Westerlund 1 W26

Westerlund 1 W26
	; Westerlund 1 with the inset showing W26 and the associated ionised hydrogen cloud; Credit: ESO
Observation data; Epoch J2000 Equinox J2000
Constellation	Ara
Right ascension	16h 47m 05.403s
Declination	−45° 50′ 36.76″
Apparent magnitude (V)	17.194
Characteristics
Spectral type	M0.5–M6(M2-M6Ia)
Apparent magnitude (B)	22.1
Apparent magnitude (J)	4.31
Apparent magnitude (H)	1.35
Apparent magnitude (K)	1.9
B−V color index	+4.906
Astrometry
Radial velocity (Rv)	-49.42 km/s
Proper motion (μ)	RA: -1.841 mas/yr ; Dec.: -3.909 mas/yr
Distance	14,200 ly ; (4,350 pc)
Details
Radius	1,145–1,240 R☉
Luminosity	276,000±10,000 L☉
Temperature	3,782±14 K
Age	7.9 Myr
Other designations
	Westerlund 1 W26, W1–26, 2MASS J16470540-4550367, Westerlund 1 BKS AS, Westerlund 1 BKS A, Gaia EDR3 5940106041452150272
Database references
SIMBAD	data

Last updated May 22, 2024

Westerlund 1 W26 (commonly abbreviated to W26) or Westerlund 1 BKS AS is a red supergiant located at the outskirts of the Westerlund 1 super star cluster. It is one of the largest known stars and the most luminous supergiant stars discovered so far with radius calculated to be in excess of a thousand times the solar radius, and a luminosity of over 200,000 times the solar luminosity. If placed at the center of the Solar System, its photosphere would engulf the orbit of Jupiter.

Discovery

Westerlund 1 was discovered by Bengt Westerlund in 1961 during an infrared survey in the Zone of Avoidance of the sky, and described as "a heavily reddened cluster in Ara". The spectral types of the component stars could not be determined at the time except for the brightest star which was tentatively considered type M.^[8]^[9]

In 1969, Borgman, Kornneef, and Slingerland conducted a photometric survey of the cluster and assigned letters to the stars they measured. This star, identified as a strong radio source, was given the letter "A".^[10] This leads to the designation Westerlund-1 BKS A as used by Simbad, although the cluster was not known as Westerlund 1 at that time. At the time it was referred to as Ara A, with another strong radio source in the cluster called Ara C. Its brightness in the radio spectrum makes it one of the rare "radio stars". Westerlund made spectroscopic observations of the cluster, still not known as Westerlund 1, published in 1987 and numbered the stars, giving the number 26 and the spectral type M2I.^[9] Westerlund also discovered another notable red supergiant, WOH G64, found in the Large Magellanic Cloud in the constellation Dorado.

Modern terminology stems from 1998 when the cluster was referred to as Westerlund 1 (Wd1), with a paper describing Ara A as star 26 and Ara C as star 9.^[11]

Physical characteristics

W26 is classified as a luminous cool supergiant. It occupies the upper right corner of the Hertzsprung–Russell diagram. The cool temperature means it emits a significant part of its energy in the infrared spectrum. It also shows huge mass loss of atmospheric material, suggesting that it may further evolve into a hotter supergiant. W26 has been observed to change its spectral class (and thus its temperature) during several periods, but it has not been seen to change its luminosity.^[12]

The star is almost obscured at visible wavelengths by extinction of around 13 magnitudes due to interstellar dust,^[2] hence it has been studied extensively in the longer infrared to radio wavelengths, which made it easier to study. Its spectral type identifies it a red star with a high luminosity. The bolometric luminosity of W26 has been calculated from its K-band infrared brightness to be 380,000 or 320,000 times higher than the sun's (L_☉), depending on the spectral type between M2 and M5. These luminosities imply a radius 1,530 or 1,580 times the Sun's radius (R_☉)^[12] based on assumed effective temperatures of 3,660 or 3,450 K for spectral types M2 and M5 respectively.^[13]^[12] These parameters make W26 one of the most luminous red supergiants and are similar to those estimated for another notable red supergiant star, VY Canis Majoris.^[12]

An earlier calculation of the luminosity and the temperature by fitting the spectral energy distribution and based on the spectrum by using DUSTY model gave a far higher luminosity near 1,100,000 L_☉, considerably more luminous than expected for a red supergiant. The model also gave a photospheric temperature of 3,700 K, corresponding to a radius of 2,519 R_☉, leading to a volume 16 billion times bigger than the Sun.^[14]^{[lower-alpha 1]}

