1998/01/14 by L. Decin, Leen Decin, Hans Van Winckel +7
Physics and Astronomy · #Astro and Planetary Science #Astronomy and Astrophysical Research #Astrophysics (astro-ph) #FOS: Physical sciences #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9801134
12 pages, 8 figures Accepted A&A
arxiv created 1998/01/14 · openalex publication_date 1998/01/14 · arxiv updated 2009/12/01 · openalex created_date 2019/06/27 · openalex updated_date 2026/07/28
We present a detailed chemical analysis on the basis of high-resolution, high signal-to-noise optical spectra of two post-AGB objects IRAS 22223+4327 and IRAS 04296+3429. Both display the unidentified 21 μm feature in their IR-spectra. The spectroscopic indicators provide accurate atmospheric parameters of Teff=6500 K, log g=1.0 and ξt = 5.5 km/s for IRAS 2223+4327 and Teff=7000 K, log g=1.0 and ξt = 4.0 km/s for IRAS 04296+3429. Both photospheres are found to be metal-deficient with [Fe/H]= -0.4 and -0.7 respectively. C and N are found to be overabundant. The mean abundance of all the measured s-process-elements is [s/Fe]=+1.0 for IRAS 2223+4327 and +1.4 for IRAS 04296+3429. The distribution of the s-process elements can best be described as due to a distribution of neutron exposures with a low mean neutron exposure of τ0 = 0.2 mbarn-1. The 21 μm stars form an interesting sub-group in the total post-AGB sample of stars, not only for their IR characteristics, but also in a broader context of stellar (chemical) evolution theory. They show, in contrast to other post-AGB stars, that the 3rd dredge-up has been efficient during their AGB evolution. The mean neutron exposure is lower than expected for their metallicity.