Elemental abundances across cosmic time

Chemical Abundances over Cosmic Time

It has recently become possible to measure directly the abundances of several chemical elements in a variety of environments at redshifts up to z 4. In this review I summarise the latest observations of Lyman break galaxies, the Lyman alpha forest and damped Lyman alpha systems with a view to uncovering any clues which these data may offer to the first episodes of star formation. The picture wh...

Interstellar propagation of cosmic rays: analysis of the Ulysses primary and secondary elemental abundances

The purpose of this investigation is to study the validity of the “leaky box” propagationmodel and determine some of its parameters. The pathlength distributions and their energy dependencies are derived from measurements of secondary-toprimary abundance ratios. A special charged particle telescope carried on the Ulysses spacecraft has provided a complete separation of elements from hydrogen to...

Massive Black Holes across Cosmic Time Massive Black Holes across Cosmic Time

Neutrino Physics and the Primordial Elemental Abundances

Limits can be placed on nonstandard neutrino physics when big bang nucleosynthesis (BBN) calculations employing standard neutrino physics agree with the observationally inferred primordial abundances of deuterium (D), He, He, and Li. These constraints depend most sensitively on the abundances of D and He. New observational determinations of the primordial D and/or He abundances could force revi...

Elemental Abundances in PG 1159 Stars

The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usuallyhidden intershell region. Thus, the photospheric elemental abundances of these stars allow to draw conclusions about details of nuclear burning and mixing processes in the pre...