Kavli Affiliate: Andrew Vanderburg
| First 5 Authors: Lily L. Zhao, Debra A. Fischer, Eric B. Ford, Alex Wise, Michaël Cretignier
| Summary:
Measured spectral shifts due to intrinsic stellar variability (e.g.,
pulsations, granulation) and activity (e.g., spots, plages) are the largest
source of error for extreme precision radial velocity (EPRV) exoplanet
detection. Several methods are designed to disentangle stellar signals from
true center-of-mass shifts due to planets. The EXPRES Stellar Signals Project
(ESSP) presents a self-consistent comparison of 22 different methods tested on
the same extreme-precision spectroscopic data from EXPRES. Methods derived new
activity indicators, constructed models for mapping an indicator to the needed
RV correction, or separated out shape- and shift-driven RV components. Since no
ground truth is known when using real data, relative method performance is
assessed using the total and nightly scatter of returned RVs and agreement
between the results of different methods. Nearly all submitted methods return a
lower RV RMS than classic linear decorrelation, but no method is yet
consistently reducing the RV RMS to sub-meter-per-second levels. There is a
concerning lack of agreement between the RVs returned by different methods.
These results suggest that continued progress in this field necessitates
increased interpretability of methods, high-cadence data to capture stellar
signals at all timescales, and continued tests like the ESSP using consistent
data sets with more advanced metrics for method performance. Future comparisons
should make use of various well-characterized data sets — such as solar data
or data with known injected planetary and/or stellar signals — to better
understand method performance and whether planetary signals are preserved.
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