[vsnet-alert 5823] Re: 12 UMi fading?

[reinder j bouma <rjbouma@wxs.nl>]

Toni Scarmato wrote:
> 
> I Have observed last nigth the star 12 UMi.
> 
> 12 UMi 20010416.8333 8.1 T.SCARMATO [Comparison stars SAO 8174 (M1=8.5),
> SAO 8162(M1=8.4) B 7x50]
> 
> Regards,
> 
> Toni Scarmato

According to Hipparcos data SAO 8174 has V = 7.84 and SAO 8162 has V =
7.46.
The values you quote appear to come from the PPM catalog, and should
NEVER EVER be used. Also I have not been able to find 12 UMi. It is not
present in my Guide6 data, and it is not shown on Atlas Borealis. So it
would have been better to use its SAO-number as well for unambiguous
identification.
I guess however that it is SAO 8208. It is close to 11 and 13 Umi (gamma
1 and 2), and its R.A. is in between. Also it has V = 7.27, making it
the brighter of the 3 stars, in perfect agreement with your observation.
As SAO 8162 is rather red (K5 star) it may appear slightly fainter,
explaining why you saw '12 UMI' as 81 and not 83.
In short, please use proper comparison stars with V-magnitudes (and
unambiguous stellar identifications) before sending out alerts!

Reinder Bouma 
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