Predictions of Astrometric Jitter for Sun-like Stars. III. Fast Rotators

TL;DR

This paper models how magnetic activity in fast-rotating Sun-like stars causes astrometric jitter, which can interfere with exoplanet detection by Gaia and similar missions, especially for highly active stars.

Contribution

It extends previous models to fast rotators, showing increased magnetic jitter and its dominance over faculae, aiding interpretation of astrometric data from space missions.

Findings

Magnetic jitter increases with stellar rotation rate.

Jitter for active Kepler stars is detectable by Gaia.

Spot dominance in magnetic jitter for rapid rotators.

Abstract

A breakthrough in exoplanet detections is foreseen with the unprecedented astrometric measurement capabilities offered by instrumentation aboard Gaia space observatory. Besides, astrometric discoveries of exoplanets are expected from the planned space mission, Small-JASMINE. In this setting, the present series of papers focuses on estimating the effect of magnetic activity of G2V-type host stars on the astrometric signal. This effect interferes with the astrometric detections of Earth-mass planets. While the first two papers considered stars rotating at the solar rotation rate, this paper focuses on stars having solar effective temperature and metallicity but rotating faster than the Sun, and consequently more active. By simulating the distribution of active regions on such stars using the Flux Emergence And Transport model, we show that the contribution of magnetic activity to the astrometric measurements becomes increasingly significant with increasing rotation rates. We further show that the jitter for the most variable periodic Kepler stars is high enough to be detected by Gaia. Furthermore, due to a decrease in the facula-to-spot area ratio for more active stars, the magnetic jitter is found to be spot-dominated for rapid rotators. Our simulations of the astrometric jitter has the potential to aid the interpretation of data from Gaia and upcoming space astrometry missions.