HD 165246: an early-type binary with a low mass ratio^⋆

¹ Astronomical Institute of the Charles University, Faculty of Mathematics and Physics, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
e-mail: mayer@cesnet.cz
² Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10 000 Zagreb, Croatia

Received: 14 September 2012
Accepted: 27 November 2012

Abstract

Analyses of 13 FEROS spectra from the ESO archive and 617 V-band photometric observations from the ASAS3 database allowed us to demonstrate that HD 165246 is a double-lined spectroscopic binary. As an earlier finding revealed, HD 165246 is also an eclipsing system. We were able to derive consistent orbital and light-curve solutions and all basic physical properties of the system. The period of this O8 V + B7 V binary is 4$\stackrel{\mathrm{d}}{.}$592706 and the semiamplitudes of the radial-velocity curves are K₁ = 55.5 km s^-1 and K₂ = 321 km s^-1. As the mass ratio is small (0.173), the secondary lines cannot be seen directly in the spectra; however the application of spectral disentangling allowed us to detect weak Balmer and He i lines of the secondary component. The primary component rotates with a high projected velocity of v sin i = 243 km s^-1. A combined radial-velocity and light-curve solution led to the component masses and radii expected for the young stars of the given spectral types. Due to the high rotation velocity, the primary component might display changes in surface abundances of some elements. However, we did not find any significant differences with respect to the abundances of slowly rotating stars.