Mira variables

A **Mira variable** is a type of pulsating red giant star that changes its luminosity, temperature, and diameter/radius over an indefinite period of time exceeding 100 days. They are in the very late stages of stellar evolution and are on the asymptotic giant branch that will expel their outer layers as planetary nebulae and become white dwarfs within the span of a few million years.

## Mira

### Aliases:

A: Omicron Ceti, Stella Mira, Collum Ceti, Wonderful StarB: Omicron Ceti B, VZ Ceti

## About the details

### Mass:

A: 1.18 M☉B: 0.7 M☉ (**if** it is an orange main-sequence star)

### Age:

6 Gyr

**Mira,** also known as **Omicron Ceti,** is a popular star system located between 200 to 400 light years away from Earth in the Cetus constellation. Mira A and B are separated by 100 AU. Mira A often fades out of visibility and back with an apparent magnitude of 2.0 to 10.1. The Mira system has a tail of gas 13 light years long and is travelling through space.

### Mira A

**Mira A** is the prototype of Mira variables. Mira A is a typical red giant with a radius varying from 332 to 402 (= 462 to 560 million km) solar radii, and one of the coolest with a temperature of 2,918 to 3,192 degrees Kelvin. If Mira A was not pulsating, it would be modelled to have a radius of only 240 solar radii (= 334 million km). In this case, Mira A would be smaller than the orbit of Mars.

### Mira B

**Mira B,** also known as **VZ Ceti**, is a small white dwarf. It is surrounded by a protoplanetary disk. Its orbit around Mira is 500 years.

In 2007, observations hinted that Mira B is rather a orange main-sequence star of with a mass of 0.7 solar masses than a white dwarf. However, a 2010 analysis of rapid optical brightness variations has indicated that this star is a white dwarf.

## W Hydrae

 File:WHYA.jpg  **W Hydrae** is a Mira-type red giant star located in the constellation Hydra. When viewed through infrared light, it has a magnitude of -1.7, making it 7th brightest star in the night sky, even brighter than Sirius. It has a diameter between 229 to 560 times greater than the Sun's, but at the same time, its mass is less than 1 solar mass. The star is orbited by a wide disk of water vapor emissions.

## R Doradus

 File:RDOR.JPG
**R Doradus** is a red giant located 178 light years away from Earth in the constellation Dorado. It has the largest angular diameter of any known star at 0.057 arcseconds. It has a diameter of 515 million km, which is equal to 370 R☉.

## R Leonis

 File:R Leonis evaporating planet.png  **R Leonis** is a Mira variable located in the Leo constellation 267 light years away from Earth with a diameter 350 times greater than the Sun's, a temperature from 2,930 to 3,080 degrees Kelvin, and a bolometric luminosity 5,617 times greater.

### Possible Exoplanet

In 2009, Wiesemeyer *et al*. proposed that quasi-periodic fluctuations observed for the star R Leonis may be due to the presence of an evaporating substellar companion, possibly an extrasolar planet. They have inferred a putative mass for the orbiting body which is twice the mass of Jupiter, an orbital period of 5.2 years and likely orbital separation of 2.7 astronomical units. If confirmed such a planetary object could likely be an evaporating planet, with long comet-like trail as hinted by intense SiO maser emissions.

## T Cephei

 File:T cephei.jpg  **T Cephei** is a Mira variable star located in the Cepheus constellation 190 parsecs away from Earth and changes its magnitude over a period of 388 days. T Cephei is a red giant with a spectral type of M6-9e with an effective temperature of 2,400 Kelvin, a radius of 329 R☉, and a luminosity of 5,700 L☉. If it were in the place of the Sun, its photosphere would at least engulf the orbit of Mars.

## Chi Cygni

 File:Chi Cygni pulsations (Credit to Lithopsian).png   File:Evolutionary track 5m.svg (credit to Lithopsian).png
**Chi Cygni** is a Mira variable located in the Cygnus constellation. Despite having a Bayer designation, at times it can fall dimmer than apparent magnitude 14.2 . Estimated to be 550 light years away from Earth, the star is believed to be of spectral class S and pulsates between 316 to 737 R☉.

## NML Tauri (IK Tauri)

**NML Tauri** is a Mira variable of spectral type M6e - M10e located 865 light years away in the Taurus constellation. It has a temperature of 2,100 degrees Kelvin, a luminosity 7,700 times greater than the Sun's, and a radius of

3.53
∗

10

1

3

{\displaystyle 3.53\*10^{1}3}

 centimeters.

## References

* https://www.aanda.org/articles/aa/abs/2004/26/aa0826/aa0826.html
* http://iopscience.iop.org/article/10.1086/517993/meta
* http://iopscience.iop.org/article/10.1088/0004-637X/723/2/1188/meta

1. ↑ http://simbad.u-strasbg.fr/simbad/sim-id?Ident=V\*+W+Hya
2. ↑ https://doi.org/10.1051%2F0004-6361%2F200913771
3. ↑ https://doi.org/10.1086%2F421700
4. ↑ https://doi.org/10.1086%2F317317
5. ↑ https://doi.org/10.1051%2F0004-6361%3A20078357
6. ↑ https://arxiv.org/abs/astro-ph/9701021
7. ↑ https://doi.org/10.1051%2F0004-6361%3A20042013
8. ↑ https://en.wikipedia.org/wiki/R\_Leonis#cite\_note-debeck-2
9. ↑ https://doi.org/10.1051%2F0004-6361%2F200811242
10. ↑ https://doi.org/10.1051%2F0004-6361%2F201526705
11. ↑ https://doi.org/10.1117%2F12.458659
12. ↑ http://adsabs.harvard.edu/abs/2009yCat....102025S
13. ↑ https://doi.org/10.1088%2F0004-637X%2F707%2F1%2F632
14. ↑ https://doi.org/10.1088%2F0004-637X%2F707%2F1%2F632
15. ↑ https://doi.org/10.1086%2F159596
16. ↑ https://doi.org/10.1051%2F0004-6361%2F200913771
17. ↑ http://adsabs.harvard.edu/abs/2009yCat....102025S
18. ↑ https://doi.org/10.1051%2F0004-6361%2F201628310
19. ↑ https://doi.org/10.1051%2F0004-6361%2F201014136