White dwarf-main sequence (WDMS) binaries are used to study several different important open problems in modern astrophysics. The Sloan Digital Sky Survey (SDSS) identified the largest catalogue of WDMS binaries currently known. However, this sample is seriously affected by selection effects and the population of systems containing cool white dwarfs and early-type companions is under-represented. Here we search for WDMS binaries within the spectroscopic data release 1 of the LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) survey. LAMOST and SDSS follow different target selection algorithms. Hence, LAMOST WDMS binaries may be drawn from a different parent population and thus help in overcoming the selection effects incorporated by SDSS on the current observed population. Here, we develop a fast and efficient routine based on the wavelet transform to identify LAMOST WDMS binaries containing a DA white dwarf and a M dwarf companion, and apply a decomposition/fitting routine to their LAMOST spectra to estimate their distances and measure their stellar parameters, namely the white dwarf effective temperatures, surface gravities and masses, and the secondary star spectral types. Finally, we identify 121 LAMOST WDMS binaries, 80 of which are new discoveries, and estimate the sample to be ∼90 per cent complete. The LAMOST and SDSS WDMS binaries are found to be statistically different. However, this result is not due to the different target selection criteria of both surveys, but likely a simple consequence of the different observing conditions. Thus, the LAMOST population is found at considerably shorter distances (∼50–450 pc) and is dominated by systems containing early-type companions and hot white dwarfs. Even though WDMS binaries containing cool white dwarfs are also missed by the LAMOST survey, the LAMOST WDMS binary sample dominated by systems containing early-type companions is an important addition to the current known spectroscopic catalogue. Future LAMOST observations however are required to increase the small number of LAMOST WDMS binaries. The results have been published in the latest volume of the well-known  international astronomical  journal Astronomical Journal.

Fig. From top to bottom: normalised distribution (solid line for LAMOST DA/M binaries, dashed line for SDSS DA/M binaries) of distance, white dwarf mass, effective temperature and surface gravity, spectral type of the companion star and g-r colour. Kolmogorov-Smirnov probabilities resulting from comparing the stellar parameter determinations from both samples are indicated in the right panels. We can see that, the LAMOST DA/M binary population is betweenness ~50-450pc and is dominated by systems containing hot white dwarfs and early-type companions.