1 Introduction

The microlensing searches, motivated by the study of dark matter in galaxies and its possible fraction of compact objects (hereafter Machos), have collected some unprecedented databases of images of neighbouring galaxies, and in particular of the Large Magellanic Cloud (LMC). The microlensing candidates are compatible with large Macho masses, and exhibit long timescale variations, typically 10-200 days (Alcock et al. 1997a,b,c; Renault et al. 1997; Palanque-Delabrouille et al. 1998; Alard et al. 1997; Udalski et al. 1994; Ansari et al. 1999). Possible contamination by variable stars is often suggested (e.g. della Valle $\&$ Livio 1996), but no systematic searches for variable objects have been undertaken so far on the microlensing databases. Whereas particular variables, such as RR Lyrae and cepheids are relatively well understood, little statistical information is known about the Long Timescale and Long Period Variable stars (hereafter LT$\&$LPV), with timescales/periods in the range of $\sim$100 to $\sim$800 days, which are an important stage of stellar evolution. They are easily rejected for these microlensing searches either with a cut on marginal stellar populations identified on the colour magnitude diagram (hereafter CMD) or by their periodicity. Aperiodic signals which do not satisfy these simple criteria are however more difficult to discriminate and to select.

In this paper, we perform a selection of variable objects on pixel light curves covering a 0.25 deg² field of the LMC Bar. We used the pixel light curves produced in Melchior et al. (1999, hereafter Paper I) adopting looser thresholds than those used for the selection of microlensing events in Melchior et al. (1998, hereafter Paper II). In Sect. 2, we summarise the characteristics of the data set. In Sect. 3, we discuss the automatic selection procedure used to keep all significant genuine variable stars. In Sect. 4, we introduce a magnitude estimate for each variable and display its position in the colour-magnitude diagram. In Sect. 5, we describe the procedure used to obtain the equatorial coordinates. In Sect. 6, we cross-identify the selected variable stars with existing databases. Finally, we provide the catalogue in Sect. 7.