Comet 29P/Schwassmann-Wachmann 1 dust environment from photometric observation at the SOAR Telescope

We report photometric observations of comet 29P/Schwassmann-Wachmann 1 made on August 12, 2016 with the broad-band B, V, R and I filters and the SOAR 4.1-meter telescope (Chile). We find the comet active at that time. Enhanced images obtained in all filters reveal three radial features in the 29P/Schwassmann-Wachmann 1 coma, regardless of the image-processing algorithm. Using a high-resolution spectrum of comet 29P/Schwassmann-Wachmann 1 reported by Ivanova et al. (2018) on the same date, we estimate the relative contribution of the gaseous emission and the continuum to the total response measured with our broadband B and V filters. The gaseous-emission contribution appears to be very small, 2.5%. We compute the dust production Afρ in 29P/Schwassmann-Wachmann 1 for the four filters and find its growth with the wavelength, from 3,393 ± 93 cm in the B filter to 8,561 ± 236 cm in the I filter. We model the color slope of dust in Comet 29P/Schwassmann-Wachmann 1 using agglomerated debris particles. Simultaneous analysis of the color slope in the B-R and R-I pairs suggests a single dominant chemical species of 29P/Schwassmann-Wachmann 1 dust particles consisting of Fe-Mg silicates and obeying a power-law size distribution with index n  ≈  2.55. This conclusion is consistent with the previous thermal-emission study of 29P/Schwassmann-Wachmann 1.