The distribution of the carbon abundances
as a function of the metallicity for these
stars is shown in Figure 4. The lower and
side panels show marginal distributions
for each quantity. The behavior is simi-
lar to that expected from high-resolution
spectroscopic samples, which makes this
subset important for two reasons: 1) as a
tool for target selection, and 2) to have an
independent estimate of quantities, such
as the fraction of carbon-enhanced metal-
poor stars as a function of [Fe/H], which is a
crucial observational constraint to Galactic
chemical evolution models.
What Have We Learned and
What's Next?
The objectives of such follow-up studies,
which can include Gemini Poor Weather ob-
servations, are two-fold: 1) build statistics of
metallicities and carbon abundances deter-
mined from medium-resolution spectros-
copy, which are crucial for studies of stellar
populations and formation of the Milky Way,
and 2) select interesting stars for further,
more targeted, high-resolution spectrosco-
py efforts. One effort that is feeding directly
from the Gemini data is called the "R-Process
Alliance" (RPA) — a multi-stage, multi-year
effort to provide observational, theoretical,
and experimental constraints on the nature
and origin of the astrophysical r-process
(rapid neutron-capture).
The parameters determined using the Gem-
ini spectra are extremely useful to tailor
target lists for the type of (high-resolution)
follow-up conducted by the RPA, and there
is already a study published based on an
extremely metal-poor star first identified at
Gemini (Cain et al., 2018). This star, J2005-
3057, shows enhancements in elements
formed by the r-process, such as europium,
iridium and thorium, among others. An-
other effort currently underway is gathering
April 2019
high-resolution data for the most carbon-
enhanced stars identified by Gemini and the
results are also promising. Collectively, these
discoveries help us paint a more cohesive
picture of how the Universe evolved chemi-
cally and how we can reshape our current
understanding of stellar evolution and gal-
axy formation. In the near future, such bright
stars will be perfect targets for high-resolu-
tion spectroscopic follow-up with GHOST,
which will be a great asset in pushing these
efforts forward.
Figure 4.
Carbon abundances,
A(C), as a function of the
metallicity, [Fe/H], for the
program stars observed
with Gemini. The side and
lower panels show the
marginal distributions for
each quantity.
References
Cain, M., Frebel, A., Gull, M., et al., The Astro-
physical Journal, 864: 43, 2018
Placco, V. M., Beers, T. C., Santucci, R. M., et al.,
The Astrophysical Journal, 155: 256, 2018
Placco, V. M., Santucci, R. M., Beers, T. C., et al.,
The Astrophysical Journal, 870: 122, 2019
Schlaufman, K. C., and Casey, A. R., The Astro-
physical Journal, 797: 13, 2014
Steinmetz, M., Zwitter, T., Siebert, A., et al., The
Astrophysical Journal, 132: 1645, 2006
Vinicius Placco is Research Assistant Professor at
the Department of Physics at the University of
Notre Dame and is located at Notre Dame, Indi-
ana. He can be reached at [email protected]
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