Yellow Hypergiant

A yellow hypergiant, formerly a late S Doradus variable, is a star that has a spectral classification between A to K. This gives them temperatures between 10,000 to 4,000 degrees Celsius. They are luminous stars with radii larger than 300 solar radii.

HR 5171
HR 5171, also known as the "Peanut star"  and V766 Centauri, is a yellow hypergiant pulsating variable star located in the Centaurus constellation 11,700 light years away from Earth. It contains the most massive, the most luminous and possibly the largest known yellow star.

The star system was originally discovered by French astronomer Olivier Chesneau. However, it was later revealed to be a binary star in 2014. The HR 5171 system is an eclipsing binary with a period of 1,304 days, semi-major axis of 2,195 solar radii (3,057,160,880 km), and an inclination over 60°.

The main component is a star named HR 5171 A(a). Its size is calculated from its angular diameter. It varies between 1,315 (1,831,510,960 km) and 1,490 (2,075,248,160 km) solar radii in diameter. It has a mass 27 to 36 times that of our sun, as well as a luminosity 630,000 times that of the sun. Its temperature vary between 4,290 to 5,050 degrees Kelvin. According to Wittkowski et al, it would rather be a red supergiant if the upper estimate and the lower temperatue are true. As for HR 5171 Ab, it is a smaller yellow hypergiant with a maximum radius of 650 solar radii (905,309,600 km), a temperature of 4,800 to 5,200 degress Kelvin, and a mass 5 times greater than the sun. Both are so close to each other that the two stars are in contact. The third component, HR 5171 B, is a blue supergiant with a radius of 28 (38,997,952 km) or 438 (610,039,392 km) solar radii.

V382 Carinae
V382 Carinae, also known as x Carinae, is the second best known yellow hypergiant. It is easily visible with the naked eye. It is located in the constellation Carina 8,900 light years away from Earth. It has a diameter 747 (1,040,409,648 km) times that of our sun and a mass 20 times that of our sun. It has a temperature approximately 5,866 degrees Kelvin. It is visible to the naked eye as it has a luminosity approximately 316,000 times brighter than the Sun.

Rho Cassiopeiae
Rho Cassiopeiae, also known as 7 Cassiopeiae, is located in the constellation Cassiopeia 8,200 light years away from Earth. It has a diameter 450 (626,752,800 km) times that of our sun on average. It has a mass 14 to 30 times that of our sun. It has a temperature between 5,777 to 7,200 degrees Kelvin. It is visible to the naked eye as it has a luminosity approximately 500,000 times brighter than the Sun.

HD 179821
HD 179821, also known as V1427 Aquilae, is located in the constellation Aquilae 19,600 light years away from Earth. It has a mass 30 times that of our sun. It is visible to the naked eye as it has a luminosity 310,000 to 600,000 times brighter than the Sun, which would indicate a diameter of 407 (566,863,088 km) to 566 (788,315,744 km) solar radii with a temperature of 6,750 degrees Kelvin but another research suggest it might be a supergiant star with a much lower lumniosity of 16,000 times brighter than the Sun, which would indicate a much smaller diameter of 92.49 solar radii (128,818,592.2 km).

V509 Cassiopeiae
V509 Cassiopeiae, also known as HR 8752, is also located in the constellation Cassiopeia 4,500 light years away from Earth. It has a diameter between 400 (557,113,600 km) to 900 (1,253,505,600 km) times that of our sun. It has a mass 11 times that of our sun. It has a temperature between 4,000 and 8,000 degrees Kelvin. Just like Rho Cassiopeiae, it is visible to the naked eye as it has a luminosity between 200,000 to 400,000 times brighter than the Sun. Also, while V509 Cassiopeiae is commonly depicted as an F-type star, Rho Cassiopeiae is commonly depicted as a hot G-type star, even though it is the other way around!

HD 33579
HD 33579, also known as R76, is a white/yellow hypergiant located in the Large Magellanic Cloud and in the constellation Dorado 165,001 light years away from Earth. It is amoung the brightest stars in the Large Magellanic Cloud. It has a diameter 380 (529,257,920 km) times that of our sun. It has a mass between 20 and 30 times that of our sun. It has a temperature 7,980 degrees Kelvin. It is visible to the naked eye as it has a luminosity 525,464 times brighter than the Sun.

IRC+10420
IRC+10420, also known as V1302 Aquilae, is a yellow hypergiant located in the Aquila constellation. It was once thought to be a red supergiant, but is now getting hotter and shrinking down to a luminous blue variable, with a current temperature of 6,000 to 8,000 degrees Kelvin. IRC+10420 is located 5,000 parsecs from Earth on average. It has a mass 10 times that of our sun. IRC+10420's radius could be as small as 357 solar radii (497,188,188 km), but is unlikely to be much larger at 1,342 solar radii (1,869,116,128 km), which could be larger than the orbit of Jupiter.

IRAS 17163-3907
IRAS 17163-3907, also known as Fried Egg Nebula, is a possible yellow hypergiant located in the constellation Scorpius 13,000 light years away from Earth. It has a diameter 350 (487,474,400 km) times that of our sun on average. Its mass is unknown. It has a temperature between 7,500 to 10,000 degrees Kelvin. It is visible to the naked eye as it has a luminosity approximately 500,000 times brighter than the Sun.

BI Cygni
BI Cygni, also known as IRAS 20194+3646, is a slow irregular variable star localed in the constellation Cygnus and 5,150 light years away from Earth. It is a member of the stellar Cygnus OB1 association. It has a mass between 13.6 and 33.4 times that of our sun. It has a luminosity 123,000 to 226,000 times brighter than the Sun. It has a diameter between 916 (1,275,790,144 km) and 1,240 (1,727,052,160 km) times that of our sun. Its evolutionary stage is uncertain. It is possibly a post-red supergiant yellow hypergiant with a temperature 5,200 degrees Kelvin. If it is really a yellow hypergiant, its luminosity would be much brigher. But it is likely a red supergiant with a cooler temperature of 3,575 degrees Kelvin.