NGC 6383 | |
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Observation data | |
Right ascension | 17h 34m 41.5s [1] |
Declination | −32° 34′ 23″ [1] |
Distance | 3,540 ± 340 ly (1,086 ± 104 pc) [2] |
Apparent dimensions (V) | 20′ [3] |
Physical characteristics | |
Estimated age | 12.1+4.2 −3.1 Myr [2] |
Other designations | NGC 6383, Cl VDBH 232 [4] |
Associations | |
Constellation | Scorpius |
NGC 6383 is an open cluster of stars in the constellation of Scorpius. It was discovered by English astronomer John Herschel in 1847. In the New General Catalogue it was also identified as NGC 6374, most likely due to a clerical error. [5] This is a large cluster of scattered stars that spans an angular diameter of 20′ . The brightest component is the O-type binary star system designated HD 159176 (HR 4962). Against the glare of this sixth magnitude star, a handful of fainter members are visible with a pair of large binoculars. [3]
The cluster NGC 6383 is located at a distance of approximately 3,540 light-years (1,086 pc ) from the Sun. [2] It forms part of the Milky Way galaxy's Carina–Sagittarius Arm in a star forming region identified as Sh 2-012, [6] and lies in front of a dust absorption cloud. The cluster is likely part of the Sagittarius OB1 association, as are the clusters NGC 6530 and NGC 6531. This cluster, and in particular the ionizing radiation from the star HD 159176, form the H II region RCW 132, which span a crescent-shaped volume that has an angular size of 110′ × 80′. [5]
This is a young cluster with age estimates ranging from 4 to 20 million years, and has not yet achieved dynamic relaxation. It has 254 members identified, with 53 forming young stellar objects, [6] and 21 being hot, massive OB stars. 76 secondary X-ray sources have been detected, with most of them concentrated near the core. [5] Newly-formed stars range in age from 1–6 million years old, indicating recent star formation activity. The cluster has a compact core radius of 1.94′±0.19′ and a tidal radius of 40.7′±14.4′. [6]
Messier 21 or M21, also designated NGC 6531 or Webb's Cross, is an open cluster of stars located to the north-east of Sagittarius in the night sky, close to the Messier objects M20 to M25. It was discovered and catalogued by Charles Messier on June 5, 1764. This cluster is relatively young and tightly packed. A few blue giant stars have been identified in the cluster, but Messier 21 is composed mainly of small dim stars. With a magnitude of 6.5, M21 is not visible to the naked eye; however, with the smallest binoculars it can be easily spotted on a dark night. The cluster is positioned near the Trifid nebula, but is not associated with that nebulosity. It forms part of the Sagittarius OB1 association.
Messier 23, also known as NGC 6494, is an open cluster of stars in the northwest of the southern constellation of Sagittarius. It was discovered by Charles Messier in 1764. It can be found in good conditions with binoculars or a modestly sized telescope. It is in front of "an extensive gas and dust network", which there may be no inter-association. It is within 5° the sun's position so can be occulted by the moon.
Messier 18 or M18, also designated NGC 6613 and sometimes known as the Black Swan Cluster, is an open cluster of stars in the constellation Sagittarius. It was discovered by Charles Messier in 1764 and included in his list of comet-like objects. From the perspective of Earth, M18 is situated between the Omega Nebula (M17) and the Small Sagittarius Star Cloud (M24).
12 Canis Majoris is a variable star located about 707 light years away from the Sun in the southern constellation of Canis Major. It has the variable star designation HK Canis Majoris; 12 Canis Majoris is the Flamsteed designation. This body is just barely visible to the naked eye as a dim, blue-white hued star with a baseline apparent visual magnitude of +6.07. It is moving away from the Earth with a heliocentric radial velocity of +16 km/s. This is the brightest star in the vicinity of the open cluster NGC 2287, although it is probably not a member based on its proper motion.
Sher 25 is a blue supergiant star in the constellation Carina, located approximately 25,000 light years from the Sun in the H II region NGC 3603 of the Milky Way. It is a spectral type B1Iab star with an apparent magnitude of 12.2. Its initial main sequence mass is calculated at 60 times the mass of the Sun, but a star of this type will have already lost a substantial fraction of that mass. It is unclear whether Sher 25 has been through a red supergiant phase or has just evolved from the main sequence, so the current mass is very uncertain.
