Chemical composition of stars
The chemical composition of a star is a very important piece of information when it comes to placing it within the HR diagram. Astronomers obtain this value from the color of the star, as this indicates the chemical elements absorbing lines of its spectrum. Through this we also have data about its temperature; For example, hotter stars have their atoms ionized (it is said to be ionized when due to heat the atoms lose their electrons). From this, data is obtained not only about the chemical elements, but also which ones are ionized due to the surface temperature of the star. It is worth mentioning that in the HR diagram, the temperature range covers between about 45,000~35,000 ºC (on the highest scale) and about 3,600~2,000 ºC (on the lowest scale). The main chemical compositions of each stellar type within the HR diagram are detailed here.
| Atoms of main spectral lines | Radiation color | Surface temperature | characteristic star | Luminosity (absolute mag.) |
|---|---|---|---|---|
| Helium, oxygen and ionized nitrogen; ionized and neutral helium lines. | ◉ | 35,000 - 40,000 °C | Cefei | -6.5 |
| Neutral helium, silicon, magnesium, oxygen, ionized nitrogen; some hydrogen. | ◉ | 11,000 - 35,000 °C | Warden | -1.5 |
| Metals (especially calcium) with intense streaks; hydrogen with faint streaks. | ◉ | 7,500 - 11,000 °C | Sirius | 1.5 |
| Metals (especially calcium) with weak streaks; hydrogen with intense stripes. | ◉ | 6,000 - 7,500 °C | Procyon | 3 |
| Potassium and ionized calcium; non-ionized metals; hydrogen (faint streaks) | ◉ | 5,100 - 6,000 °C | Sun | 5 |
| Non-ionized metals and ionized calcium (intense streaks); hydrogen (faint streaks). | ◉ | 3,600 - 5,100 °C | Arthur | 0 |
| Titanium oxide molecules; almost no hydrogen lines. | ◉ | 2,000 - 3,600 °C | Betelgeuse | -3 |
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