David's Astronomy Pages Notes - CCD Session 16 (2002-01-17)

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Drift Imaging

Before switching on LX200 tracking, the following image was taken which shows the linear star images as they drift across the fixed field of view. The image has then been squashed in the X direction to recreate a synthetic image of a 33 arc sec wide slice of a starfield. Using drift imaging and some specially written software to add and combine sequences of drift images, there would be opportunity to either image  an area several degrees wide or create an animated image showing the passage of stars.

2002-01-17 CCD Image, 11 sec exposures (#16004) 11.1 (0.5 ) x 7.4 arc min

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FWHM Analysis of Drift Scan Image

A FWHM analysis of drift scan image #16004 (see above) was conducted to measure the seeing quality expressed as a FWHM measurement without introducing uncertainty on FWHM value associated with tracking/guiding errors. 7 cross-sections across the brightest star in the image were examined, FWHM varied from 4.4 to 7.3 arc secs (average 6.6 arc secs, P50 7.0 arc secs)

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Betelgeuse

A saturated image of Betelguese was examined with different contrast settings

2002-01-17 CCD Image, 10 sec exposures (#16015) 4 different contrast settings Bright star in Betelgeuse 11.1 x 7.4 arc min

The image shows no sign of blooming. It is strongly suspected that I was supplied with a ABG camera, rather than the Non-ABG that was ordered.

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FWHM Analysis of SAO 113277 Image

A 30 sec exposures of SAO 113277 (25 arc min NE of Betelguese) was analysed. It showed a FWHM of 4.6 arc sec.

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FWHM Analysis of Vesta Images

Two 30 sec images of Vesta were taken one minute apart at different binning levels (#16017 @ 2x2, #16019 @ 1x1). Analysis of the image data showed similar FWHM estimates (4.2 to 4.4 arc secs)

1x1 binned image was further analysed to examine the low FWHM 'objects' (A-F) within the image. It was concluded that A was possibly a cosmic ray, whilst B-F were probably simply random collections of above background value, ie noise.

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Autoguiding Analysis

162 (Image #16049). The following 5 min guide session (mag +11.5 guide star, 7 sec guide exposure, aggressiveness 8, 3 sec delay) shows guiding errors  of +/-3 arc secs in X (RA) and +/- 1.5 arc secs in Y (Dec). X and Y corrections are correcting fairly well. A large 5 arc sec shift in X occurs at around 3.1/2 mins.  Scope appears to be drifting south in Dec. (note how all the Y corrections all operate in one direction)

Resulting image (#16049) shows slightly elongated stars. Elongation is greatest in X (RA) which is consistent with the larger X errors shown by guiding analysis.:

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Dew 

Towards the end of the observing session the front of the LX200 scope began to dew up.  A flat field shows the impact : 

A 300 sec exposure of NGC 925 was attempted however the impact of dew on light dispersion is event in the histogram which shows a broad background component :

FWHM analysis shows that FWHM of stars within the image is only 6.5 arc secs.

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