2001/10/18 by S. S. Larsen, Søren S. Larsen, Yu. N. Efremov +11 · 45 citations
Physics and Astronomy · #Advanced Camera for Surveys #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Blue straggler #Globular cluster #Milky Way #Red supergiant #Star cluster #Star formation #Stars #Stellar collision #Stellar, planetary, and galactic studies #Supergiant #astro-ph
paper · pdf · doi:10.1086/338385
published in The Astrophysical Journal 567(2), 896-914 (IOP Publishing) · 51 pages, including 19 figures and 4 tables. Accepted for publication in ApJ
arxiv created 2001/10/18 · openalex publication_date 2002/03/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The stellar populations in a stellar complex in NGC 6946 are analyzed on images taken with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope . The complex is peculiar because of its very high density of stars and clusters and semicircular shape. Its physical dimensions are about the same as for the local Gould Belt, but the stellar density is 1-2 orders of magnitude higher. In addition to an extremely luminous, ~15 Myr old cluster discussed in an earlier paper, accounting for about 17% of the integrated V -band light, we identify 18 stellar clusters within the complex with luminosities similar to the brightest open clusters in the Milky Way. The color-magnitude diagram of individual stars in the complex shows a paucity of red supergiants compared to model predictions in the 10-20 Myr age range for a uniform star formation rate. We thus find tentative evidence for a gap in the dispersed star formation history, with a concentration of star formation into a young globular cluster during this gap. Confirmation of this result must, however, await a better understanding of the late evolution of stars in the corresponding mass range (≳12 M ☉ ). A reddening map based on individual reddenings for 373 early-type stars is presented, showing significant variations in the absorption across the complex. These may be responsible for some of the arclike structures previously identified on ground-based images. We finally discuss various formation scenarios for the complex and the star clusters within it.