Physics
Scientific paper
Mar 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999esasp.427..483g&link_type=abstract
The Universe as Seen by ISO. Eds. P. Cox & M. F. Kessler. ESA-SP 427., p. 483
Physics
Rosat, Infrared, X-Rays, Pre-Main Sequence, Low-Mass Stars, &Rho, Oph Dark Cloud
Scientific paper
We have obtained two deep exposures of the ρ Oph cloud core region (d=160 pc) in X-rays with the ROSAT High Resolution Imager (HRI). The improved angular resolution (1-6 arcsec) with respect to previous recent observations (ROSAT PSPC, te{CMFA95}; and ASCA, te{Kamata97}) allows to remove positional ambiguities for the 63 detected sources. We cross-correlate the X-ray positions with infrared (IR) sources found in the ISOCAM LW2/LW3 survey of the same region in addition to sources (optical and IR) known from ground-based observations. These IR/optical sources are Young Stellar Objects (YSOs): protostars, T Tauri Stars, with and without circumstellar disks/IR excess; respectively Class I, II, and III sources. We thus obtain the best-studied sample of X-ray/IR sources in a star-forming region, which confirms and significantly improves the results obtained previously. We confirm that essentially all YSOs are X-ray emitters, with a large majority of T Tauri stars, and that a strong correlation exists between the stellar luminosity and the X-ray luminosity. Many of the new IR sources with IR excess observed by ISOCAM are not detected, but this is readily explained by the fact that their X-ray luminosities ``predicted'' on the basis of this correlation are too faint to be detected by the HRI. This is not inconsistent with the idea that all T Tauri Stars are X-ray emitters. Conversely, a number of previously unclassified IR sources without IR excess/circumstellar disks can, via their detection in X-rays (and only so), be classified as new Class III sources. Protostars are not detected with the HRI, with the exception of the protostar YLW15, which was detected in the course of an extraordinarily powerful flare. This is very likely due to their very high extinction (circumstellar envelope + interstellar): AV = 10-60 mag. More (maybe all) protostars, faint ISOCAM sources, and even perhaps brown dwarfs, will soon be detectable with the new generation of X-ray satellites. We anticipate that all YSOs, including brown dwarfs, will be proved to be X-ray emitters.
Andr'e P.
Bontemps Sylvain
Feigelson Eric D.
Grosso Nicolas
Montmerle Th.
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