WR 31a, commonly referred to as Hen 3-519, is a Wolf–Rayet (WR) star in the southern constellation of

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 ...

that is surrounded by an expanding

Wolf–Rayet nebula A Wolf–Rayet nebula is a nebula which surrounds a Wolf–Rayet star. WR nebulae have been classified in various ways. One of the earliest was by the nature and origin of the nebula: * HII regions * ejecta-type nebulae * wind-blown bubbles Th ...

. It is not a classical old stripped-envelope WR star, but a young massive star which still has some hydrogen left in its atmosphere.

History of observations

WR 31a was first published in 1952 as one of six peculiar

emission line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

stars, but not given a designation at that time. It was described as having numerous P Cygni type lines with unusually broad emission components. A year later it was listed as being associated with nebulosity, at the time thought to be a planetary nebula. In 1976, it was included in a catalogue of southern emission-line stars, the third catalogue of emission objects compiled by

Karl Gordon Henize Karl Gordon Henize (;JPL-80 "NASA Creates Portrait of Life and ...

. The designation , sometimes , was adopted as the most common identifier for this star. In 2001, it was listed in The Seventh Catalogue of Galactic Wolf-Rayet stars as entry 31a, but it is still frequently called . In 1994, WR 31a was first described as a candidate

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 ...

(cLBV) after a detailed

spectrographic In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...

study with the

Anglo-Australian Telescope The Anglo-Australian Telescope (AAT) is a 3.9-metre equatorially mounted telescope operated by the Australian Astronomical Observatory and situated at the Siding Spring Observatory, Australia, at an altitude of a little over 1,100 m. In 20 ...

. Measurements of its

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

, published in 2017 as a result of the ''

Gaia In Greek mythology, Gaia (; from Ancient Greek , a poetical form of , 'land' or 'earth'),, , . also spelled Gaea , is the personification of the Earth and one of the Greek primordial deities. Gaia is the ancestral mother—sometimes parthenog ...

'' mission, suggested a much closer (6,500

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

; 2,000

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

) distance to as well as to its neighbor, the luminous blue 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 ...

. It was thought that, if this distance was confirmed by ''Gaia'' second data release (DR2) in 2018, this would mean both stars wer much less luminous than previously thought, and both may instead be former

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Anta ...

stars. However,

Gaia Data Release 2 The ''Gaia'' catalogues are star catalogues created using the results obtained by '' Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, espec ...

returned a parallax of ; using

Bayesian inference Bayesian inference is a method of statistical inference in which Bayes' theorem is used to update the probability for a hypothesis as more evidence or information becomes available. Bayesian inference is an important technique in statistics, a ...

, Smith ''et al.'' (2018) calculated its distance to be (). Gaia Data Release 3 lists a parallax of , again indicating a large distance. A statistical analysis leads to a distance of .

Blue bubble

WR 31a is surrounded by a shell of ionised gas nearly wide. The

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

(HST) has captured a striking image of the nebula, rendering it as a thin blue bubble. In this false colour image, the blue colours represents red visible light (605 nm), while orange-red colours represent near

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

radiation at 814 nm. Some media sources have wrongly claimed this deep-sky object was recently discovered by the HST, but this nebula was originally found by

Ellen Dorrit Hoffleit Ellen Dorrit Hoffleit (March 12, 1907 – April 9, 2007) was an American senior research astronomer at Yale University. She is best known for her work in variable stars, astrometry, spectroscopy, meteors, and the Bright Star Catalog. She is ...

in 1953 and designated as the

planetary nebula A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to ...

Hf 39. Other planetary nebula catalogue names include ESO 128-18 and Wray 15-682. Since 2013, the nebula has been considered not as a planetary nebula, but rather as a much larger expanding gas shell, formally classified as a

or WR nebula. Its observed expansion velocity is , and is estimated to be some across. The dynamical age of the nebula is estimated at 18,000 years and the total mass of ionised gas at .

Properties

WR 31a itself, the highly luminous central star of the nebula, is invisible to the naked-eye at magnitude 10.85V. It has a spectral classification of WN11h, indicating a WR star with strong N emission but no N emission, and with hydrogen features visible in the spectrum. The spectral classification WN11 was created for this star and

since they did not fit into any existing spectral type and appeared to constitute an extension of the WR nitrogen sequence to cooler temperatures. The progenitor's mass of the central star is estimated to have been about 45 times that of the Sun, and this massive star will likely explode as a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

in the future. The spectrum of WR 31a shows

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, most strongly on the dominant H, He, and N lines. These profiles may show dramatic changes on a timescale of weeks, with the absorption components of the lines sometimes disappearing completely.

Variability

No significant brightness changes have been detected in WR 31a, but it has been listed as a candidate luminous blue variable because of its luminosity, temperature, and mass loss properties. Van Genderen catalogued it as a dormant or ex-LBV because of the lack of characteristic LBV variations.Vizie database entry
/ref> Possible small brightness changes have been seen in All Sky Automated Survey (ASAS) data, WR 31a is included as a variable star in the International Variable Star Index, although not in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...

References

{{DEFAULTSORT:WR 31a Wolf–Rayet stars Carina (constellation) J10535958-6026444 Luminous blue variables IRAS catalogue objects