R Crateris is a star about 700

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 ...

s from the Earth in the constellation

Crater Crater may refer to: Landforms *Impact crater, a depression caused by two celestial bodies impacting each other, such as a meteorite hitting a planet *Explosion crater, a hole formed in the ground produced by an explosion near or below the surfac ...

. It is a semiregular variable star, ranging in brightness from magnitude 8.1 to 9.5 over a period of about 160 days. It is not visible to the naked-eye, but can be seen with a

small telescope A small telescope is generally considered by professional astronomers to be any reflecting telescope with a primary mirror that is less than in diameter. By amateur standards, a small telescope can have a primary mirror/aperture less than in dia ...

, or

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

. R Crateris is a

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...

; the variable star and its magnitude 9.9 F8V companion are separated by 65.4 arcseconds. Although the period for large brightness changes in R Crateris is listed as ~160 days, in 1982 Silvia Livi and Thaisa Bergmann reported small (~0.1 magnitude) variations on timescales of less than one hour. The rapid variations seem to be more regular when the star is near maximum brightness. R Crateris is an oxygen-rich

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

star, losing mass at a rate of per year via a

stellar wind A stellar wind is a flow of gas ejected from the 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 spherically symmetric. D ...

. At large distances from the star, the wind is expanding into space at km/sec. Near-infrared radiation from R Crateris was detected in the first

Two-Micron Sky Survey Two-Micron Sky Survey, or IRC, or Caltech infrared catalog is the astronomical catalogue of the infrared sources published in the 1969 by Neugebauer and Leighton. Catalogue index consists of two numbers - declination rounded to multiplier of 10 d ...

, published in 1969. It was detected in the far-infrared by the '' IRAS'' satellite, and that emission was resolved by ''IRAS'', showing that the star is surrounded by a large circumstellar shell containing dust. High resolution far-infrared images of R Crateris taken by the ''

Herschel Space Observatory The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telesc ...

'' show that the emitting region of the shell, roughly 280 arcseconds (0.94 light year) across, consists primarily of two non-concentric arcs well separated from the star itself. The arcs are probably bowshocks formed as the dusty stellar wind collides with the

interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...

. The total mass of the shell, including both dust and gas, is estimated to be about . Infrared imaging of the innermost (sub-arcsecond) portion of the dust shell shows a bipolar structure. In the early 1970s, maser emission from OH and H₂O was detected in R Cratoris' circumstellar shell. SiO maser emission was detected in 1985. Thermal (non-maser) emission from CO was detected in 1986. With the high angular resolution provided by Very Long Baseline Interferometry, the H₂O maser emission is seen to arise from small (milli-arcsecond) blobs, whose

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

s through the inner region of the circumstellar shell can be measured. These observations give additional evidence that R Cratoris has developed a bipolar stellar wind.

References

{{DEFAULTSORT:R Crateris Crater (constellation) Crateris, R 095384 053809 Semiregular variable stars M-type giants Asymptotic-giant-branch stars