Mt. Wendelstein imaging of comet 41P/Tuttle-Giacobini-Kresak during the 2017 perihelion arc

Abstract

Context. In April 2017 comet 41P/Tuttle-Giacobini-Kresak (41P) passed perihelion close to Earth. Aims. We present observations of the comet and aim to use these to characterize its dust environment in the coma and of physical properties of the nucleus. Methods. 41P was imaged in the visible at the Mt. Wendelstein observatory over 45 nights between 2017 March 11 and 2017 July 17. Photometry of the coma provides information on the dust activity of the comet. Nucleus dimensions are determined by comparing radial profiles of observed images with those from models of the brightness distribution in the near-nucleus coma. Coma and tail structures in the images are enhanced using adaptive Laplace filtering and image normalization techniques. The geometry of the coma structures found are compared to results from dust models of the comet in order to obtain information on the nucleus rotation axis and the location of active regions on the nucleus. Results. Analyzing the evolution of the dust activity of the comet versus solar distance gives different results depending on the assumed phase angle corrections for the dust. Contamination from light emissions of the coma gas modified the colors in the coma and the slopes of the radial profiles. The light distribution in the very inner coma indicates some dust fragmentation close to the nucleus. The appearance of a prominent coma fan during the time period from March to May 2017 constrains the rotation axis of the nucleus (52 deg obliquity, 50 deg rotation angle of the perihelion meridian). This fan is produced by an extended region beyond about 50 deg latitude on the nucleus. Two narrow regions at low northern to equatorial latitudes were responsible for the time-variable occurrence of linear dust jets in the coma. An outburst of about 0.6 mag on 2017 May 11 generated various dust structures in the coma. The outburst originated from a region extending over a latitude range from +30 deg to -5 deg and released about 3 000 tons of dust into the coma. The brightness of the nucleus indicates an equivalent radius of about 600 m and a minimum axis ratio larger than two.

Resolving color differences of comet 41P/Tuttle-Giacobini-Kresák

“…A comprehensive analysis of these observations resulted in significantly different color slopes obtained by these different groups over different epochs. This Letter aims to clarify the color-slope conception and provide an explanation for the difference between the results reported in Boehnhardt et al (2020, and Moulane et al (2018).…”

“…(1), we find S = (18.03 ± 5.76)% per 0.1 µm. Less than one day earlier, on April 12, Boehnhardt et al (2020) report the brightness of Comet 41P/T-G-K with the SDSS-r (λ 1 = 0.6303 µm) and SDSS-i (λ 2 = 0.7595 µm) filters. Taking the corresponding color index of the Sun (0.11 m ) into account, we obtain the true color index ∆m = (−0.17 ± 0.06) mag for the aperture diameter of 10 000 km, which is the same as in Moulane et al (2018).…”

“…Multi-wavelength photometry of Comet 41P/Tuttle-Giacobini-Kresák's (hereafter 41P/T-G-K) 2017 apparition has been conducted by at least three independent groups (i.e., Boehnhardt et al 2020;Luk'yanyk et al 2019;Moulane et al 2018). A comprehensive analysis of these observations resulted in significantly different color slopes obtained by these different groups over different epochs.…”

“…However, they started their observations on March 11, 2017, a week after the phenomenon was observed by Luk'yanyk et al (2019), and this type of activity would have changed in the subsequent period between measurements. In comparison, Boehnhardt et al (2020) also considered the results from Moulane et al (2018) obtained on March 3, 2017. For this epoch, Moulane et al (2018) reported two values of the A f ρ parameter (e.g., A'Hearn et al 1984) measured with the BC (λ 1 = 0.445 µm) and RC (λ 2 = 0.715 µm) filters from the HB photometric system (Farnham et al 2000).…”

“…While Boehnhardt et al (2020) suggest differences in the results of Moulane et al (2018) with those of Luk'yanyk et al (2019), there are also differences in the results of Boehnhardt et al (2020) with those of Moulane et al (2018). For instance, we adapted the measurements from Moulane et al (2018) of the A f ρ parameter in Comet 41P/T-G-K with the above-mentioned BC and RC filters on April 13, 2017.…”