AAS 195th Meeting, January 2000
Session 39. Neutron Stars with Partners
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

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[39.05] RXTE Discovery of the Orbit of X Persei

A. M. Levine, H. Delgado-Marti, E. Pfahl, S. Rappaport (MIT Center for Space Research & Dept. of Physics)

The 837 s pulsations of the X-ray pulsar X Persei have been observed in a series of observations with RXTE extending over 450 days. The arrival times of the pulses are well-fit by a model that includes a pulse period derivative and a single sinusoidal function. The sinusoidal function is most likely due to the motion of the pulsar in an orbit around its Be star companion, and thereby yields the orbital period (250 days), the projected amplitude (450 lt-s), and the mass function (1.6 solar masses). The orbit appears to be nearly circular, with a best-fit eccentricity of 0.03, contrary to the expectation that such a wide orbit would be rather eccentric like those of other pulsars in wide orbits. We discuss theoretical calculations that show it is very unlikely for a binary system to end up with a wide circular orbit like that of X Per after one of the components explodes as a supernova and leaves a neutron star.

We wish to acknowledge NASA for support of this research.

The author(s) of this abstract have provided an email address for comments about the abstract: aml@space.mit.edu

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