High-resolution spectroscopy of the central star of the Red-Rectangle nebula.

The authors have obtained high-resolution spectroscopic observations of HD 44179, the central star of the Red-Rectangle nebula and determined photospheric abundances, using standard LTE programs. The iron abundance is extremely low, with [Fe/H] between -3.2 and -3.5, but the CNO and S abundances are solar within an order of magnitude. The fact that carbon and/or helium are suprasolar in HD 44179 confirms the interpretation that this star is a low-mass object in an advanced stage of evolution, but the abundance pattern does not agree with theoretical expectation from AGB-nucleosynthesis. The abundance anomalies of HD 44179 are shared by four other objects, three of which are also known to display an infrared excess. The authors also report on some new optical emission features in the spectrum of the Red Rectangle.