SDSS J012119.10–001949.9: a very short period M dwarf contact binary from SDSS stripe 82

We present the first multicolor photometric observations of the short period low-mass eclipsing binary SDSS J012119.10–001949.9. By using the 2013 version of the Wilson-Devinney code, the photometric solutions are derived. It is found that the system is in a contact configuration ( f = 18.9 ± 6.0%) with a moderate mass ratio of 0.5 ± 0.01. A third light contributing about 6.1 ± 1.3% of the total luminosity in the V band was found, which may come from a cool tertiary component. The derived high orbital inclination ( i = 83.9° ± 0.5°) and the almost symmetric three light curves suggest that the determined parameters are reliable. Both the color class and spectral class of the system correspond to a spectral type of M0, which may indicate that SDSS J012119.10–001949.9 belongs to a very rare class of M dwarf contact binaries that are below the theoretical short period limit.