The Lanthanide Elements in Stellar and Laboratory Spectra

The lanthanide elements (Z=57?71) are characterized by the filling of the 4f electronic subshell, which lies close in energy to the 5d and 6s subshells. As a result, the lanthanide spectra can be quite complicated in terms of the number of optical spectral lines, and in some cases their hyperfine structure and isotopic shifts are extremely large. These characteristics have great implications for astronomical investigations. We first review the stellar environments in which study of the lanthanides is important. These include the sun, chemically peculiar stars, and the oldest, most metal-deficient stars of the galaxy. We then touch on laboratory efforts directed at improving atomic data useful in analyzing astronomical spectra, in particular regarding wavelengths, line structure and line strength. Special emphasis is placed on the first three spectra of these elements and a reference list of laboratory analyses is provided.