Presentation #102.115 in the session Poster Session.
Atmospheric escape is the primary physical process sculpting the population of short-period, irradiated exoplanets, yet the dominant mass loss mechanism remains unclear. Several mechanisms likely contribute to the exosphere loss (e.g., photoevaporation, core-powered erosion, stellar wind stripping, giant impact) and they predict distinct correlations between mass-loss rates and properties of environment and planets. Directly measuring the mass loss for a large ensemble of exoplanet-host systems will differentiate these atmospheric escape processes and such measurements have been enabled by the Helium 10830A triplet, a robust probe of exospheres. Using the Habitable-zone Planet Finder Spectrograph (HPF) on the Hobby-Eberly Telescope (HET), we are conducting an extensive survey for Helium exospheres, targeting two dozens of exoplanets spanning wide ranges in (1) the planets’ surface gravities and masses, (2) the host stars’ spectral type, and (3) the system age. While K-type host stars are expected to have the ideal extreme-UV to mid-UV flux ratios for the high excitation of Helium metastable levels, our survey discovers that the planets orbiting the hottest stars (F dwarfs) possess significant excess Helium absorption during transit. These Helium excesses are among the strongest detection to date and are repeatable when re-observed. With time baselines covering much broader orbital phases of exoplanets than most similar surveys, our data also reveal the spatially extended exospheres of irradiated planets. In this talk, we will present our survey strategy, target selection, data and modeling analysis, as well as an open-source Python package we developed to enable the Helium studies. With the unique combination of the broad sample, as well as the large aperture, high spectral resolution, and significant institutional accesses to HET, our survey will reliably probe the mass-loss mechanism of irradiated exoplanets.