[Aavso-photometry] GJ 436 update and upcoming transit times

[Tom Krajci]

>From: "Geir Klingenberg" <geir.klingenberg at gmail.com>

>I have checked the flatfield using NGC7790 and the method described by
>Arne. And sure enough, I found systematics in the data. It looks like
>there is a gradient from the center towards the edges. There is some
>vignetting in this telescope, and it doesn't look like the flat
>corrects it completely.

You have identified a problem, but are you sure the cause is incorrect
calibration of vignetting?  Could it be scattered light issues?

Do you have any photos/diagrams that describe the baffling you use in your
telescope?

As for baffling (both telescope and CCD), I can send interested folks some
diagrams/graphics that show what I do to try and reduce the scattered light
issues in my telescope.

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Tom Krajci
Cloudcroft, New Mexico
http://overton2.tamu.edu/aset/krajci/

Center for Backyard Astrophysics (CBA)
http://cba.phys.columbia.edu CBA New Mexico

American Association of Variable Star
Observers (AAVSO): KTC http://www.aavso.org/
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