Astronomy:WOH G64

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Short description: Star in the constellation Dorado
WOH G64
Magellanic Cloud.jpg
Red circle.svg
Location of WOH G64 (circled) in the Large Magellanic Cloud
Credit: NASA/JPL-Caltech/M. Meixner (STScI) & the SAGE Legacy Team
Observation data
Equinox J2000.0]] (ICRS)
Constellation Dorado (LMC)
Right ascension  04h 55m 10.5252s[1]
Declination −68° 20′ 29.998″[1]
Apparent magnitude (V) 17.7 - 18.8[2]
Characteristics
Evolutionary stage OH/IR red supergiant
Spectral type M5 I[3] – M7.5e[4][5]
Apparent magnitude (K) 6.849[6]
Apparent magnitude (R) 15.69[7]
Apparent magnitude (G) 15.0971[1]
Apparent magnitude (I) 12.795[8]
Apparent magnitude (J) 9.252[6]
Apparent magnitude (H) 7.745[6]
Variable type Carbon-rich LPV (Mira?)[8]
Astrometry
Radial velocity (Rv)294±2[3] km/s
Proper motion (μ) RA: 1.108[1] mas/yr
Dec.: −1.348[1] mas/yr
Parallax (π)−0.2280 ± 0.0625[1] mas
Distance160,000 ly
(50,000[3] pc)
Absolute magnitude (MV)−6.00[3]
Details
Radius1,540±77[3][9][10] R☉
Luminosity282,000[11][3] L☉
Surface gravity (log g)+0.0[12]–−0.5[3] cgs
Temperature3,400[3] K
Age≤5[13] Myr
Other designations
WOH G064, 2MASS J04551048-6820298, IRAS 04553-6825, MSX LMC 1182
Database references
SIMBADdata

WOH G64 (IRAS 04553-6825) is an unusual[3] 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.[3][14] 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☉).

WOH G64 is surrounded by an optically thick dust envelope of roughly a light year in diameter containing 3 to 9 times the Sun's mass of expelled material that was created by the strong stellar wind.[11] If placed at the center of the Solar System, the star's photosphere would engulf the orbit of Jupiter.

Discovery

WOH G64 was discovered in the 1970s by Bengt Westerlund, Olander and Hedin. Like NML Cygni, the "WOH" in the star's name comes from the names of its three discoverers, but in this case refers to a whole catalogue of giant and supergiant stars in the LMC.[15] Westerlund also discovered another notable red supergiant star, Westerlund 1-26, found in the massive super star cluster Westerlund 1 in the constellation Ara.[16] In 1986, infrared observations showed that it was a highly luminous supergiant surrounded by gas and dust which absorbed around three quarters of its radiation.[5]

In 2007, observers using the Very Large Telescope (VLT) showed that WOH G64 is surrounded by a torus-shaped cloud.[11]

Distance

The distance of WOH G64 is assumed to be around 50,000 parsecs (160,000 ly) away from Earth, since it appears to be in the LMC.[3] The Gaia Data Release 2 parallax for WOH G64 is −0.2280±0.0625 mas and the negative parallax does not provide a reliable distance.[1]

Variability

WOH G64 varies regularly in brightness by over a magnitude at visual wavelengths with a primary period of around 800 days.[7] The star suffers from over six magnitudes of extinction at visual wavelengths, and the variation at infra-red wavelengths is much smaller.[3] It has been described as a carbon-rich Mira or long-period variable, which would necessarily be an asymptotic-giant-branch star (AGB star) rather than a supergiant.[8] Brightness variability has been confirmed by other researchers in some spectral bands, but it is unclear what the actual variable type is. No significant spectral variation has been found.[3]

Physical properties

Artist's impression of the dusty torus around WOH G64 (European Southern Observatory)

The spectral type of WOH G64 is given as M5,[3] but it is usually found to have a much cooler spectral type of M7.5, highly unusual for a supergiant star.[13][4][5]

WOH G64 is classified as an extremely luminous M class supergiant and is likely to be the largest star and the most luminous and coolest red supergiant in the LMC.[3] The combination of the star's temperature and luminosity places it toward the upper right corner of the Hertzsprung–Russell diagram. The star's evolved state means that it can no longer hold on to its atmosphere due to low density, high radiation pressure, and the relatively opaque products of thermonuclear fusion.[citation needed] It has an average mass loss rate of 3.1 to 5.8×10−4 M☉ per year, among the highest known and unusually high even for a red supergiant.[17][18]

The parameters of WOH G64 are uncertain. Based on spectroscopic measurements assuming spherical shells, the star was originally calculated to be around between 490,000 and 600,000 L☉, suggesting initial masses at least 40 M☉ and consequently larger values for the radius between 2,575 and 3,000 R☉.[19][4][20] One such of these mesaurements from 2018 gives a luminosity of 432,000 L☉ and a higher effective temperature of 3,500 K, based on optical and infrared photometry and assuming spherically-symmetric radiation from the surrounding dust. This would suggest a radius of 1,788 R☉.[12][lower-alpha 1]

WOH G64 compared to the sun.

