The pre-main-sequence star HD34282:: a very short-period δ Scuti-type pulsator

HD34282 has been found to pulsate during a systematic search for short-term photometric variability in Herbig Ae/Be stars with the goal of determining the position and size of the pre-main-sequence instability strip. Simultaneous Stromgren photometry is used in the frequency analysis, yielding two frequencies with values of nu(1) = 79.5 and nu(2) = 71.3 cycle d(-1). The light curve with the largest amplitude is that of the u band. This behaviour, which is not common for delta Scuti stars, is explained as pulsation in a high radial order in stars near the blue edge of the instability strip. The main period, with a value of 18.12 min, represents the shortest period observed so far for a Scuti-type pulsator. A seismic modelling, including instability predictions and rotation effects, has been attempted. It is found that both main-sequence and pre-main-sequence models predict modes in the range of 56 to 82 cycle d(-1) (between 648 and 949 muHz), corresponding to oscillations of radial order n from 6 to 8. The highest of the observed frequencies only becomes unstable for models of low metallicity, in agreement with results from spectroscopic measurements.