Figure 3.
Example spectra for
25 stars with [Fe/H]
< -2.5 observed with
Gemini/GMOS (North
and South). The
shaded areas highlight
regions of interest for
the determination of
metallicity (blue - [Fe/H],
Ca II K absorption
feature), carbon
abundance (red - A(C),
CH G-band), and
temperature (green - T eff ,
hydrogen Balmer lines).
The spectra are ordered
by increasing values of
[Fe/H].
the already poor weather was lost, which is a
great accomplishment for the program and
the Observatory.
Scientific Gain from
Weather Loss
The spectra gathered at Gemini/GMOS are of
sufficient quality (signal-to-noise ratios and
spectral resolution) to allow for the deter-
mination of stellar atmospheric parameters:
effective temperature (T eff ), surface gravity,
metallicity ([Fe/H]), and carbon abundances
(A(C)). Figure 3 shows the GMOS spectra of
6
GeminiFocus
25 stars with [Fe/H] < -2.5 observed under
poor weather conditions. The shaded areas
highlight absorption spectral features used
to determine [Fe/H] (Ca II K absorption fea-
ture), A(C) (CH G-band), and T eff (hydrogen
Balmer lines). The values for each parameter
are also listed. From the 666 stars, metal-
licities could be determined for 656 (98%),
including 477 stars with [Fe/H] < -1.0 (73%),
285 stars with [Fe/H] < -2.0 (43%), and 9 stars
with [Fe/H] < -3.0 (including one at [Fe/H] =
-3.65). Carbon abundances were determined
for 653 stars.
April 2019