Roberts 22 is a

protoplanetary nebula A protoplanetary nebula or preplanetary nebula (PPN, plural PPNe) is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch (LAGB) phase and the subsequent planetary ne ...

in the southern 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 ...

, located about 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 ...

s (6,500

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

s) from Earth. A 12th

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

object, it is far too faint to be seen with the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

. In 1962, Morton S. Roberts of the

Harvard College Observatory The Harvard College Observatory (HCO) is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, United St ...

included this star in his catalogue of all known Wolf-Rayet Stars as entry number 22, giving the object its commonly used name, which is often shortened to MR 22. Later studies cast doubt on its classification as a Wolf-Rayet star. The star itself is completely hidden by dust (it is fainter than 16th magnitude), but its

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

, A2 Ie, has been determined from the starlight reflected to us by the surrounding nebula. OH

maser A maser is a device that produces coherent electromagnetic waves ( microwaves), through amplification by stimulated emission. The term is an acronym for microwave amplification by stimulated emission of radiation. Nikolay Basov, Alexander Pr ...

emission at 1665 MHz was detected from Roberts 22 in 1969, but at that time its association with the star was unknown. By 1975, the maser emission had been associated with the nebula surrounding Roberts 22, but no connection with any star was noted. The association of the maser source with the Roberts 22 itself was made in 1980. Thermal (non-maser) CO emission was reported in 1991, the strength of which implied that the star is losing mass at a rate of about

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es per year, comparable to the mass loss rates of the

Egg Nebula The Egg Nebula (also known as RAFGL 2688 and CRL 2688) is a bipolar nebula, bipolar protoplanetary nebula approximately 3,000 light-years away from Earth. Its peculiar properties were first described in 1975 using data from the 11 μm survey ...

and

Westbrook Nebula Westbrook Nebula (CRL 618) is a bipolar nebula, bipolar protoplanetary nebula which is located in the constellation Auriga (constellation), Auriga. It is being formed by a star that has passed through the red giant phase and has ceased nuclear fusi ...

which are well-known protoplanetary nebulae. High resolution optical imaging of Roberts 22 with 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 ...

shows that the nebula has two bright lobes, reminiscent of a butterfly's wings, separated by a dark band of dust which obscures the central star. The lobes show a complex pattern of loops, filaments and point symmetries. The bright lobes are surrounded by a fainter halo which has several incomplete, thin shells. The timescale for the formation of these features is only a few hundred years.

References

{{Carina (constellation) Protoplanetary nebulae Carina (constellation) IRAS catalogue objects