Chromospheric activity on late-type star DM UMa using high-resolution spectroscopic observations

Abstract

We present new 14 high-resolution echelle spectra to discuss the level of chromospheric activity of DM UMa in HeI, D3, NaI D1, D2, Hα, and CaI, infrared triplet lines (IRT). It is the first time to discover the emissions above the continuum in the HeI, D3 lines on 2015 February 9 and 10. The emission on February 9 is the strongest one ever detected for DM UMa. We analysed these chromospheric active indicators by employing the spectral subtraction technique. The subtracted spectra reveal weak emissions in the NaI, D1, D2 lines, strong emission in the Hα line, and clear excess emissions in the CaI, IRT lines. Our values for the EW8542EW8498 ratio are on the low side, in the range of 1.0-1.7. There are also clear phase variations of the level of chromospheric activity in equivalent width (EW) light curves in these chromospheric active lines (especially the Hα line). These phenomena might be explained by flare events or rotational modulations of the level of chromospheric activity.