Empirically Interrelating Stellar Chromospheric Activity, Photometric Variability, and Radial Velocity Variations to Enhance Planet Discovery

Abstract

Because most extrasolar planets are detected indirectly via their influence on their host star, processes occurring on the surfaces of these stars are a significant impediment to planet detection: photometric “noise” and radial velocity “noise” can wash out or even mimic the signatures of extrasolar planets, particularly small ones like the Earth. The nature of this stellar noise is poorly understood but thought to be predominantly tied to the rotational modulation of magnetic spots. Recent high cadence, time-series photometric surveys, however, have complicated the picture by revealing a wide variety of stellar variations occurring at levels well below what we could probe before and hence very poorly characterized. We sought to analyze these newly discovered variations to quantitatively examine their potential impact on planet detection. We discover that they in fact trace the notoriously difficult to measure stellar surface gravity, yielding a simple and precise measurement of this quantity that can readily be obtained for thousands of stars. We find that they also correlate strongly with radial velocity noise; hence one can use the brightness variations to help prioritize radial velocity follow-up of interesting target stars. We also use our new surface gravity measurements to uncover an under-appreciated astrophysical bias that significantly affects ensemble studies of extrasolar planets from magnitude-limited surveys.