Infrared observations of the ellipsoidal light variation in J0422+32

Abstract

We have obtained K-band photometry of J0422+32 using the ARC 3.5 m telescope in January 1997 to search for the ellipsoidal variations expected from the secondary star. J0422+32 is a soft x-ray transient that erupted in August of 1992, containing a compact object primary and a late-type secondary star. Both a neutron star and a black hole have been proposed as the primary component for this system. The inclination of the orbit, however, is not known well enough to be able to decide between the two. We explore the use of infrared observations, where the secondary star is the dominant luminosity source, to measure the amplitude of the ellipsoidal variation of the system. The GENSYN light curve synthesis program is used in conjunction with these variations to estimate the orbital inclination, and hence the mass of the binary system.