Quiet Please: Detrending Radial Velocity Variations from Stellar Activity with a Physically Motivated Spot Model

For solar-type stars, spots and their associated magnetic regions induce radial velocity perturbations through the Doppler rotation signal and the suppression of convective blueshift, collectively known as rotation modulation. We developed the Rotation–Convection (RC) model: a method of detrending a...

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Bibliographic Details
Published in:The Astronomical journal 2024-10, Vol.168 (4), p.158
Main Authors: Siegel, Jared C., Halverson, Samuel, Luhn, Jacob K., Zhao, Lily L., Al Moulla, Khaled, Robertson, Paul, Bender, Chad F., Terrien, Ryan C., Roy, Arpita, Mahadevan, Suvrath, Hearty, Fred, Ninan, Joe P., Wright, Jason T., Ford, Eric B., Schwab, Christian, Stefánsson, Guðmundur, Blake, Cullen H., McElwain, Michael W.
Format: Article
Language:English
Subjects:
Amplitudes
Blue shift
Convection
Correlation
Exoplanet detection methods
Extrasolar planets
Modulation
Perturbation
Planet detection
Radial velocity
Rotation
Solar activity
Solar observatories
Stellar activity
Stellar atmospheres
Velocity
Wavelengths
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Summary:For solar-type stars, spots and their associated magnetic regions induce radial velocity perturbations through the Doppler rotation signal and the suppression of convective blueshift, collectively known as rotation modulation. We developed the Rotation–Convection (RC) model: a method of detrending and characterizing rotation modulation using only cross–correlation functions or one-dimensional spectra without the need for continuous high-cadence measurements. The RC method uses a simple model for the anomalous radial velocity induced by an active region and has two inputs: stellar flux (or a flux proxy) and the relative radial velocity between strongly and weakly absorbed wavelengths (analogous to the bisector–inverse slope). On NEID solar data (3 month baseline), the RC model lowers the amplitude of rotationally modulated stellar activity to below the meter–per–second level. For the standard star HD 26965, the RC model detrends the activity signal to the meter–per–second level for HARPS, EXPRES, and NEID observations, even though the temporal density and time span of the observations differ by an order of magnitude between the three data sets. In addition to detrending, the RC model also characterizes the rotation–modulation signal. From comparison with the Solar Dynamics Observatory, we confirmed that the model accurately recovers and separates the rotation and convection radial velocity components. We also mapped the amplitude of the rotation and convection perturbations as a function of height within the stellar atmosphere. Probing stellar atmospheres with our revised spot model will fuel future innovations in stellar activity mitigation, enabling robust exoplanet detection.
ISSN:0004-6256
1538-3881
DOI:10.3847/1538-3881/ad6768