Molecular chemistry and the missing mass problem in planetary nebulae


Autoria(s): Kimura, R. K.; Gruenwald, R.; Aleman, I.
Contribuinte(s)

UNIVERSIDADE DE SÃO PAULO

Data(s)

04/11/2013

04/11/2013

2012

Resumo

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.

FAPESP (Brazil)

FAPESP Brazil [03082/07]

FAPESP [2007/04498-2]

FAPESP

CNPq [PDE 201950/2008-1]

CNPq

CAPES/PRO-DOC

CAPES/PRODOC

Identificador

ASTRONOMY & ASTROPHYSICS, LES ULIS CEDEX A, v. 541, n. 2, supl. 1, Part 2, pp. 391-396, MAY, 2012

0004-6361

http://www.producao.usp.br/handle/BDPI/37978

10.1051/0004-6361/201118429

http://dx.doi.org/10.1051/0004-6361/201118429

Idioma(s)

eng

Publicador

EDP SCIENCES S A

LES ULIS CEDEX A

Relação

ASTRONOMY & ASTROPHYSICS

Direitos

restrictedAccess

Copyright EDP SCIENCES S A

Palavras-Chave #ASTROCHEMISTRY #ISM: MOLECULESS #PLANETARY NEBULAE: GENERAL #STRUCTURE FORBIDDEN TRANSITIONS #RECOMBINATION LINE-INTENSITIES #EFFECTIVE COLLISION STRENGTHS #EXCITATION RATE COEFFICIENTS #FINE-STRUCTURE LEVELS #FE-II #NGC 7027 #ELECTRON-EXCITATION #PHYSICAL PROCESSES #EMISSION-SPECTRA #ASTRONOMY & ASTROPHYSICS
Tipo

article

original article

publishedVersion