Determination The Parameters Of Post-AGB Stars And The Fraction Of Ba Isotopes

Neutron capture process is mainly divided into slow neutron and fast neutron capture process.In recent years,it has been suggested that there is a process between the two,namely the intermediate process?i-process?.The astrophysical site of i-process is still unclear.From the perspective of observation,the intermediate processes are all related to AGB star,but they are not supported by the relevant star evolution theory.Many questions remain about the i-process and need further discussion.At present,in the study of neutron capture nuclearsynthesis related to the enrichment of neutron capture elements in stars,the abundance of element is used as the observed constraint,but there are limitations.Because the same abundance can actually correspond to different isotopic proportional combinations.Isotopes can provide us with more stringent observation constraints.In order to obtain more reliable information about the process of neutron capture nuclear synthesis,it is necessary to carry out relevant research from the isotope.Post-AGB stars are generally considered as the astrophysical site where the i-process may occur,and r/s stars are suggested to be formed by the i-process.Therefore,we selected two post-AGB stars with r/s star characteristics as the samples:IRAS 08143-4406,IRAS14325-6428.The atmospheric parameters of the two post-AGB stars IRAS 08143-4406 and IRAS 14325-6428 were measured by spectroscopic method.The atmospheric parameters are T_eff=6800K,log g=0.6dex,[Fe/H]=-0.66,?=4.5km/s and T_eff=7800K,log g=1.2dex,[Fe/H]=0.71,?=5.2 km/s.The determination of atmospheric parameters of stars,we optimized the process of measuring atmospheric parameters,and carried out zero point correction for the gf value of each iron line.That is to say,the contour of the iron line in the solar spectrum was fitted by the solar iron abundance,which was the final gf value?namely the solar gf value?,guaranteeing the reliability of our measurement results to the greatest extent.For barium abundance,two secondary spectral lines 5853?and 6496?are used to obtain consistent results.The determination of the barium abundance of two stars,we considered the influence of non-local thermal dynamic equilibrium effect,which made our results more reliable.The resonance spectral line 4554?is split into multiple spectral lines under the influence of hyperfine structure.Under the condition that the abundance value ofelementbariumremains unchanged,the resonance spectral line 4554?is fitted and the chi-square test is used to obtain the best spectral line fitting,so as to obtain the odd-even isotope ratio ofelement barium.Due to the poor signal-to-noise ratio of the blue end of IRAS 08143-4406 spectrum,the resonance spectral line 4554?is severely mixed,and the isotope ratio cannot be determined.We measured the isotope ratio of IRAS 14325-6428 to be 0.40?0.06,which means that the neutron capture process in the post-AGB star was basically consistent with the r-process in termsofobservationcharacteristics.Wecalculatethatthecontributionofr-processis82.7?17.3%.The high[Ba/H]of IRAS 14325-6428 indicates that this star is an intrinsic AGB star,and the s-process elements were synthesized internally during its early AGB stage and brought to the surface of the star by the third dredge-up.We further inferred that the enrichment of heavy elements in post-AGB IRAS 14325-6428 is caused by the i-process,which has the characteristics similar to that of the r-process at least at the isotope level.