Gemini and Lowell observations of 67P/Churyumov−Gerasimenko during the Rosetta mission

Abstract

We present observations of comet 67P/Churyumov-Gerasimenko acquired in support of the Rosetta mission. We obtained usable data on 68 nights from 2014 September until 2016 May, with data acquired regularly whenever the comet was observable. We collected an extensive set of near-IR J, H, and Ks data throughout the apparition plus visible-light images in g , r , i , and z when the comet was fainter. We also obtained broadband R and narrowband CN filter observations when the comet was brightest using telescopes at Lowell Observatory. The appearance was dominated by a central condensation and the tail until 2015 June. From 2015 August onwards there were clear asymmetries in the coma, which enhancements revealed to be due to the presence of up to three features (i.e., jets). The features were similar in all broadband filters; CN images did not show these features but were instead broadly enhanced in the southeastern hemisphere. Modeling using the parameters from Vincent et al. (2013) replicated the dust morphology reasonably well, indicating that the pole orientation and locations of active areas have been relatively unchanged over at least the last three apparitions. The dust production, as measured by A(0 • )f ρ peaked ∼30 days after perihelion and was consistent with predictions from previous apparitions. A(0 • )f ρ as a function of heliocentric distance was well fit by a power-law with slope −4.2 from 35-120 days post-perihelion. We detected photometric evidence of apparent outbursts on 2015 August 22 and 2015 September 19, although neither was discernible morphologically in this dataset.

MUSE observations of comet 67P/Churyumov-Gerasimenko

“…We obtain values of 65 ± 4 cm, 75 ± 4 cm, and 82 ± 4 cm in the V, R, and I bands, respectively. Those values have not been corrected for the phase angle effect and are consistent with those reported by Boehnhardt et al (2016) at the same epoch, and they are comparable (even though slightly lower) to those reported by Knight et al (2017) once the phase angle effect is taken into account. Using the Afρ values in the different bands, we can also compute the dust reflectivity gradient defined as (Jewitt & Meech 1986):…”

“…In addition to the two jets mentioned above, we see an enhancement towards the North-West. This corresponds to the dust trail that was reported to be at least two degrees long at that epoch (Snodgrass et al 2017a;Boehnhardt et al 2016;Knight et al 2017). We do not see changes of the coma morphology over the five nights of our observations, nor over a single night.…”

The 67P/Churyumov–Gerasimenko observation campaign in support of the Rosetta mission

“…This pattern showed a slow evolution [29,39,40], with the relative intensity of the different jets approximately following the changing seasons on the comet-the southern structures are brighter around perihelion when this hemisphere of the nucleus is illuminated [41]. Preliminary analysis of coma morphology seen throughout the apparition is consistent with predictions [14] for the source regions and pole solution (JB Vincent 2016, private communication), indicating that these jets are features that reappear each orbit [29,39,42]. Further analysis of the shape of the coma reveals evidence for a short-lived change (outburst) in late August 2015, around the time of peak activity post-perihelion, and a change in the slope Images are centred on the comet and an azimuthal median profile has been subtracted to reveal the fainter underlying structure.…”

“…Although we refer to these structures as jets, they may be projections of broader dust flows (fans), and do not necessarily relate to the narrow jets seen in Rosetta images of the inner coma [38]. This pattern showed a slow evolution [29,39,40], with the relative intensity of the different jets approximately following the changing seasons on the comet-the southern structures are brighter around perihelion when this hemisphere of the nucleus is illuminated [41]. Preliminary analysis of coma morphology seen throughout the apparition is consistent with predictions [14] for the source regions and pole solution (JB Vincent 2016, private communication), indicating that these jets are features that reappear each orbit [29,39,42].…”

Narrowband Observations of Comet 46P/Wirtanen During its Exceptional Apparition of 2018/19 II: Photometry, Jet Morphology, and Modeling Results

“…We determined centroids using a 2D Gaussian fit to the inner coma and used these centroids for photometric measurements, aligning images, and for applying our standard image enhancement routines (e.g., Knight et al 2017). A variety of image enhancement techniques were utilized when exploring the data, with removal of a temporal average (based on the period determined in Paper I) preferred when sufficient data were available, and removal of an azimuthal median favored otherwise.…”