Herschel's Garnet Star

Object type: Red supergiant star
Number of stars: 1
Total mass: 25-35 Solar Masses (26,188-36,663 Jupiter Masses; 8,324,025-11,653,635 Earth Masses; 49,712-69,596 Septillion Tonnes)
Distance from the sun: ~8,000 ly

The Herschel's Garnet Star, Also Named **Mu Cephei**, **Erakis**, **HD 206936**, **HR 8316**, **HIP 107259**, **SAO 33693**, **BD +58° 2316**, **IRAS 21419+5832** or **2MASS J21433045+5846480**, is a Red Supergiant Stars in The Constellation Cepheus, The Star is Located at Around 8,000 Light Years Away From Earth

The name HD 206936 derives directly from the fact that the star is the 206,936th stars in the Henry Draper catalogue, and The name HR 8316 derives directly from the fact that the star in the 8,316th stars in the Bright Star catalogue

The name HIP 107259 derives directly from the fact that the star is the 107,259th stars in the Hipparcos catalogue, and The name SAO 33693 derives directly from the fact that the star is the 33,693rd stars in the Smithsonian Astrophysical Star catalogue

If The Herschel's Garnet Star was placed into center of the solar system, that It's will engulf Mercury, Venus, Earth, Mars, Ceres, and even Jupiter, Because The Herschel's Garnet Star's size was 1,345 to 1,485 times large as the sun

in the video game Galactic Exodus: Arena and Galactic Exodus: Odyssey, traveling to The Herschel's Garnet Star is strictly prohibited without galactic government consent or having no level B universe VIP cards, Because the star is a red supergiant star

## Information

* Right Ascension: 21h 43m 30.4610574s
* Declination: +58° 46' 48.160181"
* Apparent Magnitude (V): +4.08 (+3.43 to +5.1)
* Variable Star Type: Semi-Regular Variable Star
* U-B Color Index: +2.42
* B-V Color Index: +2.35
* Parallax: 0.35 to 0.75 Milliarcseconds
* Radial Velocity: +20.63 km/s
* Distance: ~8,000 Light Years
* Discovery Year: 1848 (by John Russell Hind)
* Evolutionary Stage: Red Supergiant Star or Red Hypergiant Star
* Metallicity [Fe/H]: -0.21 dex

### Wikipedia

* Mass: 19.2 Solar Masses (20,112 Jupiter Masses; 6,392,851 Earth Masses; 38,179 Septillion Tonnes)
* Radius: 972 Solar Radius (1,353,688,848 km in Diameter; 4.52443 AU; 944,784 Solar Areas or 918,330,048 Solar Volumes)
* Luminosity: 269,000 Solar Luminosities
* Temperature: 3,551 Kelvin (3,278 °C; 5,932 °F)
* Spectral Type: M2 -Ia
* Age: 10 Million Years

### Galactic Exodus: Arena

* Mass: 25-30 Solar Masses (26,188-31,425 Jupiter Masses; 8,324,025-9,988,830 Earth Masses; 49,712-59,654 Septillion Tonnes)
* Radius: 1,185-1,310 Solar Radius (1,650,330,540-1,824,416,040 km in Diameter; 5.51589-6.09773 AU; 1,404,225-1,716,100 Solar Areas or 1,664,006,625-2,248,091,000 Solar Volumes)
* Luminosity: 185,545-264,040 Solar Luminosities
* Temperature: 3,480-3,615 Kelvin (3,207-3,342 °C; 5,804-6,047 °F)
* Spectral Type: M4Ia
* Restriction Level: B+

### Galactic Exodus: Odyssey

* Mass: 25-35 Solar Masses (26,188-36,663 Jupiter Masses; 8,324,025-11,653,635 Earth Masses; 49,712-69,596 Septillion Tonnes)
* Radius: 1,345-1,485 Solar Radius (1,873,159,980-2,068,135,740 km in Diameter; 6.26065-6.91232 AU; 1,809,025-2,205,225 Solar Areas or 2,433,138,625-3,274,759,125 Solar Volumes)
* Luminosity: 216,520-305,013 Solar Luminosities
* Temperature: 3,395-3,520 Kelvin (3,122-3,247 °C; 5,651-5,876 °F)
* Spectral Type: M4Ia-M5Ia (M4Ia+)
* Restriction Level: B+

### Other Designations

造父四, Herschel's Garnet Star, Mu Cephei, Erakis, HD 206936, HR 8316, HIP 107259, SAO 33693, BD +58° 2316, IRAS 21419+5832, IRC +60325, TYC 3979-1616-1, 2MASS J21433045+5846480, Trumpler 37 GDPR 1319, AG +58° 1378, GSC 03979-01616, RAFGL 2802, AAVSO 2140+58, PPM 39787, GC 30440, YZ 58 12465, JP11 3398, TIC 260614141, Gaia DR2 2202630001591176064, Gaia DR3 2202630001603369856

## History

The deep red color of Mu Cephei was noted by William Herschel, who described it as "a very fine deep garnet colour, such as the periodical star Omicron Ceti". It is thus commonly known as Herschel's "Garnet Star". Mu Cephei was called Garnet sidus by Giuseppe Piazzi in his catalogue. An alternative name, Erakis, used in Antonín Bečvář's star catalogue, is probably due to confusion with Mu Draconis

In 1848, English astronomer John Russell Hind discovered that Mu Cephei was variable. This variability was quickly confirmed by German astronomer Friedrich Wilhelm Argelander. Almost continual records of the star's variability have been maintained since 1881.

