HCN observations of comets C/2013 R1 (Lovejoy) and C/2014 Q2 (Lovejoy)

TL;DR

This study reports multiple detections of HCN emissions from comets C/2013 R1 and C/2014 Q2 Lovejoy, revealing their production rates and abundances, and how these vary with heliocentric distance.

Contribution

First detailed HCN observations of comets C/2013 R1 and C/2014 Q2, showing their production rates and relative abundances at different heliocentric distances.

Findings

HCN production rate in C/2013 R1 increases as heliocentric distance decreases.

C/2014 Q2 has over 5 times higher HCN production rate than C/2013 R1 at similar distances.

HCN abundance relative to water is approximately 0.2% in C/2013 R1 and 0.09% in C/2014 Q2.

Abstract

HCN J=1-0 emission from the long-period comet C/2013 R1 (Lovejoy) was observed from the Onsala Space Observatory on multiple occasions during the month before its perihelion passage on December 22, 2013. We report detections for seven different dates, spanning heliocentric distances (R_h) decreasing from 0.94 to 0.82 au. Estimated HCN production rates are generally higher than previously reported for the same time period, but the implied increase in production rate with heliocentric distance, Q_{HCN} proportionate to R_h^{-3.2}, represent well the overall documented increase since it was first observed at R_h=1.35. The implied mean HCN abundance relative to water in R1 Lovejoy is 0.2%. We also report on a detection of HCN with the new 3 mm receiver system at Onsala Space Observatory in comet C/2014 Q2 (Lovejoy) on January 14, 2015, when its heliocentric distance was 1.3 au. Relative to comet C/2013 R1 (Lovejoy), the HCN production rate of C/2014 Q2 (Lovejoy) was more than 5 times higher at similar heliocentric distances, and the implied HCN abundance relative to water 0.09%.