[BAA Comets] CCD photometry of C/2011 L4 (PANSTARRS)

[Richard Miles]

Here's an update on photometric monitoring of this latest bright cometary 
visitor to our region of the solar system.

Observations have now been made using a 10.5-cm refractor + Astrodon 
dichroic V filter at 8 epochs from here in the UK.  So it is now worthwhile 
to examine the trend in brightness versus heliocentric distance. This can be 
seen in the following plot:

http://britastro.org/~rmiles/Documents/C2011L4_20130314-0420_redmag_Miles.png

N.B. The photometry is performed in a standard manner and the results drop 
out accordingly.  No question of subjectivity here, unlike visual 
observations. What is striking about the results so far is that they show 
that this comet exhibits uniform and regular behaviour with no evidence of 
the slightest outburst - in other words, a very "well-behaved" comet.

The brightness dependence versus heliocentric distance obeys a 2.5*n.log(rh) 
law, where n = 4.28

It would be nice if a few other observers joined in this type of work. The 
key requirement is a wide-field / astrograph-type optics with good optical 
correction plus an appropriate filter. The system I use has a FOV of 3.5x2.6 
degrees. In principle, anyone with a widefield DSLR colour camera could do 
likewise by analysing the 'Green' image provided a similar analytical method 
is followed. It is certainly a lot more laborious than visual observing but 
the results hopefully speak for themselves.

Remember this is a sort of practice run ahead of Comet ISON's apparition!

Richard Miles
BAA