Sloane Wiktorowicz (UC Santa Cruz)

Direct Detection of Exoplanets with Polarimetry

The detection of scattered light from exoplanets gives direct access to physical conditions and composition of their atmospheres. Currently, most scattered light experiments focus on nearly edge-on, transiting systems. The temporal changes that occur during planetary occultations are used to suppress systematic errors that would otherwise overwhelm the planetary signal. Linear polarimetry also has the potential to detect scattered light from exoplanets, because the polarization state of light scattered by a planetary atmosphere distinguishes it from both the direct light from the host star and thermal re-radiation from the planet. This scattered flux should be identifiable even in face-on systems, because both degree and position angle of polarization are modulated continuously throughout the orbit. Orbital inclination, mean number of scattering events, and scattering particle index of refraction and size are potentially discernable with polarimetry. I will report on the search for scattered light from known exoplanets using the POLISH2 polarimeter on the Lick 3-m telescope. This instrument has recently been upgraded with simultaneous full-Stokes capability and UBV filters. The precision of POLISH2 observations lies within 30% of the photon shot noise limit, and systematic effects have been suppressed to the part per million level. The POLISH2 polarimeter is therefore ideally suited for direct detection of close-in exoplanets. This work was supported by a UC Lab Fees Research Grant, UCO/Lick Observatory, and a NExScI Sagan Fellowship.