Discovery of a Massive Protostar near IRAS18507+0121

We have observed the massive star forming region, IRAS18507+0121, at millimeter wavelengths in 3 mm continuum emission and HCO(J=1–0) and SiO(v=0, J=2–1) line emission, and at near-infrared wavelengths between 1.2 and 2.1μm. Two compact molecular cores are detected: one north and one south separated by ∼ 40′′. 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 near-infrared wavelengths, we suggest that G34.4+0.23 MM may 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 a near-infrared cluster of young stars and an ultracompact (UC) HII region, G34.4+0.23, with a central B0.5 star. The fraction of near-infrared stars with excess infrared emission indicative of circumstellar material is greater than 50% which suggests an upper limit on the age of the IRAS18507+0121 star forming region of 3 Myrs. Subject headings: stars: formation – nebulae: HII regions – ISM: molecules National Radio Astronomy Laboratory, P.O. Box O, 1003 Lopezville Rd, Socorro, NM 87801 European Southern Observatory, Casilla 19001, Santiago 19, Chile Departamento de Astronomı́a, Universidad de Chile, Casilla 36-D, Santiago, Chile