1999A&A...345..905K

The optical spectrum of the infrared source IRAS 04296+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 C₂ 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 C₂ 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 21µm feature (Kwok et al., 1989ApJ...345L..51K), but this object has not been observed by KAO (Omont et al., 1995ApJ...454..819O). However, like IRAS 05113+1347, IRAS 05341+0852 and IRAS22223+4327 (Kwok et al., 1995ApJ...454..394K, Szczerba et al., 1996, In: Kaufl H.U., Siebenmorgen R. (eds) ESO Workshop, The role of dust in formation of stars. p. 95), our detailed modelling of its spectral energy distribution suggested that this source also should show the 30µm band. In fact, ISO discovered a broad, relatively strong feature around 30µm for IRAS 04296+3429 (Szczerba et al., 1999, A&A, submitted). 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 [M/H]_☉=-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 IRAS 04296+3429 confirms a relation between presence of the feature at 21µm in the spectrum of a carbon rich star and an excess of the s-process elements.