(22) Kalliope on 15 April 2022
A 16-second drift-scan exposure at 21:08 UTC on 15 Apr 2022, recording a
3.9 second occultation.
Another tricky occultation, where the minor planet was much brighter
than the star (mag +12.0 and +13.3 respectively) and so there was only
slight dimming, 0.2 mag, of their combined light during the occultation.
To increase the signal strength during the drift-scan, the CCD was
configured to bin the image 2x2, i.e. four pixels from the raw image
were combined into one pixel in the final image, reducing the size of
the images from 1024 x 1024 pixels to 512 x 512 pixels. Trials before
the occultation confirmed that the pixel values from 2x2 binned images
were 4 times stronger than in unbinned images and made the small drop in
brightness easier to measure.
However the down-side of binning is that by halving the number of pixels
in the trail the timing precision of the resulting measurement is
degraded by a factor of two.
The brightness and contrast of the trail of the minor planet in the
image above has been adjusted to more clearly show the small dip in
brightness during the occultation.
The shadow of Linus, the satellite of Kalliope passed some 500 km north
of Great Shefford during this occultation.