ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O B-CelestialObject O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation O B-Citation O O O O B-Citation O B-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation O O O B-Wavelength I-Wavelength O B-Citation O O O B-Wavelength I-Wavelength O O O O O O O O O B-Software O O O B-Software O B-Software O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O B-Wavelength I-Wavelength O O O
tokens: In two cases, additional variable stars are found (rms significantly larger than for the remaining objects), they are excluded from the sample of comparison stars. A small number of epochs (not more than one per field) produces outliers in the master light curve probably due to changing in atmospheric conditions not recognized during the run; these images were excluded from the analysis. The master light curve was re-calculated using the remaining set of comparison stars and images and again subtracted from the raw light curves. Fig. 2 presents the final differential light curves and rms plots (rms versus average magnitude) for each of our seven objects. In these plots, our targets are labelled. The typical photometric error (defined as the floor of the rms of the comparison stars) is ∼ 1–3 per cent, significantly smaller than the amplitudes in the variable targets. Some of the target light curves exhibit a distinctive morphology – V2737 shows a continuous downward trend, V2739 a periodic behaviour, and V2227 multiple short-period eclipses. The remaining light curves appear at least partially irregular. Although the sampling frequency of the current data set is less dense than in previous studies, the overall light-curve morphology and variability time-scales are comparable to the previously published ones for all objects. Figure 2. Observed light curves and rms plots for all seven objects. Left column contains light curves, right column contains corresponding rms plot for each target's field. The light curves for each object span four nights and shows relative magnitudes from differential photometry. We observe a spread of periodic, quasi-periodic and irregular behaviours. rms plots indicate variable objects in each target's field. Figure 2 – continued Figure 2 – continued We calculate amplitudes for the light curves by taking the min–max difference for each star. To ensure no extreme outliers are included in this calculation, we check for any 3σ outliers but find none. Table 3 lists the derived amplitudes and compares them to previously published values ( SE04 ; SE05 ). The amplitudes in SE04 and SE05 refer to the peak-to-peak values in the binned light curves. Table 3. Light-curve amplitudes ( A ) derived in this work (see Section 6.1 ) and previously published values (see text for details). a SE04 ; table 4, I band. b SE05 ; table 1, I band. 4.2 Spectroscopy Standard spectroscopic data reduction was performed with iraf routines from the onedspec and twodspec packages. Background was fit and subtracted during spectrum extraction. Wavelength calibration is done using an HeAr arclamp. The A-type star HD292956 was used for relative flux calibration. For each epoch, three spectra (see Section 3 ) were co-added using a median filter. Fig. 3 presents the complete sequences of calibrated spectra for our stars over the four nights of observations. Every spectrum is normalized to the central wavelength of the I -band filter (7680 Å). In the final