Metal Abundance Distribution Function Of G Dwarfs Near The Sun Based On LAMOST DR2

Studying the metallicity distribution function(MDF) of dwarfs in the Milky Way disk is important to understand its chemical and dynamical evolution. Cool stars, such as F, G and K dwarfs, are thought to have lifetimes greater than or equal to the age of our galaxy, so that these stars ever born in the galaxy have not yet evolved away from the main sequence. Measuring and studying the metallicity distribution function(MDF) of these cool stars can provide severe constrains on the disk’s star formation history and evolution. Naturaly, cooler stars than G dwarfs, such as K dwarfs or M dwarfs, have even longer lifetimes than that of G dwarfs. However, being less luminous, a sample based on K dwarfs or M dwarfs would be confined to smaller regions, and thus more subject to bias. So it is difficult to get a unbiased and complete sample.The Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST, also called Guo Shou Jing Telescope) can get 4000 objects with low-resolution spectra simultaneously in a single exposure. The Guo Shou Jing Telescope has a field of view as large as 20 square degrees, and at the same time a large effective aperture varying from 3.6 to 4.9 meters in diameter. The survey contains two main parts: the LAMOST Extra GAlactic Survey(LEGAS), and the LAMOST Experiment for Galactic Understanding and Exploration(LEGUE) survey of Milky Way stellar structure. We studied the metallicity distribution function(MDF) of G dwarfs in the solar neighbourhood based on the LAMOST Galactic survey.We studied the metallicity distribution function(MDF) for 282,217 G dwarfs in the solar neighbourhood based on the LAMOST DR2. Then we compared our derived distribution with the metallicity distribution function(MDF) obtained from the irfm sample, which was from Geneva-Copenhagen Survey of the Solar Neighbourhood(GCS) and a magnitude-complete, kinematically unbiased sample of 16682 nearby F and G dwarfs. We found that the G-dwarf metallicity distribution function of our sample presents higher fraction of metal-poor dwarfs than that of GCS. In conclusion,we believe that there maybe selection effects in the LAMOST Galactic survey when we study the metallicity distribution function(MDF) of G dwarfs in the solar neighbourhood.