K-type main-sequence star

orange dwarfKK-type starK-typeK dwarfK-type main sequence(K0V) orange dwarfdKeK dwarf starK star
A K-type main-sequence star (K V), also referred to as an K dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow G-type main-sequence stars.wikipedia
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Red dwarf

redred dwarf starsred dwarfs
A K-type main-sequence star (K V), also referred to as an K dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow G-type main-sequence stars.
Sometimes K-type main-sequence stars, with masses between 0.50-0.8 solar mass, are also included.

Alpha Centauri

α CentauriAlphaα Centauri A
Better known examples include Alpha Centauri B (K1 V) and Epsilon Indi. Some of the nearest K-type stars known to have planets include Alpha Centauri B, Epsilon Eridani, HD 192310, Gliese 86, and 54 Piscium.
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.

Main sequence

main-sequencemain sequence dwarfmain-sequence star
A K-type main-sequence star (K V), also referred to as an K dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow G-type main-sequence stars.
For the cooler stars, dwarfs such as red dwarfs, orange dwarfs, and yellow dwarfs are indeed much smaller and dimmer than other stars of those colors.

Epsilon Indi

ε IndEpsilon Indi Ba, Bbε Indi
Better known examples include Alpha Centauri B (K1 V) and Epsilon Indi.
Epsilon Indi (ε Indi, ε Ind) is a star system approximately 12 light-years from Earth in the constellation of Indus consisting of a K-type main-sequence star, ε Indi A, and two brown dwarfs, ε Indi Ba and ε Indi Bb, in a wide orbit around it. The brown dwarfs were discovered in 2003.

G-type main-sequence star

yellow dwarfGG-type
A K-type main-sequence star (K V), also referred to as an K dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow G-type main-sequence stars.
In addition, although the term "dwarf" is used to contrast yellow main-sequence stars from giant stars, yellow dwarfs like the Sun outshine 90% of the stars in the Milky Way (which are largely much dimmer orange dwarfs, red dwarfs, and white dwarfs, the last being a stellar remnant).

Fomalhaut

Alpha Piscis AustriniFomalhaut (α PsA)Fomalhaut A
The "anchor points" of the MK classification system among the K-type main-sequence dwarf stars, i.e. those standard stars that have remain unchanged over the years, are Epsilon Eridani (K2 V), and 61 Cygni A (K5 V). Other primary MK standard stars include 70 Ophiuchi A (K0 V), 107 Piscium (K1 V), HD 219134 (K3 V), TW Piscis Austrini (K4 V), HD 120467 (K6 V), 61 Cygni B (K7 V)
Fomalhaut, K-type main-sequence star TW Piscis Austrini, and M-type, red dwarf star LP 876-10 constitute a triple system, even though the companions are separated by several degrees.

Gliese 86

Some of the nearest K-type stars known to have planets include Alpha Centauri B, Epsilon Eridani, HD 192310, Gliese 86, and 54 Piscium.
Gliese 86 (13 G. Eridani, HD 13445) is a K-type main-sequence star approximately 35 light-years away in the constellation of Eridanus.

54 Piscium

54 Psc
Some of the nearest K-type stars known to have planets include Alpha Centauri B, Epsilon Eridani, HD 192310, Gliese 86, and 54 Piscium.
54 Piscium is an orange dwarf star approximately 36 light-years away in the constellation of Pisces.

Epsilon Eridani

ε Eridaniε EriEpsilon Erdani
The "anchor points" of the MK classification system among the K-type main-sequence dwarf stars, i.e. those standard stars that have remain unchanged over the years, are Epsilon Eridani (K2 V), and 61 Cygni A (K5 V). Other primary MK standard stars include 70 Ophiuchi A (K0 V), 107 Piscium (K1 V), HD 219134 (K3 V), TW Piscis Austrini (K4 V), HD 120467 (K6 V), 61 Cygni B (K7 V) Some of the nearest K-type stars known to have planets include Alpha Centauri B, Epsilon Eridani, HD 192310, Gliese 86, and 54 Piscium.
The estimated effective temperature is 5,084 K. With a stellar classification of K2 V, it is the second-nearest K-type main-sequence star (after Alpha Centauri B). Since 1943 the spectrum of Epsilon Eridani has served as one of the stable anchor points by which other stars are classified.

