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Re: On vsnet-obs 45730 (CCD photometry filter) Diego corrected that his AAVSO report(s?) was incorrect. His observation was CCD unfiltered (calibrated on V-band sequence). The VSNET reports were correct. It could be easy to attribute this error to himself, but I suspect that the error may be more attributabe to the reporting system itself, as I have frequently seen similar confusions (some of them were already stated in the past). > There is also another possible mattern of concern. From time to time > I received amateur photometry that diligently specifies that the data > where obtained with a "V" band or "visual" filter and CCD camera, > failing however to note that the filters in questions were ment > for photographic of photoelectric work, where the V band filter > is essentially a long-pass filter (like the standard GG14 or GG11) > and the red-edge of the band is the result of drop in sensitivity of > the detector (emulsion of photo tube). > With CCDs, the red edge extends into the far red, and if used in > conjunction with long-pass V filters (instead of more appropriate > red-blocked ones suited for use with CCDs), the range of wavelengths > imaged runs from V up to I band included. What makes the thing worse is that the AAVSO system does not specify the filters -- the systems definitions more look "visual appearance" of the filter color, as shown below: > CCDB Charge-coupled device (blue filter) > CCDI Charge-coupled device (infrared filter) > CCDO Charge-coupled device (orange filter) > CCDR Charge-coupled device (red filter) > CCDV Charge-coupled device (visual filter) From these descriptions, these filter specifications would imply that they don't neccesarily mean existing standard passbands -- these is no popular system such as "O-band" ;-). With this description, if the filter looks "blue", then the observer should report "CCDB" magnitudes, regardless of the infrared transmission; if the filter looks "infrared" (what would be the appearance?), "CCDI" magnitudes etc. Finally, if the filter looks "visual" -- visually sensible filter??, the observer would have to report "CCDV" magnitudes. The table reads such like that. But my question was why the AAVSO didn't use the standard passband nomenclatures. A more fundamental question was why the "CCD" specification should precede filter(passband?) specification? "CCD V" band is identical (disregarding the most subtle difference, if any) with "photoelectric V" band. In such cases, "V" specification is sufficient. A "CCD" as a specifier for the detector, would be meaningful, but considering the difference in spectral responses between different photomultipliers (PEP) is comparable to that between different CCDs, the distinction between CCD and PEP would be less meaningful than a clearer passband-based definition. Okay, technical details may be written somewhere deep in the AAVSO data guidelines, my question more applies to the basic concept or the design of the system specifier -- a less confusing design is undisputedly a good design. Regards, Taichi Kato
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vsnet-adm@kusastro.kyoto-u.ac.jp
