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SkyMapper Publication
The SkyMapper DR1.1 Search for Extremely Metal-Poor Stars
Da Costa, G. S. et al., 2019, Monthly Notices of the Royal Astronomical Society, 2195 | View on ADS (2019MNRAS.tmp.2195D)
Abstract
We present and discuss the results of a search for extremely metal-poor stars based on photometry from data release DR1.1 of the SkyMapper imaging survey of the southern sky. In particular, we outline our photometric selection procedures and describe the low-resolution (R ≈ 3000) spectroscopic follow-up observations that are used to provide estimates of effective temperature, surface gravity and metallicity ([Fe/H]) for the candidates. The selection process is very efficient: of the 2618 candidates with low-resolution spectra that have photometric metallicity estimates less than or equal to -2.0, 41% have [Fe/H] ≤ -2.75 and only ̃7% have [Fe/H] > -2.0 dex. The most metal-poor candidate in the sample has [Fe/H] < -4.75 and is notably carbon-rich. Except at the lowest metallicities ([Fe/H] < -4), the stars observed spectroscopically are dominated by a `carbon-normal' population with [C/Fe]1D, LTE ≤ +1 dex. Consideration of the A(C)1D, LTE versus [Fe/H]1D, LTE diagram suggests that the current selection process is strongly biased against stars with A(C)1D, LTE > 7.3 (predominantly CEMP-s) while any bias against stars with A(C)1D, LTE < 7.3 and [C/Fe]LTE > +1 (predominantly CEMP-no) is not readily quantifiable given the uncertainty in the SkyMapper v-band DR1.1 photometry. We find that the metallicity distribution function of the observed sample has a power-law slope of ∆(Log N)/∆[Fe/H] = 1.5 ± 0.1 dex per dex for -4.0 ≤ [Fe/H] ≤ -2.75, but appears to drop abruptly at [Fe/H] ≈ -4.2, in line with previous studies.
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