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Session 3 - Clusters.
Display session, Monday, June 10
We describe a Pleiades near-infrared imaging survey for brown dwarfs and very low mass stars, and present some preliminary analysis and results. More than 1200 square arcminutes of the Pleiades have been imaged at J and K-short with UCLA's two-channel infrared camera on Lick Observatory's 3-m telescope, and at I-band with a CCD on Lick's 1-m telescope. Estimates of the limiting magnitudes are I\sim20.5, J\sim19.5, and K-short\sim19. Control fields, 5-6 degrees from the cluster center and at the same galactic latitude, have been imaged (an additional \sim600 square arcminutes) to statistically approximate the contribution of background objects in the Pleiades fields.
Objects are recognized as brown dwarf candidates by their placement on color-magnitude and/or color-color diagrams. Early analysis has turned up many objects at least as red and as faint as the promising Pleiades brown dwarf candidates PPL 15 and Teide 1 (see e.g. Rebolo et al 1995, Nature, 377, 129), but most of these interesting objects have image profiles with slightly larger FWHM values, compared to brighter stellar profiles. This implies that, from this initial photometry alone, many or most of the potential brown dwarfs are actually background galaxies.
As a follow-up step to help distinguish Pleiades brown dwarfs from faint red background galaxies, five candidates from the data set were imaged in January 1996 with short exposures of the Near Infrared Camera (NIRC) on the 10-m Keck telescope. With Mauna Kea's better seeing conditions and the superior image quality from NIRC/Keck, all but one of these objects displayed an extended, non-stellar profile that was not apparent from the prior images taken at Lick.
Program listing for Monday