I recently attended a conference on the Metal Poor Galaxy at Ringberg, hosted by Karin Lind. Here are my main takeaways from the conference.

  • NLTE and 3D effects are large in metal-poor stars, but hard to compute. You cannot add corrections linearly. If you have to pick only one, use NLTE (R. Collet).
  • We need more bright metal-poor calibration stars to realize the promise of seismology (and ages). Existing models do not work for metal-poor stars ([Fe/H] < -1.5) (S. Hekker and others).
  • While in practice it is hard to get ages of old stars, in principle the stellar evolution models are good enough to get 5% absolute ages (A. Weiss). Turning into CMDs is hard.
  • The horizontal branch can potentially improve the time resolution of old stellar population CMD ages by a factor of 2 or more (E. Tolstoy).
  • Neutron-capture elements are information-rich for understanding dwarf galaxies and the stellar halo, but we still do not quite agree on what produces these elements. Just adding neutron star mergers and AGB stars seems to be insufficient, there must be at least one other major source of these elements. (M. Eichler, E. Kirby, A. Skuladottir)
  • There are actually enough Fe-poor stars ([Fe/H] < -4) to do statistics of Pop III properties (e.g. mass). However, these stars need 3D/NLTE corrections for reliable comparisons to nucleosynthesis models. (A. Heger)
  • Unlike the halo, metal-poor bulge stars are still highly statistics limited. This is slowly changing with photometric surveys. The bulge might be a different population of stars than the halo (L. Howes).
  • A question raised: is it still interesting to continue to find/study the most Fe-poor stars? It’s clear these are a special class, but how representative are they?
  • Globular clusters contribute at least 5% of the halo (at the halo MDF peak), and possibly a lot more depending on the theory of GC formation. (S. Martell)
  • It is hard to separate metal-weak kinematics into components (a large discussion on Gaia-Enceladus, high/low alpha sequences, disk vs halo). Neutron-capture elements seem useful here.
  • Big stellar surveys (Gaia, ground-based multifiber spectroscopy, TESS/plato, etc) are extremely exciting for studying stars and our galaxy. Understanding and mitigating survey systematics is an entirely different skill that requires deep knowledge of both statistics, data gathering, and stellar physics (A. Korn)
  • The immediately upcoming generation of stellar surveys will cover all stars with low-resolution spectroscopy. High-resolution followup will be the bottleneck in 10 years (N. Christlieb).