Surroundings

In October 2013, astronomers using the European Southern Observatory's Very Large Survey Telescope (VST) discovered that W26 is surrounded by a glowing cloud of ionized hydrogen. This is the first ionized nebula to have been discovered around a red supergiant star through its optical emission lines, and follows the discovery of an ionized nebula around NML Cyg in 1982.^[15]^[16] The nebula extends 1.30 parsecs from the star.^{[ citation needed ]} The nebulae of both Westerlund 1 W20 and W26 are extended outward from the cluster core and most bright at inward direction, indicating the outward cluster wind.^[17] A later study analyzed the ejecta surrounding some of Westerlund 1's stars; the study determined the mass of W26's ejecta to be 403×10⁻³ M_☉, with an uncertainty of ± 94×10⁻³ M_☉.^[18]

Notes

↑ Applying the Stefan-Boltzmann Law with a nominal solar effective temperature of 5,772 K: ${\sqrt {(5,772/3,700)^{4}*10^{6.03}}}=2,519.12\ R\odot$

Related Research Articles

Ara is a southern constellation between Scorpius, Telescopium, Triangulum Australe, and Norma. It was one of the Greek bulk described by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations designated by the International Astronomical Union.

Scutum is a small constellation. Its name is Latin for shield, and it was originally named Scutum Sobiescianum by Johannes Hevelius in 1684. Located just south of the celestial equator, its four brightest stars form a narrow diamond shape. It is one of the 88 IAU designated constellations defined in 1922.

<span class="mw-page-title-main">Red supergiant</span> Stars with a supergiant luminosity class with a spectral type of K or M

Red supergiants (RSGs) are stars with a supergiant luminosity class and a stellar classification 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 Antares A are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars.

KY Cygni is a red supergiant of spectral class M3.5Ia located in the constellation Cygnus. It is approximately 4,700 light-years away.

Westerlund 2 is an obscured compact young star cluster 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.

<span class="mw-page-title-main">Yellow hypergiant</span> Class of massive star with a spectral type of A to K

A yellow hypergiant (YHG) is a massive star with an extended atmosphere, a spectral class from A to K, and, starting with an initial mass of about 20–60 solar masses, has lost as much as half that mass. They are amongst the most visually luminous stars, with absolute magnitude (M_V) around −9, but also one of the rarest, with just 20 known in the Milky Way and six of those in just a single cluster. They are sometimes referred to as cool hypergiants in comparison with O- and B-type stars, and sometimes as warm hypergiants in comparison with red supergiants.

V354 Cephei is a red supergiant star located within the Milky Way. It is an irregular variable located over 13,000 light-years away from the Sun. It has an estimated radius of 1,139 solar radii. If it were placed in the center of the Solar System, it would extend to between the orbits of Mars and Jupiter.

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.

MY Cephei is a red supergiant located in open cluster NGC 7419 in the constellation of Cepheus. It is a semiregular variable star with a maximum brightness of magnitude 14.4 and a minimum of magnitude 15.5.

S Persei is a red supergiant or hypergiant located near the Double Cluster in Perseus, north of the cluster NGC 869. It is a member of the Perseus OB1 association and one of the largest known stars. If placed in the Solar System, its photosphere would engulf the orbit of Jupiter. It is also a semiregular variable, a star whose variations are less regular than those of Mira variables.

WOH G64 is an unusual red supergiant (RSG) star in the Large Magellanic Cloud (LMC) satellite galaxy in the southern constellation of Dorado. It is one of the largest known stars, being described as possibly being the largest star known. It is also one of the most luminous and massive red supergiants, with a radius calculated to be around 1,540 times that of the Sun (R_☉) and a luminosity around 282,000 times the solar luminosity (L_☉).

<span class="mw-page-title-main">Hypergiant</span> Rare star with tremendous luminosity and high rates of mass loss by stellar winds

A hypergiant (luminosity class 0 or Ia⁺) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term hypergiant is defined as luminosity class 0 (zero) in the MKK system. However, this is rarely seen in literature or in published spectral classifications, except for specific well-defined groups such as the yellow hypergiants, RSG (red supergiants), or blue B(e) supergiants with emission spectra. More commonly, hypergiants are classed as Ia-0 or Ia⁺, but red supergiants are rarely assigned these spectral classifications. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially star formation, stability, and their expected demise as supernovae. A common example of a hypergiant is UY Scuti, although being a supergiant UY Scuti is considered a hypergiant by some people.

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Westerlund 1-237 or Westerlund 1 BKS B is a possible red supergiant (RSG) in the constellation of Ara. It is one out of four known red supergiants in the Westerlund 1 super star cluster, although its outlying position, spectrum, and parallax, suggest it could be a foreground giant. As a red supergiant, it would be one of the largest known stars and one of the most luminous of its type.

