Free access article

A&A 475, 959-972 (2007)
DOI: 10.1051/0004-6361:20066342

Coronae in the Coronet: a very deep X-ray look into a stellar nursery

J. Forbrich^{1, 2} and T. Preibisch<sup>1

1</sup>  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    e-mail: jforbrich@cfa.harvard.edu
²  Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergäßchen 2-3, 07745 Jena, Germany

(Received 4 September 2006 / Accepted 17 September 2007)

Abstract
Aims.To study the X-ray properties of young stellar objects (YSOs), we analyze an exceptionally sensitive Chandra dataset of the Coronet cluster in the CrA star-forming region, achieving a limiting luminosity of  erg/s for lightly absorbed sources. This dataset represents one of the most sensitive X-ray observations ever obtained of a star-forming region.
Methods. The X-ray data are used to investigate the membership status of tentative members of the region, to derive plasma temperatures and X-ray luminosities of the YSOs, and to investigate variability on the timescale of several years.
Results.46 of the 92 X-ray sources in the merged Chandra image can be identified with optical or near/mid-infrared counterparts. X-ray emission is detected from all of the previously known optically visible late-type (spectral types G to M) stellar cluster members, from five of the eight brown dwarf candidates, and from nine embedded objects ("protostars") with class 0, class I, or flat-spectrum spectral-energy distributions (SEDs) in the field of view. While the Herbig Ae/Be stars TY CrA and R CrA, a close companion of the B9e star HD 176386, and the F0e star T CrA are detected, no X-ray emission is found from any of the Herbig-Haro (HH) objects or the protostellar cores without infrared source. We find indications for diffuse X-ray emission near R CrA / IRS 7.
Conclusions.The observed X-ray properties of the Coronet YSOs are consistent with coronal activity; soft spectral components hinting towards X-ray emission from accretion shocks were not found. The X-ray emission of the AeBe stars TY CrA and HD 176386 probably originates from close late-type companions. The Ae star R CrA shows a peculiar X-ray spectrum and an extremely hot plasma temperature. Finally, we discuss the differences of the X-ray properties of YSOs in different evolutionary stages.

Key words: stars: pre-main sequence -- stars: activity -- stars: magnetic fields -- X-rays: stars

© ESO 2007

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