[vsnet-chat 5927] [AAVSO-DIS] Reporting observations:Multi-letter codes

["Berto Monard" <LAGMonar@csir.co.za>]

Dear Taichi,

I must admit that my scalefactor was a bit out. It should have read
like:
"If this is applied to yellow-orange stars (G-K) one will end up with a
waveband somewhat closer to I, and for very red stars close and even
beyound (?) the I band." 

As effective wavelengths do change more considerably with unfiltered
CCDs, red stars and reddened regions are photometrically 'out' for
unfiltered CCD cameras. 

I did make the mistake once.

Regards,

Berto

>>> Taichi Kato <tkato@kusastro.kyoto-u.ac.jp> 01/28/03 11:10AM >>>
Re: [AAVSO-DIS] Reporting observations: Multi-letter codes

> For blue stars, incl CVs, the effective wavelength of this observing
> window of most CCD cameras is near that of the R band. Therefore R
> magnitudes of reference stars (with non-red colours) in the field can
be
> used. Such observations are usually reported as CR.
> If this is applied to yellow-orange stars (G-K) one will end up with
a
> waveband close to I. I magnitudes of similarly coloured reference
stars
> could be used for them. Observations are reported as CI.

   Please don't be confused.  For most of stars with usual colors, the
effective wavelengths of the most CCDs have close to that of Rc.
Effective wavelengths are integrated quntities, and little vary around
the mean wavelengths of the original CCD/filter passbands.
Your explanation only applies to extremely red objects which virtually
emit no light shorter than 650 nm.

Regards,
Taichi Kato


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