Poster Abstracts

Name/Affiliation:  Edward Dunham (Lowell Observatory)

Title:  Airborne Transit Observations of Cool Stars

Multicolor data taken during an exoplanet transit locally probe starspots, limb darkening, and surface temperature variation of the host star as well as determining important planetary parameters. The High-speed Imaging Photometer for Occultations (HIPO) is a 2-channel CCD imager for SOFIA originally designed to observe stellar occultations but now also being applied to transit work. HIPO can be co-mounted with FLITECAM, a 1-5 micron imager and grism spectrometer, the combination being known as FLIPO. By adding images from SOFIA's science-grade guide camera to the FLIPO data we can obtain simultaneous data at four wavelengths, three optical and one IR. Bright stars with no nearby comparison star are often difficult to observe, but will be among the best targets for SOFIA. Cool IR-bright stars will be good FLITECAM targets for water-sensitive observations, and will be sufficiently faint optically that nearby comparison stars are likely to be available for differential correction. We look forward to the additional targets, bright, red, or both, that the K2 and TESS missions are likely to provide. We have been exploring the precise photometric performance of FLIPO with an eye toward exoplanet transit and host star characterization work through specific tests and a demonstration transit observation involving the cool, spotted star HD 189733. We describe here the progress made to date with the HIPO data. We have had some success with absolute HIPO photometry on isolated bright stars thanks to the low and stable extinction in the stratosphere. Important corrections include: Rayleigh scattering, ozone absorption in the Chappuis band, image position sensitivity, focus errors, and mean static air density. The density effect is related to PSF broadening by scattering in the turbulent shear layer over the telescope. An expected shear layer dependence on Mach number appears to be unimportant.