A combined spectroscopic and photometric stellar activity study of Epsilon Eridani

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${}^{\prime }$ 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${}^{\prime }$ method, uses H$\alpha$ measurements as input into the FF${}^{\prime }$ model. While the Dalmatian spot modeling analysis and the FF${}^{\prime }$ method with MOST space-based photometry are currently more robust, the HH${}^{\prime }$ 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${}^{\prime }$ method may prove quite useful in disentangling stellar signals.

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