R Aquarii (R Aqr) is a

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 e ...

in the constellation

Aquarius Aquarius may refer to: Astrology * Aquarius (astrology), an astrological sign * Age of Aquarius, a time period in the cycle of astrological ages Astronomy * Aquarius (constellation) * Aquarius in Chinese astronomy Arts and entertainme ...

. R Aquarii is a symbiotic star believed to contain 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 ...

and a Mira-type variable in a binary system. The

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

is approximately 44 years. The main Mira-type star is a red giant, and varies in brightness by a factor of several hundred and with a period of slightly more than a year; this variability was discovered by

Karl Ludwig Harding Karl Ludwig Harding (29 September 1765 – 31 August 1834) was a German astronomer, who discovered 3 Juno, the third asteroid of the main-belt in 1804. The lunar crater '' Harding'' and the asteroid 2003 Harding are named in his honor. ...

in 1810. It has a distance of about 390

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, an ...

s, and is one of the nearest symbiotic stars and a well-known jet source. The two components have been resolved at a separation of 55 mas. By its gravitational pull, the white dwarf draws in material from the red giant and occasionally ejects some of the surplus in loops to form the nebula seen in the linked image. The whole system appears reddened because it is situated in a very dusty region of space, and its blue light is absorbed before reaching Earth. RAqrLightCurve

The nebula around R Aquarii is also known as Cederblad 211. It is possible that the nebula is the remnant of a nova-like outburst, which may have been observed by Japanese astronomers, in the year 930 AD. It is reasonably bright but small and dominated by its central star. Visual observations are difficult and rare. The central region of the jet shows an ejection that took place around 190 years ago, as well as much younger structures. The giant primary star is a

Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavele ...

, a star that pulsates and changes temperature, leading to very large visual brightness changes. The total range of 5.2 - 12.4 is a variation of 750 times in brightness, from a naked eye star to one beyond the range of binoculars. The pulsations occur every 390 days but are not entirely regular.

Gallery

References

External links

Weird loop image in R Aquarii
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AAVSO Variable Star of the Month. R Aquarii: Summer 2003

Visual observation of a symbiotic star {{Stars of Aquarius Aquarius (constellation) M-type giants Mira variables Spectroscopic binaries 222800 Aquarii, R 8992 117054 Durchmusterung objects Z Andromedae variables