[AZ-Observing] Re: Changes in 17P/Magnitude
- From: Brian Skiff <bas@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Thu, 25 Oct 2007 15:03:59 -0700 (MST)
Thanks for the data and profile. If I'm reading the chart
correctly, the comet is about 15 pixels diameter (and what is the
image scale in arcsec/pixel?). So I would set the sky annulus to
start at at least 15 pixels _radius_ and go out from there several
pixels to get enough counts. Leave the sky annulus fixed, and
re-do the aperture photometry with steps of maybe 2 pixel increments
from 2 to 10 or 12 pixels radius. In the list you sent, you have
evidently changed the sky annulus with each step in aperture,
so the results are not interpretable (basically you've include
some of the comet in the sky reading for the smaller annuli).
The sky annulus needs to be way outside the comet and _fixed_.
\Brian
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