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The nature of non-variable high-excitation emission lines detected in theoptical spectra of normal late-B type and chemically peculiar HgMn and PGastars is still poorly understood.  To better understand the origin of the weak emission lines in B type stars itis especially important to investigate the spectra of a variety of stars tosearch for correlations between the emergence of these lines and fundamentalstellar parameters.  We have acquired high resolution UVES spectra for the sharp-lined magnetichelium-variable star a Cen over the rotation period of 8.82 d to search for thepresence of weak emission lines.  For the first time we present observational evidence for the appearance ofvariable high-excitation Si II, Mn II and Fe II emission lines in a magnetic Bpstar. Si II emissions are the strongest at the phase corresponding to themaximum strength of He I lines. Mn II and Fe II emissions vary in antiphase tothe He I lines. A correlation is found between the probable location of Mn andFe surface spots and the strength of the emission lines. On the basis of thecurrently available data it seems possible that the same kind of selectiveexcitation process is working in the atmospheres of objects within a broadparameter space which could be defined by age, effective temperature, chemicalcomposition, rotational velocity, and magnetic field. Neutral iron linespreviously reported to appear broad and shallow at certain phases are notdetected in our spectra, although two of them are identified as He I forbiddenlines, showing maximum strength at the phase of the passage of the He richregion across the visible disk.Comment: 5 pages, 6 figures, 1 table, accepted for publication in A&

Detection of variable Si II, Mn II, and Fe II emission lines in the magnetic Bp star a Centauri