Alert Notice 476: Multicolor photometry of triple system b Per requested

January 4, 2013: Dr. Bob Zavala (U.S. Naval Observatory, Flagstaff) has requested AAVSO assistance in obtaining multicolor photometry of the bright triple system b Per in order to prepare for and detect a possible eclipse of the AB components by the C component predicted for 2013 January 23. At 4.5V, b Per, which is also a radio source, is an excellent target for photoelectric photometrists and DSLR observers.

Multi-color photometric observations are requested during the period 2013 January 23 through February 04. Based on a revised period of 702.45 +/- 0.05 days, the next time of minimum light is predicted for

                                                               HJD = 2456321.35 +/- 0.05
                                                  UT 2013 January 28 20:24UT +/- 1.5 hours

The eclipse may last for up to four days, so the coverage requested will provide both a baseline out-of-eclipse light curve and a multi-color eclipse light curve for analysis.

Photometry is needed at the level of 0.02-0.03 magnitude or better, as the eclipse may be as deep as 0.1 magnitude. For PEP observers, V coverage, and B if possible, is requested. DSLR observers should use whatever band(s) are available to them. Please use only the comparison and check stars given below:

Target: b Per = SAO 24531 = HD 26961
Coordinates for b Per: R.A. 04 18 14.62  Dec. +50 17 43.8 (2000.0)

Comparison star: lambda Per = SAO 24412 = HD 25642
V=4.285  B-V = -0.013
labeled 43 in AAVSO Variable Star Database photometry table for b Per
Coordinates for lambda Per: R.A. 04 06 35.44  Dec. +50 21 04.55 (2000.0)

Check star: SAO 24512 = HD 26764
V=5.19  B-V = 0.052
labeled 52 in AAVSO Variable Star Database photometry table for b Per
Coordinates for SAO 24512: R.A. 04 16 43.087  Dec. +53 36 42.47 (2000.0)

Charts may be created using the AAVSO Variable Star Plotter (VSP,

Observations should be submitted to the AAVSO International Database using WebObs or PEPObs and the name b PER.

Dr. Zavala and colleague Dr. J. J. Sanborn write: "The ellipsoidal variable star b Persei...consists of a non-eclipsing close binary (A-B) with a 1.5-day orbital period within a hierarchical triple system (AB-C) with a 701-day orbit (Hill et al. 1976). As with other close binary systems (e.g. beta Per) b Per exhibits flares of non-thermal radio emission (Hjellming & Wade 1973). As noted by Hill et al. (1976) the evolutionary nature of the close binary in b Per is uncertain. It may already be a mass-transferring Algol binary, or it may be a precursor to the mass-transfer stage. The absence of eclipses in the close binary and b Per's status as a single-lined spectroscopic binary limit our knowledge of this stellar radio source.

"Our observations using the Navy Precision Optical Interferometer (NPOI) resolved the AB-C components for the first time. The triple system orbit is nearly edge-on with an inclination of approximately 90 degrees...This suggests the possibility of observing eclipses of the non-eclipsing (i ~ 40 degrees; Hill et al. 1976) close binary and the third star. The third star may eclipse both components of the close binary depending on the close binary orbital phase. Eclipses are important as they allow us to add light curve modeling to our arsenal of techniques for investigating the evolutionary state of the close binary components.... Based on the expected stellar diameters (Hill et al. 1976) the eclipse duration could be as long as 4 days from ingress to egress assuming the C component totally transits the diameters of A and B. It may be possible to observe two distinct times of minima should C eclipse the secondary and the primary stars of b Persei. Eclipses of the secondary component will be useful observational constraints in the poorly understood close binary orbit." More details and an illustration of the b Per system are available in the pdf document Photometry Request-b Persei.pdf (

This campaign is being followed on the AAVSO Observing Campaigns page (

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.


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