A Formation Timescale of the Galactic Halo from Mg Isotopes in Dwarf Stars

Autor(es)

Carlos, Marilia ^{[1, 2]} ; Karakas, Amanda I. ^[2] ; Cohen, Judith G. ^[3] ; Kobayashi, Chiaki ^[4] ; Melendez, Jorge ^[1]

Afiliação do(s) autor(es)

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

^[2] Monash Univ, Sch Phys & Astron, Monash Ctr Astrophys, Clayton, Vic 3800 - Australia

^[3] CALTECH, 1200 E Calif Blvd, MC 249-17, Pasadena, CA 91195 - USA

^[4] Univ Hertfordshire, Sch Phys Astron & Math, Ctr Astrophys Res, Coll Lane, Hatfield AL10 9AB, Herts - England

• Tipo de documento: Artigo Científico
• Fonte: ASTROPHYSICAL JOURNAL; v. 856, n. 2 APR 1 2018.
• Citações Web of Science: 1

Resumo

We determine magnesium isotopic abundances of metal-poor dwarf stars from the galactic halo, to shed light on the onset of asymptotic giant branch (AGB) star nucleosynthesis in the galactic halo and constrain the timescale of its formation. We observed a sample of eight new halo K dwarfs in a metallicity range of -1.9 < {[}Fe/H] < -0.9 and 4200 < T-eff(K) < 4950, using the HIRES spectrograph at the Keck Observatory (R approximate to 10(5) and 200 <= S/N <= 300). We obtain magnesium isotopic abundances by spectral synthesis on three MgH features and compare our results with galactic chemical evolution models. With the current sample, we almost double the number of metal-poor stars with Mg isotopes determined from the literature. The new data allow us to determine the metallicity when the Mg-26 abundances start to become important, {[}Fe/H] similar to -1.4 +/- 0.1. The data with {[}Fe/H] > -1.4 are somewhat higher (1-3 sigma) than previous chemical evolution model predictions, indicating perhaps higher yields of the neutron-rich isotopes. Our results using only AGB star enrichment suggest a timescale for formation for the galactic halo of about 0.3 Gyr, but considering also supernova enrichment, the upper limit for the timescale formation is about 1.5 Gyr. (AU)

• Processo FAPESP: 12/24392-2 - Espectroscopia de alta precisão: impacto no estudo de planetas, estrelas, a galáxia e cosmologia
• Beneficiário: Jorge Luis Melendez Moreno
• Modalidade de apoio: Auxílio à Pesquisa - Temático
• Processo FAPESP: 14/18100-4 - Populações estelares na Via Láctea: bojo, halo, disco e regiões de formação de estrelas; instrumentação para espectroscopia de alta resolução
• Beneficiário: Beatriz Leonor Silveira Barbuy
• Modalidade de apoio: Auxílio à Pesquisa - Temático