EDP Sciences
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Volume 406, Number 3, August II 2003
Page(s) 1001 - 1017
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20030848

A&A 406, 1001-1017 (2003)
DOI: 10.1051/0004-6361:20030848

New low-mass members of the Lupus 3 dark cloud: Further indications of pre-main-sequence evolution strongly affected by accretion

F. Comerón1, M. Fernández2, I. Baraffe3, R. Neuhäuser4, 5 and A. A. Kaas


1  European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
    e-mail: fcomeron@eso.org
2  Instituto de Astrofísica de Andalucía, CSIC, Apdo. 3004, 18080 Granada, Spain
    e-mail: matilde@iaa.es
3  C.R.A.L. (UMR 5574 CNRS), École Normale Supérieure, 69364 Lyon Cedex 07, France
    e-mail: ibaraffe@ens-lyon.fr
4  Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85741 Garching bei München, Germany
5  Astrophysikalisches Institut, Universität Jena, Schillergässchen 2-3, 07745 Jena, Germany
    e-mail: rne@astro.uni-jena.de
6  Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
    e-mail: akaas@not.iac.es

(Received 30 September 2002 / Accepted 28 May 2003 )

A spectroscopic survey of a small area at the center of the Lupus 3 star-forming core has revealed four new mid-to-late M-type members, including a M7.5 brown dwarf. One of the new members, classified as M5, displays prominent forbidden lines and strong H $\alpha$ emission ( $EW({\rm H}\alpha) =
410$  Å), in addition to other permitted lines, and its luminosity is far below that of other members of the region with similar or later spectral types. We estimate a mass accretion rate rate of ~ $ 1.4 \times 10^{-9}$  $M_\odot$ yr -1 for this object, although with uncertainties that do not exclude values as low as 10-10  $M_\odot$ yr -1. Based on the ${\rm H}\alpha
/ {\rm [SII]}$ ratio, the detection of HeI, and the CaII infrared triplet, we argue that most of the H $\alpha$ emission is produced near the surface of the object, probably in accretion columns or at the base of jets, rather than in a low-density extended region. The strong emission-line spectrum superimposed on an unusually faint photospheric continuum thus seems to be a real, intrinsic feature rather than a result of the viewing geometry caused by an edge-on disk blocking the light from the central object. Other Lupus 3 late-type members also display noticeable underluminosity, all of them having $EW({\rm H}\alpha)
> 100$  Å as a result of the faint underlying continuum. We tentatively interpret these findings as evidence for the pre-main sequence evolution of objects with very low (possibly substellar) initial masses being significantly modified by accretion.

Key words: stars: pre-main sequence -- stars: low-mass, brown dwarfs -- stars: winds, outflows

Offprint request: F. Comerón, fcomeron@eso.org

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