M dwarf stars are very-low mass stars with reddish color. Their masses are only 0.1-0.6 times the solar mass, and their temperature is about 2000-3000 degrees lower than that of the Sun. 

Although M dwarf stars are small, they account for about 70% of the total number of stars in the Milky Way, dominating the faint magnitudes of the Galaxy. 

Based on the LAMOST low-resolution spectra, a new study led by Ph.D. Candidate LI Jiadong and Prof. LIU Chao from National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) has estimated the stellar parameters (effective temperature and metallicity) of about 300,000 M dwarf stars, providing the largest spectroscopic M dwarf stellar parameter catalog. 

The study was published in The Astrophysical Journal Supplement Series on April 9.

Fig.1 Imagining red dwarfs. (Image from https://www.space.com/23772-red-dwarf-stars.html) 

By studying the mass distribution of M dwarf stars and whether it varies with their environment such as metallicity and cosmic time, we can better understand the issues of star formation and galaxy evolution. Moreover, they can even help us gain a deeper understanding of how many obscure low-mass faint objects exist in the masses of unobserved galaxies. 

Because M dwarf stars have lifetime longer than the age of the universe, they can characterize multiple stellar populations with various ages and metal abundances. In addition, these stars are also the main type of stars in the search for exoplanet habitability. 

Using the catalog of APOGEE survey and the BT-Settl stellar atmosphere template, the researchers accurately measured the effective temperatures and metallicities of about 300,000 LAMOST-observed M dwarfs with the SLAM algorithm proposed by Dr. ZHANG Bo and Prof. LIU Chao. The precisions were in good agreement with those from different surveys. 

Fig. 2 Left: comparison between the metallicity determined in this work and the [Fe/H] from OCCAM survey. Right: distribution of the [M/H] difference. (Image by LI Jiadong) 

This work provides the first large and homogeneous spectroscopic M dwarf sample. "We hope our catalog will help future studies on the evolution of the Milky Way and galactic archaeology, the exoplanet search, and the initial mass function," said LI Jiadong, the first author of the study. 

"The paper is interesting, and I suspect these large catalogs will be increasingly useful with time," commented by an anonymous referee of the paper.