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An open cluster is a type of star cluster made of tens 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, and many more are thought to exist. They are loosely bound by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the Galactic Center. This can result in a loss of cluster members through internal close encounters and a dispersion into the main body of the galaxy. Open clusters generally survive for a few hundred million years, with the most massive ones surviving for a few billion years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, and can survive for longer. Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring.
Vela is a constellation in the southern sky, which contains the Vela Supercluster. Its name is Latin for the sails of a ship, and it was originally part of a larger constellation, the ship Argo Navis, which was later divided into three parts, the others being Carina and Puppis. With an apparent magnitude of 1.8, its brightest star is the hot blue multiple star Gamma Velorum, one component of which is the brightest Wolf-Rayet star in the sky. Delta and Kappa Velorum, together with Epsilon and Iota Carinae, form the asterism known as the False Cross. 1.95-magnitude Delta is actually a triple or quintuple star system.
The Pleiades, also known as the Seven Sisters, Messier 45, and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance of about 444 light years, it is among the nearest star clusters to Earth. It is the nearest Messier object to Earth, and is the most obvious cluster to the naked eye in the night sky. It is also observed to house the reflection nebula NGC 1432, an HII region.
The New General Catalogue of Nebulae and Clusters of Stars is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxies, star clusters and emission nebulae. Dreyer published two supplements to the NGC in 1895 and 1908, known as the Index Catalogues, describing a further 5,386 astronomical objects. Thousands of these objects are best known by their NGC or IC numbers, which remain in widespread use.
Hipparcos was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky. This permitted the first high-precision measurements of the intrinsic brightnesses, proper motions, and parallaxes of stars, enabling better calculations of their distance and tangential velocity. When combined with radial velocity measurements from spectroscopy, astrophysicists were able to finally measure all six quantities needed to determine the motion of stars. The resulting Hipparcos Catalogue, a high-precision catalogue of more than 118,200 stars, was published in 1997. The lower-precision Tycho Catalogue of more than a million stars was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000. Hipparcos' follow-up mission, Gaia, was launched in 2013.
Maia, designated 20 Tauri, is a star in the constellation of Taurus. It is a blue giant of spectral type B8 III, a chemically peculiar star, and the prototype of the Maia variable class of variable star.
Messier 62 or M62, also known as NGC 6266, is a globular cluster of stars in the south of the equatorial constellation of Ophiuchus. It was discovered in 1771 by Charles Messier, then added to his catalogue eight years later.
Brocchi's Cluster is a asterism of 10 stars. Six of the stars appear in an row, across 1.3° of the night sky. The cluster is in the south of the constellation Vulpecula, near the constellation Sagitta. Its nickname is the Coathanger. None of these ten stars are believed to be gravitationally bound to each other, thus they are not a star cluster, a fact not known until 1997. An additional 30 or so much fainter stars are considered by some to be part of the asterism.
Upsilon Scorpii, formally named Lesath, is a star located in the "stinger" of the southern zodiac constellation of Scorpius, the scorpion. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 580 light-years from the Sun. In the night sky it lies near the 1.6 magnitude star Lambda Scorpii, and the two form an optical pair that is sometimes called the "Cat's Eyes".
Merope, designated 23 Tauri, is a star in the constellation of Taurus and a member of the Pleiades star cluster. It is approximately 440 light-years (135 pc) away.
Pi Puppis, Latinized from π Puppis, also named Ahadi, is the second-brightest star in the southern constellation of Puppis. It has an apparent visual magnitude of 2.733, so it can be viewed with the naked eye at night. Parallax measurements yield an estimated distance of roughly 810 light-years from the Earth. This is a double star with a magnitude 6.86 companion at an angular separation of 0.72 arcsecond and a position angle of 148° from the brighter primary.
V533 Carinae is a white A-type supergiant variable star with a mean apparent magnitude of +4.59 in the constellation Carina. It is over 10,000 light years from Earth.
The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster of stars in the northern constellation of Perseus. To the naked eye, the cluster consists of several blue-hued spectral type B stars. The most luminous member is the ~2nd magnitude white-yellow supergiant Mirfak, also known as Alpha Persei. Bright members also include Delta, Sigma, Psi, 29, 30, 34, and 48 Persei. The Hipparcos satellite and infrared color-magnitude diagram fitting have been used to establish a distance to the cluster of ~560 light-years (172 pc). The distance established via the independent analyses agree, thereby making the cluster an important rung on the cosmic distance ladder. As seen from the Earth, the extinction of the cluster due to interstellar dust is around 0.30.
S Monocerotis, also known as 15 Monocerotis, is a massive multiple and variable star system located in the constellation Monoceros. It is the brightest star in the Christmas Tree open cluster in the area catalogued as NGC 2264.
μ Normae, Latinised as Mu Normae, is a blue supergiant star of spectral type O9.7 Iab, located in the constellation of Norma.
Phi1 Ceti is a single star located in the equatorial constellation of Cetus. It is visible to the naked eye with an apparent visual magnitude of +4.78. Based upon an annual parallax shift of 13.96 mas, it is located about 234 light years from the Sun. Based upon the motion of this star through space, Phi1 Ceti is a probable member of the proposed Wolf 630 moving group. This is a set of stars centered on Wolf 630 that are moving nearly in parallel and have an age of around 2.7±0.5 billion years. They may be former members of a dissolved open cluster.
WR 24 is a Wolf-Rayet star in the constellation Carina. It is one of the most luminous stars known. At the edge of naked eye visibility it is also one of the brightest Wolf Rayet stars in the sky.
χ Puppis, Latinised as Chi Puppis, is a single star in the southern constellation of Puppis. It has a white hue and is faintly visible to the eye at night with an apparent visual magnitude of 4.79. The star is located at a distance of approximately 1,800 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +30 km/s. O. J. Eggen listed this star as a member of the Hyades Stream based on its space motion.
V520 Persei is a blue supergiant member of NGC 869, one of the Perseus Double Cluster open clusters. It is an irregular variable star. At a magnitude of 6.55, V520 Persei is the brightest member in either NGC 869 or NGC 884, although the brighter HD 13994 lies in the foreground along the same line of sight.
References
- 1 2 3 The Astronomical Almanac, Nautical Almanac Office, Great Britain: United States Naval Observatory, p. H68
- 1 2 van Leeuwen, F. (April 2009), "Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue", Astronomy and Astrophysics, 497 (1): 209–242, arXiv: 0902.1039 , Bibcode:2009A&A...497..209V, doi:10.1051/0004-6361/200811382
- ↑ "C 0722-321 – Cluster of Stars", SIMBAD, Centre de Données astronomiques de Strasbourg , retrieved 2010-12-23
- 1 2 3 Fitzgerald, M. P.; Miller, M.; Harris, G. L. H. (April 1980), "A spectroscopic and statistical study of Collinder 140", Monthly Notices of the Royal Astronomical Society , 191: 95–114, Bibcode:1980MNRAS.191...95F, doi: 10.1093/mnras/191.1.95
- ↑ Plotner, Tammy (2007), What's Up 2007: 365 Days of Skywatching, Lulu.com, p. 87, ISBN 0-9782214-0-0
- ↑ Subramaniam, A.; Bhatt, H. C. (December 1999), "Star Formation History of the Puppis-Vela Region Using HIPPARCOS Data", in Nakamoto, T. (ed.), Star Formation 1999, Proceedings of Star Formation 1999, pp. 373–374, Bibcode:1999sf99.proc..373S