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

X-ray emission near the substellar limit: The 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 )

Abstract
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 Orionis and Taurus-Auriga associations. In 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 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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