1 Introduction

Stellar clusters present a unique playground for tests of stellar evolution. Nearby clusters like the Hyades, Pleiades, and Praesepe are especially important due to the possibility to make detailed observations of individual stars, but also open clusters like NGC 3680 (Nordström et al. 1997), IC 4651 (Meibom 1999), and NGC 6134 (Frandsen et al. 1996) have received a lot of attention. In order to do a complete test of stellar evolution providing tight constraints on stellar models, it is necessary to expand the techniques beyond the normal isochrone fitting of models to observed colour-magnitude diagrams. One possibility of expansion is the study of variable stars, in particular $\delta$ Scuti stars, that are members of the clusters.

Among the more distant clusters ($d \ge 1$ kpc) NGC 6134 still holds the record in terms of the number of $\delta$ Scuti stars, although a fair number has been detected in other clusters (Frandsen et al. 1998; Viskum et al. 1998; Choi et al. 1998).

The southern open cluster NGC 6134 has been observed several times over the last decade. The early study by Kjeldsen & Frandsen (1989) showed that this cluster was particularly interesting as the location of the turnoff region of the cluster was inside the instability strip. Hence it was expected that several $\delta$ Scuti stars could be found in the turnoff region. Kjeldsen & Frandsen (1989) found three $\delta$ Scuti stars. The multi site observations of Frandsen et al. (1996) led to the detection of several pulsation frequencies in six $\delta$ Scuti stars and the detection of a variable blue straggler.

To be able to exploit the information contained in the observed pulsation frequencies of the $\delta$ Scuti stars it is extremely important to know the fundamental parameters of the individual cluster stars, i.e. interstellar reddening, metallicity, distance, and age. In this paper we present new Strömgren photometry that leads to much improved values for these parameters.