Abstract

Direct imaging surveys have largely been limited by their reliance on detecting giant planets in thermal emission, resulting in a biased understanding of planet demographics at wide separations. Hot-start planets have higher luminosities at young ages and are therefore preferentially favored to be found in high-contrast imaging observations. In contrast, cold-start planets---those that experience a loss of initial energy through accretion luminosity---are difficult to detect, and sub-Jovian low-mass planets at wide separation remain largely unexplored. The H-alpha emission from accretion signatures of planets can be used to overcome these limitations. This approach provides an alternative assessment of planet occurrence rates regardless of their formation history and enables the search for accreting sub-Jovian-mass planets for the first time. I will present results from a deep H-alpha imaging survey of over 200 members of the ~2 Myr old star-forming region IC 348 obtained using HST/WFC3-UVIS. This study will provide important insight into the demographics of accreting long-period giant planets and their formation processes, and may uncover a hidden population of planets that are currently difficult to detect using traditional direct imaging methods.