Re: Group 17

[Tass Mailing List <tass@mail.alembic.net>]

Date: Mon, 14 Aug 2006 07:07:43 -0400
From: arne <arne@aavso.org>
To: Tass Mailing List <tass@mail.alembic.net>
Subject: Re: Group 17

Tass Mailing List wrote:
> Date: Sun, 13 Aug 2006 20:34:02 -0500
> From: Michael Sallman <msallman@pro-ns.net>
> To: Tass Mailing List <tass@mail.alembic.net>
> Subject: Group 17
>
> Group 17 stars showing significant motion in the POSS images:
>
> 3636501	= G 264-9
> 5226880	= LHS 136
>
> Quite a few close doubles. It looks like, for most of the matches to
> close doubles (or nearby bright stars), that the TASS positions tend to
> fall along a line between the 2 stars (see for example #s
> 2795657,2702547,2624106,3668167,3700316,2617362)
>
>
Yeah, that was my experience with the FASTT variables: we had
lots of stars that showed variability, but when looking at the
actual field, most of those were close doubles (usually near the
aperture size).  Seeing and focus moved the centroid, so differing
amounts of one star or another would fall within the aperture.
We removed these false positives by looking at the astrometric
residuals; such pairs always showed a larger scatter in the
derived position than comparable single stars.  Looks like Michael R.
is seeing a similar problem from a different angle.
Arne