Astronomy & Astrophysics

Table 1: Cluster member candidates which were previously identified by Béjar et al. (2001) as possible ${\sigma }$ Ori members. We also list the I-band magnitudes given by Béjar et al. (2001) as well as the difference to our I-band photometry.
Table 2: Monitoring campaigns.
Table 3: Candidates with significant periodic variability in the CA campaign. Periods (P) are determined by fitting the CLEANed periodogram peak with a Gaussian. Period errors ( $\Delta P$ ) are based on the half width at half maximum of the periodogram peak, transformed in time space. The amplitudes (A) correspond to the peak-to-peak-range of the binned lightcurve. N is the number of datapoints used for the period search.
Table 4: Candidates with significant periodic variability in the TLS campaign. Columns as in Table 3.
Table 5: Comparison of the spectra with models of Allard et al. (2000). The first two columns are the parameters of the best fitting model spectrum. The spectral types follow with the effective temperature scale of Leggett et al. (2000). For comparison, we additionally give the $T_{\rm eff}$ estimated from photometry alone, presuming cluster membership.
Table 6: Equivalent widths for prominent emission lines. The first column contains name and laboratory wavelength (in Å) of the emission line, then we list the equivalent widths for the four targets. Non-detection of the feature is indicated with a dash, "b'' means that the line is present, but strongly blended by nearby features.