The angular diameter of μ Cephei has been measured interferometrically. One of the most recent measurements gives a diameter of 18.672 milliarcseconds at 800 micrometres, modelled as a limb-darkened disk 20.584 milliarcseconds across. μ Cephei was used as one of the original "dagger stars", those with well-defined spectra that could be used for the classification of other stars, for MK spectral classifications. In 1943 it was the standard star for M2Ia, updated in 1980 to be the standard star for the new type M2- Ia.

## Distance

The distance to Mu Cephei is not very well known. The Hipparcos satellite was used to measure a parallax of 0.35 to 0.75 milliarcseconds, which corresponds to an estimated distance of 1,800 parsecs. However, this value is close to the margin of error. A determination of the distance based upon a size comparison with Betelgeuse gives an estimate of 390 parsecs

Calculation of the distance from the measured angular diameter, surface brightness, and calculated luminosity leads to 641 parsec. Averaging the distances of nearby luminous stars with similar reddening and reliable Gaia Data Release 2 parallaxes gives a distance of 940 parsec.

## Surrounding

Mu Cephei is surrounded by a shell extending out to a distance at least equal to 0.33 times the star's radius with a temperature of 1,782 °C. This outer shell appears to contain molecular gases such as carbon monoxide, water, and silicon monoxide. Infrared observations suggest the presence of a wide ring of dust and water with an inner radius about twice that of the star itself, extending to about four times the radius of the star.

The star is surrounded by a spherical shell of ejected material that extends outward to an angular distance of 6" with an expansion velocity of 10 km s−1. This indicates an age of about 2,000–3,000 years for the shell. Closer to the star, this material shows a pronounced asymmetry, which may be shaped as a torus.

## Variability

Mu Cephei is a variable star and the prototype of the obsolete class of the Mu Cephei variables. It is now considered to be a semi-regular variable star of type SRc. Its apparent brightness varies erratically between magnitude 3.4 and 5.1. Many different periods have been reported, but they are consistently near 860 days or 4,400 days.

## Properties

A very luminous red supergiant, Mu Cephei is among the largest stars visible to the naked eye, and one of the largest known cool supergiants. It is a runaway star with a peculiar velocity of 80.7 km/s, and has been described as a hypergiant.
The bolometric luminosity, summed over all wavelengths, is calculated from integrating the spectral energy distribution (SED) to be 269,000 solar luminosities, making μ Cephei one of the most luminous red supergiants in the Milky Way. Its effective temperature of 3,487 °C, determined from colour index relations, implies a radius of 1,259 solar radius. Other recent publications give similar effective temperatures. Calculation of the luminosity from a visual and infrared colour relation give 340,000 solar luminosities and a corresponding radius of 1,420 solar radius. An estimate made based on its angular diameter and an assumed distance of 2,400 light years gives it a radius of 1,650 solar radius.

A 2019 paper measurement based on the 641 parsecs distance gives the star a lower luminosity below 140,000 solar luminosities and a correspondingly lower radius of 972 solar radius, and as well as a lower temperature of 3,278 °C. These parameters are all consistent with those estimated for Betelgeuse.

The initial mass of Mu Cephei has been estimated from its position relative to theoretical stellar evolutionary tracks to be between 15 solar mass and 25 solar mass. The star currently has a mass loss rate of (4.9±1.0)×10^−7 solar mass per year.

## Supernova

Mu Cephei is nearing death. It has begun to fuse helium into carbon, whereas a main sequence star fuses hydrogen into helium. When a supergiant star has converted elements in its core to iron, the core collapses to produce a supernova and the star is destroyed, leaving behind a vast gaseous cloud and a small, dense remnant. For a star as massive as Mu Cephei the remnant is likely to be a black hole. The most massive red supergiants will evolve back to blue supergiants, Luminous blue variables, or Wolf-Rayet stars before their cores collapse, and Mu Cephei appears to be massive enough for this to happen. A post-red supergiant will produce a type IIn or type II-b supernova, while a Wolf Rayet star will produce a type Ib or Ic supernova.

## See Also

* Stephenson 2-18
* IRAS 05280-6910
* WOH G64
* Betelgeuse
* Antares
* VY Canis Majoris
* UY Scuti