Institut für Astronomie und Astrophysik

Abteilung Astronomie

Preprint 11c/97

Evolution of the Orbital Period of Her X-1: Determination of a New Ephemeris using RXTE Data

B. Stelzer(1), R. Staubert(1), J. Wilms(1), R.D. Geckeler(1), D. Gruber(2) and R. Rothschild(2)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)Center for Astrophysics and Space Science,UCSD, La Jolla, CA, USA

Contribution to the 4th COMPTON Symposium on Gamma Ray Astronomy and Astrophysics, Williamsburg, Virginia, USA, April 27-30, 1997

Abstract. Her X-1 was observed by RXTE in July 1996 during the MAIN HIGH state of its 35 day cycle. Using data from the Proportional Counter Array (PCA) we redetermine the orbital parameters of the binary system. The analysis based on pulse-timing measurements yields new estimates for the orbital elements and an accurate spin period for the time of observation. By comparing our results with previous observations of Her X-1 we are able to report a new orbital ephemeris including an improved value for the decrease in orbital period.

Paper (162k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de) Last updated 04-Aug-1997