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From: "Sebastian Otero" <varsao@fullzero.com.ar> Subject: Re: simply scatter-red Date: Sat, 2 Aug 2003 03:02:51 -0300 First of all,..... I love this kind of messsages by John! The guy loves it! and his passion is contagious! ;-)) > 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. I agree with Mike. UCAC data were there just in case but now that there are ASAS-3 data, UCAC-1 is out of business. 0.2, 0.3 errors. If it's going to be like this, I think that it would even be better just to asign letters or steps to the comparison stars!!!! But this problem is gone now at least in the South. > 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. Extensive comparison (with extensive I mean: as time goes by I have more sequences made which in turn means I have more numbers to compare) is teaching me that ASAS-3 doesn't suffer from ANY of the random errors Tycho-2 suffers from. Even at 9-10th magnitude. So, I wouldn't recommend the use of Tycho-2 magnitudes anymore in the South. Up to 8th mag. Tycho 1 is even better than 2 and of course we have GCPD and Hipparcos photometry. Then we can jump to ASAS-3 because saturation problems in ASAS-3 are completely left behind at 8.0 V. Actually, since JD 2350000, problems only start for stars 7.0 and brighter and we can even get to use (with care and discarding easy to find outliers) 6.3 mag. stars. But of course, there is no need to do this (I do it for EA research) So ASAS-3 data is the best choice when there is no PEP from 8.0 and down. At 13.5 scatter is 0.5 mag. but the mean values continue to be reliable within 0.1 mag. or better. I am using ASAS-3 data for eclipsising stuff and it's really a goldmine. Cheers, Sebastian. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.502 / Virus Database: 300 - Release Date: 19/07/03
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