The distant activity of Short Period Comets - II.

Details The distant activity of Short Period Comets - II. The distant activity of Short Period Comets - II.

Oct 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008mnras.390..265m&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 390, Issue 1, pp. 265-280.

Astronomy and Astrophysics

Astronomy

8

Comets: General

Scientific paper

The activity of the Short Period Comets (SPCs) at large heliocentric distance (Rh > 3 au) occurs in a region of the Solar system where the water sublimation rate is low and so the sublimation of other volatiles, for example CO or CO2, could drive the presence of a coma. The detection of distant activity in a SPC can therefore give important hints on its composition. Moreover, a complete characterization of the distant SPCs degree of activity is crucial in order to give correct estimates of the nucleus size and to obtain more reliable size-distribution curves of cometary nuclei.
The aim of this paper is to present the last results of a program of CCD imaging of distant SPCs, started in 2004 December and concluded with observing runs at the 3.5-m Telescopio Nazionale Galileo at La Palma, in 2005 April, and at the 2.2-m Centro Astronómico Hispano Alemán (CAHA) telescope in Spain, in 2005 May.
During the Spring 2005 campaign, 12 SPCs have been targeted in the R band (eight numbered SPCs and four still unnumbered SPCs): 61P/Schajn-Schaldach, 71P/Clark, 98P/Takamizawa, 103P/Hartley 2, 117P/Helin-Roman-Alu 1, 118P/Shoemaker-Levy 4, 121P/Shoemaker-Holt 2, 136P/Mueller 3, P/2002 T5 (LINEAR), P/2003 S1 (NEAT), P/2003 S2 (NEAT), P/2004 DO29 (Spacewatch-LINEAR). The heliocentric distance of the targets was 3.05 <= Rh <= 5.30 au.
Several levels of activity were detected in the sample, from stellar appearance to well-developed coma and tail. In some cases, the occurrence of cometary activity could be enhanced only with deep visible imaging (e.g. with very long exposure time). For comets with stellar appearance, it was possible to derive a value or a range for the nucleus radius rnucleus (assuming a `classical' albedo value of 0.04): 98P (rnucleus = 0.43 +/- 0.10 km), 136P (rnucleus = 1.2 +/- 0.2 km), P/2003 S2 (rnucleus = 0.81 to 1.55 km). For the active comets, we measured dust production levels in terms of Afρ quantity, which was 9.9 <= Afρ <= 671 cm.
Ensemble properties of the whole sample of the long-term program (a total of 17 SPCs) have been analysed in terms of the relationship among distant activity and dynamical evolution of the targets (in particular, an inward `jump' of the perihelion distance): we can conclude that, even if there is some theoretical indication that this could occur, the hypothesis of distant activity triggered by a rise in perihelion temperature cannot be univocally invoked for these comets.
Based on observations collected at the Italian Telescopio Nazionale Galileo (TNG), operated on the island of La Palma by the Centro Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, and at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institute für Astronomie and the Instituto de Astrofísica de Andalucia (CSIC).
E-mail: epifani@oacn.inaf.it

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