Herschel observations of EXtra-Ordinary Sources (HEXOS): Methanol as a probe of physical conditions in Orion KL
Wang, S. and Bergin, E.A. and Crockett, N.R. and Goldsmith, P.F. and Lis, D.C. and Pearson, J.C. and Schilke, P. and Bell, T.A. and Comito, C. and Blake, G.A. and Caux, E. and Ceccarelli, C. and Cernicharo, J. and Daniel, F. and Dubernet, M.-L. and Emprechtinger, M. and Encrenaz, P. and Gerin, M. and Giesen, T.F. and Goicoechea, J.R. and Gupta, H. and Herbst, E. and Joblin, C. and Johnstone, D. and Langer, W.D. and Latter, W.B. and Lord, S.D. and Maret, S. and Martin, P.G. and Melnick, G.J. and Menten, K.M. and Morris, P. and Muller, H.S.P. and Murphy, J.A. and Neufeld, D.A. and Ossenkopf, V. and Perault, M. and Phillips , T.G. and Plume, R. and Qin, S.-L. and Schlemmer, S. and Stutzki, J. and Trappe, N. and van der Tak, F.F.S. and Vastel, C. and Yorke, H.W. and Yu, S. and Zmuidzinas, J. (2011) Herschel observations of EXtra-Ordinary Sources (HEXOS): Methanol as a probe of physical conditions in Orion KL. Astronomy & Astrophysics, 527 (A95). pp. 1-8. ISSN 0004-6361
We have examined methanol emission from Orion KL with the Herschel/HIFI instrument, and detected two methanol bands centered at 524 GHz and 1061 GHz. The 524 GHz methanol band (observed in HIFI band 1a) is dominated by the isolated ΔJ = 0, K = −4 → −3, vt = 0 Q branch, and includes 25 E-type and 2 A-type transitions. The 1061 GHz methanol band (observed in HIFI band 4b) is dominated by the ΔJ = 0, K = 7 → 6, vt = 0 Q branch transitions which are mostly blended. We have used the isolated E-type vt = 0 methanol transitions to explore the physical conditions in the molecular gas.With HIFI’s high velocity resolution, the methanol emission contributed by different spatial components along the line of sight toward Orion KL (hot core, low velocity flow, and compact ridge) can be distinguished and studied separately. The isolated transitions detected in these bands cover a broad energy range (upper state energy ranging from 80 K to 900 K), which provides a unique probe of the thermal structure in each spatial component. The observations further show that the compact ridge is externally heated. These observations demonstrate the power of methanol lines as probes of the physical conditions in warm regions in close proximity to young stars.
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