Stephenson 2 DFK 1, also called RSGC2-01 or St2-18, is a red supergiant (RSG) or possibly an extreme red hypergiant (RHG) star in the Scutum constellation. It is located near the open star cluster Stephenson 2, which is about 5.8 kiloparsecs (19,000 light-years) away from Earth in the Scutum–Centaurus Arm of the Milky Way. This star is believed to be part of a group of stars at a similar distance, though some studies suggest it might be an unrelated or closer red supergiant.Stephenson 2 DFK 1, also called RSGC2-01 or St2-18, is a red supergiant (RSG) or possibly an extreme red hypergiant (RHG) star in the Scutum constellation. It is located near the open star cluster Stephenson 2, which is about 5.8 kiloparsecs (19,000 light-years) away from Earth in the Scutum–Centaurus Arm of the Milky Way. This star is believed to be part of a group of stars at a similar distance, though some studies suggest it might be an unrelated or closer red supergiant
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Observation Epoch J2000 Equinox J2000 |
| Constellation Scutum |
| Right Ascension 18h 39m 02.3907s |
| Declination 18h 39m 02.3907s |
| Spectral type ~M6 |
| Radial Velocity 89km/s |
| Distance 18900 light years |
| SIMBAD Data |
Stephenson 2 DFK 1, also called RSGC2-01 or St2-18, is a red supergiant (RSG) or possibly an extreme red hypergiant (RHG) star in the Scutum constellation. It is located near the open star cluster Stephenson 2, which is about 5.8 kiloparsecs (19,000 light-years) away from Earth in the Scutum–Centaurus Arm of the Milky Way. This star is believed to be part of a group of stars at a similar distance, though some studies suggest it might be an unrelated or closer red supergiant.Stephenson 2 DFK 1, also called RSGC2-01 or St2-18, is a red supergiant (RSG) or possibly an extreme red hypergiant (RHG) star in the Scutum constellation. It is located near the open star cluster Stephenson 2, which is about 5.8 kiloparsecs (19,000 light-years) away from Earth in the Scutum–Centaurus Arm of the Milky Way. This star is believed to be part of a group of stars at a similar distance, though some studies suggest it might be an unrelated or closer red supergiant
Stephenson 2 DFK 1, also called RSGC2-01 or St2-18, is a red supergiant (RSG) or possibly an extreme red hypergiant (RHG) star in the Scutum constellation. It is located near the open star cluster Stephenson 2, which is about 5.8 kiloparsecs (19,000 light-years) away from Earth in the Scutum–Centaurus Arm of the Milky Way. This star is believed to be part of a group of stars at a similar distance, though some studies suggest it might be an unrelated or closer red supergiant.Stephenson 2 DFK 1, also called RSGC2-01 or St2-18, is a red supergiant (RSG) or possibly an extreme red hypergiant (RHG) star in the Scutum constellation. It is located near the open star cluster Stephenson 2, which is about 5.8 kiloparsecs (19,000 light-years) away from Earth in the Scutum–Centaurus Arm of the Milky Way. This star is believed to be part of a group of stars at a similar distance, though some studies suggest it might be an unrelated or closer red supergiant
Stephenson 2 DFK 1, also called RSGC2-01 or St2-18, is a red supergiant (RSG) or possibly an extreme red hypergiant (RHG) star in the Scutum constellation. It is located near the open star cluster Stephenson 2, which is about 5.8 kiloparsecs (19,000 light-years) away from Earth in the Scutum–Centaurus Arm of the Milky Way. This star is believed to be part of a group of stars at a similar distance, though some studies suggest it might be an unrelated or closer red supergiant.Stephenson 2 DFK 1, also called RSGC2-01 or St2-18, is a red supergiant (RSG) or possibly an extreme red hypergiant (RHG) star in the Scutum constellation. It is located near the open star cluster Stephenson 2, which is about 5.8 kiloparsecs (19,000 light-years) away from Earth in the Scutum–Centaurus Arm of the Milky Way. This star is believed to be part of a group of stars at a similar distance, though some studies suggest it might be an unrelated or closer red supergiant
Observation history
The open cluster Stephenson 2 was discovered by American astronomer Charles Bruce Stephenson in 1990, using data from a deep infrared survey. The cluster is also known as RSGC2 and is one of several large open clusters in the Scutum constellation, all containing many red supergiants.
