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Metallicity: Fe/H
Dec. 21st, 2010 06:04 pmMany sources give a star’s metallicity as its Fe/H value rather than as a percentage of Sol’s. For the sake of convenience, when I find a metallicity, I give it here as a percentage, but if you’re doing research on your own, you should know how the Fe/H scale works.
Basically, it is logarithmic in nature. Sol has an arbitrary Fe/H number of zero, and you can figure out how metal-rich or poor a star is, compared to Sol, by raising 10 to the power of its Fe/H number.
So, for instance, let’s say a star has an Fe/H of 0.301. 10 to the power of 0.301 is exactly two, so that star is twice as enriched in metals as Sol.
If a star has an Fe/H of -0.22, 10 to the power of -0.22 is 0.6, so that star has only 60% of Sol’s metals.
You can calculate 10 to the power of a number by typing the number in to cell A1 of a Microsoft Excel spreadsheet, and then putting this formula in another cell: =10^a1. The caret mark is shift-6 on a standard keyboard.
Basically, it is logarithmic in nature. Sol has an arbitrary Fe/H number of zero, and you can figure out how metal-rich or poor a star is, compared to Sol, by raising 10 to the power of its Fe/H number.
So, for instance, let’s say a star has an Fe/H of 0.301. 10 to the power of 0.301 is exactly two, so that star is twice as enriched in metals as Sol.
If a star has an Fe/H of -0.22, 10 to the power of -0.22 is 0.6, so that star has only 60% of Sol’s metals.
You can calculate 10 to the power of a number by typing the number in to cell A1 of a Microsoft Excel spreadsheet, and then putting this formula in another cell: =10^a1. The caret mark is shift-6 on a standard keyboard.