Probing the embedded YSOs of the R CrA region through VLT-ISAAC spectroscopy

Abstract

Near IR spectra obtained with ISAAC at VLT, have been used to pose constraints on the evolutionary state and accretion properties of a sample of five embedded YSOs located in the R CrA core. This sample includes three Class I sources (HH100 IR, IRS2 and IRS5), and two sources with NIR excesses (IRS6 and IRS3). Absorption lines have been detected in the medium resolution spectra of all the observed targets, together with emission lines likely originating in the disk-star-wind connected regions. We derived spectral types, veiling and stellar luminosity of the five observed sources, which in turn have been used to infer their mass and age adopting pre-main sequence evolutionary tracks. We find that in HH100 IR and IRS2 most of the bolometric luminosity is due to accretion, while the other three investigated sources, including the Class I object IRS5a, present a low accretion activity (L_{acc}/L_{bol} < 0.2). We observe a general correlation between the accretion luminosity, the IR veiling and the emission line activity of the sources. A correlation between the accretion activity and the spectral energy distribution slope is recognizable but with the notable exception of IRS5a. Our analysis therefore shows how the definition of the evolutionary stage of deeply embedded YSOs by means of IR colors needs to be more carefully refined.