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Astron. Astrophys. 355, 629-638 (2000)

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6. Conclusions

Our ROSAT pointed observation in the Cha II dark cloud revealed 40 X-ray sources with high confidence, of which 35% were identified with YSOs. Of the 49 Cha II optical and IR members, 14 were detected in X-rays. None of the protostellar candidates in Cha II was detected in X-rays. On the basis of intermediate resolution spectroscopy, four new WTTS candidates were found. Most of the X-ray sources detected lie in the eastern side of the Cha II cloud. The north-west part of the cloud is devoid both in X-ray sources and visible PMS stars. The stars in Cha II are typically less X-ray luminous than those in Cha I. This result, together with the strong dependence of the X-ray luminosity on stellar mass, is consistent with the fact that the mass spectrum in the Cha II cloud is biased towards less massive stars. An important result of our X-ray observation in Cha II is that the number of class-III IR sources or WTTS is less than that of class-II IR sources or CTTS, contrary to the results of previous investigations in the Cha I cloud, where WTTS outnumber CTTS at least by a factor of 2. This probably indicates an earlier evolutionary stage for Cha II relative to Cha I.

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© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000