DIX Planetary Science Seminar

Ryan Rubenzahl

Standing between astronomers and the "holy grail" 10 cm/s radial velocity (RV) precision needed to discover Earth-Sun analogs is stellar activity - RV variations due to physical processes on stellar surface - which can easily be several m/s. The Keck Planet Finder (KPF) currently being commissioned at Keck Observatory will have an instrumental stability of 30 cm/s, and thus its planet-detecting capabilities will be limited by stellar noise on most stars. I will present the Solar Calibrator (SoCal for short), an instrument that feeds stable disc-integrated sunlight to KPF for taking Sun-as-a-star spectra. We finished installation of SoCal on the roof of Keck Observatory last week and will soon be starting daily operations. SoCal will obtain SNR ~1000 R ~98k optical solar spectra at ~30 sec cadence for ~6 hrs every sunny day, helping us track KPF's performance across a variety of timescales and probe stellar activity. When combined with contemporaneous resolved ground and space-based solar observatories (e.g. NASA SDO) and solar feeds on other EPRV spectrographs (e.g. NEID, EXPRES, HARPS, HARPS-N), we will study in unmatched detail how activity influences RVs so that we may apply such knowledge to our nighttime observations of exoplanet host stars.

Mike Greklek-McKeon

Models predict that planets with water-rich compositions may be common around low-mass stars, but definitive evidence for the existence of water worlds has remained elusive. Precise mass and radius measurements for small planets allow us to identify candidate water worlds which have bulk densities too low to be consistent with a rocky composition, and masses too low to retain any H-rich envelope against hydrodynamic escape. Dynamical interactions between adjacent planets in near-resonant multi-planet systems produce transit timing variations (TTVs) that can be observed with high-precision photometry, and measurements of these TTVs can be inverted to produce constraints on planetary densities. For the past two years, we have collected dozens of transit observations for small, Earth-sized exoplanets in nearby multi-planet M dwarf systems, using the 200" Hale Telescope at Palomar Observatory and other ground-based observatories. I will discuss some of the most promising early results from this survey of candidate water worlds.