So far I have described the programming and acquisition of images. Up to now, other than creating the scripts for Orchestrate, which can be saved and reused,
there is not a very large workload for the observer. I switch on at the beginning of the evening, take the cameras down to their operating temperature, focus, load the first script and off I go. The systems do most of the work. With this setup I can use either 30- or 60-second integration times. I usually opt for 60 seconds, but on a particularly clear night with good seeing I might go for 30 seconds and still reach a little short of 19th magnitude. At 30 seconds integration and allowing for settling time, I can acquire 210 images an hour using the three telescopes. In the UK in November, darkness can last for 14 hours or more. At 210 images an hour that is just under 3000 images in an evening. In practice, this is never achieved because a previous night's suspects have to be rechecked and there are pauses to change scripts or refocus. It is possible to regularly get more than 2400 images at the right time of year. This is where the real hard work begins. There is no available software that allows amateurs to automatically check images, that is both quick enough and allows the images to be checked easily at all the necessary histogram settings. A full range of stretch settings is necessary to pick up the fainter supernovae in the outer arms and in the bright central portions close to the galaxy's bulge. The only way that I have found to be reliable and quick enough is to manually compare a pair of images in CCDSoft (see Fig. 12.7).
This shows two images opened simultaneously, in the same window, ready for comparison. One is the master, the other a recently acquired patrol image. Thankfully, Windows allows multiple images to be opened simultaneously from
within Windows Explorer. I usually open the patrol images, up to 50 at a time, and then selectively open masters one by one. This allows the image settings to be changed to display the inner and outer parts of the galaxy image alternately. As well as looking for possible supernovae, I compare the new image just taken with the older master image. If it is of higher quality, I replace it. The master image stored on the hard drive is therefore the best image that I have ever taken of that particular galaxy. It is essential to use your own master images. They match your telescope setup and the color response of your camera. This saves a lot of time and helps you to dismiss unlikely candidates quicker and recognize potential candidates more easily. By all means, check your images against the Palomar Sky Survey, particularly the second-generation plates. Indeed, the Central Bureau (CBAT) will require you to have done this before submitting your report on a suspect. This is to support your claim by demonstrating that the star is not visible on the older images, but it is no substitute for good-quality masters taken on your own system. The process of image checking can take up to 40 seconds per image. That means that I can just about keep up with one telescope. If there is a string of clear nights, which is usual, I can have thousands of images in the backlog waiting to be checked. This can take up to a week to clear. I rely on the predictable British weather to cloud over for days to let me recover: it rarely lets me down.
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