, which would place the planet in the super-Earth mass range.In case of no detection, the implied mass upper limit would be ∼8 M Taking the optimistic estimate of their single-epoch accuracy to be ∼30μas, we find a probability of ∼10% to detect the astrometric signature of Barnard's Star b with ∼50 individual-epoch observations. We conclude that Gaia and the Hubble Space Telescope (HST) are currently the best-suited instruments to perform the astrometric follow-up observations. In addition, we reviewed the astrometric capabilities and limitations of current and upcoming astrometric instruments. By combining the assumption of an isotropic probability distribution of the orbital orientation with the RV-analysis results, we calculated the probability density function of the astrometric signature of the planet. The relatively long orbital period and the proximity of Barnard's Star to the Sun raises the question whether the true mass of the planet can be constrained by accurate astrometric measurements.
ASTROMETRY DETECTION SERIES
Our simulations of the astrometric jitter has the potential to aid the interpretation of data from Gaia and upcoming space astrometry missions.Ī low-amplitude periodic signal in the radial velocity (RV) time series of Barnard's Star was recently attributed to a planetary companion with a minimum mass of ∼3.2 M 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. We further show that the jitter for the most variable periodic Kepler stars is high enough to be detected by Gaia. 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. 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. This effect interferes with the astrometric detections of Earth-mass planets. 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.
Besides, Earth-like planet discoveries are expected from the planned infrared astrometry space mission, Small-JASMINE. A breakthrough in exoplanet detections is foreseen with the unprecedented astrometric measurement capabilities offered by instrumentation aboard Gaia space observatory.
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