# Stellar Properties of Active G and K Stars: Exploring the Connection Between Starspots and Chromospheric Activity

## TL;DR

This study analyzes the connection between starspots and chromospheric activity in 55 G and K stars using high-resolution spectra, revealing that more active stars tend to have higher spot covering fractions, with implications for stellar magnetic activity.

## Contribution

It introduces a spectral modeling method to estimate starspot covering fractions and demonstrates the importance of precise stellar colors in these inferences.

## Key findings

- Spot covering fractions increase with chromospheric activity.
- Stars with low activity rarely have large spot coverages.
- Spectral modeling effectively estimates starspot coverage.

## Abstract

We gathered high resolution spectra for an ensemble of 55 bright active and inactive stars using the ARC 3.5 m Telescope Echelle Spectrograph at Apache Point Observatory ($R\approx$31,500). We measured spectroscopic effective temperatures, surface gravities and metallicities for most stars in the sample with SME and MOOG. Our stellar property results are consistent with the photometric effective temperatures from the Gaia DR2 pipeline. We also measured their chromospheric $S$ and $\log R^\prime_\mathrm{HK}$ indices to classify the stars as active or inactive and study the connection between chromospheric activity and starspots. We then attempted to infer the starspot covering fractions on the active stars by modeling their spectra as a linear combination of hot and cool inactive stellar spectral templates. We find that it is critical to use precise colors of the stars to place stringent priors on the plausible spot covering fractions. The inferred spot covering fractions generally increase with the chromospheric activity indicator $\log R^\prime_\mathrm{HK}$, though we are largely insensitive to spot coverages smaller than $f_S \lesssim 20$%. We find a dearth of stars with small $\log R^\prime_\mathrm{HK}$ and significant spot coverages.