A combined spectroscopic and photometric stellar activity study of Epsilon Eridani

TL;DR

This study compares multiple methods, including a new spectroscopic-based approach, to distinguish stellar activity from planetary signals in the young star Epsilon Eridani using simultaneous RV and photometric data.

Contribution

It introduces the HH$'$ method that uses H$ extalpha$ measurements alone to model stellar activity, offering a potentially useful tool with minimal spectral data.

Findings

H$ extalpha$ measurements are strongly correlated with photometry.

The HH$'$ method shows promise but is less robust than existing methods.

Additional spectral indicators could enhance stellar activity modeling.

Abstract

We present simultaneous ground-based radial velocity (RV) measurements and space-based photometric measurements of the young and active K dwarf Epsilon Eridani. These measurements provide a data set for exploring methods of identifying and ultimately distinguishing stellar photospheric velocities from Keplerian motion. We compare three methods we have used in exploring this data set: Dalmatian, an MCMC spot modeling code that fits photometric and RV measurements simultaneously; the FF$'$ method, which uses photometric measurements to predict the stellar activity signal in simultaneous RV measurements; and H$\alpha$ analysis. We show that our H$\alpha$ measurements are strongly correlated with photometry from the Microvariability and Oscillations of STars (MOST) instrument, which led to a promising new method based solely on the spectroscopic observations. This new method, which we refer to as the HH$'$ method, uses H$\alpha$ measurements as input into the FF$'$ model. While the Dalmatian spot modeling analysis and the FF$'$ method with MOST space-based photometry are currently more robust, the HH$'$ method only makes use of one of the thousands of stellar lines in the visible spectrum. By leveraging additional spectral activity indicators, we believe the HH$'$ method may prove quite useful in disentangling stellar signals.