AN H-ALPHA OUTBURST IN THE B-EMISSION-LINE STAR HD-76534

We present the discovery of unusually rapid and strong variations in t he H alpha emission line of the emission line star HD 76534. Within tw o days, a strong emission line changed to photospheric absorption, whi le the line was in emission only two hours later. The observed timesca le is an order of magnitude shorter than has been observed before in B e-type stars. Two different scenarios that may be able to explain the observed behaviour are explored. The deduced mass loss rates are in ag reement with the mass ejection mechanism, that has been invoked to exp lain the H alpha outbursts of variable Be stars like lambda Eri and mu Cen. The fact however that the H alpha line profile appears to trace a steady-state circumstellar envelope is not in agreement with the exp ected variable emission from a disk-like structure which is being buil t up in a few days. In this paper, a new hypothesis is brought forward to take into account the sudden increase of H alpha in HD 76534, a ch ange in the ionizing continuum from the star which ionizes a different fraction of a steady state circumstellar envelope.