9 Summary

In this data paper, we presented ground-based optical and infrared follow-up observations of previously unidentified ROSAT All-Sky Survey X-ray sources in and around the R CrA star forming cloud. We identified two new cTTS and 17 new wTTS having stronger lithium absorption than ZAMS stars of the same spectral type. Radial velocities and proper motions of most of these new TTS are consistent with the previously known CrA TTS, but the new objects are distributed more widely in space. Compared to a galactic model, this sample of ROSAT TTS constitutes an excess of young stars, more than expected at this galactic latitude. We estimated that there should be in total 29 to 48 RASS detectable TTS in CrA, of which 8 to 27 hitherto unknown TTS are still hidden among as yet unobserved ROSAT Survey sources. Similar to the two new cTTS found to be located projected onto two small cloud-lets, the seemingly off-cloud wTTS found here may have formed in small cloud-lets, which have dispersed since they formed those stars. For this scenario as well as for the ejection model (run-away TTS), a larger than observed velocity dispersion would be expected. The space motions of the on-cloud and off-cloud TTS are consistent with a scenario in which cloud and stars oscillate around the galactic plane, with a very small intrinsic velocity dispersion. This could possibly be the result of a high-velocity cloud impact triggering star formation, as advocated by Lépine & Duvert (1994). However, alternative scenarios cannot be ruled out given the accuracy of the kinematical data available at present.

Acknowledgements

We would like to thank the staff at ESO La Silla and CTIO for their help as well as George Leussis for his significant contribution in the reduction of the photometric data. We are gratefull to our referee, Dr. Bruce Wilking, for many helpful comments, which improved the content of this paper. This research has made use of the Simbad database, operated at CDS, Strasbourg, France. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The ROSAT project is supported by the German Government (BMBF/DLR) and the Max-Planck-Society. RN wishes to acknowledge financial support from the Bundesministerium für Bildung und Forschung through the Deutsche Zentrum für Luft- und Raumfahrt e.V. (DLR) under grant number 50 OR 0003.