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(cba:news) V392 Persei (Joe Patterson) [2020-11-14T08:48:00Z]


Sorry, this is more of a "chat' item... but I wanted to reach as many V392 Per observers as I can.

1. We still have a very great need for European coverage, especially early-night European coverage (and preferably all night, to join with North America).

2. As usual for unfiltered data (and really for all data), it's necessary to apply additive constants to put different observers on the same scale. Those constants are determined by measurements which are SIMULTANEOUS. There are two circumstances which make this particularly difficult. (a) Changing comparison stars. When the data are simultaneous and of good quality, a good measurement is made. But when you change comparison stars (singular or plural), that additive offset could change. I've noticed some variations as high as 0.15 mag. That's fine - for the one night of observation. But simultaneity is not achieved on most nights, so use of that additive constant could be erroneous. And in searching for long periods (a few days or more), this can be a big systematic and unmeasurable error.

This has always been true, but is usually not serious since I often subtract the mean magnitude anyway, which optimizes the search for short periods. But V392 Per may have a several-day period, where it can be a problem.

(b) V392 Per has a close neighbor, and I imagine people have different strategies for dealing with it (include, exclude, report with or without subtraction, etc.). Not a big deal as long as you always do the same thing. (No particular recommendation, since it always depends on the precise details of telescope and quality of night.)

So... let me know if these issues could pose a problem with your data.
I measure the offsets in magnitude very frequently, so know that it's not a common problem. But it can be - and for this star very reluctant to yield its secrets, I wanted to be extra vigilant.

joe p
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