HD 192310

HR 7722
Some of the nearest K-type stars known to have planets include Alpha Centauri B, Epsilon Eridani, HD 192310, Gliese 86, and 54 Piscium.
This is a K-type main sequence star with a stellar classification of K2+ V. HR 7722 has about 78% of the Sun's mass and, depending on the estimation method, 79% to 85% of the radius of the Sun.

61 Cygni

61 Cyg61 Cygni A61 Cyg A
The "anchor points" of the MK classification system among the K-type main-sequence dwarf stars, i.e. those standard stars that have remain unchanged over the years, are Epsilon Eridani (K2 V), and 61 Cygni A (K5 V). Other primary MK standard stars include 70 Ophiuchi A (K0 V), 107 Piscium (K1 V), HD 219134 (K3 V), TW Piscis Austrini (K4 V), HD 120467 (K6 V), 61 Cygni B (K7 V)
61 Cygni A's long-term stability led to it being selected as an "anchor star" in the Morgan–Keenan (MK) classification system in 1943, serving as the K5 V "anchor point" since that time.

Solar analog

solar twinSun-like starsSun-like
Solar analog
Alternatively, a definition based on spectral type can be used, such as F8V through K2V, which would correspond to B−V color of 0.50 to 1.00.

Habitability of K-type main-sequence star systems

Habitability of K-type main-sequence star systems
K-type main-sequence stars may be candidates for supporting extraterrestrial life.

Stellar classification

spectral typeK-typeG-type
A K-type main-sequence star (K V), also referred to as an K dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow G-type main-sequence stars.
There are also giant K-type stars, which range from hypergiants like RW Cephei, to giants and supergiants, such as Arcturus, whereas orange dwarfs, like Alpha Centauri B, are main-sequence stars.

Hydrogen

HH 2 hydrogen gas
A K-type main-sequence star (K V), also referred to as an K dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow G-type main-sequence stars.

Star, Russia

starstellarstars
A K-type main-sequence star (K V), also referred to as an K dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow G-type main-sequence stars.

Solar mass

mass of the SunSun's masssolar masses
They have masses between 0.5 and 0.8 times the mass of the Sun and surface temperatures between 3,900 and 5,200 K.

Sun

solarSolThe Sun
They have masses between 0.5 and 0.8 times the mass of the Sun and surface temperatures between 3,900 and 5,200 K.

Effective temperature

surface temperatureeffective (surface) temperaturetemperature
They have masses between 0.5 and 0.8 times the mass of the Sun and surface temperatures between 3,900 and 5,200 K.

Kelvin

KkelvinsmK
They have masses between 0.5 and 0.8 times the mass of the Sun and surface temperatures between 3,900 and 5,200 K.

Extraterrestrial life

alienextraterrestrialaliens
These stars are of particular interest in the search for extraterrestrial life because they are stable on the main sequence for a very long time (15 to 70 billion years, compared to 10 billion for the Sun).

Terrestrial planet

terrestrial planetsrockyrocky planet
Like M-type stars, they tend to have a very small mass, leading to their extremely long lifespan that offers plenty of time for life to develop on orbiting Earth-like, terrestrial planets.

Ultraviolet

ultraviolet lightUVultraviolet radiation
In addition, K-type stars emit less ultraviolet radiation (which can damage DNA and thus hamper the emergence of nucleic acid based life) than G-type stars like the Sun.

DNA

deoxyribonucleic aciddouble-stranded DNAdsDNA
In addition, K-type stars emit less ultraviolet radiation (which can damage DNA and thus hamper the emergence of nucleic acid based life) than G-type stars like the Sun.

Exoplanet

extrasolar planetexoplanetsplanet
For all of these reasons, they may be the most favorable stars to focus on in the search for exoplanets and extraterrestrial life in the universe, especially if they are cooler (K6V–K9V, specifically those of the stellar class K7.5V temperate).