The region around G76.9+1.0 was observed using the Miyun Synthesis Telescope (Zhang et al. 1993). Table 1 (click here) gives details of the observations.
Table 1: Details of observations with the Miyun Synthesis Telescope
Figure 1: Top: Average of five 232-MHz images. The gray-scale
presentation is from -0.3 Jy/beam (lightest) to 4 Jy/beam (black).
Bottom: Approximately the same area showing contours of 2695-MHz
radio emission (Fürst et al. 1990a; Reich et al. 1990b). The contours are
at 0.5, 1, 1.5, 2.5,
5, 10, and 20 K brightness temperature. The sixteen radio sources (or merged
sources) that are used in this study are indicated by the numbered circles.
The numbers refer to Table 4 (click here). Most of these are visible in the 232-MHz
image but some are lost in the noise
Data reduction was complicated by the proximity of Cygnus A to the field
centre (at the 30% level of the primary beam).
Phase and amplitude errors in the original data generated
a high artefact level in the region of interest, and it was
necessary to process the image using the
phase and amplitude self-calibration procedures in AIPS. The original data were
processed five times, starting with different model inputs. At the
conclusion of processing, artefacts in the images due to Cygnus A had been
reduced to a background level of 
400 mJy/beam in the immediate vicinity
of G76.9+1.0 in each of the images. All 232-MHz flux densities quoted in
this paper are the average of measurements made from the five images; the
quoted error is the estimate of the standard deviation in one determination
of flux density.
The primary telescope calibration was based on a model of Cygnus A, with an integrated flux density based on the scale of Baars et al. (1977). The model is based on many observations with the Miyun Telescope (Zhang et al. 1993). For the present observations, the flux-density scale was further adjusted using three sources in the field (other than G76.9+1.0). Flux densities for these sources are available in the literature at a number of frequencies between 178 and 4850 MHz, and a flux density at 232 MHz can be predicted with good accuracy. The measured and predicted flux densities for this set of sources were compared to establish an overall flux-density scale for the 232-MHz image. We refer to these three sources as comparison sources.
Because we were working so close to the sensitivity limit of the telescope at 232 MHz, we took several further steps to establish the reliability of our flux densities. Flux densities were measured for a further twelve sources (or source blends in two cases) at 232 MHz and flux densities for these sources were also compiled from the literature, and from re-analysis of images in the same manner as the analysis of the 232-MHz images. Their spectra help establish the reliability of the 232-MHz flux densities.
The source we are studying is extended, while the comparison sources used to establish the flux-density scale are essentially unresolved. It is conceivable that our data processing has had a different effect on resolved and unresolved sources, and we therefore included some extended HII regions in the list of sources we examined.
Some of the sources included in our list prove to have inherent interest, and we comment on them wherever warranted.
At 408 MHz, we used five separate observations made with the DRAO Synthesis Telescope to determine flux densities for the sources of interest. Table 2 (click here) gives details of these observations; all have different phase centres.
Table 3: Data used to establish source flux densities
Figure 2: The new 232-MHz map in the vicinity of the SNR G76.9+1.0,
illustrating the dynamic-range problems. The dotted circle denotes the
expected position and approximate size of the SNR. The contour levels are
-0.75, -0.25, 0.25 and 0.75 Jy/beam
Table 3 (click here) lists all sources of data used in this paper. Where data were available to us in the form of source lists, any subsequent revisions to the flux density scale were applied. Where data were available to us in the form of images, even if published source flux densities existed, the flux density of each source was measured (or re-measured) in two ways. First, a flux density was derived using the DRAO Gaussian-fitting package, which fits a two-dimensional Gaussian function or functions after first removing a smoothly varying background. Second, an integrated flux density was determined using the DRAO polygon integration package, which computes the integrated flux density above a smoothly varying background fitted at polygon vertices surrounding a source. The latter procedure was carried out five times, using slightly different polygon vertices, in order to determine an appropriate average value. The adopted flux density for a source was selected from these two results, using weighting judged to be appropriate for each case. In Table 3 (click here), if an angular resolution is listed, flux densities were determined from images, otherwise published source lists were used. A systematic 3% error was added to the statistical errors in flux densities derived from images, and a 4% possible systematic error was added to the ``Texas'' flux densities.
