New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System

TL;DR

This study used the Magellan AO system to image the young brown dwarf CT Chamaeleontis B at visible wavelengths, providing new estimates of its extinction, luminosity, and accretion rate, and demonstrating the effectiveness of visible AO photometry.

Contribution

First visible wavelength adaptive optics imaging of CT Chamaeleontis B, enabling improved measurements of its properties and accretion activity compared to prior infrared-only observations.

Findings

Detected CT Cha B at multiple visible wavelengths.

Estimated mass of 14-24 Jupiter masses.

Measured significant Halpha emission indicating active accretion.

Abstract

We used the Magellan adaptive optics (MagAO) 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 Ys. With our new photometry and Teff~2500 K derived from the shape its K-band spectrum, we find that CT Cha B has Av = 3.4+/-1.1 mag, and a mass of 14-24 Mj according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates that the companion has significant Halpha emission and a mass accretion rate ~6*10^-10 Msun/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 AO photometry (r', i', z', Ys) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions.