WSRTGP - WSRT Galactic Plane Compact 327-MHz Source Catalog

Overview

The Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands has been used to survey the section of the galactic plane from +42 to +92 degrees Galactic Longitude l at a radio frequency of 327 MHz. Twenty-three overlapping synthesis fields were observed in the Galactic Latitude b band of |b| < 1.6 degrees. Each field was observed at two epochs, several years apart, to identify variable sources. Intensity data from the separate epochs were combined, and the resulting images mosaicked to produce a single image of the entire survey region. The sensitivity of the mosaic is typically a few mJy, corresponding to a detection level as low as 10 mJy/beam. The spatial resolution is 1' by 1' * cosec(Dec).

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.

Catalog Bibcode

1996ApJS..107..239T

References

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

Provenance

This table was created by the HEASARC in February 2012 based on CDS Catalog J/ApJS/107/239 file wsrt.dat.

Parameters

Name
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.

RA
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.

RA_Error
The mean error in the Right Ascension of the source, in seconds of time.

Dec
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.

Dec_Error
The mean error in the Declination of the source, in arcseconds.

LII
The Galactic Longitude of the source.

BII
The Galactic Latitude of the source.

Flux_327_MHz
The flux density of the source at 327 MHz, in mJy.

Flux_327_MHz_Error
The mean error in the flux density of the source at 327 MHz, in mJy.

IRAS_Flag
This parameter is a flag which is set to 'I' to indicate that an IRAS identification is available for this source (118 such cases).

Major_Axis
The major axis diameter of the deconvolved source, if spatially resolved, in arcseconds.

Minor_Axis
The minor axis diameter of the deconvolved source, if spatially resolved, in arcseconds.

Position_Angle
The position angle of the major axis of the deconvolved source, if spatially resolved, in degrees.

Contact Person

Questions regarding the WSRTGP database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:36:54 EDT