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The present work presents our efforts at identifying new mercury-manganese(HgMn/CP3) stars using spectra obtained with the Large Sky Area Multi-ObjectFiber Spectroscopic Telescope (LAMOST). Suitable candidates were searched foramong pre-selected early-type spectra from LAMOST DR4 using a modified versionof the MKCLASS code that probes several Hg II and Mn II features. The spectraof the resulting 332 candidates were visually inspected. Using parallax dataand photometry from Gaia DR2, we investigated magnitudes, distances from theSun, and the evolutionary status of our sample stars. We also searched forvariable stars using diverse photometric survey sources. We present 99 bonafide CP3 stars, 19 good CP3 star candidates, and seven candidates. Our sampleconsists of mostly new discoveries and contains, on average, the faintest CP3stars known (peak distribution 9.5 < G < 13.5 mag). All stars are containedwithin the narrow spectral temperature-type range from B6 to B9.5, in excellentagreement with the expectations and the derived mass estimates (2.4 < M(Sun) <4 for most objects). Our sample stars are between 100 Myr and 500 Myr old andcover the whole age range from zero-age to terminal-age main sequence. They arealmost homogeneously distributed at fractional ages on the main sequence < 80%,with an apparent accumulation of objects between fractional ages of 50% to 80%.We find a significant impact of binarity on the mass and age estimates. Eightphotometric variables were discovered, most of which show monoperiodicvariability in agreement with rotational modulation. Together with the recentlypublished catalogue of APOGEE CP3 stars, our work significantly increases thesample size of known Galactic CP3 stars, paving the way for future in-depthstatistical studies.

New mercury-manganese stars and candidates from LAMOST DR4