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

A spectroscopic survey of a small area at the center of the Lupus 3 star-forming core has revealed four new mid-tolate M-type members, including a M7.5 brown dwarf. One of the new members, classified as M5, displays prominent forbidden lines and strong Halpha emission (EW(Halpha) = 410 Angstrom), 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 similar to1.4 x 10(-9) M-. yr(-1) for this object, although with uncertainties that do not exclude values as low as 10(-10) M-. yr(-1.) Based on the Halpha/[SII] ratio, the detection of HeI, and the CaII infrared triplet, we argue that most of the Halpha 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(Halpha) > 100 Angstrom 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.