astronomy

MWC 349

MWC 349 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 MWC 349 rather than just read about it. In short: MWC 349 is a double (likely, triple) star system in the constellation Cygnus. Its properties are still debated and it may be a massive highly luminous star or a very young less luminous Herbig Ae/Be star.

Key takeaways

MWC 349 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MWC 349 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MWC 349 from memory before moving on to harder problems.

Reference excerpt

MWC 349 is a double (likely, triple) star system in the constellation Cygnus. Its properties are still debated and it may be a massive highly luminous star or a very young less luminous Herbig Ae/Be star. MWC 349 is also a variable star with the designation V1478 Cygni.

MWC 349A and B and a third star MWC 349 is a resolved double star, with its components separated by 2.4 arc seconds. The primary, MWC 349A, is a B[e] star, where the B is the spectral type and the [e] denotes forbidden emission lines. Its spectrum lacks absorption features and is variable but has been classified as B0-1.5 with a supergiant luminosity class. The secondary, MWC 349B, is a giant star with a spectral type of B0III. It has been proposed that there is a third star, of lower mass and closely orbiting MWC 349A, possibly at a distance of 12–13 AU from the primary with a period of 9 years. Such a star has not been observed but would help to explain some unusual properties of the system.

Features

MWC 349B appears to be a relatively conventional hot giant star, but it is nonetheless very unusual. It is a supergiant B[e] star, indicating that it is a luminous star with high mass loss and a disc of surrounding material. These features are shared by pre-main-sequence stars and evolved very massive stars, and it is unclear which category MWC 349A falls into. MWC 349 is one of the brightest radio sources in the sky and 2 cm observations show a prominent hourglass nebula. It also has a very faint infrared nebula with the same orientation and geometry, but 400 times larger (5 parsecs across). It is extremely unusual in showing hydrogen recombination masers and lasers, interpreted as originating in the disc. One theory is that MWC 349A is a highly luminous evolved star similar to a luminous blue variable (LBV), with an absolute magnitude somewhere between −6.7 and −7.3, and a bolometric luminosity several hundred thousand times that of the sun. It is a variable star and the General Catalogue of Variable Stars lists it as an S Doradus variable due to its erratic brightness and spectral changes. The distant association with MWC 349B and its remoteness from the dense star-forming regions that would normally host such luminous stars is unusual. One possibility is that the whole system was ejected from Cygnus OB2 and the two components have since become unbound due to mass loss from MWC 349A. The alternative theory is that MWC 349A is still condensing onto the main sequence. It is still a massive star surrounded by a disc of material but that material was not ejected from the star, and the luminosity is lower than would be the case for a more massive evolved star. The compact nature of the material absorbing and re-radiating much of the stars output suggests that it is unlikely to be extremely luminous.

Origin MWC 349 may be a runaway star ejected from the nearby, massive Cygnus OB2 association. The mass of the main component of the system, MWC 349A, is assumed to have been when the star was born 40 times the mass of the Sun, but stellar evolution left it with just 20-25 solar masses, destabilizing the system and causing MWC 349B to no longer be gravitationally bound.

Notes

References

Further reading Danchi, W. C; Tuthill, P. G; Monnier, J. D (2001). "Near-Infrared Interferometric Images of the Hot Inner Disk surrounding the Massive Young Star MWC 349A". The Astrophysical Journal. 562 (1): 440–445. Bibcode:2001ApJ...562..440D. doi:10.1086/323530.

External links MWC 349A: A hot edge-on disk SCIENTISTS DISCOVER FIRST NATURAL LASER IN SPACE

Illustrations

Worked examples

Example 1 — a first encounter with MWC 349

Start with the simplest possible case. Write down what MWC 349 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 MWC 349 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 MWC 349 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 MWC 349

In research: MWC 349 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 MWC 349 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: MWC 349 is common in secondary-school and first-year university syllabi. It links to neighbouring topics B(e) stars, B-type giants, Cygnus (constellation), so understanding it makes those chapters shorter.
In everyday life: Look for MWC 349 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study MWC 349 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MWC 349 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 MWC 349 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MWC 349 in simple terms?

Why does MWC 349 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 MWC 349?

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 MWC 349.