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Photometry of C/2011 L4 (PANSTARRS) five days after perihelion

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  • Richard Miles
    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
    Message 1 of 1 , Mar 15, 2013
      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
      possible.

      The tracked and stacked image can be seen at:
      http://www.britastro.org/~rmiles/Documents/C2011L4_20130314_RMiles_Vfilter.jpg

      The photometric growth curve (circular apertures) is available at:
      http://www.britastro.org/~rmiles/Documents/C2011L4_20130314_RMiles_Vphotometry.gif

      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
      data.
      Photometric integration out to a measured 10' tail length gives a magnitude
      of +1.0.

      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.

      Richard Miles
      British Astronomical Association
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