The Physics department colloquia are usually on Friday afternoons at 3 pm in Room 135. Coffee and cookies are served at 2:45 pm in the same room. Anyone is welcome.

Hunting the First Generations of Stars and Galaxies
Dr. Anna Frebel, Associate Professor, Dept. of Physics, Massachusetts Institute of Technology

The new Australian SkyMapper 1.3m telescope is carrying out a photometric survey of the entire Southern Sky. From using an ugriz filter plus an additionally narrow filter placed at the Ca K line at 3933 Å, stellar parameters can be obtained for all stars observed. This allows for an efficient selection of a variety of stellar types, including metal-poor stars. Recent efforts to search for the most metal-poor stars have indeed delivered a new record holder the the most iron-poor star: no iron lines were detected in the high-resolution follow-up Magellan spectrum and only an upper limit of [Fe/H]<-7.1 could be determined. Contrary to its iron deficiency, the star has a significant amount of carbon. This abundance pattern can be explained with the star being a second-generation star in the universe which formed from a gas cloud enriched by only one PopIII first star. What was the environment in which these early stellar generations formed? A spectro-scopic study of the faintest dwarf galaxy Segue 1 has shed light on this question. Given the chemical abundance patterns of some its only few stars (with metallicities ranging from -4<[Fe/H]<-1) suggest that this tiny galaxy may be a surviving first galaxy from the early universe.

This suggestion is in line with recent age measurements for similar ultra-faint dwarfs which showed these galaxies to be single-age stellar systems that are about as old as the universe itself.