67P and 103P comets TRAPPIST data

From the broadband images, we produced light curves and computed color indices for each passage, and we derived the activity slopes. We used a Haser model to compute the production rates of five gaseous species (CN, C_2_, C_3_, OH, and NH) and derived the proxy parameter Af{rho} for dust activity. We also observed both comets in spectroscopy during their most recent apparition using the Himalayan Chandra Telescope and compared the spectroscopic data to our results obtained through photometry.

For both comets, our analysis of coma colors does not reveal any significant change from one passage to the other, indicating that the properties of the released dust grains are similar. Our values of the color indices are consistent with the mean values for Jupiter-family comets. We measured a slight increase in the gas and dust activities of comet 67P between 2015 and 2021, probably due to the small change in the comet's orbit that led the perihelion distance to decrease from 1.24 au for the first apparition to 1.21 au for the second one.

Regarding 103P, we unambiguously measured a decrease (of at least 50%) in the gas and dust activities between 2010 and 2023, showing a different behavior for this young, active comet. We find a typical chemical composition for both comets and detect no variation of the C2-to-CN production rate ratios and dust-to-gas ratios from one passage to the other, indicating constant compositions, even if the level of activity has changed for 103P.