Simultaneous X-ray, radio, near-infrared, and optical monitoring of young stellar objects in the Coronet cluster

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: forbrich@mpifr-bonn.mpg.de
² Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergäßchen 2-3, 07745 Jena, Germany
³ Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA
⁴ National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
⁵ Institute of Astronomy, School of Science, The University of Tokyo, Osawa 2-21-1, Mitaka, Tokyo 181-0015, Japan
⁶ Department of Astronomical Sciences, Graduate University for Advanced Studies (Sokendai), Mitaka, Tokyo 181-8588, Japan
⁷ Department of Astronomy and Astrophysics, University of Toronto, 60 St. George Street, Toronto, ONT M5S 3H8, Canada
⁸ Université Paris 7, LESIA – Observatoire de Paris, Bâtiment 17bis, 5 place Jules Janssen, 92195 Meudon Principal Cedex, France
⁹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr. 1, 85748 Garching, Germany
¹⁰ Graduate School of Science and Technology, Kobe University, 1-1 Rokko-dai Nada-ku, Kobe 657-8501, Japan

Received: 1 August 2006
Accepted: 6 December 2006

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 ~ 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.