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(2111) Tselina occults UCAC4 491-028819


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About this observation
Alex Pratt
Time of observation
24/12/2018 - 21:52
Asteroid (2111) Tselina occults star UCAC4 491-028819
Observing location
C11 f/10 and f/3.3 focal reducer
Watec 910 video camera
IOTA-VTI GPS time inserter
OccuRec (recording)
Tangra and AOTA (reduction)
0.16s (4 integrated video frames)
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The mag 14.5 27 km diameter asteroid (2111) Tselina was predicted to occult the mag 12.4 star UCAC4 491-028819 on 2018 December 24. Their combined magnitude would drop by 2.3 mag for up to 2.2 seconds.

My observatory was 1 km inside the predicted shadow zone. The predicted probability of success at my site was 21.1% and I recorded an occultation duration of 0.96s. The times of disappearance and reappearance were:-

D     21 52 25.87 +/- 0.08s

R     21 52 26.83 +/- 0.08s

The attached plot shows the analysis of the light curve using Tangra and AOTA software. No other observers were registered for this event, so we can't derive a shape profile, but a single positive observation can give high quality astrometry at the instant of the occultation.


Ray Emery's picture

Alex - brilliant! Well done that man!  :-)

- Ray E. -

A R Pratt's picture

Thanks Ray.

The occultation of the star occurred within the prediction uncertainty of 4s, so we have to assume that it was caused by the asteroid rather than high flying reindeer...

Star positions are known to great accuracy thanks to the Gaia project, although asteroids' orbits are not (yet) to that level. The uncertainties of predictions of asteroidal occultations are much smaller than they were years ago. The later Gaia Data Releases should allow us to compute good quality predictions but the weather across our Misty Isles will continue to thwart many efforts to observe them.

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