1 Introduction

About 1/6-1/3 of all Galactic B-type stars with luminosity class III-V once showed H$\alpha$ in emission and have therefore been classified as Be stars (e.g. Zorec & Briot 1997). The optical and near-infrared spectra of Galactic Be stars usually display hydrogen, He I and singly ionized metallic emission lines, whose double-peaked shape indicate their origin in a circumstellar gaseous quasi-Keplerian disk. Detailed studies of Be stars in the Small Magellanic Cloud (SMC) have been performed only in recent years, being especially confined to open clusters like NGC 330 (e.g. Keller et al. 1999). These studies show the importance of studying Be stars in the low metallicity environment of the SMC since they serve as probes to test for the mechanisms of disk formation and of global disk oscillations (Baade et al. 2002; Hummel et al. 2001).

Over the past years, the microlensing projects (OGLE, MACHO, EROS) have monitored millions of stars in the Magellanic Clouds and Galactic bulge for variability. The huge resulting photometric databases are very well suited not only for microlensing studies but also for many other issues of modern astrophysics, including the distance scale, variable stars, star clusters etc. In particular, the OGLE II project (Udalski et al. 1997), has provided accurate BVI measurements for about 6.5 million stars from the central parts of the Magellanic Clouds (Udalski et al. 1998, 2000). Based on this same material, a unique catalog containing about 68 000 variable stars has just been released (Zebrun et al. 2001b).

The aim of this paper is to search the OGLE II database for Be star candidates and provide a much larger sample of these stars in the SMC than previously known. This will provide the basis for posterior follow-up spectroscopic studies of these objects, necessary to fully understand their nature. We will also call attention to several apparently new classes of light curves which appeared during our search for Be stars in the SMC.

The paper has the following structure. Observational data and the applied selection criteria are described in Sect. 2. Results are presented in Sect. 3, and discussed in Sect. 4. In Sect. 5, we present our current conclusions on the underlying nature of the observed types of variability.