Westerlund 2

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Westerlund 2
NASA Unveils Celestial Fireworks as Official Hubble 25th Anniversary Image.jpg
The cluster Westerlund 2 and its surroundings
Credit: Hubble Space Telescope
Observation data (J2000 epoch)
Right ascension 10h 23m 58.1s [1]
Declination −57° 45′ 49″ [1]
Distance 20000 ly (6000 pc)
Apparent magnitude  (V)10.5 [1]
Physical characteristics
Contains some of the hottest, brightest, and most massive stars.
Other designationsESO 127-18, VDBH 95 [1]
Associations
Constellation Carina
See also: Open cluster, List of open clusters

Westerlund 2 is an obscured compact young star cluster (perhaps even a super star cluster [2] ) in the Milky Way, with an estimated age of about one or two million years. It contains some of the hottest, brightest, and most massive stars known. The cluster resides inside a stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina. It is half a degree from the naked eye Cepheid variable V399 Carinae. [3]

Contents

Cluster members

The cluster contains at least a dozen early O stars, of which at least three are eclipsing binaries. All are hotter than 38,000 K and more luminous than 230,000 L☉. [4] There are around 20 further O class stars in the cluster, all main sequence objects implying a very young age for the cluster. [5]

Several Wolf–Rayet stars are found in the vicinity of Westerlund 2, although not in the central core. WR 20a, a binary consisting of two WR stars, and the single stars WR 20aa, WR 20b, and WR 20c are all thought to be members of the cluster, although possibly now runaway members. All five Wolf Rayets are extremely young massive objects with OIf*/WN spectral types, amongst the most luminous stars in the galaxy. This composite spectral type indicates young very massive hydrogen-burning stars that are just starting to convect nitrogen and helium to the surface and develop denser stellar winds so that they show the emission lines of a Wolf-Rayet star. WR21a, itself a massive binary, lies in the same direction but is unlikely to be a member of Westerlund 2. [6]

Westerlund 2 also contains a large number of pre-main sequence stars with masses below 2.5 M☉. These stars constrain the age of the cluster to near 2 Myr. [7]

Discovery

Westerlund 2 surrounded by stellar nursery RCW 49 Westerlund 2 Young.jpg
Westerlund 2 surrounded by stellar nursery RCW 49

As its name indicates, the Westerlund 2 cluster was discovered by Bengt Westerlund in the 1960s [8] but its stellar content was assessed only in later years. [9]

Hubble 25th Anniversary Image

On 23 April 2015 an image of the Westerlund 2 cluster was chosen to celebrate the 25th anniversary of the Hubble Space Telescope. [3]

See also

Related Research Articles

<span class="mw-page-title-main">Arches Cluster</span>

The Arches Cluster is the densest known star cluster in the Milky Way, about 100 light-years from its center in the constellation Sagittarius, 25,000 light-years from Earth. Its discovery was reported by Nagata et al. in 1995, and independently by Cotera et al. in 1996. Due to extremely heavy optical extinction by dust in this region, the cluster is obscured in the visual bands, and is observed in the X-ray, infrared and radio bands. It contains approximately 135 young, very hot stars that are many times larger and more massive than the Sun, plus many thousands of less massive stars.

<span class="mw-page-title-main">Westerlund 1</span> Super star cluster in the Milky Way Galaxy

Westerlund 1 is a compact young super star cluster about 3.8 kpc away from Earth. It is thought to be the most massive young star cluster in the Milky Way, and was discovered by Bengt Westerlund in 1961 but remained largely unstudied for many years due to high interstellar absorption in its direction. In the future, it will probably evolve into a globular cluster.

<span class="mw-page-title-main">WR 136</span> Star in the constellation of Cygnus

WR 136 is a Wolf–Rayet star located in the constellation Cygnus. It is in the center of the Crescent Nebula. Its age is estimated to be around 4.7 million years and it is nearing the end of its life. Within a few hundred thousand years, it is expected to explode as a supernova.

