Feb. 28th Occultation of 8.7-mag. SAO 117582 by (51) Nemausa recorded from two sites in the California desert
Unfortunately, everyone else was either clouded out, or had wind or equipment problems - New 2007 March 8, 18h UT
I video recorded the occultation of 8.7-mag. SAO 117582, about 7 deg. east of Hydra's head, by the 140-km C-class asteroid (51) Nemausa on Tuesday night/Wed. morning, 2007 February 28 UT, with portable telescopes from two locations in the desert east of Indio, California in spite of one scope missing my final connecting flight to Ontario, Calif. (I had to wait at the airport for 3.5 hrs until it arrived on a later flight; it was the one I used at my attended station) and the other two scopes partially broken in transit (Walt mentioned the slow motion, in dec., being jammed on the scope he used in his IOTAoccultations e-group message). The locations were approximately 24 km (for the remote) and 52 km north of Steve Preston's predicted central line and both had approximately 15-second occultations, indicating a shift to the north, but probably by less than 1 sigma. The sky was clear except for some clouds retreating low in the southeast, and mercifully the wind died almost to a calm (actually was calm much of the recording time) around the time of the occultation at my attended station. At my attended (northern) station, beside Highway 177 about 6 miles northeast of Desert Center, I used a 4-inch SCT with f/3.3 focal reducer, Collins I3 image intensifier, & PC164C to video record the occultation with a Kiwi OSD. Preliminary times, probably accurate to about 0.2 second, are D at 8:42:59.1 UT and R at 8:43:14.0 UT. I set the scope on the hood of my rental car, avoiding the problem that Walt mentioned of getting low to look through the finder scope. I'll send details of this and the remote station to Brad Timerson in a couple of days. At the remote station, near a dirt side road off of Hayfield Road a quarter mile north of the I-10 exit east of Chiriaco Summit, D was at 8:42:59.2 and R at 8:43:14.7 UT, nearly equal to the predicted 15.8-second maximum duration, but at least a few seconds earlier than predicted. This was with a 5-inch SCT with f/3.3 focal reducer & PC164C to video record the occultation with a Kiwi OSD. Of course, the scope was set on the ground, so I had to bend down to look through the finder to prepoint the scope to some stars in Canis Minor almost 2 hours before the event. This was really victory snapped from the jaws of defeat. When I first set up the scope with its Tuthill short metal bar "tripod", I polar aligned it, but was dismayed to find that the RA clamp did not work and the scope swung loosely from the imbalance of the finder scope; it looked like there was no way I could control the scope to point it properly. I was about ready to give up when I found that in one orientation, the RA stuck enough that I could adjust it gradually manually (although the slow motion control didn't work with the broken clamp). But that orientation didn't point anywhere near the target area with the polar alignment. So I rotated the telescope about 120 deg., destroying the polar alignment and then feared that I couldn't figure out the star field in the video, since I'm used to always having north up. But by watching a star drift, I could figure out the north direction, so, with ample time left, I decided to try it. After a couple of tries, I did get the telescope pre-pointed approximately, and then was able to fine-tune it by watching the pattern of faint stars as they drifted through; fortunately it was at low galactic latitude with a few faint stars always visible. During the time that the target star drifted across the video field, there was mild shaking due to the wind. Because of the wind and dry conditions, I did not use a dew shield. As noted in my last message before the event, several observers planned to try the event, but as I predicted, all except Rick Wasson and Walt Morgan were clouded out (including at the Lewis Center in Apple Valley at 38 km s. of the predicted center, which I inadvertently left out of my last pre-event message). Salvador Aguirre almost succeeded at Carl Sagan Observatory near Hermosillo, Sonora, Mexico. He found the target star when the clouds thinned about 15 min. before the occultation, but during the observing period, the clouds thickened too much to make an observation. This was unfortunate, it would have been a valuable observation not too far inside the predicted northern limit at 77 km north of center. On Highway 177 in Calif., I could have travelled farther northeast (as it was, I was able to record the target star 20 min. before the occultation) but decided not to do that to avoid duplicating a possible chord from Hermosillo, and also, after being burned with the huge south shift for the Palma occultation, I didn't want to be less than 1 sigma inside the northern limit (52 km was near that 1- sigma "inside" location); I wanted to get something from this trip, not being 100% confident that the remote station would work, since a very strong wind gust might have pushed the scope off-target (fortunately, that didn't happen; I did set it up near a large bush and also used the telescope box to provide a little protection from the wind, which was unusually strong that night). Unfortunately, a wind gust did spoil Rick Wasson's attempt, knocking his scope off- target a few minutes before the occultation, then not being able to re-acquire until 3 minutes after. So it's too bad that Walt Morgan also failed so that, as far as I know, no observations were obtained from the southern half of the path, and that my two stations weren't farther apart Maps and extensive pre-event predictions and plans are here. David Dunham, 2007 March 8, 18h UT home dunham@starpower.net 301-474-4722 cell 301-526-5590 office & Blackberry david.dunham@jhuapl.edu 240-228-5609