Spectroscopy of faint T dwarf calibrators: understanding the substellar mass function and the coolest brown dwarfs

Details Spectroscopy of faint T dwarf calibrators: understanding the substellar mass function and the coolest brown dwarfs Spectroscopy of faint T dwarf calibrators: understanding the substellar mass function and the coolest brown dwarfs

Jul 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009hst..prop12217l&link_type=abstract

HST Proposal ID #12217. Cycle 18

Physics

Scientific paper

More than 100 methane brown dwarfs, or T dwarfs, have now been discovered in the local field with 2MASS, SLOAN and UKIDSS, opening up a new area of physics describing objects at 450-1400 K. However, very few calibrator objects exist with well established ages and metallicities. A very surprising result from the UKIDSS sample {supported by 2MASS and SLOAN} is that the substellar mass function in the local field appears to decline to lower masses, in marked contrast to the rising initial mass function {IMF} observed in young clusters. Given that such a difference between the present day IMF and the Galactic time-averaged IMF is unlikely, it is very possible that the apparently falling IMF is an artifact of serious errors in either T model atmospheres or the evolutionary isochrones. We propose WFC3 spectroscopy of 4 faint T dwarf calibrators with well established ages and metallicities in the Pleiades and Sigma Ori clusters, and 2 faint field T dwarfs from UKIDSS for comparison. These spectra will constitute vital calibration data for T dwarf atmospheres with a wide range of surface gravities, which will be used to test and improve the model atmospheres. They will also aid preparation for future spectroscopy of the much larger numbers of field T dwarfs to soon be found by VISTA and WISE. These new surveys will permit a more precise measurement of the mass function and detection of even cooler objects.;

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