Westerlund 1-20 (abbreviated to Wd 1-20 or just W20) is a red supergiant (RSG) located in the Westerlund 1 super star cluster. Its radius was calculated to be around 965 solar radii (6.72 × 10⁸ km, 4.48 au), making it one of the largest stars discovered so far. This corresponds to a volume 899 million times bigger than the Sun. If placed at the center of the Solar System, the photosphere of Westerlund 1-20 would almost reach the orbit of Jupiter.

Westerlund 1 W75 or Wd 1-75 is a red supergiant (RSG) located in the Westerlund 1 super star cluster. Its radius is calculated to be around 668 solar radii (4.65 × 10⁸ km, 3.10 au). This corresponds to a volume 298 million times bigger than the Sun. If placed at the center of the Solar System, Westerlund 1-75 would engulf the inner limits of the asteroid belt.

Westerlund 1-243 or Wd 1-243 is a luminous blue variable (LBV) star undergoing an eruptive phase located within the outskirts of the super star cluster Westerlund 1. Located about 13,400 ly (4,100 pc) from Earth, it has a luminosity of 0.73 million L_☉ making it one of the most luminous stars known.

Stephenson 2 DFK 49 or St2-11 is a putative post red supergiant star in the constellation Scutum. It is located in the massive open cluster Stephenson 2. It is possibly one of the largest known stars with radius estimates ranging from 884 solar radii to 1,300 solar radii. If the upper estimate is correct, then Stephenson 2 DFK 49 has a volume 2.2 billion times that of the Sun. If it was placed at the center of the Solar System, its photosphere will potentially approach or engulf Jupiter's orbit. It loses mass at a very high rate, resulting in large amounts of Infrared excess.

