EDP Sciences
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Volume 431, Number 2, February IV 2005
Page(s) 565 - 574
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20040401

A&A 431, 565-574 (2005)
DOI: 10.1051/0004-6361:20040401

Evolution from AGB to planetary nebula in the MSX survey

R. Ortiz1, S. Lorenz-Martins2, W. J. Maciel3 and E. M. Rangel1

1  Departamento de Física, UFES, Av. Fernando Ferrari 514, 29075-910, Vitória, ES, Brazil
    e-mail: ortiz@cce.ufes.br
2  GEMAC, Depto. de Astronomia, OV/UFRJ, Ladeira Pedro Antonio 43, 20080-090, Rio de Janeiro, RJ, Brazil
3  Departamento de Astronomia, IAG/USP, Rua do Matão, 1226, Cidade Universitária, 05508-900, São Paulo, SP, Brazil

(Received 6 March 2004 / Accepted 27 August 2004)

We investigate the evolution of oxygen- and carbon-rich AGB stars, post-AGB objects, and planetary nebulae using data collected mainly from the MSX catalogue. Magnitudes and colour indices are compared with those calculated from a grid of synthetic spectra that describe the post-AGB evolution beginning at the onset of the superwind. We find that carbon stars and OH/IR objects form two distinct sequences in the ( K-[8.3] $)
\times($ [8.3]-[14.7]) MSX colour diagram. OH/IR objects are distributed in two groups: the bluest ones are crowded near [14.7]-[ 21.3 $]\simeq 1$ and [8.3]-[ 14.7 $]\simeq 2$, and a second, redder group is spread over a large area in the diagram, where post-AGB objects and planetary nebulae are also found. High mass-loss rate OH/IR objects, post-AGB stars, and planetary nebulae share the same region in the ( K-[8.3] $)
\times($ [8.3]-[14.7]) and [14.7]-[ 21.3 $]\times($[8.3]-[14.7]) colour-colour diagrams. This region in the diagram is clearly separated from a bluer one where most OH/IR stars are found. We use a grid of models of post-AGB evolution, which are compared with the data. The gap in the colour-colour diagrams is interpreted as the result of the rapid trajectory in the diagram of the stars that have just left the AGB.

Key words: stars: AGB and post-AGB -- stars: circumstellar matter -- stars: evolution -- ISM: planetary nebulae: general -- infrared: stars

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© ESO 2005

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