2016ApJ...828...51C

IRAS 19312+1950 is a peculiar object that has eluded firm characterization since its discovery, with combined maser properties similar to an evolved star and a young stellar object (YSO). To help determine its true nature, we obtained infrared spectra of IRAS 19312+1950 in the range 5-550 µm using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 µm, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: ≃0.22 M_☉ of material at 280±18 K, and ≃1.6 M_☉ of material at 157±3 K. The O i 63 µm line is detected on-source but no significant emission from atomic ions was found. The HIFI observations display shocked, high-velocity gas with outflow speeds up to 90 km s^-1 along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H_2O at 5.8 µm and CO_2 at 15 µm. The spectral energy distribution is consistent with a massive, luminous (∼2 x 10^4 L_☉) central source surrounded by a dense, warm circumstellar disk and envelope of total mass ∼500-700 M_☉, with large bipolar outflow cavities. The combination of distinctive far-IR spectral features suggest that IRAS 19312+1950 should be classified as an accreting, high-mass YSO rather than an evolved star. In light of this reclassification, IRAS 19312+1950 becomes only the fifth high-mass protostar known to exhibit SiO maser activity, and demonstrates that 18 cm OH maser line ratios may not be reliable observational discriminators between evolved stars and YSOs.