Publications of the MPIfR
Optical & Infrared
Interferometry Group
Forbrich, J.; Preibisch, Th.; Menten,
K. M.; Neuhäuser, R.; Walter, F. M.; Tamura, M.; Matsunaga, N.;
Kusakabe, N.; Nakajima, Y.; Brandeker, A.; Fornasier, S.; Posselt, B.;
Tachihara, K.; Broeg, C.
Simultaneous X-ray, radio, near-infrared, and
optical monitoring of young stellar objects in the Coronet cluster
Astronomy and Astrophysics, Volume 464, Issue 3,
pp.1003-1013 (2007)
Abstract
Context: .Multi-wavelength
(X-ray to radio) monitoring of Young Stellar
Objects (YSOs) can provide important information about physical
processes at the stellar surface, in the stellar corona, and/or in the
inner circumstellar disk regions. While coronal processes should mainly
cause variations in the X-ray and radio bands, accretion processes may
be traced by time-correlated variability in the X-ray and
optical/infrared bands. Several multi-wavelength studies have been
successfully performed for field stars and ~1-10 Myr old T Tauri stars,
but so far no such study succeeded in detecting simultaneous X-ray to
radio variability in extremely young objects like class I and class 0
protostars.
Aims: .Here we present the
first simultaneous X-ray, radio,
near-infrared, and optical monitoring of YSOs, targeting the Coronet
cluster in the Corona Australis star-forming region, which harbors at
least one class 0 protostar, several class I objects, numerous T Tauri
stars, and a few Herbig AeBe stars.
Methods: .In August 2005, we
obtained five epochs of Chandra X-ray
observations on nearly successive days accompanied by simultaneous
radio observations at the NRAO Very Large Array during four epochs, as
well as by simultaneous optical and near-infrared observations from
ground-based telescopes in Chile and South Africa.
Results: .Seven objects are
detected simultaneously in the X-ray,
radio, and optical/infrared bands; they constitute our core sample.
While most of these sources exhibit clear variability in the X-ray
regime and several also display optical/infrared variability, none of
them shows significant radio variability on the timescales probed. We
also do not find any case of clearly time-correlated optical/infrared
and X-ray variability. Remarkable intra-band variability is found for
the class I protostar IRS 5 which shows much lower radio fluxes than in
previous observations, and the Herbig Ae star R CrA, which displays
enhanced X-ray emission during the last two epochs, but no
time-correlated variations are seen for these objects in the other
bands. The two components of S CrA vary nearly synchronously in the I
band.
Conclusions: .The absence of
time-correlated multi-wavelength
variability suggests that there is no direct link between the X-ray and
optical/infrared emission and supports the notion that accretion is not
an important source for the X-ray emission of these YSOs. No
significant radio variability was found on timescales of days.
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