Presentation #411.03 in the session Cometary Volatiles (iPosters).
We will report on preliminary results from narrowband filter photometry and imaging of four comets observed at Lowell Observatory. The dynamically new Comet PanSTARRS (C/2017 K2) was discovered 5 years ago at 21st mag and a distance of 16 AU, and our first successful production rate measurements, for the molecules C2 and CN, occurred in October 2021 when it had reached 5.2 AU. Its very high dust-to-gas ratio made continuum subtraction more difficult than usual, precluding any earlier definitive detections; the remaining gas species (OH, NH, and C3) were measured by spring 2021 when PanSTARRS was at 3.1 AU. Our dust and CN imaging have not yet revealed any jet-like morphology, possibly indicative that this body is really on its first close approach to the Sun.
We have now observed the Jupiter-family comet 67P/Churyumov-Gerasimenko (C-G) during 5 apparitions, with its most recent appearance in 2021/22 being its best since 1982. This comprehensive data set confirms previous findings, including its large pre-/post-perihelion asymmetry in production rates, with individual gas species ranging from 2× to nearly 6× higher after perihelion than before. For dust, there is a large trend with aperture size making seasonal comparisons less clear. Unexpectedly, C-G had production rates 1.5×-2.5× higher before and surrounding perihelion during 2021/22 as compared to previous apparitions, while as the comet receded the rates dropped to levels similar to prior apparitions.
During 2018/19, comets 38P/Stephan-Oterma (S-O) and 64P/Swift-Gehrels (S-G) had their most viable apparitions since the early 1980s. The Halley-type comet S-O has an orbital period of 38 years, and we have production rates for 7 months surrounding perihelion during both the 1980/81 and 2018/19 apparitions. The comet reached peak production rates during the month prior to its closest approach, and the individual gas species range from 1.5×-3× higher before perihelion than after. We additionally see a secular decrease in production rates for S-O, with values 1.5×-2.5× lower in 2018/19. Jupiter-family comet S-G has an orbital period of 9.4 years, and we obtained about 7 months of observations surrounding its closest approach in late 2018. S-G shows strong pre-/post-perihelion asymmetry, with peak production occurring approximately one month after perihelion. Its post-perihelion production rates are 2×-8× higher for the individual gas species, and 3×-5× higher for dust than they were prior to perihelion.
These and additional results will be presented. This work was supported by NASA Solar System Observations Program grant 80NSSC18K0856.