Since a few years, digital frame cameras are being used for the recurrent conventional photogrammetric mapping tasks within Flanders (Belgium). As a result, area-wide, but mixed-sensor-type (Ultracam, DMC, ...) time series of digital airborne imagery are emerging. Since only recently, a trend can be observed that this imagery is increasingly used for environmental mapping tasks, such as agricul...

We present the discovery of optical/X-ray flux correlations on rapid timescales in the low/hard state of the Galactic black hole GX 339–4. The source had recently emerged from outburst and was associated with a relatively-faint counterpart with mag V ≈17. The optical (VLT/ULTRACAM) and X-ray (RXTE/PCA) data show a clear positive cross-correlation function (CCF) signal, with the optical peak lag...

NN Ser is a non mass-transferring pre-cataclysmic variable containing a white dwarf with a mass of ∼ 0.5M⊙ and an M dwarf secondary star with a mass of ∼ 0.2M⊙. Based on the data detected by the high-speed CCD camera ULTRACAM, it was observed that the orbital period of NN Ser is decreasing, which may be caused by a genuine angular momentum loss or the presence of a third body. However, neither ...

We present high time-resolution multicolour optical observations of the quiescent X-ray transients GRS 1124–684 (=GU Mus) and Cen X-4 (=V822 Cen) obtained with ULTRACAM. Superimposed on the secondary stars’ ellipsoidal modulation in both objects are large flares on time-scales of 30–60 min as well as several distinct rapid flares on time-scales of a few minutes, most of which show further varia...

We report on the search for optical bursts from J1819–1458, a member of the recently discovered Rotating Radio Transients (RRATs). J1819–1458 exhibits 3 millisecond bursts with a peak flux of f ν = 3.6 Jy every ∼ 3.4 minutes, implying that it is visible for only ∼ 1 second per day at radio wavelengths. Assuming that the optical light behaves in a similar manner, the most sensitive way of detect...