[Aavso-photometry] IL Aqr Sequence

[Michael Koppelman]

As a refresher, for some reason my astrometry using wcstools and the 
Tycho-2 catalog is giving me declinations which are off by 7". This 
happens to correspond to 2 pixels. It shows up as a consistent offset 
-- every star is off by two pixels in the same direction. This is with 
respect to the Tycho catalog, so my solution is off by an offset with 
respect to the stars used to create the solution. That just seems nuts 
to me. It sounds like an off-by-one error somewhere along the way. 
Would it have to be two off-by-one errors? Could a weird shaped PSF 
cause something like this?

Basically I'm feeding imwcs the fits image and a coordinates file from 
IRAF's daofind task. It finds a solution that matches my expectations 
in regard to the plate scale and rotation angle.

Any thoughts? I can't find anything parameter-wise that I am doing 
wrong.

Thanks!

Michael Koppelman
http://www.lolife.com/astronomy/

On Oct 11, 2004, at 10:46 PM, Arne Henden wrote:

> Why is the astrometry "not particularly great"?  Tycho2 is certainly
> of the same astrometric quality as is UCAC; a few arcsec is completely
> out of range for either catalog.