Astronomy:UY Scuti

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Short description: Star in the constellation Scutum

Coordinates: Sky map 18h 27m 36.53s, −12° 27′ 58.9″

For other uses, see UY Scuti (disambiguation).
UY Scuti
300px
DSS2 image of red supergiant star UY Scuti (brightest star in the image), surrounded by a dense starfield
Observation data
Equinox J2000.0]] (ICRS)
Constellation Scutum
Right ascension  18h 27m 36.5334s[1]
Declination −12° 27′ 58.866″[1]
Apparent magnitude (V) 8.29 - 10.56[2]
Characteristics
Evolutionary stage Extreme red supergiant[3] or hypergiant[4][5]
Spectral type M2-M4Ia-Iab[2]
U−B color index +3.29[6]
B−V color index +3.00[7]
Variable type SRc[8]
Astrometry
Radial velocity (Rv)18.33±0.82[9] km/s
Proper motion (μ) RA: 1.3[10] mas/yr
Dec.: −1.6[10] mas/yr
Parallax (π)0.5166 ± 0.0494[11] mas
Distance5,871+534
−446[12] ly
(1,800+164
−137[12] pc)
Absolute magnitude (MV)−6.2[13]
Details
Radius909[14] R☉
Luminosity124,000[14] L☉
Temperature3,550[14] K
Other designations
IRC −10422, RAFGL 2162, HV 3805, UY Sct, BD−12°5055
Database references
SIMBADdata

UY Scuti (BD-12°5055) is a red supergiant or hypergiant[4][5] star, located 5,900 light-years away in the constellation Scutum. It is also a pulsating variable star, with a maximum brightness of magnitude 8.29 and a minimum of magnitude 10.56, which makes it too dim for naked-eye visibility. It is considered to be one of the largest known stars, with a radius estimated at 909 solar radii (632 million kilometres; 4.23 astronomical units), thus a volume of 750 million times that of the Sun. This estimate implies that if it were placed at the center of the Solar System, its photosphere would extend past the orbit of Mars or even the asteroid belt.

Nomenclature and history

A visual band light curve for UY Scuti, plotted from ASAS data[15]

UY Scuti was first catalogued in 1860 by German astronomers at the Bonn Observatory, who were completing a survey of stars for the Bonner Durchmusterung Stellar Catalogue.[16] It was designated BD-12°5055, the 5,055th star between 12°S and 13°S counting from 0h right ascension.

On detection in the second survey, the star was found to have changed slightly in brightness, suggesting that it was a new variable star. In accordance with the international standard for designation of variable stars, it was called UY Scuti, denoting it as the 38th variable star of the constellation Scutum.[17]

UY Scuti is located a few degrees north of the A-type star Gamma Scuti and northeast of the Eagle Nebula. It is also near the Scutum OB3 association, which is located between 1.33 and 2.23 kiloparsecs (kpc) away,[18][19] although it is not considered to be a member. Although the star is very luminous, it is, at its brightest, only 9th magnitude as viewed from Earth, due to its distance and location in the Zone of Avoidance within the Cygnus rift.[20]

Characteristics

The size of UY Scuti compared to Earth's orbit and the Sun (barely visible)

UY Scuti is a dust-enshrouded bright red supergiant,[21] losing its mass at 5.8×10−5 M☉ per year, which leads to an extensive and complex circumstellar environment of gas and dust.[22] Sometimes described as an extreme red supergiant or hypergiant,[3][4][5] it has been compared to another pulsating but cooler supergiant, S Persei,[23] and is also found to be a maser source of H2O, SiO, and OH masers.[24] However, they are too weak for the star to be considered a true OH/IR supergiant, unlike VY Canis Majoris and IRC +10420.[25] It is classified as a semiregular variable with an approximate pulsation period of 740 days.[8][26][27] Based on an old radius of 1,708 R☉, this pulsation would be an overtone of the fundamental pulsation period, or it may be a fundamental mode corresponding to a smaller radius.[28]

The distance of UY Scuti is poorly known, but most estimates place it somewhere around 2 kpc.[13][29][12] It has no known companion star, and so its mass is also uncertain. However, it is expected on theoretical grounds to be between 7 and 10 M☉.[6]

