Proposal #234

The triple-star system b Persei (magnitude 4.6 V) is expected to undergo a primary eclipse centered on December 23. 4 UT (JD: 2459571.9). I wish to use observations from three BSM's: BSM-NH2b; BSM-TX or BSM-NM; and BSM-Hawaii from December 16, 2021 through January 1, 2022 to record this event along with AAVSO observers. We need wide longitudinal coverage, especially the western N. America and the Pacific to cover as much of the 3 day eclipse as possible as well as the out-of-eclipse observations both before and after the eclipse. The high brightness of b Per requires that images either be de-focused or diffused with an engineered diffuser to spread out the star profiles to enhance the distribution of star pixels to avoid saturation. Spreading the star profiles also enables longer exposures, which will reduce scintillations. The observing runs should last as long as possible each clear night with airmass <= 2.0 with a cadence consisting of a burst of 5-10 rapid successive images every 30 minutes. The BSM-NM and BSM-NH2b were successively used in October 2020 to obtain good data. Because the star undergoes ellipsoidal variations of 0.06 mag peak-to-peak and a period of 1.52 d, the out-of-eclipse data are requested in order to verify that all the observations from different observers and telescopes can be offset to a common zero point. In the relatively short time (since 2013) since the AAVSO had first discovered that bright b Per experiences eclipses by the third star in the system we have discovered that the period of the third star's orbit is clearly 2 days longer than previously believed, but the period still has an uncertainty of about half a day. Every eclipse shows a different light curve pattern. With more eclipses observed we can become more hopeful that a solution for the remaining astrophysical parameters of the three stars in the system can be determined.