A legacy sample of Red Giant stars for Galactic Archaeology: joining asteroseismology, spectroscopy and Gaia data

银河考古学是研究银河系如何形成和演化的学科，它强烈依赖于基本恒星属性的质量，如距离，质量，年龄和化学成分。红巨星是银河系研究的关键目标，这要归功于它们的数量和内在亮度，这使得我们可以对银河系的不同组成部分进行采样，例如光晕，薄盘和厚盘以及凸起。红巨星的质量、年龄和化学成分都有很大的不同，因此它们是正在进行的和未来的大型银河系光谱调查的主要目标。然而，直到最近，红巨星作为银河系考古学工具的实用性受到了严重的限制，原因有两个：i）难以确定精确的恒星表面重力log（g），这影响了元素丰度的确定，因为两者是严格耦合的; ii）当用等时线拟合的经典方法确定年龄时，年龄的不确定性很大，约为~ 80%。银河系化学动力学演化的现代复杂模型需要更严格的观测约束。我们如何达到更好地理解银河系及其形成和演化所需的精度？随着星震学的出现，情况发生了重大变化：星震学可以用来以10%的精度限制恒星质量，从而使年龄的精度达到30%，它提供的log（g）精度为0.01 dex，比经典的光谱分析要好10倍。我们已经成功地开发了一种方法和工具，将联合收割机星震学和光谱学结合起来：i）光谱分析流水线，其迭代地使用地震重力，和ii）一个贝叶斯工具的质量和年龄确定相结合的精确大气参数从光谱和盖亚数据输入的小行星地震量。我们在这里提出了一个项目，应用我们的方法来构建一个样本的红巨星，精确的距离，质量，年龄和元素丰度：红巨星遗产样本。我们已经获得了完成该项目所需的所有数据：来自各种调查的光谱以及成功的观测建议（GES，APOGEE，RAVE和ESO设施）和来自不同空间任务（CoRoT，Kepler，K2，TESS）的地震数据。所有这些数据都将使用我们的工具以均匀的方式进行分析。这个前所未有的样本将探测银河系的不同区域，特别是我们将提供对光环和凸起的独特见解。作为最后一步，遗留样品将被用作校准和学习样品，用于未来的大型光谱调查（如4 MOST）的数据驱动分析。

Galactic Archaeology, the discipline that investigates how the Milky Way has formed and evolved, strongly depends on the quality of fundamental stellar properties as distances, masses, ages, and chemical composition. Red giant stars are key targets for Galactic studies, thanks to their large number and intrinsic brightness, that allow to sample different components of our Galaxy, such as the Halo, the Thin and the Thick disc, and the Bulge. They cover a wide range in mass, age, and chemical composition and they are therefore the main targets of ongoing and future large Galactic spectroscopic surveys.Until very recently, however, the usefulness of red giants as tools for Galactic Archaeology was severely limited for two reasons: i) the difficulty in determining a precise stellar surface gravity, log(g), which affects the element abundances determination, since the two are strictly coupled; ii) the large uncertainty on the age, of about ~80%, when it is determined with the classical method of isochrone fitting. The modern, sophisticated models of the chemo-dynamical evolution of the Galaxy need much more stringent observational constraints. How do we reach the precision that is required to better understand the Milky Way and its formation and evolution?With the advent of asteroseismology, the situation has changed significantly: asteroseismology can be used to constrain stellar mass with a precision of 10%, leading to a precision of 30% in age, and it provides log(g) with a precision of 0.01 dex, ten times better than what can be achieved with the classic spectroscopic analysis. We have successfully developed both a method and the tools to combine asteroseismology and spectroscopy: i) a spectroscopic analysis pipeline that uses iteratively the seismic gravity, and ii) a Bayesian tool for mass and age determination that combines asteroseismic quantities with the precise atmospheric parameters from spectroscopy and Gaia data as input.We propose here a project that applies our approach for constructing a sample of red giant stars with precise distances, masses, ages, and element abundances: the red giant legacy sample. We have already secured all the data for the completion of the project: spectra coming from various surveys plus successful observing proposals (GES, APOGEE, RAVE and ESO facilities) and seismic data coming from different space missions (CoRoT, Kepler, K2, TESS). All these data will be analysed in a homogeneous way using our tools. This unprecedented sample will probe different regions of the Galaxy, in particular we will provide a unique insight into the Halo and the Bulge. As final step, the legacy sample will be used as calibration and learning sample for data-driven analysis by future, large spectroscopic survey such as 4MOST.