NGC 346 is a young open cluster of stars with associated nebula located in the Small Magellanic Cloud (SMC) that appears in the southern constellation of Tucana. It was discovered August 1, 1826 by Scottish astronomer James Dunlop. J. L. E. Dreyer described it as, "bright, large, very irregular figure, much brighter middle similar to double star, mottled but not resolved". On the outskirts of the cluster is the multiple star system HD 5980, one of the brightest stars in the SMC.
NGC 290 is an open cluster of stars in the southern constellation of Tucana. This cluster was discovered September 5, 1826, by Scottish astronomer James Dunlop. It lies some 200,000 light years away from the Sun in the Small Magellanic Cloud galaxy. The cluster is an estimated 30–63 million years old and is around 65 light years across.
NGC 6242 is an open cluster of stars in the southern constellation Scorpius. It can be viewed with binoculars or a telescope at about 1.5° to the south-southeast of the double star Mu Scorpii. This cluster was discovered by French astronomer Nicolas-Louis de Lacaille in 1752 from South Africa. It is located at a distance of approximately 4,350 ly (1,335 pc) from the Sun, just to the north of the Sco OB 1 association. The cluster has an estimated age of 77.6 million years.
NGC 6530 is a young open cluster of stars in the southern constellation of Sagittarius, located some 4,300 light years from the Sun. It exists within the H II region known as the Lagoon Nebula, or Messier 8, and spans an angular diameter of 14.0′. The nebulosity was first discovered by G. B. Hodierna prior to 1654, then re-discovered by J. Flamsteed circa 1680. It was P. Loys who classified it as a cluster in 1746, as he could only resolve stars. The following year, G. Le Gentil determined it was both a nebula and a cluster.
NGC 3293 is an open cluster in the Carina constellation. It was discovered by Nicolas-Louis de Lacaille in 1751. It consists of more than 100 stars brighter than 14th magnitude in a 10 arc minute field, the brightest of which are blue supergiants of apparent magnitude 6.5 and 6.7. There is also a 7th magnitude pulsating red supergiant, V361 Carinae.
HD 221246 or NGC 7686 1 is a star in open cluster NGC 7686, and it belongs to the northern constellation of Andromeda. With an apparent visual magnitude of 6.17, it can be viewed by the naked eye only under very favourable conditions. It has a spectral classification of K3III, meaning it is an evolved orange giant star. Parallax measurements place this star about 1,000 light years away from the solar system.
NGC 6604 is a young open cluster of stars in the equatorial constellation of Serpens, positioned about 1.5° north of the Eagle Nebula. The cluster was discovered by William Herschel on July 15, 1784. It is located at a distance of 4,580 light years from the Sun, about 210 ly (65 pc) above the galactic plane. NGC 6604 forms the densest part of the Ser OB2 association of co-moving stars.
WR 20a is an eclipsing binary star belonging to or recently ejected from the young, massive cluster Westerlund 2. It was discovered in 2004 to be one of the most massive binary systems known, for which the masses of the components have been accurately measured.
NGC 1817 is an open cluster of stars in the constellation Taurus. It was discovered by English astronomer William Herschel in February 1784. With an apparent magnitude of 7.7 and spanning 9.3 arc minutes across the sky, it is separated from the NGC 1807 cluster by just 26 arc minutes. Indeed, the two may actually be parts of a single extended cluster.
TW Horologii is a carbon star and semiregular variable in the southern constellation of Horologium, near the eastern constellation border with Reticulum. It has a ruddy hue and, with an apparent visual magnitude that ranges from 5.52 down to 5.95, is visible to the naked eye and one of the brightest carbon stars. Based on parallax measurements, it is located at a distance of approximately 1,370 light years from the Sun. It is drifting further away with a radial velocity of +14 km/s. In the past this star has been considered a member of the open cluster NGC 1252, but this now seems unlikely.
NGC 4349 is an open cluster in the constellation Crux. It was discovered by James Dunlop in 1826. It is located approximately 7,000 light years away from Earth.
NGC 4103 is an open cluster in the constellation Crux. It was discovered by James Dunlop in 1826. It is located approximately 5,000 light years away from Earth, in the Carina-Sagittarius arm.