CHOICE Course: CCD Photometry

Instructor: Ed Wiley.

CCD1 and CCD2 have been combined into a single six-week course. We will use the AAVSO Guide to CCD/CMOS Photometry as our basic reference.

This course will use the AAVSO platform VPhot as the basic software for performing tasks such as measuring variables. A brief introduction to VPhot is provided but is not a substitute for taking the CHOICE VPhot course. Students who are not members of AAVSO will be provided temporary access to VPhot for purposes of the course.

This course does not require students to have any equipment, not even a telescope. It does require students to have software for calibrating images and software for graphing data (example, a spreadsheet program). All images used in the first two weeks can be downloaded and processed by the student’s software. All images for the last four weeks will be available to all students as fully calibrated images uploaded to a common VPhot telescope account. When you log onto VPhot those images will appear in your list of images.

Topics covered in the first three weeks are found in Chapters 1-4 of the Guide and include system testing and basic image calibrations from bias and dark frame subtraction to flat fielding. Of interest to experienced astrophotographers are topics such as camera linearity, field-of-view as it relates to differential photometry, signal and noise as they relate to calibration and science images, the nature of photometric filters, and differences between CCD and CMOS cameras.

Topics covered in the last three weeks cover Chapters 5-7 of the Guide include the basics of differential photometry, picking comparison and check stars, ensemble techniques, and measuring variable magnitudes using differential photometry. We will discuss the statistical nature of measurement uncertainty and strategies of accessing the results of measuring a variable. The last two weeks concentrate on using standard star fields to determine transformation coefficients and how to apply those coefficients to transform data into the Standard System for color. We will then finish the course by using variable stars for comparing transformed and non-transformed magnitude estimates and explore ways to evaluate your results.

Success in completing CCD Photometry requires active participation in the Forum discussions and completion of exercises. Participants should plan on devoting sufficient time to the course.

Students are assumed to have suitable software and know how to use it for such activities as taking, manipulating, and analyzing images. If not, please inform the instructor. For photometric analysis the courses actively support the use of AAVSO’s VPhot tool. Before enrolling, please consult the AAVSO Guide to CCD/CMOS Photometry for comments on software. If you are buying photometric filters pay close attention to the spectral characteristics to ensure that they match the Johnson-Cousins color profile.