AAS 201st Meeting, January, 2003
Session 54. Compact X-Ray Sources
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[54.05] Measuring the Orbital Inclination Angle for the Low-Mass X-Ray Binary XTE J2123-058

D. M. Gelino, J. A. Tomsick, W. A. Heindl (CASS/UCSD)

We present the first near infrared ellipsoidal variations of XTE J2123-058. The data were obtained with the 3 meter telescope at Lick Observatory and are modeled with the WD98 light curve modeling program to find the inclination of the system, and hence, the mass of the NS. Precise NS mass measurements are important for constraining their equations of state, and for understanding the evolution of NS systems.

XTE J2123-058 is a high Galactic latitude Neutron Star (NS) low-mass X-ray binary with a Roche lobe-filling late type K companion star. As the distorted companion orbits the NS, the observed flux rises and falls in a predictable manner, giving rise to ``ellipsoidal variations.'' We observe this system in the near infrared since this is the wavelength regime where the secondary star is brightest and the contamination from the NS and its accretion disk is minimized. By modeling the variations observed during X-ray quiescence, we determine the orbital inclination of the system. The inclination is then combined with the observed mass function and mass ratio (q = M_2/M_1) to find the mass of the NS. An estimate of the inclination in this system was previously made based on modeling its optical outburst light curves (i = 69o - 77o; Zurita et al. 2000, MNRAS 316, 137). Since this method includes many assumptions, we investigate the previous inclination estimate by modeling the system's quiescent infrared ellipsoidal variations. This project is supported by a Center for Astrophysics and Space Sciences (CASS) Postdoctoral Fellowship.

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

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.