论文标题
R-Process增强的超生物矮星系网中的金属混合II
Metal Mixing in the R-Process Enhanced Ultra-Faint Dwarf Galaxy Reticulum II
论文作者
论文摘要
一个罕见且多产的R-Process事件丰富了超生物矮星系网状〜II。因此，网状〜II的R过程提供了一个独特的机会，可以在遗物第一星系中研究金属混合。使用VLT/长颈鹿和Magellan/M2FS的多对象高分辨率光谱法，我们在可能的情况下识别32个清晰的光谱构件星并测量MG，CA，FE和BA的丰度。我们发现$ 72^{+10} _ { - 12} $％的恒星是R-Process-hehanced，其平均$ \ weft \ langle \ langle \ mbox {[[ba/h]} \ right \ right \ rangle = -1.68〜 \ pm〜0.07 $ and Unlesolved intinsic $ nininsic $ ____________________________________________ { 0.20 $。同质的R过程丰度暗示RET〜II的金属在R-增强恒星形式的时间良好，模拟表明，这需要在恒星形成之间至少100 MYR的金属混合以均化。这是在超生物矮人银河系中爆发恒星形成的第一个直接证据。均质稀释更喜欢迅速而高收益的R过程，例如Collapsar磁盘或迅速中子星星合并。我们还发现[BA/H]和[mg/ca]的证据表明，在没有实质性原始气体积聚的情况下，RET〜II中的R-增强恒星可能表明$ {\} 70 $ {\} 70 $％的RET 〜II恒星的ret 〜II星形成后形成后形成后。
The ultra-faint dwarf galaxy Reticulum~II was enriched by a single rare and prolific r-process event. The r-process content of Reticulum~II thus provides a unique opportunity to study metal mixing in a relic first galaxy. Using multi-object high-resolution spectroscopy with VLT/GIRAFFE and Magellan/M2FS, we identify 32 clear spectroscopic member stars and measure abundances of Mg, Ca, Fe, and Ba where possible. We find $72^{+10}_{-12}$% of the stars are r-process-enhanced, with a mean $\left\langle\mbox{[Ba/H]}\right\rangle=-1.68~\pm~0.07$ and unresolved intrinsic dispersion $σ_{\rm [Ba/H]} < 0.20$. The homogeneous r-process abundances imply that Ret~II's metals are well-mixed by the time the r-enhanced stars form, which simulations have shown requires at least 100 Myr of metal mixing in between bursts of star formation to homogenize. This is the first direct evidence of bursty star formation in an ultra-faint dwarf galaxy. The homogeneous dilution prefers a prompt and high-yield r-process site, such as collapsar disk winds or prompt neutron star mergers. We also find evidence from [Ba/H] and [Mg/Ca] that the r-enhanced stars in Ret~II formed in the absence of substantial pristine gas accretion, perhaps indicating that ${\approx}70$% of Ret~II stars formed after reionization.
