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

Abstract

In order 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 LXmin=5E26 erg/sec for lightly absorbed sources. This dataset represents one of the most sensitive X-ray observations ever obtained of a star-forming region. 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. 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 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. The observed X-ray properties of the Coronet YSOs are consistent with coronal activity; no soft spectral components hinting towards X-ray emission from accretion shocks were found. The X-ray emission of the AeBe stars TY CrA and HD 176386 originates probably 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.

arXiv comment18 pages, 6 figures, accepted for publication in A&A

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