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Session 12 - Binary Stars.
Display session, Monday, June 08
Atlas Ballroom,
The Fine Guidance Sensor is a white light shearing interferometer which is sensitive to the tilt of the wavefront presented to its Koesters Prisms. If the wavefront is planar, the instrument is remarkably insensitive to large shifts (3mm) of the pupil on the face of the prisms. However, in the presence of HST's spherically aberrated wavefront, any internal misalignment of the instrument which leads to small ( 0.3mm) displacements of the pupil at the Koesters Prism rapidly degrades the interferometer's fringe visibility and morphology. FGS1r, installed in HST during the Second Servicing Mission, benefits from an articulating mirror (FF3) which can be adjusted to recenter the pupil on the Koesters Prisms to optimize the interferometer's performance. We report the results of an on-orbit test, using the optimized FGS1r, to measure the angular separation of the components of the binary system ADS11300. In this test, the roll angle of HST was varied so that the projected angular separation of the binary's components along FGS1r's X axis ranged from 6 to 20 mas. We discuss the class of science observations for which this instrument is best suited and STScI's consideration of offering FGS1r as a science instrument in cycle 8. Updated information about the FGSs can be found at http://www.stsci.edu/ftp/instrument_news/fgs/html/TOPfgs.html.
