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Observations requested for b Per December 2016 eclipse

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發表於 2016-12-3 06:36:13 | 顯示全部樓層 |閱讀模式
AAVSO Alert Notice 563

December 2, 2016

Observations requested for b Per December 2016 eclipse

An AAVSO campaign on the bright star b Per has been launched at
the request of Dr. Donald F. Collins, who writes:

"Dr. Donald F. Collins (AAVSO member, Swannanoa, NC), Dr. Robert
Zavala (US Naval Observatory, Flagstaff Station), Dr. Anatoly
Miroshnichenko (University of North Carolina at Greensboro), and
Jason Sanborn (Lowell Observatory) have requested high
time-resolution observations of the bright star b Persei [HIP 20070,
SAO 29531, HR 1324, HD 26961, V ~ 4.57] during the next predicted
eclipse, or transit, of the third star across the system as it is
predicted to transit the inner pair of the triple system **DURING
THE WEEK CENTERED ON DECEMBER 15, 2016**. Well-sampled light curves
can provide timing data for the orbits with much greater precision
than astrometry or spectroscopy alone.

"Three campaigns by the AAVSO (AAVSO Alert Notice 476, January 4,
2013; AAVSO Alert Notice 507, January 7, 2015; and AAVSO Alert
Notice 537, February 26, 2016) have successfully observed three
transits between the inner A-B pairs each with the third star. The
second transit (January 2015) was observed 704 days after the first
observed transit. Long time-series observations of the January 2015
transit detected multiple dips in the light curve as the third star
alternately transited the A and B components and the inner rotating
system. A third transit was observed successfully by AAVSO observers
in March 2016. During March 2016 transit the third star transited on
the opposite sides of the inner A-B pair from the first two observed
transits. We are trying to sort out whether the third star is
blocked by the inner A-B pair or the A-B pair blocks the light of
the third star in each. Results of the previous campaigns may be
seen at the links below:

January 2013:  http://inside.warren-wilson.edu/~dcollins/bPersei/

January 2015:  https://www.aavso.org/campaign-highlight-b-persei

and http://inside.warren-wilson.edu/~dcollins/bPersei/bPersei2015Eclipse/b_Persei2015eclipse.html

The last link above includes an animation attempting to simulate
the eclipse of the orbiting stars in the system.

The plot showing the result of the March 2016 campaign may be seen
on the AAVSO webpage for this Alert Notice
(https://www.aavso.org/aavso-alert-notice-563).

"The inner pair of stars [in b Per] 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. This is shown as the small
out-of-eclipse eclipse oscillations in the [figure showing the
March 2016 eclipse that may be seen on the AAVSO webpage for this
Alert Notice]. The third star of the system transits the inner pair
every 702 - 705 days, no eclipse had been detected before the 2013
AAVSO campaign.  

"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
DECEMBER 8, 2016, [AND CONTINUING FOR ABOUT A WEEK AFTER THE
ECLIPSE]** in order to calibrate the varying offsets from different
observing systems. It is recommended to use the star HIP 20156 =
SAO 39457 = HR 1330 = HD 27084 (the star labeled '55') in 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.

"CCD and DSLR 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 or lenses - 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 (between 5 and 20 observations averaged) or
stacking the same number of images will reduce the point-to-point
noise even further. It is also important to obtain out-of-eclipse
observations both before and after the event in order to match the
varying zero point offsets from different observers and to match
the out-of-eclipse light curves with the ellipsoidal light curve of
b Persei. Observers should also concentrate on obtaining time-series
of long duration each night - especially in mid-eclipse as the
transit time duration between any two stars is about six hours.

"We also need a wider longitudinal spread in observers in order to
insure that observations cover the entire transit event that
experiences several eclipses and re-emergences during the 2-4 day
event. Observers from western N. America, Pacific islands, and
Asia are especially needed in addition to continued good coverage
from Europe and eastern North America.

"Photoelectric observers are especially encouraged to contribute to
the campaign.

"Dr. Anatoly Miroshnichenko and his students at the University of
North Carolina at Greensboro have been obtaining extensive
high-resolution spectroscopy of the b Persei system this observing
season to help with the campaign."

A thread has been created on the Campaigns and Observation Reports
forum at (https://www.aavso.org/content/december-2016-b-per-campaign)
to share rapid developments, observing techniques, and notices
concerning the eclipse progress.

Coordinates for b Per:  R.A. 04 18 14.62  Dec. +50 17 43.8  (J2000)

Charts with a comparison star sequence for b Per may be created
using the AAVSO Variable Star Plotter (VSP, https://www.aavso.org/vsp).
Please choose comp/check stars as requested above, if possible.

Please submit observations to the AAVSO International Database
using the name b PER. Do NOT also send observations to Dr. Collins.

This campaign is being followed on the AAVSO Observing Campaigns
webpage (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:
https://www.aavso.org/webobs

ALERT NOTICE ARCHIVE AND SUBSCRIPTION INFORMATION

An Alert Notice archive is available at the following URL:
https://www.aavso.org/alert-notice-archive

Subscribing and Unsubscribing may be done at the following URL:
https://www.aavso.org/observation-notification#alertnotices

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