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

Comerón, F., Fernández, M., Baraffe, I., Neuhäuser, R., and Kaas, A. A.
Astronomy and Astrophysics, v.406, p.1001-1017 (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 Hα emission (EW(Hα ) = 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 x 10-9 Msun yr-1 for this object, although with uncertainties that do not exclude values as low as 10-10 Msun yr-1. Based on the Hα / [SII] 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 EW(Hα ) > 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.

Based on observations obtained at the European Southern Observatory using the Very Large Telescope in Cerro Paranal (program 67.C-0549(A)), the ESO New Technology Telescope in La Silla (program 69.B-0126(A)), and the 1.5 Danish telescope, also in La Silla (program 69.C-0423(B)).