Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40922r&link_type=abstract
Spitzer Proposal ID #40922
Physics
Scientific paper
We request Spitzer 70 micron observations of two brown dwarfs, 2MASSW J1207334-393254 (2M1207) and 2MASSW J1139511-315921 (2M1139), in the TW Hydrae Association (TWA). From our previous Spitzer observations, we had shown that 2M1207 shows excess in all of the IRAC and MIPS 24 micron bands, while 2M1139 shows a small excess at 24 micron, but none in the IRAC bands. Using these existing observations, we have tried to model the disk around 2M1207. While we are able to obtain a good fit using a disk mass of 10^(-5) Msun, an inclination angle of 63degree, and an outer disk radius of 100 AU, there are degeneracies in the values for these disk parameters. As our model fits indicate, the variations in the model SEDs for different values of these disk parameters are more evident at mid-IR wavelengths. Thus observation obtained for 2M1207 at 70 micron would help in narrowing down the range of possible values for these important disk parameters. For the case of 2M1139, a small excess is seen at 24 micron that is only ~1.8 times the expected photospheric emission. However, the SED for this brown dwarf up to 24 micron is very similar to TWA 7, for which a cool debris disk has been detected at 70 micron. TWA 7 also shows a very small excess (only ~1.1 times the expected photospheric emission) at 24 micron, but flares up at 70 micron. Thus we request 70 micron observation for 2M1139 in order to confirm the presence of a debris disk around this brown dwarf, similar to TWA 7. If the presence of such a disk is confirmed for 2M1139, then this would be the first transition disk detected yet among the sub-stellar members of TWA.
Gizis John
Riaz Basmah
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