Modeling Velocities

[Arnold Rots]

 Steve Allen Wrote:



*In historical data each catalog is its own reference frame, and the
literature of constructing recent catalogs using the old data shows the
painstaking measures needed to remove the*
* systematic effects present in the original catalogs.*

I will grant you that it is extremely important to get this right for the
positions that were used to derive the PM.
However, the PM itself is a different matter - with some notable
exceptions; Polaris comes to mind.

  - Arnold

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Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
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On Sat, Dec 22, 2018 at 2:09 PM Steve Allen <sla at ucolick.org> wrote:

> On Sat 2018-12-22T13:40:40-0500 Arnold Rots hath writ:
> >   which reference frames apply?
> > Depends on what the provider of the data used; for modern data one would
> > hope ICRS, but historical data could be any FK
>
> In historical data each catalog is its own reference frame,
> and the literature of constructing recent catalogs using the
> old data shows the painstaking measures needed to remove the
> systematic effects present in the original catalogs.
>
> > On the other hand, I suspect that for proper motions with any reasonable
> > precision this won't make a bit of difference
>
> That statement would remove volumes of painstaking efforts from the
> literature.
>
> --
> Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
> UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat
> +36.99855
> 1156 High Street               Voice: +1 831 459 3046         Lng
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> Santa Cruz, CA 95064           http://www.ucolick.org/~sla/   Hgt +250 m
>
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