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

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

Corresponding author: F. Comerón, fcomeron@eso.org

Received: 30 September 2002
Accepted: 28 May 2003

Abstract

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 Hα emission ( 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 ~  yr^-1 for this object, although with uncertainties that do not exclude values as low as 10^-10  yr^-1. Based on the ratio, the detection of HeI, and the CaII infrared triplet, we argue that most of the Hα 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  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.