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An Astrometric Study of the Binary Star α Ophiuchi
The work reported here combines data from the Multichannel AstrometricPhotometer (MAP), the European astrometric satellite, Hipparcos, andinfrared speckle observations of the nearby subgiant binary star systemα Oph. The A5 IV primary is found to have a mass of 2.84+/-0.19Msolar, while the approximately K2 V companion has a mass of0.78+/-0.058 Msolar. The distance modulus is 0.834+/-0.024mag, yielding an absolute visual magnitude of 1.248+/-0.025 mag and anabsolute K magnitude of the secondary of 4.3+/-0.2 mag. Tables list theMAP data and an ephemeris that indicates that the next 4 yr are idealfor further interferometry.
| A magnitude limited stellar X-ray survey and the F star X-ray luminosity function
An X-ray survey has been conducted of stars brighter than visualmagnitude 8.5 that have serendipitously fallen into the fields of viewof the Imaging Proportional Counter of the Einstein Observatory. Thesurvey includes 227 separate 1 x 1 deg fields, containing 274 stars witha visual magnitude of no more than 8.5 and covering a wide range ofspectral types and luminosity classes. X-ray emission was detected from33 stars, and upper limits have been determined for the remainder of thesample. F type stars dominate the detected sample, and most of these areshown to be dwarfs. An X-ray luminosity function for dF stars has beendeduced, and reveals that the average 0.2-4.0 keV luminosity of thesestars is around 10 to the 29th erg/sec. Constraints have been placed onthe high luminosity tails and medians of the X-ray luminosity functionsfor other types of stars.
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