Session 63 - Stars and A Radio Source.
Oral session, Tuesday, January 14
Our imaging survey for very low mass stars and brown dwarfs covers greater than 1200 square arcminutes in the Pleiades, and reaches estimated limiting magnitudes of I\sim20, J\sim18.5, and K-short\sim17.5. Theoretical models suggest that such depths should allow sampling of masses into the high end of the brown dwarf regime, perhaps down to \sim0.04 solar masses. Six large mosaiced fields were imaged at Lick Observatory, with UCLA's 2-channel infrared camera on the 3-m telescope, and with a CCD on the 1-m telescope. Analysis and results from at least two of these big fields will be presented.
The largest of the mosaics covers an area approximately 19' x 19', which alone comprises one of the largest Pleiades areas yet imaged at infrared wavelengths. For comparison in the infrared, there are the studies of Williams et al (1996, ApJ, 464, 238) and Simons amp; Becklin (1992, ApJ, 390, 431), which imaged \sim400 and \sim200 square arcminutes, respectively, of the Pleiades at K. Larger Pleiades surveys have been carried out at optical wavelengths, where brown dwarf emission is weaker, and have turned up brown dwarfs such as Teide 1 and Calar 3 (see e.g. Rebolo et al, 1996, ApJL, 469, L53).
I will describe how brown dwarf candidates are being diagnosed amongst the vast numbers of objects for whom photometry is (or can be) derived. In particular, color-magnitude and color-color diagrams (such as I vs. I-K, and I-J vs. I-K) will be shown, with their utility and importance discussed. Other useful diagnostics in deciphering Pleiades brown dwarf candidates from compact red background galaxies, for instance, are image profile data (e.g. plots of either FWHM values or peak counts as a function of measured magnitude).