Stephenson 2-18: Star in the open cluster Stephenson 2
Stephenson 2-18 (St2-18, also known as Stephenson 2-18 and RSGC2-18) is a red supergiant (RSG) or red hypergiant (RHG) star.
It is close to, and a possible member of, the open cluster Stephenson 2. It is about 6,000 parsecs (20,000 ly) away from Earth in the constellation of Scutum and is one of the largest known stars.
 Dense starfield around the red supergiant star St2-18 (brightest star in the image) as seen from the 2MASS astronomical survey. The picture was published in 2003. Credit: Université de Strasbourg/CNRS | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Scutum |
| Right ascension | 18h 39m 02.3709s |
| Declination | −06° 05′ 10.5357″ |
| Characteristics | |
| Evolutionary stage | Red supergiant |
| Spectral type | ~M6 |
| Apparent magnitude (G) | 15.2631±0.0092 |
| Apparent magnitude (J) | 7.150 |
| Apparent magnitude (H) | 4.698 |
| Apparent magnitude (K) | 2.9 |
| Astrometry | |
| Proper motion (μ) | RA: −3.045±0.511 mas/yr Dec.: −5.950±0.480 mas/yr |
| Parallax (π) | −0.0081 ± 0.3120 mas |
| Distance | 19,560 ly (6,000 pc) |
| Details | |
| Radius | 2,150 R☉ |
| Luminosity | 90,000–440,000; 630,000 L☉ |
| Temperature | 3,200 K |
| Other designations | |
Stephenson 2-18, Stephenson 2 DFK 1, RSGC2-18, 2MASS J18390238-0605106, IRAS 18363-0607 | |
| Database references | |
| SIMBAD | data |
It is also one of the most luminous of its type. It has a radius of 2,150 times that of the Sun, and has a volume 10 billion times that of the Sun. However, its radius is bigger than what we expect (as theories say stars can only be about 1,600 solar radii in radius).
This star has a spectral type of M6, which is pretty unusual for a supergiant star and corresponds to its cool temperature of 3,200 Kelvin. It can fit about 13 quadrillion Earths in it.
The clear single image of stephenson 2-18 was first taken in the year 2007 using 2MASS All-Sky Survey camera from Cerro Tololo Inter-American observatory in Chile.
References
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