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 comet's inner coma morphology 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 comet's nucleus, at an estimated latitude of -50° ± 15°. 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°-radius centered at RA = 60°, Dec = 0°. 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°), 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° 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.

Rotation of cometary nuclei: new light curves and an update of the ensemble properties of Jupiter-family comets

“…While the method used in Manzini et al (2014) has been used successfully to derive other rotations periods of comets with weak jet activity (e.g. Reyniers et al 2009), we regard the results on 260P with caution.…”

“…260P was discovered in 2012, and the most reliable estimate of its effective radius to date is 1.54 +0.09 −0.08 km (Fernández et al 2013). Its rotational characteristics were studied by Manzini et al (2014) with ground photometric observations while the comet was around perihelion in 2012 and 2013. Manzini et al (2014) used coma structures to constrain the pole orientation of the comet, but they were unable to use the coma morphology to derive a rotational period.…”

“…Its rotational characteristics were studied by Manzini et al (2014) with ground photometric observations while the comet was around perihelion in 2012 and 2013. Manzini et al (2014) used coma structures to constrain the pole orientation of the comet, but they were unable to use the coma morphology to derive a rotational period. Instead, the comet's lightcurve was obtained by measuring the coma brightness with apertures larger than the seeing disc but small enough to include only contribution from the coma at a distance up to 2000 -2500 km from the surface (Manzini et al 2014).…”

“…Manzini et al (2014) used coma structures to constrain the pole orientation of the comet, but they were unable to use the coma morphology to derive a rotational period. Instead, the comet's lightcurve was obtained by measuring the coma brightness with apertures larger than the seeing disc but small enough to include only contribution from the coma at a distance up to 2000 -2500 km from the surface (Manzini et al 2014). The resulting lightcurve had a variation of 0.07 mag and could be phased with a few possible periods, best summarised as 8.16 ± 0.24 hours.…”