High-resolution SOFIA/EXES Spectroscopy of water absorption lines in the massive young binary W3 IRS5 Jialu Li 1 , Adwin Booger 2 , Andrew G. Barr 3 , Curtis DeWitt 4 , Alexander G.G.M. Tielens 1,2 1 University of Maryland College Park, USA, 2 University of Hawaii, USA, 3 Leiden University, The Netherlands, 4 SOFIA Science Center, USA High spectral resolution, pencil beam absorption line studies at mid-IR wavelengths provide a unique opportunity to study the physical conditions and chemical inventory of embedded phases in massive star formation [1, 2, 3]. The size of the mid-IR continuum emission region provides the effective spatial resolution of such spectroscopic observations. Thespectralresolution down to a few km/s enables individual components such as shocked gas, disks, or foreground envelopes to be resolved dynamically. Therefore, we are able to understand the interactions of the massive protostars with their environment in a better way. Among the rich chemical inventory in the regions associated with the protostars, water is one of the most abundant moleculesin both the gas and ice phaseand has a powerfuldiagnostic capability in probing physical conditions [4]. However, water is very difficult to observe from the ground. We present in this work the power of combining the SOFIA which flies high above most of the water in the Earth's atmosphere and EXES which resolves lines to several km/s in realizing water's diagnostic capability. We conducted high spectral resolution(R=50,000)spectroscopyfrom 5-8 um with SOFIA/EXES toward the hot core region close to the massive binary protostar W3 IRS5, and detected ~200 rovibrational water lines (the ν2 band). Multiple velocity components are identified and will be analyzed with complementary M-band studies on CO lines toward the same region [5]. Our preliminary rotation diagram analysis shows that the detected water lines are tracing hot gas in temperatures of ~700 K. To correctly derive the temperatures and column densities (or abundances), we will apply curve-of-growth analyses following [3] to account for the opacity effects. Once the temperatures and column densities are properly constrained, we can link individual components to those detected and distinguished by CO absorption lines. We will explore the implication of the oxygen budget by analyzing dynamically resolved water and CO in the gas and ice phase. We will also investigate the constraints of the results on the potentially existing disks around the protostars. We emphasize that many of the involved physics and chemistry in disks or hot cores in massive protostars are similar toplanet-forming disks or hot corinos around low-mass protostars thatfuture JWST/MIRI studies are interested in.However, JWST/MIRI (R=3,000) lacks the spectral resolution to separate individual dynamical components and even blends multiple transition lines into one feature. Therefore,the SOFIA/EXES studies will be instrumental in guiding future MIRI/JWST observations. References 1. Beltran, M. T. & de Wit, W. J. 2016, A&AR, 24, 6 2. Barr, A. G., et al. 2020, ApJ, 900, 104Barr, A. G., et al. 2022, ApJ, 935, 165van Dishoeck, et al. 2021, A&A, 648, A24 3. Li, J., et al. 2022, ApJ, 935, 161
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© The Author(s), 2023
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