2 Data

We have studied the AGAPEROS catalogue of 584 variable stars detected over a 0.25 deg² field in the LMC Bar (Melchior et al. 2000, hereafter referred to as Paper I). These stars have been selected on the basis of their variability on a 120-days window with a bias towards long-timescale variations (>few days), which are not necessarily periodic. The original data set has been taken at ESO by the EROS-1 collaboration (Arnaud et al. 1994a,b; Renault et al. 1997) using a 40 cm telescope, equipped with a wide field camera composed of 16 CCD chips, each of $400\times579$ pixels of 1.21 arcsec (Arnaud et al. 1994b). We use 9 chips, and study light curves in the red ( $\bar{\lambda}=670$ nm) filter. Table 1 gives a short description of the dataset. See Melchior et al. (1998, 1999) for a more detailed description of the data treatment.

The study of the position of these stars in the colour-magnitude diagram showed that this catalogue is dominated by a population of Long Timescale & Long Period variables, while a few "bluer'' variables have also been detected. A cross-correlation with various existing catalogues showed that about 90$\%$ of those variable objects were undetected before. We extended the corresponding light curves to the whole EROS-1 database of the LMC (900-days). We improved the photometry of the corresponding light curves with image subtraction using the ISIS2.1 algorithm of Alard (2000). We follow the same definition of the magnitude system as in Paper I, but we rely here on image subtraction photometry.

 

 

Table 1: Description of the dataset.

time range (JD)	2448611 - 2449462
seasonal gaps	2448721 - 2448860
	2449076 - 2449207*
mean number of data
in each light curve	448
mean sampling	1.6 days

^* 54 light curves have a larger gap of 482 days.

Figure 1: Example light curves for each group of variables: the upper row illustrates regular light variation, the middle panels shows representatives of the semiregular variables, and the bottom row gives light variations classified as irregular. Periods used for the fit are given in the plot. The amplitudes ( $\Delta R_{\rm EROS}$) are given in mmag.

The published DENIS catalogue (I, J and $K_{\rm S}$) for the LMC (Cioni et al. 2000) has been used to make a cross-identification between the AGAPEROS variables and the DENIS magnitudes. A search radius of 3 $^{\prime\prime}$ was chosen to avoid misidentification. Out of the 584 variables 468 were detected by DENIS ($\sim$80%). Note that the positional accuracy of these variables is about 1 $^{\prime\prime}$, as discussed in Paper I.