Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-07-08
Astronomy and Astrophysics
Astrophysics
19 pages, 9 figures, accepted for publication in A&A
Scientific paper
The binary star HD 45166 has been observed since 1922 but its orbital period has not yet been found. It is considered a peculiar Wolf-Rayet star, and its assigned classification varied along the years. High-resolution spectroscopic observations show that the spectrum, in emission and in absorption, is quite rich. The emission lines have great diversity of widths and profiles. The Hydrogen and Helium lines are systematically broader than the CNO lines. Assuming that HD 45166 is a double-line spectroscopic binary, it presents an orbital period of P = 1.596 days, with an eccentricity of e = 0.18. In addition, a search for periodicity using standard techniques reveals that the emission lines present at least two other periods, of 5 hours and of 15 hours. The secondary star has a spectral type of B7 V and, therefore, should have a mass of about 4.8 solar masses. Given the radial velocity amplitudes, we determined the mass of the hot (primary) star as being 4.2 solar masses and the inclination angle of the system, i = 0.77 degr. As the eccentricity of the orbit is non zero, the Roche lobes increase and decrease as a function of the orbital phase. At periastron, the secondary star fills its Roche lobe. The distance to the star has been re-determined as d = 1.3 kpc and a color excess of E(B-V)=0.155 has been derived. This implies an absolute B magnitude of -0.6 for the primary star and -0.7 for the B7 star. We suggest that the discrete absorption components (DACs) observed in the ultraviolet with a periodicity similar to the orbital period may be induced by periastron events.
Oliveira Alexandre
Steiner Joao Evangelista
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