Brightness evolution of comet C/2011 L4 (Panstarrs)
Comet C/2012 L4 (Panstarrs) seems to be very tricky. After its discovery, it started brightening with unexpected speed, that leads to very optimistic prospects for this year. If the trend would continue, comet could became very bright even with negative magnitude values. Unfortunately, as it usually happens in case of dynamically new comets to which comet Panstarrs belongs, when it reach closer then 3 AU to Sun, brightening speed decreased a lot. This leads to opposite, very pessimistic scenario with maximum magnitude between 3-4 mag while comet is almost unobservable.
However visual estimates of comet brightness in past weeks suggesting another change in its brightening speed. Brightness of comet is again greater then expected, looks that comet get second breath. Because we are following comet for more then year with our robotic telescope FRAM, we tried to look into our CCD data if this trend is supported also by CCD measurements provided by one telescope and one measuring technique which should leads to very accurate data.
We note that accuracy of CCD measurements for comets is not that accurate as for example variable stars. Comets as diffuse objects are very sensitive to observing conditions, stars in coma etc. Because of that, we estimate magnitude error of our measurements between 0.2-0.3 mag. Still error is much smaller then for visual observations, where difference between observers reach almost 4 mag error, that prevent us of some detail light curve analysis.
Our data are in very good agreement with means values calculated from visual observations. Comet seems to really started brightening faster. It is very probable, that it could reach magnitude 2 or even more and become good naked eye object on northern sky after passing Sun.
Also very interesting is comet V-R color index. V filtered magnitudes representing brightness near green color, while R in red. While in green color, most of comet light coming from ionized gas, in R, main component is sunlight reflected on dust grains. Comet Panstarrs is brighter in red which shows it as very unusual dust rich comet. Our V-R values obtained in February also shows that comet brightening more in red and its dust do gas ratio is still growing.