Constraining Metallicity-dependent Mixing and Extra Mixing using [C/N] in Alpha-Rich Field Giants
Matthew Shetrone, Jamie Tayar, Jennifer A. Johnson, Garrett Somers, Marc H. Pinsonneault, Jon A. Holtzman, Sten Hasselquist, Thomas Masseron, Szabolcs Meszaros,… 展开作者
Matthew Shetrone, Jamie Tayar, Jennifer A. Johnson, Garrett Somers, Marc H. Pinsonneault, Jon A. Holtzman, Sten Hasselquist, Thomas Masseron, Szabolcs Meszaros, Henrik Jonsson, Keith Hawkins, Jennifer Sobeck, Olga Zamora, D. A. Garcia-Hernandez
Internal mixing on the giant branch is an important process which affects the evolution of stars and the chemical evolution of the galaxy. While several mechanisms have been proposed to explain this mixing, better empirical constraints are necessary. Here, we use [C/N] abundances in 26097 evolved stars from the SDSS-IV/APOGEE-2 Data Release 14 to trace mixing and extra mixing in old field giants with -1.7< [Fe/H] < 0.1. We show that the APOGEE [C/N] ratios before any dredge-up occurs are metallicity dependent, but that the change in [C/N] at the first dredge-up is metallicity independent for stars above [Fe/H] ~ -1. We identify the position of the red giant branch (RGB) bump as a function of metallicity, note that a metallicity-dependent extra mixing episode takes place for low-metallicity stars ([Fe/H] <-0.4) 0.14 dex in log g above the bump, and confirm that this extra mixing is stronger at low metallicity, reaching $Δ$ [C/N] = 0.58 dex at [Fe/H] = -1.4. We show evidence for further extra mixing on the upper giant branch, well above the bump, among the stars with [Fe/H] < -1.0. This upper giant branch mixing is stronger in the more metal-poor stars, reaching 0.38 dex in [C/N] for each 1.0 dex in log g. The APOGEE [C/N] ratios for red clump (RC) stars are significantly higher than for stars at the tip of the RGB, suggesting additional mixing processes occur during the helium flash or that unknown abundance zero points for C and N may exist among the red clump RC sample. Finally, because of extra mixing, we note that current empirical calibrations between [C/N] ratios and ages cannot be naively extrapolated for use in low-metallicity stars specifically for those above the bump in the luminosity function.
Measuring the alpha-abundance of subsolar-metallicity stars in the Milky Way's central half-parsec: testing globular cluster and dwarf galaxy infall scenarios
Evolution of Thermally Pulsing Asymptotic Giant Branch Stars V: Constraining the Mass Loss and Lifetimes of Intermediate Mass, Low Metallicity AGB Stars
Constraining the structure and formation of the Galactic bulge from a field in its outskirts. FLAMES-GIRAFFE spectra of about 400 red giants around (l,b)=(0°,-10°)
Constraining the original composition of the gas forming first-generation stars in globular clusters
通过使用被称为染色体图（ChM）的伪双色图，沿着球状星团（GC）的红巨星分支（RGB）解开不同的恒星星族是可能的。最有趣的发现之一是，所谓的第一代（1G）恒星，其特征是与其出生云相同的化学成分，在ChM中表现出扩展的序列。未解析的双星和氦或金属丰度的内部变化被认为可以解释这一现象。在这里，我们推导出高精度的哈勃空间望远镜测光的GC NGC 6362和NGC 6838，并建立他们的ChM。我们发现，1G的RGB和主序（MS）星表现出更广泛的ChM序列比第二代（2G）。即使在未演化的1G MS恒星中也有这种特征的证据，表明化学不均匀性在原始气体中留下了印记。我们引入了一个伪二等图来区分氦和金属丰度，并证明了恒星到恒星的金属丰度变化是扩展的1G序列的原因。相反，二进制文件提供了一个小的贡献的现象。我们估计55个GC中1G星的金属丰度变化范围从小于[Fe/H]~0.05到~0.30，与星团质量有一定的相关性。我们利用这些发现来约束多个种群的形成情景，表明它们在质量上与多代的发生是一致的。相比之下，2G恒星比1G恒星具有更均匀的铁含量，这一事实挑战了基于大质量1G恒星中处理的物质吸积到现有原恒星上的情况。
Carbon abundance in Small Magellanic Cloud planetary nebulae through Advanced Camera for Surveys prism spectroscopy: constraining stellar evolution at low metallicity
The SLoWPoKES Catalog of Low-mass Ultra-wide Binaries: A Cool Stars Resource for Testing Fundamental Properties and for Constraining Binary Formation Theory
凌日系外行星调查卫星（TESS）已经开始发现附近冷亮恒星周围最终会有数千颗系外行星。这些潜在的宿主恒星必须得到很好的理解，才能在个体和种群水平上准确地描述系外行星。我们使用来自Gaia DR 2，APOGEE，GALAH，RAVE，LAMOST的调查数据和SkyMapper的光度导出的恒星特性，列出了TESS候选目标列表中2，218，434颗恒星的化学运动学特性目录。我们计算了这些恒星的运动学薄盘、厚盘和晕成员概率，发现尽管大多数TESS目标位于薄盘中，但其中4%位于厚盘中，<1%位于晕中。我们样本中的TESS感兴趣对象也显示了来自薄盘、厚盘和晕的类似贡献，其中大部分在薄盘中。我们还探讨了金属丰度和[α/Fe]分布的每个银河系的组成部分，并表明，每个交叉匹配的调查表现出金属丰度和[α/Fe]分布函数，峰值从高到低的金属丰度和低到高的[α/Fe]从薄盘的晕。这个目录将有助于探索行星的出现率，除其他事项外，关于运动学，组件成员，金属丰度，或[阿尔法/铁]。
