Analysis On The Element Abundances And Stellar Populations Of Stars In The Solar Neighborhood

The Galactic disk is a major part of the Milky Way,the element abundance and kinematics characteristics of stars provide the main basis for the classification of stellar population.Specially,the F and G dwarfs in the solar neighborhood provide a complete sample for the high-resolution spectral analysis.The chemical abundances and their distributions provide the most direct observations for investigating the stellar populations and the chemical evolution of the Galactic disk.We selected a sample of F/G dwarfs from the catalogue of GCS(Geneva-Copenhagen Survey),and obtained the high-resolution(R>37,000)and high signal-to-noise ratio(S/N>100)stellar spectra using the 2.16 m telescope at the Xinglong Observatory Base of the National Astronomical Observatories and the 1.8m telescope at Lijiang Observatory Station of the Yunnan Astronomical Observatories.We measured the chemical abundances of 174 sample stars,including 13 elements such as Na,Mg,Zn,Y,Ba,etc.and the star population composition of the sample stars was determined by kinematics analysis,In the meantime,chemical abundance distribution,orbital parameters and stellar age distribution of different star population composition are discussed,and the following results are obtained.(1)The relative abundances of the four ? elements [Mg/Fe],[Si/Fe],[Ca/Fe] and [Ti/Fe]have the same general trend with the change of the metal abundances [Fe/H].However,the chemical abundances of Mg are higher in the metal-poor end than those of the other three elements Si,Ca and Ti,so the decreasing gradient is larger with the increase of [Fe/H];When the Fe/H> 0,the abundance of Mg and Ca will continue to decrease,while the abundance of Si and Ti will show a reversal trend with the increase of [Fe/H] in different degrees.(2)The [?/Fe] abundance of the thick disk stars is generally higher than that of the thin disk stars,but the [?/Fe] abundance of the thin disk stars and thick disk stars still exists a certain degree of crossover,there is no obvious abundance boundary.(3)The abundance of O element is significantly higher than that of the other four ?elements,and the [O/Fe] mixing between the thin and thick disk stars is more serious in kinematics,so it is almost indistinguishably.Another characteristic of [O/Fe] abundance is that the decreasing gradient of [Fe/H] with the increase of [Fe/H] is obviously larger than that of other ? elements,and there is a "knee jump" of accelerating decline at [Fe/H]=-0.5.(4)Three of iron group elements Cr,Ni,the abundance distribution of Zn and Fe elements,namely,[Cr/Fe] ? [Ni/Fe] and [Zn/Fe] abundance throughout the metallicity are within the scope of the average is almost zero,but the Cr and Zn element abundance of dispersion is relatively large,and Ni abundance less dispersion,and the thin disk and thick disk on the kinematics of stars in the three elements of iron group on the abundance of almost no difference.(5)The abundance distribution of odd Z element Na is complex.The [Na/Fe] in the thin disk stars varies with [Fe/H] similar to that of ? element Ti,and the [Na/Fe] in thick disk stars almost does not change with [Fe/H],which is similar to that of iron group elements.However,the [Na/Fe] in the thick disk stars is relatively overabundant with an average value of about0.1 dex.On the other hand,the abundance distribution of Al element is basically the same as that of ? element,and the kinematics of [Al/Fe] in the thick disk is obviously different from that in the thin disk,and the [Al/Fe] in thick disk is obviously higher than that in the thin disk.(6)The neutron capture elements Ba and Y are both s-process elements,and the most important characteristic of them is that the dispersion of [Ba/Fe] and [Y/Fe] is large,which reflects the complexity of their formation environment.In particular,the [Ba/Fe] of a the thick disk star at the metal-poor end [Fe/H],when [Fe/H] <-1.0,it decreases with the increase of[Fe/H],and when [Fe/H] >-1.0,it decreases with the increase of [Fe/H].The [Ba/Fe] of the thin disk stars increases with the increase of [Fe/H],but the dispersion is larger.The variation trend of [Y/Fe] with [Fe/H] is similar to that of [Ba/Fe].In addition,the [Ba/Fe] and [Y/Fe]mixing is also serious in the overlap region of the thick and thin disk star metallicity,so it is impossible to strictly distinguish the kinematic thick disk from thin disk in terms of abundance.(7)Our sample stars show an obvious age-metallicity relationship on the whole,and the age of the thick disk stars is higher than that of the thin disk stars on the whole,showing a decreasing trend of age with the increase of metallicity.(8)By kinematics standard of the thin disk and thick disk,the thin and thick disk of stars on the orbit direction of V speed can separate,but the thin disk and thick disk of stars on the radial velocity U can't distinguish,the thick disk is greater than the vertical speed of stars W thin disk of stars,show that the thick disk movement of the stars more far away from the Galactic disk,movement of the stars and the thin disk mainly near the Galactic disk,this is different from the two star family composition in the Rm-Zmax spatial distribution is consistent.In addition,the eccentricity e of the thick disk stars is generally greater than that of the thin disk stars,which further indicates that the orbits of the thick disk stars deviate from the Galactic disk and have higher ellipticity,while the orbits of the thin disk stars are closer to the circular orbits near the Galactic disk.(9)Our results show that the Galactic disk star radial metallicity gradient is discontinuous,the thin disk are mainly distributed in outside dish and negative radial metallicity gradient,and are mainly distributed in the thick disk inside dish and a positive radial metallicity gradient Method to the metallicity gradient distribution of Galactic disk is linear continuous,whether it is a thin disk or thick disk there are obvious negative normal metallicity gradients.(10)How to select the pure thick or thin disk star samples for us to further study the properties of the thick disk of stars is a key problem,our results show that the combination of pure kinematics and chemical abundance distribution([?/Fe]-[Fe/H])selected the thin disk and thick disk of stars in space position and age distribution also can distinguish clearly,is far less than the degree of mixing of pure kinematics results,show that this method can be used as an effective method to distinguish between the thick disk of stars.