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G. M. Wahlgren (Lund Univ.), I. Ilyin (Oulu Univ.), O. Kochukhov (Uppsala Univ.)
The detection of spectral line profile variability for stars of the HgMn class of chemical peculiarity has been poorly documented in the literature yet holds a special significance for understanding relationships between observed spectral anomalies, stellar surface structure, and magnetic fields. The HgMn stars have until now not been confirmed to vary in their light or spectral characteristics in ways unattributable to binarity, as opposed to the classical Ap stars for which such variations are explainable by the magnetic oblique rotator model.
Alpha And (V = 2.1 mag, B8IVp HgMn) is a bright, prototypical HgMn star in a binary system of orbital period 96.8 days. Several authors have singled out this star as having line profile variations, but most of these reports are purely suggestive. We have made spectral observations of \alpha And during the observing seasons 1999, 2000, and 2001. The spectra were taken using resolving powers of R = 25000 and 80000, and were especially directed toward detection of variations in the line Hg II 3984 Å, for which Ryabchikova et al. (1999) note a possible variation. Radial velocity measurements of our data were used to enhance the binary orbital solution. From a periodogram of this Hg II line in our data a consistent peak is evident for a period of approximately 2.38 days, which we interpret to be the rotational period of the primary star. When all high resolution spectra are binned by phase according to this period the Hg II line profile displays an undulating nature with the line width at the continuum level not varying. Results from our Doppler image mapping show surface structures of a similar nature to those observed for magnetic Ap stars. We continue to analyse the spectra in a search for variability of other spectral lines, the direct determination of a magnetic field, and the characterization of the surface distribution of the elements.
The author(s) of this abstract have provided an email address for comments about the abstract: glenn.wahlgren@astro.lu.se