Comet C/2011 L4 (PanStarrs): Small nucleus, fast rotator and dust rich comet observed after perihelion

Abstract

Orbital elements of C2011 L4 (PanStarrs) Oort cloud comet, computed by MPC (Minor Planet Center, Minor Planet Electronic Circular 2012-T08), show that the closest approach to the Sun occurred on 2013 March 10th, at about 0.3 A.U., then about 4,51x10^7 km. Discovered by Richard Wainscoat (Institute for Astronomy, University of Hawaii) on four CCD images taken with the 1.8-m "Pan-STARRS 1" telescope at Haleakala taken on 2011 June 6th. My first observation of the comet was on 2013 March 10th whit the comet visible in the twilight. I did the following visual estimation; Mar. 10.73,-1.0*,5'(T. Scarmato, Calabria, Italy, 7x50 binoculars; altitude 7 deg, tail 1 deg in pa 140 deg), reported to the ICQ (International Comet Quarterly). Easy comet in 7x50 binoculars I started to see C/2011 L4 at 18:35 L.T. when the comet was at about 7{\deg} above the horizon. I saw a tail long about 1,5{\deg} in pa 140{\deg} with a coma well condensed and large about 5'. I followed the comet until to the set at 18:55 L.T., still clearly visible at so low altitude about 1{\deg} or less! I don't saw Mars (1.39 mag) at the same altitude, so I esteemed the comet using Aldebaran (1.1 mag) at 62,44{\deg} of altitude also using the ICQ Table of Atmospheric Extinction; but remembering C/2006 P1 in the same conditions of observation I could to assume that the comet was at negative apparent total magnitude m1= -1.0. The image of the comet was impressive (see Fig. 2). Here, I present my observations and results on the size of the nucleus, period of rotation, dust production and peculiar structures in the inner coma. Key words: General: general; comets: C/2011 L4 (PanStarrs), PanStarrs, comets, afrho, photometry of aperture, flux, apparent magnitude, absolute magnitude; comet nucleus: size, rotation.