The protoplanetary disks in the nearby massive star-forming region cygnus OB2
American Astronomical Society
This is the final version of the article. Available from the American Astronomical Society via the DOI in this record.
The formation of stars in massive clusters is one of the main modes of the star formation process. However, the study of massive star-forming regions is hampered by their typically large distances to the Sun. One exception to this is the massive star-forming region Cygnus OB2 in the Cygnus X region, at the distance of ∼1400 pc. Cygnus OB2 hosts very rich populations of massive and low-mass stars, being the best target in our Galaxy to study the formation of stars, circumstellar disks, and planets in the presence of massive stars. In this paper, we combine a wide and deep set of photometric data, from the r band to 24 μm, in order to select the disk-bearing population of stars in Cygnus OB2 and identify the class I, class II, and stars with transition and pre-transition disks. We selected 1843 sources with infrared excesses in an area of 1° × 1° centered on Cyg OB2 in several evolutionary stages: 8.4% class I, 13.1% flat-spectrum sources, 72.9% class II, 2.3% pre-transition disks, and 3.3% transition disks. The spatial distribution of these sources shows a central cluster surrounded by an annular overdensity and some clumps of recent star formation in the outer region. Several candidate subclusters are identified, both along the overdensity and in the rest of the association. © 2013. The American Astronomical Society. All rights reserved.
We thank the anonymous referee for the useful comments. The authors are indebted with Raffaele D'Abrusco and Ignazio Pillitteri for their precious help. This article makes use of data obtained with observations made with the Gran Telescopio CANARIAS (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de CANARIAS, in the island of La Palma; data obtained as part of the INT Photometric Hα Survey (IPHAS) of the northern Galactic plane carried out at the Isaac Newton Telescope (INT; all IPHAS data are processed by the Cambridge Astronomical Survey Unit, at the Institute of Astronomy in Cambridge); SDSS data, founded by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England; data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation; data based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The paper is also based on data obtained as part of the UKIRT Infrared Deep Sky Survey (UKIDSS; Lawrence et al. 2007; we are grateful to Charles Williams for his support of the Apple Mac X-grid cluster in Exeter, on which the UKIRT data were reduced). UKIDSS uses the UKIRT Wide Field Camera (WFCAM; Casali et al. 2007). The photometric system is described in Hewett et al. (2006), and the calibration is described in Hodgkin et al. (2009). The pipeline processing and science archive are described in M. J. Irwin et al. (in preparation) and Hambly et al. (2008). M.G.G. is supported by the Chandra grant GO0-11040X. J.J.D., V.L.K., and T.A. are supported by NASA contract NAS8-39073 to the Chandra X-ray Center (CXC) and thank the Director, Harvey Tananbaum, and the CXC science staff for advice and support. D.G.A. acknowledges support from the Spanish MICINN through grant AYA2008-02038. R.A.G. would like to acknowledge the support of NASA Astrophysics Data Analysis Program (ADAP) grants NNX11AD14G and NNX13AF08G, and Caltech/JPL awards 1373081, 1424329, and 1440160 in support of Spitzer Space Telescope observing programs.
Astrophysical Journal, 2013, Vol. 773, Number 2