Cometary Coma Extraction and Nucleus Size Determination with NEOWISE

The Wide-field Infrared Survey Explorer (WISE), launched in 2009, and surveyed the sky in the mid-infrared for nearly an eight-month cryogenic-mission timespan, collecting images at 3.4, 4.6, 12, and 22 microns. 164 cometary bodies were detected during the cryogenic survey phase, and these detections yielded 155 nucleus size estimates (Bauer et al. 2017) in part by employing coma fitting and subtraction techniques for those that were active during the times of observation. While subsequent analysis of the coma fitting technique has been conducted (Hui and Li 2018), an in-depth analysis of these conclusions supports the application of the technique to the NEOWISE data.

By October 2010, the primary and secondary cryogen tanks were depleted, making the 12 and 22 micron channel inoperable, while the mission continued in its post-cryo phase to collect data until February 2011, when the spacecraft was placed in hibernation. The spacecraft was reactivated in October 2013 and re-named NEOWISE, and the survey was resumed on December 23^rd 2013, continuing to this date. The coma fit and extraction in the two shorter-wavelength bands is potentially more complex, owing in part to the presence of gas emission signal in the 4.6 micron band. However, an updated version of the technique was recently successfully employed to obtain estimates of the nucleus size of C/2020 F3 (NEOWISE). We will re-examine the coma fitting and extraction technique as applied to the WISE and NEOWISE infrared data, including its limitations in the cryogenic, post-cryo, and reactivated mission phases, and examine its possible application in the analysis of data from future observing missions, like NEOSM and JWST.

1. Bauer, J. M., Grav, T., Fernandez, Y. R., et al. 2017, AJ, 154, 53

2. Hui, M.-T. & Li, J.-Y. 2018, PASP, 130, 104501