Near-perihelion Near-infrared High-dispersion Spectroscopy of Comet C/2013 R1 (Lovejoy) with IRTF/CSHELL

Chemical compositions of comets offer invaluable insights into the chemical and physical properties of the early solar system. High-dispersion spectroscopy, particularly in the near-infrared region, facilitates the direct detection of various species released from the cometary nucleus, including H₂O, CO, hydrocarbons, and N-bearing species. However, variations in chemical composition could be influenced by differences in sublimation temperatures among species and rotation if the cometary nucleus is heterogeneous. Therefore, studying temporal variations in chemical compositions at various timing and/or heliocentric distances can help elucidate the outgassing mechanism from the nucleus and enable more rigorous analysis of their compositions. Perihelion passages are especially significant events for comets, characterized by notable changes such as increased amount of released materials and associated orbital alterations. Observations of the variations in chemical compositions near perihelion are therefore crucial.

Comet C/2013 R1 (Lovejoy), a nearly isotropic comet (e~0.998), reached ~5th magnitude in V-band during its pre-perihelion passage (r_h~0.84 au) on December 22.7, 2013. We conducted high-dispersion near-infrared spectroscopic observations of C/2013 R1 using IRTF/CSHELL during December 10 to 12, 2013, almost 10 days before its perihelion passage. We selected multiple spectral configurations to cover H₂O, CO, and other minor species (HCN, NH₃, C₂H₂, CH₄, C₂H₆, CH₃OH, H₂CO, OCS) within the limited wavelength range of CSHELL. Observations of C/2013 R1 were also conducted at r_h~1.28 au using Keck2/NIRSPEC at the end of November 2013 (Kobayashi et al., 2023). We will discuss the temporal variations in chemical compositions over these three days near perihelion and compare our results with other observational results, including those obtained during the Keck2/NIRSPEC observations.

This work was supported by NSF (2009398) (B.P.B).