Alert Notice 537: Observations of a secondary eclipse of b Persei requested

February 26, 2016: Dr. Donald F. Collins (AAVSO member, Swannanoa, NC), Dr. Robert Zavala (US Naval Observatory, Flagstaff Station), and Jason Sanborn (Lowell Observatory) request high time-resolution observations of the bright eclipsing star b Persei (not beta) during an expected secondary eclipse of the third star of the system as it is expected to pass behind the close orbiting stars of the system in the two weeks centered on March 7, 2016. Dr. Collins provides the information below.

Two campaigns by the AAVSO (AAVSO Alert Notice 476 in January 2013 and AAVSO Alert Notice 507 in January 2015) successfully observed the first-ever detected primary eclipses of the inner A-B pairs by the third star. The first eclipse detection occurred on February 5-7, 2013. About 700 days later, high time-resolution observations of multiple eclipses were detected in mid-January 2015 as the third star alternately eclipsed the alternate A or B components as it transited the rotating system. Results of the January-February 2013 campaign may be viewed at the following web page:

Results from the January 2015 campaign may be viewed at the following pages:


The last link includes an animation simulating the eclipse of the orbiting stars in the system.

b Persei (HIP 20070, SAO 29531, HR 1324, HD 26961) is located at the following coordinates (J2000):
R.A. 04 18 14.62  Dec. +50 17 43.8

The inner pair of stars orbit in a low-inclination (non-eclipsing) orbit with a 1.523-day period that shows a small ellipsoidal variation (0.06 V p-p) due to the gravitational distortion of the two stars. The third star of the system actually eclipses the inner pair every 702 days, but an eclipse had not been detected before the 2013 AAVSO campaign. The secondary eclipse - when the outer star passes behind the inner pair - is predicted for March 7, 2016, based on stellar interferometry data from the Navy Precision Optical Interferometer (NPOI) at Lowell. More observations of the eclipses by a worldwide distribution of observers are extremely valuable to learn the relative sizes and luminosities of each of the three stars as we obtain more continuous coverage of the events.

Observers are asked to obtain high-resolution time-series observations in V during the eclipses as well as time-series observations of the system out of eclipse beginning about March 1, 2016, in order to calibrate the varying offsets from different observing systems. Observations should continue at least one week after the eclipse has occured and b Per has returned to maximum.

It is recommended to use the star HIP 20156 (SAO 39457, HR 1330, HD 27084; the star labeled '55') on the AAVSO finder chart at 5.456 V as the comparison star. For a check star HIP 20370 (J2000 RA, dec = 04 19 13.24, +50 02 55.30) may be used if the observer's field of view is about one degree. This star is not in the AAVSO sequence. Any other AAVSO sequence stars may be used as check stars if available in the observer's field of view. Charts with a comparison star sequence for b Per may be created using the AAVSO Variable Star Plotter (VSP).

CCD observers should follow some simple guidelines to observe bright stars: Integration times should be kept longer than about 15 seconds by stopping down the aperture of the optics if necessary. Otherwise atmospheric scintillations add significantly to the noise. With short focal-length telescopes - needed for large fields of view for bright stars and the sequences - de-focusing (FWHM ~ 4 pixels) is also necessary to avoid under-sampling among pixels on the detector array. Co-adding the photometry data (about 5 observations averaged) or stacking the same number of images will reduce the point-to-point noise even further.

Photoelectric observers are especially encouraged to contribute to the campaign.

Please send observations in AAVSO format directly to as well as to the AAVSO. Please use the name "b PER" when submitting observations to the AAVSO International Database.

An AAVSO observing campaign discussion thread on the topic "b Persei" has been initiated under the Campaigns & Observation Reports forum here to share rapid developments, observing techniques, and notices concerning the eclipse progress.

The expected light curve of the secondary eclipse may be seen in the figure below provided by Jason Sanborn. In this figure, the horizontal axis is the Julian date with 2016 March 7.5 UT indicated. The vertical axis is the V magnitude relative to an out-of-eclipse value of 1.

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

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen primarily utilizing text provided by Dr. Donald Collins.


Information on submitting observations to the AAVSO may be found at‭:‬


An Alert Notice archive is available at the following URL‭:‬

Subscribing and Unsubscribing may be done at the following URL‭:‬

Please support the AAVSO and its mission -- join or donate today: