Photometry and imaging of comet C/2004 Q2 (Machholz) at Lulin and la Silla

Aims. We have investigated the development of the dust and gas coma of the comet C/2004 Q2 (Machholz) from December 2004 to January 2005 using observations obtained at the Lulin Observatory, Taiwan and the European Southern Observatory at La Silla, Chile. Methods. We determined the dust-activity parameter Afρ and the dust color and derived Haser production rates and scale lengths of C₂ and NH₂. An image enhancement technique was applied to study the morphology of the gas and dust coma. Results. Two jets were observed in the coma distributions of C₂ and CN of comet Machholz that were not formed in the dust coma. The jets showed a spiral-like structure and pointed at different position angles at different observing times. The formation of these jets can be explained by the presence of two active surface regions on a rotating cometary nucleus.