Re: [TASS] photometric vs. non-photometric

[Alan McCallum <almac@ICONNECT.NET.AU>]

Perhaps you could compare tassm16 to the current positions to get an idea of
the the "jitter".

Alan.

Stupendous Man wrote:

>   Chris writes:
>
> > Before the first Mk III data is imported, we "seed" the catalog with
> > Arne's "tassm16" data.  That is we creat a TASS catalog with a few
> > million stars in it all with "number of observations" set to zero.
> > The tassm16 list is a subset of the FAAST catalog which has good
> > astrometry.  As I remember, we use the FASST astrometry until
> > the "number of observations" reaches some threshold then we
> > compute and use a mean.  The idea was to mimimize the "wandering"
>
>   I have verified that we _do_ use the USNO-A 2.0 catalog subset
> provided by Arne -- which is called "tassm16" for short -- to seed
> the catalog before we begin importing stars.
>
>   Unfortunately, I have also verified that the threshold in number
> of observations required before we use a floating mean position is ...
> just one.  Ooops.  So, when a star is observed for the SECOND time,
> its position begins to "wander".
>
>   Too late for the Mark III database here at RIT, but definitely
> something to keep in mind for the Mark IV, or for other versions
> of the Mark III database.
>
>                                             Michael Richmond

--
Alan McCallum   (almac@iconnect.net.au)

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