HD-53975 - AN O-TYPE SPECTROSCOPIC BINARY WITH A LARGE MASS-RATIO

We present radial velocities and line profiles of the O-type star HD 5 3975, which we find to be a spectroscopic binary with a period of 6.01 73 days. Although there are no obvious signatures of the secondary in the line profiles, we have used the merit function of Shafter et al. ( 1980) to show that a secondary component is present in lines found in B-type spectra. We have compared the observed merit functions with mer it functions for model profiles constructed assuming a main-sequence s econdary, and this comparison consistently indicates a companion with a mass ratio of q = M2/M1 = 0.23 +/- 0.04 and a magnitude difference D ELTAm = 3.3 +/- 0.4. We present a tomographic reconstruction of the sp ectrum of the secondary for these parameters. We suggest that other la rge mass ratio binaries may be found among the O stars when observed w ith high-resolution and high signal-to-noise ratio spectroscopy.