projspec - UCF Physics AST 5765 Astronomical Data Analysis...

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UCF Physics: AST 5765: Astronomical Data Analysis Fall 2009 Final Project Radial Velocity and Dark Matter in a Galaxy Measure the velocity and mass vs. radius in a galaxy. NOTE: These instructions will be made more explicit, particularly as to the purpose and method of each step, in an update to be posted soon. 1. Create bias frames. These CCD spectra automatically have electronics offsets (“bias”) sub- tracted from them. However, just to be certain, we will create bias frames, which are akin to dark frames. Median combine the bias frames to form a master bias frame. 2. Create a flat field. Subtract bias from the dome flats and normalized-median-combine them to create a master dome image. This is your flat field image, already normalized to unity. 3. Process the images. Subtract the bias frame from the target galaxy and the reference star frames. Divide by the flat field. 4. Find bad pixels. Use to make a mask of bad pixels in the processed frames. 5. Extract background spectra. Taking advantage of the long slit, create a spectrum of the sky background. That is, for each galaxy and star spectrum, locate regions free of target flux and containing sky flux near the top and bottom. Mask the rest of the image. For each column (i.e., each wavelength) calculate a masked mean. Ensure that the result is not contaminated by bad pixels. Subtract the spectrum from each row in the frame. The sky lines should almost go away. 6. Extract target spectra. We now wish to extract multiple spectra from our target galaxy. Over the range of the target flux (e.g., y -pixel range 65–220 for the galaxy), extract a spectrum every 5 or 7 pixels by repeating the masked mean procedure above over that 5–7 pixel range. 7. Cross correlation. Pick a nice-looking spectrum as your reference (relative velocity defined
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This note was uploaded on 11/09/2009 for the course AST 4762 taught by Professor Harrington during the Fall '09 term at University of Central Florida.

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projspec - UCF Physics AST 5765 Astronomical Data Analysis...

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