Distribution of stellar Hα chromospheric activity with
respect to stellar atmospheric parameters (effective temperature
Teff, surface gravity logg, and metallicity [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
Hα activity index (IHα) and the
HαR-index (RHα) are evaluated for the
MRS spectra. The Hα chromospheric activity distributions with
individual stellar parameters as well as in the Teff -- logg
and Teff -- [Fe/H] parameter spaces are analyzed based
on the RHα index data. It is found that: (1) for the
main-sequence sample, the RHα distribution with
Teff 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 RHα
distribution first increase with decrease of Teff and then drop to
a lower activity level at about 4300 K, revealing the different activity
characteristics at different stages of stellar evolution; (3) for both the
main-sequence and giant samples, the upper envelope of the
RHα distribution with metallicity is higher for stars with
[Fe/H] greater than about −1.0, and the lowest-metallicity stars
hardly exhibit high Hα indices. A dataset of Hα
activity indices for the LAMOST MRS spectra analyzed is provided with this
paper.Comment: 32 pages, 12 figures, 1 table, accepted for publication in
Astrophysics and Space Scienc