UCL Astrophysics Group


The Carina Nebula imaged by the VLT Survey Telescope Credit: ESO


About COBRaS

The e-MERLIN Cyg OB2 Radio Survey (COBRaS) is designed to exploit e-MERLIN’s enhanced capabilities to conduct uniquely probing, targeted deep-field mapping of the tremendously rich Cyg OB2 association in our Galaxy. The project aims to deliver the most detailed radio census for the most massive OB association in the northern hemisphere, offering direct comparison to not only massive clusters in general, but also young globular clusters and super star clusters. As such Cygnus OB2, shown in Figures 1 and 2 below, offers a direct insight into the type of environment found in the larger super star clusters observed in other galaxies.

Figure 1: IPHAS image of the Cygnus OB2 region. Copyright 'Nick Wright / IPHAS

Figure 2: Westerbork telescope 1.4 GHz observations of the Cygnus OB2 region. Resolution 0.6 arcseconds. Setia Gunawan et al. 2003 ApJS 149,123-156

With the COBRaS Legacy project we will assemble a uniform dataset of lasting value that is critical for advancing our understanding of current astrophysical problems in the inter-related core themes of

  1. mass loss and evolution of massive stars
  2. the formation, dynamics and content of massive OB associations
  3. the frequency of massive binaries and the incidence of non-thermal radiation

Based on a total awarded allocation of 252 hrs and 42 hrs for C- (5GHz) and L-band (1.6GHz) observations, respectively, the substantial COBRaS dataset will be powerfully combined with other multi-waveband surveys of the Cygnus X region, both current (IPHAS, Spitzer, and Chandra) and in future programmes (Herschel and JWST). This project will therefore not only yield substantial results for the key science areas identified above, but it will also provide new perspectives for numerous additional archival studies in stellar and extragalactic astrophysics. The COBRaS project will thus yield a very valuable Legacy dataset for the wider community.

What is e-MERLIN

e-MERLIN is an upgrade to the MERLIN (Multi-Element Radio Linked Interferometer Network) array of radio telescopes, run by the University of Manchester. This upgrade will provide a 30-fold increase in sensitivity (at resolutions that can match or better the Hubble Space Telescope). e-MERLIN is currently well into the commissioning phase and observations for this project are expected to begin mid-late 2010.  In preparation for the start of observing, work currently being undertaken within the group includes development of data reduction pipelines and imaging procedures.

Survey Regions

The figures below show the proposed mosaicing of the Cyg OB2 cluster (left: C-band, right: L-band). The chosen step sizes of 2.50 (Cband) and 7.50 (L-band) provide excellent coverage compatible with the primary beam (including the Lovell telescope for both bands).

The background figure is the Knödlseder (2000 A&A, 360, 539) outline of the Cyg OB2 association (based on counts from the 2MASS survey). Blue symbols indicate some well-known radio sources (O and WR stars).

97 fields are plotted for C-band, 21 for L-band.

Figure 3: C-band survey regions.

Figure 4: L-band survey regions