Spitzer Observations of Two TW Hydrae Association Brown Dwarfs

We present Spitzer Space Telescope observations of two TW Hydrae Associationbrown dwarfs, 2MASSW J1207334-393254 and 2MASSW J1139511-315921, in the IRACand MIPS 24 micron bands. Based on their IRAC colors, we have classified themas Classical and Weak-line T Tauri stars, respectively. For 2MASSWJ1207334-393254, we have found that a flat disk model fits the data very well.This brown dwarf shows the presence of warm (T > 100 K) circumstellar dustclose (R < 0.2 AU) to it, and does not display any signs of cleansing of dustwithin several AU of the star. In comparison with other TWA members that showexcess in IR, we suggest that there exists a different disk evolution/dustprocessing mechanism for stellar and sub-stellar objects. 2MASSWJ1139511-315921 does not show any significant excess in any of the IRAC bands,but a small one at 24 micron, which is not significant enough to suggest thepresence of warm dust around this star. It shows signs of dust cleansing in theinner several AU, similar to most of the other TWA members.Comment: 13 pages, 3 figures, published in Ap