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(4288) Tokyotech occults TYC 1219-00564-1


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About this observation
Alex Pratt
Time of observation
01/12/2019 - 19:52
(4288) Tokyotech occults TYC 1219-00564-1
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)
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The mag 14.7 main-belt asteroid (4288) Tokyotech, 12 km in diameter, was predicted to occult a mag 11.2 star in Aries on 2019 December 1. Observers within the 12 km wide shadow track could see a drop in brightness of 3.5 magnitudes for up to 1.4s.

My site was 10 km south of the predicted shadow zone, with an 11% probability of success. I was fortunate to record the brief disappearance of the target star, 1.12s in duration. The attached screenshot shows the analysis of the light curve using Tangra and AOTA.

    D  - 19 52 19.34 ± 0.02
    R  - 19 52 20.46 ± 0.02

This is the first chord observed across Tokyotech; there are no previous observations listed in the Occult database. These timings confirm that the asteroid is at least 9 km in diameter and the Gaia position of the target star will give high-precision astrometry of the asteroid at the mid-time of the occultation.

After I submitted my formal report to the Planoccult list server I received an interesting reply from Raoul Behrend (Geneva Observatory). He leads the CdR &CdL team which analyses asteroids' light curves, searching for binary systems. He commented that Tokyotech is a binary asteroid, and two hours before my occultation event its components were predicted to be in mutual eclipse. Because I recorded one brightness dip and not two, this would help to constrain their model of the Tokyotech system.


Ray Emery's picture

Alex - another superb observation!  Well done that man (again)!

A R Pratt's picture

Many thanks, 'Ragnar'.

We're hoping that the Gaia Data Release 3 in 2020-2021 will give us high quality asteroid orbital elements, leading to much-improved occultation predictions, removing a lot of the uncertainties in this work.

Clear skies,


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