Publications of the MPIfR
Optical & Infrared
Interferometry Group
J. Forbrich, Th. Preibisch, K.M. Menten
Radio and X-ray variability of Young Stellar
Objects in the Coronet Cluster
Astronomy & Astrophysics, vol.446, pg.155-170
(2006)
Abstract
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.
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