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Activity time series of old stars from late F to early K: V. Effect on exoplanet detectability with high-precision astrometry

Abstract : Context. Stellar activity strongly affects and may prevent the detection of Earth-mass planets in the habitable zone of solar-type stars with radial velocity technics. Astrometry is in principle less sensitive to stellar activity because the situation is more favourable: the stellar astrometric signal is expected to be fainter than the planetary astrometric signal compared to radial velocities.Aims. We quantify the effect of stellar activity on high-precision astrometry when Earth-mass planets are searched for in the habitable zone around old main-sequence solar-type stars.Methods. We used a very large set of magnetic activity synthetic time series to characterise the properties of the stellar astrometric signal. We then studied the detectability of exoplanets based on different approaches: first based on the theoretical level of false positives derived from the synthetic time series, and then with blind tests for old main-sequence F6-K4 stars.Results. The amplitude of the signal can be up to a few times the solar value depending on the assumptions made for activity level, spectral type, and spot contrast. The detection rates for 1 MEarth planets are very good, however, with extremely low false-positive rates in the habitable zone for stars in the F6-K4 range at 10 pc. The standard false-alarm probability using classical bootstrapping on the time series strongly overestimates the false-positive level. This affects the detection rates.Conclusions. We conclude that if technological challenges can be overcome and very high precision is reached, astrometry is much more suitable for detecting Earth-mass planets in the habitable zone around nearby solar-type stars than radial velocity, and detection rates are much higher for this range of planetary masses and periods when astrometric techniques are used than with radial velocity techniques.
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https://hal.archives-ouvertes.fr/hal-03037166
Contributeur : Edp Sciences <>
Soumis le : jeudi 3 décembre 2020 - 02:48:50
Dernière modification le : mercredi 16 décembre 2020 - 03:15:01

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N. Meunier, A.-M. Lagrange, S. Borgniet. Activity time series of old stars from late F to early K: V. Effect on exoplanet detectability with high-precision astrometry. Astronomy and Astrophysics - A&A, EDP Sciences, 2020, 644, pp.A77. ⟨10.1051/0004-6361/202038710⟩. ⟨hal-03037166⟩

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