<span class="mw-page-title-main">R136a1</span> Wolf–Rayet star with one of the highest mass and luminosity of any known star

R136a1 is one of the most massive and luminous stars known, at 196 M☉ and nearly 4.7 million L☉, and is also one of the hottest, at around 46,000 K. It is a Wolf–Rayet star at the center of R136, the central concentration of stars of the large NGC 2070 open cluster in the Tarantula Nebula in the Large Magellanic Cloud. The cluster can be seen in the far southern celestial hemisphere with binoculars or a small telescope, at magnitude 7.25. R136a1 itself is 100 times fainter than the cluster and can only be resolved using speckle interferometry.

<span class="mw-page-title-main">WR 22</span> Binary star in the constellation Carina

WR 22, also known as V429 Carinae or HR 4188, is an eclipsing binary star system in the constellation Carina. The system contains a Wolf-Rayet (WR) star that is one of the most massive and most luminous stars known, and is also a bright X-ray source due to colliding winds with a less massive O class companion. Its eclipsing nature and apparent magnitude make it very useful for constraining the properties of luminous hydrogen-rich WR stars.

WR 147 is a multiple star system in the constellation of Cygnus. The system is extremely reddened by interstellar extinction – that is, dust in front of the star scatters much of the blue light coming from WR 147, leaving the star appearing reddish.

WR 142 is a Wolf-Rayet star in the constellation Cygnus, an extremely rare star on the WO oxygen sequence. It is a luminous and very hot star, highly evolved and close to exploding as a supernova. It is suspected to be a binary star with a companion orbiting about 1 AU away.

<span class="mw-page-title-main">Melnick 34</span> Binary star in the Large Magellanic cloud

Melnick 34, also called BAT99-116, is a binary Wolf–Rayet star near R136 in the 30 Doradus complex in the Large Magellanic Cloud. Both components are amongst the most massive and most luminous stars known, and the system is the most massive known binary system.

<span class="mw-page-title-main">WR 20a</span> Star in the constellation Carina

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.

<span class="mw-page-title-main">CD Crucis</span> Eclipsing binary star system in the constellation Crux

CD Crucis, also known as HD 311884, is an eclipsing binary star system in the constellation Crux. It is around 14,000 light years away near the faint open cluster Hogg 15. The binary contains a Wolf–Rayet star and is also known as WR 47.

<span class="mw-page-title-main">WR 21a</span> Star in the constellation Carina

WR 21a is an eclipsing binary star in the constellation Carina. It includes one of the most massive known stars and is one of the most massive binaries.

<span class="mw-page-title-main">WR 30a</span> Binary star in the constellation Carina

WR 30a is a massive spectroscopic binary in the constellation Carina. The primary is an extremely rare star on the WO oxygen sequence and the secondary a massive class O star. It appears near the Carina Nebula but is much further away.

WR 111 is a Wolf-Rayet (WR) star in the constellation Sagittarius. It is magnitude 7.8 and lies about 5,150 light-years away. It is one of the brightest and most closely studied WR stars.

WR 3 is a Wolf-Rayet star located around 9,500 light years away from Earth in the constellation of Cassiopeia.

<span class="mw-page-title-main">HD 151932</span> Star in the constellation of Scorpius

HD 151932, also known as WR 78, is a Wolf-Rayet star located in the constellation Scorpius, close to the galactic plane. Its distance is around 1,300 parsecs away from the Earth. Despite being a blue-colored Wolf-Rayet star, it is extremely reddened by interstellar extinction, so its apparent magnitude is brighter for longer-wavelength passbands. HD 151932 lies about 22′ west of the open cluster NGC 6231, the center of the OB association Scorpius OB1; it is not clear whether it is a part of the association or not. With an apparent magnitude of about 6.5, it is one of the few Wolf-Rayet stars that can be seen with the naked eye.

