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

银河系考古学是一门研究银河系如何形成和演化的学科，它强烈依赖于恒星基本性质的质量，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固有亮度，这使得我们可以采样我们银河系的不同成分，如光晕、薄盘和厚盘，以及凸起。红巨星的质量、年龄和化学成分范围很广，因此是目前和未来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工具的有效性受到严重限制，原因有两个：i)很难确定精确的恒星表面重力log(G)，这会影响元素丰度的测定，因为两者是严格耦合的；ii)用经典的等时线拟合法确定年龄时，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，情况发生了显著变化：星震学可以用来约束恒星质量，精度为10%，导致年龄的精度为30%，它为log(G)提供了0.01Dex的精度，比经典光谱分析的精度高出10倍。我们已经成功地开发了一种方法和工具来结合星震学和光谱学：i)迭代使用地震重力的光谱分析管道，以及ii)用于确定质量和年龄的贝叶斯工具，该工具结合了来自光谱和GAIA数据的精确大气参数作为输入。我们在这里提出了一个项目，该项目应用我们的方法来构建具有精确距离、质量、年龄和元素丰度的红巨星样本：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：来自各种勘测的光谱加上成功的观测建议(GES、远地点、RAVE和ESO设施)以及来自不同空间飞行任务(CoRoT、开普勒、K2、TESS)的地震数据。所有这些数据都将使用我们的工具以统一的方式进行分析。这一史无前例的样本将探测银河系的不同区域，特别是我们将提供对光晕和凸起的独特洞察。作为最后一步，遗留样本将被用作校准和学习样本，用于未来4MOST等大型光谱调查的数据驱动分析。

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.