Variation of the water production rate of comet C/2013 X1 (PanSTARRS) from SOHO/SWAN observations throughout its apparition
Abstract
The all-sky hydrogen Lyman-alpha camera, SWAN (Solar Wind ANisotropies), on the SOlar and Heliospheric Observatory (SOHO) satellite makes observations of the hydrogen coma of comets. Most water vapor produced by comets is ultimately photodissociated into two H atoms (in addition to one O atom) producing a huge atomic hydrogen coma that is routinely observed in the daily full-sky SWAN images in comets of sufficient brightness. Water production rates are calculated using our time-resolved model (Mäkinen & Combi, 2005, Icarus 177, 217), typically yielding about 1 observation every 2 days on the average over an apparition. Here we describe the analysis of observations of bright comet C/2013 X1 (PanSTARRS) observed during 2016. C/2013 X1 reached a perihelion distance of 1.314278 AU on 20.72 April 2016. Its brightening toward the end of June 2016 is influenced by a somewhat close geocentric distance of 0.64 AU. A status update on the entire SOHO/SWAN archive of water production rates in comets will also be given. Support from grants NNX15AJ81G from the NASA Solar System Observations Planetary Astronomy Program and NNX13AQ66G from the NASA Planetary Mission Data Analysis Program are gratefully acknowledged, as is support from CNRS, CNES, and the Finnish Meteorological Institute (FMI).