| Proposal | Good morning, I'm Sauro Gaudenzi, my observer code is GSAD. In support of AAVSO alert no. 908, I kindly request the use of a telescope to observe the Persei triple-b binary system. I request that observations be made once a week from now until December 31, 2025. I request that 30 60-second photographs be taken with a B filter and 30 60-second photographs with a V filter. Abstract:
Donald Collins (Swannanoa, NC) writes: The hierarchical triple-star system, b Persei = HIP 20070, spectral type A2 V, magnitude 4.6 V (not beta Per) consists of a close binary pair, designated A-B, and a third star, C, that orbits the 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. AAVSO observers have contributed vital data to multiple earlier campaigns on b Per, and their essential participation is requested again. 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. Waiting for your reply, thank you very much and have a good day everyone |
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