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

[Radu Corlan]

> 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. 

Do you know what causes the up-slope?

> To further
> improve precision, I will have to stop down aperture of my telescope by
> using a mask with a cutout hole.

I'm not sure stopping down is the best strategy: say you stop down to 1/3 
aperture. You can then expose each frame 9 times longer, and get factor of 
three improvment in scintillation noise due to that. But the reduced 
aperture will increase scintillation by a factor of about 2. So your total 
gain is only about 1.5 times. OTOH, if in the same time you would have 
taken 4 short-exposure frames and averaged them together, you would have 
gotten a factor of 2 improvment (and i think you can get even more short 
exposure frames, depending on the camera's download time).

I think you can gain more by using an ND filter (or just use B instead 
of V) and/or slightly defocus the stars.

Radu

> 
> Best regards,
> Tonny
> 
> Tonny Vanmunster
> CBA Belgium Observatory
> http://www.cbabelgium.com 
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Radu Corlan       Snail Mail: Bucuresti sect. 1, 
rcorlan at pcnet.ro  str. Argentina nr. 28, Romania

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