J0023+0307: A Mega Metal-poor Dwarf Star from SDSS/BOSS

Aguado, D. S.; Allende Prieto, C.; González Hernández, J. I.; Rebolo, R.
Bibliographical reference

The Astrophysical Journal Letters, Volume 854, Issue 2, article id. L34, 4 pp. (2018).

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2
2018
Number of authors
4
IAC number of authors
4
Citations
48
Refereed citations
45
Description
Only a handful of stars have been identified with an iron abundance [Fe/H] <‑5, and only one at [Fe/H] <‑7. These stars have very large carbon-to-iron ratios, with {\boldsymbol{A}}({\boldsymbol{C}}) ∼ 7.0, most likely due to fallback in core-collapse supernovae, which makes their total metallicity Z much higher than their iron abundances. The failure to find population III stars, those with no metals, has been interpreted, with support from theoretical modeling, as the result of a top-heavy initial mass function. With zero or very low metal abundance limiting radiative cooling, the formation of low-mass stars could be inhibited. Currently, the star SDSS J1029+1729 sets the potential metallicity threshold for the formation of low-mass stars at {log}Z/{Z}ȯ ∼ -5. In our quest to push down the metallicity threshold we have identified SDSS J0023+0307, a primitive star with T eff = 6188 ± 84 K, and {log}g=4.9+/- 0.5, an upper limit [Fe/H] <‑6.6, and a carbon abundance A(C) < 6.3. We find J0023+0307 to be one of the two most iron-poor stars known, and it exhibits less carbon that most of the stars at [Fe/H] <‑5. Based on observations made with William Herschel Telescope (WHT) and the Gran Telescopio de Canarias (GTC), at the Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in La Palma.
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