Hi Alessandro,

Still a puzzler... here's what I'm getting, using the new version with
300 asteroids :

http://www.projectpluto.com/temp/mpec.htm

Specifically, for your three observations, residuals are...

560310 261 3.35- 1.46+
560310 261 3.39- 1.41+
560310 261 3.36- 1.47+

All very consistent with one another. The cross-residuals are
all under .1 arcsecond, with time residuals of about seven minutes.

I'd have to say it's either a timing error of seven minutes for
all three plates, or an asteroid perturber that isn't among the 300
considered by Baer and Chesley. (This last possibility would be
very interesting indeed, if true, but I'd check the timing error
issue first.)

I assume that if Jim Baer and Steve Chesley were able to find
300 objects for which they could find perturbed asteroids with
measurable effects, then there must be a few more that can be
determined with more observations. Maybe you've found the 301st.
Unfortunately, I don't have software readily at hand to solve the
question, "what asteroids did (6995) approach between 1956 and 2012?"

(Actually, I _can_ answer that for the 300 objects in BC-405,
using the same trick I used to determine that Pallas had perturbed
(70401). Turns out that (6995) also came close to (2) Pallas,
within .01 AU, in early 1968. And one does see a little "twitch" in
the residuals when asteroids are turned on as perturbers... not much
of one, though; the flyby was apparently a little too fast, distant,
and/or in the wrong direction to modify the orbit a lot.)

-- Bill

On 02/07/2013 01:26 AM, alessandro odasso wrote:
> Bill,
>
> many thanks for all faster than light response!
>
> You make me wonder whether I am wrong in the astrometry, but here is what I found:
>
> 1956 03 10.36875 12 42 59.07 +02 28 39.8
> 1956 03 10.37431 12 42 58.82 +02 28 41.3
> 1956 03 10.40556 12 42 57.43 +02 28 50.1
>
> --Alessandro