[vsnet-chat 5337] Re: (fwd) R Cas and CCD profile

[Brian Skiff <Brian.Skiff@lowell.edu>]

     If you look at where the TiO bands in late-type Miras are, it is
easy to see that there's not much light coming out of R Cas below 500nm.
     Among the published calibrated photometry for R Cas in the 
Mermilliod database are:

V=10.05  B-V=2.1  V-R=4.4   ...from the Russian WBVR catalogue.  The R band
here is close to Johnson R, so is shifted redward of Cousins R, and the
V-R color is larger than Cousins V-R would be.  In the seven-color Vilnius
system we have:

V=8.1   V-S = 2.4     ...where the 'S' band is centered on H-alpha at around
6500A, or roughly where Cousins R would be.  If we take V-Rc to be ~2.5,
you can see that unfiltered CCD observations can be oddly bright.  Remember
also the R Cas is becoming strongly brighter as you go to longer wavelengths,
just about compensating for the decline in sensitivity of the CCD.  So even
though the chip is down to 10 percent (relative) sensitivty at 900nm, the
star is also 10x brighter at that wavelength!

     I suppose the main thing to mention is "please use a filter---any 
standard filter passband" when making observations of any and all variable
stars.  Without one it is difficult to correlate one's observations with
anyone else's, as this example shows.

\Brian

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