A Chandra observation of the TW Hydrae association brown dwarf 2MASSW J1139511-315921.
CASTRO P.J., GIZIS J.E. and GAGNE M.
Abstract (from CDS):
We report on a sequence of Chandra X-Ray Observatory observations of the TW Hydrae brown dwarf (BD) 2MASSW J1139511-315921 (2M1139). In the combined 31 ks ACIS-S exposure, 2M1139 is detected at the 3σ confidence level. We find an X-ray luminosity of LX= 1.4+2.7_- 1.0_x1026 erg/s or log LX/Lbol= -4.8±0.3. This object is similar to another TW Hydrae BD member, CD-33 7795B (TWA 5B): both have Hα emission, both show no signatures of accretion, and both have comparable ages and spectral types. TWA 5B was previously detected in X-rays with a luminosity of LX= 4x1027 erg/s or log LX/Lbol= -3.4, an order of magnitude more luminous in X-rays than 2M1139. We find that the discrepancy between the X-ray luminosity of 2M1139 and TWA 5B is consistent with the spread in X-ray luminosity in the Orion Nebula Cluster for BDs of similar spectral types. Though rotation may play a role in the X-ray activity of ultracool dwarfs like 2M1139 and TWA 5B, the discrepancy cannot be explained by rotation alone. We also examine two X-ray bright objects in the field of view of our Chandra observations and find one to be of spectral type K0IV and identify it as a possible RS Canum Venaticorum, and another X-ray bright object whose light curve clearly shows the decay phase of an X-ray flare.
brown dwarfs - open clusters and associations: individual: TW Hydrae - stars: activity - stars: coronae - stars: individual: 2MASSW J1139511-315921 - X-rays: stars