Observatory Setup
 
Got the dome open again tonight. Beautiful night at a pleasant 67˚F. Sitting on the field of SS Cyg again trying to figure out that ever more confusing star known as GSC 3196-641.
 
Anyway, I thought tonight, more for my own amusement than anything else, I would describe my little procedure when I get to my observatory.
 
  1. 1. Hook up the power. This seems much more inelegant than it is. I currently have a super long extension cord that I keep in the trunk of my car. When I arrive I open the trunk, take one end and walk to the house and the other to my observatory. When I pack up I reverse the process. I will probably run permanent power at some point but this works so easily, there hasn’t been a need.
  2. 2. Boot up the laptop. I like to get the CCD camera cooling as soon as possible, so I hook up my PC laptop right away, connect to the camera with CCDSoft and turn the chiller on.
  3. 3. Open the dome. Next I want to get the observatory cooling off, too. I open the dome, take the canvas cover off the scope and take the lens cap off of the telescope.
  4. 4. Get the telescope synched and tracking. I point at a bright star in the eastern sky, center it in my finder scope and turn on the power to the telescope mount, which moves the telescope at the same speed that the earth turns. I then use the focus tool in CCDSoft to repeatedly take pictures while I center the bright star. Then I boot up TheSky, link to the telescope computer and synch to the bright star. After this is done TheSky knows exactly where the telescope is pointing and I can point and click to move the telescope to other objects.
  5. 5. Go to my target. At this point I slew to my target for the night. I generally re-synch the telescope, since it is quick and easy to do and it refines the pointing. This involves just taking an image and pasting it in TheSky, which matches it up to its catalog of stars. I can then get the image framed up exactly the way I want to put the variable star, comparison stars and guide star in the desired positions.
  6. 6. Find a guide star and start guiding. My CCD camera has two chips, one which takes the main images of the target and a second smaller chip which takes images every few seconds and recenters a selected star. The telescope is moving at the same angular speed that the earth is turning but the image will still shift around due to imperfect alignment and slight imperfections in the gears. By auto-guiding, we can correct for all of these effects and keep the telescope pointed in exactly the same place to a very high degree of precision. On a normal night, the guide star does not shift more than about 3/4 of a pixel, which on my system is less than 2 arc seconds (or about 0.00006 degrees).
  7. 7. Start getting data. At this point I am ready to start taking science images. I usually take images alternately with a V filter (which has a similar response as the human eye) and an Ic filter, which is in the near infrared. Taking images in two different colors allows me to estimate the temperature of stars and detect the change in temperature over time.
  8. 8. Take calibration frames. When the night is through I have to take a series of calibration frames to correct for noise sources and optical system imperfections. These includes bias (or zero) frames, dark frames and flat frames. I’m not going to explain these in detail here, but the purpose is to subtract out systematic (i.e. not random) sources of uncertainty from my particular setup.
  9. 9. Close down and go home. By now it is dawn and I close up and drive home. I probably slept through much of #7 above and now will go home and sleep a few more hours.
  10. 10. Process the data. I work with the data to apply the calibrations and perform photometry to extract the information I am interested in – the change in brightness and color of the star over time.
  11. 11. Do the science! Steps 1-10 were just to get to the starting line; the purpose of all of this is to try to understand stars better. For me the science is still pretty lightweight and involves things like finding periodic signals in the brightness changes, identifying the type of variable star and figuring out various physical parameters, such as spectral type, mass, density and temperature.
 
Now you know!
Monday, August 14, 2006