Radio and X-ray variability of Young Stellar Objects in the Coronet   Cluster
  The Coronet Cluster in the nearby R CrA dark cloud offers the rare opportunity to study at least four "class I" protostellar sources as well as one candidate "class 0" source, a Herbig Ae star, and a candidate brown dwarf within a few square arcminutes - most of them detected at radio- and X-ray wavelengths. These sources were observed with the Very Large Array (VLA) at 3.5cm on nine occasions in 1998, spread over nearly four months. The source IRS 5, earlier shown to emit circularly polarized radio emission, was observed to undergo a flux increase accompanied by changes in its polarization properties. Comparison with VLA measurements taken in January 1997 allows for some analysis of longer-term variability. In addition to this radio monitoring, we analyze archival Chandra and XMM-Newton X-ray data of these sources. Three class I protostars are bright enough for X-ray spectroscopy, and we perform a variability analysis for these sources, covering a total of 154 ksec spread over more than two and a half years. Also in X-rays, IRS 5 shows the most pronounced variability, whilst the other two class I protostars IRS 1 and IRS 2 have more stable emission. X-ray data is also analyzed for the recently identified candidate class 0 source IRS 7E, which shows strong variability as well as for the Herbig Ae star R CrA for which we find extremely hot X-ray-emitting plasma. For IRS 1,2 and 5, the hydrogen column densities derived from the X-ray spectra are at about half the values derived with near-infrared techniques, a situation similar to what has been observed towards some other young stellar objects. 
Jan Forbrich (1,2), Thomas Preibisch (1), & Karl M. Menten (1) ((1)   MPIfR Bonn, (2) AIU Jena)