2 Selection of the fields

With the aim of studying M giants in the galactic bulge, Blanco & Terndrup (1989) and Blanco (1988) collected from the literature, low-extinction windows evenly distributed in galactic latitude and longitude and selected new regions with analysis of old photographic plates. The distribution of the resulting 31 windows, that we adopted for our observational programme, can be seen in Fig. 1. Since we needed to develop the necessary tools and analysis methodology to start the project, we decided to use only 12 windows for the first stage of the work. Table 1 summarizes the list of these low-extinction windows, as displayed in Fig. 1.

  

Figure 2: Position of the center of the 31 low-extinction windows collected or discovered by Blanco & Terndrup (1989) and Blanco (1988). The hollow symbols indicate the 12 windows that we monitored in the first stage of the project

The great advantage of this sample of windows is that they cover almost all bulge area. The monitoring programmes with the aim to discover microlensing events (MACHO and OGLE I, for examples) are concentrated in areas near the Baade window, basically in the interval $-6^\circ < l < 6^\circ$ and $-6^\circ< b < -2^\circ$ (Stanek et al. 1996; Bennett et al. 1994). In this sense, our shallower but spatially extended search can be considered as complementary of the massive databases of the central regions.

  

Table 1: Coordinates of the 12 low-extinction windows that we choose for monitoring in the search for variable stars