Varsavia Occultation July 18 timed in w. North America
Updated: 2003 December 2
See the bottom of this message for a new analysis of the
observations, much more complete now than described immediately
below, and with different numbers for the stations. There are
still a few discrepancies in the video observations that need to be
resolved before a final analysis of all of the observations can be
completed, but the new results are better than the mid-Nov. ones.
So far, I have reports of 41 positive observations
of the July 18th occultation of 6.4-mag. SAO 100819 by (1263)
Varsavia, and several miss observations, too, from Nanaimo, BC down
to Rancho Palos Verdes, Calif. (south of Los Angeles). At the time,
it was the 3rd best-observed (in numbers of positive observations)
asteroidal occultation, after the 1983 May Pallas - 1 Vulpeculae
event and the 2002 Sept. Tercidina - 43 Tauri event, but now it is
in 4th place since 2nd place is now taken by the
highly successful occultation of 8.7-mag. SAO 144929 by (420)
Bertholda from Poland to Portugal on August 26. Varsavia's path
shifted about a quarter path-width west of Steve Preston's last
prediction and not quite half a path-width west of his July 6th
prediction that I used as the basis for the station track
calculations. I have updated Rohith Adavikolanu's plot to now
include 36 positive and 10 negative (miss) observations (several
more miss observations are listed but are not plotted since
including them on the plot compresses it so that the numbers of the
positive contacts become hopelessly illegible; the ones closest to
Varsavia are included); the 800-kilobyte plot is here with a
similar-sized black on white background version here. Those
with slow Web connections can download a much smaller (7 kilobyte)
compressed .zip file here and unzip them on their computer for viewing
and/or printing. The observations used in the plot are in a plain
text file here; you might double-check your numbers, especially
if they are plotted far from the 54 km by 36 km ellipse that I have
fitted to the observations. Print the file in landscape mode using
a small fixed-space font size to prevent line wrapping or cut-off.
There may be a few more observations to add since I haven't
carefully examined all of my messages about the Varsavia occultation
received after July 23; I will try to complete the process towards
the end of this week. But now I have most of the observations, with
mainly a few from British Columbia not yet having times reported
(as of October 10, they still had not been reported, but Frank Anet
has nearly completed analysis of those tapes to determine their
accurate times).
A 0.9-sec. occultation was timed by Patton Echols at Gresham,
Oregon, near Portland at track 6E and #51 on the plot, while Frank
Szczepanski timed an occultation less than half a second from
Eugene, Oregon, at track 79W (#26 on the plot). On the east side,
no occultation occurred at track 14W as confirmed both by my remote
station (video with 50mm f/1.4 lens) east of Reedley, CA and by Dale
Ireland at Bainbridge Is., WA (stations 21 & 30, respectively; the
remote station was actually about 300m closer to the path).
Bracketing the path closer on the west side was Ed Edwards' miss
observation at Carpinteria, CA at track 81W (#51 on the plot), only
2 km west of Szczepanski's positive observation in Eugene, OR.
The plot, which has not been updated since the posting on Aug. 6,
shows that the video observations are starting to define
the shape of Varsavia, but there are discordancies among them
because many of them are based on preliminary times obtained by
essentially visual means by playing back the tape. Full-accuracy
(to the nearest 1/30th-second frame, or even 1/60th-second field)
times will be needed from all of the videotapes, obtainable either
via real-time GPS 1PPS time insertion (STVastro) or by accurately
correlating the start of the WWV minute tones with the frame
counts, either with a Manly time inserter (such as used by Rick
Frankenberger, Derald Nye, and myself), computer processing of
a digitized video record, or other specialized (expensive) video
equipment. I'm not sure on some of the reports whether the video
timings are full-accuracy or not, which might explain the
discrepancies between stations 37 and 44, and between 16 and 17 (at
least 37 and 17 I believe have full video accuracy times). The
errors of most of the visual timings are too large to define the
shape of Varsavia that will be determined from the final video
timings, but some of them will be needed and included, especially in
areas with no video observations such as near the east and west ends
of the asteroid. As explained at the bottom of the list of
observations, constant time corrections (or shifts, given in the
last column of the list) have been applied to many of the visual
observations, and a few of the video ones (with preliminary times),
for the plot. An example of an observation (Bruce Herrick's)
plotted with full video time resolution is here (added Aug. 12).
Clouds from Claudette moved into southern California, affecting
observers as far north as Fresno. Some observers in southern
California observed the occultation in breaks in the clouds there.
I recorded the occultation with a C90 just east of Selma, Calif. at
4W (#20 on the plot). I recorded KFI at 640 kHrtz in Los Angeles,
Walt Morgan recorded KIRO at 710 kHrtz in Washington, and Steve
Preston recorded the Seattle AM station at 1000 kHrtz in Seattle, so
if anyone used those for timing, we can calibrate your tape. So
far, nobody has reported using those, but the observers reporting
only durations could have used them if they didn't have a WWV
receiver.
Brian Warner and others obtained a light curve of Varsavia during
April and May. See Warner's Web site and click on the box
for Varsavia. Prediction information about the occultation is here.
_____________________________________________________
Rohith Adavikolanu and I recently (Dec. 2nd) completed another
analysis of the observations, which are now all listed here.
We have concentrated on the video observations, all of which are
plotted here, including the nearer miss observations and only a
few of the visual observations that are useful for determining
the shape of Varsavia because they seem to be relatively accurate
and/or no video observations are nearby. If I print the .gif image,
it is clipped; to avoid that, use the Word version of it here.
There are still a few discrepancies among these observations,
discussed here, that need to be resolved before a final
analysis can be completed.
David Dunham