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20. METAL-WEAK F-TYPE STARS

Two metal-weak stars with temperature types near to F8 are compared in this illustration with the F8 V standard star (HD 27808). Notice that while the hydrogen lines of these three stars are very similar in strength, indicating similar temperatures, the metallic-line spectrum in HD 22879 is noticeably weaker than in the solar-abundance standard star, while HD 19445 shows an extreme degree of metal-weakness. The degree of metal weakness can be expressed by a metallicity parameter; HD 22879 belongs to metallicity class "-2", while HD 19445 belongs to metallicity class "-4" on the system developed by Gray (1989).

Figure 19

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