High-resolution spectra of comet C/2013 R1 (Lovejoy)

Abstract

Context. High-resolution spectra of comets permit deriving the physical properties of the coma. In the optical range, relative production rates can be computed, and information about isotopic ratios and the origin of oxygen atoms can be obtained. Aims. The main objective of the work presented here was to obtain information about the chemical composition of comet C/2013 R1 (Lovejoy), a bright and long-period comet that passed perihelion (0.81 au) on 22 December 2013. Methods. We used the HARPS-North echelle spectrograph at the 3.5 m telescope TNG to obtain high-resolution spectra of comet C/2013 R1 (Lovejoy) in the optical range immediately after its perihelion passage during four consecutive nights in the period December 23 to 26, 2013. Results. Our results demonstrate the ability of HARPS-North to efficiently obtain cometary spectra. Very faint emission lines, such as those of 15 NH 2, have been detected, leading to a rough estimate of the 14 N/ 15 N ratio in NH 2. The 12 C/ 13 C ratio was measured in the C 2 lines and is equal to 80 ± 30. The oxygen lines were studied as well (green to red line intensity ratios and widths), confirming that H 2 O is the main parent molecule that photodissociates to produce oxygen atoms. This suggests that this comet has a high CO 2 abundance. Relative production rates for C 2 and NH 2 were computed, but we found no significant deviation from a typical NH 2 /C 2 ratio.