A dataset provided by the European Space Agency

Name OT2_pvanhoof_2
Title Molecule formation in planetary nebulae


DOI 10.5270/esa-xdm00dd
Author van hoof, p.
Description We propose to observe a sample of highly evolved planetary nebulae that we believe to have ongoing molecular chemistry inside dense knots that formed only a few thousand years ago inside recombining gas. The proposed Herschel observations will allow us to either prove or disprove this new, still controversial, formation scenario of the knots. If proven correct, these knots will allow us a unique opportunity to test the theory of time-dependent molecular chemistry. Two famous examples of such objects are the Helix nebula (NGC 7293) and the Ring nebula (NGC 6720). They have knots that are currently embedded in the ionized gas as the ionization front has moved outwards since the knots formed. The Helix nebula has very strong H _2 emission coming from the knots. A static photoionization model cannot explain this emission, but a hydrodynamic model can. This model indicates that the knots are quickly eroded by the radiation field of the central star. This poses a problem for rival theories as they assume that the knots formed much earlier, and must have survived through the entire photoionized phase of the nebula. We believe that the knots cannot survive that long in such a harsh environment and formed after the central star entered the cooling track and the nebulae started to recombine. In order to prove this we need more accurate models of the advection flows off the knots that need to be constrained by Herschel observations of the full CO emission line spectrum. To sample various stages of evolution, we have searched for evolved planetary nebulae with knots which were sufficiently bright. After removal of duplications with earlier proposals, we were left with a sample of 5 planetary nebulae, including the Helix nebula. We propose to obtain SPIRE full range spectroscopy and PACS deep line scans on individual CO lines, allowing us to observe the CO spectrum from the 4--3 line up to the 24--23 line.
Publication Herschel spectral mapping of the Helix nebula (NGC 7293). Extended CO photodissociation and OH+ emission . Etxaluze M. et al. . Astronomy & Astrophysics, Volume 566, id.A78, 10 pp. . 566 . 10.1051\/0004-6361\/201322941 . 2014A&A...566A..78E ,
Instrument SPIRE_SpireSpectrometer_, PACS_PacsLineSpec_point
Temporal Coverage 2012-12-17T14:56:43Z/2013-04-16T17:45:15Z
Version SPG v14.2.0
Mission Description Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 ┬Ám range, bridging the gap between earlier infrared space missions and groundbased facilities.
Creator Contact https://support.cosmos.esa.int/herschel/
Date Published 2013-10-16T15:37:27Z
Publisher And Registrant European Space Agency
Credit Guidelines European Space Agency, 2013-10-16T15:37:27Z, OT2_pvanhoof_2, SPG v14.2.0. https://doi.org/10.5270/esa-xdm00dd