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Herschel/HIFI detections of hydrides towards AFGL 2591. Envelope emission versus tenuous cloud absorption [Letter]

Bruderer, S., Benz, A. O., van Dishoeck, E. F., Melchior, M., Doty, S. D., van der Tak, F., Staeuber, P., Wampfler, S. F., Dedes, C., Yildiz, U. A., Pagani, L., Giannini, T., de Graauw, Th., Whyborn, N., Teyssier, D., Jellema, W., Shipman, R., Schieder, R., Honingh, N., Caux, E., Baechtold, W., Csillaghy, A., Monstein, C., Bachiller, R., Baudry, A., Benedettini, M., Bergin, E., Bjerkeli, P., Blake, G. A., Bontemps, S., Braine, J., Caselli, P., Cernicharo, J., Codella, C., Daniel, F., di Giorgio, A. M., Dominik, C., Encrenaz, P., Fich, M., Fuente, A., Goicoechea, J. R., Helmich, F., Herczeg, G. J., Herpin, F., Hogerheijde, M. R., Jacq, T., Johnstone, D., Jorgensen, J. K., Kristensen, L. E., Larsson, B., Lis, D., Liseau, R., Marseille, M., McCoey, C., Melnick, G., Neufeld, D., Nisini, B., Olberg, M., Parise, Berengere, Pearson, J. C., Plume, R., Risacher, C., Santiago-Garcia, J., Saraceno, P., Shipman, R., Tafalla, M., van Kempen, T. A., Visser, R. and Wyrowski, F. 2010. Herschel/HIFI detections of hydrides towards AFGL 2591. Envelope emission versus tenuous cloud absorption [Letter]. Astronomy and Astrophysics 521 , L44. 10.1051/0004-6361/201015098

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The Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory allows the first observations of light diatomic molecules at high spectral resolution and in multiple transitions. Here, we report deep integrations using HIFI in different lines of hydrides towards the high-mass star forming region AFGL 2591. Detected are CH, CH+, NH, OH+, H2O+, while NH+ and SH+ have not been detected. All molecules except for CH and CH+ are seen in absorption with low excitation temperatures and at velocities different from the systemic velocity of the protostellar envelope. Surprisingly, the CH(JF,P = 3/22,- - 1/21,+ ) and CH+(J = 1–0, J = 2–1) lines are detected in emission at the systemic velocity. We can assign the absorption features to a foreground cloud and an outflow lobe, while the CH and CH+ emission stems from the envelope. The observed abundance and excitation of CH and CH+ can be explained in the scenario of FUV irradiated outflow walls, where a cavity etched out by the outflow allows protostellar FUV photons to irradiate and heat the envelope at larger distances driving the chemical reactions that produce these molecules.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Uncontrolled Keywords: ISM: molecules ; stars: formation ; astrochemistry ; ISM: individual objects: AFGL 2591
Additional Information: Pdf uploaded in accordance with publisher's policy at (accessed 17/04/2014)
Publisher: EDP Sciences
ISSN: 0004-6361
Date of First Compliant Deposit: 30 March 2016
Last Modified: 19 Mar 2016 09:41

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