[vsnet-campaign-v838mon 408] Bessell filters and V838 Mon CCD observations by Kis

[Thom Gandet <tgandet@mindspring.com>]

Arne Henden wrote:
> 
> Ic is about a half magnitude too bright.  My guess here is that
> a Bessell prescription Ic filter is being used.  These filters
> work fine for normal stars, but they have a red tail that influences
> measures of red stars.  The spectrum is so cut up with molecular
> bands that even small differences between filters will be amplified.
.
.
> This is one case where you either need to ignore
> transformations (since most V filters are pretty close
> to the standard system), or else observe with B as
> well as VRI.


   For the Bessell Ic filter (perhaps the Rc as well?), weird
transforms are the norm.  I learned this the hard way.  And by 
"weird", I mean significantly non-zero coefficients and large constant
terms relative to the Bessell filter UBV tranforms (which are pretty
good).


Regards,
Thom

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