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R99
Observation data; Epoch J2000 Equinox J2000
Constellation	Dorado
Right ascension	05h 22m 59.809s
Declination	−68° 01′ 46.57″
Apparent magnitude (V)	11.46
Characteristics
Spectral type	LBV
U−B color index	−0.92
B−V color index	+0.25
Variable type	LBV
Astrometry
Radial velocity (Rv)	293±16.2 km/s
Proper motion (μ)	RA: 3.4±2.5 mas/yr ; Dec.: −0.4±2.3 mas/yr
Distance	50,000 pc
Absolute magnitude (MV)	−8.48
Details
Mass	103 M☉
Radius	74.8 R☉
Luminosity	3.2×106 L☉
Temperature	28,000 K
Other designations
	HD 269445, BAT99-33, AAVSO 0523-68, 2MASS J05225978-6801466
Database references
SIMBAD	data

R99 (HD 269445) is a star in the Large Magellanic Cloud in the constellation Dorado. It is classified as a possible luminous blue variable and is one of the most luminous stars known.

R99 has a peculiar spectrum that has been described as OBf:pe,^[6] "unclassifiable", peculiar WN10, "similar to the unusual LBV HD 5980",^[7] "unique", and Ofpe/WN9.^[8] The Ofpe/WN9 type remains even though other stars of this type have been reclassified to types between WN9 and WN11.^[4] R99 has significant differences from those other stars which preclude it being given a simple WN spectral type: the ultraviolet spectrum is strongly blanketed over a different range of wavelengths; highly ionised iron lines are seen in absorption instead of emission; the Hi lines are unusually narrow and have no P Cygni profile; 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 excess.^[9]

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.^[9] Significant polarisation of the spectrum continuum is also seen, suggesting an asymmetric wind. This has not been observed in other WR stars.^[10]

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.^[11] It has been classified as a luminous blue variable on account of the variability and spectrum, although it has never been observed in outburst.^[3] Others still list it only as a candidate.^[12]^[13]

References

^ ^a ^b ^c ^d Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862.
^ ^a ^b ^c 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.
^ ^a ^b Van Genderen, A. M. (2001). "S Doradus variables in the Galaxy and the Magellanic Clouds". Astronomy and Astrophysics. 366 (2): 508–531. Bibcode:2001A&A...366..508V. doi:10.1051/0004-6361:20000022.
^ ^a ^b Schnurr, O.; Moffat, A. F. J.; St-Louis, N.; Morrell, N. I.; Guerrero, M. A. (2008). "A spectroscopic survey of WNL stars in the Large Magellanic Cloud: General properties and binary status". Monthly Notices of the Royal Astronomical Society. 389 (2): 806–828. arXiv:0806.2801. Bibcode:2008MNRAS.389..806S. doi:10.1111/j.1365-2966.2008.13584.x. S2CID 6590534.
^ ^a ^b ^c ^d ^e Hainich, R.; Rühling, U.; Todt, H.; Oskinova, L. M.; Liermann, A.; Gräfener, G.; Foellmi, C.; Schnurr, O.; Hamann, W. -R. (2014). "The Wolf-Rayet stars in the Large Magellanic Cloud". Astronomy & Astrophysics. 565: A27. arXiv:1401.5474. Bibcode:2014A&A...565A..27H. doi:10.1051/0004-6361/201322696. S2CID 55123954.
^ Walborn, N. R. (1977). "Spectral classification of O and B0 supergiants in the Magellanic Clouds". Astrophysical Journal. 215: 53. Bibcode:1977ApJ...215...53W. doi:10.1086/155334.
^ Crowther, P. A.; Smith, L. J. (1997). "Fundamental parameters of Wolf-Rayet stars. VI. Large Magellanic Cloud WNL stars". Astronomy and Astrophysics. 320: 500. Bibcode:1997A&A...320..500C.
^ Bohannan, Bruce; Walborn, Nolan R. (1989). "The Ofpe/WN9 class in the Large Magellanic Cloud" (PDF). Publications of the Astronomical Society of the Pacific. 101: 520. Bibcode:1989PASP..101..520B. doi:10.1086/132463.
^ ^a ^b Pasquali, Anna; Langer, Norbert; Schmutz, Werner; Leitherer, Claus; Nota, Antonella; Hubeny, Ivan; Moffat, Anthony F. J. (1997). "O Stars in Transition. II. Fundamental Properties and Evolutionary Status of Ofpe/WN9 Stars from HST Ultraviolet Observations". The Astrophysical Journal. 478 (1): 340–357. Bibcode:1997ApJ...478..340P. doi:10.1086/303767.
^ Vink, Jorick S. (2007). "Constraining GRB progenitor models by probing Wolf-Rayet wind geometries in the Large Magellanic Cloud". Astronomy and Astrophysics. 469 (2): 707–711. arXiv:0704.2690. Bibcode:2007A&A...469..707V. doi:10.1051/0004-6361:20077302. S2CID 19013584.
^ Van Genderen, A. M.; Sterken, C.; De Groot, M.; Reijns, R. A. (1998). "Light variations of massive stars (alpha Cyg variables). XV. The LMC supergiants R99 (LBV), R103, R123 (LBV) and R128". Astronomy and Astrophysics. 332: 857. Bibcode:1998A&A...332..857V.
^ Smith, Nathan; Tombleson, Ryan (2015). "Luminous blue variables are antisocial: Their isolation implies that they are kicked mass gainers in binary evolution". Monthly Notices of the Royal Astronomical Society. 447 (1): 598–617. arXiv:1406.7431. Bibcode:2015MNRAS.447..598S. doi:10.1093/mnras/stu2430. S2CID 119284620.
^ Richardson, Noel D.; Mehner, Andrea (2018). "The 2018 Census of Luminous Blue Variables in the Local Group". Research Notes of the American Astronomical Society. 2 (3): 121. arXiv:1807.04262. Bibcode:2018RNAAS...2..121R. doi:10.3847/2515-5172/aad1f3. S2CID 119509358.