A comparative study of two X2.2 and X9.3 solar flares observed with HARPS-N. Reconciling Sun-as-a-star spectroscopy and high-spatial resolution solar observations in the context of the solar-stellar connection

Vol. 682
9. The Sun and the Heliosphere

A comparative study of two X2.2 and X9.3 solar flares observed with HARPS-N. Reconciling Sun-as-a-star spectroscopy and high-spatial resolution solar observations in the context of the solar-stellar connection

By virtue of its proximity, the Sun has always been observed and treated differently than the more distant exemplars. However, with advances in detectors and spectrographs, it has become increasingly more feasible to obtain a similar level of information for more remote systems. The "Sun as a star" approach of this study treated observations of two X-class flares (those with fluences of Nx10³¹ erg) observed with the same instrumentation that has been used for TESS and Kepler spectroscopy for which the flares have been up to 100 times the dissecting total energy of the solar cases. The HARPS-N spectra were sampled with a five-minute cadence at a resolution of 10⁵, precisely as for the stellar observations. The authors used a range of line probes of the events, dissecting the line profile and intensity variations to create similar indices to the stellar case for, for instance, the Balmer, He I (no variations detected), Na In (line asymmetries noted but otherwise no detected variability), and Ca II (distinct flare-strength-dependent variations with a different duration) lines and radial velocity measurements of the profile to a stability of better than 10 m/s. The authors discuss other features of the events that can be targeted for this sort of comparative measurement. The paper is a pioneering illustration of a new approach to unraveling the activity-related phenomena on solar-type stars.