Boundaries whereįully-ionized H II regions transition to neutral/molecular photodissociation Regions of massive star formation offer some of the best and mostĮasily-observed examples of radiation hydrodynamics. The results are important for the placement of the stars in the Hertzsprung–Russell diagram, the interpretation of their spectroscopic analyses, and for future mass determinations through measurement of orbital motion. These results confirm studies of high-mass stars in other environments that find that massive stars are born with a high-multiplicity fraction. Including known spectroscopic binaries, our sample includes 27 binary, 12 triple, and 9 systems with 4 or more components. This assessment indicates that 47% of the targets have at least one resolved companion that is probably gravitationally bound. Companion stars with a field membership probability of less than 1% are assumed to be physical companions. We assigned a simple probability of chance alignment to each companion based upon its separation and magnitude difference from the central target star and upon areal star counts for the general star field of Cyg OB2. This faint contrast limit due to read noise continues out to 10'' near the edge of the detector. The observations are sensitive to equal-brightness pairs at separations as small as 0.”08, and progressively fainter companions are detectable out to ΔK = 9 mag at a separation of 2''. We observed 74 O- and early-B-type stars in Cyg OB2 in the JHK infrared bands in order to detect binary and multiple companions. We present results of a high angular resolution survey of massive OB stars in the Cygnus OB2 association that we conducted with the Near-Infrared Imager camera and ALTAIR adaptive optics system of the Gemini North telescope.

Century red giant download