Stellar Abundance Studies

The broad stellar abundance areas G-CLEF is designed to study are:

  • The primordial stellar mass function (IMF)
  • The first supernovae (SNe), their yields and explosion properties (energy, ejected mass, mixing)
  • The critical metallicity for transition from Pop III to Pop II
  • The role of reionisation on galactic evolution
  • The origin and evolution of the elements and the associated nucleosynthesis processes
  • The efficiency of gas mixing in the early Galaxy

Characterization of Metal Poor Stars

Metal poor stars in the local Universe (specifically the Milky Way halo) are the present-day fossils of the earliest phase of star and galaxy formation soon after the Big Bang. In their atmospheres, they preserve the chemical composition of their birth gas cloud which enables reconstruction of the first heavy element enrichment events by massive supernova that first lit up the universe. Additionally, abundance distributions of these elements as observed in the metal-poor stars today yield valuable information about the nature (e.g. mass, explosion energy) of these very first stars and in what environments were formed. This field is often referred to as near-field cosmology. Consequently, there have been extensive efforts focused on systematically finding the most metal-poor stars in the Milky Way and its dwarf satellite galaxies over the last two decades.

The dearth of stars at the lowest iron metallicities, which are the most valuable tracers of the first stars as stars with [Fe/H]<−4, is believed to be representative of the second or third generation of stars that have formed in the universe. Keller S. et al. (2014) had discovered that star SMSS J031300.36-670839.3 has an [Fe/H] ratio of <−7.1. However, no iron lines (in the 3500-3800A region) were detectable in an R~35,000, S/N~120, spectrum after an exposure time of 13 hours. The star has proved too faint and too metal-poor for currently available instrumentation and telescopes to measure these features.

With a resolution of up to 110,000, good sensitivity at blue wavelengths, and GMT’s large surface area (~380 square meters), G-CLEF is expected to identify iron lines and other low abundance elements in these old, dim stars.