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Astron. Astrophys. 345, 905-914 (1999)

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The peculiar post-AGB supergiant IRAS 04296+3429: optical spectroscopy and its spectral energy distribution

V.G. Klochkova 1, R. Szczerba 2, V.E. Panchuk 1 and K. Volk 3

1 Special Astrophysical Observatory, N.Arkhyz, 357147 Russia
2 N. Copernicus Astronomical Center, PL-87-100 Toru, Poland
3 The University of Calgary, Calgary, Alberta T2N 1N4, Canada

Received 8 April 1998 / Accepted 5 March 1999

Abstract

The optical spectrum of the infrared source IRAS 04296+3429 (optical counterpart - G0 Ia star, V = 14.2) was obtained with the echelle spectrometer PFES at the prime focus of the 6 m telescope. We discover emission bands (0,0) and (0,1) of the Swan system of the [FORMULA] molecule in the optical spectrum of IRAS 04296+3429. Comparison with the spectrum of the Hale-Bopp comet leads us to propose that in both cases the same mechanism (resonance fluorescence) is responsible for the emission in the [FORMULA] molecular bands.

Several strong absorption features whose positions coincide with known diffuse interstellar bands (DIBs) are revealed in the spectrum of IRAS 04296+3429.

The infrared spectrum of IRAS 04296+3429 shows the famous 21 µm feature (Kwok et al. 1989), but this object has not been observed by KAO (Omont et al. 1995). However, like IRAS 05113+1347, IRAS 05341+0852 and IRAS 22223+4327 (Kwok et al. 1995, Szczerba et al. 1996), our detailed modelling of its spectral energy distribution suggested that this source also should show the 30 µm band. In fact, ISO discovered a broad, relatively strong feature around 30 µm for IRAS 04296+3429 (Szczerba et al. 1999).

The surface chemical composition of the source IRAS 04296+3429 is metal-deficient (the averaged value of the abundances of the iron group elements Ti, V, Cr and Fe relative to the solar values is [FORMULA]) and has been considerably altered during the evolution: carbon, nitrogen and s-process elements are overabundant relative to the metallicity.

The totality of physical and chemical parameters derived for IRAS 04296+3429 confirms a relation between presence of the feature at 21 µm in the spectrum of a carbon rich star and an excess of the s-process elements.

Key words: stars: abundances – stars: AGB and post-AGB – stars: individual: IRAS 04296+3429

Send offprint requests to: V.G. Klochkova (valenta@sao.ru)

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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999
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