GW Orionis is a T Tauri type pre-main sequence hierarchical triple star system. It is associated with the

Lambda Orionis Meissa , designated Lambda Orionis (λ Orionis, abbreviated Lambda Ori, λ Ori) is a star in the constellation of Orion (constellation), Orion. It is a multiple star approximately away with a combined apparent magnitude of 3.33. The ...

star-forming region and has an extended circumtrinary

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...

Observational history

GW Orionis first came to the attention of astronomers when it was published, as MHA 265–2, in a list of stars whose spectra have bright H and K lines of calcium. The multiple nature of GW Orionis was first discovered by Robert D. Mathieu, Fred Adams, and David W. Latham during a radial velocity survey of late-type

H-alpha H-alpha (Hα) is a specific deep-red visible spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared wit ...

emission stars in the Lambda Orionis Association, published in 1991. Radial velocities of the primary star were measured from 45 high-resolution spectra and were used to determine the orbital elements. A trend in the radial velocity residuals indicated either an additional stellar companion with an orbital period of years or a global asymmetric gravitational instability in a

circumstellar disc A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the re ...

. GW Orionis B and the third member of the system, GW Orionis C, were detected directly in 2011 using the

IOTA Iota (; uppercase: Ι, lowercase: ι; ) is the ninth letter of the Greek alphabet. It was derived from the Phoenician letter Yodh. Letters that arose from this letter include the Latin I and J, the Cyrillic І (І, і), Yi (Ї, ї), and ...

interferometer located on Mount Hopkins in

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

Variability

GW Orionis is a variable star with quasi-periodic brightness changes. The apparent magnitude varies between 9.7 and 10.4 with dimming events of between 0.1 and 0.7 magnitudes roughly every 30 days, as well as more sinusoidal variations with an amplitude of 0.2 magnitudes over 11.6 years. An initial interpretation of the variability was that a disk of material around component B was eclipsing component A and causing the dimming events, but it is now thought that the eclipses are caused by partial obscuration of both stars by a much larger ring which precesses around the pair.

Protoplanetary disk

GW Orionis has a large and massive protoplanetary disk surrounding it. The dust continuum emission suggests a disk radius of approximately 400

astronomical unit 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 ...

s. The disk has an inclination of 137.6°. Observations of the disk made with the

Atacama Large Millimeter Array The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths. The ...

identified three separate dust rings located at ~46, 188, and 338 astronomical units from the center of the system. The three rings have estimated dust masses 74, 168, and 245 times that of the Earth. According to Jiaqing Bi and coauthors, the outermost ring is the largest protoplanetary dust ring they are aware of. The dust rings are misaligned and the innermost dust ring is eccentric probably due to ongoing dynamical interactions between the triple stars and the circumtriple disk.

Orbital architecture

The A and B components of GW Orionis form a double-lined spectroscopic binary with a 241-day period while component C orbits the inner pair with an 11.5 year period. It is likely that at least one of the stellar orbital planes is misaligned with the plane of the protoplanetary disk by as much as 45°.

References

{{Stars of Orion Circumstellar disks 244138 25689 Orionis, GW Orion (constellation) Triple star systems T Tauri stars J05290838+1152126