The 8190-A Sodium Doublet in Cataclysmic Variables - Part Three - too Cool for Credibility

Details The 8190-A Sodium Doublet in Cataclysmic Variables - Part Three - too Cool for Credibility The 8190-A Sodium Doublet in Cataclysmic Variables - Part Three - too Cool for Credibility

Oct 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.246..654f&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. 246, NO.4/OCT15, P. 654, 1990

Astronomy and Astrophysics

Astronomy

59

Scientific paper

This third and final paper of the series uses the λ8190-Å Na I doublet for radial- velocity studies of the secondary star in the four long-period cataclysmic variables CH UMa, MU Cen, SS Cyg and RU Peg. The observations of CH UMa and MU Cen, which are the first accurate secondary star radial-velocity studies, have been used to derive improved periods of 8.23±0.04 and 8.21±0.03 hr, respectively. The semi-amplitudes of the resulting radial-velocity curves are 78±3 and 165±3 km s-1. The radial-velocity studies for SS Cyg and RU Peg provide results in excellent agreement with those produced using optical absorption features and thus validate the use of the Na I lines for these studies.
The radial-velocity curve for CH UMa has a significant apparent eccentricity of 0.10±0.03. It was not possible to explain this distortion through the standard irradiation mechanism and it is suggested that contamination of the Na I lines by disc emission may be making a significant contribution. In principle the best way to determine corrections for any distortion is through measurements of the Na I line strength variations around the orbit. The observations of SS Cyg and RU Peg provide a test of this process, which shows that for these K stars the line strength variations are too poorly determined to distinguish clearly between different models.
All four secondary stars have apparent spectral types that are cooler than predicted by main-sequence assumptions. Those for CH UMa and RU Peg are over 1000 K cooler than required, and the secondary stars are significantly less massive than expected. These results and those of the previous two papers show that the secondary stars in cataclysmic variables are not normal main-sequence stars and, therefore, main-sequence assumptions should be used with extreme caution.

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