The secondary star and distance of the polar V1309 Orionis
Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany e-mail: email@example.com
2 Dept. of Astronomy and Space Science, Chungbuk National University, Cheongju, 360-763 Korea e-mail: firstname.lastname@example.org
Accepted: 3 July 2006
Context. The first phase-resolved JHK light curves of the eclipsing polar (AM Herculis binary) V1309 Ori are presented and interpreted.
Aims. We separate the contributions from the secondary star and from other sources with the aim of determining a photometric distance.
Methods. Simple model calculations show that the accretion stream and the cyclotron source on the accreting white dwarf are minor contributors to the infrared light, allowing an accurate determination of spectral type and absolute flux of the secondary star.
Results. The unilluminated backside of the secondary star as seen in eclipse has spectral type dM0 to dM0+. Its dereddened magnitude is at orbital phase (eclipse). Using the calibrated surface brightness of M-stars and the published mass of the secondary, , we obtain a distance pc which scales as . The radius of the Roche-lobe filling secondary exceeds the main-sequence radius of an M0 star by %.
Conclusions. The debated origin of the infrared light of V1309 Ori has been settled in favor of the secondary star as the main contributor and an accurate distance has been derived that will place estimates of the luminosity and synchronization time scale on a more secure basis.
Key words: stars: binaries: eclipsing / stars: novae, cataclysmic variables / stars: distances / stars: late-type / stars: magnetic fields / stars: individual: V1309 Ori
© ESO, 2006