Kavli Affiliate: Bruce Macintosh
| First 5 Authors: Avi Kaplan-Lipkin, Bruce Macintosh, Alexander Madurowicz, Sowmya Krishnamurthy, Alexander Shapiro
| Summary:
Astrometric detection of exoplanets by stellar reflex motion will be made
possible for giant planets by the recent Gaia mission and for Earth-like
planets by proposed missions such as LUVOIR. At the theoretical limits,
astrometry would allow for the detection of smaller planets than previously
seen by current exoplanet search methods, but stellar activity may make these
theoretical limits unreachable. Astrometric jitter of a Sun-like star due to
magnetic activity in its photosphere induces apparent variability in the
photocenter of order $0.5 textrm{mR}_odot$. This jitter creates a
fundamental astrophysical noise floor preventing detection of lower mass
planets in a single spectral band. By injecting planet orbits into simulated
solar data at five different passbands, we investigate mitigation of this
fundamental astrometric noise using correlations across passbands. For a true
solar analog and a planet at 1 au semi-major axis, the 5-sigma detection limit
set by stellar activity for an ideal telescope at the best single passband is
$0.01$ Earth masses. We found that pairs of passbands with highly correlated
astrometric jitter due to stellar activity but with less motion in the redder
band enable higher precision measurements of the common signal from the planet.
Using this method improves detectable planet masses at 1 au by up to a factor
of $8$, corresponding to at best $0.004$ Earth masses for a Sun-like star with
a perfect telescope. Given these results, we recommend that future astrometry
missions consider proceeding with two or more passbands to reduce noise due to
stellar activity.
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