Yellow Hypergiants

A yellow hypergiant (also known as a post-red supergiant/hypergiant), formerly a late S Doradus variable, is a star that has a spectral classification between A0 to K2. This gives them temperatures between $$4,000$$ and $$8,000$$ K. Yellow hypergiants are very luminous with $$200,000$$ to $$600,000-750,000$$ times greater than the Sun. It is a star that was once a red supergiant, but is now getting hotter and shrinking down to a luminous blue variable and then a Wolf-Rayet star. All yellow hypergiants stars are in an extremely active phase of their evolution.

This article will cover a few examples of yellow hypergiants.

Rho Cassiopeiae
Rho Cassiopeiae, also known as 7 Cassiopeiae, is the best known yellow hypergiant. It is located in the constellation Cassiopeia 8,200 light years away from Earth. It has a diameter of 450 (= 627 million km) times that of our sun, a mass of 14 and 30 times that of our sun and a temperature between $$5,777$$ and $$7,200$$ degrees Kelvin. It is visible to the naked eye as it has a luminosity approximately 500,000 times brighter than the Sun.

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 of $$747 (= 1.04$$ billion km) times that of our sun and a mass of $$20$$ 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.

HR 5171
HR 5171, also known as the "Peanut star"  or V766 Centauri, is a yellow hypergiant located in the Centaurus constellation $$11,700$$ light years away from Earth.

The star system was originally discovered by French astronomer Olivier Chesneau. However, it was later revealed to be a binary star in $$2014$$. Both are so close to each other that the two stars are in contact.

HR 5171 A
The main component is a star named HR 5171 A. It has a diameter of $$1,315 (= 1.83$$ billion km) times greater than the Sun, based on a distance of $$11,700$$ light years and an angular diameter of $$3.39$$ milliarcseconds, making it the largest known yellow hypergiant star. It has a mass $$27 to 36$$ times that of our sun, as well as a luminosity of 630,000 to a million times that of the sun. Its temperature vary between $$4,290 to 5,050$$ degrees Kelvin.

HR 5171 Ab
HR 5171 Ab is a small yellow hypergiant with a diameter between $$401$$ and $$650$$ times greater than the sun $$(= 558$$ to $$905$$ million km), with a temperature of $$4,800 - 5,200$$ degress Kelvin, and a small mass of only 5 times greater than the sun.

HR 5171 B
HR 5171 B, is a blue supergiant with a temperature of $$26,000$$ Kelvin and a luminosity of $$316,000$$ times brighter than our sun. This star is not in contact.

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 and 900 (= 557 to 1,253 million km) times that of our sun. It has a mass of 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 and 400,000 times brighter than the Sun.

HD 179821
HD 179821 is a yellow hypergiant star in the Aquila constellation, surrounded by a detached dust shell. It is a semi-regular variable and either a post-AGB star or what it is more likely to be, a yellow hypergiant.

Yellow Evolutionary Void
The Yellow Evolutionary Void separates yellow hypergiants from luminous blue variables, although yellow hypergiants are the hottest and luminous blue variables are the coolest, meaning they can have approximately the same temperature (between $$7,500$$ and $$10,000$$ K). They are sometimes considered as stars in a Pre-Luminous Blue Variable stage. This section will cover two yellow hypergiants that are near in the bounds of the Yellow Evolutionary Void.

HD 33579
HD 33579, also known as R76, is a white/yellow hypergiant located in the Large Magellanic Cloud and in the constellation Dorado $$165,000$$ light years away from Earth. It is amoung the brightest stars in the Large Magellanic Cloud. It has a diameter $$380$$ $$(= 530$$ million km), a mass between $$20$$ and $$30$$. It has a temperature $$7,980$$ degrees Kelvin. It is visible to the naked eye as it has a luminosity approximately $$525,000$$ times brighter than the Sun.

IRC +10420


IRC+10420, also known as V1302 Aquilae, is a yellow hypergiant located in the Aquila constellation at a distance of $$5,000$$ parsecs $$(= 16,300$$ light years) from Earth on average. Its temperature is $$6,000$$ to $$8,000$$ degrees Kelvin, which mean that the star has increased its own temperature into the LBV range. It has a mass $$10$$ times that of our sun and a diameter varying between $$357$$ and $$1,342$$ times that of the sun $$(= 497$$ to $$1,869$$ million km).

IRAS 17163-3907


IRAS 17163-3907 (or Hen 3-1379), also known as Fried Egg Nebula, is a possible yellow hypergiant located in the constellation Scorpius at $$13,000$$ light years away from Earth. It has a diameter of $$(= 417$$ to $$557$$ million km), with a temperature between $$7,500$$ to $$10,000$$ degrees Kelvin, which mean that the star is in a pre-LBV stage. Assuming the higher temperature is true, IRAS $$17163-3907$$ would be the hottest yellow hypergiant star. It is visible to the naked eye as it has a luminosity approximately $$500,000$$ times brighter than the Sun.

IRAS 17163-3907 has also a double dust envelope, and like VY Canis Majoris and IRC +10420, this star has ejected much of its mass off of its atmosphere, it may explode into a supernova.