Erika Holmbeck

Hubble Postdoctoral Fellow


In a nutshell, I study some of the oldest stars in the Milky Way with high-resolution spectroscopy to obtain their chemical abundance signatures. Then, I run nucleosynthesis network simulations and compare their theoretical elemental yields with observations to place constraints on astrophysical events and nuclear data.

The r-process
The abundance of roughly half of the elements heavier than iron in the Solar System attribute their production to the rapid neutron-capture ("r-") process. Although first identified as an astrophysical production mechanism of the elements over sixty years ago, it wasn't until recently that a host site for the r-process was idenfied observationally: neutron star mergers. With one confirmed astrophysical environment for the r-process identified, many questions still remain: Do mergers account for the majority of r-process production over the history of the Galaxy? What is the extent of their elemental production?  Can mergers occur in dwarf galaxies and explain the observed r-process enrichment of some galaxies?

Kilonovae and metal-poor stars
With the rise of multi-messenger astronomy---reinvigorated by the same neutron-star merger detection in 2017---models of r-process production in merger sites can be put to the test by comparing modeled light curves with those associated with mergers. However, only one such merger-associated light curve exists. Not all hope is lost; another, less transient r-process observable exists: the chemical records of metal-poor stars. An r-process event occuring in the ancient history of the Galaxy would enrich its surrounding environment with a signature of its elemental production. Subsequent stars formed from that gas would show this signature in their photospheres. Nearly 100 metal-poor (low-iron) stars with imprints of the r-process have been found, notably through dedicated obsevational efforts by the R-Process Alliance (RPA), of which I am a Core member. These data are one of the primary observables for r-process studies, and questions surrounding the elemental production, extent, event rates, gas mixing, etc. of r-process sites must agree with observations of metal-poor stars.

Observation and theory
I use the observations of metal-poor stars to probe specific conditions of r-process sites, exploring how physical differences in the r-process environments manifest into unique elemental signatures.


Ph.D. Physics, University of Notre Dame (2020)
M.S. Physics, University of Notre Dame (2019)
B.S. Astrophysics, University of California, Los Angeles (2014)

Nuclear Astrophysics, Galactic Archaeology, Stellar Spectroscopy, Compact Object Mergers