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Title: Massive Stars in CYG OB2
Authors: Massey, Philip; Thompson, A. B.
Affiliation: Massey, Philip: Kitt Peak National Observatory, Tucson, AZ
Thompson, A. B.: Kitt Peak National Observatory, Tucson, AZ
Publication: Astronomical Journal v.101, p.1408
Date: 04/1991
Keywords: B Stars; O Stars; Stellar Mass; Supergiant Stars; Ubv Spectra; Charge Coupled Devices; Color-Magnitude Diagram; Hertzsprung-Russell Diagram; Interstellar Extinction; Stellar Spectra; Stellar Spectrophotometry; Astrophysics; STARS: EARLY-TYPE
DOI: 10.1086/115774
ADS: 1991AJ....101.1408M  [Bibtex entry]

Abstract

The stellar content of Cyg OB2 has been investigated using CCD photometry and spectroscopy. The intrinsically bluest stars have been isolated for spectroscopy by using a reddening-free parameter. The spectroscopy has made it possible to determine an improved distance modulus to the association (11.2 + or - 0.1) and has provided the means of accurately placing stars in the H-R diagram. The H-R diagram shows a well-defined main sequence extending upward to 85 solar masses. There are a few slightly evolved B supergiants of lower mass, suggesting that star formation did not take place strictly in a coeval manner. The initial mass function of Cyg OB2 is found to have a slope of -0.1 + or - 0.1, much flatter than that generally found for massive stars in the Galaxy or Magellanic Clouds.

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