The dust coma environment of the short period comets 32P/Comas Sola, 56P/Slaughter-Burnham and 78P/Gehrels 2 from ground-based observations

Aims. The aim of this paper is to contribute to the characterisation of the general properties, differences, and commonalities of the short period comet family and, more in particular, to characterise the dust environment of three poorly studied members of the family: 32P/Comas Solá, 56P/Slaughter-Burnham, and 78P/Gehrels 2. Methods. Multicolour broad-band photometry of the comets observed around their perihelion in October 2004 from the Loiano telescope has been used to characterise their dust coma morphology and properties and to model the dust production rate Results. 32P/Comas Solá shows no remarkable dust coma features, while both 56P/Slaughter-Burnham and 78P/Gehrels 2 show departures from regular brightness distribution, with a north/south asymmetry and axysimmetric lobes, respectively, probably indicating emission features on the nucleus surface. For comet 78P, it has been possible to compute a 1-D surface brightness profile with slope m = −1.54 ± 0.05. In an aperture of radius ρ = 7.2 × 103 km, the measured Afρ is 127 ± 10 cm, 102 ± 8 cm (weighted average between two observing nights) and 846 ± 55 cm for comets 32P, 56P and 78P, respectively. All comets have a redder dust coma than the Sun. Comets 32P (dust production rate Qd from 2 to 46 kg/s) and 56P (Qd from 1 to 24 kg/s) are quite standard dust emitters among the short-period comet family, while comet 78P (Qd from 14 to 345 kg/s) is more active than the average at that heliocentric distance.