The Maximum Ages of Trapezium Systems

Abstract

Allen et al. (1977) compiled a catalog of 968 possible Trapezium systems by scanning the IDS for systems of three or more stars whose relative separations within the system did not exceed a factor of 3. We explored whether a sample of 265 of those systems were actually physical systems. We used CCD pictures in U, B, and V magnitudes to obtain evidence for common proper motions and consistent color-magnitude and color-color diagrams. We also obtained a spectral classification for at least one star in each system to get the space reddening and distance.We found only 14 possible Trapezium systems; the remainder are 126 purely optical systems, 109 physical pairs, 14 hierarchical systems, and two small clusters. Nine of the Trapezium systems have ages less than 25 million yr, so that probably is the maximum age of such unstable systems. The remaining five systems are probably hierarchical systems appearing to be Traepzium systems in projection. The reason why so few of the proposed Trapezium systems are physical systems is because the faint IDS magnitudes are both systematically and accidentally very incorrect, causing the attempt by Allen et al. to eliminate faint background stars to fail in most cases. But for the Allen et al. systems with 05-B2 primaries, 45% were found to be true Trapezium systems.