2007ApJ...668L.175M

We introduce an alternative hypothesis to explain the very low luminosity of the cool (L-type) companion to the ∼25 M_Jup, ∼8 Myr old brown dwarf 2M1207A. Recently, Mohanty et al. found that effective temperature estimates for 2M1207B (1600±100 K) are grossly inconsistent with its lying on the same isochrone as the primary, being a factor of ∼10 underluminous at all bands between I (0.8 µm) and L' (3.6 µm). Mohanty et al. explain this discrepancy by suggesting that 2M1207B is an 8 M_Jup object surrounded by an edge-on disk comprised of large dust grains producing 2.5 mag of achromatic extinction. We offer an alternative explanation: the apparent flux reflects the actual source luminosity. Given the temperature, we infer a small radius (∼49,000 km), and for a range of plausible densities, we estimate a mass < M_Jup. We suggest that 2M1207B is a hot protoplanet collision afterglow and show that the radiative timescale for such an object is ≳1% the age of the system. If our hypothesis is correct, the surface gravity of 2M1207B should be an order of magnitude lower than that predicted by Mohanty et al.