Description
Coordinates and photometry of probable cluster members in the sigma Ori cluster. Time series observations of this cluster were carried out using the CCD cameras at the 2m Schmidt telescope of the Thuringer Landessternwarte Tautenburg (TLS) and the 1.23m telescope on Calar Alto (CA). From these images, we derived coordinates (columns 2 and 3) as well as photometry in the R- and I-band (columns 5 and 6). Additional near- infrared photometry in J, H, K comes from the 2MASS database (columns 7-9). The cluster member selection is based on (I,I-J) colour magnitude diagrams. The R-I and J-H colours were used to reject contaminating field stars. The column 4 indicates whether the object was identified with the CA photometry (c), the TLS photometry (t), or both. The masses given in column 10 were estimated by comparing the near-infrared photometry with the evolutionary tracks of Baraffe et al. (1998A&A...337..403B). These tracks cover the mass range from 0.02 to 1.4 solar masses, for some objects with lower or higher masses we give upper or lower mass limits. The last two columns contain information about the results of the time series analysis. Column 10 gives the RMS of the CA lightcurve for targets No 1-52 and the RMS of the TLS lightcurve for all others. The last column indicates whether the target is classified as variable (v) and/or periodically variable (p). For a few objects, time series analysis was not possible, because they are either too faint or too bright in most of the images.
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