From: "Mike Simonsen" <mikesimonsen@mindspring.com> Subject: Re: simply scatter-red Date: Sat, 2 Aug 2003 00:37:43 -0400 It seems from the graphical representations, that UCAC is pretty much shite fainter than 13.0. I came to the same conclusion some time ago after trying to make preliminary sequences based on UCAC data. There is no way to transform these numbers to anything like Johnson V, and even though individual fields may be linear within themselves, the data was taken on many less than photometric nights, so it really isn't a good photometric dataset. Which leaves us with ASAS-3 down to ~12.5 depending on errors, for determination of visual sequences for variable star charts. For now, it seems best to use Tycho 2 V to ~10.5, ASAS-3 to ~12.5 and USNO A2.0 V for fainter magnitudes and colors. This is contrary to what has been suggested to me by others, but I just can't reconcile UCAC magnitudes to anything useful past 13.0. I have experimented with some fields in Aql and Equ where ASAS-3 and TASS data exist and found them to be quite consistent to around 12.5 or better. Errors are typically +/-0.03V. This is encouraging. If TASS can get it together like ASAS-3 we would have a decent photometric catalog for the whole sky down to ~13.0. Mike
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