42 Draconis is a K1.5 giant star located approximately 3207 light-years away. Very close in mass to our Sun, it is 22 times larger. It is about 9.49 billion years old, and has a planetary companion about four times the mass of Jupiter. Arcturus is a red, K1.5 giant about 26 times larger than the sun, and 210 times brighter, although it emits much of this energy in the infra-red. It is about 37 light-years away. As a giant, weighing in at around 1.1 times the mass of the Sun, it has stopped fusing hydrogen, and has probably started helium to carbon fusion. It is thought to be lder than the Sun; perhaps 8 billion years old, and looks much like the Sun will when it enters its red giant phase. There is some evidence that Arcturus originated in a small galaxy that merged with the Milky Way some time after the star formed. Aldebaran is a type K5 orange/red giant about 44 times larger than the sun, and 425 times brighter, though only about 150 times brighter in the visible spectrum. It is about 65 light-years away. Weighing around 1.7 times the mass of the Sun, it has stopped fusing hydrogen, but has not started to fuse its helium core which is contracting and heating, causing the outer layers of the star to continue to expand and brighten.
Type K Stars
Epsilon Pegasi is a good example of a type K2 supergiant, and, though relatively young, probably has only a few million years left. It is about 670 to 700 light-years away. Its mass of 10 to 11 Earth masses is borderline for going supernova, so it may end up as an Earth-sized, rare, heavy neon-oxygen white dwarf. It is about 150 times larger than the Sun. It is also a flare star, and a slow irregular variable star that varies from magnitude +0.7 to +3.5, tending to be around magnitude 2.4 most of the time. Somewhat further away at 810 light-years is Pi Puppis, a K3 supergiant. This star is 11.7 times the mass of the Sun, and about 290 times larger.
K-type main sequence stars are intermediate in size between M-type main sequence stars and G-type main sequence stars like our Sun. Generally, their masses range from about from 50% to 80% the mass of the Sun, with somewhat cooler surface temperatures. Because of their lower masses, they remain on the main sequence for around 15 to 30 billion tears, compared to 10 billion for the Sun. 10.5 light-years away is Epsilon Eridani, a K2 main sequence, orange-red dwarf star. This is a young star, between 500 million to a billion years old. It is about 85% of the suns mass and diameter, and cooler than the sun. It is in a similar state to where the Sun was about 4 billion years ago. It has a relatively dense cloud of dust around it, and one or two planets have been found; one gas giant around 1.55 times the mass of Jupiter, the other, not confirmed, believed to be very much lighter, perhaps only 10% Jupiter's mass. Recent research shows that the star has two distinct asteroid belts, as well as an outer ring of icy objects akin to the Kuiper Belt in the Solar System.
Arcturus and some of its local stars. © Royal Observatory, Edinburgh &
Anglo Australian Observatory
Having been occulted by the moon, Aldebaran can be seen emerging from the dark limb.
Delta Eridani is only about 29 light-years away. It is a K0 sub-giant star that has started to burn helium into carbon. It is expanding and heating up as it moves off the main sequence. It weighs about 1.2 times the mass of the Sun, and is about 2.3 to 2.7 times larger; evidence of its helium burning. It is about 7.5 billion years old; somewhat younger than the Sun will be at a comparable stage of its evolution due to its higher mass. HD 148427 is another K0 sub-giant about 193 light-years away. It weighs about 1.45 solar masses with a diameter approximately 3.22 times that of the Sun. At 2.5 billion years, it is about half the age of the Sun, but is, of course, evolving faster due to its mass. It has a plane close to the mass of Jupiter that orbits the star slightly closer in than the Earth's orbit around the Sun.
Gamma Aquilae is a K3 bright giant, about 460 light-years away. Weighing about five solar masses, it is 110 times the diameter of our Sun. While only about 100 million years old, it has already moved off the main sequence to burn helium into carbon. Gamma Aquilae together with Altair and Beta Aquilae form a straight line of stars called the Family of Aquila. Another example is V337 Carinae, about 740 light-years away and about 350 times the diameter of the Sun. Finally, HD 13189 was a main sequence type B star that has evolved into a K3 bright giant. It is about 3.5 solar masses, and 46 time larger than the Sun. It is 603 light-years away. It has a companion HD 13189b which orbits it at a distance of about 277 million km that is either a large planet or a brown dwarf, a with mass somewhere around 8 to 20 times Jupiter's mass.
Astronomy & Cosmology
Stars - Stellar Classes
K type stars are generally somewhat lighter than the Sun, though they may be considerably larger. They tend to be very stable and long lived, and as there are between three and four times as many type K stars as there are type G, they are very interesting to searches for extraterrestrial life.