References

1 2 3 4 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
1 2 3 Lim, Beomdu; Chun, Moo-Young; Sung, Hwankyung; Park, Byeong-Gon; Lee, Jae-Joon; Sohn, Sangmo T.; Hur, Hyeonoh; Bessell, Michael S. (2013). "The Starburst Cluster Westerlund 1: The Initial Mass Function and Mass Segregation". The Astronomical Journal. 145 (2): 46. arXiv: 1211.5832 . Bibcode:2013AJ....145...46L. doi:10.1088/0004-6256/145/2/46. S2CID 56143904.
1 2 3 4 5 6 Arévalo, Aura (2019). The Red Supergiants in the Supermassive Stellar Cluster Westerlund 1 (Thesis). doi: 10.11606/D.14.2019.tde-12092018-161841 .
↑ Clark, J. S.; Ritchie, B. W.; Negueruela, I.; Crowther, P. A.; Damineli, A.; Jablonski, F. J.; Langer, N. (2011). "A VLT/FLAMES survey for massive binaries in Westerlund 1" (PDF). Astronomy & Astrophysics. 531: A28. arXiv: 1105.0776 . Bibcode:2011A&A...531A..28C. doi:10.1051/0004-6361/201116990. S2CID 119299122.
1 2 Clark, J. S.; Negueruela, I.; Crowther, P. A.; Goodwin, S. P. (2005). "On the massive stellar population of the super star cluster Westerlund 1". Astronomy and Astrophysics. 434 (3): 949. arXiv: astro-ph/0504342 . Bibcode:2005A&A...434..949C. doi:10.1051/0004-6361:20042413. S2CID 119042919.
↑ Piatti, A. E.; Bica, E.; Claria, J. J. (1998). "Fundamental parameters of the highly reddened young open clusters Westerlund 1 and 2". Astronomy and Astrophysics Supplement. 127 (3): 423. Bibcode:1998A&AS..127..423P. doi: 10.1051/aas:1998111 .
1 2 Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics . 649: A1. arXiv: 2012.01533 . Bibcode:2021A&A...649A...1G. doi: 10.1051/0004-6361/202039657 . S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
↑ Westerlund, Bengt (1961). "A Heavily Reddened Cluster in ARA". Publications of the Astronomical Society of the Pacific. 73 (430): 51. Bibcode:1961PASP...73...51W. doi:10.1086/127618. S2CID 119636689.
1 2 Westerlund, B. E. (1987). "Photometry and spectroscopy of stars in the region of a highly reddened cluster in ARA". Astronomy and Astrophysics Supplement Series. 70: 311. Bibcode:1987A&AS...70..311W. ISSN 0365-0138.
↑ Borgman, J.; Koornneef, J.; Slingerland, J. (1970). "Infra-red photometry of a heavily reddened cluster in Ara". Astronomy and Astrophysics. 4: 248. Bibcode:1970A&A.....4..248B.
↑ Clark, J. S.; Fender, R. P.; Waters, L. B. F. M.; Dougherty, S. M.; Korrnneef, J.; Steele, I. A.; Van Blokland, A. (1998). "Discovery of extended radio emission in the young cluster Wd1". Monthly Notices of the Royal Astronomical Society. 299 (4): L43. arXiv: astro-ph/9807303 . Bibcode:1998MNRAS.299L..43C. doi:10.1046/j.1365-8711.1998.02038.x. S2CID 16663149.
1 2 3 4 Wright, N. J.; Wesson, R.; Drew, J. E.; Barentsen, G.; Barlow, M. J.; Walsh, J. R.; Zijlstra, A.; Drake, J. J.; Eisloffel, J.; Farnhill, H. J. (16 October 2013). "The ionized nebula surrounding the red supergiant W26 in Westerlund 1". Monthly Notices of the Royal Astronomical Society: Letters. 437 (1): L1–L5. arXiv: 1309.4086 . Bibcode:2014MNRAS.437L...1W. doi:10.1093/mnrasl/slt127. S2CID 14889377.
↑ Levesque, Emily M.; Massey, Philip; Olsen, K.A.G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (2005). "The effective temperature scale of galactic red supergiants: Cool, but not as cool as we thought". The Astrophysical Journal. 628 (2): 973–985. arXiv: astro-ph/0504337 . Bibcode:2005ApJ...628..973L. doi:10.1086/430901. S2CID 15109583.
↑ Fok, Thomas K. T.; Nakashima, Jun-Ichi; Yung, Bosco H. K.; Hsia, Chih-Hao; Deguchi, Shuji (2012). "Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated with Massive Clusters". The Astrophysical Journal. 760 (1): 65. arXiv: 1209.6427 . Bibcode:2012ApJ...760...65F. doi:10.1088/0004-637X/760/1/65. S2CID 53393926.
↑ Morris, M.; Jura, M. (1983). "The nature of NML Cygnus". Astrophysical Journal. 267: 179. Bibcode:1983ApJ...267..179M. doi: 10.1086/160856 .
↑ Habing, H. J.; Goss, W. M.; Winnberg, A. (1982). "An H II region near NML Cygnus". Astronomy and Astrophysics. 108: 412. Bibcode:1982A&A...108..412H.
↑ Andrews, H.; Fenech, D.; Prinja, R. K.; Clark, J. S.; Hindson, L. (2018), "Asymmetric ejecta of cool supergiants and hypergiants in the massive cluster Westerlund 1", Monthly Notices of the Royal Astronomical Society: Letters, 477 (1): L55–L59, arXiv: 1803.07008 , Bibcode:2018MNRAS.477L..55A, doi:10.1093/mnrasl/sly046
↑ Andrews, H (June 2018). "Asymmetric ejecta of cool supergiants and hypergiants in the massive cluster Westerlund 1". Monthly Notices of the Royal Astronomical Society. 477 (1): L55–L59. arXiv: 1803.07008 . Bibcode:2018MNRAS.477L..55A. doi:10.1093/mnrasl/sly046.

Observation data Epoch J2000 Equinox J2000
Westerlund 1 with the inset showing W26 and the associated ionised hydrogen cloud Credit: ESO
Constellation	Ara
Right ascension	16^h 47^m 05.403^s^[1]
Declination	−45° 50′ 36.76″^[1]
Apparent magnitude (V)	17.194^[2]
Characteristics
Spectral type	M0.5–M6^[3](M2-M6Ia^[4])
Apparent magnitude (B)	22.1^[5]
Apparent magnitude (J)	4.31^[1]
Apparent magnitude (H)	1.35^[1]
Apparent magnitude (K)	1.9^[6]
B−V color index	+4.906^[2]^[5]
Astrometry

Radial velocity (R_v)	-49.42 km/s
Proper motion (μ)	RA: -1.841^[7] mas/yr Dec.: -3.909^[7] mas/yr
Distance	14,200 ly (4,350^[3] pc)

Details

Radius	1,145–1,240^[3] `R`_☉
Luminosity	276,000±10,000^[3] `L`_☉
Temperature	3,782±14^[3] K
Age	7.9^[3] Myr

Other designations
Westerlund 1 W26, W1–26, 2MASS J16470540-4550367, Westerlund 1 BKS AS, Westerlund 1 BKS A, Gaia EDR3 5940106041452150272
Database references
SIMBAD	data