[vsnet-chat 5469] Re: [vsnet-campaign-v838mon 376] V838 Mon photometry/imaging techniques

[aah@nofs.navy.mil]

Kiyota-san wrote:
>But my old Rc filter may change color during storage and difficult to transform.
>And Rc=14.7 is near limiting magnitude of my telescope. I will try to take long exposure or to 
>stack images.
  A long total exposure is fine; the nova does not appear to vary on
a short time scale.  Like I said, professionals will be far more likely
to use your data if you use a standard filter, and V or Rc is preferred
over a Bessell Ic.  I have not seen an Rc filter that changed color
significantly with time; you do see pitting of the AR coating, but
the glass itself is pretty stable.

>But FOV is about 4 arc second/pixel in combination of AP-7 and my telescope.                                       
>Thus I do not know that small aperture size works well or not.
  I suggested ~5arcsec radius; this is 2.5 pixels diameter according
to your estimate of the pixel scale.  That should be fine.  You may
be able to use an even larger aperture, but at some point your measurement
aperture will start including some of the light-echo shell and your
photometry will suffer.  You can tell when this occurs by performing
differential photometry with respect to nearby comparison stars, and
plotting the differential magnitude as a function of aperture diameter.
Somewhere the magnitude will start increasing, and you need to keep
your measurement aperture smaller than this diameter.
Arne

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