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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.
Page 6
The Electronic Universe Project
e-mail: nuts@moo.uoregon.edu