<span class="mw-page-title-main">HM 1</span> Open cluster in the constellation Scorpius

HM 1, also known as Havlen-Moffat 1, is an open cluster located in the constellation of Scorpius, close to the galactic plane. It was first observed by R. J. Havlen and A. F. J. Moffat in 1976. HM 1 is thought to be 9,500 to 12,700 light-years away from the Earth, beyond the Carina–Sagittarius Arm. It is heavily reddened by interstellar extinction, so although it comprises mostly blue-colored stars, it appears brighter for longer-wavelength passbands. It is projected against the H II region known as RCW 121, and appears to be the source of ionization for the nearby regions RCW 122 and RCW 123.

<span class="mw-page-title-main">HD 152408</span> Star in the constellation of Scorpius

HD 152408, also known as WR 79a, is a Wolf-Rayet star located in the constellation Scorpius, close to the galactic plane. Its distance is around 2,020 parsecs away from the Earth.

<span class="mw-page-title-main">WR 120</span> Binary star system in the constellation Scutum

WR 120 is a binary containing two Wolf-Rayet stars in the constellation of Scutum, around 10,000 light years away. The primary is a hydrogen-free weak-lined WN7 star, the secondary is a hydrogen-free WN3 or 4 star, and the system is a possible member of the cluster Dolidze 33. From our point of view, WR 120 is reddened by 4.82 magnitudes, and it has the variable designation of V462 Scuti.

References

  1. 1 2 3 4 "Cl Westerlund 2". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 1 May 2018.
  2. ↑ Y. Fukui; et al. (2015). "Cloud-cloud collision which triggered formation of the super star cluster RCW38". The Astrophysical Journal. 1504 (1): 26. arXiv: 1504.05391 . Bibcode:2016ApJ...820...26F. doi: 10.3847/0004-637X/820/1/26 . S2CID   118096773.
  3. 1 2 "Hubble Space Telescope Celebrates 25 Years of Unveiling the Universe". NASA. 23 April 2015.
  4. ↑ Rauw; et al. (1 March 2007). "Early-type stars in the core of the young open cluster Westerlund 2". Astronomy & Astrophysics. 463 (3): 981–991. arXiv: astro-ph/0612622 . Bibcode:2007A&A...463..981R. doi:10.1051/0004-6361:20066495. S2CID   17776145.
  5. ↑ Hur, Hyeonoh; Park, Byeong-Gon; Sung, Hwankyung; Bessell, Michael S.; Lim, Beomdu; Chun, Moo-Young; Sohn, Sangmo Tony (2015). "Reddening, distance, and stellar content of the young open cluster Westerlund 2". Monthly Notices of the Royal Astronomical Society. 446 (4): 3797–3819. arXiv: 1411.0879 . Bibcode:2015MNRAS.446.3797H. doi:10.1093/mnras/stu2329.
  6. ↑ Carraro, G.; Turner, D.; Majaess, D.; Baume, G. (2013). "The distance to the young open cluster Westerlund 2". Astronomy. 555: A50. arXiv: 1305.4309 . Bibcode:2013A&A...555A..50C. doi:10.1051/0004-6361/201321421. S2CID   53756444.
  7. ↑ Ascenso, J.; Alves, J.; Beletsky, Y.; Lago, M. T. V. T. (2007). "Near-IR imaging of Galactic massive clusters: Westerlund 2". Astronomy and Astrophysics. 466 (1): 137–149. Bibcode:2007A&A...466..137A. doi: 10.1051/0004-6361:20066433 .
  8. ↑ Bengt Westerlund (1 March 1961). "A Heavily Reddened Cluster in Ara". Astronomical Journal. 70: 57. Bibcode:1961AJ.....66T..57W. doi: 10.1086/108585 .
  9. ↑ Moffat; et al. (1 August 1991). "New Wolf-Rayet stars in Galactic open clusters - Sher 1 and the giant H II region core Westerlund 2". Astronomical Journal. 102: 642–653. Bibcode:1991AJ....102..642M. doi:10.1086/115897.
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