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Paper: The Infancy of Massive Stars: Looking into the Cradle
Volume: 267, Hot Star Workshop III: the Earliest Stages of Massive Star Birth
Page: 95
Authors: Kaper, L.; Bik, A.; Hanson, M. M.; ComerĂ³n, F.
Abstract: With the aim to directly detect the photospheres of newly born, massive stars, we have obtained near-infrared spectra of the deeply embedded, candidate ionizing stars of (ultra-)compact HII regions with the Very Large Telescope. The targets were selected on the basis of their near-infrared luminosity and colour measured from narrow-band images collected in a survey of 45 southern UCHII's. Although the UC HII sample was compiled using the IRAS-colour criterium of Wood &Churchwell, the association with ultracompact (radio) sources, and therefore the secure identification with infant HII regions, is often not obvious. However, the K-band spectroscopy confirms the OB-star nature of 36 strongly reddened stars, among them O stars of very early spectral type. Another twenty stars do not show photospheric absorption lines, but include a strong and broad Brγ emission line. These stars share characteristics with objects classified as massive YSOs (such as, e.g., in M17). We present arguments that they are likely surrounded by a circumstellar disk.
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