[vsnet-newvar 1505] Re: [vsnet-chat 5415] Re: CGCS 2792

[jg <jg@jgws.freeisp.co.uk>]

> Mati morel@ozemail.com.au wrote:


> Which raises the question: where do these other classifications (F0, G0 V)
> come from?

Now I think about it, the likeliness is good that these are from
objective prism plates, which means that in this case the two stars'
spectra are likely to be merged.

Type G classification needs detection of molecular banding: there could
have been confusion here with some C banding being mistaken for G
banding???  Not sure of the wavelengths.  The 'V' may just as easily
have ended up as a "default" appendation given by a catalogue compiler,
ie there was no evidence of III or I in the spectra.

Also, unlike type S which more or less parallels types K and M, C goes a
little earlier, such that something like R CrB will be classed F8pe-G0p
"old style" (in agreement with a B-V of around 0.7) whilst classed C0,0
"new style".  Though this probably doesn't quite add up in this case
where there is a B-V of ~ 4.

To some extent spectral classification is properly a nomenclatural
system, although frequently used/forced into a taxonomic sense, and
things can seem more meaningful than they really are.

It certainly manages to trip me up from time to time ;)

Cheers

John

JG

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