An F star is a white or yellowish-white star of spectral type F whose spectrum shows strong absorption lines of ionized calcium which are more prominent than the hydrogen lines. Moderately strong lines due to iron and other heavier elements are also in evidence. Main sequence F stars, of which Procyon is an example, have a surface temperature of 5,800 to 6,900 °C, a mass of 1.2 to 1.6 solar masses, and a luminosity of 2 to 6 times that of the Sun. Relatively nearby, late-type members of this category are generally included in the list of target stars for extrasolar planet searches and targeted SETI programs. F-type supergiants, of which Canopus and Polaris (the Pole Star) are examples, have a mass up to 12 solar masses and a luminosity up to 32,000 times that of the Sun.