Important message to all planning mobile stations for the July 19th 
Antiope occultation

This is perhaps the most important occultation that IOTA has ever 
deployed for, a unique chance to profile in detail the largest 
main-belt binary asteroid.  I don't want to screw it up, like we did 
for the May 29th Eudora occultation, with almost all stations 
crowding into the predicted path, netted only one positive result 
(maybe two if the star's duplicity is confirmed) because the actual 
path was entirely north of the predicted one. 

The only way we can succeed with Antiope is with a systematic 
approach organized by one person.  As president of IOTA, I excercise 
my executive perogative to be the organizer for this occultation 
with a plan, described below, that I believe will optimize the 
overall coverage of the occultation with the finite resources that 
we can deploy, and give a good result even if a shift significantly 
larger than predicted occurs.  And the possibility of a large shift 
may be high; Steve Preston notes that the star has "proper motion 
issues" and may be a previously unknown double, the same recipe for 
disaster that preceded the Eudora occultation (but that was a much 
smaller asteroid, so if we have a similar shift for Antiope, it will 
not be nearly as disastrous).

As a first step, all mobile stations currently on Occult Watcher 
(OW) are not part of the new plan and should not be used - sorry to 
those who have already spent some effort setting them up.  Those at 
fixed observatories are encouraged to sign up with Occult Watcher, 
or let me or Scotty Degenhardt (scotty@scottysmightymini.com) know 
your plans, so you can be added, and the mobile stations positioned 
around you to optimize the coverage.  But those planning mobile 
stations should first let me know (email dunham@starpower.net or 
cell 301-526-5590), and I will specify lines that you should aim 
for, and you can then use OW (or let Scotty do this for you) to 
select a site (or sites for those with mobile stations).  But you 
might need to change a site if a fixed observer later says that 
he/she will observe at a site within 2 km of your line.  I will 
maintain the actual plan offline (OW will just be used as a site 
selection tool), but will post updated versions of it periodically 
in Brad Timerson's IOTA meeting section Web site.  A final version 
of it might not be determined until our pre-occultation meeting for 
the occultation Monday morning, July 18, in Rocklin; that will be 
our last "horse trading" session, to finalize the plan.  If you 
can't be there in person, we can probably use EVO for you to attend 
virtually, but I think most mobile observers for this event will be 
in northern California.

The plan is meant to maximize the number of stations that those 
depoying multiple remote stations can set up, while optimizing the 
overall coverage of the event, as explained below.  The orientation 
of the two components of Antiope make this a very wide (expected 221 
km) path, but the 1-sigma uncertainty range, including coverage of 
the PPMXL star position path as well as the HIP2 path, is half again 
larger, 336 km; to have a reasonable chance of good coverage of the 
event, we need to cover that entire range (actually, a 340-km range 
since we want to use a spacing of 10 km between stations)  
uniformly.  This should maximize the change for covering both 
components of Antiope well, but if we have a very large shift, like 
the approximately 90-km (almost 3-sigma) shift that we had for the 
May 29th Eudora occultation, we will still cover one of the 
components completely, and at least 1/3rd (and probably 1/2 or more) 
of the other component.  Although this plan I hope results in 
success, I don't want to spread resources too thinly by spreading 
out more for a less likely larger shift; as it is, covering the 340 
km range will result in 1/3rd of the stations having no occultation 
- I don't want to increase that fraction by spreading out more.  
Fixed-site observers within a 100 km outside the 340-km range, north 
and south, will be strongly encouraged to observe in order to extend 
the coverage to guard against a possible very large shift, as well 
as to look for other small satelloids that might be in the Antiope 
system. 

Specifically, I want to cover the range from 155 km north to 185 km 
south (farther south to cover the PPMXL path) at 10-km intervals; 
that makes a total of 35 stations.  None of them will be at the 
center, and each observer should cover only lines on one side of the 
predicted central line; until the 35 lines are occupied, nobody will 
"own" the central line (unless they have a fixed observatory there).  
The lines will start at 5 km north and 5 km south of center, then go 
out at 10-km intervals, until 155 km north and 185 km south are 
reached.  Observers should select sites for their stations within 
+/-2 km of their assigned line(s); Derek Breit's google map Web page 
for this event at 
http://www.poyntsource.com/New/Google/20110719_23903.HTM is best for 
this.  For example, if you are given the 25 km north line, just 
enter +27 and +23 in the boxes at the top of the map, and select the 
best site you can find between the two gray lines that are displayed 
as you zoom in on the path.  A first step is that those planning to 
deploy more than one station should let me know how many stations 
you think you can run as soon as possible.  I want to follow the 
following rules for those planning remote-station deployments: 

1. All of your stations will have adjacent lines, so they should all 
be about 10 km (no more) apart, to shorten the total travel time.

