Research Note

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

¹ Department of Earth and Space SciencesChalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
e-mail: eva.wirstrom@chalmers.se
² Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 412 96 Gothenburg, Sweden
³ Department of Applied Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden

Received: 30 September 2015
Accepted: 18 February 2016

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 ∝ 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%.