1 Introduction

The photoelectric astrolabes Mark II were built at the Nanjing Astronomical Instrument Factory in 1974. These instruments are used for determinations of astronomical time, latitude, and star positions as well as for research in astrogeodynamics.

The photoelectric astrolabe Mark II No. 2 was installed at the Shahe Station of the Beijing Astronomical Observatory at the end of 1975 and was put into operation since Mar. 1976 (Luo 1979). The aperture of the primary mirror is 200 mm and that of the secondary mirror 49 mm. The equivalent focal length is 2400 mm. The zenith distance of observation is 30$^{\circ}$. A vacuum telescope tube and two reflecting mirrors with a stable angle are used. This optical system of the astrolabe is quite stable.

Before modernization, the astrolabe was a semi-automatic instrument with a limiting magnitude of only 7.0. Since 1987, the astronomers of the Beijing Astronomical Observatory began to improve the instrument. Automatic observation with the instrument started in 1988. A new method of photon-counting was used for data processing in 1990, and the limiting magnitude of observation correspondingly increased to 11.5.

Since 1980, several general catalogues (Zhu et al. 1981; Working Group of GCPA 1983; Working Group of CGSC 1991; Lu 1991) of stars have been compiled using the data observed with the different types of Chinese photoelectric astrolabes.

The Fundamental Reference System of Stars project is important for astrometry. Although Hipparcos has made remarkable achievements, there are many things to do after Hipparcos (Clauzet et al. 1990; Kovalevsky 1991), such as: the improvement of fundamental reference system of stars; the extension of fundamental catalogue to faint stars; the maintenance of Hipparcos reference system; the extension of the Hipparcos catalogue. Two types of ground-based instruments can do these works: the photoelectric meridian circles and the photoelectric astrolabes which both give star positions with a rms precision of the order of 0.1''.

During the IAU 20th General Assembly at Baltimore in 1988, the Working Group "Astrolabe", established by Commission 8 had decided to undertake the compilation of a New General Astrolabe Catalogue (NCGA). Astronomers from China and Argentina were interested in the project. According to the cooperation between Beijing, San Juan, and La Plata Astronomical Observatories, the photoelectric astrolabe Mark II No. 2 of the Beijing Astronomical Observatory was moved and installed at San Juan Observatory, Argentina in January 1992 for observations of the catalogue of stars in the southern hemisphere.

Using the data observed with the instrument from Feb. 1992 to Feb. 1995, the First San Juan Catalogue was published (Lu et al. 1996). In this paper, we present all results obtained during the first stage of the cooperation from Feb. 1992 to Mar. 1997. The second stage started in April, 1997, and will be continued until Mar. 2002. We hope that these observations will make a contribution to new fundamental reference system of stars.