Shadowing the Sun I: Testing Synthetic Granulation Spectra with NEID Solar Eclipse Observations

Elizabeth Gonzalez; Michael L. Palumbo III; Suvrath Mahadevan; Eric B. Ford; Sarah E. Logsdon; Chad F. Bender; Andrea S. J. Lin; Daniel M. Krolikowski; Ashutosh Joshi; Joe P. Ninan; Jason T. Wright; Ansgar Reiners; Samuel Halverson; Michael W. McElwain; Jayadev Rajagopal; Paul Robertson; Arpita Roy; Christian Schwab; Gudmundur Stefansson; Ryan C. Terrien

arXiv · 2611.03898

Shadowing the Sun I: Testing Synthetic Granulation Spectra with NEID Solar Eclipse Observations

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Abstract

The subtle Doppler radial velocity (RV) signature of an Earth-mass exoplanet in the Habitable Zone around a nearby Sun-like star is difficult to detect due to stellar variability. While multiple techniques aim to mitigate rotationally-modulated stellar activity, granulation, introducing 0.1-1 m s$^{-1}$ RV shifts, currently sets the floor for detecting Earth-mass RV signals for low-activity stars. Observations of the Rossiter-McLaughlin (RM) effect during a solar eclipse, with a peak-to-trough amplitude of $\sim$1.4 km s$^{-1}$, are a rigorous test of granulation and convective blueshift in the solar spectrum. Using NEID solar feed data of the October 2023 solar eclipse and GRASS-E (a geometry-modified version of GRASS), we compare the observed RVs for 22 lines with the simulated RVs from the synthetic granulation-driven spectra. Residuals of the GRASS-E Fe I 5434 angstrom model show an RMS of 13.47 m s$^{-1}$ over the RM signal. We find that a model with an optimized convective blueshift polynomial for Fe I 5434 significantly outperforms GRASS-E with an RMS of only 2.90 m s$^{-1}$, suggesting that GRASS-E is currently limited by sparse center-to-limb observations. By combining a set of spectral lines, we achieve a weighted RMS of 5.2 m s$^{-1}$ over the RM signal ($\sim$0.37\%), a level of accuracy well beyond the reach of current exoplanet transit observations. In all, we demonstrate that solar eclipse observations allow us to recover the center-to-limb variation of the convective blueshift for individual spectral lines.

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Elizabeth Gonzalez, Michael L. Palumbo III, Suvrath Mahadevan, Eric B. Ford, Sarah E. Logsdon, Chad F. Bender, Andrea S. J. Lin, Daniel M. Krolikowski, Ashutosh Joshi, Joe P. Ninan, Jason T. Wright, Ansgar Reiners, Samuel Halverson, Michael W. McElwain, Jayadev Rajagopal, Paul Robertson, Arpita Roy, Christian Schwab, Gudmundur Stefansson, Ryan C. Terrien. 2026-11-02. Shadowing the Sun I: Testing Synthetic Granulation Spectra with NEID Solar Eclipse Observations. https://arxiv.org/abs/2611.03898

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