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[vsnet-chat 6236] Re: V4641 Sgr, Discrepance between Visual and CCDV mags

Re: [vsnet-chat 6233] V4641 Sgr, Discrepance between Visual and CCDV mags

> Mystery solved.  Ron Stubbings kindly sent me the Henden/Sumner photometry 
> for the field.  Comparing the AAVSO chart 1813-25e for V4641 Sgr with the 
> Henden photometry there is approximately a 0.4 mag difference in zero point.

   (??)  I wonder why there was a so large (0.4 mag) difference betwen
"Henden photometry" and "Henden/Sumner photometry", which must have been
derived from the same photometric material?

   I also noticed that there were several CCD estimates in the past which
were systematically fainter than visual observations.  I don't think
all these observers used the AAVSO chart; there may have been a common
origin of zero-point mistake.

Regards,
Taichi Kato

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