|Hyperfine structure resolved OH map of the high-mass star-forming region W3 IRS5
|Water is one of the most important molecules in star-forming regions because of its high abundance. However, the relative importance of its various formation and destruction routes is not well understood. OH is a key species in the H2O chemistry as it is closely linked to the H2O formation and destruction through OH + H2 &amp;lt;-&amp;gt; H2O + H. Herschel offers a unique opportunity to study the H2O reaction network, because OH cannot be observed from the ground. The first hyperfine structure resolved OH far-infrared spectrum from the high-mass star-forming region W3 IRS5 was obtained with HIFI previously. OH emission was expected to arise from the innermost parts of the protostellar envelope. The spectrum however showed a strong outflow component. From the hyperfine resolved OH we could derive physical properties of the emitting gas and the comparison with H2O constrained the chemistry: the gas-phase OH and H2O abundances are consistent with photodesorption from grain mantles in the outer envelope. In the inner envelope almost all OH is driven into H2O, consistent with high-temperature chemistry. To obtain the lacking spatial information on the OH distribution in W3 IRS5, we propose to map W3 IRS5 with HIFI. From the map we will learn how the relative contributions from the outflow and the envelope and the H2O chemistry change with position. HIFI is crucial to resolve the hyperfine structure OH, allowing us to derive the excitation temperature, column density, and optical depth. The second goal is to test predictions from theoretical calculations of the OH with H2 collision rates. A strong asymmetry, caused by an asymmetry in the collision coefficients, in the line strengths of the two OH line triplets belonging to the same rotational states is predicted by theory. We propose to observe a second OH line triplet, which is complementary to the one from the previous observation, towards the center of W...3 IRS5. Comparison of the two triplets will allow us to test the predictions and to validate the rate coefficents.
|Linking low- to high-mass young stellar objects with Herschel-HIFI observations of water . San José-García I. et al. . Astronomy & Astrophysics, Volume 585, id.A103, 30 pp. . 585 . 10.1051/0004-6361/201525708 . 2016A&A...585A.103S ,
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT2_swampfle_2, SPG v14.1.0. https://doi.org/10.5270/esa-spxcnkd