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FO Aqr time-series observations requested

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發表於 2016-7-14 06:09:35 | 顯示全部樓層 |閱讀模式
[size=13.3333px]AAVSO Alert Notice 545
[size=13.3333px]July 13, 2016

[size=13.3333px]FO Aqr time-series observations requested

[size=13.3333px]Dr. Colin Littlefield (University of Notre Dame) and colleagues
[size=13.3333px]Drs. Peter Garnavich (Notre Dame), Erin Aadland (Minnesota State),
[size=13.3333px]and Mark Kennedy (University College Cork) have requested AAVSO
[size=13.3333px]assistance in monitoring the intermediate polar cataclysmic
[size=13.3333px]variable FO Aqr beginning immediately.

[size=13.3333px]Dr. Littlefield, who with his colleagues recently published ATel
[size=13.3333px]#9216 ([size=13.3333px]http://www.astronomerstelegram.org/?read=9216[size=13.3333px]) and #9225
[size=13.3333px]([size=13.3333px]http://www.astronomerstelegram.org/?read=9225[size=13.3333px]), writes:

[size=13.3333px]"This system is in a faint state for the first time in its
[size=13.3333px]observational record, implying a dropoff in the mass-transfer rate.
[size=13.3333px]AAVSO observations contributed by Shawn Dvorak [the only observer
[size=13.3333px]following FO Aqr at the time] were particularly helpful in detecting
[size=13.3333px]this low state. Since early May, the system has recovered to V~15,
[size=13.3333px]but it is still well below its normal brightness. In addition, our
[size=13.3333px]time-series photometry shows a very strong 11.26-minute photometric
[size=13.3333px]period. By contrast, during its bright state, FO Aqr's light curve
[size=13.3333px]is dominated by a 20.9-minute period, corresponding with the spin
[size=13.3333px]period of the white dwarf. We interpret our observations as evidence
[size=13.3333px]that the system's accretion processes have changed dramatically as
[size=13.3333px]a result of the reduced mass-transfer rate.

[size=13.3333px]"We have...determined that...[the 11.26-min] periodicity is
[size=13.3333px]dependent on the orbital phase of the binary. The 11.26-min period
[size=13.3333px]is dominant for about half of the orbit, but for the other half, a
[size=13.3333px]22.5-min period is stronger. AAVSO observers can help us study both
[size=13.3333px]of these periods as well as their dependence on the orbital phase.
[size=13.3333px]We are particularly interested in any changes in this behavior as
[size=13.3333px]the system continues to brighten.

[size=13.3333px]"...Time-series photometry of FO Aqr [is requested] in order to
[size=13.3333px]better study the evolution of the 11.26-minute period as the system
[size=13.3333px]rebrightens. Unfiltered photometry reduced with a V zeropoint would
[size=13.3333px]be the most useful to us... A cadence of less than 60 seconds per
[size=13.3333px]image is important, given the brevity of these periods (especially
[size=13.3333px]the 11.26-min period). Long, uninterrupted time series would be
[size=13.3333px]especially valuable, but even a short time series would be useful
[size=13.3333px]in terms of monitoring the 11-minute period. Also, it's critical
[size=13.3333px]that observers ensure that their computer clocks are accurate to
[size=13.3333px]within a few seconds."

[size=13.3333px]Littlefield reports that as of 2016 July 12-13, FO Aqr was "still
[size=13.3333px]much fainter than usual, at V~14.93 (unfiltered with V zeropoint).
[size=13.3333px]The data remain consistent with a gradual rebrightening at an
[size=13.3333px]average rate of about -0.01 mag/day." FO Aqr's normal brightness
[size=13.3333px]is V~13.4.

[size=13.3333px]"We would like the time-series observations to continue until the
[size=13.3333px]system returns to its normal brightness level or until it gets too
[size=13.3333px]close to the Sun to be observed (whichever comes first)."

[size=13.3333px]Coordinates (2000.0): R.A. 22 17 55.38  Dec. -08 21 03.8

[size=13.3333px]Charts: Charts for FO Aqr with an expanded comparison star sequence
[size=13.3333px]may be created using the AAVSO Variable Star Plotter (VSP) at
[size=13.3333px]https://www.aavso.org/vsp[size=13.3333px]. For observers who have been following
[size=13.3333px]FO Aqr as part of the CBA program, the comparison stars used for
[size=13.3333px]that program have been retained.

[size=13.3333px]Please submit observations to the AAVSO International Database
[size=13.3333px]using the name FO AQR.

[size=13.3333px]This campaign is being monitored on the AAVSO Observing Campaigns
[size=13.3333px]webpage at [size=13.3333px]https://www.aavso.org/observing-campaigns[size=13.3333px].


[size=13.3333px]This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.

[size=13.3333px]----------------------------------
[size=13.3333px]SUBMIT OBSERVATIONS TO THE AAVSO

[size=13.3333px]Information on submitting observations to the AAVSO may be found at:
[size=13.3333px]https://www.aavso.org/webobs

[size=13.3333px]ALERT NOTICE ARCHIVE AND SUBSCRIPTION INFORMATION

[size=13.3333px]An Alert Notice archive is available at the following URL:
[size=13.3333px]https://www.aavso.org/alert-notice-archive

[size=13.3333px]Subscribing and Unsubscribing may be done at the following URL:
[size=13.3333px]https://www.aavso.org/observation-notification#alertnotices

[size=13.3333px]-------------------------------------------------

[size=13.3333px]Please support the AAVSO and its mission -- Join or donate today:
[size=13.3333px]https://www.aavso.org/apps/donate/



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