I tested my strange method of stacked images photometry for TOM and O-C determination, and results were no bad. So I began to think about optimal targets, and found in Target Tool comparely bright EA V798 Cep without UID.
The star has a period 16.08d, so I tried to get phase plot from ASASSN-SP data for understanding of minimum duration - and was surprised by double minimum appearance, not similar to usual primary-secondary eclipses. All attempts to join minimums by period variations were unsuccessful.
Would you please explain the reason of unusual phase curve? Is there a sence to observe the star?
Mikhail, newbie in EB
Understood. Is it some kind of AR Cas with closer brightness difference? Or higher?..
Mikhail,
I think the phase plot is the result of eccentric orbits. The secondary eclipse is not midway between two primary eclipses.
Roy
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Like Roy suggested, it’s an EB with an eccentric orbit. It is noted in VSX:
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Yes, yes, it’s combination of high eccentricity and close brightness. Or sizes???
I need to be more careful with the VSX information.
Hi, Mikhail.
I have a digression.
Where does this picture you attached come from? I think I’m a bit curious about it.
Cheers, Lucas.
The figure is also very very similar to fig 125, p 201, of “Variable Stars” by Hoffmeister, Richter, and Wenzel" (Springer, 1985), which is translation of an earlier book in German). I highly recommend this book: they put a huge amount of effort in to preparing the many figures in the book, has an extensive index that includes the many stars they mention, etc.
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Yes, absolutely, an eccentric system. These are interesting to observe, particularly re times of minima of both eclipses. An eccentric system like this might undergo “apsidal precession”, i.e. the elliptical orbit is rotating, so the eclipses occur at different phases (more correctly, different values of “the true anomaly”) of the orbit. The result of this is the relative positions (time separation) of both eclipses will vary (and primary and secondary eclipses will appear to have different periods), and the depths of the two eclipses might vary. Time scale: decades to centuries and more for a full rotation of the apse… but you can sometimes see the effects over just several years of observing.
I’m attaching some results I got for V1103 Cas (presented at 2018 meeting). After solving for the light curve and apsidal motion, I simulated what the phased light curve should look like over the next 750 years. Positions of the eclipses change, relative depths change.
Great fun!
Gary Billings
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Endless forms most beautiful and most wonderful 
Adding to my own note: the figure in Hoffmeister et al. says “After STRUVE (1962)”. Also a German book.
The effect can be seen in O-C diagrams in which the O-C values for the primary and secondary minima converge and diverge over time. Below are examples for NO Pup showing data from the Variable Stars South database, and for PV Cas from the literature.
Roy
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Yes, yes, Gary - the same figure is shown in russian edition of Hoffmeister, well as an example of apsidal rotation of RU Mon and list of eccentric doubles with apsidal motion.
Indeed, Hoffmeister is absolutely classical book!
PV Cas O-C during space era 
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V0477 Cyg e=0.3
For summer…
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…and for winter.
FT Ori e=0.4
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