\(\mathrm{H}{\alpha }\) chromospheric activity of F-, G-, and K-type stars observed by the LAMOST medium-resolution spectroscopic survey

Abstract

The distribution of stellar \(\mathrm{H}\alpha \) chromospheric activity with respect to stellar atmospheric parameters (effective temperature \(T_{\mathrm{eff}}\), surface gravity \(\log \,g\), and metallicity \(\mathrm{[Fe/H]}\)) and main-sequence/giant categories is investigated for the F-, G-, and K-type stars observed by the LAMOST Medium-Resolution Spectroscopic Survey (MRS). A total of 329,294 MRS spectra from LAMOST DR8 are utilized in the analysis. The \(\mathrm{H}\alpha \) activity index (\(I_{\mathrm{H}{\alpha }}\)) and \(\mathrm{H}\alpha \) \(R\)-index (\({R_{\mathrm{H}{\alpha }}}\)) are evaluated for the MRS spectra. The \(\mathrm{H}\alpha \) chromospheric activity distributions with individual stellar parameters, as well as in the \(T_{\mathrm{eff}}\) – \(\log \,g\) and \(T_{\mathrm{eff}}\) – \(\mathrm{[Fe/H]}\) parameter spaces, are analyzed based on the \({R_{\mathrm{H}{\alpha }}}\) index data. It is found that: (1) for the main-sequence sample, the \({R_{\mathrm{H}{\alpha }}}\) distribution with \(T_{\mathrm{eff}}\) has a bowl-shaped lower envelope with a minimum at about 6200 K, a hill-shaped middle envelope with a maximum at about 5600 K, and an upper envelope continuing to increase from hotter to cooler stars; (2) for the giant sample, the middle and upper envelopes of the \(R_{\mathrm{H}{\alpha }}\) distribution first increase with a decrease of \(T_{\mathrm{eff}}\) and then drop to a lower activity level at about 4300 K, revealing different activity characteristics at different stages of the stellar evolution; (3) for both the main-sequence and giant samples, the upper envelope of the \(R_{\mathrm{H}{\alpha }}\) distribution with metallicity is higher for stars with \(\mathrm{[Fe/H]}\) greater than about −1.0, and the lowest-metallicity stars hardly exhibit high \(\mathrm{H}\alpha \) indices. A dataset of \(\mathrm{H}\alpha \) activity indices for the LAMOST MRS spectra analyzed is provided with this paper.