Study On Element Abundance Of C-H Stars And Identification Of CEMP Stars

The accurate and efficient determination of stellar atmosphere parameters is the key to carry out large-scale sky surveys for the purpose of galactic archaeology and stellar evolution history research.Accurate determination of stellar atmospheric parameters and element abundance plays an important role in many astrophysical fields.As carbon stars with increased abundance of carbon elements and neutron capture elements,C-H stars provide abundant information for studying the early nucleation process in galaxies.Based on 284 C-H stars with LAMOST low-resolution spectra with high signal-to-noise ratio,the stellar atmospheric parameters and Ba element abundance were determined.In addition,38 C-H stars with LAMOST resolution spectra were selected to re-determine the abundance of Ba elements and increased mearsuring the abundance of C and Eu elements.The effective temperature of C-H star was measured in the range of 4000-5600 K,with a wide distribution range and a peak value of 4800 K,belonging to G or K type.The mearsured surface gravity is mainly between 1.5 and 2.5 dex and there are a few stars larger than 3.5 dex,which also indicates that C-H stars are mainly giant or subgiant stars.The mearsured metallicity is concentrated between-0.6 and-3 dex,indicating that C-H star is metal-poor,which is consistent with the recognition that C-H star belongs to halo star.In the 38 C-H stars with medium resolution spectrum,the measurement results show that the abundance of C and Ba elements in most C-H stars is increased,which also verifies that C-H stars generally have the characteristics of s-process element abundance.However,the enrichment of Eu elements([Eu/Fe]>1.0)was a minority and most Eu elements showed the characteristic of weak enrichment,The abundance of C,Ba and Eu elements is negatively correlated with the metallicity.In the process of selecting CEMP star candidates from 38 C-H stars as samples,11 stars whose metallicity is less than-1 are removed first.Among the remaining 27C-H stars,8 have C element abundance that is not in conformity with CEMP star standards.Among the remaining 19 stars,we have recently certified 9 CEMP-s star candidates and 9 CEMP-r/s star candidates,but there are no candidates that meet the criteria of CEMP-r and CEMP-no stars.CEMP star candidates selected by us are more concentrated in high silver latitudes than C-H stars,which is consistent with the recognition that CEMP stars belong to older and lower metallicity members of C-H stars.In the follow-up,we will apply for high-resolution spectral observation for the selected 18 CEMP star candidates and use the high-resolution spectra to conduct detailed element abundance analysis,so as to further test the accuracy of our measured element abundance and the reliability of the selection method.