南方基地知识库

We present new 14 high-resolution echelle spectra to discuss the level of chromospheric activity of DM UMa in He I D-3, Na I D-1, D-2, H alpha, and Ca II infrared triplet lines (IRT). It is the first time to discover the emissions above the continuum in the He I D-3 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 Na I D-1, D-2 lines, strong emission in the Ha line, and clear excess emissions in the Ca II IRT lines. Our values for the EW8542/EW8498 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 Ha line). These phenomena might be explained by flare events or rotational modulations of the level of chromospheric activity.