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High-resolution SOFIA/EXES Spectroscopy of Water Absorption Lines in the Massive Young Binary W3 IRS 5

Abstract:
We present in this paper mid-infrared (5-8~$\mu$m) spectroscopy toward the massive young binary W3~IRS~5, using the EXES spectrometer in high-resolution mode ($R\sim$50,000) from the NASA Stratospheric Observatory for Infrared Astronomy (SOFIA). Many ($\sim$180) $\nu_2$=1--0 and ($\sim$90) $\nu_2$=2-1 absorption rovibrational transitions are identified. Two hot components over 500 K and one warm component of 190 K are identified through Gaussian fittings and rotation diagram analysis. Each component is linked to a CO component identified in the IRTF/iSHELL observations ($R$=88,100) through their kinematic and temperature characteristics. Revealed by the large scatter in the rotation diagram, opacity effects are important, and we adopt two curve-of-growth analyses, resulting in column densities of $\sim10^{19}$ cm$^{-2}$. In one analysis, the model assumes a foreground slab. The other assumes a circumstellar disk with an outward-decreasing temperature in the vertical direction. The disk model is favored because fewer geometry constraints are needed, although this model faces challenges as the internal heating source is unknown. We discuss the chemical abundances along the line of sight based on the CO-to-H$_2$O connection. In the hot gas, all oxygen not locked in CO resides in water. In the cold gas, we observe a substantial shortfall of oxygen and suggest that the potential carrier could be organics in solid ice.Comment: Accepted for publication in ApJ. 34 pages, 13 figures, and 14 tables. Comments are more than welcome
Publication status:
Published
Peer review status:
Peer reviewed

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Publisher copy:
10.3847/1538-4357/ace16e

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Role:
Author
ORCID:
0000-0001-9344-0096
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Role:
Author
ORCID:
0000-0003-4909-2770
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Role:
Author
ORCID:
0000-0002-6528-3836
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Institution:
University of Oxford
Role:
Author
ORCID:
0000-0002-3936-2469


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Funder identifier:
10.13039/100018624
Grant:
NNA17BF53C


Publisher:
American Astronomical Society
Journal:
The Astrophysical Journal More from this journal
Volume:
953
Issue:
1
Pages:
103-103
Publication date:
2023-08-08
DOI:
EISSN:
1538-4357
ISSN:
0004-637X


Language:
English
Keywords:
Pubs id:
1522158
Local pid:
pubs:1522158
Source identifiers:
W4385663966
Deposit date:
2026-05-12
ARK identifier:
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