1 Introduction

Planetary Nebulae (PNe) are bright emission line objects, observable throughout the Galaxy. They are excellent probes of abundance gradients, the chemical enrichment history of the interstellar medium, the effects of metallicity on stellar evolution, and kinematics.

Most small PNe ($\sim$90$\%$) within 10$^\circ$ of the galactic center are physically close to it (Pottasch & Acker 1989). Since they can be assumed to be at the same known distance of $\sim$7.8 kpc, their distance-dependent parameters, such as luminosity and size, can be determined. These parameters are needed to define the underlying population. The chemical composition and the central star parameters are computed via self-consistent photo-ionization modelling of the nebula. Because luminosity correlates with the central star mass, which correlates with the progenitor mass, which, in turn, correlates with stellar age, the relationship between age and composition can be deduced (Dopita et al. 1997; Walsh et al. 2000). The chemical enrichment history of the Bulge could be tracked using PNe.

We surveyed a $4 \times 4$ degree field centered on the galactic center in [S III]$\lambda$9532 and a continuum band at KPNO with the 60-cm Schmidt telescope and a $2048 \times 2048$ pixels thick STIS CCD in July 1994 and June 1995. The field of view was $65\hbox{$^\prime$ }\times 65$$^\prime$ and the pixel size 2 $^{\prime\prime}$. This survey has uncovered 95 new PN candidates in addition to the 34 previously known in this region (Acker et al. 1992; Kohoutek 1994). 45 PNe were confirmed via optical spectroscopy with the 1.52-m ESO telescope and the Boller & Chivens spectrograph, while 19 fainter ones were confirmed at the CTIO 4-m with the RC spectrograph (Van de Steene & Jacoby 2001, in preparation).

Accurate radio flux densities and angular diameters are crucial to obtain a good photo-ionization model of the PNe (van Hoof & Van de Steene 1999). The very high extinction causes the H$\beta$ line to be faint or even undetected in the optical spectra. Hence the radio flux density is needed to determine the extinction and the total ionizing flux.

In this article we present the radio continuum observations of 64 PNe confirmed spectroscopically with the ESO 1.52-m and CTIO 4-m telescopes. We describe the observations in Sect. 2 and the data reduction in Sect. 3. The results are presented in Sect. 4. The improved method for determining the distances, based on a relationship between radii and radio surface brightness (Van de Steene & Zijlstra 1995) is used in Sect. 5 to determine the distances of the PNe and discuss their distribution in the galactic bulge. In Sect. 6 we determine the extinction values of these new bulge PNe.