GQ Lup B visible and near-infrared photometric analysis

We have reanalyzed archival HST and Subaru data of the recently discovered planetary mass companion (PMC) GQ Lup B. With these we produce the first R- and I-band photometry of the companion and fit a radius and effective temperature using detailed model atmospheres. We find an effective temperature of 2335 +/- 100 K, a radius of 0.38 +/- 0.05 R-circle dot, and a luminosity of log (L/L-circle dot) = -2.42 +/- 0.07(at 140 pc). Since we fit wavelengths that span , most of the emitted radiation from GQ Lup, this luminosity estimate is robust, with uncertainty dominated by the distance uncertainty (+/- 50 pc). The radius obtained for 140 pc (0.38 R,) is significantly larger than the one originally derived and larger than model predictions. The mass of the object is much more model-dependent than the radiative properties, but for the Gaia dusty models we find a mass between 10M(Jup) and 20M(Jup), in the range of the brown dwarf and PMC deuterium-burning boundary. Assuming a distance of 140 pc, observations fit to 1 sigma the Baraffe evolution model for an similar to 15M(Jup) brown dwarf. Additionally, the F606W photometric band is significantly overluminous compared to model predictions and other brown dwarfs. Such overluminosity could be explained by a bright H alpha emission from chromospheric activity, interaction with another undetected companion, or accretion. Assuming that GQ Lup B has a bright H alpha emission line, its H alpha emission strength is 10(-1.71 +/- 0.10) L-bol, significantly larger than field late-type dwarfs. GQ Lup B might be strongly accreting and might still be in its formation phase.