RW Ursae Minoris (Nova Ursae Minoris 1956) is a

cataclysmic variable In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (), since ones with an outburst brightness visible to ...

star system that flared up as a

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

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 origins of the e ...

Ursa Minor Ursa Minor (Latin: 'Lesser Bear', contrasting with Ursa Major), also known as the Little Bear, is a constellation located in the far northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, h ...

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 ( tg, Душанбе, ; ; russian: Душанбе) is the capital and largest city of Tajikistan. , Dushanbe had a population of 863,400 and that population was largely Tajik. Until 1929, the city was known in Russian as Dyushambe (r ...

. On 24 September 1956 it had an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

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, but RW Ursae Minoris has a

galactic latitude The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane parallel to an ap ...

of 33 degrees, which is far from the plane of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

. 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 is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

in another galaxy. It was eventually identified as a nova in the galactic halo on the basis of its light curve and spectrum. All novae are binary stars, with a "donor" star orbiting 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 fro ...

. 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 shell. In 1985, Judith Cohen reported its radius as 1 arc second based observations with the Hale Telescope. 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 (constellation) Novae Ursae Minoris, RW