Stellar archaeology: Exploring the Universe with metal‐poor stars

Abstract

The abundance patterns of the most metal-poor stars in the Galactic halo and small dwarf galaxies provide us with a wealth of information about the early Universe. In particular, these old survivors allow us to study the nature of the first stars and supernovae, the relevant nucleosynthesis processes responsible for the formation and evolution of the elements, early star-and galaxy formation processes, as well as the assembly process of the stellar halo from dwarf galaxies a long time ago. This review presents the current state of the field of "stellar archaeology" -the diverse use of metal-poor stars to explore the high-redshift Universe and its constituents. In particular, the conditions for early star formation are discussed, how these ultimately led to a chemical evolution, and what the role of the most iron-poor stars is for learning about Population III supernovae yields. Rapid neutron-capture signatures found in metal-poor stars can be used to obtain stellar ages, but also to constrain this complex nucleosynthesis process with observational measurements. Moreover, chemical abundances of extremely metal-poor stars in different types of dwarf galaxies can be used to infer details on the formation scenario of the halo and the role of dwarf galaxies as Galactic building blocks. I conclude with an outlook as to where this field may be heading within the next decade. A table of ∼ 1000 metal-poor stars and their abundances as collected from the literature is provided in electronic format.

Are ancient dwarf satellites the building blocks of the Galactic halo?

“…In particular, the data we use for Galactic halo stars are from Gratton et al (2003), Cayrel et al (2004), Akerman et al (2004), Mashonkina, Korn & Przybilla (2007) and Shi et al (2009). For Ba, we use the data of Frebel (2010), as selected and binned by Cescutti et al (2013).…”

The Carina Project

“…For a detailed comparison with field halo stars, the large sample of elemental abundances compiled by Frebel (2010) is shown as purple dots. These abundances are based on high-resolution spectra of field stars of all evolutionary stages.…”

Tracing the Evolution of High-Redshift Galaxies Using Stellar Abundances

“…We compare our results to the limited set of elemental-abundance ratios ([Mg/Fe], [C/Fe]) determined for the large sample of low-resolution stellar spectra from the SEGUE database (Yanny et al 2009)and to the much smaller sample of metal-poor stars with available high-resolution spectroscopic elemental-abundance ratios assembled by Frebel (2010). Figure 3,with observational data from SEGUE (Yanny et al 2009) and Frebel (2010) overplotted in red and yellow, respectively. Data from these sources havebeen binned in 0.25 dex increments in [Fe/H], with the stellar number weighted mean plotted as a continuous line, the 68% confidence interval shown as thick lines, and the minimum and maximum extentsshown as thin lines.…”

“…We consider a range of model inputs, including a haloʼs chemically enriched SFE, the escape fraction of H 2 -photodissociating LW photons, the choice of IMF fitting function, and the choice of nucleosynthetic abundances that are put into the SSPs. We compare our model outputs to two observational data sets:the SEGUE stellar sample (Yanny et al 2009)and also a sample of several hundred metal-poor stars with detailed abundances compiled by Frebel (2010). Our primary results are as follows:…”

“…The interpretation of these data will require a model that incorporates as many relevant physical processes as possible while still maintaining computational efficiency. We are currently able to compare to observational data from SEGUE (Yanny et al 2009) and the high-resolution stellar abundance measurements collected by Frebel (2010). We make quantitative comparisons between our model and observations, allowing for constraints on model parameters such as the nature of the stellar initial mass function (IMF), the efficiency with which gas forms stars, and the accuracy of theoretical stellar yields.…”