2022MNRAS.514.4398S

M dwarfs are the dominating type of stars in the solar neighbourhood. They serve as excellent tracers for the study of the distribution and properties of the nearby interstellar dust. In this work, we aim to obtain high accuracy reddening values of M dwarf stars from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Data Release 8 (DR8). Combining the LAMOST spectra with the high-quality optical photometry from the Gaia Early Data Release 3 (EDR3), we have estimated the reddening values E(G_BP - G_RP) of 641 426 M dwarfs with the machine learning algorithm random forest regression. The typical reddening uncertainty is only 0.03 mag in E(G_BP - G_RP). We have obtained the reddening coefficient R_(GBP_–GRP_), which is a function of the stellar intrinsic colour (G_BP - G_RP)₀ and reddening value E(B - V). The values of E(B - V) are also provided for the individual stars in our catalogue. Our resultant high accuracy reddening values of M dwarfs, combined with the Gaia parallaxes, will be very powerful to map the fine structures of the dust in the solar neighbourhood.