Stellar jitter from variable gravitational redshift: implications for RV confirmation of habitable exoplanets

TL;DR

This paper identifies a new source of stellar jitter caused by variable gravitational redshift from stellar radius fluctuations, which can significantly affect radial velocity measurements in exoplanet detection.

Contribution

It introduces the concept of gravitational redshift variability as a source of stellar jitter and explores its mechanisms and potential correction methods.

Findings

Stellar radius fluctuations can cause detectable gravitational redshift variations.

Magnetic activity and starspots significantly contribute to radius-induced redshift changes.

This jitter can mimic or mask signals from Earth-like exoplanets.

Abstract

A variation of gravitational redshift, arising from stellar radius fluctuations, will introduce astrophysical noise into radial velocity measurements by shifting the centroid of the observed spectral lines. Shifting the centroid does not necessarily introduce line asymmetries. This is fundamentally different from other types of stellar jitter so far identified, which do result from line asymmetries. Furthermore, only a very small change in stellar radius, ~0.01%, is necessary to generate a gravitational redshift variation large enough to mask or mimic an Earth-twin. We explore possible mechanisms for stellar radius fluctuations in low-mass stars. Convective inhibition due to varying magnetic field strengths and the Wilson depression of starspots are both found to induce substantial gravitational redshift variations. Finally, we investigate a possible method for monitoring/correcting this newly identified potential source of jitter and comment on its impact for future exoplanet searches.