ROSAT X-ray Detection of a Young Brown Dwarf in the Chamaeleon I Dark Cloud

Abstract

Photometry and spectroscopy of the object Cha Hα 1, located in the Chamaeleon I star-forming cloud, show that it is a ∼10 ⁶ -year-old brown dwarf with spectral type M7.5 to M8 and 0.04 ± 0.01 solar masses. Quiescent x-ray emission was detected in a 36-kilosecond observation with 31.4 ± 7.7 x-ray photons, obtained with the Röntgen Satellite (ROSAT), with 9σ detection significance. This corresponds to an x-ray luminosity of 2.57 × 10 ²⁸ ergs per second and an x-ray to bolometric luminosity ratio of 10 ^−3.44 . These are typical values for late M-type stars. Because the interior of brown dwarfs may be similar to that of convective late-type stars, which are well-known x-ray sources, x-ray emission from brown dwarfs may indicate magnetic activity.