- Erika Böhm‐Vitense 2006 PASP 118 419
- In the puzzle of the metallic line (Am) stars, there still seem to be missing pieces. While the “normal” A stars have elemental abundances close to solar, the classical Am stars show stronger absorption lines for most heavy elements in their spectra. Elements with ionization potentials that nearly agree with those of hydrogen or helium have reduced abundances. The Ca ii and Sc ii lines are especially weak. The Am stars have no ultraviolet emission lines. They are binaries that, with very few exceptions, have rotational velocities vsin i lower than 100 km s−1. Of the main‐sequence A stars, 20% to 30% are Am stars. Here we rediscuss previous suggestions that tried to explain the peculiar line strengths in the Am star spectra. In particular, we compare the well‐studied properties of Hyades A and Am stars in order to identify reasons that can or cannot explain the differences. We find that accretion of interstellar material by A stars with distorted magnetic fields, which are weaker than those in peculiar A (Ap) stars, has the best chance of explaining the main characteristics of the peculiar heavy‐element abundances in Am star photospheres. Charge‐exchange reactions also seem to be important.
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The United States Secretary of the Interior is the head of the United States Department of the Interior. The secretary and the Department of the Interior are responsible for the management and conservation of most federal land along with natural resources, leading such agencies as the Bureau of Land Management, the United States Geological Survey, Bureau of Indian Affairs and the National Park Service. The secretary also serves on and appoints the private citizens on the National Park Foundation Board. The secretary is a member of the United States Cabinet and reports to the president of the United States. The function of the U.S. Department of the Interior is different from that of the interior minister designated in many other countries.