The O-type eclipsing contact binary LY Aurigae – member of a quadruple system^⋆

¹ Astronomical Institute of Charles University, Faculty of Mathematics and Physics, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
e-mail: mayer@cesnet.cz
² Dr Karl Remeis Observatory & ECAP, Astronomical Institute, Friedrich-Alexander University Erlangen-Nuremberg, Sternwartstr. 7, 96094 Bamberg, Germany
³ Physics & Astronomy Department, University of Victoria, PO Box 3055 STN CSC Victoria, BC V8W 3P6, Canada
⁴ Astronomical Institute, Academy of Sciences of the Czech Republic, 251 65 Ondřejov, Czech Republic

Received: 27 June 2013
Accepted: 25 August 2013

Abstract

The eclipsing binary LY Aur (O9 II + O9 III) belongs to the rare class of early-type contact systems. We obtained 23 new spectra at the Ondřejov and Dominion Astrophysical Observatories, which were analysed with four older Calar Alto and one ELODIE archive spectra. A new result of this study is that the visual companion of LY Aur – the spectral lines of which are clearly seen in our spectra – is also an SB1 binary having an orbital period of 20$\stackrel{\mathrm{d}}{.}$46, an eccentric orbit, and a radial velocity semi-amplitude of 33 km s^-1. The Hα line blend contains an emission component, which shows dependence on the orbital phase of the eclipsing system, with the strongest emission around the secondary eclipse. Revised elements of the eclipsing binary and the orbital solution of the companion binary are determined from our set of spectra and new light-curve solutions of the eclipsing pair. The mass of the primary of 25.5 M_⊙ agrees well with its spectral type, whereas the secondary mass of 14 M_⊙ is smaller than expected. From an O−C analysis of the minimum times of LY Aur  that span more than 40 years, we found that the orbital period is decreasing, indicating the presence of interaction processes. The system is likely in a phase of non-conservative mass exchange.