[Aavso-photometry] Baseline photometry of HD 74156 at CBA Belgium Observatory - results

[Tonny Vanmunster]

Dear colleagues,

In order to prepare for the end of year transit observations of HD 74156
(and HD 37605), I started a baseline photometry session on HD 74156 in the
night of Dec 2/3, 2004. Observations lasted for about 5 hours (1h22m UT till
6h22m UT), resulting in more than 1200 CCD images. I used a 0.35-m f/6.3
telescope, with a V-filter and SBIG ST-7XME CCD camera. Due to the
brightness of HD 74156 (V = 7.61), I had to keep exposure times extremely
short (3 to 4 seconds), to avoid pixel saturation. Clearly, this had a
negative impact on the final precision of my photometric results (see
further).

The photometric analysis was done using MaxIm DL/CCD v4, using both single
and multiple comparison stars. The light curve is available at
www.cbabelgium.com. After having performed bias-dark-and-flatfielding,
images were stacked together per 5 and measured using aperture photometry.
Each data point in the light curve is the average of 4 photometric results
(each result representing 5 stacked CCD images). Also shown is the standard
deviation per bin.

The resulting light curve depicts - as expected - a nearly flat pattern. The
level of noise is higher than what I'd like to see, and likely is caused by
: (1) scintillation because of too short exposure times, (2) a nearby moon,
(3) poor photometric sky conditions. I reached an overall accuracy of about
0.005 mag, which will need to be increased for the next campaign. To further
improve precision, I will have to stop down aperture of my telescope by
using a mask with a cutout hole.

Best regards,
Tonny

Tonny Vanmunster
CBA Belgium Observatory
http://www.cbabelgium.com 
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PERANSO : The Final Frontier of Period Analysis Software
http://www.peranso.com
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