Collaborative Research: Understanding exoplanets orbiting fully convective stars with the Habitable-zone Planet Finder

The team will use the Habitable-zone Planet Finder (HPF), a Doppler spectrometer on the 10-m Hobby-Eberly Telescope, to conduct a survey of Class M red dwarf stars within 8 parsecs of Earth, as well as stars smaller than Class M4 further from Earth. The team will attempt to identify exoplanets in these systems from characteristic radial velocity (RV) color fluctuations in light emitted by the host stars. The exoplanet population around these smaller stars is poorly understood. The team seeks to answer the question of what exoplanetary systems look like around fully convective stars, and whether there is an increase in the fraction of super-Earths around lower-mass host stars. The team hopes to build a population of targets for follow-up imaging by upcoming Extremely Large Telescopes. The team will conduct a variety of outreach activities, including a teacher workshop at the MacDonald Observatory, mentorships at UC Irvine for students from under-represented groups, and participation on the HPF blog. The team will also train graduate students as part of the work.

The HPF survey will provide data principally to answer two questions. First, the team will determine the occurrence rates for exoplanets orbiting fully-convective stars as a function of planet size and orbital period. Previous exoplanet surveys have shown that M dwarfs typically host small planets, and there is tenuous evidence that the frequency of larger super-Earth and Neptune-sized planets increases for mid-to-late M stars. However, these surveys are still dominated by early-M subtypes (more massive stars); this survey will offer empirical evidence for the planet population of the fully-convective end of the M type. Second, the team will tackle the problem of stellar jitter. Astrophysical noise, or 'jitter,' originating from stellar magnetic activity is rapidly becoming the limiting noise source in RV measurements, and M dwarfs are no exception. However, fully convective stars have poorly understood magnetic dynamos and very red spectral energy distributions. This means both the magnetic phenomena on their surfaces and the observables used to diagnose them may differ from those of Sunlike stars. With its stable instrument profile and NIR wavelength coverage, HPF will provide critical insights into jitter phenomena and support sophisticated models of its contribution.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.