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 \mu m using the Herschel and Spitzer space observatories .
The Herschel PACS maps exhibit a compact , slightly asymmetric continuum source at 170 \mu m , indicative of a large , dusty circumstellar envelope .
The far-IR CO emission line spectrum reveals two gas temperature components : \approx 0.22 M _ { \odot } of material at 280 \pm 18 K , and \approx 1.6 M _ { \odot } of material at 157 \pm 3 K. The O i 63 \mu m 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 _ { 2 } O at 5.8 \mu m and CO _ { 2 } at 15 \mu m. The spectral energy distribution is consistent with a massive , luminous ( \sim 2 \times 10 ^ { 4 } L _ { \odot } ) central source surrounded by a dense , warm circumstellar disk and envelope of total mass \sim 500 - 700 M _ { \odot } , 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 5th 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 .