We monitor the inner coma of comet 41P/Tuttle-Giacobini-Kresák searching for variations of its colour. Fast changes in colour of the comet 41P/Tuttle-Giacobini-Kresák provide important clues for better understanding of the microphysical properties of its dust. Using the 61-cm and 70-cm telescopes we measured the apparent magnitude of the comet with the V and R Johnson-Cousins filters from January 29 until April 25 of 2017. The inner coma (2000 km) reveals fast and significant variations of colour. The most significant change was found between March 3 and 4 of 2017, when it changed from blue with a colour slope S  (-10.15 ± 3.43)% per 0.1 μm to red with S  (16.48 ± 4.27)% per 0.1 μm. This finding appears in good accordance with what was previously reported by Ivanova et al. (2017) for long-period comet C/2013 UQ4 (Catalina),suggesting that fast and significant variations of colour of dust could be a common feature of short-and long-period comets. We model observations of comet 41P/Tuttle-Giacobini-Kresák using the agglomerated debris particles and conclude that its inner coma consists of a mixture of at least two types of particles made of Mg-rich silicates and organics or Mg-Fe silicates.

We report results of our polarimetric observations of comet 21P/Giacobini-Zinner made at phase angles, α ≈ 76-78°, between 10 and 17 of September, 2018, and compare them with previous measurements. We find significant variations in the polarimetric signals that appear consistent with those reported previously. These variations and subsequent modeling suggest that the particles in the coma are replenished within a period of approximately one day. This period is significantly shorter for highly absorbing carbonaceous particles than for non-absorbing Mg-rich silicate particles. Such a difference in the relative abundances of these components can lead to variations in the polarization response of the coma. The strong positive polarization in the subsolar direction suggests a large relative abundance of carbonaceous material, which may be an indicator of jet-type activity.

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