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An Orion variable is a variable star which exhibits irregular and eruptive variations in its luminosity and is typically associated with diffuse nebulae. It is thought that these are young stars which will later become regular, non-variable stars on the zero-age main sequence. Brightness fluctuations can be as much as several magnitudes.
T Tauri stars are Orion variables exhibiting characteristic fluorescent violet emission lines from singly ionized iron (FeII) in their star spectra, and also emission from lithium, a metal that usually is destroyed by the nuclear fusion in the stars.
FU Orionis stars or simply "Fuors", are Orion variables that rise 5–6 magnitudes, then sink up to one magnitude and stay there for many decades. The prototype is FU Orionis, and other specimens are V1057 Cygni and V1515 Cygni.
Of this diverse class of stars, some Orion variables may exhibit a small amplitude (up to 1 magnitude) periodic variation, some are characterized by abrupt fadings, and some show spectral characteristics indicating mass downfall upon the star (YY Orionis stars). Many of these characteristics may occur in any one Orion variable.
The term 'Orion Variable' was a handy catch-all term but is now tending to drop out of disuse among the astronomical community, though for historical reasons the GCVS still uses it. Astronomers use more specialised terms which refer to actual physical differences among the 'zoo' of young variable stars, such as 'Classical T Tauri' or 'UX Orionis' stars.
V1500 Cygni or Nova Cygni 1975 was a bright nova occurring in 1975 in the constellation Cygnus. It had the second highest intrinsic brightness of any nova of the 20th century, exceeded only by CP Puppis in 1942.
A Gamma Cassiopeiae variable is a type of variable star, named for its prototype γ Cassiopeiae.
Alpha Cygni variables are variable stars which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time other parts expand. They are supergiant stars of spectral types B or A. Variations in brightness on the order of 0.1 magnitudes are associated with the pulsations, which often seem irregular, due to beating of multiple pulsation periods. The pulsations typically have periods of several days to several weeks.
V382 Carinae, also known as x Carinae, is a yellow hypergiant in the constellation Carina. It is a G-type star with a mean apparent magnitude of +3.93, and a variable star of low amplitude.
S Orionis is an asymptotic giant branch star in the constellation Orion, approximately 480 parsecs (1,600 ly) away. It varies regularly in brightness between extremes of magnitude 7.2 and 14 every 14 months.
Tau Cygni, Latinised from τ Cygni, is a binary star system in the constellation Cygnus, approximately 69 light years away from Earth. This visual binary system has a period of 49.6 years.
V380 Ori is a young multiple star system located near the Orion Nebula in the constellation Orion, thought to be somewhere between 1 and 3 million years old. It lies at the centre of NGC 1999 and is the primary source lighting up this and other nebulae in the region.
HD 37974 a variable B[e] hypergiant in the Large Magellanic Cloud. It is surrounded by an unexpected dust disk.
A slow irregular variable is a variable star that exhibit no or very poorly defined periodicity in their slowly changing light emissions. These stars have often been little-studied, and once more is learnt about them, they are reclassified into other categories such as semiregular variables.
25 Orionis, less commonly known by its Bayer designation Psi1 Orionis is a fifth-magnitude star in the constellation Orion. It lies among a dense cluster of low-mass pre-main-sequence stars in the Orion OB1a.
47 Cygni is a triple star system in the northern constellation of Cygnus, and is located around 4,000 light years from the Earth. It is visible to the naked eye with a combined apparent visual magnitude of 4.61. The system is moving closer to the Earth with a heliocentric radial velocity of −4.6 km/s.
Omicron1 Orionis is a binary star in the northeastern corner of the constellation Orion. It is visible to the naked eye with an apparent visual magnitude of 4.7. Based upon an annual parallax shift of 5.01±0.71 mas, it is located approximately 650 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an interstellar absorption factor of 0.27 due to intervening dust.
22 Orionis is a binary star in the equatorial constellation of Orion. It has the Bayer designation o Orionis, while 22 Orionis is the Flamsteed designation. This system is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude of 4.74. It is located approximately 1,100 light years away from the Sun based on parallax. The system is moving further from the Earth with a heliocentric radial velocity of +28.80
W Cygni is a semi-regular variable star in the constellation Cygnus, located 570 light-years from Earth. It lies less than half a degree southeast of ρ Cygni. W Cygni is, at times, a naked-eye star but it was not given a Bayer or Flamsteed designation. It has been proposed as a binary star system with a hotter main sequence companion, but this has not been confirmed.
Psi2 Orionis a binary star system in the equatorial constellation of Orion. It has an apparent visual magnitude of 4.6, indicating that it is visible to the naked eye. Based upon an annual parallax shift of 2.87 mass, it is roughly 1,100 light years distant from the Sun.
IK Tauri or NML Tauri is a Mira variable star located about 280 parsecs (910 ly) from the Sun in the zodiac constellation of Taurus.
Theta1 Orionis B, also known as BM Orionis, is a multiple star system containing at least five members. It is also one of the main stars of the Trapezium Cluster, with the others being A, C, and D. The primary is an eclipsing variable and one of the youngest known eclipsing binary systems.
VV Orionis is an eclipsing binary located in the belt region of the constellation Orion. It is a faint naked eye star.
W Orionis is a carbon star in the constellation Orion, approximately 400 parsecs (1,300 ly) away. It varies regularly in brightness between extremes of magnitude 4.4 and 6.9 roughly every 7 months.
FU Tauri is a brown dwarf binary system in the constellation of Taurus about 429 light years away. The secondary is very close to the lower limit for brown dwarfs and several databases list it as a distant massive exoplanet.
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| Eruptive |
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| Eclipsing | |||||||||
