Observing the Sun with the Lowell Observatory Solar Telescope and the EXtreme PREcision Spectrograph

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) is one of the newest high-resolution spectrographs designed for obtaining EPRV measurements of stars to search for Earth-sized exoplanets. 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 25,000 RV measurements of the Sun. This work will present the first year of data, comparisons with disk-resolved data from NASA's Solar Dynamics Observatory, and prospects for correcting the RV variability induced by stellar activity.