astronomy

WR 111

WR 111 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 WR 111 rather than just read about it. In short: WR 111 (HD 165763) is a Wolf-Rayet (WR) star in the constellation Sagittarius. It is magnitude 7.8 and lies about 5,150 light-years away.

Key takeaways

WR 111 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect WR 111 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of WR 111 from memory before moving on to harder problems.

Reference excerpt

WR 111 (HD 165763) is a Wolf-Rayet (WR) star in the constellation Sagittarius. It is magnitude 7.8 and lies about 5,150 light-years away. It is one of the brightest and most closely studied WR stars.

History In 1880, Edward Pickering reported that BD−21°4864 had a spectrum similar to a nova, but it was apparently a non-variable star that had been near 8th magnitude since at least 1849. It was included in Campbell's 1894 paper The Wolf-Rayet stars. In the Henry Draper Catalogue, BD−21°4864 was listed as entry 165763 with a spectral type of Oa. It was described in 1925 as a "Be star" due to its very strong emission lines, and in 1927 as a class-O star with unusually broad emission features. After the classification of WR stars onto either the nitrogen or carbon sequence, HD 165763 was designated as WC6 and its temperature estimated from the strength of Ov and Civ emission. In 1968, the WR spectral classes were revised and HD 165763 was used as an example of class WC5. In this catalogue, considered as the fifth catalogue of Wolf Rayet stars, it was designated MR 84. In the sixth WR catalogue, the current naming convention was adopted and this star was numbered as WR 111.

Location WR 111 is one of the 20 brightest Wolf Rayet stars in the sky. It lies in a rich Milky Way field near to V4381 Sagittarii and HD 165516, but not apparently a member of the associated cluster.

Properties WR 111 is considered an archetypal WC5 star, having dominant emission lines of Civ, plus strong Ciii emission as well as Oiii, Oiv, and Ov, but not Ovi. Non-hydrodynamical atmospheric models calculate a "surface" temperature of 89,000 K. The surface in this context is defined as the depth in the atmosphere at which the optical depth reaches 20. This differs from the convention used for many types of star, due to the optically dense stellar winds of WR stars. The corresponding radius is at 2.10 R☉. A more detailed individual study of WR 111 using a hydrodynamical atmospheric model gives a temperature of 140,000 K and a radius of 0.905 R☉. The apparently large difference is due largely to a difference in the depth within the atmosphere at which the radius is defined. The luminosity of WR 111 is similar in both models at 245,000 L☉ - 282,000 L☉, and the masses are found to be 13.0 M☉ and 13.63 M☉, respectively. The stellar wind from WR 111 is ejecting 20 millionths of the Sun's mass every year at a speed of 2,398 km/s. The mechanism driving the intense stellar wind is found to be an opacity bump deep within the atmosphere caused by highly ionised iron. The winds are then accelerated to high velocity in the outer atmosphere by less highly ionised iron and by carbon and oxygen.

References

Worked examples

Example 1 — a first encounter with WR 111

Start with the simplest possible case. Write down what WR 111 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 WR 111 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 WR 111 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 WR 111

In research: WR 111 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 WR 111 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: WR 111 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, Henry Draper Catalogue objects, Hipparcos objects, so understanding it makes those chapters shorter.
In everyday life: Look for WR 111 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 WR 111 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what WR 111 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 WR 111 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is WR 111 in simple terms?

WR 111 (HD 165763) is a Wolf-Rayet (WR) star in the constellation Sagittarius. It is magnitude 7.8 and lies about 5,150 light-years away.

Why does WR 111 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 WR 111?

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 WR 111.