astronomy

GW Orionis

GW Orionis is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand GW Orionis rather than just read about it. In short: GW Orionis is a T Tauri type pre-main sequence hierarchical triple star system. It is associated with the Lambda Orionis star-forming region and has an extended circumtrinary protoplanetary disk.

Key takeaways

GW Orionis belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GW Orionis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GW Orionis from memory before moving on to harder problems.

Reference excerpt

GW Orionis is a T Tauri type pre-main sequence hierarchical triple star system. It is associated with the Lambda Orionis star-forming region and has an extended circumtrinary protoplanetary disk.

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 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. GW Orionis B and the third member of the system, GW Orionis C, were detected directly in 2011 using the IOTA interferometer located on Mount Hopkins in Arizona.

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. The lightcurve of GW Orionis varies with periods of 3.02 and 1.92 days, which likely correspond to the rotation periods of GW Orionis A and B, respectively. 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 units. The disk has an inclination of 137.6°. Observations of the disk made with the Atacama Large Millimeter Array 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°.

Illustrations

Worked examples

Example 1 — a first encounter with GW Orionis

Start with the simplest possible case. Write down what GW Orionis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to GW Orionis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about GW Orionis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of GW Orionis

In research: GW Orionis appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses GW Orionis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: GW Orionis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Circumstellar disks, Henry Draper Catalogue objects, Hipparcos objects, so understanding it makes those chapters shorter.
In everyday life: Look for GW Orionis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study GW Orionis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GW Orionis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain GW Orionis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GW Orionis in simple terms?

GW Orionis is a T Tauri type pre-main sequence hierarchical triple star system. It is associated with the Lambda Orionis star-forming region and has an extended circumtrinary protoplanetary disk.

Why does GW Orionis matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study GW Orionis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on GW Orionis.