RE: Star.exe help

[mgutzwiller@lanvision.com]

A couple of things come to mind for the catalog mismatch.  The match
routines try to match the N brightest stars in an image to the N brightest
stars in the catalog where N is the "Number of Stars to Match" in the
options dialog.  If the image's N brightest unsaturated stars don't
correlate to the N brightest stars in the catalog sections star uses the
ctalog match will fail.  This could be caused by a several things:
 
* Different image size - star uses Mark III sized sections of the catalog to
try to match.  If the image is significantly different in size the match
will fail.
* Different saturation levels - the tyc_good catalog has the brighter stars
deleted as well as stars that would be too close to resolve in a Mark III
image.  If your artificial image has no such limits the match may fail.
* If the PSF of the generated stars is not consistent, i.e. brighter stars
are bigger, not just brighter, star will not measure the magnitude correctly
and might not have the correct N brightest stars.
 
Hope this helps,
 
Mike G.
 

-----Original Message-----
From: John Phillips [mailto:jdp@indy.net]
Sent: Monday, March 15, 1999 9:21 PM
To: tass@wwa.com
Subject: Star.exe help


I can sense the excitement in the group as Tom's gets ever closer to making
the Mark IV work.  I am anxious to see the data from these first shots.
 
Please, have mercy on a beginner, as he changes the subject back to
something you all learned long ago!
 
I have been working with Star.exe and have been able to successfully process
all of the images from the 'archive of early images' page.  I then used my
skymap program to create a fts file of stars near the equator.  When I ran
Star.exe on this file, it didn't find any stars at all.  It seems that the
'sky' didn't have any noise in it, so the routines using sigma didn't work. 
I wrote a little program to add gausian noise to each pixel.  Now Star.exe
can find all of the stars in the image, but can only find the x,y
coordinates of the stars.  I get the dreaded 'match to catalog failed'
comment in the generated file.  I think I have the CTYPEn, CRPIXn, CDELTn,
and CROTAn keywords set up properly to point Star.exe to the right portion
of the sky.  At least the generated RA and DEC are very nearly right for
these stars.  Still, I would get a warm fuzzy feeling if I could make the
match work.
 
Does anyone have any clues to what may be going wrong?  Any comments are
welcome.
 
Thanks,
 
John Phillips
jdp@indy.net