Occultation of SAO 118999 by (302) Clarissa 2004 June 24 timed in NY & CT
Clarissa larger than expected and may have a satellite
Updated: 2004 Aug. 6The available observations are summarized below Occ'n Track Dur. Observer, location 163N miss Alan MacRobert, Bedford, MA 52N 0.25s Phil Dombrowski, Glastonbury, CT 42N -- predicted northern limit 32N miss Brad Timerson, Newark, NY 16N 2-3s Michael Richmond, RIT Obs., Rochester, NY 17S 3.1s David Dunham, Walden, NY 25S 2.3s Frank Suits, Garrison, NY 42S -- predicted southern limit 54S miss Frank Melillo, Holtsville, L.I., NY The positive observations were all video recorded. The observations at RIT Observatory are described here. We have some surprises from the 2004 June 24th occultation of SAO 118999 by (302) Clarissa! First, the predicted central duration was only 1.8 seconds, but the two longest chords (confirmed video) were just over 3.0 seconds long. Miss observations closely bound the asteroid's shape on the north (Timerson) and south (Melillo). My preliminary reduction (video times have so far only been obtained manually, and so are accurate to about +/-0.2 second, except for the Rochester observation, where the time resolution was only +/-0.5 second) gives an ellipse 64 km long by 36 km wide, considerably bigger than the expected diameter of 38 km. The motion was almost in the direction of the major axis. A plot of the observations is here, with an expanded view of the ellipse here. But the biggest surprise is Phil Dombrowski's short event (station 4). I thought that it must mark the northern limit, but Brad Timerson, farther south, reported a miss, and he was confident that he had the right star on his video. The analysis showed the truth - Dombrowski's event doesn't match the others at all! We need to double-check everything, but it appears, that if Dombrowski's event is a real occultation, it was caused by a satellite of Clarissa about 258 km in the sky plane (4 times the major axis) from the center of Clarissa. Dombrowksi's duration of about a quarter second would indicate an object of the order of 5 - 6 km in size. Recently, Frank Anet performed a careful analysis of Phil Dombrowski's secondary extinction which casts some doubt on that event, mainly because Phil had to use a small portable telescope rather than his obstructed fixed main telescope so that the star was quite faint in the video and was not present in some of the other frames as well. But Phil saw the event in real time, which is often better than the recording, and it appeared quick but clear to him at the time. Also shown on the plot is a dimming recorded at Rochester, "chord" #9, but it is very uncertain, one of the larger of other seeing variations in the record, so it is most likely atmospheric in origin. Sta. Observer name, location E.Longitude Latitude height # o ' " o ' " m 1 David Dunham, Walden, NY -741207.6 +413218.9 133 2 Frank Suits, Garrison, NY -735459.5 +4123 4.7 203 3 Michael Richmond, RochesterIT Obs, NY -773953. +430433. 168 4 Phil Dombrowski, Glastonbury, CT -723445.1 +414334.8 46 5 Brad Timerson, Newark, NY -77 537.4 +43 210.1 144 6 Predication, Steve Preston, June 20 -74 0 0. +413847. 0 7 Frank Melillo, Holtsville Long Is, NY -73 231.2 +404836.0 0 8 Alan MacRobert, Bedford, MA -711842.8 +422929.8 42 9 Michael Richmond, RochesterIT Obs, NY -773953. +430433. 168 Universal Times Sta. Observer name Disappear Reappear # h m s h m s 1 David Dunham 3 323.12 3 326.22 2 Frank Suits 3 324.3 3 327.3 3 Michael Richmond 3 311.8 3 313.8 4 Phil Dombrowski 3 336.9 3 337.15 5 Brad Timerson 3 313.9 3 313.9 miss; closest approach time 6 Predication 3 327. 3 327. predicted time 7 Frank Melillo 3 330.0 3 330.0 miss; closest approach time 8 Alan MacRobert 3 323.6 3 323.6 miss; closest approach time 9 Michael Richmond 3 332.8 3 333.8 dimming, probably atmospheric Thanks to all observers who tried this event; we will certainly be able to fit an ellipse to these observations. I give my condolences to the observers in Ontario who were clouded out shortly before the event. Much prediction information (maps and detailed station data) can be found here. David Dunham, 2004 June 28; updated 2004 Aug. 6