Proposal #445

Request BSM NH2b, BSM-TX, BSM-New Mexico, and BSM-Hamren (Hawaii) to observe b Persei for the primary eclipse by the third star in the triple-star system.

The triple-star system b Persei (magnitude 4.6 V) is predicted to undergo a primary eclipse centered on November 28.3 UT (JD: 2460276.8). I wish to use observations from four Bright Star Monitors: BSM-NH2b; BSM-TX, BSM-NM; and BSM-Hamren (Hawaii) from November 14, 2023 using both V and B bands. 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.

BSM-HN2b should use VDIFF, and BDIFF filter designations for V and B images. The diffuser spreads out the star images to a wide FWHM which permits long integration times (30 – 60 sec). The use of the diffuser filter was highly successful for the September 2022 and the December 2021 eclipses by greatly reducing the image-to-image scatter caused by short exposures. A cadence of 10 minutes through the night is highly desirable. The highly broadened diffuser images prevent plate solving and Vphot processing in the AAVSONet pipeline, but I have succesfully processed these by further binning with my laptop.

The BSM-NM, BSM-TX, and BSM-Hamren require both defocusing, and multi-image stacking to obtain successful images for time-series observations of such a bright star that is subject to excessive atmospheric scintillations. With a cadence of 30 min to 60 min throughout the night it is requested that a burst of at least 5 images be stacked with three bursts within each cadence interval. It is important to observe the statistical variation of each burst result hence the multiple bursts per cadence interval. If possible, the rapid bursts should stack without plate-solving to minimize observing overhead when negligible tracking errors abound. (Images from BSM-TX in on calendar date 20220921 (1x1 bin, 3sec exp, FWHM 3.2 px, max adu: 60,000, intensite 1x10^6 ADU were almost adequate, except for possible saturation.)

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 (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 9 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.