[vsnet-chat 3378] RE: V348 Sgr comparison stars

[Sebastián Otero <varsao@fullzero.com.ar>]

Thanks, Bruce for the table.  I will check the sequences the first clear night I can observe.

But it seems there is too much error in Tycho 2 data.

For example, it's very unlikely that GSC 6858-02176 has a -0.32 colour index lying in the middle of the Milky Way Saggitarius zone. And if the star is close enough for not suffering from interstellar absorption , then IT SHOUD BE A VERY BRIGHT TYPE O STAR !!!

I hope next week I can report my visual impression of the sequence.

 

Best regards,

Sebastián Otero.

 

 

 

 

> Sebastian Otero asked for a comparison table 
to check the magnitudes 
> in the field of V348 Sgr. Here is the data. I 
will leave it to others
> to make any analysis.
> 
> 
GSC         UCAC1  AAVSO  
Heck  Tycho err   Tycho  err
> 
             
'V'           
V      
V          B-V 
> 
6858-02252  10.77        10.75  
10.49 0.07   0.93  0.11
> 6858-02278  
10.36               
10.52 0.08   1.26  0.21
> 6858-01964  11.19  
110   11.05  10.87 0.09   0.62  0.10
> 
6858-01727  10.78  109   11.06 
> 6858-02920  
11.73        11.54  11.23 
0.13   0.57  0.15
> 6858-02438  11.72  
115   11.48  11.41 0.15   0.41  0.14
> 
6858-01425  
11.80               
11.42 0.16   0.54  0.18
> 6858-02962  
11.91        11.77  11.69 
0.20   0.41  0.19
> 6858-02176  11.00  
106          11.75 0.24  
-0.32  0.09
> 
> The V (PEP) magnitudes are from Heck et.al., 
A&AS,61,375H,1985, 
> and are the means from several nights 
observations. Errors are 
> quoted as being < +/-0.04 mag. 
> 
> The UCAC1 'V' values are from the polynomial regression: 
> 
V=0.027U**2 - 0.666U + 3.784, were U is the raw UCAC1 magnitude.
> 
> I have included the errors for the Tycho-2 magnitudes, as 
> 
suggested by Brian Skiff, so that an indication of the accuracy 
> of the 
derived Tycho-2 magnitudes can be obtained.
> 
> Note that GSC 
6858-01727 is quite red (b-y=1.10, Heck, et.a al.) 
> and was therefore 
not measured during the Tycho experiment. The 
> UCAC1 'V' magnitude for 
this star would thus also be about 0.2 
> too bright.
> 
> The 
Tycho-2 magnitude of 11.75 for GSC 6858-02176 appears 
> to be about 1 
magnitude too faint, as a check of the 4 minute 
> SERC-V DSS image (20 
July 1987) will show.
> 
> Bruce Sumner

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