Research Note

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

¹ University of Franche-Comté, Observatoire des Sciences de l’Univers THETA, Institut UTINAM – UMR CNRS 6213, BP 1615, 25010 Besançon Cedex, France
e-mail: rousselot@obs-besancon.fr
² LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
³ Main Astronomical Observatory of NAS of Ukraine, 27 Akademika Zabolotnoho Street, 03680 Kyiv, Ukraine
⁴ Département d’Astrophysique, de Géophysique et d’Océanographie, Université de Liège, Allée du Six Août, 4000 Liège, Belgium

Received: 24 March 2015
Accepted: 29 May 2015

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 ¹⁵NH₂, have been detected, leading to a rough estimate of the ¹⁴N/¹⁵N ratio in NH₂. The ¹²C/¹³C ratio was measured in the C₂ lines and is equal to 80 ± 30. The oxygen lines were studied as well (green to red line intensity ratios and widths), confirming that H₂O is the main parent molecule that photodissociates to produce oxygen atoms. This suggests that this comet has a high CO₂ abundance. Relative production rates for C₂ and NH₂ were computed, but we found no significant deviation from a typical NH₂/C₂ ratio.