The Mag. Range of R Scl in VSX is listed as 9.1 - 12.9 p (photographic).
The AAVSO light curve (all observations, mainly visual) shows the mag range to be about 5.5 - 9.5 V.
Does the explanation for this apparent inconsistency lie in the nature of the photographic data?
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Hi Roy,
yes, the range was based on blue photographic plates and the star is a carbon star, which means it is very red, thus the difference between p and V is very large.
B-V in the GCPD ranges from 3.8 to 4.8!
I have revised the entry in VSX.
Cheers,
Sebastian
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Hi Sebastian,
Thank you. Of course! If I had not been a bit rushed for time I might have had the good sense to think about it and look at the data before posting.
It can a bit arcane, but also sometimes simply unsolvable. The zero-points of the photographic photometry are frequently inconsistent, and the scale can be off, too (i.e. not a linear Pogson scale) depending on how the measuring was done and how good the comp stars are. Then for a carbon star, as Sebastian notes, even a small difference in the nominal ‘blue’ sensitivity of various plates in use can change the apparent brightness dramatically. In the earliest days, the plates might not reach even as far as H-beta (4861A), whereas later standard orthochromatic ‘blue’ plates would go out to (say) 5200A or so. Even that makes a big shift in how bright a carbon star would appear.
It is for reasons analogous to these that using a filter (or various standard filters) is encouraged in current observing, so that there is better hope of tying together data series from different observers and instrument set-ups.
\Brian
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