EDP Sciences
Free access
Volume 393, Number 3, October III 2002
Page(s) L85 - L88
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20021251

A&A 393, L85-L88 (2002)
DOI: 10.1051/0004-6361:20021251


Discovery of a very cool object with extraordinarily strong H $\mathsf{\alpha}$ emission

D. Barrado y Navascués1, M. R. Zapatero Osorio1, 1, E. L. Martín1, V. J. S. Béjar1, R. Rebolo1, 1 and R. Mundt1

1  Laboratorio de Astrofísica Espacial y Física Fundamental, INTA, PO Box 50727, 28080 Madrid, Spain Institute of Astronomy, University of Hawaii at Manoa. 2680 Woodlawn Drive, Honolulu, HI 96822, USA Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain Consejo Superior de Investigaciones Científicas, CSIC, Spain Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

(Received 22 July 2002 / Accepted 27 August 2002)

We report on the finding of the strongest H $\alpha$ emission - pseudoequivalent width of 705 Å - known so far in a young, late type dwarf. This object, named as S Ori 71, is a substellar candidate member of the 1-8 Myr star cluster $\sigma$ Orionis. Due to its overluminous location in color-magnitude diagrams, S Ori 71 might be younger than other cluster members, or a binary of similar components. Its mass is in the range 0.021-0.012 $M_\odot$, depending on evolutionary models and possible binarity. The broad H $\alpha$ line of S Ori 71 appears asymmetric, indicative of high velocity mass motions in the H $\alpha$ forming region. The origin of this emission is unclear at the present time. We discuss three possible scenarios: accretion from a disk, mass exchange between the components of a binary system, and emission from a chromosphere.

Key words: open clusters and associations: individual: $\sigma$ Orionis -- stars: low-mass, brown dwarfs -- stars: individual: S Ori 71 -- stars: pre-main sequence

Offprint request: D. Barrado y Navascués, barrado@laeff.esa.es

© ESO 2002

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