(cba:news) V392 Persei

Joe Patterson jop at astro.columbia.edu
Sat Nov 14 03:47:49 EST 2020

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 
(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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