------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 2552 2009 May 22 20.37UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074 INTERNET: GUY@TAHQ.DEMON.CO.UK Backup: gmh@wdcc1.bnsc.rl.ac.uk WORLD WIDE WEB http://www.theastronomer.org ------------------------------------------------------------------- (50 000) QUAOAR APPULSE J. Lecacheux, France has reported on the Occultations network that the large transneptunian object 50 000 QUAOAR (~ 1250 km) will pass very close to the faint star 2UCAC 26252200 (V= 14.1, R= 13.8) on the morning of Saturday 2009 May 23 at about 02:47 UT. Unfortunately we expect that QUAOAR will miss our planet (see http://www.euraster.net/pred/20090523-Quaoar-13.9.gif ) However QUAOAR possesses a large satellite (of diameter ~ 95 km) that the "Hubble" Space Telescope detected at 11 000km WSW from the main body on 2006 Feb.14. The orbital radius and orbital pole of this satellite are unknown at the present time. We do not know if the orbit appears to us edge-on or roughly pole-on. As 11 000 km was the vector radius projected on the sky, the true elongation of the satellite relative to QUAOAR could reach 15 000 km or so (very rough approximation). According to Euraster -who used the nominal UCAC2 star position, the miss distance of QUAOAR's centre to west Europe should be 15 000 km. Using recent astrometry, the team of Rio-de-Janeiro Observatory has revised the track by 4 000 km inward, so is now putting the miss distance close to 11 000 km. So clearly our continent will cross a region of the space where the shadow of the satellite could be present. To summarize, and according to the Brazilian update : - The southern limb of QUAOAR should miss west-Europe (for example Brussels) by 10 400 +/- 7 300 km (2 sigmas uncertainty) So the probability of occultation by QUAOAR itself is only 0.2 %. - The satellite should miss us by zero (-12 000 km, +33 000 km) Its probability of occultation is almost impossible to calculate in reason of the quasi absolute orbit undetermination, but should be comparable to 100 / 45 000 , i.e. 0.2 % too. The star is too faint for video recording at 25 frames/s with any usual amateur instrument, but as the maximum duration of occultation by the satellite will be 4 seconds, integrations within the range [0.32 s - 1.28 s] seem fully acceptable. The uncertainty of QUAOAR along the track is sigma= 9 600 km according to AstDys. The satellite could precede or follow it by 10 000 km, if passing close to us. The J2000 speed motion will be 23.5 km/s. It results that a 40 min long record (i.e. +/- 20 mn around 02:47 UT, ending at 03:07) should be enough. Because of solsticial dawn, only the West of Europe is concerned. The time of twilight will be the following at some locations : Nautical Civil Quaoar elevation (degrees) ---------------------------------------- -Lisboa : 04:10 04:48 34 -Madrid : 03:41 04:20 31 -Barcelona : 02:57 03:46 29 -Paris : 02:33 03:24 22 -London : 02:13 03:14 20 -Brussels : 02:02 03:01 20 Guy M Hurst