Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21711304s&link_type=abstract
American Astronomical Society, AAS Meeting #217, #113.04; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Mid-infrared spectroscopy provides unique and crucial information that can be used to characterize massive young stellar objects (MYSOs) and resolve questions regarding the evolutionary states of these objects. We have used the Spitzer Space Telescope Infrared Spectrograph in the Short-Low, Short-High, and Long-High modules (5-36 micron) to map the thirteen very red sources that we found in Spitzer IRAC (GLIMPSE) and MIPS (MIPSGAL) images of the G333 giant molecular cloud. The objects, which have luminosities ranging from 2X103 Lsun to 5X104 Lsun, are divided into two groups: seven MYSOs associated with extended emission in IRAC band 2 at 4.5 micron ("outflow sources", also known as "EGOs" or "green fuzzies") and six MYSOs that have extended emission in all IRAC bands peaking at the longest wavelengths ("red sources"). All the YSOs associated with outflows show evidence of massive envelopes surrounding the star, which produce deep silicate absorption features and absorption by ices at 6.0, 6.8, and 15.2 micron. There is shocked gas associated with the 4.5 micron emission, as seen by the presence of [S I] 25 micron line emission in over half of the outflows (but not by any associated H2 line emission, as has been suggested elsewhere). For four of the red sources, our spectral maps show that there are ionized neon and sulfur lines concentrated to the YSO locations, from which we infer that these red YSOs can already ionize H II regions. For several objects of both types, the lines from the highly excited Ne++ ions peak at some distance from the peak of the low excitation lines. We conclude that both types of MYSO have outflows that produce shocked gas and that the outflow MYSOs, which have slightly cooler spectral energy distributions than the red YSOs, are younger than the H II region producing, red MYSOs.
Bains Indra
Burton Michael G.
Cotera Angela S.
Cunningham Maria
Lo Nadia
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