Author(s): , , ,
Institution(s): 1. Copenhangen University, 2. Heidelberg University, 3. University of Notre Dame
The outer atmosphere of the first generation of low-mass stars retain to a great extend the original composition of the interstellar medium at the time and place of their birth. Hence the earliest phases of Galactical chemical evolution and nucleosynthesis can be investigated by means of studying the old metal-poor stars. It has been recognized that a large fraction of metal-poor stars possess significant over-abundances of carbon relative to iron. These so-called carbon enhanced metal-poor (CEMP) stars ([C/Fe] > +0.7) make up ~30% of the stars with [Fe/H] < -3.0, and ~80% of the stars with [Fe/H] < -4.5. The CEMP stars can be divided into a number of sub-classes based on the behavior of their neutron-capture elements. At the lowest metallicity the CEMP-no stars, showing no over-abundance of neutron-capture elements, is the dominant sub-class, hence these stars are most likely associated with elemental-abundance patterns that were produced by the very first generation of massive stars to form in the Galaxy.
I will present the results of a 23-star homogeneously analyzed sample of metal-poor candidates from the Hamburg/ESO survey. We have derived abundances for a large number of elements ranging from Li to Pb, covering production processes from hydrostatic burning to neutron-capture. The sample includes four ultra metal-poor stars ([Fe/H] < -4.0), six CEMP-no stars, five CEMP-s stars, two CEMP-r stars and two CEMP-r/s stars. This broad variety of the sample stars gives us an unique opportunity to explore different abundance patterns at