EXPRES. III. Revealing the Stellar Activity Radial Velocity Signature of $\epsilon$ Eridani with Photometry and Interferometry

Abstract

The distortions of absorption line profiles caused by photospheric brightness variations on the surfaces of cool, main-sequence stars can mimic or overwhelm radial velocity (RV) shifts due to the presence of exoplanets. The latest generation of precision RV spectrographs aims to detect velocity amplitudes $\lesssim 10$ cm s${}^{-1}$, but requires mitigation of stellar signals. Statistical techniques are being developed to differentiate between Keplerian and activity-related velocity perturbations. Two important challenges, however, are the interpretability of the stellar activity component as RV models become more sophisticated, and ensuring the lowest-amplitude Keplerian signatures are not inadvertently accounted for in flexible models of stellar activity. For the K2V exoplanet host $\epsilon$ Eridani, we separately use ground-based photometry to constrain Gaussian processes for modeling RVs and TESS photometry with a light-curve inversion algorithm to reconstruct the stellar surface. From the reconstructions of TESS photometry, we produce an activity model, which reduces the rms scatter in RVs obtained with EXPRES from 4.72 m s${}^{-1}$ to 1.98 m s${}^{-1}$. We present a pilot study using the CHARA Array and MIRC-X beam combiner to directly image the starspots seen in the TESS photometry. With the limited phase coverage, our spot detections are marginal with current data but a future dedicated observing campaign should allow for imaging, as well as the stellar inclination and orientation with respect to its debris disk to be definitely determined. This work shows that stellar surface maps obtained with high cadence, time-series photometric and interferometric data can provide the constraints needed to accurately reduce RV scatter.

24 pages, 12 figures, 5 tables, accepted for publication in AJ

References in corpus (29)

• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• SOAP 2.0: A tool to estimate the photometric and radial velocity variations induced by stellar spots and plages
• The Extrasolar Planet epsilon Eridani b - Orbit and Mass
• SONS: The JCMT legacy survey of debris discs in the submillimetre
• Three Years of HARPS-N High-Resolution Spectroscopy and Precise Radial Velocity Data for the Sun
• Radial-Velocity Fitting Challenge. II. First results of the analysis of the data set
• Magnetic Activity Cycles in the Exoplanet Host Star epsilon Eridani
• pyaneti II: A multidimensional Gaussian process approach to analysing spectroscopic time-series
• Separating planetary reflex Doppler shifts from stellar variability in the wavelength domain
• HARPS-N Solar Radial-Velocity Variations Are Dominated By Large, Bright Magnetic Regions
• Performance Verification of the EXtreme PREcision Spectrograph
• Insights on the Spectral Signatures of Stellar Activity and Planets from PCA
• An Extreme Precision Radial Velocity Pipeline: First Radial Velocities from EXPRES
• The Northern Arc of $\epsilon$ Eridani's Debris Ring as Seen by ALMA
• The limb-darkened Arcturus; Imaging with the IOTA/IONIC interferometer
• Mapping stellar surfaces II: An interpretable Gaussian process model for light curves
• Toward Extremely Precise Radial Velocities: II. A Tool For Using Multivariate Gaussian Processes to Model Stellar Activity
• Decoding the radial velocity variations of HD41248 with ESPRESSO
• EXPRES I. HD~3651 an Ideal RV Benchmark
• Contemporaneous Imaging Comparisons of the Spotted Giant $\sigma$ Geminorum Using Interferometric, Spectroscopic, and Photometric Data
• A combined spectroscopic and photometric stellar activity study of Epsilon Eridani
• Photometry as a proxy for stellar activity in radial velocity analyses
• Observing and modelling the young solar analogue EK Draconis: starspot distribution, elemental abundances, and evolutionary status
• Dynamical Surface Imaging of lambda Andromedae
• KOI-1003: A new spotted, eclipsing RS CVn binary in the Kepler field
• EXPRES. II. Searching for Planets Around Active Stars: A Case Study of HD 101501
• A Stellar Activity F-statistic for Exoplanet Surveys (SAFE)
• Observing the changing surface structures of the active K giant sigma Gem with SONG

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• The Lowell Observatory Solar Telescope: A fiber feed into the EXtreme PREcision Spectrometer
• Correlating Intrinsic Stellar Parameters with Mg II Self-Reversal Depths
• Flaring Latitudes in Ensembles of Low Mass Stars
• Radial velocity analysis of stars with debris discs
• SPORES-HWO. II. Companion Mass Limits and Updated Planet Properties for 120 Future Exoplanet Imaging Targets from 35 yr of Precise Doppler Monitoring
• Eighteen Exoplanet Host Stars from the NPOI Data Archive