2. One observer will have no more than ten assigned lines, for a 
total range of at most 90 km; if you can deploy more stations, let 
me know and you can start filling in lines halfway between your 
assigned lines.

3. If you are deploying five or fewer stations, all of your lines 
will be on one side of the central line, either all to the north or 
all to the south of it. 

Scotty Degenhardt and I will each be planning on ten stations, and 
we will take the outer reaches, so that others, most or all of whom 
will be deploying fewer stations, will be in the higher probability 
areas.  Scotty plans to take the northern side, lines +65 to +155, 
while I'll cover the southern part, from -95 to -185.

After all 35 mobile station lines have been assigned, the 36th 
mobile station will get the central line (if a fixed-site station is 
not already within 2 km of it).  Other mobile stations over 36 will 
be given locations halfway between the others already assigned, at + 
and -10 km, + and -20 km, etc., so we can accommodate up to 69 
mobile stations at 5-km intervals; I doubt that we'll have that 
many, but I think we will have more than 36, and I'll be happy with 
that.
________

Below is my calculation of the predicted path-width for the 
occultation, and for the planned coverage zone.  Go towards the 
bottom of the 2011 IOTA annual meeting Web page, at 
http://www.asteroidoccultation.com/observations/NA/2011Meeting/index.htm 
- Brad Timerson has put much information about the occultation of 
ZC 3339 by the (90) Antiope system.  About 2/3rds of the way down 
the page is a black background sky-plane predicted view of the 
Antiope system labelled "Preliminary Miriade Model of (90) Antiope 
at 10:25 UT".  Below it, I inverted the colors to make a white-
background version of it, and drew a long arrow showing the 
direction of motion of Antiope in the sky, from position angle 48.6 
deg.  I printed that figure, and measured the distances of the 
farthest edge of each component of Antiope from the center, 
obtaining 79 km to the north and 83 km to the south, in the sky 
plane.  However, the path projects by a factor of 1.3667 (= 164/120, 
Steve Preston's values for the path width/asteroid diameter) onto 
the Earth's surface, so the shadow on the ground will extend beyond 
Preston's blue limits, with the n. limit 108 km north of center and 
the s. limit 113 km south of center.  Entering +108 and -113 in the 
boxes on Derek Breit's google map for the event (the link for it is 
given above), I've produced a map of northern Calif. and 
northwestern Nevada, shown below the sky-plane diagrams and labelled 
"Resulting Path (GRAY lines) IF Prediction and star position are 
correct!".  It assumes that Steve Preston's prediction, as well as 
the Miriade model for the asteroid components, are both perfect; the 
real path width should be 221 km, within which at least one 
component will occult the star, and in a range extending from near 
center only to about 10 km south, both components might occult the 
star.  Of course, the prediction probably won't be perfect; the 
PPMXL catalog predicts a 36 km south shift, and Steve Preston's 1-
sigma error is 46 km.  Consequently, I've produced a 2nd map, shown 
below the first one and labelled "Ground coverage (GRAY lines) 
required to take into account possible prediction/star position 
errors".  It shows with the gray lines the area that I think we 
should try to cover with mobile stations, with the northern gray 
line at 108 + 46 (1-sigma) = +154 km and the southern gray line at 
-113 -36 (PPMXL shift) -46 (1-sigma) = -182 km.  Rounding up to the 
nearest 5 km, the range becomes +155 km to -185 km for a range of 
340 km, so the actual path should cover about 2/3rds of this planned 
coverage.  I don't want to "waste" mobile resources by extending 
them beyond these distances, but we'll encourage fixed-site 
observers to monitor the star at greater distances.  I hope (and 
believe) that we can deploy enough remote and mobile stations to 
cover the 340 km at 10 km spacing or less.

This coverage plan might be modified to take into account later 
information that we might learn about the prediction.  We might 
obtain a better idea of the true error of the star's current 
position by comparing the current HIP2 positional information about 
the star with the old HIP1 positional information; although we've 
compared HIP2 with other catalogs, the comparison with HIP1 has not 
yet been done.  Also, only a few days before the occultation, as 
Antiope moves far enough from the Sun, we might actually obtain new 
adaptive optics large-telescope observations of Antiope that might 
allow us to update the sky-plane figure of the system.  If the 
components are rotated more in the clockwise direction, the actual 
path width will be narrower than the 221 km mentioned above, but 
we'll probably keep the same coverage, which just then increases our 
margin for coverage in case of a larger than 1-sigma shift.  If the 
components are rotated more in the counter-clockwise direction, the 
actual path-width will increase and we then might expand the 
coverage by 10 or 20 km in each direction, but since the components 
are already opened rather widely, the expansion of the path width is 
unlikely to be more than what I mention.

David