The TAROT telescope measures the size of a Kuiper Belt object

The asteroid Quaoar is a member of large planetoid located beyond the orbit of Pluto. Discovered in 2002, Quaoar dimensions were determined roughly by the measurement of its brightness and some assumptions about the nature of its soil. This leads to large uncertainties.

The technique for observing the occultation of a star by the asteroid Quaoar is to take a photo of the star for three minutes dragging gently the image on the sensor to record the temporal variations the brightness of the star. The star hidden in the middle of the image, shows a drop of brightness for about fifty seconds. From the delay of the star occultation we deduce the diameter of Quaoar.

The telescope TAROT at Calern (France), driven by astronomers of IRAP, observed the passage of Quaoar front of a star on the night of 16 to 17 February 2012. This passage has obscured the star that seemed to be extinguished for 56 seconds. Knowing the speed of Quaoar, we conclude that the diameter must be greater than 1020 km. The measurement method is highly accurate since the precision obtained is about 50 km while the asteroid is more than 4 billion kilometers from the Earth!
 
These results will be added to those obtained last year by astronomers in South America and they constrain the size and shape of Quaoar.
 
The TAROT telescope is normally intended to observe the optical emission from star explosions (gamma ray-bursts) but it is also used for various other astrophysical studies. It was built in 1998 by a team of astronomers from IRAP. A second copy is installed in Chile.

IRAP Contact

  • Alain Klotz: aklotz@irap.omp.eu

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