MBCAA Observatory

FO Aqr 2016 low state

Observed: 10 Jul, 31 Oct, 6, 8 Nov, 26 Dec 2015, 28 Jun, 3, 9, 18, 28 Jul, 3, 12, 13, 22, 25 Aug, 1, 6, 28 Sep 2016

Michel Bonnardeau
14 July 2016
Updated 18, 29 Aug, 5, 11 Sep 2016 with more data


In 2016, the intermediate polar FO Aqr is observed in an unusual low state.


FO Aqr is a cataclysmic variable star, that is a binary star with an accreting white dwarf. The white dwarf is magnetic, funneling the accretion, and FO Aqr is classified as an Intermediate Polar. The orbital period is Porb=4.849 hours and the spin period of the white dwarf is Prot=20.9 minutes.

I have been monitoring FO Aqr every season since 2004.


The observations were carried out with a 203 mm Schmidt-Cassegrain telescope, a Clear filter, and a SBIG ST7E camera (KAF401E CCD), mostly red sensitive. The exposure durations were 60 s. 385 useful images were obtained in 5 nights in 2015, and so far 341 images in 3 nights in 2016.

For the differential photometry, the comparison star is GSC 5803-398 (UCAC4 409-138153 with V=10.921 mag). The check star is UCAC4 409-138161.

Season 2015

The magnitudes are the differences with the comparison star. Red: FO Aqr, Blue: the check star shifted by +0.3 mag. The error bars are the quadratic sum of the 1-sigma statistical uncertainties on the variable and of the comparison star.

There was an interruption to observe an occultation.

Saison 2016

FO Aqr is dimmer by about one and a half mag:

The check star is shifted by +1.6 mag.

The data are noisy because of the Moon.


With the magnitudes averaged over each night:

The error bars are the standard deviations over each night.

A close up for 2016:


This low state was reported by Littlefield et al (ATEL #9216). They also discovered a 11.26-minute periodicity (ATEL #9225).

Technical notes

Telescope and camera configuration.

Computer and software configuration.

Data processing.

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