2007 measurements using the Very Large Telescope (VLT) gave the star a bolometric luminosity of 282,000+40,000
−30,000 L☉ based on radiative transfer modelling of the surrounding torus, suggesting an initial mass of 25±5 M☉ and a radius around 1,730 R☉ based on the assumption of an effective temperature of 3,200 K.[11] In 2009, Levesque calculated an effective temperature of 3,400±25 K by spectral fitting of the optical and near-UV SED. Adopting the Ohnaka luminosity with this new temperature gives a radius of 1,540 R☉ but with a margin of error of 5% or 77 R☉.[3] Those physical parameters are consistent with the largest galactic red supergiants and hypergiants found elsewhere such as VY Canis Majoris and with theoretical models of the coolest, most luminous and largest possible cool supergiants (e.g. the Hayashi limit or the Humphreys–Davidson limit).[3][11][4] Ignoring the effect of the dusty torus in redirecting infrared radiation, estimates of 1,970 - 1,990 R☉ based on a luminosity of 450,000+150,000
−120,000 L☉ and an effective temperature of 3,372 - 3,400 K have also been derived.[3]

Spectral features

WOH G64 was discovered to be a prominent source of OH, H2O, and SiO masers emission, which is typical of an OH/IR supergiant star.[3] It shows an unusual spectrum of nebular emission; the hot gas is rich in nitrogen and has a radial velocity considerably more positive than that of the star.[3] The stellar atmosphere is producing a strong silicate absorption band in mid-infrared wavelengths, accompanied a line emission due to highly excited carbon monoxide.[21]

Possible companion

WOH G64 has a possible late O-type dwarf companion of a bolometric magnitude of −7.5 or a luminosity of 100,000 L☉, which would make WOH G64 a binary star although there has been no confirmation of this observation and the intervening dust clouds makes the study of the star very difficult.[3]

See also

  • HV 888, another red supergiant in the Large Magellanic Cloud
  • VY Canis Majoris, considered to be possibly the largest star in the Milky Way
  • NML Cygni
  • R136a1, one of the most massive and luminous stars known

