GeminiFocus April 2019 - Page 8

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