AAVSO Alert Notice 537
February 26, 2016
Observations of a secondary eclipse of b Persei requested
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 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
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
http://inside.warren-wilson.edu/~dcolli ... lipse.html
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 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; https://www.aavso.org/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
Please send observations in AAVSO format directly to
firstname.lastname@example.org as well as to the AAVSO. Please use the
name "b PER" when submitting observations to the AAVSO International
An AAVSO observing campaign discussion thread on the topic "b Persei"
has been initiated under the Campaigns & Observation Reports forum
at https://www.aavso.org/b-persei-campaign to share rapid developments,
observing techniques, and notices concerning the eclipse progress.
The expected light curve of the secondary eclipse may be seen in a
figure provided by Jason Sanborn and posted on the AAVSO web page
for this Alert Notice (https://www.aavso.org/aavso-alert-notice-537).
In that 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 at https://www.aavso.org/observing-campaigns.
This AAVSO Alert Notice was compiled by Elizabeth O. Waagen primarily
utilizing text provided by Dr. Donald Collins.
SUBMIT OBSERVATIONS TO THE AAVSO
Information on submitting observations to the AAVSO may be found at:
ALERT NOTICE ARCHIVE AND SUBSCRIPTION INFORMATION
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Subscribing and Unsubscribing may be done at the following URL:
https://www.aavso.org/observation-notif ... ertnotices
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