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HD 37974 (or R 126) a variable B
NASA's Spitzer Uncovers Hints of Mega Solar Systems
, Nasa.gov, accessed 11 Feb 2006
The brightness of R126 varies in an unpredictable way by around 0.6 magnitude over timescales of tens to hundreds of days. The faster variations are characteristic of
hypergiant
A hypergiant ( luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term ''hypergiant'' is defined as luminosity class 0 (zero) in the MK ...
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 ...
. It is surrounded by an unexpected dust disk.
Properties
R126, formally RMC (Radcliffe observatory Magellanic Cloud) 126, is a massive luminous star with several unusual properties. It exhibits the B phenomenon where forbiddenemission line
A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...
s appear in the spectrum due to extended circumstellar material
A circumstellar envelope (CSE) is a part of a star that has a roughly spherical shape and is not gravitationally bound to the star core. Usually circumstellar envelopes are formed from the dense stellar wind, or they are present before the formatio ...
. Its spectrum also shows normal (permitted) emission lines formed in denser material closer to the star, indicative of a power stellar wind
A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...
. The spectra include silicate
A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...
and polycyclic aromatic hydrocarbon
A Polycyclic aromatic hydrocarbon (PAH) is any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter— by engine exhaust fumes, tobacco, incine ...
(PAH) features that suggest a dusty disc.
The star itself is a hot supergiant thought to be seventy times more massive than the Sun and over a million times more luminous. It has evolved away from the main sequence (being an O-class star, when it was in MS) and is so luminous and large that it is losing material through its stellar wind over a billion times faster than the Sun. It would lose more material than the Sun contains in about 25,000 years.
It is expected to evolve into Wolf–Rayet star
Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectroscopy, spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very ...
in several hundred thousand years.
Dusty disc
The dust cloud around R126 is surprising because stars as massive as these were thought to be inhospitable to planet formation due to powerful stellar winds making it difficult for dust particles to condense. The nearby hypergiant HD 268835 shows similar features and is also likely to have a dusty disc, so R126 is not unique. The disc extends outwards for 60 times the size of Pluto's orbit around the Sun, and probably contains as much material as the entireKuiper belt
The Kuiper belt ( ) is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...
. It is unclear whether such a disc represents the first or last stages of the planet-forming process., Nasa.gov, accessed 11 Feb 2006
Variability
The brightness of R126 varies in an unpredictable way by around 0.6 magnitude over timescales of tens to hundreds of days. The faster variations are characteristic of α Cygni variable
Alpha Cygni variables are variable stars which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time other parts expand. They are supergiant stars of Stellar classification, spectral types ...
s, irregular pulsating supergiants. The slower variations are accompanied by changes in the colour of the star, with it being redder when it is visually brighter, typical of the S Doradus
S Doradus (also known as S Dor) is one of the brightest stars in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way, located roughly 160,000 light-years away. The star is a luminous blue variable, and one of the List ...
phases of 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 ...
s.
See also
*List of most massive stars
This is a list of the most massive stars that have been discovered, in solar mass units ().
Uncertainties and caveats
Most of the masses listed below are contested and, being the subject of current research, remain under review and subject to con ...
References