First high-precision differential abundance analysis of extremely metal-poor stars

Autor(es)

Reggiani, Henrique ^[1] ; Melendez, Jorge ^[1] ; Yong, David ^[2] ; Ramirez, Ivan ^{[3, 4]} ; Asplund, Martin ^[2]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Insituto Astron Geofis & Ciencias Atmosfer, Dept Astron, IAG, Rua Matao 1226, Cidade Univ, BR-05508900 Sao Paulo, SP - Brazil

^[2] Australian Natl Univ, Res Sch Astron & Astrophys, Weston, ACT 2611 - Australia

^[3] Univ Texas Austin, Dept Astron, Austin, TX 78712 - USA

^[4] Univ Texas Austin, McDonald Observ, Austin, TX 78712 - USA

• Tipo de documento: Artigo Científico
• Fonte: Astronomy & Astrophysics; v. 586, FEB 2016.
• Citações Web of Science: 9

Resumo

Context. Studies of extremely metal-poor stars indicate that chemical abundance ratios {[}X/Fe] have a root mean square scatter as low as 0.05 dex (12%). It remains unclear whether this reflects observational uncertainties or intrinsic astrophysical scatter arising from physical conditions in the interstellar medium at early times. Aims. We measure differential chemical abundance ratios in extremely metal-poor stars to investigate the limits of precision and to understand whether cosmic scatter or observational errors are dominant. Methods. We used high-resolution (R similar to 95 000) and high signal-to-noise (S/N = 700 at 5000 angstrom) HIRES/Keck spectra to determine high-precision differential abundances between two extremely metal-poor stars through a line-by-line differential approach. We determined stellar parameters for the star G64-37 with respect to the standard star G64-12. We performed EW measurements for the two stars for the lines recognized in both stars and performed spectral synthesis to study the carbon abundances. Results. The differential approach allowed us to obtain errors of sigma(T-eff) = 27 K, sigma(log g) = 0 : 06 dex, sigma({[}Fe/H]) = 0.02 dex and sigma(v(t)) = 0 : 06 km s(-1). We estimated relative chemical abundances with a precision as low as sigma({[}X/Fe]) approximate to 0 : 01 dex. The small uncertainties demonstrate that there are genuine abundance differences larger than the measurement errors. The observed Li difference cannot be explained by the difference in mass because the less massive star has more Li. Conclusions. It is possible to achieve an abundance precision around approximate to 0 : 01 0 : 05 dex for extremely metal-poor stars, which opens new windows on the study of the early chemical evolution of the Galaxy. (AU)

• Processo FAPESP: 10/50930-6 - Evolução química e populações estelares galácticas e extragalácticas, por espectroscopia e imageamento
• Beneficiário: Beatriz Leonor Silveira Barbuy
• Linha de fomento: Auxílio à Pesquisa - Temático
• Processo FAPESP: 12/24392-2 - Espectroscopia de alta precisão: impacto no estudo de planetas, estrelas, a galáxia e cosmologia
• Beneficiário: Jorge Luis Melendez Moreno
• Linha de fomento: Auxílio à Pesquisa - Temático