RW Ursae Minoris (Nova Ursae Minoris 1956) is a cataclysmic variable star system that flared up as a

nova A nova ( novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", Latin for "new") that slowly fades over weeks or months. All observed novae involve white ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Ursa Minor Ursa Minor (, contrasting with Ursa Major), also known as the Little Bear, is a constellation located in the far northern celestial hemisphere, northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of ...

in 1956. Although the nova eruption of RW UMi occurred in 1956, it was not noticed until nearly six years later when, in 1962, V. Satyvaldiev found it on sky-patrol plates of the Astrophysical Institute of the Tajik Academy of Sciences in

Dushanbe Dushanbe is the Capital city, capital and largest city of Tajikistan. , Dushanbe had a population of 1,564,700, with this population being largely Tajiks, Tajik. Until 1929, the city was known in Russian as Dyushambe, and from 1929 to 1961 as St ...

. On 24 September 1956 it had an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, 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 (astronomy), ...

of 6. It may have been as bright as magnitude 3.5 around 19 September 1956, which would have made it easily visible to the naked eye, but the full moon on 20 September 1956 would have hampered observations around that date. RW Ursae Minoris's pre-nova brightness was about magnitude 21, but early in the 21st century it was still two magnitudes brighter than that. Novae tend to be found near the

galactic plane The galactic plane is the plane (geometry), plane on which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. In actual usage, the terms ''galactic plane'' and ''galac ...

, but RW Ursae Minoris has a galactic latitude of 33 degrees, which is far from the plane of the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. Because of this, and its large outburst amplitude, astronomers were initially unsure about whether RW Ursae Minoris was a nova in the Milky Way or a

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

in another galaxy. It was eventually identified as a nova in the galactic halo on the basis of its

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

and spectrum. All novae are binary stars, with a "donor" star orbiting a

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 ...

. The donor star is so close to the white dwarf that material from the donor is transferred to the white dwarf. In 1995 Retter and Lipkin detected a low amplitude (0.1 - 0.2 magnitude) variation in RW Ursae Minoris's brightness with a period of 1.4 hours. They argued that this 1.4 hour period is probably the orbital period of the binary pair, which would make it the shortest period orbit for any known nova. RW Ursae Minoris is surrounded by a small

nova remnant A nova remnant is made up of the material either left behind by a sudden explosive fusion eruption by classical novae, or from multiple ejections by recurrent novae. Over their short lifetimes, nova shells show expansion velocities of around 1000& ...

shell. In 1985, Judith Cohen reported its radius as 1 arc second based observations with the

Hale Telescope The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in San Diego County, California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation in 1928, he orchestrated the planning, de ...

. In 1995 Esenoglu ''et al.'' observed it with the Copernico 1.82 m telescope and measured a radius of ~1.5 arc seconds.

References

{{DEFAULTSORT:RW Ursae Minoris Ursa Minor Novae Ursae Minoris, RW