Infrared Compositional Measurements in Comet C/2017 K2 (Pan-STARRS) at Heliocentric Distances Beyond 2.3 AU

Chemeda Ejeta; Erika Gibb; Michael A. DiSanti; Hideyo Kawakita; Boncho P. Bonev; Neil Dello Russo; Nathan Roth; Younas Khan; Adam J. McKay; Michael R. Combi; Lori Feaga; Mohammad Saki; Ronald J. Vervack; Yinsi Shou

paper

Infrared Compositional Measurements in Comet C/2017 K2 (Pan-STARRS) at Heliocentric Distances Beyond 2.3 AU

arXiv:2409.05789

Abstract

Comet C/2017 K2 (Pan-STARRS) provided a rare opportunity to investigate the evolution of coma composition and outgassing patterns over a transitional heliocentric distance (Rh) range where activity drivers in comets are thought to change from "hypervolatile" (CO, CH $_{4}$ , C $_{2}$ H $_{6}$ , and/or CO $_{2}$ )-dominated to H2O-dominated. We performed high-resolution, cross-dispersed, near-infrared spectroscopy of C/2017 K2 with iSHELL at the NASA Infrared Telescope Facility (IRTF) and NIRSPEC at the W. M. Keck 2 Observatory. We report gas rotational temperatures (Trot) and molecular production rates (Q; mol/s) or upper limits for the hypervolatile species CH $_{4}$ , CO, and C $_{2}$ H $_{6}$ , together with less volatile ices (CH $_{3}$ OH, H $_{2}$ O, HCN, C $_{2}$ H $_{2}$ , NH $_{3}$ , and OCS) over a range of pre-perihelion distances, Rh= 3.15 - 2.35 au. We also report (or stringently constrain) abundance ratios (mixing ratios) of the targeted species with respect to CO, C $_{2}$ H $_{6}$ , and (when detected) H $_{2}$ O. All volatiles were enriched relative to water in C/2017 K2 when compared to their mean values among Oort Cloud comets, whereas abundances relative to C2H6 were consistent with their average values from other long-period comets.

Submitted to the Astronomical Journal for publication