An F-type main-sequence star is a main-sequence, core-hydrogen-fusing star of spectral type F. The spectral luminosity class is . They have from around 1.1 to 1.6 times the mass of the Sun and surface temperatures between about 6,000 and . F-type stars appear white from space due to having a higher temperature than the Sun. Notable examples of F-type stars include Procyon A, Gamma Virginis A and B, and Tabby's Star.
Subdwarfs
There are subdwarf stars, that is stars of luminosity class VI, of spectral class F although these are much less common than G, K, and M subdwarfs. These stars are fusing hydrogen in their cores like normal main-sequence stars, but due to their low metallicity they lie up to two magnitudes below the main sequence (ie. less luminous).
Spectral standard stars
{| class="wikitable floatright" style="text-align:center; font-size:smaller;"
|+ Properties of typical F-type main-sequence stars
|-
!Spectral<br/>type
!Mass ()
!Radius ()
!Luminosity ()
!Effective<br/>temperature<br/>(K)
!Color<br/>index<br/>
|-
| F0V
| 1.60
| 1.728
| 7.31
| style="background-color:#"|7,220
| 0.30
|-
| F1V
| 1.50
| 1.679
| 6.17
| style="background-color:#"|7,020
| 0.33
|-
| F2V
| 1.43
| 1.622
| 5.13
| style="background-color:#"|6,820
| 0.37
|-
| F3V
| 1.41
| 1.578
| 4.66
| style="background-color:#"|6,750
| 0.39
|-
| F4V
| 1.38
| 1.533
| 4.19
| style="background-color:#"|6,670
| 0.41
|-
| F5V
| 1.32
| 1.473
| 3.60
| style="background-color:#"|6,550
| 0.44
|-
| F6V
| 1.25
| 1.359
| 2.70
| style="background-color:#"|6,350
| 0.49
|-
| F7V
| 1.21
| 1.324
| 2.45
| style="background-color:#"|6,280
| 0.50
|-
| F8V
| 1.16
| 1.221
| 1.96
| style="background-color:#"|6,180
| 0.53
|-
| F9V
| 1.12
| 1.167
| 1.64
| style="background-color:#"|6,050
| 0.56
|}
The revised Yerkes Atlas system (Johnson & Morgan 1953) listed a dense grid of F-type dwarf spectral standard stars; however, not all of these have survived to this day as stable standards.
The anchor points of the MK spectral classification system among the F-type main-sequence dwarf stars, i.e. those standard stars that have remained unchanged over years and can be used to define the system, are considered to be 78 Ursae Majoris (F2 V) and Pi Orionis (F6 V). In addition to those two standards, Morgan & Keenan (1973) considered the following stars to be dagger standards: HR 1279 (F3 V), HD 27524 (F5 V), HD 27808 (F8 V), HD 27383 (F9 V), and Beta Virginis (F9 V).
Other primary MK standard stars include HD 23585 (F0 V), HD 26015 (F3 V), and HD 27534 (F5 V). Note that two Hyades members with almost identical HD designations (HD 27524 and HD 27534) are both considered strong F5 V standard stars, and indeed they share nearly identical colors and magnitudes.
Gray & Garrison (1989) provide a modern table of dwarf standards for the hotter F-type stars. F1 and F7 dwarf standards stars are rarely listed, but have changed slightly over the years among expert classifiers. Often-used standard stars in this class include 37 Ursae Majoris (F1 V) and Iota Piscium (F7 V). No F4 V standard stars currently have been officially published.
F9 V defines the boundary between the hot stars classified by Morgan, and the cooler stars classified by Keenan a step lower, and there are discrepancies in the literature on which stars define the F/G dwarf boundary. Morgan & Keenan (1973)
Life cycle
F-type stars have a life-cycle similar to G-type stars. They are hydrogen-fusing and will eventually grow into a red giant once the supply of hydrogen in their cores is depleted. Eventually they shed their outer layers, creating a planetary nebula, and leaving behind, at the center of the nebula, a hot white dwarf.
F-type stars spend 2-6 billion years on the main sequence. In comparison, G-type stars, like the Sun, remain on the main sequence for about 10 billion years.
Planets
Some of the nearest F-type stars known to support planets include Upsilon Andromedae, Tau Boötis, HD 10647, HD 33564, HD 142 and HD 60532.
Habitability
Some studies show that there is a possibility that life could also develop on planets that orbit an F-type star. It is estimated that the habitable zone of a relatively hot F0 star would extend from about 2.0 AU to 3.7 AU and between 1.1 and 2.2 AU for a relatively cool F8 star. Thus, for its native lifeforms to survive, the hypothetical planet would need to have sufficient atmospheric shielding, such as a denser ozone layer in the upper atmosphere.