摘要：We present a unique data set of more than one year’s worth of regular observations of
comet C/2013 A1(Siding Spring) taken with TRAPPIST, along with low-resolution spectra
obtained with the ESO/VLT FORS 2 instrument. The comet made a close approach to Mars on
October 19, 2014, and was then observed by many space-borne and ground-based telescopes.
We followed the evolution of the OH, NH, CN, C3, and C2 production rates as well as the Afρ parameter, a proxy for
the dust production. We detected an outburst two weeks after perihelion, with gas and dust
production rates increased by a factor of five within a few days. By modelling the shape
of the CN and C2
radial profiles, we determined that the outburst happened on November 10 around 15:30 UT
(±5 h) and measured a gas
expansion velocity of 1.1 ±
0.2 km s-1. We used a thermal evolution model to reproduce the
activity pattern and outburst. Our results are consistent with the progressive formation
of a dust mantle explaining the shallow dependence of gas production rates, which may be
partially blown off during the outburst. We studied the evolution of gas composition,
using various ratios such as CN/OH, C2/OH, or C3/OH, which showed little or no variation with
heliocentric distance, including at the time of the outburst. This indicates a relative
level of homogeneity of the nucleus composition.
