Composite spectra: XVIII HR 6497, a triple system containing a baffling double secondary

We present a full description of, and parameters for, the component stars in the triple‐lined composite‐spectrum system HR 6497. Both the outer and the inner orbits have already been computed with fair accuracy, but the improved orbits resulting from this new analysis have precisions that are up to an order of magnitude tighter. By applying the proven technique of spectral subtraction to a large sample of new, high‐quality spectra we separate the spectra of the inner pair cleanly for the first time, and show that it has characteristics which cannot be explained at all easily by conventional models. Since the inner pair are separated by only 4 times their own radii, we expect their rotations to be synchronized to their orbital revolution, or close to 28 km/s, but in fact they have almost no visible rotation at all. The Mg II line at λ 4481 Å, itself a close doublet with a separation of 0.2 Å, is clearly resolved in the spectra of both components of the inner system. Such resolution is extremely rare in our experience, and we are unable to suggest a satisfactory explanation for it (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)