2015ApJ...801....4W

We used the Magellan adaptive optics system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths. We detect it at r', i', z', and Y_S. With our new photometry and T_eff∼ 2500 K derived from the shape of its K-band spectrum, we find that CT Cha B has A_V= 3.4±1.1 mag, and a mass of 14-24 M_J according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates that the companion has significant Hα emission and a mass accretion rate ∼6x10^–10 M_☉/yr, similar to some substellar companions. Proper motion analysis shows that another point source within 2'' of CT Cha A is not physical. This paper demonstrates how visible wavelength adaptive optics photometry (r', i', z', Y_S) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions.