HDE 316285 is a

blue supergiant A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They are usually considered to be those with luminosity class I and spectral class B9 or earlier, although sometimes A-class supergiants are also deemed blu ...

star in the constellation

Sagittarius Sagittarius ( ) may refer to: *Sagittarius (constellation) *Sagittarius (astrology), a sign of the Zodiac * Sagittarius of Gap, a 6th century bishop *Sagittarius A*, the supermassive black hole at the center of the Milky Way galaxy Ships *'' S ...

. It is a candidate

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 ...

and lies about 6,000 light years away in the direction of the

Galactic Center The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...

Discovery

HD 316285 was identified in 1925 as an unusual star having

P Cygni 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 hypergian ...

lines in its spectrum, lines with both emission and absorption components offset by a doppler shift. It was classified as a

Be star Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer ...

although it is now known to be a supergiant and the class of Be stars excludes supergiants, and was included in the Mount Wilson Observatory catalogue of B and A stars with bright lines of hydrogen (MWC) as entry 272. In 1956, it was reported that the emission was due to an expanding atmosphere rather than the circumstellar discs of less evolved Be stars. In 1972 it was discovered to have an

infrared excess An infrared excess is a measurement of an astronomical source, typically a star, that in their spectral energy distribution has a greater measured infrared flux than expected by assuming the star is a blackbody radiator. Infrared excesses are of ...

, an unusually high emission at infrared wavelengths due to surrounding warm dust. In 1961, HD 316285 was catalogued as planetary nebula Bl3-11, although that classification was quickly cast into doubt.

Variability

HD 316285 is listed in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars in the Milky Way Galaxy. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR, edited by and Pavel Parenago. Second a ...

as a variable

with a range of about one tenth of a magnitude. The International Variable Star Index classifies it as an

S Doradus 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 ...

and it is considered to be a candidate luminous blue variable.

Properties

The spectrum shows that HD 316285 has only 1.5 times as much hydrogen as helium and elevated levels of carbon, nitrogen, and oxygen, so it can be identified as a highly evolved star. It has been calculated to be losing mass at the rate of every four thousand years via its

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 ...

Gaia In Greek mythology, Gaia (; , a poetic form of ('), meaning 'land' or 'earth'),, , . also spelled Gaea (), is the personification of Earth. Gaia is the ancestral mother—sometimes parthenogenic—of all life. She is the mother of Uranus (S ...

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other Astronomical object, celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, th ...

suggests a distance much larger than the accepted 1.9kpc, and would imply a much higher luminosity. It may even lie close to the

. HD 316285 has been identified as a possible type II-b or type IIn

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

candidate in modelling of the fate of stars 20 to 25 times the mass of the Sun. It has been shown that these supernovae may explode directly from stars in an LBV phase after spending time as a

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

. A possible companion has been reported on the basis of a helical outflow of material apparently originating from HD 316285. This would be caused by a jet being twisted into a spiral shape by orbital motion.

References

{{DEFAULTSORT:HD 316285 Sagittarius (constellation) Luminous blue variables Sagittarii, V4375 087136 316285 CD-27 11944 Emission-line stars B-type supergiants