Nucleus of the active Centaur C/2011 P2 (PANSTARRS)^⋆

¹ INAF–Osservatorio Astronomico di Roma, via Frascati 78, 00040 Monte Porzio Catone, Roma, Italy
e-mail: elena.epifani@oa-roma.inaf.it
² LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place J. Janssen, 92195 Meudon, France
³ Universitá Parthenope, Dipartimento di Scienze e Tecnologie, Centro Direzionale Isola C4, 80143 Napoli, Italy
⁴ INAF–IAPS, via Fosso del Cavaliere 100, 00133 Roma, Italy
⁵ INAF–Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
⁶ ESA SSA-NEO Coordination Centre, Frascati, Roma, Italy
⁷ Deimos Space, Strada Buchesti 75-77, Bucharest, Romania

Received: 29 February 2016
Accepted: 8 September 2016

Abstract

Aims. In this paper we present observations of the active Centaur C/2011 P2 (PANSTARRS), showing a compact comet-like coma at the heliocentric distance of r_h = 9 au. The observations were obtained in the framework of a wider program on Centaurs aimed at searching for comet-like activity in several targets outside Jupiter’s aphelion.

Methods. We analysed visible images of the Centaur taken at the TNG telescope in the R filter to investigate the level of coma contributing to the target brightness and to derive information on its nucleus size.

Results. Centaur C/2011 P2 (PANSTARRS) shows a faint but still detectable comet-like activity, which accounts for more than 50% to the observed brightness. The coma contribution has been subtracted in order to derive an estimate for the Centaur’s diameter of D ~ 16 km, assuming an albedo of A = 0.07 (average of albedo measured within the Centaur group). The results for Centaur C/2011 P2 (PANSTARRS) fit in the general picture of the group: Centaurs with smaller perihelion distance q and semi-major axis a are smaller than those remaining farther from the Sun during their orbital path, thus reinforcing the idea that active Centaurs are “comets in fieri”.