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08 (08.01.1; 08.01.3; 08.16.4; 08.09.2 IRAS 04296+3429 )

V.G. Klochkova

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

The peculiar post-AGB supergiant IRAS04296+3429:
optical spectroscopy and its spectral energy distribution

V.G.Klochkova¹, R.Szczerba², V.E.Panchuk¹, K.Volk³

Received...... / Accepted......

Abstract:

The optical spectrum of the infrared source IRAS04296+3429 (optical counterpart - G0Ia star, V=14.2) was obtained with the echelle spectrometer PFES at the prime focus of the 6m telescope. We discover emission bands (0,0) and (0,1) of the Swan system of the ${\rm C_2}$ molecule in the optical spectrum of IRAS04296+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 ${\rm C_2}$ molecular bands.

Several strong absorptional features whose positions coincide with known diffuse interstellar bands (DIBs) are revealed in the spectrum of IRAS04296+3429.

The infrared spectrum of IRAS04296+3429 shows the famous 21${\mu}$m feature (Kwok et al. 1989), but this object has not been observed by KAO (Omont et al. 1995). However, like IRAS05113+1347, IRAS05341+0852 and IRAS22223+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${\mu}$m band. In fact, ISO discovered a broad, relatively strong feature around 30${\mu}$m for IRAS04296+3429 (Szczerba et al. 1998, in preparation).

The surface chemical composition of the source IRAS04296+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 ${\rm [M/H]_{\odot}\,= \,-0.9}$) 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 IRAS04296+3429 confirms a relation between presence of the feature at 21${\mu}$m in the spectrum of a carbon rich star and an excess of the s-process elements.

Stars: abundances - Stars: atmospheres - Stars: AGB and post-AGB - Stars: individual: IRAS04296+3429