ES-03-0027

Turn down the noise! Disentangling planetary and stellar signals by observing the Sun with EXPRES

Joe Llama, Lily Zhao, John Michael Brewer, Debra Fischer, Andrew Szymkowiak

The signal induced by a temperate, terrestrial planet orbiting a Sun-like star is an order of magnitude smaller than the host stars' intrinsic variability. Understanding stellar activity is, therefore, a fundamental obstacle in confirming the smallest exoplanets The EXtreme PREcision Spectrograph (EXPRES) has been obtaining EPRV measurements of stars to search for Earth-sized exoplanets since 2019. Recently, we integrated a solar feed into EXPRES to observe the Sun during the day in an analogous way to the stars at night. The Lowell Observatory Solar Telescope (LOST) is a 70-mm aperture lens that is fiber-fed into EXPRES. In clear conditions, the EXPRES solar observations have a cadence of approximately 300-s and single measurement uncertainty of just 35 cm/s. Since first light in late 2020, we have obtained over 35,000 RV measurements of the Sun. In this presentation, I will present our first results including comparisons with other solar telescopes, comparisons with disk-resolved data from NASA's Solar Dynamics Observatory, and prospects for correcting the RV variability induced by stellar activity.