Last updated 02 Apr 2024

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Minor Planet Occultations

(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.

Screenshot of drift-scan measurement using Scanalyzer (see page by John Broughton, Reedy Creek Observatory, Australia here).

Chord diagram and DAMIT model from

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