# Intro - 'Metals' In astronomy, things typically operate differently - perhaps our forefathers had a power trip of their own while crafting the very fabric of the subject. As a result, the term "metals" - which you may have heard about before reading articles, has a completely different meaning in astronomy! For astronomers, "metallicity" refers to the **ratio** of anything heavier than hydrogen or helium in a star. It can be difficult to transition to using that; it can even leave you scarred for life, forever referring to oxygen as a metal - but it's a worthwhile one at that! ## Metals - Stellar Enrichment In the beginning, the four nations lived in harmony... Enough with that! Back to metallicity! In the beginning, there was only hydrogen and helium[^1], where clouds of gas floated in harmony. And all that changed when a gas cloud collapsed. Or something like that. With this cataclysmic event [[Stars (Astro)|stars]], [[Classifying Galaxies (Astro)|galaxies]], [[Black Holes (Astro)|black holes]], [[Basics of Neutron Stars (Astro)|neutron stars]], stellar processes - each and every single intricate process was kickstarted. In the cores of these [[Populations of Stars (Astro)#Population III|massive early stars]], quantities of hydrogen were fused into helium, then carbon, then oxygen, then silicon and finally iron. [^2] [^2]: There are intermediary steps, which you can learn about [[Fission and Fusion (Nuclear & Quantum)|here.]] [^1]: We're only taking the period *after recombination* here, if you insist. --> the amount of metals in a star will describe the composition of the initial interstellar cloud --> we can probe the evolution of stellar populations through checking metallicity and separate them into **populations!** stars might not be complete black bodies --> depends on the spectral type ## The Effects of Metallicity Stellar enrichment leads to interesting real world consequences - for starters, we can't Metallicity affects... --> star formation rate --> the interior of the star (all over) --> temperature of the star --> lifetime of the star --> mass loss rates during main sequence/red giant older stars will "dredge up" the products from their core, changing their surface composition! --> our sun can ionise metals into their second state --> diagram for reference, wavelength shows us the strength of the ionisation of metals within our star . ![[Pasted image 20230711093352.png]] metallicity effect on stellar isochrones. a metallicity power of -4 would mean a star that has 1/10000th of the metallicity of the Fe/H = 0. ![[Pasted image 20230711093518.png]] >[!Example]- Case Study - Epsilon Aurigae >Heard of Auriga? No? > >Epsilon Aurigae --> binary variable star (spectrum, brightness varies), primary = F supergiant, 67 day unstable brightness oscillation period >orbited by invisible dark object (significantly more massive than the star) >believed to be a cold cloud dusk/gas disk, with a B star or binary system embedded within it > ![[Pasted image 20230711094335.png]] # What's Next? There's not meant to be a set 'roadmap' for any of this so feel free to just go back to the main menu: [[Everything Astronomy]]