FUNDAMENTAL PARAMETERS, HELIUM ABUNDANCE AND DISTANCE OF X-PERSEI

We present spectral observations of the Be/X-ray binary system X Perse i/4U 0352 + 30 taken during the recent (1989-91) low-luminosity discle ss phase. On the basis of new spectroscopic and photometric data the f ollowing self-consistent values of effective temperature T-eff, surfac e gravity g and interstellar absorption A(v) for the visible component of the system are determined: T-eff = 29 500 +/- 1500 K, log g = 4.0 +/- 0.2 and A(v) = 1.05 +/- 0.02. The corresponding spectral classific ation of the star is B0 V. The helium overabundance He/H = 0.19 is fou nd, as well as the enhanced nitrogen abundance log epsilon(N) approxim ate to 8.4. Two possible explanations of the He excess are proposed: ( a) internal enrichment of the outer layers of a massive star by CNO-cy cle products because of a mixing on the main-sequence evolutionary pha se or (b) external accretion during the evolution of a massive close b inary. The star has a rotational velocity v sin i = 215 +/- 10 km s(-1 ) and is located at a distance d = 700 +/- 300 pc. The X-ray flux corr esponding to this revised distance is of the order of 1-2 x 10(34) erg s(-1) the normal state, and around 10(35) erg s(-1) in the only brigh t state observed (1974-75). Non-LTE analysis of more recently obtained high-resolution profiles of the He II lambda 4686 line shows that the re is no evidence for additional heating during the high-luminosity ph ase.