Notes

  1. ↑ Applying the Stefan-Boltzmann Law with a nominal solar effective temperature of 5,772 K:
    [math]\displaystyle{ \sqrt{(5772/3500)^4 * 432,190} = 1787.94\ R\odot }[/math]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 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.
  2. ↑ Bhardwaj, Anupam; Kanbur, Shashi; He, Shiyuan; Rejkuba, Marina; Matsunaga, Noriyuki; De Grijs, Richard; Sharma, Kaushal; Singh, Harinder P. et al. (2019). "Multiwavelength Period-Luminosity and Period-Luminosity-Color Relations at Maximum Light for Mira Variables in the Magellanic Clouds". The Astrophysical Journal 884 (1): 20. doi:10.3847/1538-4357/ab38c2. Bibcode: 2019ApJ...884...20B. 
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 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. 
  4. ↑ 4.0 4.1 4.2 4.3 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. 
  5. ↑ 5.0 5.1 5.2 Elias, J.H. (March 1986). "Two Supergiants in the Large Magellanic Cloud with Thick Dust Shells". Astrophysical Journal 302: 675. doi:10.1086/164028. Bibcode: 1986ApJ...302..675E. 
  6. ↑ 6.0 6.1 6.2 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E. et al. (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. http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/246. 
  7. ↑ 7.0 7.1 Fraser, Oliver J.; Hawley, Suzanne L.; Cook, Kem H. (2008). "The Properties of Long-Period Variables in the Large Magellanic Cloud from MACHO". The Astronomical Journal 136 (3): 1242–1258. doi:10.1088/0004-6256/136/3/1242. Bibcode: 2008AJ....136.1242F. 
  8. ↑ 8.0 8.1 8.2 Soszyñski, I.; Udalski, A.; Szymañski, M. K.; Kubiak, M.; Pietrzyñski, G.; Wyrzykowski, Ł.; Szewczyk, O.; Ulaczyk, K. et al. (2009). "The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. IV. Long-Period Variables in the Large Magellanic Cloud". Acta Astronomica 59 (3): 239. Bibcode: 2009AcA....59..239S. 
  9. ↑ Levesque, E. M. (June 2010). "The Physical Properties of Red Supergiants". Hot and Cool: Bridging Gaps in Massive Star Evolution ASP Conference Series. 425. pp. 103. Bibcode: 2010ASPC..425..103L. https://articles.adsabs.harvard.edu/pdf/2010ASPC..425..103L. 
  10. ↑ Beasor, Emma R.; Smith, Nathan (2022-05-01). "The Extreme Scarcity of Dust-enshrouded Red Supergiants: Consequences for Producing Stripped Stars via Winds". The Astrophysical Journal 933 (1): 41. doi:10.3847/1538-4357/ac6dcf. Bibcode: 2022ApJ...933...41B. 
  11. ↑ 11.0 11.1 11.2 11.3 11.4 Ohnaka, K.; Driebe, T.; Hofmann, K. H.; Weigelt, G.; Wittkowski, M. (2009). "Resolving the dusty torus and the mystery surrounding LMC red supergiant WOH G64". Proceedings of the International Astronomical Union 4: 454–458. doi:10.1017/S1743921308028858. Bibcode: 2009IAUS..256..454O. 
  12. ↑ 12.0 12.1 Groenewegen, Martin A. T.; Sloan, Greg C. (2018). "Luminosities and mass-loss rates of Local Group AGB stars and Red Supergiants". Astronomy & Astrophysics 609: A114. doi:10.1051/0004-6361/201731089. ISSN 0004-6361. Bibcode: 2018A&A...609A.114G. 
  13. ↑ 13.0 13.1 Davies, Ben; Crowther, Paul A.; Beasor, Emma R. (2018). "The luminosities of cool supergiants in the Magellanic Clouds, and the Humphreys–Davidson limit revisited". Monthly Notices of the Royal Astronomical Society 478 (3): 3138–3148. doi:10.1093/mnras/sty1302. Bibcode: 2018MNRAS.478.3138D. 
  14. ↑ Jones, Olivia; Woods, Paul; Kemper, Franziska; Kraemer, Elena; Sloan, G.; Srinivasan, Sivakrishnan; Oliveira, Joana; van Loon, Jacco et al. (May 7, 2017). "The SAGE-Spec Spitzer Legacy program: the life-cycle of dust and gas in the Large Magellanic Cloud. Point source classification – III". Monthly Notices of the Royal Astronomical Society 470 (3): 3250–3282. doi:10.1093/mnras/stx1101. https://www.researchgate.net/publication/316780448. Retrieved 23 June 2022. 
  15. ↑ Westerlund, B. E.; Olander, N.; Hedin, B. (1981). "Supergiant and giant M type stars in the Large Magellanic Cloud". Astronomy & Astrophysics Supplement Series 43: 267–295. Bibcode: 1981A&AS...43..267W. 
  16. ↑ Westerlund, B. E. (1987). "Photometry and spectroscopy of stars in the region of a highly reddened cluster in ARA". Astronomy and Astrophysics. Supplement 70 (3): 311–324. ISSN 0365-0138. Bibcode: 1987A&AS...70..311W. 
  17. ↑ Steven R. Goldman; Jacco Th. van Loon (2016). "The wind speeds, dust content, and mass-loss rates of evolved AGB and RSG stars at varying metallicity". Monthly Notices of the Royal Astronomical Society 465 (1): 403–433. doi:10.1093/mnras/stw2708. Bibcode: 2017MNRAS.465..403G. 
  18. ↑ de Wit, S.; Bonanos, A.Z.; Tramper, F.; Yang, M.; Maravelias, G.; Boutsia, K.; Britavskiy, N.; Zapartas, E. (2023). "Properties of luminous red supergiant stars in the Magellanic Clouds". Astronomy and Astrophysics 669: 17. doi:10.1051/0004-6361/202243394. Bibcode: 2023A&A...669A..86D. 
  19. ↑ Elias, J. H; Frogel, J. A; Schwering, P. B. W (1986). "Two Supergiants in the Large Magellanic Cloud with Thick Dust Shells". The Astrophysical Journal 302: 675. doi:10.1086/164028. Bibcode: 1986ApJ...302..675E. 
  20. ↑ Monnier, J. D; Millan-Gabet, R; Tuthill, P. G; Traub, W. A; Carleton, N. P; Coudé Du Foresto, V; Danchi, W. C; Lacasse, M. G et al. (2004). "High-Resolution Imaging of Dust Shells by Using Keck Aperture Masking and the IOTA Interferometer". The Astrophysical Journal 605 (1): 436–461. doi:10.1086/382218. Bibcode: 2004ApJ...605..436M. 
  21. ↑ The mass-loss rates of red supergiants at low metallicity: Detectionof rotational CO emission from two red supergiants in the LargeMagellanic Cloud

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