RRS8C38MHZ - 8C Revised Rees Survey 38-MHz Source Catalog

Overview

This table contains a revised machine-readable source list for the Rees 38-MHz (or '8C') survey with improved positions and no redundancy. The Rees 38-MHz survey covers an area of about 1 sr north of declination +60 degrees. The angular resolution is 4.5 x 4.5 cosec(Dec) arcmin² and the limiting flux density over much of the survey area is about 1 Jy. Both of these figures were an improvement by nearly an order of magnitude on previous surveys at this frequency.

Users of these data should consult and cite the original survey paper by Rees as primary reference (1990MNRAS.244..233R) with the present publication (1995MNRAS.274..447H) as a supplementary revision. The recommended style of reference is thus: "The revised Rees 38-MHz survey (Rees 1990, catalogue revised Hales et. al 1995)."

In the Hales et al. (1995) paper, the authors aimed to improve the accuracy of the source positions to <~ 1 arcminute, so that a search radius smaller than the survey resolution of 4.5 arcminutes was practicable everywhere.

Note that for interest the source list includes data on some sources at declinations lower than +60 degrees, but that the right ascension coverage is not complete below +60 degrees.

Catalog Bibcodes

1995MNRAS.274..447H
1990MNRAS.244..233R

References

A revised machine-readable source list for the Rees 38-MHz survey.
     Hales S.E.G., Waldram E.M., Rees N., Warner P.J.
    <Mon. Not. R. Astron. Soc. 274, 447 (1995)>
    =1995MNRAS.274..447H
A deep 38-MHz radio survey of the area declination > +60 degrees.
     Rees N.
    <Mon. Not. R. Astron. Soc. 244, 233 (1990)>
    =1990MNRAS.244..233R

Provenance

This table was created in November 2010 based on CDS catalog VIII/31 file 8c.dat. Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018.

Parameters

Name
The position-based source designation recommended by the CDS Dictionary of Nomenclature of Celestial Objects, viz., '8C HHMM+DDdA', where the numerical part of the name is the truncated B1950.0 position of the radio source (to 1 minute of time in RA and 0.1 degrees in Dec). Where there are two apparently independent sources which would otherwise have the same abbreviated source name, the authors added an a 'A' or 'B' to the name. The HEASARC created these names from the positions, as they were not present in the original table.

RA
The Right Ascension of the 38-MHz radio source in the selected equinox. This was given in B1950.0 equatorial coordinates in the original table to a precision of 1 second of time. A comparison of these positions with those in the Taxas and 6C catalogs showed that, although small systematic effectes undoubtedly remained, the target accuracy of 1 arcminute was comfortably achieved. For example, of those sources which had 1 Jy (0.5 Jy) counterparts in the Texas survey, 68% were within ~ 20 (~ 30) arcseconds of their Texas positions.

Dec
The Declination of the 38-MHz radio source in the selected equinox. This was given in B1950.0 equatorial coordinates in the original table to a precision of 1 arcsecond. A comparison of these positions with those in the Taxas and 6C catalogs showed that, although small systematic effectes undoubtedly remained, the target accuracy of 1 arcminute was comfortably achieved. For example, of those sources which had 1 Jy (0.5 Jy) counterparts in the Texas survey, 68% were within ~ 20 (~ 30) arcseconds of their Texas positions.

LII
The Galactic Longitude of the 38-MHz radio source.

BII
The Galactic Latitude of the 38-MHz radio source.

Source_Flag
This flag parameter characterizes the source morphology as follows:

      P = Simple source with only one local maximum within the
          source region (defined by the contour which encircles
          the local maximum and is 2.5 times the local noise level).
          The position is that of the peak flux brightness.
      C = Component or source associated with a single local
          maximum within an integrated complex. The peak and
          integrated flux for each such component represent
          values for that component only, and the position is
          that of the peak brightness. The components of a
          complex are not necessarily immediately adjacent to each other in
          the revised list, when it is ordered in right ascension.

Flux_38_MHz
The peak brightness of the 38-MHz radio source or component, in mJy/beam. (These values were converted by the HEASARC from the Jy/beam units used in the original table). The beam is not of constant size, the resolution being 4.5 x 4.5 cosec(Dec) arcmin². The point of quoting the peak brightness in mJy/beam is that, for a source which is not significantly resolved or distorted by ionospheric effects, the peak brightness in those units will give a reasonable estimate of the flux density of the source (and be numerically comparable to the integrated flux density in mJy). The provided source extent parameter also ties in with this idea by comparing the integration area of a source to the area of a synthesised beam.

The original paper by Rees contains much discussion about the relative merits of peak brightness and integrated flux density as estimates of a source flux density, including consideration of the behaviour of this ratio; all this hinges on the idea of flux being smeared out with respect to the theoretical synthesised beam, so that the concept of a beam area is crucial to the discussion.

Int_Flux_38_MHz
The integrated flux density of the 38-MHz radio source or component, in mJy. (These values were converted by the HEASARC from the Jy units used in the original table).

Source_Extent
This parameter is an indicator of the extent of the source and is the ratio of the integration area of the source to the area of a synthesised beam, calculated using the same integration level. Thus, size = 1 indicates a point source, size < 1 indicates some over-resolution due to noise effects, and size > 1 an apparently extended source. Most sources appear slightly extended because of distortions created by the ionosphere. Remember that the survey is confusion limited!

SNR
The signal-to-noise, i.e., the ratio of the peak brightness to the local noise level calculated at the position of the source. The revised list contains only sources or components with signal-to-noise >= 5.0. It excludes the components with signal-to-noise < 5.0 listed in Rees (1990) for some complexes.

Cntr_Plot_Number
The number of the contour plot on which the source appears in the atlas provided in Rees (1990), provided so as to enable the user to check the appearance and environment of the source

Contact Person

Questions regarding the RRS8C38MHZ database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:34:11 EDT