Mon. Not. R. Astron. Soc., 489, 5900-5918 (2019/November-2)
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. and YONG D.
Abstract (from CDS):
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 per cent have [Fe/H] <= -2.75 and only approximately seven per cent 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]1D,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 Δ(Log N)/Δ[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.
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
stars: abundances - stars: Population II - Galaxy: halo - Galaxy: stellar content
VizieR on-line data:
<Available at CDS (J/MNRAS/489/5900): table1.dat table2.dat table3.dat>
Table 1: SDSS J1024+1201 is a misprint for SDSS J1204+1201 (SDSS J120441.38+120111.5).
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