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1998ApJS..117..361Condon & Kaplan
PLANETARY NEBULAE IN THE NRAO VLA SKY SURVEY
J.J. Condon, D.L. Kaplan
The 1.4 GHz NRAO VLA Sky Survey (NVSS) images and source catalog were
used to detect radio emission from the 885 planetary nebulae north of
J2000 declination $\delta = -40^\circ$ in the Strasbourg-ESO Catalogue
of Galactic Planetary Nebulae. We identified 680 radio sources
brighter than about $S = 2.5$ mJy beam$^{-1}$ (equivalent to $T
\approx 0.8$ K in the $45''$ FWHM NVSS beam) with planetary nebulae
by coincidence with accurate optical positions measured from Digitized
Sky Survey (DSS) images. Total extinction coefficients $c$ at $\lambda =
4861$ \AA~were calculated for the 429 planetary nebulae with available
H$\beta$ fluxes and low free-free optical depths at 1.4 GHz. The
variation of $c$ with Galactic latitude and longitude is consistent
with the extinction being primarily insterstellar and not intrinsic.
The initial sample contains 885 ``true'' or ``probable'' planetary
nebulae north of J2000 $\delta = -40^\circ$. The NVSS images do not
yet cover the positions of 26; these are noted as ``blanked'' (B) in
the final column of Table 1. There are another 20 nebulae so extended
($\phi > 300''$) and smooth that the NVSS might miss them altogether, even
if their flux densities were quite high. They are labeled ``extended''
(E) in Table 1. Four were clearly detected, but only lower
limits to their flux densities can be estimated. Another 676
planetary nebulae were detected, and their flux densities were
measured, for a total of 680 detections. There are 115 flux-density
upper limits $S < 2.5$ mJy and 48 cases in which higher upper limits
were set because the nebula was extended more than $45''$ or because a
stronger confusing radio source was present. Confused sources are labeled C in
the last column of Table 1.
The NVSS radio positions (equinox J2000 only), 1.4 GHz flux densities,
and the rms uncertainties in these quantities are listed in Table 1.
The NVSS flux densities are based on the absolute scale of Baars {\it
et al.}~(1977). A small fraction of the radio sources (e.g., PN
G104.1$+$07.9 in Figure~\ref{fcfig}) are significantly resolved by the
$45''$ FWHM Gaussian point-source response of the NVSS images. Their
deconvolved Gaussian FWHM major and minor axes (arcsec) also appear in
Table 1. Note that the FWHM diameters of partially resolved sources
should be multiplied by shape factors as large as 2 to yield estimates
for the actual diameters of homogeneous spherical or cylindrical
sources (Panagia \& Walmsley 1978).