Infrared Spectra of Young Stars Embedded in the R Coronae Australis Cloud

Abstract

ABSTRACTInfrared spectra are presented for a magnitude-limited (K < 12.5 mag) sample of stellar objects observed toward the R Coronae Australis molecular core. These spectra, which are used to identify young stellar objects in the cloud, include the wavelengths of emission lines from [Fe II] and H 2, four of the Brackett series lines, the CO bandheads, as well as photospheric absorption lines of Al, Na, Mg, Si, and Ca. For a subset of the sample, the spectra are compared to those of infrared spectral standard stars to derive spectral types and luminosity classes. By comparing their placement in a Hertzsprung-Russell diagram with theoretical pre–main-sequence tracks and isochrones, we estimate the stellar masses and assess the evolutionary states of the members of this young aggregate. All of the sources classified via near-IR spectroscopy have masses in the range 0.2–2.5 M ⊙. The locus of points in the H-R diagram is lower than observed for other embedded clusters (e.g., NGC 2024 and the ρ Oph core), suggesting either a more advanced evolutionary state or a difference in the intrinsic stellar birthline for very young clusters. We discuss the implications of our results for the shape of the initial mass function of the embedded young cluster and the star-forming history of the cloud.