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UBC Theses and Dissertations

Discovery of a double binary and nonradial pulsations in the Be star omicron Andromedae Hill, Grant Michael


The multiple star system omicron Andromedae has been studied using high signal-to-noise ratio Reticon spectra. The narrow absorption features superimposed on the rotationally broadened Mg II ⋋ 4481 line of o And A are almost certainly from the spectrum of o And B which is shown to be a double-lined spectroscopic binary with a period of 33 days. The speckle interferometrically measured separations of A-a and A-B indicate that the system contains at least two binaries separated by some 25 AU, based on a parallax of 0.015 ± 0.008 arcseconds. Based on this parallax the A-a separation of is about 4 AU. The two stars which make up the unresolved spectroscopic binary o And B are separated by about 0.4 AU based on an orbital solution. The periods, based on the parallax and reasonable mass estimates, for A-a and Aa-B, are on the order of four and thirty years respectively. The two stars which constitute o And B are shown to most likely be late B stars of luminosity class V-IV. After compensating for the presence in the spectrum of a contribution from component B, o And A is reclassified as B5lIIe. The spectral type of o And a is not known and no contribution to the spectrum from it is observed. High signal-to-noise time series of spectra have revealed the presence of nonradial pulsations. An intermediate order, Ɩ = 6 mode, reveals itself through moving subfea-tures in the line profiles. Line width variations are detected which probably arise from an Ɩ = 2 low order mode. The co-existence of these two modes is capable of explaining the 1.57 day photometric variations. This period is twice that of the line width variations. Rapid radial velocity variations measured from the line wings were found but the line profile variations and the nature of the light curve do not support the existence of a fifth star. The measured radial velocity variations could be a result of the underlying profile variations as opposed to motion of o And A.

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