OS UMa (08 19 17.16 +62 30 25.8 (J2000.0)) is an interesting long period bright (V= 5.7) eclipsing binary.
It has a period of 89.0737 d. and MASCARA (Burggraaff et al., 2018) data suggest that it may be chromospherically active. X-ray detections also support that.
The amplitude of the primary eclipse is only 0.05 mag. (see its light curve with all available survey data) so it is a very difficult object. But won't our observers be willing to take up such a challenge? ;)
You can see the VSX information on the system here.
Observer Dinko Nazor is trying to model the system but more data are needed to constrain the system's parameters.
The interesting news is that the next eclipse is happening next week!
Predictions based on the latest analysis are:
Beginning of the eclipse: 25 Oct 2021 10:57
Mideclipse: 26 Oct 2021 08:20
End of the eclipse: 27 Oct 2021 05:42
(of course these times have uncertainties)
So observers should be observing the nights of October 24, 25 and 26, especially on the 26th, when mideclipse will take place, because we need to see if the light curve is flat-bottomed, this is something that is still not confirmed with the available (sparse data).
Continuous observations over these days will be very valuable, so observe it as soon as possible. It won't be so easy to establish the light curve shape if people do not observe it during several hours.
Observations before and after the eclipse are also needed to establish a magnitude baseline and correct any potential offset between observers, so do not restrict to the above dates.
Beware of saturation, this is a 5.7 mag. star!
B and V data would be great to see if there is a difference in amplitude, but again, with such small amplitude, it will be a real challenge. Data in any filter -or unfiltered- will be useful. DSLR/CCD/PEP.
A nearby comparison star has been added to be used as the main one so everybody is on the same page. It is HD 70177 (V= 7.682; B-V= -0.034)
I hope there will be interested observers and we can have some discussion on the object here in this thread. Dino will be monitoring it too.
Good luck!
Sebastian