British Astronomical Association
Supporting amateur astronomers since 1890

Secondary menu

Main menu

BAA Gallery Asteroids and Remote Planets
Image search

Asteroid (38476) 1999 TA91 occulting star 4U 444-161

Image
About this observation
Observer
Alex Pratt
Time of observation
05/01/2017 - 17:42
Object
Asteroid (38476) 1999 TA91 and star 4U 444-161
Observing location
Z92
Equipment
C11 and f/3.3 focal reducer
Watec 910 video camera
IOTA-VTI GPS time inserter
Exposure
1/50th sec (0.02sec exposures)
Like This Image
Share

The mag 20 asteroid (38476) 1999 TA91 was predicted to occult the mag 8.6 star 4U 444-161 on 2017 January 5 at 17:42:25 UT +/- 5s, as seen from my location. The asteroid is small, producing a ground track shadow only 8km in diameter, and the maximum duration of the occultation would be 0.3s with a probability of success of about 2%.

The star is bright, so the Watec camera was set to run at 50 fields per second, 0.02s exposures. I was most fortunate to record the target star blink out for 0.3s as it was covered by the asteroid (see the light curve created using Limovie). I must have been on the centreline of the ground track. A short extract of the video is currently available on the BAA ARPS website.

The reduced timings are:-

17:42:22.54 +/- 0.02s     Disappearance

17:42:22.84 +/- 0.01s     Reappearance

Multiple observations of occultations by larger asteroids produce chords across the ground shadow of the body, allowing us to create a shape profile of the asteroid.

Accurate timings of asteroidal occultations also give an astrometric measurement of the position of the asteroid, of particular value now that Gaia is delivering a star catalogue of unprecedented accuracy.

Comments

Tim Haymes's picture

A fine result for such a small asteroid. Congratulations...

A R Pratt's picture

Thanks Tim.

It's nice to record one of these low probability occultations after so many negative results. Let's hope 2017 brings us clear skies to obtain multi-chord observations of wide track events across the British Isles.

Richard Miles's picture

Well done Alex on this rare achievement: being in the shadow of a tiny 7km object as seen from 406 million km away. Eventually when the Gaia data reaches fruition in about 5 year's time, observations of this kind will be able to be targeted with much greater certainty and so hopefully it will be possible to obtain chords from several observers. You never know, this one might have been a binary system.

Copyright of all images and other observations submitted to the BAA remains with the owner of the work. Reproduction of the work by third-parties is expressly forbidden without the consent of the copyright holder. For more information, please contact the webmaster.