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FO Aqr 2018 campaign

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weo's picture
FO Aqr 2018 campaign

AAVSO Alert Notice 644 announces an observing campaign on the intermediate polar FO Aqr. Please see the notice for details and observing instructions.

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ

wluding's picture
Comp stars for FO Aqr

I don't find any comp stars for FO Aqr on the VSP charts. What am I doing wrong? I've looked at A chart scale and F chart scale.

Whit Ludington, LWHA

FO Aqr Sequence

There is a sequence for FO Aqr on a F chart.  You might want to check your magnitude limit, and make sure you don't have one of the Special Charts checked.

Eric Dose
Eric Dose's picture
CCD chart FO Aqr

Late 2016 I set up the CCD chart I stlll use for FO Aqr, id = X16927BD. I just pulled it up from the Variable Star Plotter as:

and it still looks OK, no problems among the comp stars. So at worst you may consider starting with that.

No charge  :)


wluding's picture
Comp stars for FO Aqr

jji  - your suggestion was on target. My problem was the Special Chart was checked.  I was getting M11 charts for doing transform coeficients a several days ago and forgot to uncheck Special Chart.



Great.  Glad things worked

Great.  Glad things worked out.


Update: unusual variability throughout August

Hi everyone,

Thank you for observing FO Aqr. During the past ~20 days, FO has shown at least four ~0.3-mag flares in its light curve, during which the 20.9-minute spin pulse has become extremely strong. Outside of the flaring episodes, the spin pulsation has been comparatively weak or absent, possibly attributable to an increase in the strength of the system's 22.5-min beat period. This suggests that FO's accretion mechanism is changing during these flares.

During the flares, the system briefly reaches its brightness from before the start of the current low state (V~13.9), implying that the low state might almost be over. Thus, I suspect that the recent flares might be related to the reappearance of the system's accretion disk. During its bright state, FO Aqr contains a Keplerian accretion disk, but Hameury & Lasota (2017) predict that the disk dissipates during a low state. If they are correct, I would expect a transitional state near the end of a low state as the system reestablishes its accretion disk, and that might be what's responsible for these oscillations in the light curve.

Regardless of the cause of the system's recent behavior, it's important to continue monitoring it. Keep up the good work!


PVEA's picture
unusual variability throughout August

Hi Colin,

The results from the night of 2018-08-22 are submitted. Indeed the 0.3 to 0.5 mag flares with about 21 min period are clearly detectable. I will continue with observations.




The low state has ended; intensive observations aren't necessary

Hello everyone,

Thank you for the outstanding coverage of FO Aqr during the past six weeks. Since approximately Aug. 18, FO Aqr has been in a bright state at about V = 13.9. During this time, the WD spin period at 20.9 minutes has dominated the light curve, and the strong 22.5-minute beat period observed throughout the low state has been weak or absent in most light curves. Consequently, it seems that this year's low state has ended, and intensive observations are no longer necessary.

The attached light curve shows the average magnitude of FO Aqr in light curves submitted by various observers, and you can see a series of flares and dips in the first half of August. The horizontal dashed line represents the system's brightness before the low state. The different marker styles correspond to different observers. The errorbars are derived from simulations involving the Kepler K2 light curve of FO Aqr, and their sizes are dictated solely by the length of the underlying time series. This is because longer time series do a better job of averaging over both the periodic and aperiodic variability in FO Aqr, giving a better sense of the system's overall brightness.

Even in the absence of an active observing campaign, FO Aqr is a unique and dynamic system, and there is a lot of merit in observing it occasionally. There's no telling when its next low state will begin, how deep that low state will be, or how long it will last. A very deep low state (fainter than V = 15) would be of particular interest, as it would present an opportunity to detect the donor star in spectra for the first time ever. Even if FO stays bright, your observations of the 20.9-minute spin pulsations provide direct measurements of the unpredictable evolution of the white dwarf's spin period, a subject that has received significant attention in the literature. The bottom line is that it will be scientifically fruitful to check in on FO Aqr from time to time.





File upload: 
ldj's picture
Thanks for the update. I'm

Thanks for the update. I'm sad that (intensive) observations are no longer necessary - I was just getting into the routine of observing it!

Dave LDJ

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