eprintid: 1427243 rev_number: 37 eprint_status: archive userid: 608 dir: disk0/01/42/72/43 datestamp: 2014-04-19 18:50:41 lastmod: 2021-09-20 00:06:50 status_changed: 2014-04-19 18:50:41 type: article metadata_visibility: show item_issues_count: 0 creators_name: Etxaluze, M creators_name: Cernicharo, J creators_name: Goicoechea, JR creators_name: Van Hoof, PAM creators_name: Van De Steene, GC creators_name: Groenewegen, MAT creators_name: Swinyard, BM creators_name: Barlow, MJ creators_name: Matsuura, M creators_name: Lim, TL creators_name: Pearson, C creators_name: Polehampton, ET creators_name: Kerschbaum, F creators_name: Lique, F creators_name: Royer, P creators_name: Ueta, T title: Herschel spectral mapping of the Helix nebula (NGC 7293): Extended CO photodissociation and OH+ emission ispublished: pub divisions: UCL divisions: B04 divisions: C06 divisions: F60 note: Reproduced with permission from Astronomy & Astrophysics, © ESO abstract: Context. The Helix nebula (NGC 7293) is our closest planetary nebulae. Therefore, it is an ideal template for photochemical studies at small spatial scales in planetary nebulae. Aims. We aim to study the spatial distribution of the atomic and the molecular gas, and the structure of the photodissociation region along the western rims of the Helix nebula as seen in the submillimeter range with Herschel. Methods. We used five SPIRE FTS pointing observations to make atomic and molecular spectral maps. We analyzed the molecular gas by modeling the CO rotational lines using a non-local thermodynamic equilibrium (non-LTE) radiative transfer model. Results. For the first time, we have detected extended OH emission in a planetary nebula. The spectra towards the Helix nebula also show CO emission lines (from J = 4 to 8), [N ii] at 1461 GHz from ionized gas, and [C i] (P- P), which together with the OH lines trace extended CO photodissociation regions along the rims. The estimated OH column density is ~ 10 - 10 cm . The CH (1-0) line was not detected at the sensitivity of our observations. Non-LTE models of the CO excitation were used to constrain the average gas density (n(H) ~ (1 - 5) × 10 cm) and the gas temperature (T ~ 20-40 K). Conclusions. The SPIRE spectral-maps suggest that CO arises from dense and shielded clumps in the western rims of the Helix nebula, whereas OH and [C i] lines trace the diffuse gas and the UV and X-ray illuminated clump surfaces where molecules reform after CO photodissociation. The [N ii] line traces a more diffuse ionized gas component in the interclump medium. © ESO, 2014. date: 2014-06 official_url: http://dx.doi.org/10.1051/0004-6361/201322941 vfaculties: VMPS oa_status: green full_text_type: pub language: eng primo: open primo_central: open_green verified: verified_manual elements_source: Scopus elements_id: 941603 doi: 10.1051/0004-6361/201322941 lyricists_name: Barlow, Michael lyricists_name: Matsuura, Mikako lyricists_name: Swinyard, Bruce lyricists_id: MJBAR75 lyricists_id: MMATS97 lyricists_id: BSWIN93 full_text_status: public publication: Astronomy and Astrophysics volume: 566 article_number: A78 issn: 0004-6361 citation: Etxaluze, M; Cernicharo, J; Goicoechea, JR; Van Hoof, PAM; Van De Steene, GC; Groenewegen, MAT; Swinyard, BM; ... Ueta, T; + view all <#> Etxaluze, M; Cernicharo, J; Goicoechea, JR; Van Hoof, PAM; Van De Steene, GC; Groenewegen, MAT; Swinyard, BM; Barlow, MJ; Matsuura, M; Lim, TL; Pearson, C; Polehampton, ET; Kerschbaum, F; Lique, F; Royer, P; Ueta, T; - view fewer <#> (2014) Herschel spectral mapping of the Helix nebula (NGC 7293): Extended CO photodissociation and OH+ emission. Astronomy and Astrophysics , 566 , Article A78. 10.1051/0004-6361/201322941 <https://doi.org/10.1051/0004-6361%2F201322941>. Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/1427243/1/aa22941-13.pdf