The Galactic Disk Structure Revealed By The Distribution Of [?/Fe] Ratios In The LAMOST Red-clump Stars

The Galactic disk is the main component of the Milky Way,it is very important to study its sub-structure and their formation and evolution mechanism for understanding of the formation and evolution of the Galaxy.The Galactic disk consists of different stellar populations,the elemental abundances of the disk stars can be used as a probe to track the chemical evolution of the Galaxy,and the spatial position distributions of disk stars can reveal the sub-structure of the Galactic disk.The large number of stellar spectra observed from the LAMOST?The Large Sky Area Multi-Object Fibre Spectroscopic Telescope?-survey provides a complete and ideal sample for us to explore the structure of the Galactic disk and the stellar populations.We use 96,290 primary red clump?RC?stars,selected from the DR4 of LAMOST survey,as our research sample.Firstly,we divided the whole RC sample stars into four sub-samples?i.e.,the mono-abundance populations,MAPs?according to the distributions of[?/Fe]ratios with metallicity[Fe/H].Then,using star counting method,we calculated the stellar number densities in each of the individual MAPs and fit the vertical and radial density profiles of each MAP to investigate the structure of the Galactic disk.Our paper consists of six parts.The first chapter introduces the background of our research subject,including the latest progress of the studies on the structure of the Galactic disk,problems to be solved,the research purpose and the text structure of our paper.The second chapter introduces the method of sample selection and the data adopted,as well as the partition of four sub-samples and their distribution in the three-dimensional position space.In the third chapter,firstly,the selection effect is corrected to achieve the spatial completeness of samples;then the spatial density points of the four subsamples are divided,and the scale heights and the scale lengths are calculated according to the density model of stars;finally,we give our results including of the stellar number density distributions in R-Z space and the vertical density and radial density profiles of the four subsamples In the fourth chapter,we discussed our results by means of comparing them with previous results and combining them with kinematics characteristics.In the fifth chapter,we summarize the research results and give our research conclusion.Our results show that:?1?The galactic disk is composed of a thick disk with high-[?/Fe]and a thin disk with low-[?/Fe];?2?Both the thin disk and the thick disk have obvious flaring phenomenon;?3?The vertical density profile of the thick disk and the thin disk is obviously distinguished,the scale heights of the thick disk increases steadily with the increase of R,while that of the thin disk increases exponentially with the increase of R;?4?The radial surface density profile of the four sub-samples cannot be fitted by a single exponential model,but a broken exponential model with a peak radius R_peakeak is needed to fit,and the peak radius of the sub-sample with high-[?/Fe]element abundance is at R_peak=7 kpc,while that of the sub-samples with low-[?/Fe]element abundance are at R_peak=8 kpc;?5?the sub-samples with high-[?/Fe]metallicity are more consistent with the thick disk with high[?/Fe]in spatial distribution and kinematics.