Comet McNaught (260P/2012 K2): spin axis orientation and rotation period

Abstract

Extensive observations of comet 260P (McNaught) were carried out between August 2012 and January 2013. The images obtained were used to analyze the inner coma morphology of the comet at resolutions ranging from 250 to about 1000 km/pixel. A deep investigation of the dust features in the inner coma allowed us to identify only a single main active source on the nucleus of the comet, at an estimated latitude of -50 deg +/-15 deg. A thorough analysis of the appearance and of the motion of the morphological structures, supported by graphic simulations of the geometrical conditions of the observations, allowed us to determine a pole orientation located within a circular spot of a 15 deg-radius centered at RA=60 deg, Dec=0 deg. The rotation of the nucleus seems to occur on a single axis and is not chaotic, furthermore no precession effects could be estimated from our measurements. The comet's spin axis never reached the plane of the sky from October 2012 to January 2013; during this period it did not change its direction significantly (less than 30 deg), thus giving us the opportunity to observe mainly structures such as bow-shaped jets departing from the single active source located on the comet's nucleus. Only during the months of August 2012 and January 2013 the polar axis was directed towards the Earth at an angle of about 45 deg from the plane of the sky; this made it possible to observe the development of faint structures like fragments of shells or spirals. A possible rotation period of 0.340 +/-0.01 days was estimated by means of differential photometric analysis.