The star is extremely luminous, radiating 450,000 times the luminosity of the Sun from its photosphere. It shines at an effective temperature of approximately 6,000K (10,340°F), slightly hotter than the Sun, giving it a yellowish-white hue.[3] Given the temperature and luminosity, its radius can be calculated at around 622 R☉. An evolutionary mass of ~30 M☉ from the measured nitrogen-carbon ratio.[6] Glatzel & Kraus (2024) present an initial mass of 32–40 M☉ and a current mass of 20–30 M☉.[3]
Given its considerable angular separation from the core of the LMC, the star's distance from Earth is somewhat uncertain even relative to LMC distance estimates. Trigonometric parallax efforts by Gaia have been inconclusive thus far: DR2 estimates 15.7±26.5μas[11] while EDR3 estimates −3.5±11.3μas[1]. (The LMC, at around 50 kpc, has a notional parallax of 20μas; the future DR5 best-case parallax uncertainty will be around 7μas,[12] which will likely be insufficient to directly measure the distance between the star and the core of the LMC.)
Spectra and abundances
As early as 1960, the star's spectral type was classified as F8Ia, corresponding to a yellow-white "super-supergiant" (a hypergiant in modern terms). The star has weaker hydrogenspectral lines than a normal F8Ia star, which implies a later type, but all the other lines point towards an earlier type between F5Ia and F8Ia. Compared to Delta Canis Majoris, another F8Ia star, it shows a weaker line of neutral iron (Fe I) at 4118.5 Å.[9] The Ca II H and K emission profile closely resembles that of the galactic YHGs Rho Cassiopeiae and V382 Carinae. This indicates similar behavior in their outer atmospheres, such as non-radiativechromospheric heating, mass loss and stellar winds in the order of 1×10−6M☉/yr.[13]
The star has a low metallicity of [Fe/H]=−0.50 dex,[15] meaning it only has 10−0.50≈32% the Sun's iron content, which is lower than the LMC average for young stars at around 50%.[16] It is also depleted in carbon and oxygen, but very enhanced in nitrogen ([N/Fe]=1.53 dex).[15]
Variability
A light curve for HD271182, plotted from ASAS data.
In 1983, Olin J. Eggen reported that HD 271182 was a pseudo-Cepheid variable,[18] a supergiant in the Hertzsprung gap with less periodic light variations than true Cepheids.[19] This star in particular showed an amplitude of 0.25 mag in the V band. Similarities were noted between it and two other pseudo-Cepheids, namely R Puppis and HD 269879.[18] Grieve et al. confirmed this in 1985, and a period of roughly 250 days was determined. They referred to this type of star, which they classified as a high-luminosity long-period Cepheid, as a Leavitt variable in homage to Henrietta Swan Leavitt, who first discovered the period-luminosity relations in Cepheids and pseudo-Cepheids back in 1907.[10]
In 1989, van Genderen & Hadiyanto claimed that the variations were not of a Cepheid nature due to the highly unstable light curves, and that the star was an Alpha Cygni variable instead.[4] This classification has been upheld by later studies. One of which, van Leeuwen et al. (1998), provided a period of 260 days (0.71 years) and stated that there may be another oscillation with a significantly longer period.[20] Light curves provided by Kourniotis et al. (2022)[21] show a pulsation period of 833 days (2.28 years).[3]
Between December 2016 and August 2017, the effective temperature was observed to have risen from 6100±50K to 6500±100K, mirroring the strong pulsations.[21]
The star is not known to exhibit fast yellow pulsating supergiant (FYPS) characteristics.[14]
2008 outburst
Kourniotis et al. discovered that the star underwent an outburst in late 2008. This was less energetic than the ones seen in Rho Cassiopeiae in 2000 and 2013, but nevertheless caused a 0.4-magnitude dip in brightness followed by a period of substantial brightening, and possibly resulted in mass ejection. Much like Rho Cassiopeiae's 2000 outburst, it may have been caused by the collapse of the deep photosphere. They conclude that the star is a post-red supergiant and a "modest" Rho Cassiopeiae analog.[21]
1 2 Høg, E.; etal. (February 2000). "The Tycho-2 Catalogue of the 2.5 Million Brightest Stars". Astronomy and Astrophysics. 355 (1): L27 –L30. Bibcode:2000A&A...355L..27H.
1 2 van Genderen, A. M.; Hadiyanto Nitihardjo, G. (September 1989). "Light variations of massive stars (alpha Cygni variables). X. The F type supergiants G 266 = HDE 271182 = R 92 and G 322 = HDE 269612 in the LMC". Astronomy & Astrophysics Supplement Series. 79: 401-406. Bibcode:1989A&AS...79..401V.
1 2 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; etal. (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.
1 2 Grieve, G. R.; Madore, B. F.; Welch, D. L. (1985). "Leavitt variables - Bright variable supergiants and their implications for the distance scale". The Astrophysical Journal. 294: 513. Bibcode:1985ApJ...294..513G. doi:10.1086/163318. ISSN0004-637X.
1 2 Hill, V.; Barbuy, B.; Spite, M. (July 1997). "Carbon, nitrogen, oxygen and lithium abundances of six cool supergiants in the SMC". Astronomy & Astrophysics. 323: 461–468. Bibcode:1997A&A...323..461H.
↑ Wood, P. R.; Habing, H. J.; McGregor, P. J. (August 1998). "Infrared monitoring of OH/IR stars near the Galactic Center". Astronomy & Astrophysics. 336: 925–941. Bibcode:1998A&A...336..925W.
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