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D.B. Caton, B.D. Walls (Appalachian State University)
The venerable Sky and Telescope Lab Exercise, Variable Stars in M15, demonstrates how RR Lyrae variable stars are used as distance indicators to find the distance to M15. In the S&T exercise, students estimate brightnesses of variables on offset reprints made from plates taken over one night.
We have updated that exercise by obtaining a 60 images of M3, over a 9-hr night. We chose M3 since we get better seeing conditions in the spring, when M3 is well-placed, compared to the August skies required for M15. Imaging was done using the DFM 32-inch telescope at our Dark Sky Observatory. The 5-minute exposures used a Photometrics CH250 camera with a Tektronix 10242 CCD and V-filter. Darks were obtained through the night, as well as sky flats at dusk and dawn.
For analysis by Introductory Astronomy students, we pre-processed these images to remove the thermal and flat effects. The students used Axiom Research's MIRA AP software for doing the aperture photometry. From the distance modulus, the students calculate the distance to M3, getting results good to within about 1
By doing the photometry this way, the students get a flavor of how modern photometry is done with CCDs and image processing, as contrasted the outdated photographic techniques in the S&T reprint version. The MIRA software is easy to use, with auto-centroiding and calibration built in. Students were able to do this after only one introductory lab on the use of MIRA.
We will have available a number of copies of a CD-R with the images, lab exercise writeups, and associated materials. These will be available on the Web as well.
We acknowledge the support of the National Science Foundation and the Fund for Astrophysical Research. We would also like to thank Mike Corwin for his advice.
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The author(s) of this abstract have provided an email address for comments about the abstract: catondb@appstate.edu