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

[Arne Henden]

I agree with Radu - you should use full aperture if possible
to decrease scintillation, and instead defocus, use a narrower
passband (such as Halpha), use a neutral density filter,
or use a filter bandpass to which your CCD is less sensitive
(such as B or U) to increase your exposure times.
   The upslope is probably due to differential color extinction
between the target and the comp star.
Arne

Tonny Vanmunster wrote:
> 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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