R99 (HD 269445) is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the

Large Magellanic Cloud The Large Magellanic Cloud (LMC) is a dwarf galaxy and satellite galaxy of the Milky Way. At a distance of around , the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal Galaxy, Sagittarius Dwarf ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Dorado Dorado (, ) is a constellation in the Southern Sky. It was named in the late 16th century and is now one of the 88 modern constellations. Its name refers to the mahi-mahi (''Coryphaena hippurus''), which is known as ''dorado'' ("golden") in Sp ...

. It is classified as a possible

luminous blue variable Luminous blue variables (LBVs) are rare, massive, evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of th ...

and is one of the most luminous stars known. R99 has a peculiar spectrum that has been described as OBf:pe, "unclassifiable", peculiar WN10, "similar to the unusual LBV HD 5980", "unique", and Ofpe/WN9. The Ofpe/WN9 type remains even though other stars of this type have been reclassified to types between WN9 and WN11. R99 has significant differences from those other stars which preclude it being given a simple WN spectral type: the

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

spectrum is strongly blanketed over a different range of wavelengths; highly ionised iron lines are seen in absorption instead of emission; the H lines are unusually narrow and have no

P Cygni profile P Cygni (34 Cygni) is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in ''Uranometria'' as a nova. Located about 5,300 light-years (1,560 parsecs) from Earth, it is a hypergiant ...

; a lack of any significant absorption features near H_δ; a number of metal lines are unusually strong or weak compared to other stars of the type; there is a small unexplained

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

excess. The wind structure of R99 may be significantly different from most WR stars and LBVs. The normal temperature-stratified WR wind is accelerated to terminal velocity, causing lines of different ionisation levels of Helium to be created at different distances from the star. This does not seem to apply to R99. Significant polarisation of the spectrum continuum is also seen, suggesting an asymmetric wind. This has not been observed in other WR stars. R99 shows brightness variations of about 0.3 magnitude over a period of decades, and smaller amplitudes with the strongest periods at two and ten days. The colour also varies, with the star being bluer at minimum light. It has been classified as a luminous blue variable on account of the variability and spectrum, although it has never been observed in outburst. Others still list it only as a candidate.

References

{{Stars of Dorado Stars in the Large Magellanic Cloud Large Magellanic Cloud Wolf–Rayet stars Dorado 269445 Luminous blue variables J05225978-6801466 Extragalactic stars

See also

References