The SkyMapper DR1.1 Search for Extremely Metal-Poor Stars

Da Costa, G. S.; Bessell, M. S.; Mackey, A. D.; Nordlander, T.; Asplund, M.; Casey, A. R.; Frebel, A.; Lind, K.; Marino, A. F.; Murphy, S. J.; Norris, J. E.; Schmidt, B. P.; Yong, D.

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The SkyMapper DR1.1 Search for Extremely Metal-Poor Stars

MPS-Authors

Da Costa, G. S.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Bessell, M. S.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Mackey, A. D.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Nordlander, T.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Asplund, M.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Casey, A. R.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Frebel, A.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Lind, K.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Marino, A. F.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Murphy, S. J.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Norris, J. E.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Schmidt, B. P.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Yong, D.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

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https://ui.adsabs.harvard.edu/abs/2019MNRAS.tmp.2195D
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Citation

Da Costa, G. S., Bessell, M. S., Mackey, A. D., Nordlander, T., Asplund, M., Casey, A. R., et al. (2019). The SkyMapper DR1.1 Search for Extremely Metal-Poor Stars. Monthly Notices of the Royal Astronomical Society, 2195.

Cite as: https://hdl.handle.net/21.11116/0000-0005-D16C-6

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.