Re: GSC 00279 00321 paper

[aah@nofs.navy.mil]

Michael K. wrote:
>Well, I decided to go back and redo my photometry using V-C and the same 
>guide star that Dirk used. The guide star in question is GSC 00279-00356. 
>By using the Tycho2 formula I come up with a magnitude of V=10.78 for it. 
>I looked it up on CD23 (seq 92576) and averaged it out and I get V=10.98. 
>GSC has it at 10.76. You think I should use the TASS value of 10.98? Or 
>should I just leave it as differential and forget it? The TASS data is not 
>differential, is the only thing.
  If you go to the VizieR service and pull up the full Tycho2 reference,
you will find tha the Bt error is 0.232mag and the Vt formal error is 0.116mag.
An 11th magnitude star is pretty faint for Tycho.  As Brian Skiff has
said many times, the actual errors are larger than this. In other words,
Tycho2=10.78 +/- 0.3 or so, so the TASS magnitude is within the one-sigma error.
Likewise, GSC is always +/- 0.25mag or more.  Just because Tycho2 and GSC
agree with one another doesn't mean that either one is correct!
I'd still use the TASS magnitude since it is probably +/- 0.05mag.
Arne