The stellar IMF is one of the most important astrophysical distribution and plays vital role in galactic astronomy. Both constant and variable IMFs across different environments have been claimed despite a large number of theoretical and observational efforts. However, the measurement of the IMF in Galactic stellar populations has been limited by the relatively small number of photometrically observed stars, leading to high uncertainties.
In this talk, I will briefly introduce what we have known about IMF in sense of observation. Then, I will talk about how did we revisit the IMF using a star-counting approach based on approximately 93,000 spectroscopically observed M-dwarf stars, an order of magnitude more than previous studies, in the 100–300 parsec solar neighborhood. I will show unambiguous evidence, for the first time, of a variable IMF that depends on both metallicity and stellar age. The variable abundance of low-mass stars in our Milky Way establishes a powerful benchmark for models of star formation and can heavily affect results in Galactic chemical-enrichment modelling, mass estimation of galaxies and planet-formation efficiency. I near future, when the Chinese space station telescope (CSST) come to work, we expect that the IMF will be much better constrained by space-borne deep and accurate photometry observations for nearby resolved galaxies as well as the Milky Way.
