Herschel-HIFI detections of hydrides towards AFGL 2591 (Envelope emission versus tenuous cloud absorption)

S. Bruderer , A. O. Benz , E. F. van Dishoeck , M. Melchior , S. D. Doty , F. van Der Tak (1) , P. Stäuber , S. F. Wampfler , C. Dedes , U. A. Yildiz , L. Pagani (2) , T. Giannini , Th. de Graauw , N. Whyborn , D. Teyssier (3) , W. Jellema , R. Shipman , R. Schieder , N. Honingh , E. Caux (4) , W. Bächtold , A. Csillaghy , C. Monstein , R. Bachiller (1) , Alain Baudry (5, 6, 7, 8) , M. Benedettini (1) , E. Bergin , P. Bjerkeli , G. A. Blake (9) , Sylvain Bontemps (5, 6, 7, 8) , J. Braine (5, 6, 7, 8) , P. Caselli (10) , J. Cernicharo (11) , C. Codella (1) , F. Daniel , A. M. Di Giorgio , C. Dominik (12) , P. Encrenaz (2) , M. Fich , A. Fuente (1) , J. R. Goicoechea (2) , F. Helmich (1) , G. J. Herczeg , Fabrice Herpin (5, 6, 7, 8) , M. R. Hogerheijde , T. Jacq (5, 6, 7, 8) , D. Johnstone , J. K. Jørgensen , L. E. Kristensen , B. Larsson (1) , D. Lis (1) , R. Liseau , M. Marseille (5, 6, 7, 8, 13) , C. Mccoey , G. Melnick (1) , D. Neufeld (1) , B. Nisini (14) , M. Olberg (15) , B. Parise (4) , J. C. Pearson , R. Plume , C. Risacher (16) , J. Santiago-Garcia , P. Saraceno (17) , M. Tafalla , T. A. van Kempen , R. Visser , F. Wyrowski (18)

1 LAOG - Laboratoire d'Astrophysique de Grenoble
2 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
3 Herschel Science Center [Madrid]
4 CESR - Centre d'étude spatiale des rayonnements
5 LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac]
6 OASU - Observatoire aquitain des sciences de l'univers
7 UB - Université Sciences et Technologies - Bordeaux 1
8 L3AB - Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux
9 LOCIE - LabOratoire proCédés énergIe bâtimEnt
10 OAA - INAF - Osservatorio Astrofisico di Arcetri
11 CSIC - Centro de Investigaciones Biológicas
12 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
13 SRON - SRON Netherlands Institute for Space Research
14 OAR - INAF - Osservatorio Astronomico di Roma
15 Onsala Space Observatory
16 ESO
17 IFSI - Istituto di Fisica dello Spazio Interplanetario
18 MPIFR - Max-Planck-Institut für Radioastronomie

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 = 3/2_2,- - 1/2_1,+) 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.

Mots clés: Astrophysics; Solar and Stellar Astrophysics

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]; Astrophysique stellaire et solaire [astro-ph.SR]

S. Bruderer, A. O. Benz, E. F. van Dishoeck, M. Melchior, S. D. Doty, et al.. Herschel-HIFI detections of hydrides towards AFGL 2591 (Envelope emission versus tenuous cloud absorption). Astronomy and Astrophysics - A&A, 2010, 521, pp.L44. ⟨10.1051/0004-6361/201015098⟩. ⟨hal-00521370⟩