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The figure is an artificial representation of the "sky" seen by Gaia when passing through the Omega Centauri globular cluster. The dots in the figure show the positions where cameras of Gaia have detected and measured stars in one pass. The seven Video Processing Units (VPUs) running the automatic image handling algorithm on-board extract around separately detected stars small windows, which are sent down to the Earth. The size and brightness of each dot is proportional to the brightness measured for each star, so overall it gives a realistic idea of the actual sky.
In this case, despite observing a region 15,800 light-years away (4,850 parsecs), in about a minute Gaia was able to detect and measure over 137 thousand stars, sending all their information to the ground segment where the Data Processing and Analysis Consortium (DPAC) systems were eager to process all these precious data.
The figure clearly shows the traces of the seven VPUs (with small gaps in between) scanning the globular cluster from right to left and from bottom to top. Actually, the figure is incomplete, as expected, because that sky region is so dense that the hardware resources onboard become saturated at the densest parts. We can also see some ``trails'' following bright stars, which are actually spurious detections at the wings of the point spread function of those bright stars. These will be cleaned up by the data processing systems on ground. These results are being analysed to fine tune the on-board parameters for the densest regions on the sky.
These figures are just an example of the automatic diagnostics that the Initial Data Treatment system (IDT) generates every day on the data received from the satellite. IDT will detect the densest regions processed every day and will generate these plots, as well as other plots showing the stars for which we found matching entries in ground-based catalogues (the so-called matched transits), plots showing the unmatched transits, others showing the spurious detections that were successfully identified, etc.
credits: ESA/Gaia/DPAC/UB/IEEC
[Published: 13/11/2014]
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