Image Analysis of the 2012 Pluto ( Near ) Occultation Keith T . Knox

Imagery was gathered at the AMOS observatory on the 3.6-meter telescope for the expected occultation of a star by the dwarf planet, Pluto, on 29 June 2012. The imagery was taken at 5 Hz for 40 minutes before and after the expected time of occultation. The initial analysis of the photometry indicated that Pluto did not occult the star. This conclusion could not be determined from a simple visual inspection of the imagery. Understanding why and by how much Pluto missed occulting the star can aid in predicting future occultations. To analyze the imagery, a least squares method was developed to measure the closest approach, in arc seconds. The method is based on averaging the modulus squared of the Fourier transform of the imagery. This is similar to Labeyrie’s technique in speckle interferometry. From this method, fringes were detected and measured as a function of time over the period before and after the near occultation. The analysis showed that Pluto missed the star by 0.135 arcsec with an accuracy of 0.003 arcsec. The use of over 24,000 image frames leads to this high level of precision. In addition, Labeyrie’s technique applied to the images of Pluto by itself, shows that Pluto and its moon, Charon, were oriented perpendicularly to the direction of travel, making it even less likely that Pluto would overlap with the star. The methods developed to conduct this analysis and the conclusions reached are described in this paper.