Physical studies of 81P/Wild 2 from the last two apparitions

Abstract

Context. We downloaded data for the comet 81P/Wild 2 for May and June 2004 from the ESO archive and monitored this comet from January to August 2010 during its 6th perihelion passage since its discovery in 1978. Photometric data were used to monitor the comet's gas and dust activity as a function of heliocentric distance. Non-photometric data were used for an analysis of the evolution of the dust coma morphology. Aims. The goal of the analysis of the observational data was to characterize the evolution of the cometary activity as the nucleus approaches the Sun. We also aimed to assess the gas and dust production rates for the last two apparitions and investigated the evolution of the dust coma morphology during the last passage in 2010. Methods. The long-slit spectra data were acquired with the EFOSC2 instrument mounted at the 3.6. m ESO telescope in Chile, while narrowband and broadband images were obtained using the 1-m telescope at the Lulin Observatory in Taiwan. Image enhancing techniques were used to investigate the evolution of the dust coma morphology in the R-broadband images, and we modeled the evolution of these dust jets. Where possible, we studied the dust and gas production rate, and the radial profiles of the dust brightness in the Sun-anti-sunward directions.Results. The morphological analysis helped us to detect the jet structures in the dust coma by using the Larson-Sekanian filter. In May 2004, only one feature had been found on the sunward side. In 2010, one of the jet features had been switched-off after January, and at least four new jets were found from April to May. The physical properties show an average reddening between 4420 Å and 6840 Å of 8.4% per 1000 Å and the average resulting log of the C 2 -to-CN production rate ratio is -0.454 ± 0.13, which would place Wild 2 in the "depleted" category according to the taxonomic classification. The slope of the radial dependence of the gas production rates for CN and C 2 is very consistent with observations of many other Jupiter-family comets. The slopes of the surface brightness lie between 0.98 and 1.38 in the images taken at the Lulin observatory, whose the range interval from 2000 km to 30 000 km is roughly consistent with the ρ −1 law. However, the gradient of the radial profile in the sunward direction in the outer region (4.0 ≤ log ρ(km) ≤ 4.5) is slightly steeper than that in the inner region (3.3 ≤ log ρ(km) ≤ 4.0).

Spin and activity of comet 67P/Churyumov-Gerasimenko

“…Over the past four years we have developed a model of dust coma structures, aiming at simulating the behavior of dust jets from the subsurface of cometary nuclei up to thousands of kilometers away from the surface. Our model was used successfully to study several targets: 73P/Schwassmann-Wachmann 3 (Vincent et al 2010a), 9P/Tempel 1 (Vincent et al 2010b), and 81P/Wild 2 (Lin et al 2012). For the last two targets, we have reproduced the behavior of the jets from ground-based observations only, with results that agree with in situ measurements by the Deep Impact and Stardust spacecrafts.…”

“…However, a full understanding of the origin of these collimated outflows is not required to perform simulations at the scale of our observed images. As we have shown in Vincent et al (2010b) and Lin et al (2012), good approximations of the initial size and velocity distributions of the particles are sufficient to fully reproduce the behavior of the jets. Thus our model does not simulate the initial acceleration phase of the dust particles when they are lifted from the surface and accelerated by the gas.…”

“…It has been shown, though, that most of the very collimated features such as thoses described in this paper can be explained by the presence of active regions on the surface, which rotate with the nucleus. For several in-situ missions and comets, Farnham et al (2007Farnham et al ( , 2012, Vincent et al (2010b), and Lin et al (2012) could follow the evolution of the dust jets and connected them unambiguously to specific regions of the surfaces without requiring large-scale gas flows and a specific topography to constrain the jets. Although we understand the importance of the nucleus concavities on the global flows and broad features observed in the coma (for instance Szegö et al 2002 on jets of comet 1P/Halley), they are not needed to explain the narrow, collimated structures described here.…”

TRAPPIST monitoring of comet C/2012 F6 (Lemmon)

“…A reddening between 5 and 12%/1000 Å was found by Lin et al (2013) for comet Hartley 2. Lin et al (2012) found that comet 81P/Wild 2 was redenned by approximately 8.2-8.6%/1000 Å. Dust reddening for comet C/2000 WM1 was also around the same value (Lara et al 2004).…”

Observations and analysis of a curved jet in the coma of comet 67P/Churyumov-Gerasimenko

“…This is the first time that a spiral structure was seen in the near-coma region of a comet, and it was made possible by the close distance of the Rosetta spacecraft to the comet nucleus. Nevertheless, from groundbased observations (Samarasinha & A'Hearn 1991;Lin et al 2007Lin et al , 2012Lin et al , 2013, we also saw a repeated curved appearance of the gaseous and dust jets that was related to the rotation of the nucleus. The curved appearance of the jets might also have been caused by solar gravity and radiation pressure.…”