astronomy

W Serpentis

W Serpentis 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 W Serpentis rather than just read about it. In short: W Serpentis is an eclipsing binary star in the constellation Serpens. It is always too faint to be seen with the naked eye, varying between apparent magnitudes 8.42 and 10.2 with a period of just over 14 days.

Key takeaways

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

Reference excerpt

W Serpentis is an eclipsing binary star in the constellation Serpens. It is always too faint to be seen with the naked eye, varying between apparent magnitudes 8.42 and 10.2 with a period of just over 14 days. Annie Jump Cannon's discovery that the star is a variable star was published in 1907. Its variable brightness is mainly due to eclipses; however, variations in its period indicate there are some innate changes in luminosity of one or both component stars as they interact with each other, and it has been difficult to disentangle the light to determine their nature. The period is increasing by 14 seconds a year, indicating that a massive amount of material is being transferred from the larger fainter star to the smaller brighter one. The system has been found to contain an accretion disk, and was one of the first discovered W Serpentids, which are eclipsing binaries containing exceptionally strong far-ultraviolet spectral lines. These systems have a high rate of mass transfer between one star and the other, and are thought to evolve first into double periodic variables and then classical Algol variables. In the late stages of mass transfer, such systems can develop an optically thick disc and are segregated as a separate class of W Serpentis stars. The classes may also represent different types of system altogether, with the W Serpentis type being younger and more massive. The spectral types of the component stars are not known; the hotter brighter component appears spectrally similar to an F-type giant. However, the central star appears to be completely obscured by material and may be a B-type main sequence star. The spectrum of the cooler fainter star has not been identified. Examining the polarised light shows that a jet of material is probably coming from the primary star as well. The properties of the two components are highly uncertain. Their orbital separation has been calculated to be as low as 17.2 R☉ or as high as 48.7 R☉. The orbit is generally assumed to be circular, although the 9th catalogue of spectroscopic binary orbits gives an eccentric orbit from a very old source. The accretion disc has been calculated at 14.9 R☉ across. The sizes of the two stars are disputed: different sources give masses of 5.7 M☉ and 2.0 M☉ or 1.5 M☉ and 1.0 M☉ for the hot and cool components respectively, and radii of 3.8 R☉ and 14.3 R☉ or 1.3 R☉ and 1.0 R☉ for the hot and cool components respectively.

References

Further reading https://www.eso.org/sci/publications/messenger/archive/no.39-mar85/messenger-no39-40-42.pdf

Illustrations

Worked examples

Example 1 — a first encounter with W Serpentis

Start with the simplest possible case. Write down what W Serpentis 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 W Serpentis 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 W Serpentis 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 W Serpentis

In research: W Serpentis 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 W Serpentis 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: W Serpentis is common in secondary-school and first-year university syllabi. It links to neighbouring topics A-type main-sequence stars, Algol variables, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for W Serpentis 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 W Serpentis in 20 minutes

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

Frequently asked questions

What is W Serpentis in simple terms?

Why does W Serpentis 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 W Serpentis?

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 W Serpentis.