Observations and detectability of young Suns' flaring and CME activity in optical spectra

TL;DR

This study monitored young solar analogues over three years to detect flares and CMEs, finding limited activity but establishing upper limits on CME occurrence rates and assessing the detectability of solar-like events in optical spectra.

Contribution

It provides the first long-term spectroscopic monitoring of young solar analogues for flares and CMEs, and evaluates the detectability thresholds of such events in optical spectra.

Findings

Detected four flares and one filament eruption on EK Dra.

Established upper limits on CME occurrence rates from non-detections.

Demonstrated that solar-sized events are not detectable in the current observational setup.

Abstract

The Sun's history is still a subject of interest to modern astrophysics. Observationally constrained CME rates of young solar analogues are still lacking, as those require dedicated monitoring. We present medium resolution optical spectroscopic monitoring of a small sample of bright and prominent solar analogues over a period of three years using the 0.5m telescope at observatory Lustb\"uhel Graz (OLG) of the University of Graz, Austria. The aim is the detection of flares and CMEs from those spectra. In more than 1700 hours of spectroscopic monitoring we found signatures of four flares and one filament eruption on EK Dra which has been reported in previous literature, but we complementarily extended the data to cover the latter phase. The other stars did not reveal detectable signatures of activity. For these non-detections we derive upper limits of occurrence rates of very massive CMEs, which are detectable with our observational setup, ranging from 0.1 to 2.2 per day , but these may be even smaller than the given rates considering observational biases. Furthermore, we investigate the detectability of flares/CMEs in OLG spectra by utilizing solar 2D H{\alpha} spectra from MEES solar observatory. We find that solar-sized events are not detectable within our observations. By scaling up the size of the solar event, we show that with a fractional active region area of 18% in residual spectra and 24% in equivalent width time series derived from the same residuals that solar events are detectable if they had hypothetically occurred on HN Peg.