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CCD Astronomy Magazine Article Page 5

The Backyard Astronomers Wide Field CCD System

Figure 8 (90 Kbytes) shows an image of M31. While this is not a particularly spectacular image of M31 it is nevertheless unique as it was taken in a suburban backyard using a Lynxx CCD camera. The exposure is unfiltered. For unfiltered exposures, the effective wavelength is the convolution of the intrinsic energy distribution of the galaxy and the QE curve of the detector. Both of these peak in the red, and so, in essence, this exposure is quite red. The green ellipse marks an isophotal region which is 1% that of the background light. In days past, this isophotal level could only be reached on long exposure photographs using large telescopes. The remarkable aspect of this image is that NO telescope was used. Rather, a 75 mm achromatic lens was used in front of the CCD. The CCD was then bolted onto the side of a Celestron-8 inch which was then used for tracking. The image scale in this system is 41 arcseconds per pixel which yields a total field size of 2.2 x 1.9 square degrees. At this pixel resolution M32 blends into the light of M31, although NGC 205 (marked with a red arrow) is plainly visible.

Figure 9 shows the resulting surface brightness profile of M31 taken with this configuration and illustrates that real science can be extracted from this kind of backyard data. The magnitude scale corresponds closely to the I-band and indicates that approximately 7 magnitudes of galaxy light over a radius of about 1.25 degrees, have been detected in this one, relatively short exposure.

The Parking Lot Camera System: The Ultimate Wide Field CCD

Several years ago, Ian Thompson of the Mt. Wilson and Las Camapanas Observatories and myself played around with the idea of building a CCD imaging system that would allow the entire Large Magellanic Cloud to be imaged in a single CCD frame. As the LMC is some 6 degrees in angular size, this was a somewhat daunting proposition. Nonetheless, a good challenge usually stirs up the creative side of an astronomer and so we put together a system that would accomplish the task. An 800x800 TI CCD was used as the detector. The image scale of 36 arcseconds per pixel was accomplished by using a Nikon 85 mm lens with anti-reflection coating. The resulting field size is then 8x8 degrees. The entire system was mounted on an old Celestron drive and moved to the parking area outside the 40-inch dome at the Las Campanas Observatory. Given this coarse of pixel scale, accurate tracking over the duration of the exposures (a few minutes) was not necessary and hence a crude alignment with the south celestial pole was all that was required. While processing a CCD frame which covers this much sky (the sky brightness is variable on these kind of angular scales) was another challenge, we were nevertheless able to extract very useful images from this Parking Lot arrangement.

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