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Astron. Astrophys. 334, 606-608 (1998)

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2. Observations

HD 213637 was observed on seven nights during late July and early August 1997 using the Radcliffe Peoples Photometer attached to the 0.75-m telescope of the South African Astronomical Observatory at Sutherland. Our observations comprised continuous 10-s integrations in Johnson B light with occasional interruptions for sky background measurements. No comparison stars were observed. Fig. 1 shows the light curve we obtained on night 26/27 July 1997, JD 2 450 656.

[FIGURE] Fig. 1. The Johnson B light curve of HD 213637 on night 26/27 July 1997.

The data where corrected for coincidence counting losses, sky background and extinction, respectively. Gradual extinction variations (T [FORMULA]  hr) were removed in the Fourier domain, as described by Martinez (1993). The data were finally binned to 40-s integrations and the times were converted to Heliocentric Julian Dates to an accuracy of [FORMULA]  day ([FORMULA] 1 s).

Table 1 is a journal of our observations. For each night it lists the Heliocentric Julian Date (HJD) of the first and last observation, the duration in hr, the number of 40-s integrations, and the standard deviation, [FORMULA], of the observations with respect to the mean for the night. The quantity [FORMULA] includes contributions from residual sky transparency variations, scintillation, photon statistics, as well as the actual variations in the star. Fig. 2 shows the Deeming (1975) Discrete Fourier Transform (DFT) for each light curve listed in Table 1, computed according to the prescription of Kurtz (1985). Inspection of this figure shows that the oscillations in HD 213637 are strongly modulated in amplitude on a night-to-night basis.


Table 1. Journal of observations of HD 213637.

[FIGURE] Fig. 2. Amplitude spectra of the Johnson B light curves of HD 213637. The frequency and amplitude scales are identical for all panels.

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© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998