HOPI - a high-speed occultation photometer and imager for SOFIA

HOPI is a special-purpose science instrument for SOFIA that is designed to provide simultaneous high-speed time resolved imaging photometry at two optical wavelengths. We intend to make it possible to mount HOPI and FLITECAM on the SOFIA telescope simultaneously to allow data acquisition at two optical wavelengths and one near-IR wavelength. HOPI will have a flexible optical system and numerous readout modes, allowing many specialized observations to be made. The instrument characteristics required for our proposed scientific pursuits are closely aligned to those needed for critical tests of the completed SOFIA Observatory, and HOPI will be used heavily for these tests. Our main scientific interest is in the use of HOPI for observing stellar occultations. In a stellar occultation, a star serves as a small probe of the atmospheric structure of a solar system object or the surface density structure of a planetary ring or comet. Such observations provide information at kilometer-scale spatial resolution that would otherwise require a space mission to obtain. This work makes use of SOFIA's mobility, freedom from clouds, and near-absence of scintillation noise to provide the best possible occultation data. The addition of a coarse grism in a filter position would make it suitable for lunar occultations and other spectrally resolved time series observations. Also, the low atmospheric scintillation for airborne photometry gives HOPI the potential to detect P-mode stellar oscillations in sunlike stars. HOPI will be available for Guest Investigator use on a collaborative basis, and potential Guest Investigators should contact the PI prior to proposing to insure that the proposed observations are feasible and make the best use of HOPI's capabilities.