V 1162 Ori: A multiperiodic delta Scuti star with variable period and amplitude

We present the results of multisite observations of the delta Scuti star V1162 Ori. The observations were done in the period October 1999 - May 2000, when 18 telescopes at 15 observatories were used to collect 253 light extrema during a total of 290 hours of time-series observations. The purpose of the observations was to investigate amplitude and period variability previously observed in this star, and to search for low-amplitude frequencies. We detect, apart from the main frequency and its two first harmonics, four additional frequencies in the light curves, all with low amplitudes (1-3 mmag). Combining the present data set with data obtained in 1998-99 at ESO confirms the new frequencies and reveals the probable presence of yet another pulsational frequency. All five low-amplitude frequencies are statistically significant in the data, but at least one of them (f(5)) suffers from uncertainty due to aliasing. Using colour photometry we find evidence for a radial main frequency (f(1)), while most or all low-amplitude frequencies are likely non-radial. We show that the main frequency of V1162 Ori has variable amplitude and period/phase, the latter is also displayed in the O-C diagram from light extrema. The amplitude variability in our data is cyclic with a period of 282 d and a range of nearly 20 mmag, but earlier amplitude values quoted in the literature cannot be explained by this cyclic variation. O-C analysis including data from the literature show that the period of V1162 Ori displays a linear period change as well as sudden or cyclic variations on a time scale similar to that of the amplitude variations.