My hats off to those who are truly remote imaging from a distant site! I have spent probably the last 2 weeks troubleshooting the focuser, the guiding and was having trouble with the usb connection from the mount to the laptop timing out. Lots of things can go wrong! I suppose a lot of these remote areas people use from 2,000 miles away have tech support on site available to do this, but I am happy I am just 50 feet away! Anyway last night I ran the system an entire night unattended for the first time in the new permanent location. We took about 5 hours of luminance, some dark frames, bias frames and dawn flats. Our target this time is NGC7331. This is a bright spiral galaxy in the constellation Pegasus. Many believe the structure is similar to our own Milky Way.
One of the things we have to do when processing images is remove all of the stuff in the image that isn’t actually part of the object but is artifact either from the camera electronics or from extraneous light. Light gets into the optical tube and can create odd patterns of illumination due to the way the mirrors are postioned inside of the tube. There is also dust that gets on the mirrors, the camera chip and filters that also can be problematic. The way to eliminate this is by using what are called flat frames. These are created by taking an image of a flatly illuminated, uniform source of light. The result will be an image of all the imperfections in the optical train. Here is an example from last night’s data:
This is a 10 minute raw image of NGC 7331. It was actually a better than average night and we captured a lot of excellent data! However you can see the donut shaped light patch surrounding the galaxy. This is artificial and the result of excess ambient light and the way the light bounces around inside of the optical tube with the 2 mirrors there.
Here is what is called a “flat frame” . This is a picture of a uniformly lit area, in this case the dawn sky just before sunrise. These are called “sky flats”, a subject for a later blog entry. For now we are just illustrating the ability to take an image of the artifacts in your system. You see the donut patch of light and you can also see a small dark circle on the right. This is from dust in the system. Now one glitch with the sky flat is that if you take them too early at dawn or too late at dusk, you can get stars in there which you don’t want! I have pointed these out! You will then see what happens when you subtract this flat image from the original
And now you can see how nicely this works! By subtracting the flat field image we have eliminated the donut patch and created a pretty uniform image! Unfortunately we have the 3 black spots from the subtraction of the stars. Typically I will go through the flats and throw out the ones with star images in them so this doesn’t happen!