Stephenson 2 DFK 52
Red Supergiant Star in Open Cluster Stephenson 2
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Stephenson 2 DFK 52 is a red supergiant star located in the open cluster Stephenson 2 in the constellation Scutum at a distance of about 4,900 light-years from Earth.[1] The star gained attention in 2025 following Atacama Large Millimeter/submillimeter Array (ALMA) observations that revealed a large circumstellar outflow of dust and gas, the largest known circumstellar outflow around any red supergiant star.[3]
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ALMA image of Stephenson 2 DFK 52 and its sorrounding dust and gas cloud Credit: ALMA(ESO/NAOJ/NRAO)/M. Siebert et al. | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Scutum |
| Right ascension | 18h 39m 23.4s[1] |
| Declination | −06° 02′ 16″[1] |
| Apparent magnitude (V) | 17.6[2] |
| Characteristics | |
| Evolutionary stage | Red supergiant[3] |
| Spectral type | M0I[3] |
| Apparent magnitude (J) | 11.27[2] |
| Apparent magnitude (H) | 8.76[2] |
| Apparent magnitude (K) | 7.42[2] |
| Astrometry | |
| Distance | 4,900[4] ly |
| Details | |
| Radius | 335[4] – 357[5] R☉ |
| Luminosity | 20,900[4] – 24,000[5] L☉ |
| Temperature | 3,790[4] – 3,800[5] K |
| Other designations | |
| Stephenson 2 DFK 52, TIC 328138534, 2MASS J18392341-0602158[6] | |
| Database references | |
| SIMBAD | data |
Observation history
The open cluster Stephenson 2 was discovered by American astronomer Charles Bruce Stephenson in 1990 in the data obtained by a deep infrared survey.[1][7] The cluster is also known as RSGC2, one of several massive open clusters in Scutum, each containing multiple red supergiants.[8] The 52nd brightest star in the K band was given an identifier number of 52.[1]
Circumstellar environment
ALMA observations in 2023–2024 revealed that Stephenson 2 DFK 52 is surrounded by a large dust and gas outflow extending up to 50,000 AU in radius (or approximately 0.8 light-years).[3] If the star was located at the distance Betelgeuse is from our Solar System, this circumstellar cocoon would appear roughly one-third the angular width of the full moon.[9]
This suggests that the star went through a dramatic mass-loss event ~4,000 years ago, resulting in the incredibly large dust envelope.[3] Estimates suggest the total mass loss to the extended circumstellar material at 0.1–1 M☉.[3] The scale and asymmetry of the mass ejection cannot be easily explained by radiation pressure alone, suggesting possible additional mechanisms such as a short-lived superwind phase or multiple star interactions and the star is a progenitor for a Type II-P supernova explosion.[3]