astronomy

RS Sagittarii

RS Sagittarii 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 RS Sagittarii rather than just read about it. In short: RS Sagittarii is an eclipsing binary star system in the southern constellation of Sagittarius, abbreviated RS Sgr. It is a double-lined spectroscopic binary with an orbital period of 2.416 days, indicating that the components are too close to each other to be individually resolved.

Key takeaways

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

Reference excerpt

RS Sagittarii is an eclipsing binary star system in the southern constellation of Sagittarius, abbreviated RS Sgr. It is a double-lined spectroscopic binary with an orbital period of 2.416 days, indicating that the components are too close to each other to be individually resolved. The system has a combined apparent visual magnitude of 6.01, which is bright enough to be faintly visible to the naked eye. During the primary eclipse the brightness drops to magnitude 6.97, while the secondary eclipse is of magnitude 6.28. The distance to this system is 418 parsecs (1,360 light-years).

History of observations The variability of this system was initially suspected by B. A. Gould in 1879, then confirmed by A. W. Roberts in 1895. Roberts determined this to be an Algol-type variable with a period of 2.416 days. In his 1915 study of eclipsing binaries, H. Shapley listed a low orbital eccentricity of 0.091 for this binary system. He considered both eclipses to be partial, but only after correcting for limb darkening. R. S. Dugan and F. W. Wright in 1939 discovered evidence that suggested the period is varying. R. L. Baglow in 1948 found an essentially circular orbit with a primary component of spectral class B5. By 1986, O. E. Ferrer and J. Sahade were able to extract spectral information about the secondary component, finding the system consists of ordinary main sequence stars of classes B5V and A2V. Hydrogen alpha emission lines suggested that the stars are interacting.

Physical characteristics RS Sagittarii has a very tight orbit; both stars are separated by 17.32 solar radii (0.0805 au; 12,050,000 km) and take roughly 2 days and 10 hours to complete an orbit around the center of mass. The system appears to be semidetached. The secondary component is currently evolving away from the main sequence and expanding in size. It currently fills its roche lobe, having a teardrop shape. The roche lobe filling results in mass transfer to the primary star, which has an accretion disk and a hot spot at the impact location. Emission lines of hydrogen alpha is a consequence of the mass transfer. The primary component of the system is the larger and more massive of the pair, having 8.846 times the mass of the Sun (M☉) and 5.523 times the Sun's radius (R☉), compared to 2.875 M☉ and 5.524 R☉ for the secondary member. The primary is radiating 3,700 times the Sun's luminosity from its photosphere at an effective temperature of 19,000 K. The cooler secondary is 9,680 K and radiates 195 times the luminosity of the Sun. RS Sgr shares a common proper motion with the 9th-magnitude stars TYC-7400-1102-1 and HD 167669, and they would form a quadruple system. Any orbits would take hundreds of thousands of years. TYC-7400-1102-1 is an A1 main-sequence star with a mass around twice that of the Sun, while HD 167669 is a slightly brighter B9 main sequence star with a mass about three times the Sun's. HD 167669 itself has a close optical companion, but it appears to be much more distant. Together with RS Sgr, these stars have the Washington Double Star Catalog designation WDS J18176-3406.

References

Illustrations

Worked examples

Example 1 — a first encounter with RS Sagittarii

Start with the simplest possible case. Write down what RS Sagittarii 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 RS Sagittarii 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 RS Sagittarii 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 RS Sagittarii

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

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “RS Sagittarii” →

Affiliate

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

How to study RS Sagittarii in 20 minutes

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

Frequently asked questions

What is RS Sagittarii in simple terms?

Why does RS Sagittarii 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 RS Sagittarii?

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 RS Sagittarii.