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On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?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 microns using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 microns, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: approx. = 0.22 Stellar Mass of material at 280+/-18 K, and ≈1.6 Me of material at 157+/-3 K. The OI 63 micron 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 along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H2O at 5.8 microns and CO2 at 15 microns. The spectral energy distribution is consistent with a massive, luminous (approx. 2 × 10(exp 4) Stellar Luminosity) central source surrounded by a dense, warm circumstellar disk and envelope of total mass approx. 500-700 Stellar Mass with large bipolar outflow cavities. The combination of distinctive far-IR spectral features suggest that IRAS19312+1950 should be classified as an accreting, high-mass YSO rather than an evolved star. In light of this reclassification, IRAS19312+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.
Document ID
20170002488
Document Type
Reprint (Version printed in journal)
Authors
Cordiner, M. A. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Boogert, A. C. A. (Universities Space Research Association Moffett Field, CA, United States)
Charnley, S. B. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Justtanont, K. (Chalmers Univ. of Technology Goeteborg, Sweden)
Cox, N. L. J. (Toulouse Univ. France)
Smith, R. G. (New South Wales Univ. Canberra, Australia)
Tielens, A. G. G. M. (Leiden Univ. Netherlands)
Wirstrom, E. S. (Chalmers Univ. of Technology Goeteborg, Sweden)
Milam, S. N. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Keane, J. V. (Hawaii Univ. Honolulu, HI, United States)
Date Acquired
March 23, 2017
Publication Date
August 29, 2016
Publication Information
Publication: The Astrophysical Journal
Volume: 828
Issue: 1
ISSN: 2041-8205
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN40387
Distribution Limits
Public
Copyright
Other
Keywords
ISM: molecules aEuro" masers aEuro" stars