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Session 43 - Binary Stars.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
The HST Fine Guidance Sensors (FGS) have the unique astrometric capabilities of revealing faint companions in close binary systems. They can measure their position angles and component separations, with a precision which exceeds that which is possible using any ground based techniques for primary components in the magnitude range V = 9 to 14. In addition, the intensity data which are produced by the FGS PMTs provide high precision relative photometry on rapid time scales. In previous HST observing Cycles, while in guiding mode, these FGS data were telemetered to the ground at a 1 Hz rate. In mid Cycle 4 a new telemetry format was adopted for all normal operations which serendipitously provide these astrometric and photometric data at 40 Hz for all guide star acquisitions and periods of active guiding.
We have initiated a systematic program to examine these data, obtained from the HST engineering telemetry, to perform a search for stellar duplicity to determine the incidence of doubles in the Guide Star Catalog as well as the separations, position angles, and relative brightnesses of the individual stellar components in such binaries. We are analyzing all such acquisition data, not just failure cases. While we are finding that such failures often are due to the presence of a close companion of nearly equal magnitude, a well-separated fainter companion will not necessarily cause a fine-lock failure, but is detectable and measurable from the acquisition data. We will also examine the light curves and power spectra of the photometric data in an effort to perform an astroseismological survey of these stars, as well as look for and characterize variations due to other intrinsic mechanisms. The development of a data calibration and reduction pipeline, methods of analysis, and preliminary results from individual cases are discussed.
Support for this work was provided by NASA through grant number AR-05811.01-94A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555.
