HR Carinae is a

luminous blue variable Luminous blue variables (LBVs) are 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 the Larg ...

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

located in the constellation

Carina Carina may refer to: Places Australia * Carina, Queensland, a suburb in Brisbane * Carina Heights, Queensland, a suburb in Brisbane * Carina, Victoria, a locality in Mildura Serbia * Carina, Osečina, a village in the Kolubara District ...

. It is surrounded by a vast

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

of ejected nuclear-processed material because this star has a multiple shell expanding atmosphere. This star is among the

most luminous stars This is a list of stars arranged by their absolute magnitude – their intrinsic stellar luminosity. This cannot be observed directly, so instead must be calculated from the apparent magnitude (the brightness as seen from Earth), the distance t ...

in the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

. It has very broad emission wings on the

Balmer lines The Balmer series, or Balmer lines in atomic physics, is one of a set of six named series describing the spectral line emissions of the hydrogen atom. The Balmer series is calculated using the Balmer formula, an empirical equation discovered b ...

, reminiscent from the broad lines observed in the spectra of O and

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface ...

s. A distance of 5 kpc and a

bolometric magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it w ...

of -9.4 put HR Car among the most luminous stars of the galaxy.

Discovery

HR Carinae was first noticed at the start of the 20th century because of its H_β emission. It was placed in

Secchi class In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

I, corresponding to modern A and F-type stars. It was catalogued in 1933 as a Be star and was discovered to be variable in 1940. A more detailed spectroscopic study gave it the type B2eq with emission line of

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

, and ionised

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

and

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 ...

s on some lines. By 1970, HR Carinae and the similar variable

AG Carinae AG Carinae (AG Car) is a star in the constellation Carina. It is classified as a luminous blue variable (LBV) and is one of the most luminous stars in the Milky Way. The great distance (20,000 light-years) and intervening dust mean that ...

were recognised as being related to the P Cygni variables, unstable hot supergiants. The group was formally recognised as S Doradus variables to avoid confusion with the P Cygni spectral features shared with other types of star. HR Carinae became one of the best-studied examples of the class, clearly showing the brightness and spectral variations that came to characterise the stars known as luminous blue variables.

Brightness variation

HR Carinae undergoes spectral variations apparently correlated with the light variations similarly to other luminous blue variables. It has undergone several outbursts during which the visual brightness increases and the temperature drops, but the bolometric luminosity remains approximately constant. The visual brightness increased erratically but consistently during the later decades of the 20th century to a record peak of mag 6.8, then dropped straight to a record minimum of mag 8.8 by 2010.

Characteristics

HR Carinae has a temperature around when quiescent and the spectrum is of an early B

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 ...

, but in outburst it cools to below . HR Carinae is a lot like

Eta Carinae Eta Carinae (η Carinae, abbreviated to η Car), formerly known as Eta Argus, is a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun, located around distant in t ...

, both luminous blue variables, and both surrounded by ejected material. HR Carinae is also likely to be a binary system with a similar separation, period, and ratio of component sizes to Eta Carinae. However, the Eta Carinae system is more massive and more luminous. It has been identified as a possible

type IIb supernova A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo this ...

candidate in modelling of the fate of stars 20 to 25 times the mass of the Sun (with LBV status as the predicted final stage beforehand).

Binary system

AMBER Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In Ma ...

and

PIONIER PIONIER is the Polish national research and education network created to provide high-speed Internet access and to conduct network-based research. Most of the government founded higher education organisations and all of metropolitan area networks ...

interferometry Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

has shown that HR Carinae is a binary star system. The orbit is only weakly constrained but the most likely orbit has a semi-major axis of 3.3 mas, eccentricity of 0.4, and a period of 12.5 years. The possible orbits vary from nearly circular orbits of just a few years to highly eccentric orbits of several hundred years, all with the closest separation of the two stars at about 2 mas. The companion appears to be larger than the primary LBV star, but much less bright. It is most likely a red supergiant with an angular diameter of , translating to a radius about , and also with a mass of and a temperature of 3,600–. The diameter of the primary star was also measured directly at , corresponding to a radius of at .

References

{{DEFAULTSORT:HR Carinae B-type supergiants B-type hypergiants M-type supergiants Luminous blue variables Carina (constellation) Carinae, HR 090177 50843 Durchmusterung objects Binary stars