The O-Type Binary 15 Monocerotis Nears Periastron

摘要

We present new radial velocity measurements for the massive binary 15 Monocerotis which indicate that the system is now very close to periastron (1996.9) in its 24 yr orbit. The velocity separation in the coming year may be large enough to permit an accurate estimate of mass ratio. We also present our first astrometric measurement of 15 Mon made with the Hubble Space Telescope Fine Guidance Sensors FGS). The FGS transfer functions are consistent with an advanced orbital position close to periastron, and we present preliminary orbital elements for the combined spectroscopic and astrometric orbit.