A survey on the distant activity of short period comets^*

¹ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: epifani@na.astro.it
² Universitá Parthenope, Dip. Scienze Applicate, Centro Direzionale Isola C4, 80143 Napoli, Italy

Received: 1 June 2009
Accepted: 3 October 2009

Abstract

Aims. The aim of this paper is to build up an inventory of observations of short period comets (SPCs) far from the Sun, and perform an analysis of general properties of the family, investigating the link between distant activity and present and historical orbital parameters.

Methods. We gathered all the data available in the literature (as per June 2009) on SPCs ground-based and space observations at heliocentric distance r_h > 3 AU. We analyzed the occurrence of distant activity with respect to: position on orbital branch, present orbital parameters (in particular the perihelion distance q), and their recent variations.

Results. There is no sharp cut-off at any heliocentric distance, beyond which the cometary activity fades and only bare nuclei are observed. SPCs are more likely to be active post-perihelion than pre-perihelion: among a dataset of 90 comets (for which a heliocentric distance of analysis has been unequivocally established), 59% of the comets observed post-perihelion were detected as active targets, while only 22% of the comets observed pre-perihelion were active. There is a weak trend of comets with increasing perihelion distance to be more likely active at large heliocentric distance: among comets with q < 1.5 AU, only 5 out of 18 comets (28%) have been reported as active at large heliocentric distance, while among those with q > 3 AU, 14 out of 16 comets (88%) have been classified as active. A much less clear trend has been observed for distant cometary activity with semi-major axis a. No apparent appreciable link of a recent (or secular) increase of the perihelion temperature  (due to a rapid decrease in the perihelion distance) with the present degree of distant activity has been observed.