The brightest star in the cluster's region was initially labeled as number 1 in the first study of the cluster's stars. However, because it was far from the main group, unusually bright, and had slightly unusual movement, it was thought to be an unrelated red supergiant, not a member of Stephenson 2.
Later, the same star was given the number 18 and placed in a separate group of stars called Stephenson 2 SW, which is believed to be at a similar distance to the main cluster. The star is often referred to as St2-18, based on a 2010 study. To avoid confusion, the star is also sometimes called Stephenson 2 DFK 1 or simply D1, especially in references from a 2007 study
Physical properties
Evolutionary stage
When Stephenson 2 was first discovered in 1990, the distance to the cluster, to Stephenson 2 DFK 1, was estimated to be about 30 kiloparsecs (98,000 light-years), much farther than it is now believed to be. A study in 2007, based on the cluster's radial velocity, determined a kinematic distance of 5.83+1.91−0.78 kiloparsecs (19,000+6,200−2,500 light-years), much closer than the original estimate. However, because Stephenson 2 DFK 1's membership in the cluster was uncertain, its distance was not directly calculated. This revised distance was later adopted in more recent studies of the cluster.A similar kinematic distance of 5.5 kiloparsecs (18,000 light-years) was reported in a 2010 study. This value was based on the average radial velocity of four of the cluster's stars (96 kilometers per second) and the cluster's association with a nearby group of stars
Membership
In 2012, Stephenson 2 DFK 1, along with 56 other red supergiants, was studied for its maser emissions as part of a galaxy-wide survey. The study used the Australia Telescope Compact Array (ATCA) and the DUSTY model to analyze the properties of these stars. Stephenson 2 DFK 1 was included in this study. That same year, it was observed again in another study about masers in red supergiants within clusters.In 2013, Stephenson 2 DFK 1 (called D1) was observed in a study focused on red supergiants in the Stephenson 2 cluster. Later studies described it as a “very late-type red supergiant.”In 2020, a study by Humphreys et al. mistakenly referred to it as RSGC1-01, another large and bright red supergiant in the Scutum constellation.
In 2012, Stephenson 2 DFK 1, along with 56 other red supergiants, was studied for its maser emissions as part of a galaxy-wide survey. The study used the Australia Telescope Compact Array (ATCA) and the DUSTY model to analyze the properties of these stars. Stephenson 2 DFK 1 was included in this study. That same year, it was observed again in another study about masers in red supergiants within clusters.
In 2013, Stephenson 2 DFK 1 (called D1) was observed in a study focused on red supergiants in the Stephenson 2 cluster. Later studies described it as a "very late-type red supergiant."
In 2020, a study by Humphreys et al. mistakenly referred to it as RSGC1-01, another large and bright red supergiant in the Scutum constellation.
Uncertainties in measurements
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The distance to Stephenson 2 DFK 1 has a high level of uncertainty, over 50%. Because its membership in Stephenson 2 is uncertain, its distance is unclear, and its radial velocity is different from other stars in the cluster, some researchers believe the star may be a red supergiant unrelated to Stephenson 2 or any other red supergiant clusters in the Scutum–Centaurus Arm.
The star's radius, estimated at 2,150 times the size of the Sun, could be too high because of the method used to calculate it, especially since stellar evolutionary theory suggests that a star's size should be closer to 1,500 times the Sun's size. The star's luminosity is also uncertain. One estimate puts its luminosity at 90,000 times that of the Sun, but this might be an underestimate because it relies on a small range of fluxes.