000002150 001__ 2150
000002150 005__ 20160706150013.0
000002150 0247_ $$2DOI$$a10.1051/0004-6361/201322941
000002150 037__ $$aASTROimport-307
000002150 100__ $$aEtxaluze, M.
000002150 245__ $$aHerschel spectral mapping of the Helix nebula (NGC 7293). Extended CO photodissociation and OH+ emission
000002150 260__ $$c2014
000002150 520__ $$aContext. The Helix nebula (NGC 7293) is our closest planetary nebulae. Therefore, it is an ideal template for photochemical studies at small spatial scales in planetary nebulae.  Aims: We aim to study the spatial distribution of the atomic and the molecular gas, and the structure of the photodissociation region along the western rims of the Helix nebula as seen in the submillimeter range with Herschel.  Methods: We used five SPIRE FTS pointing observations to make atomic and molecular spectral maps. We analyzed the molecular gas by modeling the CO rotational lines using a non-local thermodynamic equilibrium (non-LTE) radiative transfer model.  Results: For the first time, we have detected extended OH+ emission in a planetary nebula. The spectra towards the Helix nebula also show CO emission lines (from J = 4 to 8), [N ii] at 1461 GHz from ionized gas, and [C i] (3P2-3P1), which together with the OH+ lines trace extended CO photodissociation regions along the rims. The estimated OH+ column density is ~ 1012 - 1013 cm-2. The CH+ (1-0) line was not detected at the sensitivity of our observations. Non-LTE models of the CO excitation were used to constrain the average gas density (n(H2) ~ (1 - 5) × 105 cm-3) and the gas temperature (Tk ~ 20-40 K).  Conclusions: The SPIRE spectral-maps suggest that CO arises from dense and shielded clumps in the western rims of the Helix nebula, whereas OH+ and [C i] lines trace the diffuse gas and the UV and X-ray illuminated clump surfaces where molecules reform after CO photodissociation. The [N ii] line traces a more diffuse ionized gas component in the interclump medium. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.The reduced images as FITS files are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr ( or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/566/A78
000002150 700__ $$aCernicharo, J.
000002150 700__ $$aGoicoechea, J. R.
000002150 700__ $$avan Hoof, P. A. M.
000002150 700__ $$aSwinyard, B. M.
000002150 700__ $$aBarlow, M. J.
000002150 700__ $$avan de Steene, G. C.
000002150 700__ $$aGroenewegen, M. A. T.
000002150 700__ $$aKerschbaum, F.
000002150 700__ $$aLim, T. L.
000002150 700__ $$aLique, F.
000002150 700__ $$aMatsuura, M.
000002150 700__ $$aPearson, C.
000002150 700__ $$aPolehampton, E. T.
000002150 700__ $$aRoyer, P.
000002150 700__ $$aUeta, T.
000002150 773__ $$cA78$$pAstronomy and Astrophysics$$v566$$y2014
000002150 85642 $$ahttp://esoads.eso.org/abs/2014A%26A...566A..78E
000002150 905__ $$apublished in
000002150 980__ $$aREFERD