2008/02/26 by Janet E. Drew, R. Greimel, M. J. Irwin +1 · 3 citations
Physics and Astronomy · Social Sciences · #Astronomy and Astrophysical Research #Blue straggler #Distance modulus #Educational Leadership and Practices #Galactic plane #Open cluster #Photometry (optics) #Sky #Star cluster #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2008.13147.x
15 pages, 15 figures, accepted for publication in MNRAS
arxiv created 2008/02/26 · openalex publication_date 2008/04/23 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Stellar photometry derived from the INT/WFC Photometric Hα Survey (IPHAS) of the Northern Galactic plane can be used to identify large, reliable samples of A0–A5 stars. For every A-type star, so identified, it is also possible to derive individual reddening and distance estimates, under the assumption that most selected objects are on or near the main sequence, at a mean absolute r′ magnitude of 1.5–1.6. This study presents the method for obtaining such samples and shows that the known reddenings and distances to the open clusters NGC 7510 and NGC 7790 are successfully recovered. A sample of over 1000 A-type stars is then obtained from IPHAS data in the magnitude range 13.5 < r′ < 20 from the region of sky including the massive northern OB association Cyg OB2. An analysis of these data reveals a concentration of ∼200 A stars over an area about a degree across, offset mainly to the south of the known 1–3 Myr old OB stars in Cyg OB2: their dereddened r′ magnitudes fall in the range 11.8–12.5. These are consistent with a ∼7 Myr old stellar population at distance modulus DM = 10.8, or with an age of ∼5 Myr at DM = 11.2. The number of A-type stars found in this clustering alone is consistent with a lower limit to the cluster mass of ∼104M⊙.