Active stars in the LAMOST-K2 field

After the training on the spectra of the selected inactive stars, the VAE model can efficiently generate the synthetic reference templates needed by the spectral subtraction procedure, without knowing any stellar parameters. Then, we detect the peculiar spectral features, such as chromospheric emissions, strong nebular emissions, and lithium absorptions, in our sample.

We measure the emissions of the chromospheric activity indicators, H{alpha} and CaII infrared triplet (IRT) lines, to quantify the stellar magnetic activity. The excess emissions of H{alpha} and CaII IRT lines of the active stars are correlated well to the rotational periods and the amplitudes of light curves derived from the K2 photometry. We degrade the LAMOST spectra to simulate the slitless spectra of the China Space Station Telescope (CSST) and apply the VAE to the simulated data.