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Astron. Astrophys. 331, 639-650 (1998)

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2. Observations and ephemeris

The observation log is summarized in Table 1. The echelle spectra have a S/N of 200 over the larger part of the covered wavelength region, but 100 or less below 3900 Å. They were taken very near quadrature, at HJD 2 447 191.542 and 2 447 193.691, and have been reduced with the software described in Verschueren et al. (1997 ). The original 2-pixel resolving power is R = 16300, and the spectra were rebinned to a slightly smaller bin width of 8.4 km/s. The differential photometry is quite accurate. The scatter in the results for HD 31 587-HD 31 640 suggest an rms for the final HD 30 861-HD 31 640 data smaller than 7 mmag in y, [FORMULA] and [FORMULA] and smaller than 9 mmag in [FORMULA]. The Walraven data have an rms of 5 mmag in [FORMULA], 4 mmag in 2.5 ([FORMULA]), 2.5 ([FORMULA]) and 2.5 ([FORMULA]), and 7 mmag in 2.5 ([FORMULA]) respectively, as judged from results obtained in the same run for stars in the open cluster NGC 2244. Notice that it is common practice to express Walraven photometry in log units; the factor of 2.5 is introduced for ease of comparison with the Strömgren photometry.


Table 1. Observation log

All differential photometry is listed in Tables 4, 5 and 6. Table 5 lists the data shown in Verschueren et al. (1987 ). Visual magnitudes, colours and indices are given in Table 2. The combined runs define the periodicity of the light variations and the number of cycles elapsed between the runs, without ambiguity (Fig. 1). The ephemeris published earlier is confirmed and considerably refined:


The zero point for the phases is defined with respect to the secondary light maximum, rather than to the deepest eclipse, because the two minima are almost indistinguishable in depth. The deepest eclipse in our data set occurs at HJD 2 447 183.664, at phase 0.229.

[FIGURE] Fig. 1. Light curve of TV Pic in Strömgren b, relative to HD 31 640. Different symbols refer to different runs. Circles refer to the Walraven data -2.5 ([FORMULA] [FORMULA] [FORMULA] [FORMULA], where the constant and the colour term correct for the difference in luminosity and for the colour dependence of the variation between the effective wavelengths of the B and b filters. The data obtained after HJD 2 447 000 were shifted to the differential scale fixed by the data obtained before HJD 2 447 000 ([FORMULA] [FORMULA] + [FORMULA] [FORMULA]) by subtracting 8.186 from the data given in Table 6. The phases at which the spectra were observed are indicated by vertical dashed lines. The full line corresponds to the model with the spot on the secondary, while the model with the spot on the primary is shown as a dashed-line curve (see Table 8 for the model parameters). For comparison, the model without spot (fitted to the part of the light curve around the secondary maximum) is shown as a dashed-dotted curve.

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© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998