High-resolution SOFIA/EXES Spectroscopy of Water Absorption Lines in the Massive Young Binary W3 IRS 5. (arXiv:2306.13798v1 [astro-ph.GA])

High-resolution SOFIA/EXES Spectroscopy of Water Absorption Lines in the Massive Young Binary W3 IRS 5. (arXiv:2306.13798v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Li_J/0/1/0/all/0/1">Jialu Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Boogert_A/0/1/0/all/0/1">Adwin Boogert</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bar_A/0/1/0/all/0/1">Andrew G. Bar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+DeWitt_C/0/1/0/all/0/1">Curtis DeWitt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rashman_M/0/1/0/all/0/1">Maisie Rashman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Neufeld_D/0/1/0/all/0/1">David Neufeld</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Indriolo_N/0/1/0/all/0/1">Nick Indriolo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pendleton_Y/0/1/0/all/0/1">Yvonne Pendleton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Montiel_E/0/1/0/all/0/1">Edward Montiel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Richter_M/0/1/0/all/0/1">Matt Richter</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chiar_J/0/1/0/all/0/1">J. E. Chiar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tielens_A/0/1/0/all/0/1">Alexander G. G. Tielens</a>

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 ($Rsim$50,000) from the NASA Stratospheric Observatory for Infrared
Astronomy (SOFIA). Many ($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.

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 ($Rsim$50,000) from the NASA Stratospheric Observatory for Infrared
Astronomy (SOFIA). Many ($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.

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