EDP Sciences
Free Access
Volume 391, Number 3, September I 2002
Page(s) 1025 - 1032
Section Formation, structure and evolution of stars
DOI https://doi.org/10.1051/0004-6361:20020887

A&A 391, 1025-1032 (2002)
DOI: 10.1051/0004-6361:20020887

X-ray emission near the substellar limit: The $\sigma$ Orionis and Taurus star forming regions

F. Mokler and B. Stelzer

Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

(Received 19 April 2002 / Accepted 11 June 2002 )

We have carried out an extensive search for X-ray emission from young, very low-mass objects near and beyond the substellar limit, making use of archived ROSAT PSPC and HRI observations pointed at Brown Dwarfs and Brown Dwarf candidates in the young $\sigma$ Orionis and Taurus-Auriga associations. In $\sigma$ Ori we identify three Brown Dwarf candidates with X-ray sources; in Taurus-Auriga we add one further X-ray detection of a Brown Dwarf to the list published earlier. We combine this data with all previously X-ray detected Brown Dwarfs and Brown Dwarf candidates in young stellar associations and star forming regions to perform a study of stellar activity parameters on the as yet largest sample of young, very low mass objects. A similar relation between X-ray and bolometric luminosity, and H ${\alpha}$ emission, respectively, as is known for T Tauri stars seems to hold for young objects down to the substellar limit, too. No signs for a change in X-ray activity are found on the transition to substellar masses.

Key words: X-rays: stars -- stars: formation, low-mass, Brown Dwarfs, coronae, activity

Offprint request: F. Mokler, fmokler@mpe.mpg.de

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© ESO 2002

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