Differential photometry experiment on Comet 17P - 2.59v

Differential photometry - not color index corrected - was attempted as
an experiment on Comet 17P on 2007-10-27 9:15 UTC. Using a wide-field
camera consisting of a Meade DSI adapted to a fish-eye lens, a wide
field (~14 deg) image of the region of Perseus around Comet 17P was
taken. The image was dark flatted but not white flatted. Using lam Per
as a reference star and AIP4WIN's single star photometry tool, a zero-
point was adopted that yielded the Tycho V catalogue magnitude for lam
Per. Using lam Per as the reference magnitude, differential
photometry was tested on del Per and V 48 Per (MX Per). Estimated
magnitudes were within the range of the small variation known for
those stars.

Differential photometery was then tried on Comet 17P resulting in an
estimate of 2.59v+-2%.

The comet is probably dimmer than this estimate as color index
correction could not be included. There is no internet published
color index for the comet.

This experiment illustrates how wide-field digital SLRs
might be used to prepare a time-series of differential photometry for
Comet 17P.

Comments and corrections to the above are welcomed and appreciated, as
I am doing this as a hobbyist learning exercise.

- Canopus56

Links -

Image with data annotations
http://gallery.utahastronomy.com/d/1...17P_Photom.PNG

(image with explanation)
http://gallery.utahastronomy.com/v/k...hotom.PNG.html

Photos about the adapted Meade DSI used to take the image
http://gallery.utahastronomy.com/v/k...est/?g2_page=2

On Oct 28, 9:40 pm, canopus56 wrote:
snip all

http://gallery.utahastronomy.com/d/1...Photometry.PNG

At Little Mtn, Utah, outside Salt Lake City, differential photometry -
not color index corrected - was repeated as an experiment on Comet 17P
on 2007-11-01 6:15 UT. (See prior obs rep 2007-10-27.) Using a wide-
field camera consisting of a Meade DSI adapted to a fish-eye lens, a
wide field (~14 deg) image of the region of Perseus around Comet 17P
was taken. The image was dark flatted but not white flatted. Using lam
Per as a reference star and AIP4WIN's single star photometry tool, a
zero-point was adopted that yielded the Tycho V catalogue magnitude
for
lam Per.

Differential photometery was then tried on Comet 17P resulting in an
estimate of 2.56+-2%. The same method was used on 2007-10-27 9:15UT,
at a higher altitude near the zenith of 2.59v+-2%.

The rough photometry image was taken in a mag 5.0 sky, just after a
3rd quarter moonrise on the eastern horizon at 6:00UT.

Before moonrise, 17P had a faint extended object appearance to the
naked eye. In 10x50 binoculars, a faint outer halo could be detected
outside the diffuse coma. The comet continues to present an end-on
annular appearance without a tail.

17P appeared dimmer than del Per to the naked-eye and after moonrise,
Comet 17P had a stellar appearance to the naked-eye. But these were
contrast illusions.

In 10x50 binoculars, the circumference of the diffuse coma of 17P had
the same angular size as the arc seen in the Pleaides defined by
17-16-19-20 Tau. Based on this comparision, the diffuse coma of 17P
had a size of approximately 20 arcmins. On 2007-10-27, it was less
than one-half this size. The continuing stellar appearance of Comet
17P appears related to its bright central nucleus - which has more
contrast to the naked-eye as compared diffuse coma.

While the total brightness of 17P appears to have remained the same
between 10-27 and 11-1, it appears dimmer to the naked eye due to the
rapid increase in its true and apparent sizes.

- Canopus56