Short-term variability of comet C/2012 S1 (ISON) at 4.8 AU from the Sun

Abstract

Context. We observed comet C/2012 S1 (ISON) during six nights in February 2013 when it was at 4.8 AU from the Sun. At this distance and time the comet was not very active and it was theoretically possible to detect photometric variations likely due to the rotation of the cometary nucleus. Aims. The goal of this work is to obtain differential photometry of the comet inner coma using different aperture radii in order to derive a possible rotational period. Methods. Large field of view images were obtained with a 4 k × 4 k CCD at the f/3 0.77 m telescope of La Hita Observatory in Spain. Aperture photometry was performed in order to get relative magnitude variation versus time. Using calibrated star fields we also obtained ISON's R-magnitudes versus time. We applied a Lomb-Scargle periodogram analysis to get possible periodicities for the observed brightness variations, directly related with the rotation of the cometary nucleus. Results. The comet light curve obtained is very shallow, with a peak-to-peak amplitude of 0.03 ± 0.02 mag. A tentative synodic rotational period (single-peaked) of 14.4 ± 1.2 h for ISON's nucleus is obtained from our analysis, but there are other possibilities. We studied the possible effect of the seeing variations in the obtained periodicities during the same night, and from night to night. These seeing variations had no effect on the derived periodicity. We discuss and interpret all possible solutions for the rotational period of ISON's nucleus.

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

“…As most observations leading to these size estimates occurred beyond Mercury's orbit, and Comet ISON was entering the inner solar system for the first time, the size estimates do not inform our specific understanding of near-Sun comets. Tentative measurements of ISON's rotation period seem to indicate that it was < 24 hours (Lamy et al 2014;Knight and Schleicher 2015;Santos-Sanz et al 2015). ISON is suspected to have broken up multiple times as it approached the Sun, evidenced by several changes in activity levels (Meech et al 2013;Opitom et al 2013).…”

Schroedinger’s Code: A Preliminary Study on Research Source Code Availability and Link Persistence in Astrophysics

“…Or even when the software used is not named, as in Santos-Sanz et al (2015), which said "A common reduction software programmed in IDL was used for the photometry of all the previously calibrated images." We do not know what software was used, but we do know something was.…”

2008 OG19: a highly elongated Trans-Neptunian object

“…Because of all the above we have been carrying out a rotational light curve survey of TNOs and Centaurs, for nearly two decades (e.g. Ortiz et al 2002Ortiz et al , 2004Ortiz et al , 2006Ortiz et al , 2007Ortiz et al , 2011Duffard et al 2008;Santos-Sanz et al 2008, 2015Lellouch et al 2002;Belskaya et al 2006;Thirouin et al ⋆ E-mail: estela@iaa.es (IAA) 2010) to gather important physical information about them. In the course of our survey the TNO with provisional designation 2008 OG19 showed interesting features such as a large amplitude of variability that encouraged us to make a very detailed study.…”