Class K — K-type (Orange)

K-type stars are orange main-sequence stars with surface temperatures of 3,700 to 5,200 K. They are relatively common, making up about 12% of main-sequence stars. K-type stars are increasingly considered prime candidates in the search for habitable exoplanets — they are stable, long-lived (15-30 billion years), and less prone to stellar flares than M dwarfs. Notable examples include Arcturus (K1.5IIIFe-0.5), the brightest star in the northern hemisphere, and Epsilon Eridani (K2V).

K-type stars are orange stars with surface temperatures between 3,700 and 5,200 K, comprising about 12.1% of main-sequence stars. They have emerged as increasingly attractive targets in exoplanet habitability studies: their habitable zones are closer-in than the Sun's (making transiting planets easier to detect), they are less active than M dwarfs (reducing atmospheric stripping of orbiting planets), and their main-sequence lifetimes of 15-30 billion years exceed the current age of the universe — offering exceptionally stable environments.

Characteristics

K-type spectra show strong neutral metal lines (iron, calcium, sodium) and the beginnings of molecular absorption bands (TiO) in the coolest K-types. Their deep convective envelopes drive moderate magnetic activity with well-defined starspot cycles. K dwarfs are less variable than M dwarfs, avoiding the violent flare activity that may sterilize planets around red dwarfs. With masses of 0.45-0.8 solar masses and luminosities of 0.08-0.6 solar, K dwarfs are sometimes called 'Goldilocks stars' — not too hot, not too cool, not too variable for life.

Notable Examples

Arcturus (Alpha Bootis, K1.5III) is the brightest star in the northern celestial hemisphere and a K-type giant 25 times the Sun's diameter, whose orange color is immediately apparent. Aldebaran (Alpha Tauri, K5III), the Eye of the Bull, is another prominent orange giant 44 times solar diameter. Epsilon Eridani (K2V) at 10.5 light-years is one of the nearest stars known to host a confirmed exoplanet and a debris disk. Alpha Centauri B (K1V) is the secondary component of our nearest stellar system.

HIP 107150HIP 115470HIP 115471HIP 115472HIP 115473HIP 115474HIP 115476HIP 115477HIP 115483HIP 115485HIP 115486HIP 115487HIP 115494HIP 115498HIP 28615HIP 12631HIP 12641HIP 12650HIP 12651HIP 1155HIP 11550HIP 115512HIP 115517HIP 115523HIP 12666HIP 12667HIP 12680HIP 12681HIP 12684HIP 12686HIP 12687HIP 115526HIP 115528HIP 115539HIP 115544HIP 115545HIP 115546HIP 115549HIP 12699HIP 12702HIP 143HIP 83085HIP 115557HIP 115558HIP 115561HIP 115569HIP 17802HIP 17805

Frequently Asked Questions

What is a class K star?
Class K (K-type (Orange)) stars are orange stars. K-type stars are orange main-sequence stars with surface temperatures of 3,700 to 5,200 K. They are relatively common, making up about 12% of main-sequence stars. K-type stars are increasingly conside
How hot are class K stars?
Class K stars have surface temperatures between 3,700 K and 5,200 K.
What color are class K stars?
Class K stars appear orange.
How many class K stars are in the StarFYI database?
StarFYI currently catalogs 32,180 class K stars.
How luminous are class K stars?
Dim, 0.08-0.6 solar luminosities