The first phase-resolved JHK light curves of the eclipsing polar (AM Herculis
binary) V1309 Ori are presented and interpreted. We separate the contributions
from the secondary star and from other sources with the aim of determining a
photometric distance. 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. The unilluminated backside of the
secondary star as seen in eclipse has spectral type dM0 to dM0+. Its dereddened
magnitude is K = 13.58 at orbital phase phi = 0 (eclipse). Using the calibrated
surface brightness of M-stars and the published mass of the secondary, M2 =
0.46 Msun, we obtain a distance d = 600 +/- 25 pc which scales as M2^(1/2). The
radius of the Roche-lobe filling secondary exceeds the main-sequence radius of
an M0 star by 21 +11/-6 %. 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.Comment: 5 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
