Detalles de publicación
PP 015066
s-process enrichment in the planetary nebula NGC 3918. Results from deep echelle spectrophotometry
(1) IAC, Spain, (2) U. La Laguna, Spain, (3) U. West Georgia, USA, (4) IA-UNAM, Mexico)
The chemical content of the planetary nebula NGC3918 is investigated through deep, high-resolution (R∼40000) UVES at VLT spectrophotometric data.We identify and measure more
than 750 emission lines, making ours one of the deepest spectra ever taken for a planetary nebula. Among these lines we detect very faint lines of several neutron-capture elements (Se, Kr,
Rb, and Xe), which enable us to compute their chemical abundances with unprecedented accuracy,
thus constraining the efficiency of the s-process and convective dredge-up in NGC3918s
progenitor star. We find that Kr is strongly enriched in NGC3918 and that Se is less enriched
than Kr, in agreement with the results of previous papers and with predicted s-process nucleosynthesis. We also find that Xe is not as enriched by the s-process in NGC3918 as is Kr
and, therefore, that neutron exposure is typical of modestly sub-solar metallicity AGB stars.
A clear correlation is found when representing [Kr/O] vs. log(C/O) for NGC3918 and other
objects with detection of multiple ions of Kr in optical data, confirming that carbon is brought
to the surface of AGB stars along with s-processed material during third dredge-up episodes,
as predicted by nucleosynthesis models. We also detect numerous refractory element lines
(Ca, K, Cr, Mn, Fe, Co, Ni, and Cu) and a large number of metal recombination lines of C,
N, O, and Ne. We compute physical conditions from a large number of diagnostics, which
are highly consistent among themselves assuming a three-zone ionization scheme. Thanks to
the high ionization of NGC3918 we detect a large number of recombination lines of multiple
ionization stages of C, N, O and Ne. The abundances obtained for these elements by using
recently-determined state-of-the-art ICF schemes or simply adding ionic abundances are in
very good agreement, demonstrating the quality of the recent ICF scheme for high ionization
planetary nebulae.
than 750 emission lines, making ours one of the deepest spectra ever taken for a planetary nebula. Among these lines we detect very faint lines of several neutron-capture elements (Se, Kr,
Rb, and Xe), which enable us to compute their chemical abundances with unprecedented accuracy,
thus constraining the efficiency of the s-process and convective dredge-up in NGC3918s
progenitor star. We find that Kr is strongly enriched in NGC3918 and that Se is less enriched
than Kr, in agreement with the results of previous papers and with predicted s-process nucleosynthesis. We also find that Xe is not as enriched by the s-process in NGC3918 as is Kr
and, therefore, that neutron exposure is typical of modestly sub-solar metallicity AGB stars.
A clear correlation is found when representing [Kr/O] vs. log(C/O) for NGC3918 and other
objects with detection of multiple ions of Kr in optical data, confirming that carbon is brought
to the surface of AGB stars along with s-processed material during third dredge-up episodes,
as predicted by nucleosynthesis models. We also detect numerous refractory element lines
(Ca, K, Cr, Mn, Fe, Co, Ni, and Cu) and a large number of metal recombination lines of C,
N, O, and Ne. We compute physical conditions from a large number of diagnostics, which
are highly consistent among themselves assuming a three-zone ionization scheme. Thanks to
the high ionization of NGC3918 we detect a large number of recombination lines of multiple
ionization stages of C, N, O and Ne. The abundances obtained for these elements by using
recently-determined state-of-the-art ICF schemes or simply adding ionic abundances are in
very good agreement, demonstrating the quality of the recent ICF scheme for high ionization
planetary nebulae.