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Refining extreme precision radial velocity measurements by understanding stellar activity’s effect on asymmetric line shifts

Presentation #1150 in the session “Open Engagement Session B”.

Published onMar 17, 2021
Refining extreme precision radial velocity measurements by understanding stellar activity’s effect on asymmetric line shifts

Recent advances in extreme-precision radial-velocity measurements on the order of 30 cm/s have made it easier to detect Earth-sized planets with longer periods around Solar-like stars by analyzing the reflex motion of their host stars with high-resolution spectroscopy. True Earth analogs, with radial-velocity semi-amplitudes of ~10 cm/s, still remain just out of reach. The precision of radial-velocity measurements is currently constrained by stellar activity, contamination in telluric modeling, and instrumental drift. By analyzing spectra taken from potential host stars over time, we can see changes in line symmetry that could lead to spurious RV shifts. However, it is not clear how much stellar activity can induce a long-term and asymmetric modification to spectral line shapes, compromising the radial-velocity extraction process. We use high signal-to-noise time-series spectra from the EXPRES spectrograph to empirically compare line shape changes of known activity sensitive lines to more static lines. We then quantify the effects that these lines can have on radial velocity precision. The implications for understanding stellar activity sensitivity for specific lines include being able to reduce the radial velocity scatter enough to eventually fill in a new parameter space of Earth-analog exoplanet radial-velocity detection.


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