A star of spectral type K, somewhat cooler than the Sun and appearing orange in colour. K-type stars on the main sequence have surface temperatures in the range 3900–5200 K, while giants are about 100–400 K cooler, and supergiants a few hundred degrees cooler still. Masses of main-sequence K stars are 0.5–0.8 solar masses, and their luminosities 0.1–0.4 times the Sun's. Giants are of 1.1–1.2 solar masses and have luminosities 60–300 times the Sun's, while K supergiants can be up to 13 solar masses and have luminosities as much as 40 000 times the Sun's. The dominant spectral features of K-type stars are the neutral metal lines of iron and titanium, with calcium (both Ca I and Ca II) being particularly strong. The molecular bands due to cyanogen (CN) and titanium oxide (TiO) strengthen considerably from K0 to K9. The best-known stars of this type are Arcturus, a K1 giant, and Aldebaran, a K5 giant.
Subjects: Astronomy and Astrophysics.