PI: Dawn M. Gelino, University of California, San Diego, firstname.lastname@example.org
Address: Center for Astrophysics and Space Sciences 0424, 9500 Gilman Drive, La Jolla, CA 92093-0424
CoI: Thomas Harrison, New Mexico State University
Title: Measuring the Mass of the Black Hole in GS 2000+25
Abstract: Low mass x-ray binaries (LMXBs) contain black hole (BH) or neutron star (NS) primaries, and cool, low-mass secondary stars. A limited number of BHs and NSs have accurate mass measurements. It is important to determine the primary mass of the LMXBs to better define the BH and NS mass distributions, and to better constrain the NS equations of state. To determine the mass of the primary object we need to measure the orbital inclination, i. Previously published primary masses of GS 2000+25, a BH LMXB, fall in the range 4.8 to 25.1 M_\odot; in 2000 we found M_1=7.7+/-0.7M_\odot. Since then, we have found evidence that the shape of its ellipsoidal variations has changed. In order to understand the nature of these changes and the possible effect on the measurement of the inclination and primary mass of the system, we need high S/N data as well as good phase resolution. SQIID's capability of obtaining simultaneous JHK observations makes it prefectly suited for this task. The inclination of the system will be found through modeling of infrared ellipsoidal variations. Because most LMXBs are not eclipsing, modeling their light curves is currently the \it only feasible method for determining the inclination. We will model the light curves with the WD98 modeling program. We have successfully used NOAO facilities and this modeling technique to find accurate BH masses in five LMXBs. In order to confirm and understand the sample of known BH and NS systems, we request four nights on the KPNO 4m to obtain infrared data on GS 2000+25.
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