Abstract: The hierarchical triple-star system, b Persei = HIP 20070, spectral type A2 V, magnitude 4.6 V consists of a close binary pair, designated A-B, and a third star, C, that orbits inner binary pair in a much larger orbit. The close-orbiting A-B pair, period = 1.5327d, does not exhibit eclipses, but does exhibit ellipsoidal variations of about 0.06 magnitude peak-to-peak. The third star (C) will eclipse the close-orbiting binary pair on JD: 2460981.01 ± 0.10 (calendar date: 2025 November 1; 14:24 UT) and will last for about 3 days. Extended time-series photometry from AAVSO observers is requested during the 4 weeks centered on November 1, 2025. Past eclipses have lasted about 3 days.
Justification: Five previous primary events (time series) have been observed by AAVSO observers since March 2016. Five secondary events (when the third star passes behind the close-orbiting A-B binary) have also been observed since January 2015. The inclination of the A-B orbit is considerably smaller than the C orbit. Thus the C star during it’s transit past the A-B pair alternately can transit separately across the two stars of the A-B pair. This results in rather complicated light curves during the transits. The long ~700 d orbital period for the C star is not a rational multiple of the short close binary period (~1.5d). Thus every C star transit encounters a different phase of the binary’s orbit at the mid-point of each transit causing every transit’s light curve to be drastically different. Past primary transit light curves are displayed on D. Collins’ b Persei blog. Many transits will need to be observed in order to determine the many unknown parameters of the three stars. The spectral type (A2 V) is that only of the brightest star. The B and C stars are considerably fainter and more late type. Their spectral signatures are not determined. It is hoped that modeling the light curves can determine the relative sizes, brightness, and A-B separation as well as orbital inclination can be determined by fitting models to every light curve. It is also conceivable that the orbits of the b Persei stars are evolving due to the large inclination difference between the binary orbit and the outer orbit and the resulting torques. . Our photometric determination of the obital period of the third star of the b Persei system tis significantly longer than the latest comprehensive spectroscopic study of b Persei (Hill, 1976), 701.76 ± 0.44 d based on about 60 years of radial velocity observations.
I am pleased to see some activity on the forum for the b Per eclipse. The eclipse is expected to begin next Friday, October 31 - Happy Halloween! Be fore that time be sure to practice and get time series - a number of observations throughout the night to cover as much time as possible. Once every hour for manual DSLR cameras. Out of eclipse observations are important to obtain a baseline for the eclipse observations since b Persei is a variable star with a well-defined almost sinusoidal variation in brightness of about 0.06 mag peak-to-peak and a period of about 1.5 days. - Good Observing! D. Collins (CDK)
I’m also pleased to be on board, as usual.
Things are beginning slowly, because the last 10 days have been horrific, from the weather point of view. More, the forecast is somewhat pessimistic for the coming week-end.
Anyway, the eclipse has not begun, so let’s see what happens. Tonight will be clear.
What are the expected instants for the beginning / end of the eclipse ?
Have you constructed a prospective LC, as you did for the last eclipses ?
I noticed, in your reported measurements, that you were using a “DIFFUSER WITH V FILTER”. Have you a link about this device ?
The eclipse might have begun last night, possibly near 00:00 ; at least somewhere between 00:00 and 02:50 UT, 2025 10 31.
Conditions were not good, with a sky mostly clouded out, low altitude rolling clouds, and some opening ith clear skies.
The errors are sometimes huge, in my data, but I tought to be interesting not to delete those observations.
I hope there will be some confirmations coming from elsewhere in Europa, or from America.
The coming nights should be worse, with no observations at all - or very marginal observations.
I managed to get some measurements through thin clouds around Nov 1, 19:30-19:35 UT: b Persei is clearly in eclipse. I will try to use whatever holes in the clouds may be there. Observations are in the AID now.
Nov 4, 2025. Hello all, It looks like the deepest part of the eclipse was a couple of nights ago. We are as of calendar date Nov. 3-4 we may be still in eclipse. Please keep observing time series, not snapshots, so we can determine clearly the out-of-eclipse data for all observers. Even if you did not “catch” the eclipse, we need the time series out-of-eclipse data to standardize all our observations! Out -of-eclipse data are also important to determine when the eclipse begins and ends.
Thank you all for observing and contributing your observations!
I just have uploaded some data from the last couple of days. The configuration between your data and mine seems quite complicated around JD 60982/984. Apparently, you were as low as I was “normal”.
Interesting situation.
About the data I got during the eclipse, which were obtained constantly through clouds : feel free to do some binning, or to discard them if necessary. Those were the worst photometric observations in my life, unfortunately.
Thank you and congratulations to all observers who observed b Persei both during the recent eclipse and the one-to-two weeks prior to and subsequent after the eclipse! Observers data that don’t include any eclipse data are also valuable to pinpoint better the times of “contact” events at beginnings and ends of the eclipse.
I will be further processing the data from all contributors to find a common out-of-eclipse baseline as well as attempting to model this eclipse and the 8-9 other eclipses of b Per from the last 12 years when we first observed b Persei eclipses by AAVSO observers. I will ask AAVSO to keep this forum open so I can post updates to the analysis. If anyone has contributed data during the eclipse, but has not observed out-of-eclipse, please try to observe more out-of-eclipse enough to obtain statistical meaning and let the forum know when you have contributed more data.