Elemental Abundance Study Of Stars In The Solar Neighbourhood

The elemental abundance of F and G dwarf stars in the solar neighbourhood which called Historical "living fossil" can show us the evolution of Galaxy,so it has great significance for us to study abundance of these stars.Our work is to observe stars like this and calculate and study elemental abundance in atmosphere of these F and G dwarfs,and know history and evolution of Galaxy at last.By use Xinglong 2.16 m telescope(Revolution≈40000) of NAOC,we get high revolution spectra of 100 stars from F and G dwarfs in the solar neigbourhood.We extract the spectra to one dimension and measure the equivalent widths by IRAF which provided by NAOC,then calculate elemental abundance of 13 elements of the100 stars combine with the Geneva-Copenhagen Survey(GCS) catalog with Kurucz local thermodynamic equilibrium model,and,the computing tool is ABUNTEST8 program package.And finally we obtained follow results:(1) We can not distinguish thin disk stars and thick disk by ɑelements(Mg,Si,Ca,Ti).Some thin disk stars have thick ɑ elements abundance and some thick disk stars have thin ɑ elements abundance.The mean value of abundance of thick disk is higher than thin disk,but at-0.7≤[Fe/H]≤-0.3,the ɑ elements abundance have severe mixing.(2) We can not divide thin disk and thick disk with oxygen abundance either.The mean value of oxygen abundance of thick disk stars higher than thin disk stars,and[O/Fe] shows a decreasing trend with the increase of [Fe/H]. There is a “knee”cut-down at [Fe/H]≈-0.3.(3) For the iron-group elements(Cr,Ni,Zn),their abundance have different trend.The abundance of Cr and Ni are nearly flat around their values in solar system.For the three elements,the abundance of thin disk stars and thick disk stars have obvious mixing.(4) [Na/Fe] have a trend like iron-group elements,at [Fe/H]≤-0.8,the thick disk stars likely have a decreasing trend with the decline of [Fe/H].[Al/Fe] trends similar as [ɑ/Fe],abundance of thick disk higher than it of thin disk.(5) For the neutron capture elements(Ba,Y),the abundance also have obvious mixing,and [Ba/Fe] have a trend similar as [Y/Fe].The abundance of thin disk stars higher than abundance of thick disk stars,and thin disk abundance has a greater dispersion.(6) We can not use average orbital radius Rm distinguish the thin disk stars and thick disk stars.There is a separation of [ɑ/Fe] at Rm=7kpc,but it also has mixing.On a statistical average,there is a separation of thin disk stars and thick disk stars.(7) There is not a obvious separation for [ɑ/Fe] at the maximum distance from the Galactic plane Zmax.Most thin disk stars distribution in Zmax≤1kpc,and thick stars widely distribution in 0<Zmax≤4kpc.(8) The age of thick disk stars on average higher than thin disk stars, but we can not find obvious trend of age of stellar and [Fe/H],but the abundance of ɑ elements increasing with the age of stars.All of these results show that though there is a different of elemental abundance of different group stars,but we still can’t separate them by abundance accurately.So we need more samples and more accurately parameters for us to study.