Flare Activity and Magnetic Feature Analysis of the Flare Stars II: Sub-Giant Branch

TL;DR

This study analyzes magnetic activity and flare characteristics of sub-giant stars from Kepler data, revealing increased magnetic features and flares compared to main-sequence stars, with unique dependencies on stellar properties.

Contribution

It provides a comparative analysis of magnetic activity and flares between sub-giant and main-sequence stars, highlighting differences in magnetic behavior and dependencies.

Findings

Magnetic features and flares increase on the SGB due to deeper convective zones.

Magnetic activity in SGB F and G stars does not depend on rotation rate.

Magnetic proxies and flare indexes increase with the convective zone mass.

Abstract

We present an investigation of the magnetic activity and flare characteristics of the sub-giant stars mostly from F and G spectral types and compare the results with the main-sequence (MS) stars. The light curve of 352 stars on the sub-giant branch (SGB) from the Kepler mission is analyzed in order to infer stability, relative coverage and contrast of the magnetic structures and also flare properties using three flare indexes. The results show that: (i) Relative coverage and contrast of the magnetic features along with rate, power and magnitude of flares increase on the SGB due to the deepening of the convective zone and more vigorous magnetic field production (ii) Magnetic activity of the F and G-type stars on the SGB does not show dependency to the rotation rate and does not obey the saturation regime. This is the opposite of what we saw for the main sequence, in which the G-, K- and M-type stars show clear dependency to the Rossby number; (iii) The positive relationship between the magnetic features stability and their relative coverage and contrast remains true on the SGB, though it has lower dependency coefficient in comparison with the MS; (iv) Magnetic proxies and flare indexes of the SGB stars increase with increasing the relative mass of the convective zone.