WSRTGP - WSRT Galactic Plane Compact 327-MHz Source Catalog
The survey image provided the first high resolution view of the Galaxy at low radio frequencies, and included sections of the Sagittarius and Cygnus arms. These sections contain numerous extended features, among them supernova remnants, H II regions, "bubbles" of thermal emission, and large patches of amorphous galactic thermal emission. The inter-arm region is characterized by lower densities of extended features, but numerous discrete compact radio sources, most of which are background objects such as quasars and other types of active galactic nuclei. However, the resolution, sensitivity and low frequency of this survey make it ideal for detecting weak, non-thermal compact galactic sources, e.g. compact, low surface brightness SNRs and radio stars.
Inspection of the survey image has produced a catalog of nearly 4000 discrete sources with sizes of less than about 3'. Gaussian model parameters for each compact source in the mosaicked images were obtained using the AIPS routine IMFIT. The background-removed intensity distribution of each source was fitted by a 2-dimensional Gaussian, parametrized by the source position, peak intensity, major and minor axes, and the position angle of the major axis. The catalog contains all sources having peak intensity > 5 times the rms noise level measured in the surrounding area of the image, and lists RA, Dec, flux density, and, if the source is resolved, the deconvolved major and minor axis and the position angle of the source. Sources were identified based on visual inspection of the images. In practice, a source had to have dimensions of less than a few arcminutes to be classified as a compact source. Most (85%) of the sources are either unresolved or only slightly resolved (major axis < 60"), but some sources have dimensions as large as 6'. A source was considered resolved if the area of its Gaussian model was greater than the area of the beam by more than 4 times its uncertainty.
Approximately 15% of the sources are resolved, with dimensions of 1'- 3'. The spatial distribution of resolved sources shows concentrations toward the spiral arms and follows the warping of the Galactic disk over the length of the survey region, indicating that a sizable fraction is Galactic. In the reference paper, spectral indices are calculated for 1313 sources detected in other radio surveys at frequencies greater than 408 MHz. The resolved sources exhibit a bimodal spectral index distribution, with distinct non-thermal and thermal populations. Comparison with the IRAS Point Source Catalogue results in 118 identifications between WSRT and IRAS sources, which are listed in Table 1 of the reference paper. Most of these are thermal radio sources associated with compact Galactic objects such as H II regions and planetary nebulae. A search for variability among 2148 of the compact sources has resulted in 29 candidate low-frequency variable sources, which are listed in Table 2 of the reference paper.
See the project website at http://www.ras.ucalgary.ca/wsrt_survey.html for the WSRTGP images available in JPEG, PostScript, and FITS formats.
A Westerbork synthesis radio telescope 327 MHz survey of the galactic plane. Taylor A.R., Goss W.M., Coleman P.H., van Leeuwen J., Wallace B.J. <Astrophys. J. Suppl. Ser. 107, 239 (1996)> =1996ApJS..107..239T
The name of the radio source using the IAU-style designation for the source based on the truncated B1950.0 equatorial coordinates of the source, viz., 'WSRTGP HHMM+DDMMA', as registered with the CDS Dictionary of Nomenclature of Celestial Objects, where the WSRT prefix stands for 'Westerbork Synthesis Radio Telescope, Galactic Plane', and suffixes A, B and c are used to differentiate close multiple sources which would otherwise have duplicate names.
The Right Ascension of the source in the selected equinox. This was given in B1950.0 coordinates to a precision of 0.01 seconds of time in the original table.
The mean error in the Right Ascension of the source, in seconds of time.
The Declination of the source in the selected equinox. This was given in B1950.0 coordinates to a precision of 1 arcsecond in the original table.
The mean error in the Declination of the source, in arcseconds.
The Galactic Longitude of the source.
The Galactic Latitude of the source.
The flux density of the source at 327 MHz, in mJy.
The mean error in the flux density of the source at 327 MHz, in mJy.
This parameter is a flag which is set to 'I' to indicate that an IRAS identification is available for this source (118 such cases).
The major axis diameter of the deconvolved source, if spatially resolved, in arcseconds.
The minor axis diameter of the deconvolved source, if spatially resolved, in arcseconds.
The position angle of the major axis of the deconvolved source, if spatially resolved, in degrees.