Re: [find_orb] RE: (6995) Minoyama

Bill Gray Feb 9, 2013

Hi Alessandro,

I think your measurements for (6995) are indeed probably Just Fine.

I'd been running calculations using the new 300 asteroid version, which
has the code to exclude perturbers more than about .15 AU away. I _thought_
that was a reasonable limit, but it appears not to be. If I have it
include Ceres, Pallas, and Vesta, I get reasonable residuals for your
three observations... but only if I leave CPV turned on at all times,
even when more than .15 AU away :

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

Here, your observations have residuals of about one arcsec in RA and
.3 in dec.

I'm both disappointed and surprised to find out the asteroid perturbers
are significant over longer ranges. I can get around this a _little_ by
having that .15 AU be adjusted according to asteroid mass: i.e., maybe
we need to go to, say, .5 AU for Pallas, but others can be scaled by
the cube root (I think, need to work that out) of their masses.

This did cause me to see a possible "problem case": an object with
pretty much the same semimajor axis as a larger asteroid, but orbiting
slightly ahead or behind that object. In such a case, the perturbation
due to that larger asteroid would be consistently accelerating or
decelerating the object. Which would mean you'd get a significant
effect on the orbit, even though the perturber might never get all that
particularly close. You'd have fifty years (for an object observed from
1956 to 2006) of a gradual force, instead of the sudden effect of a
close flyby. (I don't think that's happening here, incidentally.
(6995) doesn't have a semimajor axis close to that of Ceres, Pallas,
or Vesta.)

-- Bill

On 02/09/2013 02:46 PM, alessandro odasso wrote:
> I have found another asteroid in the same DSS plate:
>
> asteroid (4597) Consolmagno
>
> The measures are:
> 56 03 10.36875 261 12 30 50.55 +05 08 25.5
> 56 03 10.37431 261 12 30 50.29 +05 08 27.3
> 56 03 10.40556 261 12 30 48.82 +05 08 37.5
>
> Residuals:
> .05+ .03-
> .07+ .03-
> .05+ .02+
>
> the dT are as follows:
> -6.46 sec
> -8.70 sec
> -4.36 sec
>
> This seems to prove that the timing of the images is correct also for (6995) Minoyama.
>
> Looking at (6995) Minoyama I still wonder whether the 1956 astrometric measurements are correct or affected by some sistematic error: would this explain why the measures, though consistent, show those high residuals?
>
> An indipendent measure taken from some more expert person is really needed.
>
> Best wishes,
> Alessandro
>
>
>
>
>> Date: Thu, 7 Feb 2013 07:58:14 -0500
>> From: pluto@...
>> To: find_orb@yahoogroups.com
>> CC: alessandro_odasso@...
>> Subject: Re: [find_orb] (6995) Minoyama
>>
>> 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
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>