DISCOVERY OF A MASSIVE PROTOSTAR NEAR IRAS 18507+0121

Abstract

We have observed the massive star-forming region IRAS 18507+0121 at millimeter wavelengths in 3 mm continuum emission, H13CO+ ( J ¼ 1 0) and SiO (v ¼ 0, J ¼ 2 1) line emission, and at near-infrared (NIR) wavelengths between 1.2 and 2.1 m. Two compact molecular cores are detected: one north and one south, separated by 4000. The northern molecular core contains a newly discovered, deeply embedded, B2 protostar surrounded by several hundred solar masses of warm gas and dust, G34.4+0.23 MM. Based on the presence of warm dust emission and the lack of detection at NIR wavelengths, we suggest that G34.4+0.23MMmay represent the relatively rare discovery of a massive protostar (e.g., analogous to a low-mass ‘‘Class 0’’ protostar). The southern molecular core is associated with an NIR cluster of young stars and an ultracompact H ii region, G34.4+0.23, with a central B0.5 star. The fraction of NIR stars with excess infrared emission indicative of circumstellar material is greater than 50%, which suggests an upper limit on the age of the IRAS 18507+0121 starforming region of 3 Myr.