1996A&A...309..787S

We present results of nearly simultaneous monitoring of uvby light and He I 667.81 nm line-profile variations of the equatorial Be star DX Eri in November 1991. They are analysed along with numerous uvby photometry in the period 1986-1995. The brightness of DX Eri varies on three distinct time scales. The time scales of the rapid- and medium-term variations differ by a factor of ten and can only be separated if the time resolution is sufficiently high and if the phase is well covered. Our data meet these conditions on four observing seasons. The period of the rapid variation derived from data spanning almost ten years is 1.267080 d. Due to the complex nature of the variability, we cannot decide whether the period is secularly stable on a time scale of years or whether it varies within a few per cent from season to season. The light curve is slightly non-sinusoidal with a shallow light maximum at approximately 0.50P after light minimum. It has an average peak-to-peak amplitude of 0.08-0.10mag in all passbands. The u-b, c₁ and b-y indices vary with the same period but with amplitudes lower than 0.05mag and varying from season to season. The m₁ index is constant within the errors. The star is bluest in u-b near light maximum. The radial velocity (RV) of He I 667.81nm, as measured in the line wings, exhibits a sinusoidal variation with a period which is the same as the photometric period of 1.26d and with an amplitude of 42km/s. The first moment of the line profile has a somewhat lower amplitude and larger scatter. More data of better quality are needed to confirm the phase-dependent variations of equivalent width, FWHM and line depth of He I 667.81 nm. The shape of the RV curve differs significantly from the light curve. The RV minimum occurs at 0.20P and the maximum at 0.65P after light minimum. The light and low-order line-profile variations are compared with those of η Cen (Stefl et al., 1995). The observations are discussed in terms of non-radial pulsation, rotational modulation and binarity. None of these models is able to explain the observed light, colour and radial velocity amplitudes.