DIX Planetary Science Seminar
A planet-forming disk starts out thick with gas and dust, until those materials are blown out of the system, dragged into the star, or gathered up into new planets. Once planetesimals are formed, some crash together in a collisional cascade, producing a dusty disk around the star. These are known as debris disks, a stage of solar system evolution containing the ground up remnants of planet formation, somewhat like our own Kuiper belt and asteroid belt. Debris disks are substantially fainter than their host stars; in order to image these structures, high-contrast imaging techniques are necessary. Polarimetry further improves sensitivity for debris disk imaging, because the light from a disk is polarized due to scattering, whereas starlight is generally unpolarized. This creates a natural separation between the two and therefore a way to remove unwanted starlight. Polarimetry also provides additional leverage for determining the composition of a debris disk, as the observed brightness distribution depends on the scattering properties (e.g. polarization fraction, phase function) of the dust. The Gemini Planet Imager (GPI) Exoplanet Survey resolved and characterized 26 debris disks in polarized light, with one particularly unique example around HD 156623. HD 156623's disk was resolved in scattered light for the first time by GPI, and is the only disk in the sample that lacks a visible inner clearing. New analysis of GPI H-band polarimetric data on the HD 156623 system constrains the geometric/morphological parameters of the disk, including the unresolved inner radius, and presents measurements of scattering properties including an empirical phase function. Observational constraints such as these are crucial for informing models of planet formation and evolution, especially how gas and dust are cleared and resupplied during the debris disk phase. In this talk, I will also briefly discuss recent observations of Europa in polarized light with Subaru SCExAO/CHARIS, and results from education research that illustrate the importance of bringing research literature into the undergraduate classroom as demonstrated by Astrobites.