HST Fine Guidance Sensors Survey For Binaries Among The Massive Stars

¹ Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, PO Box 5060, Georgia State University, Atlanta, GA 30302-5060, USA
² Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ US Naval Observatory, Astrometry Department, 3450 Massachusetts Avenue NW, Washington, DC 20392-5420, USA
⁵ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía, s/n. 18008, Granada, Spain
⁶ Département de Physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, CP 6128 Succ. A., Centre-Ville, Montréal, Québec H3C 3J7, Canada
⁷ Department of Natural Science, University of South Carolina, Beaufort, 801 Carteret Street, Beaufort, SC 29902, USA
⁸ Institute for Astronomy, Astrophysics, Space Applications & Remote Sensing, National Observatory of Athens, Lofos Nymfon, Thiseio, PO Box 20048, 11810 Athens, Greece

Abstract

We present the results of an all sky survey for binary systems among the massive stars that we made with the HST Fine Guidance Sensors. The sample of 225 stars is comprised mainly of Galactic O- and B-type stars and Luminous Blue Variables, plus a few luminous stars in the LMC. The FGS TRANS mode observations are sensitive to detection of companions with an angular separation of 0.01–1 arcsec and brighter than △m = 5 mag. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets, yielding a companion detection frequency of 29%. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample. These results confirm the high multiplicity fraction. The period distribution is essentially flat in increments of log P, although there remains an observational gap in detections for periods of years and decades.