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Re: (fwd) problems with AIP4win > DAOPHOT II (I presume you are talking about the second version) is > pretty typical Fortran code IMHO, I know both versions. How the code looks like to a person will strongly depend on the person's experience. I am one of the persons who consider "average Fortran codes" don't look elegant; perhaps I am demanding top 10% elegance in codes, but with this elegance, a talented programmer can easily understand them in detail and improve the code when necessary. With codes less than the average elegance, bugs will contiue to appear, and are easily added, even after ten years' maintainance. In a long run, the advantage of the former is apparent. Anyway, this is not a software technology discussion forum, and back to the main issue. > with considerable effort to add logic for input errors Yes, this is a modern standard. > handling cases like saddle points in solutions. This is probably one of the logical improvements in DAOPHOT II. The history tells that the introduction of these improvements was ironically urged by the "vastly extened PSF" of the pre-COSTAR HST images. > but remember that DAOPHOT also includes a full aperture photometry section. Yes, it is hard to think of a software package handling PSF photometry only. Aperture photometry is a specialized and an idealized form (in mathematical concept) of PSF photometry. > I'm just making the point that reliable, extremely well tested software > like DAOPHOT does not happen very often and should not be denigrated > just because it may not be written with the current compiler-de-jour. In optical astronomy, only a small number of reliable PSF photometry packages are available, since people are usually taught to first learn DAOPHOT or an equivalent. However, don't forget about other fields of astronomy. In analysis of X-ray imaging observations, PSF modeling is usually a necessary step, and does not usually take a too much empirically assumed form as in the optical. DAOPHOT is not surprizingly superior among the various field of applications in astronomy. I don't want to blame DAOPHOT in any practical aspects, but if the initial code were written with the modern (high quality) elegance, the progress in this field may have been more striking, and an easy-to-understand algorithm may have already been ported to commercial photometry software. > Certainly by the time you get down to S/N=3 (a Poisson error of 0.3mag) > as Kato-san suggests, you should be very careful of how you reduce > your data for optimal results. I generally use a Poisson error of > 0.1mag (S/N=10) as my personal dividing point between automatic processing > and hands-on processing of important data, and try very hard to never reach > that decision point! If possible, I stack frames to increase the > signal/noise before extraction just to avoid systematic effects. This is > similar to how Tycho2 improved its photometry over Tycho1. Kato-san has a > different regime of interest, often looking for rapidly evolving features > while using low signal/noise data from small telescopes. It can be done, > as he has admirably shown, but I'd rather use my observing and > processing time looking at objects better suited for my aperture. Remeber that S/N=3 indicates a very low signal. At this S/N, the object is around the detection threshold by human eyes. This means that "if the object is detected by eye on unprocessed images, the image will be able to produce reasonable photometry". The level at which people often turn off the telescope is much higher than this. My interpretation is that the software limit is partly responsible for this seeming inability. Even if the object is directly visible, there is some chance to detect the signal, but this is often a very difficult task, and I usually don't recommend it except for a small number of occasions (early GRB afterglow, fading part of a rarely outbursting dwarf nova etc.). In these special circumstances and there is no availablity of a larger telescope at the given epoch of observation, I decisively encourage observing even with a small telescope with a low S/N. Regards, Taichi Kato
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