ON THE NATURE OF THE ENIGMATIC OBJECT IRAS 19312+1950: A RARE PHASE OF MASSIVE STAR FORMATION?
- Astrochemistry Laboratory, NASA Goddard Space Flight Center, Code 691, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)
- Universities Space Research Association, Stratospheric Observatory for Infrared Astronomy, NASA Ames Research Center, MS 232-11, Moffett Field, CA 94035 (United States)
- Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92, Onsala (Sweden)
- Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, bus 2401, B-3001, Leuven (Belgium)
- School of Physical, Environmental and Mathematical Sciences, The University of New South Wales, Australian Defence Force Academy, Canberra ACT 2600 (Australia)
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 μ m using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 μ m, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: ≈0.22 M {sub ⊙} of material at 280 ± 18 K, and ≈1.6 M {sub ⊙} of material at 157 ± 3 K. The O i 63 μ 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{sup −1} along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H{sub 2}O at 5.8 μ m and CO{sub 2} at 15 μ m. The spectral energy distribution is consistent with a massive, luminous (∼2 × 10{sup 4} L {sub ⊙}) central source surrounded by a dense, warm circumstellar disk and envelope of total mass ∼500–700 M {sub ⊙}, 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.
- OSTI ID:
- 22667466
- Journal Information:
- Astrophysical Journal, Vol. 828, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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