astronomy

Pismis 24-1

Pismis 24-1 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 Pismis 24-1 rather than just read about it. In short: Pismis 24-1, also known as HD 319718, is the brightest star of the open cluster Pismis 24 within the nebula NGC 6357 about 6,500 light-years away. It was once thought to be the most massive star known, but is composed of at least three individual objects, each still among the most luminous and most massive stars known.

Key takeaways

Pismis 24-1 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pismis 24-1 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pismis 24-1 from memory before moving on to harder problems.

Reference excerpt

Pismis 24-1, also known as HD 319718, is the brightest star of the open cluster Pismis 24 within the nebula NGC 6357 about 6,500 light-years away. It was once thought to be the most massive star known, but is composed of at least three individual objects, each still among the most luminous and most massive stars known.

Discovery Pismis 24-1 was first catalogued as HD 319718, later resolved into both Pismis 24-1 and the fainter Pismis 24-16. The surrounding H II region NGC 6357 is prominent, but the compact 10th-magnitude open cluster Pismis 24 was not identified until 1959. In 1973, Pismis 24 was resolved into 15 components of which 12 were considered member stars. The brightest was numbered first as Pismis 24-1 and tentatively considered a supergiant. It was later resolved into an O3.5 supergiant spectroscopic binary and an O4 giant star separated by approximately 500 AU.

System

Pismis 24-1 has been resolved visually into two components, usually labelled as NE and SW from their orientation with each other. Pismis 24-1NE is slightly more luminous and hotter than 24-1SW, but is known to be a spectroscopic binary. This is surprising given the spectral luminosity classes, because it would make the individual supergiant stars less luminous than a single cooler giant star. It could be that the interaction between the components of 24-1NE is confusing its classification, or the O4 giant may also be a close binary. Pismis 24-1 is actually a shallow eclipsing binary with a period of 2.4 days. It is presumed to be the NE component which produces the eclipses, but the separate light curves for the components have not been resolved. The light curve is symmetrical, indicating a near circular orbit, and the two eclipsing stars have very similar masses and temperatures. The Catalog of Components of Double and Multiple Stars lists Pismis 24-1 as having two fainter companions 5.5 and 16.4 arcseconds distant. This is not surprising since it is a member of a rich open cluster only 1.5 arcminutes across.

Properties

The two components of Pismis 24-1NE cannot be detected separately, but analysis of their eclipses shows that they are almost identical, with temperatures around 42,000 K. The pair combined is nearly 800,000 times as luminous as the sun, making each individual star likely to be under 400,000 L☉. The spectral type of the combined object is O3.5 If* indicating an expanded star with strong emission lines of highly ionised nitrogen. Separate spectral signatures cannot be detected so it is assumed that both stars have similar spectra. The mass as a single object has been calculated to be 74 M☉ but each star would have a smaller mass. Hard X-ray radiation from the vicinity of Pismis 24-1 is assumed to be caused by the colliding winds of these two supergiants. Pismis 24-1SW is apparently a single star with a spectral type of O4 III(f+), indicating a temperature around 40,000 K and emission lines of ionised nitrogen, silicon and helium. The luminosity is around 650,000 L☉, the radius 17 R☉, and the mass 66 M☉. It is classified as a giant star on the basis of its spectrum, but the hottest O stars develop these spectral features while still burning hydrogen in their cores, as a result of vigorous convection and powerful stellar winds. When first modelled, Pismis 24-1 was thought to be a single star with a mass of 300 M☉ or more, higher than expected to be theoretically possible. This estimate has decreased as the star was discovered to be a binary, then a triple, and as newer models of stellar atmospheres have been developed. The latest mass estimates are well within theoretical expectations for star formation without exotic explanations.

External links Massive Stars in Open Cluster Pismis 24 , 2006 December 19

References

Illustrations

Worked examples

Example 1 — a first encounter with Pismis 24-1

Start with the simplest possible case. Write down what Pismis 24-1 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 Pismis 24-1 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 Pismis 24-1 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 Pismis 24-1

In research: Pismis 24-1 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 Pismis 24-1 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: Pismis 24-1 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, Eclipsing binaries, Emission-line stars, so understanding it makes those chapters shorter.
In everyday life: Look for Pismis 24-1 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 Pismis 24-1 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pismis 24-1 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 Pismis 24-1 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pismis 24-1 in simple terms?

Why does Pismis 24-1 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 Pismis 24-1?

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 Pismis 24-1.