Orion variable

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 star

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

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.


  • Samus N.N., Durlevich O.V., et al. Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.)
  • Glasby, J. S. The Nebular Variables: International Series of Monographs in Natural Philosophy
  • Cohen, M.; Dewhirst, D. W. (1973). "Infra-Red Observations of Young Stars-II: T TAURI STARS AND THE ORION POPULATION". Monthly Notices of the Royal Astronomical Society. 161: 97. Bibcode:1973MNRAS.161...97C. doi:10.1093/mnras/161.1.97.

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AE Aurigae

AE Aurigae (abbreviated as AE Aur) is a runaway star in the constellation Auriga; it lights the Flaming Star Nebula.

Astronomical filter

An astronomical filter is a telescope accessory consisting of an optical filter used by amateur astronomers to simply enhance the details of celestial objects (much as with amateur photography). In contrast, research astronomers use filters on telescopes in order to understand the astrophysics (such as stellar classification and placement of a celestial body on its Wien Curve), occurring for the object in a given bandpass via photometry.

Most astronomical filters work by blocking a specific part of the color spectrum above and below a bandpass, significantly increasing the signal to noise of the interesting wavelengths, and so making the object gain detail and contrast. While the color filters transmit certain colors from the spectrum and are usually used for observation of the planets and the Moon, the polarizing filters work by adjusting the brightness, and are usually used for the Moon. The broadband and narrowband filters transmit the wavelengths that are emitted by the nebulae (by the Hydrogen and Oxygen atoms), and are frequently used for reducing light pollution.

FU Orionis star

In stellar evolution, an FU Orionis star (also FU Orionis object, or FUor) is a pre–main-sequence star which displays an extreme change in magnitude and spectral type. One example is the star V1057 Cyg, which became 6 magnitudes brighter and went from spectral type dKe to F-type supergiant. These stars are named after their type-star, FU Orionis.

The current model developed primarily by Lee Hartmann and Scott Jay Kenyon associates the FU Orionis flare with abrupt mass transfer from an accretion disc onto a young, low mass T Tauri star. Mass accretion rates for these objects are estimated to be around 10−4 solar masses per year. The rise time of these eruptions is typically on the order of 1 year, but can be much longer. The lifetime of this high-accretion, high-luminosity phase is on the order of decades. However, even with such a relatively short timespan, as of 2015 no FU Orionis object had been observed shutting off. By comparing the number of FUor outbursts to the rate of star formation in the solar neighborhood, it is estimated that the average young star undergoes approximately 10–20 FUor eruptions over its lifetime.

The prototypes of this class are: FU Orionis, V1057 Cygni, V1515 Cygni, and the embedded protostar V1647 Orionis, which erupted in January 2004.

HD 87643

HD 87643 is a B[e] class binary star embedded in a reflection nebula.

The system is described as having "one of the most extreme infrared excesses for this object class. It harbours a large amount of both hot and cold dust, and is surrounded by an extended reflection nebula." and is important for astronomers in their study of stellar formation.All the properties of HD 87643 are highly uncertain. Its distance has been estimated anywhere from one to six kpc. The General Catalogue of Variable Stars classifies it as an Orion variable, a pre-main sequence star, but other authors consider it to be a supergiant B[e] star. It has been confirmed to be a binary star system with the two stars separated by about 52 AU, but the nature of the companion is unknown.

HD 97048

HD 97048 or CU Chamaeleontis is a Herbig Ae/Be star 603 ly away in the constellation Chamaeleon. It is a variable star embedded in a dust cloud containing a stellar nursery, and is itself surrounded by a dust disk.

HD 97048 is a young star still contracting towards the main sequence. Its brightness varies between magnitudes 8.38 and 8.48 and it is classified as an Orion variable. It was given the variable star designation CU Chamaeleontis in 1981. Its spectrum is also variable. The spectral class is usually given as A0 or B9, sometimes with a giant luminosity class, sometimes main sequence. The spectrum shows strong variable emission lines indicative of a shell surrounding the star.HD 97048 is a mamber of the Chamaeleon T1 stellar association and is still embedded within the dark molecular cloud that it is forming from. It illuminates a small reflection nebula against the dark cloud. This young star has a substantial dust disk having a central cavity with a 40−46 AU radius

List of stars in Auriga

This is the list of notable stars in the constellation Auriga, sorted by decreasing brightness.

List of stars in Cassiopeia

This is the list of notable stars in the constellation Cassiopeia, sorted by decreasing brightness.

List of stars in Chamaeleon

This is the list of notable stars in the constellation Chamaeleon, sorted by decreasing brightness.

List of stars in Corona Australis

This is the list of notable stars in the constellation Corona Australis, sorted by decreasing brightness.

List of stars in Monoceros

This is the list of notable stars in the constellation Monoceros, sorted by decreasing brightness.

List of stars in Orion

This is the list of notable stars in the constellation Orion, sorted by decreasing brightness.

List of stars in Vulpecula

This is the list of notable stars in the constellation Vulpecula, sorted by decreasing brightness.

List of variable stars

There are over 41,638 known variable stars (2008), with more being discovered regularly, so a complete list of every single variable is impossible at this place (cf. GCVS). The following is a list of variable stars that are well-known, bright, significant, or otherwise interesting.

Outline of astronomy

The following outline is provided as an overview of and topical guide to astronomy:

Astronomy – studies the universe beyond Earth, including its formation and development, and the evolution, physics, chemistry, meteorology, and motion of celestial objects (such as galaxies, planets, etc.) and phenomena that originate outside the atmosphere of Earth (such as the cosmic background radiation).

PV Cephei

PV Cep is variable star of Orion type located in the constellation of Cepheus at a distance of over 1600 light-years from Earth. Although the terms 'Orion variable/Orion type' are now no longer used by most astronomers. The term 'Young Stellar Object' or YSO is preferred, since 'Orion Variable' is a term which was given at a time when these objects were thought to be more homogeneous than is now known to be the case. It has been used by the CGVS compilers but astronomers generally do not use these terms any more.

T Tauri star

T Tauri stars (TTS) are a class of variable stars associated with youth. They are less than about ten million years old. This class is named after the prototype, T Tauri, a young star in the Taurus star-forming region. They are found near molecular clouds and identified by their optical variability and strong chromospheric lines. T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence along the Hayashi track, a luminosity–temperature relationship obeyed by infant stars of less than 3 solar masses (M☉) in the pre-main-sequence phase of stellar evolution. It ends when a star of 0.5 M☉ develops a radiative zone, or when a larger star commences nuclear fusion on the main sequence.

Theta2 Orionis

Theta2 Orionis (θ2 Ori) is a multiple star system in the constellation Orion. It is a few arc minutes from its more famous neighbour the Trapezium Cluster, also known as θ1 Orionis.

V380 Orionis

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.

V3903 Sagittarii

V3903 Sagittarii is an eclipsing binary star system in the constellation Sagittiarus.


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