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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Molecular chemistry and the missing mass problem in planetary nebulae

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Author(s):
Kimura, R. K. [1] ; Gruenwald, R. [1] ; Aleman, I. [1, 2, 3]
Total Authors: 3
Affiliation:
[1] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, BR-05508090 Sao Paulo - Brazil
[2] Univ Fed Rio Grande do Sul, Inst Fis, Dept Astron, BR-91501970 Porto Alegre, RS - Brazil
[3] Univ Manchester, Sch Phys & Astron, Jodrell Bank Ctr Astrophys, Manchester M13 9PL, Lancs - England
Total Affiliations: 3
Document type: Journal article
Source: Astronomy & Astrophysics; v. 541, MAY 2012.
Web of Science Citations: 17
Abstract

Context. Detections of molecular lines, mainly from H-2 and CO, reveal molecular material in planetary nebulae. Observations of a variety of molecules suggest that the molecular composition in these objects differs from that found in interstellar clouds or in circumstellar envelopes. The success of the models, which are mostly devoted to explain molecular densities in specific planetary nebulae, is still partial however. Aims. The present study aims at identifying the influence of stellar and nebular properties on the molecular composition of planetary nebulae by means of chemical models. A comparison of theoretical results with those derived from the observations may provide clues to the conditions that favor the presence of a particular molecule. Methods. A self-consistent photoionization numerical code was adapted to simulate cold molecular regions beyond the ionized zone. The code was used to obtain a grid of models and the resulting column densities are compared with those inferred from observations. Results. Our models show that the inclusion of an incident flux of X-rays is required to explain the molecular composition derived for planetary nebulae. We also obtain a more accurate relation for the N(CO)/N(H-2) ratio in these objects. Molecular masses obtained by previous works in the literature were then recalculated, showing that these masses can be underestimated by up to three orders of magnitude. We conclude that the problem of the missing mass in planetary nebulae can be solved by a more accurate calculation of the molecular mass. (AU)