A POSSIBLE EXPLANATION FOR THE ANOMALOUS RADIAL-VELOCITY AMPLITUDE FROM HYDROGEN LINES IN BM ORI

The radial-velocity amplitude derived from hydrogen lines in BM Ori di ffers from the value obtained from helium lines by a factor of 2 (Popp er and Plavec 1976). An analysis of the spectrograms taken on the 6-m telescope (BTA) confirms this effect. An attempt is made to explain th is phenomenon in terms of binarity of the star: the observed hydrogen spectrum is a combination of the spectra of the primary (B3 ZAMS) and secondary (A-F) components. Calculations of the combined synthetic spe ctrum near the H gamma and H delta Lines show that at both elongations , the radial velocity derived from the synthetic spectrum is close to the observed value if the secondary-to-primary flux ratio is 0.16+/-0. 13 in the B band. This ratio is used to determine the radius of the se condary embedded in the dust shell: R(2) = 1.9 +/- 0.2..