A new estimation of astrometric exoplanet detection limits in the habitable zone around nearby stars

Abstract

Astrometry is less sensitive to stellar activity than the radial velocity technique when attempting to detect Earth mass planets in the habitable zone of solar-type stars. This is due to a smaller number of physical processes affecting the signal, and a larger ratio of the amplitude of the planetary signal to the stellar signal. A few high-precision astrometric missions have therefore been proposed over the past two decades. We aim to re-estimate the detection limits in astrometry for the nearby stars which are the main targets proposed for the THEIA astrometric mission, the most elaborate mission to search for planets, and to characterise its performance. This analysis is performed for the 55 F-G-K stars in the THEIA sample. We used realistic simulations of stellar activity and selected those that correspond best to each star in terms of spectral type and average activity level. Then, we performed blind tests to estimate the performance. We find worse detection limits compared to those previously obtained for that sample based on a careful analysis of the false positive rate, with values in the Earth-mass regime for most stars of the sample. The difference is attributed to the fact that we analysed full time series, adapted to each star in the sample, rather than using the expected solar jitter only. Although these detection limits have a relatively low signal-to-noise ratio, the fitted parameters have small uncertainties. We confirm the low impact of stellar activity on exoplanet detectability for solar-type stars, although it plays a significant role for the closest stars such as alpha Cen A and B. However, for the few stars in the sample with a habitable zone corresponding to long periods, namely subgiants, the THEIA observational strategy is not well adapted and should prevent the detection of planets in the habitable zone, unless a longer mission can be proposed.

Accepted in Astronomy and Astrophysics

References in corpus (18)

• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Southern Sample
• Radial-Velocity Fitting Challenge. II. First results of the analysis of the data set
• An Activity Catalogue of Southern Stars
• Theia: Faint objects in motion or the new astrometry frontier
• Variability in stellar granulation and convective blueshift with spectral type and magnetic activity. II. From young to old main-sequence K-G-F stars
• Unexpectedly strong effect of supergranulation on the detectability of Earth twins orbiting Sun-like stars with radial velocities
• Limits of ultra-high-precision optical astrometry: Stellar surface structures
• Faint objects in motion: the new frontier of high precision astrometry
• Activity time series of old stars from late F to early K. I. Simulating radial velocity, astrometry, photometry, and chromospheric emission
• The Mass-Activity relationships in M and K dwarfs. I. Stellar parameters of our sample of M and K dwarfs
• Radial-velocity variations due to meridional flows in the Sun and solar-type stars: impact on exoplanet detectability
• A detector interferometric calibration experiment for high precision astrometry
• Predictions of Astrometric Jitter for Sun-like Stars. II. Dependence on Inclination, Metallicity, and Active-Region Nesting
• Astrometric effects of solar-like magnetic activity in late-type stars and their relevance for the detection of extrasolar planets
• On the Iron Abundance Anomaly in K-dwarf and Hyades Stars
• Activity time series of old stars from late F to early K. V. Effect on exoplanet detectability with high-precision astrometry
• Astrometric Detection of exo-Earths in the Presence of Stellar Noise

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• Activity time series of old stars from late F to early K VI. Exoplanet mass characterisation and detectability in radial velocity
• Closeby Habitable Exoplanet Survey (CHES). I. Astrometric Noise and Planetary Detection Efficiency due to Stellar Spots and Faculae
• Predictions of Astrometric Jitter for Sun-like Stars. III. Fast Rotators
• On the follow-up efforts of long-period transiting planet candidates detected with Gaia astrometry
• Combining Photometry and Astrometry to Improve Orbit Retrieval of Directly Imaged Exoplanets
• Challenges in focal plane and telescope calibration for High-Precision Space Astrometry
• Astrometric exoplanet detection survives solar-like stellar contamination