![cover image](https://wikiwandv2-19431.kxcdn.com/_next/image?url=https://upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Tinsley_Wallerstein_Diagram.png/640px-Tinsley_Wallerstein_Diagram.png&w=640&q=50)
(α/Fe) versus (Fe/H) diagram
Graph used in astrophysics / From Wikipedia, the free encyclopedia
The [α/Fe] versus [Fe/H] diagram refers to the graph, commonly used in stellar and galactic astrophysics. It shows the logarithmic ratio number densities of diagnostic elements in stellar atmospheres compared to the solar value. The x-axis represents the abundance of iron (Fe) vs. hydrogen (H), that is, [Fe/H]. The y-axis represents the combination of one or several of the alpha process elements (O, Ne, Mg, Si, S, Ar, Ca, and Ti) compared to iron (Fe), denoted as [α/Fe].
![The diagram shows the iron abundance on the x-axis and the abundance of alpha process elements on the y-axis.](http://upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Tinsley_Wallerstein_Diagram.png/640px-Tinsley_Wallerstein_Diagram.png)
These diagrams enable the assessment of nucleosynthesis channels and galactic evolution in samples of stars as a first-order approximation. They are among the most commonly used tools for Galactic population analysis of the Milky Way. The diagrams use abundance ratios normalised to the Sun, (placing the Sun at (0,0) in the diagram). This normalisation allows for the easy identification of stars in the Galactic stellar high-alpha disk (historically known as the Galactic stellar thick disk), typically enhanced in [α/Fe], and stars in the Galactic stellar low-alpha disk (historically known as the Galactic stellar thin disk), with [α/Fe] values as low as the Sun. Furthermore, the diagrams facilitate the identification of stars that are likely born in times or environments significantly different from the stellar disk. This includes metal-poor stars (with low [Fe/H] < -1), which likely belong to the stellar halo or accreted features.[1]