Presentation #111.05 in the session “Comet Comae: C/2020 F3 (NEOWISE)”.
We will report on preliminary results from recent and upcoming narrowband filter imaging and photometry data of four comets obtained from Lowell Observatory in 2020. Comet NEOWISE (C/2020 F3) was the brightest object in more than a decade but only became accessible for us in late July. By that time, water production had decreased to 1.6×1029 molecules/s, while the dust-to-gas ratio was significantly lower than average as compared to our database. CN imaging exhibits a counter-clockwise spiral rotation with successive outward moving arcs implying a possible period of about 7-8 hr; however, variations in the spacing and brightness of arcs in early August suggests multiple jets might be present, with the actual period perhaps twice the apparent value. The rapidly brightening Comet ATLAS (C/2019 Y4) suffered a major fragmentation event in April, about a month prior to perihelion. Though characterized in the press as having disappeared, we obtained additional photometry and imaging of the remnants in mid-May; the images showed that fragmentation was continuing to take place with the location and brightness of features changing from night-to-night. Furthermore, a CN coma was observed nightly, suggesting that at least one fragment remained active.
We began our observations of Comet PanSTARRS (C/2017 T2) in early October 2019 at a distance of 3.15 AU. By perihelion (1.61 AU), water production reached 6×1028 molecules/s, following an r-dependence log-log slope of -4.3, and a steeper slope thus far outbound. Although early imaging showed little in morphological features, CN imaging in June revealed a pair of apparently side-on jets; however, these were no longer evident just a month later. Comet 88P/Howell, the only Jupiter Family object in this group, continues to have relatively unfavorable apparitions though the current one is the best since its discovery. Between mid-May and mid-August, and still approaching perihelion, water production is following an extremely steep r-dependence of -9.1, possibly suggesting that a dominant, isolated source region is rapidly “moving” from winter to summer.
These and additional results from our observing campaigns will be presented. This work is supported by NASA’s Solar System Observations Program grant 80NSSC18K0856.