Proposal #649

Request Bright Star Monitors BSM NH2b, BSM-TX, BSM-New Mexico, and BSM-Hamren (Hawaii) to observe b Persei (4.6 V) for the primary eclipse by the third star in the triple-star system. The eclipse lasts for about 3 days centered on JD: 2460981.01 ± 0.10 (calendar date: 2025 November 1; 14:24 UT). All night monitoring is requested for 6 days beginning JD: 2460975 (October 28, 2025 through November 4, 2025 (N. American times) in both V and B bands. Use the diffuser attachment for the BSM NH2b (Vdiff and Bdiff). Out of eclipse observations are needed as well as during eclipse for baseline levels within the ellipsoidal variations during out-of-eclipse observations. 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 BSM’s compliment the observations by AAVSO observers in the study of the complicated behavior of triple star eclipses.
The diffuser for BSM NH2b spreads out the star images to a wide FWHM which permits long integration times (30 – 60 sec). The diffuser filter has been highly successful in previous b Persei events by greatly reducing the image-to-image scatter caused by short exposures. Two rapid sequence VDIFF exposures two BDIFF exposures about every 30 minutes throughout the night is the proper cadence based on previous successful events. (The images do not need to be plate-solved, but will need dark, bias, and flat field corrections. I will download from the FTP. My photometry programs will not process photometry for widely-diffused star images. I perform floating point off-chip binning enough times to bring the FWHM down to manageable sizes).
The BSM’s without the diffuser will require a rapid burst of 10 - 20 images every 30 – 60 minutes throughout the night.
In the relatively short time (2013 to present) 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 reported from RV studies. The uncertainty in the new period has been reduced to ± 0.2 days due to observations of 10 time-series eclipses observed by previous AAVSO campaigns. Unlike binary star light curves, every transit of the C star across the rapidly-rotating AB pair shows a different 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.
I request receiving test images (a burst of 10 once each night) to test exposures and scintillation from each BSM as soon as possible until we have a satisfactory burst quantity and scintillation evaluation before going to all night cadences.