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C offset won't work if the images rotate, true. C-offset is NOT the default setting in AIP4WIN. Since I don't have rotating images, it works perfectly for me even when the variable is non-existent. Centering is sensitive to other stars nearby, and when that ocurs, you need to reduce the radius of the search somewhat. Lew --- Berto Monard <LAGMonar@csir.co.za> wrote: > I don't think the C-offset is the default in AIP4WIN. > > The default setting for C tracking will IMO be able to > process timeseries taken in altaz. It will even allow to > hook V or K on a moving comet on the images to do > photometry on it. > > The problem with the default setting is that the C > selection/centering is quite nervous as if the aperture > wants to jump away from the selected C star. However > there is no problem if C is somewhat isolated (more than > 20 -30 (?) arcsec away from any other star of similar or > slightly fainter brightness). > > Multiple image photometry in manual mode (pe for faint > stars) is not working well and therefore not accurate and > time consuming. If I remember well, it doesn't work in > C-offset at all.. > > Berto > > >>> Taichi Kato <tkato@kusastro.kyoto-u.ac.jp> 07/08/03 > 12:15PM >>> > Re: Software problem in time-series photometry > > > The centering error on faint stars that Taichi-san > mentions > > in AIP4WIN can be avoided altogether by doing > photometry as > > C-Offset where the comparison xtar (presumably bright > > enough to be reliably centered on all images and the > > variable and check are not centered except on the first > > image of the set and the apertures are rigidly placed > in > > the same location relative to the comparison star. > > Thanks, Lew! Is everyone using this option? (In > precise photometry, > I regard this option as a default -- we use multiple > stars to compensate > a small-order deviation from a constant offset. With an > Alt-Az mount, > one also need to incorporate image rotation). Use this > option whenever > applicable. If everyone uses this option and still gets > unrealistic > depressions in the light curve or other unusual features, > we should search > for a different explanation -- in any case, this would > provide a critical > test for the software. > > Regards, > Taichi Kato > > > > -- > This message has been scanned for viruses and > dangerous content by MailScanner, and is > believed to be clean. > Mailscanner thanks transtec Computers for their support. > ===== Regards, Lew CBA Concord http://vsnet.geocities.com/lcoo/eng29.htm The CBA Concord telescope is in the debugging process CBA Pahala http://vsnet.geocities.com/lcoo/pahala.htm
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