Occultation by (253) Mathilde, 2006 October 15 - New Oct. 16

Dan Caton at Dark Sky Observatory, NC, recorded a 5-sec. occultation

His observation, plus my miss observed just inside the predicted southern limit, shows that the path shifted a little more than one path-width (close to 1 sigma) south

Observations of occultations by Mathilde are important to obtain some data on the half of the asteroid that was in the shadow and thus not imaged by the NEAR spacecraft during the 1997 flyby

My message to Dan Caton:

Dan,

      Thanks for this observation from your observatory near Boone, 
North Carolina.  You were 76 km s. of the predicted central line of 
the expected 60-km path.  I recorded a miss from a site in a dark 
Burger King parking lot about 1/2 km southwest of I-95 exit 121 at 
Lamm, NC, about 27 km south of the predicted central line and just 
inside the predicted southern limit.  So there must have been an 
approximately 1 path-width (1 full sigma) path shift to the south, 
meaning that the path also must have passed over Ogden, UT (Salt 
Lake City near s. limit); Greeley & Ft. Collins, Colo.; Kansas City 
and probably St. Louis, MO (unfortunately, it was probably cloudy 
from Colo. to Kentucky); and Greensboro and Raleigh, NC 
(Fayetteville maybe near the s. limit).  I'm copying this to others 
to whom I sent this notice who were in that path, and hope that some 
of them might have observed, but none besides you in that path said 
beforehand that they would try this event. This just underscores 
once again that observers throughout at least the 1-sigma 
uncertainty zone should try to observe these events, and sometimes 
(less often, but not impossible) shifts of 2-sigma [in this case it 
would have been 2 path-widths] can and do occur. 

I also ran a remote station just inside the predicted northern limit 
at an abandoned gas station just east of I-95 exit 154 near Enfield, 
NC about 26 km north of the predicted center, but your observation 
implies that a miss must have occurred there (I played back the end 
of the recording made there, showing that the system was recording 
stars several minutes after the event, but I haven't played back the 
critical section yet - I'll do that later today when I get a chance 
and distribute details). NEAR did a thorough reconnaissance of the 
space around Mathilde and found no satellites, but there's a small 
chance one was lurking in her shadow during the 1997 flyby. 

David

At 05:39 AM 10/15/2006, you wrote:
>David-
>
>   I got the event, using a CCD drift scan.  Although I was supposedly 
>outside the track but within one sigma I had 5.3-second occultation.
>This is a rough, fuzzyminded analysis before going to sleep.  I will do 
>the dark, flat-fielded analysis in the clear light of (Monday) morning.
>  But no doubt about the event--I was not expecting it and to see that 
>gap when the image came up I knew I got it.  It also appears to have 
>occured several seconds later than my predicted time.
>   More later...
>
>Dan Caton
>Dark Sky Observatory
>Appalachian State University
>
___________________________

On June 27, 1997, the NEAR spacecraft obtained spectacular images of 
half of this slow-rotating asteroid enroute to Eros.  Mathilde was 
found to be a rubble pile with huge craters, some almost half its 
diameter.  But only the sunlit half of Mathilde could be 
photographed - click here. The mass of Mathilde was 
determined from the small gravitational deflection of NEAR's 
trajectory as it sped past, but the volume remains uncertain.  By 
obtaining points on both the (June 1997) sunlit and dark sides of 
Mathilde during the occultation, it may be possible to refine the 
volume and density of this curious asteroid.

Prediction information about the occultation is here.
_____________________________________

David Dunham, 2006 October 16
Phones home 301-474-4722; office 240-228-5609; car 301-526-5590
emails dunham@starpower.net or office david.dunham@jhuapl.edu