In mid 2012, AMBER interferometry with the Very Large Telescope (VLT) in the Atacama Desert in Chile was used to measure the parameters of three red supergiants near the Galactic Center region:[6] UY Scuti, AH Scorpii, and KW Sagittarii. They determined that all three stars are over 1,000 times bigger than the Sun and over 100,000 times more luminous than the Sun. The stars' sizes were calculated using the Rosseland radius, the location at which the optical depth is ​2⁄3,[30] with distances adopted from earlier publications. UY Scuti was analyzed to be the largest, the most luminous and the coolest of the three stars measured, at 1,708 ± 192 R☉ (1.188×109 ± 134,000,000 km; 7.94 ± 0.89 astronomical unit|AU) based on an angular diameter of 5.48±0.10 mas and an assumed distance of 2.9±0.317 kpc (about 9,500±1,030 light-years) which was originally derived in 1970 based on the modelling of the spectrum of UY Scuti.[13] The luminosity is then calculated to be 340,000 L☉ at an effective temperature of 3,365±134 K, giving an initial mass of 25 M☉ (possibly up to 40 M☉ for a non-rotating star).[6] The calculated radius has led UY Sct to be sometimes described as the largest star known,[23] although potentially larger radius estimates have been implied and published for other supergiant stars, such as VX Sagittarii, NML Cygni, MY Cephei, and Stephenson 2 DFK 1. In addition, other leading candidates have been suggested, such as frequently both VY Canis Majoris and the extragalactic WOH G64 A,[31][32][33] which resides within the Large Magellanic Cloud.

Direct measurements of the parallax of UY Scuti published in the Gaia Data Release 2 give a parallax of 0.6433±0.1059 mas,[9] implying a closer distance of approximately 1.5 kiloparsecs (4,900 ly),[29] and consequently much lower luminosity and radius values of around 86,300–87,100 L☉ and 755 R☉ respectively.[34] However, the Gaia parallax might be unreliable due to a very high level of astrometric noise.[9] The distance of UY Scuti has been re-measured by Bailer-Jones et al. in 2021, based on a method that uses the stellar parallax from Gaia EDR3, its color and apparent brightness, giving it a much closer distance of 1,800 pc (5,900 ly).[12] A 2023 measurement based on the multimessenger monitoring of supernovae, puts the radius at a value of 909 R☉, together with a luminosity of 124,000 L☉ and effective temperature of 3,550 K.[14]

Supernova

Based on current models of stellar evolution, UY Scuti has begun to fuse helium and continues to fuse hydrogen in a shell around the core. The location of UY Scuti deep within the Milky Way disc suggests that it is a metal-rich star.[35]

After fusing heavy elements, its core will begin to produce iron, disrupting the balance of gravity and radiation in its core and resulting in a core collapse supernova. It is expected that a star like UY Scuti should evolve back to hotter temperatures to become a yellow hypergiant, luminous blue variable, or a Wolf–Rayet star, creating a strong stellar wind that will eject its outer layers and expose the core, before exploding as a type IIb, IIn, or type Ib/Ic supernova.[36]

