +/- 0.2 for component B. These parameters correspond to the spectral types B0.5-B1 (II-Ib) for A and B0.5 III for B. The helium abundance is enhanced in the atmospheres of both components: He/H = 0.23 +/- 0.03 and 0.18 +/- 0.02 for A and B, respectively. This helium abundance excess confirms that He/H depends on age, and is consistent with the fact that both the components of V373 Cas are near the end of the main sequence stage. The magnesium abundance for the primary is close to the solar value, suggesting that its metallicity may be normal. The rotation velocities sin i = 130 +/- 10 km/s (A) and 60 +/- 5 km/s (B) are derived from the He I lines. These confirm the conclusion of Hill and Fisher that the rotation of the components in their orbital motion is asynchronous. The masses M_ev estimated using evolutionary tracks are overestimated by 34% for the both components, compared to the more accurate values M_orb determined from the orbit analysis. This is the largest known discrepancy between M_ev and M_orb for a binary system of this type. The age of the system is 7-8 million years.
Lyubimkov Leonid S.
Rachkovskaya Tamara M.
Rostopchin Sergey I.
Tarasov Anatolii E.
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