[vsnet-chat 4310] re Comparison star problem

[crawl@zoom.co.uk]

>Hello!
>My name is Sonka Bruno.My AAVSO code is SBX.
>I made observations of SV Cassiopeiae and I noticed
>that the comparison star labeled 88 and West of SV Cas
>has a magnitude of approximative 9.2 when compared
>with 96 and 94 comparison stars. The 87 magnitude star
>is much brighter than 88 (about 0.5 magnitude
>brighter).
>The chart used is from AAVSO PC3/1991.
>Here are my observations:
>
>2451957.3 9.4 87,96
>2451973.3 9.3 87,96
>2451977.3 9.4 87,96
>2451981.3 9.2 87,96
>2451987.3 9.3 87,96
>
>The instrument: Refractor 100mm F/7
>The AAVSO chart is PC3/1991
>
The star HD 222131 lies about 12' almost due west of SV Cas, is V 8.77, and
I assume the star you mean.

If so it is not really suitable as a comparison star as it is an M2 star of
Johnson B-V about 1.4 (Tycho source), and an IRAS point source to boot!

NB the HD catalogue spectrum is "Mb": I can't remember exactly, but I
_think_ HD spectra are split such that Ma stars turned out to be mostly
dwarfs, and Mb stars turned out to be mostly giants.  So this star could be
a red giant (which doesn't necessarily mean it is variable, but causes
further worries).

Cheers

John

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