The Massive Star Population of Cygnus OB2

Abstract

We have compiled a significantly updated and comprehensive census of massive stars in the nearby Cygnus OB2 association by gathering and homogenising data from across the literature. The census contains 169 primary OB stars, including 52 O-type stars and 3 Wolf-Rayet stars. Spectral types and photometry are used to place the stars in a Hertzprung-Russell diagram, which is compared to both non-rotating and rotating stellar evolution models, from which stellar masses and ages are calculated. The star formation history and mass function of the association are assessed, and both are found to be heavily influenced by the evolution of the most massive stars to their end states. We find that the mass function of the most massive stars is consistent with a `universal' power-law slope of Gamma = 1.3. The age distribution inferred from stellar evolutionary models with rotation and the mass function suggest the majority of star formation occurred more or less continuously between 1 and 7 Myr ago, in agreement with studies of low- and intermediate mass stars in the association. We identify a nearby young pulsar and runaway O-type star that may have originated in Cyg OB2 and suggest that the association has already seen its first supernova. Finally we use the census and mass function to calculate the total mass of the association of 16500^+3800_-2800 Msun, at the low end, but consistent with, previous estimates of the total mass of Cyg OB2. Despite this Cyg OB2 is still one of the most massive groups of young stars known in our Galaxy making it a prime target for studies of star formation on the largest scales.

22 pages, 9 figures, 4 tables. Accepted for publication in Monthly Notices of the Royal Astronomical Society

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• FEEDBACK: a SOFIA Legacy Program to Study Stellar Feedback in Regions of Massive Star Formation
• Disentangling the spatial substructure of Cygnus OB2 from Gaia DR2
• Unlocking Galactic Wolf-Rayet stars with $\text{Gaia}$ DR2 II: Cluster and Association membership
• External photoevaporation of protoplanetary discs in Cygnus OB2: linking discs to star formation dynamical history
• e-MERLIN 21cm constraints on the mass-loss rates of OB stars in Cyg OB2
• Variability survey of brightest stars in selected OB associations
• Identifying Galactic Sources of High-Energy Neutrinos
• Globules and pillars in Cygnus X. II. Massive star formation in the globule IRAS~20319+3958
• Near-infrared time-series photometry in the field of Cygnus OB2 association II. Mapping the variability of candidate members
• TRES Survey of Variable Diffuse Interstellar Bands
• Variable millimetre radiation from the colliding-wind binary Cyg OB2 #8A
• Gamma-rays from the binary system containing PSR J2032+4127 during its periastron passage
• The velocity structure of Cygnus OB2
• A High Angular Resolution Survey of Massive Stars in Cygnus OB2: $JHK$ Adaptive Optics Results from the Gemini Near-InfraRed Imager
• Massive Young Stellar Objects and Outflow in the Infrared-Dark Cloud G79.3+0.3
• Population Synthesis of Massive Close Binary Evolution
• Massive Stars in Molecular Clouds Rich in High-energy Sources: The Bridge of G332.809-0.132 and CS 78 in NGC 6334