Spatially resolving X-ray emission from a Class I Pre-Main Sequence Binary System
Kenji Hamaguchi (NASA/GSFC/ASD) , Minho Choi (International Center for Astrophysics, Korea Astronomy and Space Science Institute), Ken'ichi Tatematsu (National Astronomical Observatory of Japan), Chul-Sung Choi (International Center for Astrophysics, Korea Astronomy and Space Science Institute), Rob Petre (NASA/GSFC), Michael F. Corcoran (CRESST and X-ray Astrophysics Laboratory NASA/GSFC)
Many, if not most, stars are born as a member of a binary system through fragmentation of the parent molecular cloud. Because pre-main sequence (PMS) stars that form as a binary system are the same age, any variation in their X-ray activity would be due to their mass difference or the presence of the companion star. PMS binaries are therefore a useful probe to test models of the dependence of X-ray activity on stellar parameters. Separations of binary PMSs are less than 10” at the typical distance to nearby star forming regions. Chandra’s spatial resolution down to 1” can be used to study the X-ray properties of individual components of PMS binaries for the first time. Using a sub-pixel event repositioning technique, we spatially resolved X-ray emission from the Class I PMS binary system IRS5 in the R Corona Australis molecular cloud with 0.8” separation. As far as we know, this result - obtained from 8 Chandra archival observations between 2000 and 2005 - is the first X-ray study of individual sources in a Class I PMS binary system with a projected separation less than 200AU. We extracted light curves and spectra of the individual sources with a two-dimensional image fitting method using Sherpa. The brighter near-infrared source (IRS 5a) showed three X-ray flares lasting >20 ksec, while the fainter source (IRS 5b) was quiescent almost through the observations. In quiescence, these sources showed almost identical X-ray spectra, with NH 4e22 cm-2, kT 2 keV and Lx 1e30 ergs s-1. Their X-ray properties are typical of Class I protostars although variable cm radio emission with circular polarization from IRS 5 favors it to be a pair of young T-Tauri stars behind a molecular cloud. We discuss their evolutionary stages and the connection between their radio and X-ray activity.