References

  1. ↑ 1.0 1.1 Hog, E.; Kuzmin, A.; Bastian, U.; Fabricius, C.; Kuimov, K.; Lindegren, L.; Makarov, V. V.; Roeser, S. (1998). "The TYCHO Reference Catalogue". Astronomy and Astrophysics 335: L65. Bibcode: 1998A&A...335L..65H. 
  2. ↑ 2.0 2.1 "VSX: Detail for UY Sct". American Association of Variable Star Observers. https://www.aavso.org/vsx/index.php?view=detail.top&oid=34154. 
  3. ↑ 3.0 3.1 Dorda, R.; Negueruela, I.; González-Fernández, C. (2018). "The red supergiant population in the Perseus arm". Monthly Notices of the Royal Astronomical Society 475 (2): 2003–2015. doi:10.1093/mnras/stx3317. 
  4. ↑ 4.0 4.1 4.2 Tabernero, H. M.; Dorda, R.; Negueruela, I.; Marfil, E. (February 2021). "The nature of VX Sagitarii: Is it a TŻO, a RSG, or a high-mass AGB star?". Astronomy & Astrophysics 646: 13. doi:10.1051/0004-6361/202039236. Bibcode: 2021A&A...646A..98T. 
  5. ↑ 5.0 5.1 5.2 Jones, Terry (2025). "Red and Yellow Hypergiants". Galaxies 13 (2): 43. doi:10.3390/galaxies13020043. Bibcode: 2025Galax..13...43J. 
  6. ↑ 6.0 6.1 6.2 6.3 Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H. (2013). "The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii". Astronomy & Astrophysics 554: A76. doi:10.1051/0004-6361/201220920. Bibcode: 2013A&A...554A..76A. 
  7. ↑ Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues 2237: 0. Bibcode: 2002yCat.2237....0D. 
  8. ↑ 8.0 8.1 Kholopov, P. N.; Samus, N. N.; Kazarovets, E. V.; Perova, N. B. (1985). "The 67th Name-List of Variable Stars". Information Bulletin on Variable Stars 2681: 1. Bibcode: 1985IBVS.2681....1K. 
  9. ↑ 9.0 9.1 9.2 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  10. ↑ 10.0 10.1 Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P. et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27. doi:10.1888/0333750888/2862. ISBN 978-0333750889. Bibcode: 2000A&A...355L..27H. 
  11. ↑ Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G.  Gaia EDR3 record for this source at VizieR.
  12. ↑ 12.0 12.1 12.2 12.3 Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Demleitner, M.; Andrae, R. (2021). "Estimating Distances from Parallaxes. V. Geometric and Photogeometric Distances to 1.47 Billion Stars in Gaia Early Data Release 3". The Astronomical Journal 161 (3): 147. doi:10.3847/1538-3881/abd806. Bibcode: 2021AJ....161..147B.  Data about this star can be seen here.
  13. ↑ 13.0 13.1 13.2 Lee, T. A. (1970). "Photometry of high-luminosity M-type stars". Astrophysical Journal 162: 217. doi:10.1086/150648. Bibcode: 1970ApJ...162..217L. 
  14. ↑ 14.0 14.1 14.2 14.3 Healy, Sarah; Horiuchi, Shunsaku; Molla, Marta Colomer; Milisavljevic, Dan; Tseng, Jeff; Bergin, Faith; Weil, Kathryn; Tanaka, Masaomi (2024-03-23), "Red Supergiant Candidates for Multimessenger Monitoring of the Next Galactic Supernova", Monthly Notices of the Royal Astronomical Society 529 (4): 3630–3650, doi:10.1093/mnras/stae738, ISSN 0035-8711, Bibcode: 2024MNRAS.529.3630H 
  15. ↑ "ASAS All Star Catalogue". The All Sky Automated Survey. http://www.astrouw.edu.pl/asas/?page=aasc. 
  16. ↑ Bonner Durchmusterung (Argelander 1859–1862) (clicking on "bd.gz" downloads the gzipped 10.1 MB catalogue)
  17. ↑ Prager, R. (1927). "Katalog und Ephemeriden veraenderlicher Sterne fuer 1927". Kleine Veroeffentlichungen der Universitaetssternwarte zu Berlin Babelsberg 1: 1.i. Bibcode: 1927KVeBB...1....1P. 
  18. ↑ Melnik, A. M.; Dambis, A. K. (2020). "Distance scale for high-luminosity stars in OB associations and in field with Gaia DR2. Spurious systematic motions". Astrophysics and Space Science 365 (7): 112. doi:10.1007/s10509-020-03827-0. Bibcode: 2020Ap&SS.365..112M. 
  19. ↑ Humphreys, R. M. (1978). "Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way". Astrophysical Journal 38: 309. doi:10.1086/190559. Bibcode: 1978ApJS...38..309H. 
