Konkoly Observatory, MTA Research Centre for Astronomy and Earth
Konkoly Thege 15-17,
2 Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, Giessenbachstr., 85741 Garching, Germany
3 Herschel Science Centre, ESAC, European Space Agency, 28691 Villanueva de la Cañada, Madrid, Spain
4 STAR, Stockholm Amateur Astronomers, Drottninggatan 120, 11360 Stockholm, Sweden
Received: 8 October 2014
Accepted: 23 December 2014
The thermal emission of comet C/2013 A1 (Siding Spring) was observed on March 31, 2013, at a heliocentric distance of 6.48 au using the PACS photometer camera of the Herschel Space Observatory. The comet was clearly active, showing a coma that could be traced to a distance of ~10′′, i.e. ~50 000 km. Analysis of the radial intensity profiles of the coma provided a dust mass and dust production rate and the derived grain size distribution characteristics indicate an overabundance of large grains in the thermal emission. We estimate that activity started about 6 months before these observations at a heliocentric distance of ~8 au.
Key words: techniques: photometric / comets: individual: C/2013 A1 (Siding Spring) / comets: general
Herschel is an ESA space observatory with science instruments provided by European-lead Principal Investigator consortia and with important participation from NASA.
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2015