X-rays from the Brown Dwarf BD TWA-5B

Y. Tsuboi G. Chartas, E. Feigelson, G. Garmire, Y. Maeda, K. Mori, L. Townsley (The Pennsylvania State University) S. Pravdo (JPL)

Abstract

With mass well below the hydrogen burning mass limit (<0.08 M$_{\odot}$), brown dwarfs (hereafter BDs) had been expected to have no high energy activity. Surprisingly, however, persistent X-rays from several young BDs and BD candidates (1-5 Myr old) in star-forming regions, were detected with ROSAT and Chandra(ex. Neuhäuser et al. 1999, Imanishi et al. 2001). Recently, X-ray flares from old BDs (0.5-1 Gyr) were also observed with Chandra(Fleming et al. 2000; Rutledge et al. 2000), while no steady X-ray was found from them. On the other hand, no X-ray data has been available for BDs of intermediate ages (3-100 Myr).

To give definite restriction to the evolution of BDs, we executed Chandra observations of an intermediate age (10 Myr) BD TWA-5B. The BD lies 55 pc away from the earth with mass of 15-40 M_jup, and is a companion of a T Tauri star TWA-5A. Although the separation to the primary is only 2'', we detected X-rays from TWA-5B, with superior spatial resolution of Chandra/ACIS. We will present X-ray properties obtained from spectral and timing analysis, and discuss the X-ray evolution of BDs.

CATEGORY: NORMAL STARS AND WHITE DWARFS