Alessandro Feb 9, 2013
--- In find_orb@yahoogroups.com, Bill Gray wrote:
>
> 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]
> >
> >
> >
> > ------------------------------------
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