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Session 60 - Multiple Stars.
Display session, Wednesday, June 12
Great Hall,
The Faint Object Spectrograph (FOS) onboard HST is being used in imaging cornonographic mode to search for faint companions about four nearby stars: Wolf 359, LHS 292, GL 293, and Proxima Cen. GJ 1245 AC and Wolf 424, each with known companions, are included as calibration targets.
The FOS is ideal for detecting faint companions because of its large dynamic range, sensitivity, sub-arcsecond resolution, low detector noise, and an occulting bar aperture. This program is the first to make use of this unique coronographic capability of the HST. The FOS camera mirror images the aperture onto the photocathode. The on-orbit ACQIMAGE is created by electronically substepping the diode array across the photocathode. Deconvolution of the on-orbit image produces an image of the aperture with a scale of 0\farcs 08 per pixel. Modeling indicates a companion can be detected as close as 0\farcs 2 for a system of nearly equally bright stars, and as close as 0\farcs 8 if the magnitude difference between the primary star and its companion is ten magnitudes. In the image of GJ 1245 AC (separation \sim0\farcs 5, V magnitude difference \sim2), the companion was easily distinguishable, verifying the substance of the model predictions.
FOS observations of Wolf 424 and Wolf 359, which are scheduled during April-May 1996, will be discussed. Additional analysis for previously reported observations of GL 293 and GJ 1245 AC will also be presented.
