Photometry of C/2011 L4 (PANSTARRS) five days after perihelion
- C/2011 L4 (PANSTARRS) from Stourton Caundle on March 14.80:
Have managed to carry out V photometry of C/2011 L4 some 4.7 days
post-perihelion when at a solar elongation of 16.2°. Observing conditions
were (just) satisfactory in that I was able to take a series of 22 images
during a clear sky interval whilst the comet was at an altitude of 6.0-6.3°.
It was extraordinary and fortuitous that an A0 comparison star was located
just 17' from the nucleus and so an absolute precision of +/-0.03 mag was
The tracked and stacked image can be seen at:
The photometric growth curve (circular apertures) is available at:
Total (m1) magnitude (2013 March 14.797): +0.8 mag (+/-0.1)
Tail length: 30'
Note that this determination is based on a limited extrapolation of the
Photometric integration out to a measured 10' tail length gives a magnitude
The ephemeris prediction indicates the comet would have faded by 0.5
magnitudes on March 14.80 compared to when brightest close to perihelion.
So the conclusion is that this comet reach a minimum m1 of +0.3 and so never
attained a negative magnitude. Hopefully these observations should help put
the lightcurve on a sounder footing.
British Astronomical Association