HD 101584 is a suspected post-common envelope binary about 1,800 to 5,900

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s distant in the constellation of

Centaurus Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...

. The system is bright at optical wavelengths with an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of about 7. The primary is either a

post-AGB A post-AGB star (pAGB, abbreviation of post-asymptotic giant branch) is a type of luminous supergiant star of intermediate mass in a very late phase of stellar evolution. The post-AGB stage occurs after the asymptotic giant branch (AGB or second-as ...

star, but more likely a post-

RGB The RGB color model is an additive color model in which the red, green, and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three ...

star. The secondary is a

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

or possibly a low-luminosity

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

, which orbits the primary every 150-200 days. The system is surrounded by a slowly rotating circumbinary disk, probably with a face-on orientation towards the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

and a size of about 150

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

Variability

In 1991, Jean Manfroid ''et al.'' published

photometry Photometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electr ...

that showed that HD 101584 is a

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

. HD 101584 has been given the

variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...

V885 Centauri. The International Variable Star Index states that the star varies between visual magnitude 6.90 and 7.02, over a period of 87.9 days. However Koen and Eyer detected, in the star's ''

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...

'' data, an oscillation of the star's brightness with a period of 6.744 days and an amplitude of only 0.02 magnitudes.

Nebula

The

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

image shows a diffuse circumstellar environment with a circular ring around HD 101584.

ALMA Alma or ALMA may refer to: Arts and entertainment * ''Alma'' (film), a 2009 Spanish short animated film * ''Alma'', an upcoming film by Sally Potter * ''Alma'' (Oswald de Andrade novel), 1922 * ''Alma'' (Le Clézio novel), 2017 * ''Alma'' ( ...

mapped the nebula around HD 101584 and was able to map the region close to the central binary. The nebula consists of a central compact source, an equatorial density enhancement (disk), a high-velocity bipolar outflow and an hourglass structure surrounding the outflow. The outflow reaches a maximum velocity of about 150

km/s The metre per second is the unit of both speed (a scalar quantity) and velocity (a vector quantity, which has direction and magnitude) in the International System of Units (SI), equal to the speed of a body covering a distance of one metre in a ...

and is inclined to the line of sight by °. There is evidence for a second bipolar outflow with a different orientation from the major outflow. The inner disk, heated to 1540 K, currently has been sublimated by the increasing luminosity of the star.

Evolution

The companion of this system was captured a few hundred years ago, for example when the red giant reached its critical size. It spiralled towards the red giant but stopped before it merged with the core of the primary. During this stage the outer layers of the red giant were ejected. During the

common envelope In astronomy, a common envelope (CE) is gas that contains a binary star system. The gas does not rotate at the same rate as the embedded binary system. A system with such a configuration is said to be in a common envelope phase or undergoing comm ...

phase the red giant phase of the primary was terminated and the core was revealed. Later, the bipolar jets formed and met the ejected material, forming the hourglass-shaped structure. Ejected material shows prominent spectral features of magnesium, while outer ejected structures contain

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

and

formaldehyde Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...

References

{{DEFAULTSORT:HD 101584 Binary stars Protoplanetary nebulae Centauri, V885 046992 IRAS catalogue objects J11405880-5534258 A-type supergiants Variable stars 101584 Centaurus