Changing a Large Deployment at the Last Minute – more Eudora

David DunhamJuly 16, 2011

Occultation of SAO 141925 = HIP 87494 by (217) Eudora, 2011 May 29

• 7.0-mag. star good for mighty mini’s• PPMX catalog indicated only a small north shift• Medium-sized asteroid, estimated 66 km• Path crossed USA on holiday weekend • So many other observers would contribute• Fla. was farthest east, giving a maximum five hours of dark

time for deploying stations• Joan and I decided to fly to Florida to try it• from nine stations across the path• Orlando, just n. of the predicted path, had the best logistics

for our effort• Covered the north uncertainty zone avoided by others

Occult Watcher plan to deploy nine mighty mini stations across w. Florida

Site selection for one of the stations

Issues with Weather• The rainy season starts in Florida in May• Orlando is central, so possible to travel to• East or west parts of Florida• Thunderstorms form during the day, then largely dissipate during the

evening• I believe that the west side of Fla. is a little drier, but the pattern of

thunderstorms varies each day• The direction of the prevailing wind has big effect• Northwest to s.e. geometry favored deployment on west side, selected for

Occult Watcher plan• Avoid more populated coastal areas that also often have more clouds• With the daily weather uncertainties, I decided to be prepared with a “Plan

B” that would preserve the spacing of my planned stations relative to other observers as declared on OW

• Winds from the east were expected, so the east side might clear out first.

IR satellite image at event timeThe view was much worse five hours before, near sundown. A large thunderstorm system formed north of Orlando and Tampa, while the winds were from the north-northeast; it was obvious my Plan A would be mostly clouded out

Google maps of Florida printedEach map showed two of my lines, with maps prepared from D. Breit’s google map site for the western, central, and eastern parts of Florida; printed night before our flight; this one is the eastern map for my stations 5 and 6

DeLorme Florida Gazetteer

was used during our flight, comparing with the google maps to find where the linescrossed several roads that we might use. Lat. and long. accurate to 0.1’ could be scaledfrom the map using its grid. This didn’t need the internet, which wasn’t available on theflight, and didn’t need a computer, which would have been more difficult to use.

Plan B Lat. & Long. on OW ListThe lat. and long. values measured from the atlas for what seemed to be the best eastern alternative highway were written next to our stations on the OW list

Location of 6 Plan B SitesBrad Timerson prepared this map of Florida showing the locations of the six sites from which we successfully recorded the target star. We ran out of time, causing us to skip one site; another also had to be skipped due to clouds; and at one site, the camcorder battery died before the occultation.

Large north shift yields one positiveDue to the 3-sigma 1.3-path-width north shift, only our northernmost station, well within the northern uncertainty zone, had an occultation. Chord plot by Brad Timerson of only our observations.

Large north shift yields one positiveDue to the 3-sigma 1.3-path-width north shift, only our northernmost station, well within the northern uncertainty zone, had an occultation. Chord plot by Brad Timerson showing all observations. There were many disappointed observers.

Issues with Star Positions• S. Preston warned that the star might be “non-single” and had proper

motion discrepancies between catalogs• We thought that the latter would not be so large, according to the star

catalog comparison• A star of about 9th-mag., near the limit of the mighty mini’s sensitivity,

remained visible during the short occultation at Station 1• But the asteroid was mag. 13, much fainter than can be recorded with

a mighty mini• So the star is most likely double• Still investigating Tony George’s probable occ’n of the secondary star

much farther north• Such duplicity should shift the path south rather than north, so star

catalog issues I believe are dominant in this case• Astrometric observations of the star requested to try to resolve this

Occultation of 10.5-mag. PPM 719647 = TYC 5696-01680-1 by (1166) Sakuntala on June 3

Just 5 nights after the Eudora occultation, this occultation by the relatively smallasteroid Sakuntala was predicted for the n.e. USA with large uncertainties, soI spread six stations across the zone, with 4 recording the star.

Steve Preston’s prediction had less than 0.1-sigma error so the asteroid slipped between 2 of my stations