On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?
Journal article, 2016

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 solar masses of material at 280 ± 18 K, and ≈1.6 solar masses 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 along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H2O at 5.8 μm and CO2 at 15 μm. The spectral energy distribution is consistent with a massive, luminous (~2 × 10^4 solar luminosities) central source surrounded by a dense, warm circumstellar disk and envelope of total mass ~500–700 solar masses, 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.

masers

ISM: molecules

stars: formation

stars: winds

stars: protostars

outflows

stars: AGB and post-AGB

Author

M. A. Cordiner

Catholic University of America

NASA Goddard Space Flight Center

A. Boogert

Universities Space Research Association

S.B. Charnley

NASA Goddard Space Flight Center

Kay Justtanont

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

N. L. J. Cox

KU Leuven

University of Toulouse

R. G. Smith

University of New South Wales (UNSW)

Aggm Tielens

Leiden University

Eva Wirström

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

S. N. Milam

NASA Goddard Space Flight Center

J. V. Keane

University of Hawaii

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 828 1 51

Subject Categories

Astronomy, Astrophysics and Cosmology

Roots

Basic sciences

DOI

10.3847/0004-637X/828/1/51

More information

Latest update

7/4/2018 7