F Stars Definition

Stars of spectra type F have surface temperatures between 6100 and 7400 K on the main sequence, but the giants and the supergiants are about 300K cooler.

F Stars Description

F dwarfs range in mass from about 1.2 to 1.7 times solar mass, but most of the giants and supergiants have evolved from considerably higher mass stars. The great majority of F stars have chemical compositions very similar to the sun’s. The cool end of the peculiar A stars, however, just reaches into the F star range, producing Fp stars, and the oldest (pop II) dwarf stars have low metal abundances, which give them an F subdwarf classification. The coolest F stars are slow rotators, but the hottest F dwarfs rotate as fast as the A stars. Canopus F0Ib, Procyon F5IV.

As many as 303 or more stars of spectral type "F" (not including white dwarf stellar remnants) are currently believed to be located within 100 light-years or (or 30.7 parsecs) of Sol. Only around 37 are located within 50 light-years (ly), while some 265 are estimated to lie between 50 and 100 light-years -- a volume of space that is seven times as large as the inner sphere within 50 ly of Sol. A comparison of the density of F-type stars between the two volumes of space indicates that the outer spherical shell has nearly 103 percent of the spatial density of known F-type stars as the inner spherical volume, which suggests that astronomers have identified virtually all of the F-type stars that are actually located within 100 ly of Sol, assuming the same spatial distribution in the Solar neighborhood.

Of those three hundred some F-type stars, astronomers believe that five have evolved out of the main sequence into giant stars, while an additional 82 or so may be subgiants (more on nearby giants and subgiants). As many as eight F-type stars have been identified as being located in Sol's immediate neighborhood (within 10 parsecs or 32.6 light-years): Procyon A, Pi3 Orionis, Chi Draconis A, Alula Australis Aa, Zeta Tucanae, Gamma Leporis A, Beta Comae Berenices, and Gamma Pavonis. Due in part to their relatively proximity and abundance, many F-type stars can be seen with the naked eye in Earth's night sky. As of October 2005, astronomers have been able to detect the presence of planets around only seven F-type stars -- or 2.3 percent -- of those 301 stars located within 100 light-years of Earth, although many may have been searching primarily around the late F, G, and early K stars (that are most hospitable to Earth-type life) until years.

Compared to hotter and brighter OBA type stars, F ang G type stars radiate more light towards the infrared end of the spectrum. Main-sequence F stars have surface temperatures of 5,950 to 7,100 K and luminosities of two to 6.5 times that of Sol's. F-type dwarf stars appear to have between 1.1 to 1.5 Solar-masses, which indicates that these stars may spend from seven to as few as three billion years in the main sequence fusing core hydrogen. Canopus is a prominent example of an F-type supergiant, which has eight to nine Solar-masses and a luminosity up to around 15,000 times that of the Sun.

For F-type stars, the spectral lines of neutral atoms are weak relative to those of ionized atoms. Moreover, hydrogen lines are not as strong as those in A-type stars. Spectral lines show calcium (Ca) II absorption, and neutral and singly ionized, metallic lines become noticeable.

Main sequence stars have internal zones which are either convective or radiative. Massive stars (with "several" Solar masses) are convective deep in their cores, and are radiative in their outer layers. By comparison, low mass stars (Sol-type F and G and cooler stars) have convective outer layers and radiative cores. Intermediate mass stars (i.e., spectral type A) may be radiative throughout.

F class main sequence stars are brighter and shorter lived than the Sun. Their hydrogen lasts for about a billion years.
Like A and G stars, they pass through a series of Red Giant phases. Their spent cores become White Dwarfs.

F Stars Variability/Peculiarity