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

{\displaystyle 4,000}

 and

8
,
000

{\displaystyle 8,000}

 K. Yellow hypergiants are very luminous with

200
,
000

{\displaystyle 200,000}

 to

600
,
000
−
750
,
000

{\displaystyle 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

 File:RHOCAS.png

**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

{\displaystyle 5,777}

 and

7
,
200

{\displaystyle 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

 File:Gstar.png

**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

{\displaystyle 8,900}

 light years away from Earth. It has a diameter of

747
# (
1.04

{\displaystyle 747 (= 1.04}

 billion km) times that of our sun and a mass of

20

{\displaystyle 20}

 times that of our sun. It has a temperature approximately

5
,
866

{\displaystyle 5,866}

 degrees Kelvin. It is visible to the naked eye as it has a luminosity approximately

316
,
000

{\displaystyle 316,000}

 times brighter than the Sun.

## HR 5171

### Aliases:

V766 Centauri, Peanut Star, HD 119796, HIP 67261, SAO 252448, CD−61°3988, WDS J13472-6235, AAVSO 1340-62

## About the details

### Mass:

Aa: 27 - 36 M☉
Ab: 5 M☉

### Radius/Diameter:

Aa: 1,315 - 1,490 R☉ (If it is a red supergiant)
Ab: 401-650 R☉

### Temperature:

Aa: 4,290 - 5,050 K
Ab: 4,800 - 5,200 K

### Age:

Aa: <5 Myr
Ab: 3.5 Myr

**HR 5171,** also known as the **"Peanut star"**  or **V766 Centauri**, is a yellow hypergiant located in the Centaurus constellation

11
,
700

{\displaystyle 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

{\displaystyle 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

{\displaystyle 1,315 (= 1.83}

 billion km) times greater than the Sun, based on a distance of

11
,
700

{\displaystyle 11,700}

 light years and an angular diameter of

3.39

{\displaystyle 3.39}

 milliarcseconds, making it the largest known yellow hypergiant star. It has a mass

27
t
o
36

{\displaystyle 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
t
o
5
,
050

{\displaystyle 4,290 to 5,050}

 degrees Kelvin.

### HR 5171 Ab

HR 5171 Ab is a small yellow hypergiant with a diameter between

401

{\displaystyle 401}

 and

650

{\displaystyle 650}

 times greater than the sun

# (
558

{\displaystyle (= 558}

 to

905

{\displaystyle 905}

 million km), with a temperature of

4
,
800
−
5
,
200

{\displaystyle 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

{\displaystyle 26,000}

 Kelvin and a luminosity of

316
,
000

{\displaystyle 316,000}

 times brighter than our sun. This star is not in contact.

### Gallery

VYCMAVSHR5171.png**Size comparison of HR 5171 A and its companion compared to VY Canis Majoris, which is the largest known star, and the Sun.**

## V509 Cassiopeiae

 File:V509CAS.png  **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

 File:HD 179821.jpg
**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

{\displaystyle 7,500}

 and

10
,
000

{\displaystyle 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

 File:HD33579.png  **HD 33579,** also known as **R76,** is a white/yellow hypergiant located in the Large Magellanic Cloud and in the constellation Dorado

165
,
000

{\displaystyle 165,000}

 light years away from Earth. It is amoung the brightest stars in the Large Magellanic Cloud. It has a diameter

380

{\displaystyle 380}

 R☉

# (
530

{\displaystyle (= 530}

 million km), a mass between

20

{\displaystyle 20}

 and

30

{\displaystyle 30}

 M☉. It has a temperature

7
,
980

{\displaystyle 7,980}

 degrees Kelvin. It is visible to the naked eye as it has a luminosity approximately

525
,
000

{\displaystyle 525,000}

 times brighter than the Sun.

### IRC +10420

 File:IRC10420.png

**IRC+10420,** also known as **V1302 Aquilae,** is a yellow hypergiant located in the Aquila constellation at a distance of

5
,
000

{\displaystyle 5,000}

 parsecs

# (
16
,
300

{\displaystyle (= 16,300}

 light years) from Earth on average. Its temperature is

6
,
000

{\displaystyle 6,000}

 to

8
,
000

{\displaystyle 8,000}

 degrees Kelvin, which mean that the star has increased its own temperature into the LBV range. It has a mass

10

{\displaystyle 10}

 times that of our sun and a diameter varying between

357

{\displaystyle 357}

 and

1
,
342

{\displaystyle 1,342}

 times that of the sun

# (
497

{\displaystyle (= 497}

 to

1
,
869

{\displaystyle 1,869}

 million km).

#### Gallery

IRC10420VSVYCMA.pngIRC +10420 is surrounded by a complex structure that includes filaments and arcs, like that of the largest known star VY Canis Majoris. ***Credits to R. Humphreys from the university of Minnesota.***

### IRAS 17163-3907

 File:Fried Egg Nebula.jpg

**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

{\displaystyle 13,000}

 light years away from Earth. It has a diameter of

300
t
o
400

{\displaystyle 300 to 400}

 R☉

# (
417

{\displaystyle (= 417}

 to

557

{\displaystyle 557}

 million km), with a temperature between

7
,
500

{\displaystyle 7,500}

 to

10
,
000

{\displaystyle 10,000}

 degrees Kelvin, which mean that the star is in a pre-LBV stage. Assuming the higher temperature is true, IRAS

17163
−
3907

{\displaystyle 17163-3907}

 would be the hottest yellow hypergiant star. It is visible to the naked eye as it has a luminosity approximately

500
,
000

{\displaystyle 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.

## References

* http://iopscience.iop.org/article/10.1088/0004-637X/697/1/409/meta
* https://www.aanda.org/articles/aa/abs/2010/15/aa13771-09/aa13771-09.html
* https://www.aanda.org/articles/aa/abs/2011/10/aa17521-11/aa17521-11.html
* https://www.aanda.org/articles/aa/abs/2012/10/aa17166-11/aa17166-11.html
* http://iopscience.iop.org/article/10.1086/507590/meta
* http://adsabs.harvard.edu/abs/1992A&A...259..600A

1. ↑ http://adsabs.harvard.edu/doi/10.1086/191373
2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 https://www.aanda.org/articles/aa/abs/2014/03/aa22421-13/aa22421-13.html
3. ↑ 3.0 3.1 3.2 https://www.aanda.org/articles/aa/abs/2017/10/aa31569-17/aa31569-17.html
4. ↑ 4.0 4.1 4.2 https://www.aanda.org/articles/aa/abs/2017/01/aa29349-16/aa29349-16.html
5. ↑ http://iopscience.iop.org/article/10.1088/0004-637X/697/1/133/meta
6. ↑ https://www.aanda.org/articles/aa/abs/2011/10/aa17521-11/aa17521-11.html