Multiperiodic Line-profile Variability and a Tentative Ephemeris for Line-Emission Outbursts of the Be Star MU CEN
The bright Be star mu Cen was in 1995 and 1996 for 4 months each monitored with the high-resolution (20,000) fiber-linked echelle spectrograph HEROS covering the spectral range 345 - 862 nm. A thorough period analysis of the stellar absorption line profiles was performed. Thanks to the long time base line, the previously suspected 0.505- day period could be resolved into 3 distinct, closely spaced periods. The result was obtained both by applying CLEAN to the power spectrum of the flux in fixed wavelength bins of the line profiles and by Fourier analyses of the variability of the mode of various sets of stellar lines. The variations associated with all three periods are about the same and can be best described as a roughly sinusoidal low-order modulation of the line profiles. The variability extends over the entire line core. In stronger lines such as He I 667.8 or 587.6, significant power was also detected beyond the range of 1 v sin i. Qualitatively, low-order NRP g-modes of (different) high radial degree can readily serve as a possible interpretation. From the phases and mean amplitudes of the individual periods derived from the Fourier analysis of the line profile modes, the times of maximal amplitude superposition were re-constructed. These times are well correlated with the times of the observed increases of the emission line strength. Our current, crude model also provides the magnitude of the increases. This may lead to a revival of the notion of pulsationally-driven outbursts of Be stars.On an experimental basis, we have submitted a detailed forecast for the period March through August, 1997 for publication in the 1997 spring issue of the Be Star Ne wsletter. We shall attempt to compare new observations, that may be available by the time of the meeting, with our predictions.
A Half Century of Stellar Pulsation Interpretation
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