We present follow-up observations and analysis of the recently discovered short period low-mass eclipsing binary, SDSS J001641–000925. With an orbital period of 0.19856?days, this system has one of the shortest known periods for an M dwarf binary system. Medium-resolution spectroscopy and multi-band photometry for the system are presented. Markov Chain Monte Carlo modeling of the light curves and radial velocities yields estimated masses for the stars of M 1 = 0.54 ± 0.07 M ☉ and M 2 = 0.34 ± 0.04 M ☉, and radii of R 1 = 0.68 ± 0.03 R ☉ and R 2 = 0.58 ± 0.03 R ☉, respectively. This solution places both components above the critical Roche overfill limit, providing strong evidence that SDSS J001641–000925 is the first verified M-dwarf contact binary system. Within the follow-up spectroscopy we find signatures of non-solid body rotation velocities, which we interpret as evidence for mass transfer or loss within the system. In addition, our photometry samples the system over nine years, and we find strong evidence for period decay at the rate of 8?s yr–1. Both of these signatures raise the intriguing possibility that the system is in over-contact, and actively losing angular momentum, likely through mass loss. This places SDSS J001641–000925 as not just the first M-dwarf over-contact binary, but one of the few systems of any spectral type known to be actively undergoing coalescence. Further study of SDSS J001641–000925 is ongoing to verify the nature of the system, which may prove to be a unique astrophysical laboratory.
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