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I'd like to make a couple of comments. My goal in posting is to make everyone a good photometrist; I may come down hard on a poster, but they should not take it personally. I am not the most diplomatic of posters! Likewise, I tend to concentrate on CCD questions, not because visual observations are not important, but because that is where my expertise lies. >BailyHill@aol.com wrote: > What do you do with a CV that is in outburst and you are the only observation > in outburst and your estimate is 1-2 magnitudes brighter than typical that > previous observations in the light curve generator? > > Suppose a star is an LPV. Your observation differs from the last one, 10 > days ago in the quick look file. How large a deviation would you accept > before discarding it. > These two questions are related. You should *never* change your data to conform with someone else. You *should* use the data from others to highlight potential problems; then go back and see if there was a mistake in your report. If no obvious error, then the report should stay as-is. I've had several occasions personally where the software reported a certain error, which seemed reasonable, but the data were wrong. Often such problems can be identified (log notes might indicate a few clouds were around, but you thought they were not in the program field; wrong filter in the header because of a hardware failure, but you could tell after the fact because of the image appearance, etc.), but sometimes you just can't find any reason why that particular point was "bad". Report it anyway. My experience indicates that accuracy and precisions of 0.05-0.1mag for filtered photometry of well-exposed stars is trivial to obtain. If you are not obtaining this level of accuracy, you should go back to the basics or ask for help. Progressing to levels of 0.03, 0.01 and millimag require correspondingly more careful attention to detail, but are obtainable. I've seen lots of amateur light curves with remarkable precision. Remember, the quality of amateur CCD cameras and software is not that much different than what the professionals are using; all that really differs is aperture. Find the range of star magnitudes for which your system works effectively and then concentrate on projects in that range. I've done millimag work at 14th magnitude with the 1.0m for some projects, and pushed hard to do 0.1mag precision at 24th magnitude (try it some day!) for other projects. Both types of projects were difficult and required careful attention to details, but both were a lot of fun. There are plenty of things to try with any telescope/CCD without exceeding its limitations; the trick is in finding out where the limitations occur, and that generally just takes experience. Expect to make mistakes (I still goof up after 30 years of photometry!), but learn from them. Arne
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