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

TL;DR

This study presents high-resolution spectroscopic observations of DM UMa, revealing unprecedented chromospheric emissions, phase-dependent activity variations, and potential flare events, advancing understanding of stellar activity in late-type stars.

Contribution

First detection of emissions above the continuum in He I D3 lines on DM UMa, providing new insights into its chromospheric activity and variability.

Findings

Detected strongest He I D3 emission ever in 2015.

Observed phase variations in chromospheric activity indicators.

Identified possible flare events or rotational modulation effects.

Abstract

We present new 14 high-resolution echelle spectra to discuss the level of chromospheric activity of DM UMa in {He I} D3, {Na I} D1, D2, Halpha, and {Ca II} infrared triplet lines (IRT). It is the first time to discover the emissions above the continuum in the {He I} 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 {Na I} D1, D2 lines, strong emission in the Halpha 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 Halpha line). These phenomena might be explained by flare events or rotational modulations of the level of chromospheric activity.