Cepheid Variables in the Andromeda Galaxy from Simon Fraser University's Trottier Observatory

This is a report on observations of 17 Cepheid variable stars in the Andromeda Galaxy, from Simon Fraser University's Trottier Observatory. The observatory is a teaching and public outreach facility with a 0.7-m aperture telescope under suburban skies. The observations were done as a group project by a team that included students, staff, and faculty at the university, and members of the Vancouver Centre of The Royal Astronomical Society of Canada. The Cepheid periods range from about 7 to 44 days, and observations were made on 26 nights over the course of two years. Images were taken through a luminance filter, and the instrumental magnitudes were converted to the Johnson-Cousins F-band using a calibration procedure whose precision is thoroughly characterized. The mean apparent magnitudes range from about 19.3 to 20.7, and they exhibit a correlation with the period that clearly reproduces the famous period-luminosity relation discovered by Henrietta Leavitt. We estimated the distance modulus μ (difference between apparent and absolute magnitudes) using a well-established calibration of the Leavitt relation, along with a correction for interstellar extinction from a professional study of this region of M31. We obtained μ = 24.37 ± 0.21, which is in excellent agreement with the known value, and corresponds to a distance of 2.44 ± 0.25 million light-years.