HR 4049, also known as HD 89353 and AG Antliae, is a

binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that t ...

post- asymptotic-giant-branch (post-AGB) star in the constellation

Antlia Antlia (; from Ancient Greek ''ἀντλία'') is a constellation in the Southern Celestial Hemisphere. Its name means " pump" in Latin and Greek; it represents an air pump. Originally Antlia Pneumatica, the constellation was established by N ...

. A very metal-poor star, it is surrounded by a thick unique circumbinary disk enriched in several molecules. With an apparent magnitude of about 5.5, the star can readily be seen under ideal conditions. It is located approximately distant. HR 4049 has a peculiar spectrum. The star appears, based on its spectrum in the

Balmer series 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 ...

, to be a

blue supergiant A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They have luminosity class I and spectral class B9 or earlier. Blue supergiants are found towards the top left of the Hertzsprung–Russell diagram, above an ...

, although in reality it is an old low-mass star on the post-AGB phase of its life. Its atmosphere is extremely deficient in heavy elements, over with a

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

over 30,000 lower than the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. It also shows a strong

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 o ...

, corresponding closely to a

blackbody A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body ...

produced by a disk of material surrounding the star. The star is also undergoing intense mass-loss HR 4049 has an unseen companion, detected from variations in the

doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

of its

spectral 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 ...

s. The properties of the companion can only be estimated by making certain assumptions about the inclination of the orbit and the mass function. Given those assumptions, it is thought to be a low luminosity

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star. HR 4049 is an unusual

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

, ranging between magnitudes 5.29 and 5.83 with a period of 429 days. It has been given the

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...

AG Antliae, but is still more commonly referred to as HR 4049. It has been described as pulsating in a similar fashion to an

RV Tauri variable RV Tauri variables are luminous variable stars that have distinctive light variations with alternating deep and shallow minima. History and discovery German astronomer Friedrich Wilhelm Argelander monitored the distinctive variations in brightne ...

, although the preferred interpretation is that the variations are produced by variable

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

produced by the material around the star and that the period is the same as the orbital period. Although HR 4049 apparently has the spectrum of a

, it is an old low-mass star which has exhausted nuclear fusion and is losing its outer layers as it transitions towards a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

and possibly a

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 ...

. During this phase it has a luminosity several thousand times that of the Sun, although a mass around half that of the sun. The mass can only be guessed from the expected mass of the white dwarf that it is becoming.

References

External links

The Spatial Distribution of Grains Around the Dual Chemistry Post-AGB Star

* ttp://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2006/17/aa3553-05/aa3553-05.html Post-AGB stars as testbeds of nucleosynthesis in AGB stars
The post-AGB evolution of AGB mass loss variations
{{DEFAULTSORT:HR 4049 Antlia Post-asymptotic-giant-branch stars 089353 J10180758-2859308 DENIS objects Antliae, AG 4049 B-type supergiants 050456 Durchmusterung objects Spectroscopic binaries