drift scan image
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Errors in positions in RA and DEC probable caused by atmospheric fluctuations

Some preliminary results.
From: Christoph Flohr

Some details on the drift-scan image:
(The telescope drive was shut off)
The seeing was bad, so results form other sides should be better.
DEC, centre of the image 11.9588023 deg
(same declination as alpha Leo)
RA, centre of the image 162.9756104 deg
Alt: 45.87, Az: 147.93
RA, start of the image 155.91 deg
RA, end of the image 170.04 deg

DATE-OBS= '2002-03-10' / UT date of integration
TIME-OBS= '21:02:20.01' / UT time
(The time the integration was started )
( End of the exposure was: 21:58:42.30
Width of the image in pixels: 765
Height of the image in pixels: 20135
INSTRUME= 'SBIG ST-7' / Camera Type
TELESCOP= '6 inch reflector 751 mm focal length'
Software: 'WinScan2.02'
Effective Exposure time: 85.67 sec
(SHIFTIME * CCDHEIGH, time to shift all lines from the CCD )
PIXWIDTH= 0.00900 / in mm
PIXHEIGH= 0.00900 / in mm
FOCALLEN= 29.567000 / in inch
APERTURE= 28.27000 /in square_inch
FILTER = 'None' / filter used
SHIFTIME= 0.1679806808510600 / interval to read out one line
CCDHEIGH= 510 / number of lines on the CCD

Astrometry by ViewScan:
Reference stars (1542, form mag 9 - mag 16) were added form the GSC- ACT
Positions and residuals were calculated (linear fit)
The errors in RA and DEC in relation to the positions in RA are shown in the following diagrams (XY) :

As you can see, the errors in RA and DEC are changing with the position in RA (and so also with the midexposure time) .
Between the positions in DEC and errors in RA or DEC I found no relations.
To get the exact position of an object, it may be a good idea to slice the image in smaller parts.

see also:
SDSS Astrometry
Carlsberg Meridian Catalogue 12
documentation for CMC12 (4.86 MB)

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