WOH G64

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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
Epoch J2000.0        Equinox J2000.0
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  mas [1]
Distance 160,000  ly
(50,000 [3]   pc)
Absolute magnitude  (MV)−6.00 [3]
Details
Mass 25±5 (initial mass) [3]   M☉
Radius 1,540±77 [3] [9] [10]   R☉
Luminosity 282,000+34,400
−30,700 [3]   L☉
Surface gravity (log g)+0.0 [11] –−0.5 [3]   cgs
Temperature 3,400±25 [3]   K
Age ≤5 [12]   Myr
Other designations
WOH G064, 2MASS  J04551048-6820298, IRAS  04553-6825, MSX LMC 1182
Database references
SIMBAD data

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] [13] 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☉).

Contents

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. [14] 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. [14]

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) WOH G64 Particular.jpg
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. [12] [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 measurements 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☉. [11] [lower-alpha 1]

WOH G64 compared to the sun. WOH G64 and The Sun.jpg
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 . [14] 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] [14] [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, H
2O , 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 main-sequence star 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

Notes

  1. ↑ Applying the Stefan-Boltzmann Law with a nominal solar effective temperature of 5,772  K:

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References

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  2. ↑ Bhardwaj, Anupam; Kanbur, Shashi; He, Shiyuan; Rejkuba, Marina; Matsunaga, Noriyuki; De Grijs, Richard; Sharma, Kaushal; Singh, Harinder P.; Baug, Tapas; Ngeow, Chow-Choong; Ou, Jia-Yu (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. arXiv: 1908.01795 . Bibcode:2019ApJ...884...20B. doi: 10.3847/1538-4357/ab38c2 . S2CID   199452754.
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  7. 1 2 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. arXiv: 0808.1737 . Bibcode:2008AJ....136.1242F. doi:10.1088/0004-6256/136/3/1242. S2CID   2754884.
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  9. ↑ Levesque, E. M. (June 2010). The Physical Properties of Red Supergiants. Hot and Cool: Bridging Gaps in Massive Star Evolution ASP Conference Series. Vol. 425. p. 103. arXiv: 0911.4720 . Bibcode:2010ASPC..425..103L. S2CID   8921166.
  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. arXiv: 2205.02207 . Bibcode:2022ApJ...933...41B. doi: 10.3847/1538-4357/ac6dcf . S2CID   248512934.
  11. 1 2 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. arXiv: 1711.07803 . Bibcode:2018A&A...609A.114G. doi:10.1051/0004-6361/201731089. ISSN   0004-6361. S2CID   59327105.
  12. 1 2 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. arXiv: 1804.06417 . Bibcode:2018MNRAS.478.3138D. doi:10.1093/mnras/sty1302. S2CID   59459492.
  13. ↑ Jones, Olivia; Woods, Paul; Kemper, Franziska; Kraemer, Elena; Sloan, G.; Srinivasan, Sivakrishnan; Oliveira, Joana; van Loon, Jacco; Boyer, Martha; Sargent, Benjamin; Mc Donald, I.; Meixner, Margaret; Zijlstra, A.; Ruffel, Paul; Lagadec, Eric; Pauly, Tyler (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. arXiv: 1705.02709 . doi: 10.1093/mnras/stx1101 . Retrieved 23 June 2022.
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  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. Bibcode:1987A&AS...70..311W. ISSN   0365-0138.
  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. arXiv: 1610.05761 . Bibcode:2017MNRAS.465..403G. doi:10.1093/mnras/stw2708. S2CID   11352637.
  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. arXiv: 2209.11239 . Bibcode:2023A&A...669A..86D. doi:10.1051/0004-6361/202243394. S2CID   252519285.
  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. Bibcode:1986ApJ...302..675E. doi:10.1086/164028. hdl: 1887/6514 .
  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; Morel, S; Perrin, G; Porro, I. L; Schloerb, F. P; Townes, C. H (2004). "High-Resolution Imaging of Dust Shells by Using Keck Aperture Masking and the IOTA Interferometer". The Astrophysical Journal. 605 (1): 436–461. arXiv: astro-ph/0401363 . Bibcode:2004ApJ...605..436M. doi:10.1086/382218. S2CID   7851916.
  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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