WOH G64

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WOH G64

VLTI image of the dusty torus around the star.
Credit: ESO
Observation data
J2000.0
Constellation Dorado
Right ascension 04h 55m 10.5252s[1]
Declination −68° 20′ 29.998″[1]
Apparent magnitude (V) 17.7 - 18.8[2]
Characteristics
A
Evolutionary stage Yellow hypergiant[3]
Apparent magnitude (K) 6.849[4]
Apparent magnitude (R) 15.69[5]
Apparent magnitude (G) 15.0971[1]
Apparent magnitude (I) 12.795[6]
Apparent magnitude (J) 9.252[4]
Apparent magnitude (H) 7.745[4]
Variable type Slow irregular variable + symbiotic[3]
B
Spectral type B[3]
Distance
160,000 ly
(50,000[8] pc)
Absolute magnitude (MV)−6.00[8]
Details
A
Myr
Other designations
WOH G064, 2MASS J04551048-6820298, IRAS 04553-6825, MSX LMC 1182
Database references
SIMBADdata

WOH G64 (IRAS 04553-6825) is a

B-type star. This system also exhibits features of B(e) stars.[3]

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.[10]

Observational history

WOH G64 was discovered in the 1970s by

Westerlund 1-26, found in the massive super star cluster Westerlund 1 in the constellation Ara.[12] 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.[13]

In 2007, observers using the Very Large Telescope (VLT) showed that WOH G64 is surrounded by a torus-shaped cloud.[10] In 2024, the dusty torus around WOH G64 was directly imaged by VLTI, showing the elongated and compact emission around the hypergiant. This is also the first interferometric imaging of a star outside the Milky Way.[14]

Variability

As a red supergiant, WOH G64 A varies regularly in brightness by over a magnitude at visual wavelengths with a primary period of around 800 days.

asymptotic-giant-branch star (AGB star) rather than a supergiant.[6] 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.[8] It is now classified as an irregular variable.[3]

Physical properties

Red supergiant stage

Artist's impression of the dusty torus and elliptical cocoon of dust surrounding WOH G64 (European Southern Observatory)

The spectral type of WOH G64 A in its red supergiant stage was given as M5,[8] but it is usually found to have a much cooler spectral type of M7.5, highly unusual for a supergiant star.[9][15][13]

WOH G64 was likely to be the largest star and the most luminous and coolest red supergiant in the LMC.[8] The combination of the star's temperature and luminosity placed it toward the upper right corner of the Hertzsprung–Russell diagram. It had 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.[16][17]

Based on spectroscopic measurements assuming spherical shells, the star was originally calculated to have luminosity 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☉.[13][15][18] 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☉.[19][a]

WOH G64 as a yellow hypergiant compared to the sun.

The dust surrounding WOH G64 was revealed in 2007 to have a torus-like shape which was being viewed pole-on, meaning that the previous radius and luminosity estimates which assumed spherical dust shells were overestimated, as the radiation escape through the cavity (i.e. toward us). A much lower luminosity of 282,000+40,000
−30,000 

Humphreys–Davidson limit).[8][10][15]

WOH G64 was discovered to be a prominent source of

OH/IR supergiant star.[8] 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.[8] The stellar atmosphere is producing a strong silicate absorption band in mid-infrared wavelengths, accompanied a line emission due to highly excited carbon monoxide.[20]

Yellow hypergiant stage

WOH G64 has shrunk in size since 2014, and has become a smaller

B-type companion.[3]

Companion

Since 2016, the spectrum of WOH G64 exhibits features of both B[e] stars and yellow stars, which is interpreted as the spectral signature of a massive symbiotic binary consisting of a yellow hypergiant losing material to an accreting B-type star companion.[3] The persistent presence of surrounding hot dust, elongated appearance of the hypergiant in interferometric imaging, and the lack of a violent outburst during WOH G64's transition out of the red supergiant stage further supports the binary nature of WOH G64.[3][14] The interacting binary system HR 5171 is considered an analog to WOH G64, as it also contains a yellow hypergiant with a B-type star companion.[3] The presence of a hot stellar companion of WOH G64 was first suspected by Levesque et al. in 2009, who proposed that a late O-type main-sequence star companion could be ionizing the nebula surrounding WOH G64 in order to explain the 50 km/s shift between the nebular emission lines and WOH G64's spectral features.[3][8]

See also

  • B90, red supergiant in the Large Magellanic Cloud
  • NML Cygni
  • R136a1, one of the most massive and luminous stars known
  • IRC +10420, a yellow hypergiant evolving bluewards

Notes

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

References

  1. ^
    doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR
    .
  2. S2CID 199452754
    .
  3. ^
    arXiv:2411.19329 [astro-ph.SR
    ].
  4. ^
    Bibcode:2003yCat.2246....0C
    .
  5. ^
    S2CID 2754884
    .
  6. ^
    Bibcode:2009AcA....59..239S
    .
  7. S2CID 244398875
    . Gaia DR3 record for this source at VizieR.
  8. ^
    S2CID 18074349
    .
  9. ^
    S2CID 59459492
    .
  10. ^
    doi:10.1017/S1743921308028858
    .
  11. ISSN 0365-0138
    .
  12. ISSN 0365-0138
    .
  13. ^
    ISSN 0004-637X
    .
  14. ^
    ISSN 0004-6361
    .
  15. ^
    S2CID 16724272
    .
  16. S2CID 11352637
    .
  17. S2CID 252519285
    .
  18. S2CID 7851916
    .
  19. S2CID 59327105
    .
  20. ISSN 0035-8711
    .
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