abunds

Abunds is a shorthand plural used in some astronomy and astrophysics contexts to refer to chemical abundances measured in astronomical objects such as stars, galaxies, and the interstellar medium. It is not a formal term with a strict definition in all dictionaries, and its exact usage can vary by dataset or author. In practice, abunds denote a collection of abundance values—either for multiple elements within a single object or for a given element across many objects.

Chemical abundances are typically expressed relative to hydrogen or relative to the Sun. Common notations include [X/H], which compares the abundance of element X to its solar value, and [X/Fe], which compares X to iron. An alternative format is the absolute scale 12 + log10(N_X/N_H), where N_X and N_H are number densities. Solar abundances serve as a reference point for metallicity and chemical-evolution studies, and abunds often accompany uncertainties and correlation information in catalogs.

Measurement methods rely on spectroscopy. Stellar abundances are inferred from absorption lines in stellar atmospheres, while gas-phase abundances in H II regions and galaxies are derived from emission lines. Analyses typically involve model atmospheres and may include corrections for non-local thermodynamic equilibrium (NLTE) effects and three-dimensional structure, as well as considerations of dust depletion in the interstellar medium.

Applications of abunds include tracing the chemical evolution of galaxies, constraining nucleosynthesis yields, dating stellar populations, and testing models of galaxy formation. Limitations arise from systematic uncertainties, choice of solar reference scale, line blending, NLTE and 3D effects, and, for the ISM, depletion of elements onto dust grains. See also chemical abundance, metallicity, and stellar spectroscopy.