A POSSIBLE STELLAR OCCULTATION

BY TRANS-NEPTUNIAN OBJECT (50000) QUAOAR

Friday May 1 2009 around 13:45 UT

On May 1 2009 at 13:40 – 13:50 UT (depending on location on Earth, see map below), Trans-Neptunian object (50000) Quaoar might occult star 2UCAC 26252549, R=14.3, J=12.0, K=11.2. If positive, this would become the first predicted stellar occultation of a known solar system object beyond Pluto.

Please note that the event is worth observing with a small, amateur telescope even with an integration time of several seconds. Although the radius would remain constrained as an upper-limit only, and there would be no constraint for a possible atmosphere, any "on-off" detection would become an ephemeris reference point for years to come, and validate our prediction process.

J2000 stellar coordinates : 17 18 12.5402 -15 24 49.845

This event will be potentially visible from Australia and New Zealand, and with less probability from Hawaii. Its maximum duration is about 1 min. We recommend observing between 13:30 and 14:00. Care must be given to include nearby UCAC stars in the field for photometrical calibration. Please send all observing reports whether positive or negative (including bad weather, with observerπs latitude / longitude / altitude data, telescope, instrument, integration time, and timing method description) to Paris Observatory at the following email addresses :

thomas.widemann @ obspm.fr

bruno.sicardy @ obspm.fr

Quaoar's shadow is moving from right to left with a ground velocity of 18.5 km s^-1. Dots are spaced by 1 min intervals. Predicted time for geocentric predicted closest approach C/A = 0.26 arcsec is 13:42 UT.

This recently updated prediction is derived from a reanalysis of the star position by the Rio group of its 2008 observations, with an ephemeris offset for Quaoar of 0.015 arcsec in RA and -0.175 arcsec in DEC. A stellar occultation by Quaoar's satellite, which has been observed at a distance of about 0.35 arcsec, with an estimated diameter of 100 km, or any additional orbiting material, might also be observed, from any station on Earth's hemisphere facing the star.