A Westerbork Synthesis Radio Telescope 1400 and 350 MHz Continuum Survey of the Cygnus OB2 Association, in Search of Hot Massive Stars

Details A Westerbork Synthesis Radio Telescope 1400 and 350 MHz Continuum Survey of the Cygnus OB2 Association, in Search of Hot Massive Stars A Westerbork Synthesis Radio Telescope 1400 and 350 MHz Continuum Survey of the Cygnus OB2 Association, in Search of Hot Massive Stars

Nov 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003apjs..149..123s&link_type=abstract

The Astrophysical Journal Supplement Series, Volume 149, Issue 1, pp. 123-156.

Astronomy and Astrophysics

Astronomy

15

Stars: Binaries: General, Galaxy: Open Clusters And Associations: Individual: Name: Cygnus Ob2, Radio Continuum: Stars, Stars: Winds, Outflows, Surveys

Scientific paper

We present a radio continuum survey at 1400 and 350 MHz of a region of 2deg×2deg centered on the Cygnus OB2 association (d=1.7 kpc), using the Westerbork Synthesis Radio Telescope (WSRT) with angular resolutions of, respectively, 13" and 55". The resulting 5 σ flux-density limits of, respectively, ~2 mJy and ~10-15 mJy are a significant improvement over previous surveys. We detected 210 discrete sources with sizes less than 1.9θbeam (beam size), 98 of which at both frequencies. We also detected 28 resolved sources (sizes>1.9θbeam) still having well-defined peak intensities. The observed spectral index α1400350 distribution and source count strongly suggest an excess of sources of Galactic origin in the direction of Cyg OB2.
We have searched for positional coincidences of the detected sources in our list with other radio, infrared, and optical objects from various surveys by using the likelihood ratio (LR) method. Furthermore, we looked for objects that show characteristics of either optically thick stellar winds (α >~ +0.6), or nonthermal emission (-1<~α<~+0.6) and/or variable spectral flux density. The LR method resulted in 108 identifications. Eighty unidentified sources, i.e., ~2/3, show characteristics of sources of Galactic origin, 10 of which may be stars. The remaining unidentified sources are probably of extragalactic origin.
We identified one source with the O7 star Cyg OB2-335 and consider it to be a candidate colliding-wind binary. We also identify 19 point sources with known infrared and optical objects: these have nearly flat or inverted spectral indices, and some of them show flux-density variability. Follow-up multifrequency monitoring of these sources will be important in establishing the reality of the flux variabilities and to assess the nature of these sources.
Based on observations made with the Westerbork Synthesis Radio Telescope (WSRT), operated by the Netherlands Foundation for Research in Astronomy (NFRA).

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