Early-A stars from IPHAS, and their distribution in and around the Cyg OB2 association

Abstract

Stellar photometry derived from the INT/WFC Photometric H$\alpha$ Survey of the Northern Galactic Plane (IPHAS) can be used to identify large, reliable samples of A0-A5 dwarfs. For every A 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 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. 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 to 12.5. These are consistent with a ~7 Myr old stellar population at DM = 10.8, or with an age of ~5 Myr at DM = 11.2. The number of A stars found in this clustering alone is consistent with a lower limit to the cluster mass of ~10000 M-sun.

15 pages, 15 figures, accepted for publication in MNRAS

References in corpus (2)

• Old open clusters in the outer Galactic disk
• WFCAM, Spitzer-IRAC and SCUBA observations of the massive star forming region DR21/W75: II. Stellar content and star formation

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• External photoevaporation of protoplanetary discs in Cygnus OB2: linking discs to star formation dynamical history
• BD+43 3654 -- a blue straggler?
• The historical record of massive star formation in Cygnus
• Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex -- I: Introduction, Photometry and Source Catalog
• Exploring the structure and kinematics of the Milky Way through A stars
• Candidate Hα emission and absorption line sources in the Galactic Bulge Survey
• Mapping H$\alpha$-Excess Candidate Point Sources in the Southern Hemisphere Using S-PLUS Data
• The velocity structure of Cygnus OB2
• COBRaS: The e-MERLIN 21 cm Legacy survey of Cygnus OB2
• Morphology of Young Massive Stellar Clusters with Next-Generation IACTs