Occultation of TYC 0613-00905-1 by (231) Vindobona on Aug. 2 - Updated 2007 Aug. 7, 17h UT
The occultation occurred about 15s early and the path apparently was a half path-width north of the prediction
The northern limit probably crossed Washington, DC; Baltimore; and the n.w. Philadelphia suburbs, but unfortunately nobody observed there
Posted here now are .avi files for the central and northern stations in Maryland
Our overall prediction plan was as follows: Distance from center, km +91.4 Roger Venable N in Georgia +50.8 David Dunham N, Sandy Point, MD +30.3 Roger Venable C in Georgia +7.4 David Dunham N2, s. Stumptown, MD -15.7 David Dunham S1, Mill Rd., MD -35.9 Roger Venable S in Georgia -63.7 David Dunham S2, w. Willards, MD The only other person I've heard from about this outside of our group is from Mark Lang in Cary, NC, at the central line; he tried a visual observation with an 11-inch SCT, but with haze and light from the 87% sunlit Moon, 28 deg. away, he wasn't able to see the target star. We did run three stations. I would have set up a 4th remote station, the one at Mill Rd. at -15.7 km, but in the rush to leave, I left behind a special cable that is needed for video input for one of my camcorders, so I only had 3 recording systems. Also in the rush I left behind two tripods, but we had two with us, plus the small Tuthill "stick" mount that I used effectively at the southernmost station, although I had to dig an inch-deep trench to make room for the end of my camera attached to the image intensifier with the 60- deg. altitude above the horizon. Joan and I created .avi files of the occultation, as described below: North station (w. of Sandy Point, 213 megabytes) Central station (s. of Easton, 118 megabytes) Zane Nitzkorski successfully recorded the occultation with a 20cm SCT, f/3.3 focal reducer, & Stellacam II with 2-frame integrations at the planned location at Stumptown, MD, a few miles south of Easton and only 7 km north of center. At that location, at longitude 76 deg. 03.825' W., latitude 38 deg. 43.489' N., h 15m, the star disappeared at 9:05:11.1 UT and reappeared 5.4s later, at 9:05:16.5 UT, so the occultation occurred 14s earlier (nearly the same as the predicted central duration) than the predicted time for the location. Although the location was only 7 km north of center, the event was only 1/3rd the predicted duration, indicating an actual location near one of the limits. I could see the target star, and the occultation events, when I played the .avi file on my laptop at home, but on my desktop here in my office, for some reason playing the .avi file the view is quite dark so that I can't see the target, whereas the other file is o.k. (that is, as good a quality as when I played it on my laptop). Let me know if you have troubles with the view too dark with this video file. If you look at Steve Preston's charts, you'll see a 10th-mag. star preceding the target, and closer to the target but following it is 8.8-mag. SAO 109738; for awhile, around the time of the occultation, both of these stars are in the field of view of the Stellacam II, which I understand has a Watec half-inch chip. Registax might be used to determine event times better than I could just using a stopwatch with streaming video playback. I had a miss at Whaleyville, MD, using a 13cm SCT, f/3.3 focal reducer, and image intensifier at long. 75.3005 deg. W., lat. 38.3933 deg. N., h 11m, about 12 miles west of Ocean City; this location was 67 km south of the predicted center or 74 km south of Zane's location, less than the 91 km predicted path-width, so the actual path probably shifted about half a path-width, or about 0.8 sigma, north of Steve Preston's predicted path. The actual northern limit would have then been at about +90 km, which was over the US Naval Observatory in Washington, DC; over College Park and Baltimore, MD; and just s. of Narvon and Allentown, PA, but unfortunately nobody observed in those areas, as far as I know. But there is some chance that the path shifted south instead, in which case the asteroid was probably a little smaller (or elongated in the direction of motion) than predicted, narrowing the path some so that my location was very close to the southern limit. We set up and used Altair to pre-point a 20cm SCT with f/3.3 focal reducer and PC164C camera at Skidmore, MD, a couple of miles west of Sandy Point at long. 76 deg. 25.5994' W., lat. 39 deg. 01.3535' N., h 12m. Two young women, intern students like Zane, stayed in the area and turned on the camcorder a few minutes before the occultation. Unfortunately, the target star is not visible in the video, too faint under the conditions without the benefit of the integration or image intensification of the other stations. But the 10th-mag. star preceding the target star and the 8.8-mag. star following it can be seen at the right time, so the pointing was correct. The telescope was a little out of optical collimation, probably from the air flight back from the Hilda occultation and IOTA meeting in Washington State, which I discovered when we pre- pointed the scope but didn't have time to fix; about 50% of the star's light was concentrated in a point while the rest was in a coma-like small circle. Since this just used a 1/3rd-inch chip Supercircuits PC164C, the field of view is significantly smaller than the view in the video at Zane's station. The 10th-mag. star preceding the target exits the field at 9:05:06 and SAO 109738 enters the field at 9:05:19 UT; those are around the times when the occultation events probably occurred. So the 10th-mag. star can be used as a guide for the Registax process for the D, and probably SAO 109738 can serve that purpose for the R. Unfortunately, Roger Venable was not able to set up any of his telescopes due to a family emergency that lasted all night. It's too bad that nobody observed the occultation from the Washington, DC - Baltimore region since they probably would have observed a short occultation near the northern limit that would have been valuable for determining the size and shape of Vindobona. Pre-event predictions and plans are here. David Dunham, 2007 Aug. 7, 1 pm EDT Phones home 301-474-4722; office 240-228-5609; cell 301-526-5590 e-mail david.dunham@jhuapl.edu home e-mail: dunham@starpower.net .