PREDNASAJUCI / LECTURER :

Július Koza

(1) Astronomical Institute, Slovak Academy of Sciences,
059 60 Tatranská Lomnica

NAZOV / TITLE :

From the Sun to the Stars: Synthesizing Sun-as-a-Star Observations of Flares

ABSTRAKT / ABSTRACT :

The topic of "the Sun as a star" has seen a substantial revival in the context
of exoplanet research and planetary habitability, particularly regarding the
impact of stellar flares, filament eruptions, and coronal mass ejections on
exoplanetary environments. A key question is whether stellar flare spectroscopy
can provide a reliable estimate of the energy that an exoplanet receives during
a flare. Our results suggest that it can.

We propose an energy-scaling law for Sun-like stars, based on chromospheric line
intensities, showing that the peak flare-to-pre-flare contrast in these lines
scales approximately with the square root of the flare’s bolometric energy. To
establish this, we produced and analyzed synthetic full-disk spectra derived from
19 small-field-of-view optical observations of solar flares obtained with the
Swedish 1-m Solar Telescope (SST) between 2011 and 2024. Using the Numerical
Empirical Sun-as-a-Star Integrator, which generates full-disk integrated spectral
line emission from smaller field-of-view inputs while accounting for center-to-limb
variations and differential rotation, we produced pseudo-Sun-as-a-star spectra from
the SST observations. We demonstrate that limited-area solar observations can be
extrapolated to accurately represent the full solar disk, closely matching what is
achievable with dedicated Sun-as-a-star instruments. Notably, we identify a
relationship between the heliocentric angle of flares and the width of their excess
emission, as well as a potential source of false-positive coronal mass ejection
signatures.