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> Having seen this kind of confusion so many times, I see there is a need > for some sort of accrediting system (though I don't want to mean > an authorization system, but I am inclined to provide some "self-check" > points) for chart makers. The similar things would be valid for authors of > astronomy software packages (e.g. star plotting software, photometry software > etc.). Taichi, I think it would be useful to make some suggestions "a la Brian" regarding catalogues heirarchy. I have been comparing different data for a long while now and the different sources are really different. Any of them has some advantage at some point and that is what makes the task even more difficult. But noone said it would be easy... ;-)) This is mostly for bright stars since those are my targets. 1) PEP photometry from the ground. The GCPD is a great source of data but VizieR can include even more if needed (For bright stars it's generally not the case, but in some examples just like the variable comparison star in the AAVSO "e" chart of eta Car, it can help). Of course, Arne's photometry and the great LONEOS when you go fainter. 2) Hipparcos magnitudes properly transformed to V. (stop saying Tycho is better. It is not. Excepting for M stars when no convertion is possible) 3) Tycho-1 for stars brighter than 8. (always transformed to V, not the Vt mag.) 4) Tycho-2 for stars fainter than 8 and brighter than ~9.5. Tycho-2 magnitudes (transformed to V) suffer for some systematic color -term that makes white and yellow stars to appear with a whiter B-V color (peaking around B-V 0.5 with a difference of 0.06-0.07 mag.) and white and blue stars to appear with a V mag 0.01-0.02 mag. brighter than Johnson's V. In Tycho-1 this effect is less pronounced and thus negligible, but accuracy falls steeper beyond 8th magnitude. 5) (Only now!) ASAS-3 data (PROPERLY CHOSEN according to aperture and star's magnitude) for stars fainter than 9th magnitude 6) UCAC-1 data transformed to V when there are not ASAS-3 data and correcting for zero-point errors, but with uncertainties up to 0.3 mag. sometimes (although I usually find results better than that) 7) I think a visually look at the field through an experienced observer's eyepiece would be more reliable than the catalogues left..... ;-)) I agree with most of your suggestions concerning what one must have in mind before mking a good sequence. Regards, Sebastian
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