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Spectroscopic Atlas for Amateur Astronomers 75

Table 31: Effect of the luminosity on spectra of the F-class: Porrima (γ Vir), Caph (β Cas) and
Mirfak (α Per).

Porrima (39 ly) is classified with F0V and is, like our Sun, a Dwarf on the Main Sequence of
the HRD. Its surface temperature is about 7,100 K and its apparent rotation speed remains
here unknown.

Caph (55 ly) is classified with F2 III-IV, thus moving from the Main Sequence to the Giant
Branch in the HRD. Its surface temperature is about 6,700 K. His apparent rotation speed is
reported by Kaler [506] with 70 km/s.

Mirfak (600 ly) is classified with F2 lb and therefore one of the Supergiants. The surface
temperature is about 6,180 K. The apparent rotation speed is reported with 18 km/s. Mir-
fak is a former Main Sequence Star of the B-Class [506].

The comparison of these three equally normalised spectra shows no striking differences
between the luminosity classes. A difference regarding the intensity and width of the
H-lines is here visually not recognisable. The metal lines of the Supergiant Mirfak are
somewhat more intensive than in the profile of the Giant Caph. Between Caph and the Main
Sequence Star Porrima differences are hardly discernible.