Activity of main-belt comet 324P/La Sagra

Aims. We study the activity evolution of the main-belt comet 324P/La Sagra over time and the properties of its emitted dust. Methods. We performed aperture photometry on images taken by a wide range of telescopes at optical and thermal infrared wavelengths between 2010 and 2021. We derived the combined scattering cross section of the nucleus and dust (when present) as a function of time, and we derived the thermal emission properties. Results. Fitting an IAU H-G phase function to the data obtained when 324P was likely inactive, we derived an absolute nucleus magnitude H R = (18.4 ± 0.5) mag using G = 0.15 ± 0.12. The activity of 324P/La Sagra during the 2015 perihelion passage has significantly decreased compared to the previous perihelion passage in 2010, and it decreased even further during the 2021 perihelion passage. This decrease in activity may be attributed to mantling or to the depletion of volatile substances. The A f ρ profile analysis of the coma of the main-belt comet suggests a near-perihelion transition from a lower-activity pre-perihelion to a higher-activity post-perihelion steady state. We calculate a dust geometric albedo in the range of (2–15)%, which prevents us from constraining the spectral type of 324P/La Sagra, but we found an indication of dust superheating at 4.5 μm.