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U Orionis (abbreviated U Ori) is a Mira-type variable star in the
It was discovered on 1885 December 13 by J.E. Gore and initially it was thought to be a nova in the early stages of decline (''Gore's Nova'' and ''NOVA Ori 1885'' as still listed in SIMBAD), but a spectrum taken at Harvard showed features similar to that of Mira. Thus U Orionis became the first long period variable to be identified by a photograph of its spectrum.
The star has a low effective temperature (variable with the pulsations, but roughly 2,700 K), a large and bloated radius of , and a high luminosity, 7,000 times higher than the Sun. If the Sun were replaced with U Orionis, its radius would extend beyond
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 ...
Orion. It is a classical long period variable
The descriptive term long-period variable star refers to various groups of cool luminous pulsating variable stars. It is frequently abbreviated to LPV.
Types of variation
The General Catalogue of Variable Stars does not define a long-period vari ...
star that has been well observed for over 120 years.
Discovery
It was discovered on 1885 December 13 by J.E. Gore and initially it was thought to be a nova in the early stages of decline (''Gore's Nova'' and ''NOVA Ori 1885'' as still listed in SIMBAD), but a spectrum taken at Harvard showed features similar to that of Mira. Thus U Orionis became the first long period variable to be identified by a photograph of its spectrum.
Location
U Orionis lies less than half a degree east of the small-amplitude variable star χ1 Orionis and less than an arc-minute from the much fainter eclipsing variable UW Orionis. χ1 Orionis is slightly brighter than U Orionis at its brightest maximum, while UW Orionis is more than a thousand times fainter, similar to U Orionis at minimum.Stellar parameters
The star has a low effective temperature (variable with the pulsations, but roughly 2,700 K), a large and bloated radius of , and a high luminosity, 7,000 times higher than the Sun. If the Sun were replaced with U Orionis, its radius would extend beyond Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
's orbital zone (about 1.7 astronomical units
The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...
).
Possible planetary system
According to Rudnitskij, a 12- to 15-year "super-periodicity" has been observed. The author infers such periodicity could coincide with the revolution period of an invisible companion, probably planetary. So far no clear hint of planetary objects has been detected.References
{{DEFAULTSORT:U Orionis Orion (constellation) Mira variables Orionis, U M-type giants 0398162063
In contemporary history, the third millennium of the anno Domini or Common Era in the Gregorian calendar is the current millennium spanning the years 2001 to 3000 ( 21st to 30th centuries). Ongoing futures studies seek to understand what is l ...
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