Stephenson 2 , also known as RSGC2 (''Red Supergiant Cluster 2''), is a young massive

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, an ...

belonging to the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

galaxy. It was discovered in 1990 as a cluster of red supergiants in a photographic, deep infrared survey by the astronomer

Charles Bruce Stephenson Charles Bruce Stephenson (February 9, 1929 – December 3, 2001) was an American astronomer. He was born on a ranch in Little Rock, Arkansas, the only son of Chauncey Elvira Stephenson and Ona Richards. During his youth he made a telescope and w ...

, after whom the cluster is named. It is located in the constellation

Scutum The ''scutum'' (; plural ''scuta'') was a type of shield used among Italic peoples in antiquity, most notably by the army of ancient Rome starting about the fourth century BC. The Romans adopted it when they switched from the military formati ...

at the distance of about 6 kpc from the Sun. It is likely situated at the intersection of the northern end of the Long Bar of the Milky Way and the inner portion of the

Scutum–Centaurus Arm The Scutum–Centaurus Arm, also known as Scutum-Crux arm, is a long, diffuse curving streamer of stars, gas and dust that spirals outward from the proximate end of the Milky Way's central bar. The Milky Way has been posited since the 1950s to ...

—one of the two major spiral arms.

Description

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Ant ...

s have been confirmed as members of the cluster, far more than any other known cluster, both in and out of the Milky Way. This includes

Stephenson 2-18 Stephenson 2-18 (abbreviated to St2-18), also known as Stephenson 2 DFK 1 or RSGC2-18, is an enigmatic red supergiant (RSG) or possible extreme red hypergiant (RHG) star in the constellation of Scutum. It lies near the open cluster Ste ...

, which is one of the largest stars currently known. A more recent study has identified around 80 red supergiants in the line of sight of Stephenson 2, approximately 40 of them with

radial velocities The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection o ...

consistent with being cluster members. However these stars are spread over a wider area than a typical cluster, indicating an extended stellar association similar to that found around the nearby cluster

RSGC3 RSGC3 (''Red Supergiant Cluster 3'') is a young massive open cluster belonging to the Milky Way galaxy. It was discovered in 2010 in the GLIMPSE survey data. The cluster is located in the constellation Scutum at the distance of about 7 kp ...

. The age of Stephenson 2 is estimated at 14–20 million years. The observed red supergiants with the mass of about 12–16 solar masses are

type II supernova A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo th ...

progenitors. The cluster is heavily obscured and has not been detected in the

visible light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

. It lies close to other groupings of red supergiants known as

RSGC1 RSGC1 (''Red Supergiant Cluster 1'') is a young massive open cluster in the Milky Way galaxy. It was discovered in 2006 in the data generated by several infrared surveys, named for the unprecedented number of red supergiant members. The cluster ...

Alicante 7 Alicante 7, also known as RSGC5, (''Red Supergiant Cluster 5'') is an open cluster rich in red supergiants found in the Scutum-Crux Arm of the Milky Way Galaxy, along with RSGC1, Stephenson 2, RSGC3, Alicante 8, and Alicante 10 Alicante 10 ...

, Alicante 8, and

Alicante 10 Alicante 10, also known as RSGC6 (''Red Supergiant Cluster 6''), is a young massive open cluster belonging to the Milky Way galaxy. It was discovered in 2012 in the 2MASS survey data. Currently, eight red supergiants have been identified in thi ...

. The mass of the open cluster is estimated at 30–50 thousand solar masses, which makes it the second most massive open cluster in the Galaxy.

Stephenson 2 SW

Some of the stars in the vicinity of the cluster lie in a loose grouping near the cluster, including Stephenson 2-18, Stephenson 2-11 (DFK 49 in Davies 2007) and Stephenson 2-26. This grouping was first mentioned in Deguchi (2010) and was named Stephenson 2 SW because it lies south-west of the main cluster. While the radial velocities of its members are somewhat different from the main cluster's radial velocity,(by about 7.7 km/s) The difference between the 2 velocities is still relatively small, and not enough to rule out its association with the main cluster. Thus, it was assumed that it is possibly related to Stephenson 2 itself.

Members

Stars whose rows are colored in yellow are stars supposed to be part of Stephenson 2-SW.

References

{{DEFAULTSORT:Stephenson 2 Open clusters Scutum (constellation)

Description

Stephenson 2 SW

Members

See also

References