  20. ↑ "UY Sct (UY Scuti)". http://www.kusastro.kyoto-u.ac.jp/vsnet/gcvs2/SCTUY.html. 
  21. ↑ Van Loon, J. Th.; Cioni, M.-R. L.; Zijlstra, A. A.; Loup, C. (2005). "An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars". Astronomy and Astrophysics 438 (1): 273–289. doi:10.1051/0004-6361:20042555. Bibcode: 2005A&A...438..273V. 
  22. ↑ Sylvester, R. J.; Skinner, C. J.; Barlow, M. J. (1998). "Silicate and hydrocarbon emission from Galactic M supergiants". Monthly Notices of the Royal Astronomical Society 301 (4): 1083–1094. doi:10.1046/j.1365-8711.1998.02078.x. Bibcode: 1998MNRAS.301.1083S. https://discovery.ucl.ac.uk/10096081/1/sylvester98_msgts.pdf. 
  23. ↑ 23.0 23.1 Dorda, Ricardo; González-Fernández, Carlos; Negueruela, Ignacio (2016). "Characterisation of red supergiants in the Gaia spectral range". Astronomy & Astrophysics 595: A105. doi:10.1051/0004-6361/201628422. 
  24. ↑ "Object G19.144-0.472". https://maserdb.net/object.pl?object=G19.144-0.472. 
  25. ↑ Bowers, P. F. (December 1981). "Supergiant OH/IR stars.". The Astronomical Journal 86: 1930–1934. doi:10.1086/113074. ISSN 0004-6256. Bibcode: 1981AJ.....86.1930B. 
  26. ↑ Whiting, Wendy A. (1978). "Observations of Three Variable Stars in Scutum". The Journal of the American Association of Variable Star Observers 7 (2): 71. Bibcode: 1978JAVSO...7...71W. 
  27. ↑ Jura, M.; Kleinmann, S. G. (1990). "Mass-losing M supergiants in the solar neighborhood". The Astrophysical Journal Supplement Series 73: 769. doi:10.1086/191488. Bibcode: 1990ApJS...73..769J. 
  28. ↑ Joyce, Meridith; Leung, Shing-Chi; Molnár, László; Ireland, Michael; Kobayashi, Chiaki; Nomoto, Ken'Ichi (2020). "Standing on the Shoulders of Giants: New Mass and Distance Estimates for Betelgeuse through Combined Evolutionary, Asteroseismic, and Hydrodynamic Simulations with MESA". The Astrophysical Journal 902 (1): 63. doi:10.3847/1538-4357/abb8db. Bibcode: 2020ApJ...902...63J. 
  29. ↑ 29.0 29.1 Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Mantelet, G.; Andrae, R. (2018). "Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2". The Astronomical Journal 156 (2): 58. doi:10.3847/1538-3881/aacb21. Bibcode: 2018AJ....156...58B. 
  30. ↑ Wehrse, R.; Scholz, M.; Baschek, B. (June 1991). "The parameters R and Teff in stellar models and observations". Astronomy and Astrophysics 246 (2): 374–382. Bibcode: 1991A&A...246..374B. 
  31. ↑ Smith, Nathan; Beasor, Emma; Close, Laird (2025). "Spectroscopy of the complex core of VY Canis Majoris". HST Proposal: 18007. Bibcode: 2025hst..prop18007S. 
  32. ↑ Alcolea, J; Bujarrabal, V; Planesas, P; Teyssier, D; Cernicharo, J; De Beck, E; Decin, L; Dominik, C et al. (2013). "HIFISTARSHerschel/HIFI observations of VY Canis Majoris. Molecular-line inventory of the envelope around the largest known star". Astronomy & Astrophysics 559: A93. doi:10.1051/0004-6361/201321683. Bibcode: 2013A&A...559A..93A. 
  33. ↑ Levesque, E. M.; Massey, P.; Plez, B.; Olsen, K. A. G. (2009). "The Physical Properties of the Red Supergiant WOH G64: The Largest Star Known?". The Astronomical Journal 137 (6): 4744. doi:10.1088/0004-6256/137/6/4744. Bibcode: 2009AJ....137.4744L. 
  34. ↑ Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal 158 (1): 20. doi:10.3847/1538-3881/ab1cbd. Bibcode: 2019AJ....158...20M. 
  35. ↑ Meynet, Georges (2008). Israelian, Garik. ed. The metal-rich universe. Cambridge: Cambridge University Press. ISBN 9780521879989. http://www.cambridge.org/asia/catalogue/catalogue.asp?isbn=9780521879989. Retrieved 15 January 2016. 
  36. ↑ Groh, Jose H.; Meynet, Georges; Georgy, Cyril; Ekström, Sylvia (2013). "Fundamental properties of core-collapse supernova and GRB progenitors: Predicting the look of massive stars before death". Astronomy & Astrophysics 558: A131. doi:10.1051/0004-6361/201321906. Bibcode: 2013A&A...558A.131G. 



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