GQ Lup B Visible and Near-Infrared Photometric Analysis

Abstract

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 K, a radius of 2335 ‫ע‬ 100 R , , and a luminosity of (at 140 pc). Since we fit wavelengths that span 0.38 ‫ע‬ 0.05 log (L/L) p Ϫ2.42 ‫ע‬ 0.07 , most of the emitted radiation from GQ Lup, this luminosity estimate is robust, with uncertainty dominated by the distance uncertainty (‫05ע‬ 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 j the Baraffe evolution model for an ∼15M Jup brown dwarf. Additionally, the F606W photometric band is significantly overlu-minous compared to model predictions and other brown dwarfs. Such overluminosity could be explained by a bright Ha emission from chromospheric activity, interaction with another undetected companion, or accretion. Assuming that GQ Lup B has a bright Ha emission line, its Ha emission strength is , significantly larger than Ϫ1.71‫01.0ע‬ 10 L bol field late-type dwarfs. GQ Lup B might be strongly accreting and might still be in its formation phase.