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Session 44 - Double Stars.
Display session, Thursday, January 08
We have obtained simultaneous optical photometry and spectroscopy of the low mass X-ray binary (and Z-source) GX 349+2 with the CTIO 0.9 m and 4 m telescopes in July 1997. The spectrum of GX 349+2 only shows strong, narrow H\alpha emission. The observed radial velocities indicate that our previously reported 22 hour photometric modulation is indeed the orbital period. We find \gamma=-250\pm10 km s^-1 and K=65\pm6 km s^-1 for the systemic and semi-amplitude velocities respectively. The photometric light curve and radial velocity curve are offset by 0.25 in phase. Doppler tomography shows the H\alpha emission centered on the position of the neutron star. The relative phasing implies that the photometric variability is probably caused by the heated face of the companion star while the H\alpha emission may arise in an accretion disk and traces the motion of the neutron star. It also indicates that the emission region is symmetric around the neutron star. If the H\alpha emission does originate in the accretion disk, the narrowness of the line suggests a low inclination for the system.
Program listing for Thursday