astronomy

Upsilon Sagittarii

Upsilon 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 Upsilon Sagittarii rather than just read about it. In short: Upsilon Sagittarii (Upsilon Sgr, υ Sagittarii, υ Sgr) is a spectroscopic binary star system in the constellation Sagittarius. Upsilon Sagittarii is the prototypical hydrogen-deficient binary (HdB), and one of only four such systems known.

Key takeaways

Upsilon 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 Upsilon Sagittarii to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Upsilon Sagittarii from memory before moving on to harder problems.

Reference excerpt

Upsilon Sagittarii (Upsilon Sgr, υ Sagittarii, υ Sgr) is a spectroscopic binary star system in the constellation Sagittarius. Upsilon Sagittarii is the prototypical hydrogen-deficient binary (HdB), and one of only four such systems known. The unusual spectrum of hydrogen-deficient binaries has made stellar classification of Upsilon Sagittarii difficult.

System υ Sgr is a binary system with an orbital period of 137.939 days and is approximately 1,800 light years from Earth. The primary star dominates the visible radiation and spectrum, but the secondary is hotter and more massive. Some sources consider the "invisible" component to be the primary on the basis of its mass. There is also a disc of material being stripped from the primary and transferring material to the secondary, but no eclipses The system is classified as a single-lined spectroscopic binary, but high excitation lines from the secondary can be detected in the ultraviolet. Radial velocity variations were discovered in 1899, The first orbit was calculated in 1914, reasonably close to modern understanding of the system. Analysis of optical interferometry finds the two stars to be separated by 1.3 mas and have a difference in brightness of about 3.5 magnitudes.

Properties

The primary component appears as an A type supergiant, although published spectral types vary from F2p to B5II. Contrasting components in the spectrum may originate from disc material, polar jets, or the star itself. The low mass and unusual chemical composition are also thought to produce misleading spectral calibrations, with the star not as massive or as luminous as the Ia luminosity class would suggest. The visible component is a helium star, almost entirely deficient of hydrogen. It has also been described as a neon star, due to the very high relative levels of that element. It has been stripped of its outer hydrogen layers after it expanded away from the main sequence. It is thought to have originated as a main sequence star with around 8 M☉, expanded when it exhausted its core hydrogen, and now only 2.5 M☉ remains, highly inflated and giving the appearance of a supergiant star. Other estimates give higher masses, as much as 5.45 M☉ and 8.56 M☉ at the known inclination of 50°. The supergiant component is also classified as an PV Telescopii variable, although it was originally catalogued as an eclipsing binary. It shows apparent magnitude fluctuations between +4.51 and +4.65 with a period of approximately 20 days. The companion is more massive than the supergiant primary, but so dim at visible frequencies as to be undetectable, although it can be seen in ultraviolet spectra. It is thought to be a B-type main sequence star accreting mass from the primary.

Naming υ Sagittarii has two entries in the Henry Draper Catalogue, HD 181615 and HD 181616. In Chinese, 建 (Jiàn), meaning Establishment, refers to an asterism consisting of υ Sagittarii, ξ² Sagittarii, ο Sagittarii, π Sagittarii, 43 Sagittarii and ρ¹ Sagittarii. Consequently, the Chinese name for υ Sagittarii itself is 建六 (Jiàn liù, English: the Sixth Star of Establishment.)

References

Further reading Dudley, R. E., Jeffery, C. S., 1990. Mon. Not. R. astr. Soc. 247, 400

Illustrations

Worked examples

Example 1 — a first encounter with Upsilon Sagittarii

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

In research: Upsilon 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 Upsilon 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: Upsilon Sagittarii is common in secondary-school and first-year university syllabi. It links to neighbouring topics A-type supergiants, B-type main-sequence stars, Bayer objects, so understanding it makes those chapters shorter.
In everyday life: Look for Upsilon 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 “Upsilon Sagittarii” →

Affiliate

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

How to study Upsilon Sagittarii in 20 minutes

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

Frequently asked questions

What is Upsilon Sagittarii in simple terms?

Why does Upsilon 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 Upsilon 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 Upsilon Sagittarii.