Variability of H$\hat{I}\pm$ chromospheric activity of solar-like stars revealed by the time-domain data of LAMOST Medium-Resolution Spectroscopic Survey

Abstract

The variability of H$\hat{I}\pm$ chromospheric activity of solar-like stars is investigated by using the time-domain data of LAMOST Medium-Resolution Spectroscopic Survey (MRS). We use $R_{\mathrm{H}\hat{\mathrm{I}}\pm }$ index (ratio of H$\hat{I}\pm$ luminosity to bolometric luminosity) to measure the H$\hat{I}\pm$ activity intensity of a spectrum, and utilize the median of the $R_{\mathrm{H}\hat{\mathrm{I}}\pm }$ values of multiple observations ($R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{median}}$) as the representative activity intensity of a stellar source. The H$\hat{I}\pm$ variability of a stellar source is indicated by the extent of $R_{\mathrm{H}\hat{\mathrm{I}}\pm }$ fluctuation ($R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{EXT}}$) of multiple observations. Our sample shows that $R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{EXT}}$ of solar-like stars is about one order of magnitude smaller than $R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{median}}$. The distribution of $\log R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{EXT}}$ versus $\log R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{median}}$ reveals the distinct behaviors between the stellar source categories with lower ($\log R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{median}}<-4.85$) and higher ($\log R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{median}}>-4.85$) activity intensity. For the former stellar source category, the top envelope of the distribution first increases and then decreases with $\log R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{median}}$; while for the latter category, the top envelope of the distribution is largely along a positive correlation line. In addition, for the stellar sources with lower activity intensity, the large-$\log R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{EXT}}$ objects near the top envelope of the $\log R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{EXT}}$ versus $\log R_{\mathrm{H}\hat{\mathrm{I}}\pm }^{\mathrm{median}}$ distribution tend to have long-term and regular variations of H$\hat{I}\pm$ activity; while for the stellar sources with higher activity intensity, the H$\hat{I}\pm$ variations are more likely to be random fluctuations.

43 pages, 19 figures, 2 tables, Accepted for publication in Astrophysics and Space Science