AAVSO: American Association of Variable Star Observers

Beyond the Milky Way: Comparison Stars for Photometry in M31 and M33 (Abstract)

Volume 48 number 2 (2020)

John C. Martin
Henry R Barber Observatory, University of Illinois Springfield, Springfield, IL; Jmart5@uis.edu


(Abstract only) At the start of the 20th century, professional astronomers had not imaged individual stars in the great spiral nebulae of Andromeda (M31) and Triangulum (M33). Present day, non-professional astronomers have the capability to regularly image individual luminous stars in both galaxies, attempting science that Edwin Hubble himself would have only dreamed of a century earlier. But obtaining calibrated photometry from images of M31 and M33 is significantly hindered by having too few reliable faint photometric comparison stars. We present an updated list of comparison stars fainter than 12th magnitude that the University of Illinois Springfield Luminous Stars Survey uses to measure photometry for luminous stars in M31 and M33. The list is derived from the AAVSO Photometric All Sky Survey (data release 10) and checked for accuracy and stability over the eight years of imaging in our survey. The list reliably yields ensemble photometry with better than 0.1 magnitude error for 20 × 20 arcminute fields covering the spiral arms of both galaxies.