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Session 77 - Binary Stars.
Display session, Wednesday, January 15
The capabilities for close double star detection and characterization from HST Fine Guidance System acquisition data have been described by the authors previously (1996, BAAS 27,1340). Subsequently, data from approximately 6000 guide star acquisitions spanning a six month period, representing approximately 1/4 of the stars in our current survey, have been searched for evidence of stellar duplicity with an automated tool. We have found that 8in this sample give evidence of possessing a stellar companion.
For the great majority of cases where fine lock is reached (>99acquisition attempts) differential correction solutions from the FGS fringe visibility function are performed. Approximately 70on successive orbits resulting in multiple acquisitions on many guide stars, thus providing multiple data sets for duplicity analysis. To ascertain the possibility of a secondary component, two position constants and two fringe amplitude constants are sought. For potential blended pairs (separation < 100 mas) the parameter space near the interferometric null-crossing is fit. Another solution searches for the presence of secondary fringes through the remainder of the roughly half arcsecond walkdown path. Solutions where both amplitudes exceed their formal errors by a factor of 2 in the first case, and 1.6 in the latter, are flagged for probable duplicity and subjected to further analysis. Separations as close as 30 mas sometimes reach the ratio-of-2 criterion.
The detection limits are difficult to ascertain without independent checks and some fraction of those stars identified as double may be spurious. We are currently working on quantifying our multi-parametric detection limits and sample completeness, which will be ascertained before the publication of a duplicity catalog of our complete survey.
Support for this work was provided by NASA through grant AR5811 from STScI, which is operated by AURA, Inc. under NASA contract NAS5-26555.
Program listing for Wednesday