Proposal #279

The triple-star system b Persei (magnitude 4.6 V) is predicted to undergo a secondary eclipse centered on September 29.91 UT (JD: 245852.41). I wish to use observations from four BSM's: BSM-NH2b; BSM-TX or BSM-NM; and BSM-Hawaii from September 19, 2022 through October 8, 2022 to record time series of this event in V and B 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 multiple short exposure images be averaged or two diffused images of long exposure (~60 sec) if an image diffuser is available. This procedure serves to average out the atmospheric scintillations. In the absence of a diffuser, the images should be slightly de-focused (about double the sharply-focused FWHM) yet preserve Gaussian-like star profiles. The multi-image no-diffuser observations should consist of a burst of images such that the total integration time for each observation approximates 60 sec (for example a burst of 12 images at 5 sec each). The observing runs should last as long as possible each clear night with airmass <= 2.0. The image bursts should be repeated about every 15-30 minutes each night. 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.