High Frequency Observation of Iapetus on the Green Bank Telescope Aided by Improvements in Understanding the Telescope Response to Wind

Ries, Paul A., Department of Astronomy, University of Virginia
Hunter, Todd, Department of Astronomy, University of Virginia

The Green Bank Telescope is a 100m, fully steerable, single dish radio telescope located in Green Bank, West Virginia and capable of making observations from rne -ter wavelengths to 3mm. However, observations at wavelengths short of 2 cm pose significant observational challenges due to pointing and surface errors, The First part of this thesis details efforts to combat wind - induced pointing errors, which reduce by half the amount of time available for high - frequency work on the telescope. The primary tool used for understanding these errors was an optical quadrant detector that monitored the motion of the telescope's feed arrn, In this work, a calibration was developed that tied quadrant detector readings directly to telescope pointing error. These readings can be used for single - bearn observations in order to determine if the telescope was blown off - source at some point due to wind. With observations with the 3 mm MUSTANG bolorneter array, pointing errors due to wind can mostly be removed (> during data reduction. Iapetus is a moon known for its stark albedo dichotorny, with the leading herni -sphere only a tenth as bright as the trailing. In order to investigate this dichotorny, Iapetus was observed repeatedly with the GBT at wavelengths between 3 and 11 mm, with the original intention being to use the data to determine a thermal light - curve, Instead, the data showed incredible wavelength - dependent deviation from a black -body curve, with an ernissivity as low as 0.3 at 9 rnrn. Nurnerous techniques were used to demonstrate that this low emissivity is a physical phenornenon rather than an observational one, including some using the quadrant detector to make sure the low ernissivities are not due to being blown off source, This emissivity is the among the lowest ever detected in the solar system, but can be achieved using physically realistic ice models that are also used to model rnicrowave emission from snowpacks and glaciers on Earth, These models indicate that the trailing hernisphere contains a iv scattering layer of depth 100 cm and grain size of 1 - 2 mm. The leading hemisphere is shown to exhibit a thermal depth effect.

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PHD (Doctor of Philosophy)
Green Bank Telescope, wind
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