F-type main-sequence star
An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VII and VIII. This temperature range gives the F-type stars a yellow-white hue. Because a main-sequence star is referred to as a dwarf star, this class of star may also be termed a yellow-white dwarf. Famous examples include Procyon A, Gamma Virginis A and B, and KIC 8462852.
Spectral Standard StarsEdit
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 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 pi3 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 names (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 include 37 Ursae Majoris (F1 V) and Iota Piscium (F7 V). No F4 V standard stars have been published. Unfortunately F9 V defines the boundary between the hot stars classified by Morgan, and the cooler stars classified by Keenan, and there are discrepancies in the literature on which stars define the F/G dwarf boundary. Morgan & Keenan (1973) listed Beta Virginis and HD 27383 as F9 V standards, but Keenan & McNeil (1989) listed HD 10647 as their F9 V standard. Eta Cassiopeiae A should probably be avoided as a standard star because it was often considered F9 V in Keenan's publications, but G0 V in Morgan's publications.
Some studies show that there is a possibility that life could also develop on planets that orbit a 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. However, relative to a G-type star the main problems for a hypothetical lifeform in this particular scenario would be the more intense light and the shorter stellar lifespan of the home star.
F-type stars are known to emit much more higher energy forms of light, such as UV radiation, which in the long term can have a very profound and negative effect on DNA molecules. Studies have shown that placing a hypothetical planet at the same distance from an F-type star as the Earth is from the Sun would cause about 2.5 to 7.1 times more damage from UV light compared to that inflicted by the Sun. This indicates that the hypothetical planet would need to have a sufficient atmospheric shielding from the UV radiation, like an ozone layer in the upper atmosphere, in order to protect the lifeforms on the surface. Without the ozone layer life could still theoretically develop on the planet's surface, but it would most likely be confined to the underwater or underground regions.
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- SIMBAD, entries on Gamma Virginis A, Gamma Virginis B, accessed June 19, 2007.
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- MK Anchor Points, Robert F. Garrison
- Spectral Classification, W.W. Morgan & P.C. Keenan, 1973, Annual Review of Astronomy and Astrophysics, vol. 11, p.29
- Revised MK Spectral Atlas for stars earlier than the sun, W.W. Morgan, W. W., H.A. Abt, J.W. Tapscott, 1978, Williams Bay: Yerkes Observatory, and Tucson: Kitt Peak National Observatory
- The early F-type stars – Refined classification, confrontation with Stromgren photometry, and the effects of rotation, R. O. Gray & R. F. Garrison, R. F., 1989, Astrophysical Journal Supplement Series, vol. 69, p. 301
- The Perkins Catalog of Revised MK Types for the Cooler Stars, P.C. Keenan & R.C McNeil, "Astrophysical Journal Supplement Series" 71 (October 1989), pp. 245–266.
- Hadhazy, Adam (1 May 2014). "Could Alien Life Cope with a Hotter, Brighter Star?". space.com. Space.com. Retrieved 31 March 2018.