Comet C/2013 X1 (PanSTARRS): Spin axis and rotation period

Abstract

Applying image processing and enhancement techniques to our CCD images we could investigate the structures of the inner coma of comet C/2013 X1; the dust tail and a broad fan-shaped structure that originated from a different area of the nucleus than the tail were clearly detected.The triangular shape of the fan suggested that it was the result of a continuous outflow of dust from a single active source located at mid-high latitude (about 60° on a supposed spherical nucleus) on the surface of the comet's nucleus oriented in sunward direction, and that the comet's spin axis was placed near the sky plane. This allowed us to estimate its orientation at RA 240°±10° (=16h00m) and declination +00°±10°. The fan structure remained quite stable in the 4-months observation period, indicating that the comet's spin axis remained steadily lying near the sky plane; a slow clockwise rotation of the fan in sunward direction appeared to be directly connected with the geometrical conditions of observation.Differential photometry applied to the inner coma, near the cometary nucleus, showed a light curve with an amplitude of 0.053 magnitudes, characterized by a highly repetitive periodicity throughout the entire observation period, and most likely related to the comet's rotation period, estimated at 0.498±0.015 days.Computer simulations of the coma features, as well as of the tail and spin axis positions, are fairly comparable with our observations, confirming the correctness of the findings.