The RMS survey: near-IR spectroscopy of massive young stellar objects

Abstract

Near-infrared H- and K-band spectra are presented for 247 objects, selected\nfrom the Red MSX Source (RMS) survey as potential young stellar objects (YSOs).\n195 (~80%) of the targets are YSOs, of which 131 are massive YSOs (L_BOL >\n5x10^3 L_solar), M > 8M_solar. This is the largest spectroscopic study of\nmassive YSOs to date, providing a valuable resource for the study of massive\nstar formation. In this paper we present our exploratory analysis of the data.\nThe YSOs observed have a wide range of embeddedness (2.7 < A_V < 114),\ndemonstrating that this study covers minimally obscured objects right through\nto very red, dusty sources. Almost all YSOs show some evidence for emission\nlines, though there is a wide variety of observed properties. The most commonly\ndetected lines are Brgamma, H_2, fluorescent FeII, CO bandhead, [FeII] and HeI\n2-1 2^1S-2^1P, in order of frequency of occurrence. In total, ~40% of the YSOs\ndisplay either fluorescent FeII 1.6878um or CO bandhead emission (or both),\nindicative of a circumstellar disc; however, no correlation of the strength of\nthese lines with bolometric luminosity was found. We also find that ~60% of the\nsources exhibit [FeII] or H_2 emission, indicating the presence of an outflow.\nThree quarters of all sources have Brgamma in emission. A good correlation with\nbolometric luminosity was observed for both the Brgamma and H_2 emission line\nstrengths, covering 1 L_solar< L_BOL < 3.5x10^5 L_solar. This suggests that the\nemission mechanism for these lines is the same for low-, intermediate-, and\nhigh-mass YSOs, i.e. high-mass YSOs appear to resemble scaled-up versions of\nlow-mass YSOs.\n