astronomy

HIP 81208

HIP 81208 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 HIP 81208 rather than just read about it. In short: HIP 81208 (HD 149274) is a young triple or quadruple hierarchical star system in the constellation of Scorpius. It consists of a B-type main sequence star (component A), a brown dwarf (B), and a red dwarf (C), the latter two distantly orbiting the primary star.

Key takeaways

HIP 81208 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HIP 81208 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HIP 81208 from memory before moving on to harder problems.

Reference excerpt

HIP 81208 (HD 149274) is a young triple or quadruple hierarchical star system in the constellation of Scorpius. It consists of a B-type main sequence star (component A), a brown dwarf (B), and a red dwarf (C), the latter two distantly orbiting the primary star. The stars are part of the Scorpius–Centaurus association. In 2023, HIP 81208 C was found to be orbited by a substellar object, which is at the border between being a massive exoplanet and a low-mass brown dwarf. This made HIP 81208 the first stellar binary with substellar objects orbiting both stellar components ever discovered by direct imaging. With an apparent magnitude of 6.64, it is barely visible by the naked eye under dark skies.

Stellar properties The dominant component of the system, HIP 81208 A is a bright blue-white star with a spectral type of B9V, which is about 2.2 times larger, 2.6 times more massive, and 60 times more luminous than the Sun. It is very young at only 17 million years old, less than 0.4% the age of the Solar System (4.6 billion years). In 2023, two smaller objects, respectively designated HIP 81208 B and C, were detected near the star using the SPHERE instrument at the Very Large Telescope in Antofagasta Region, Chile. They both have similar proper motions to HIP 81208 A, strongly supporting that the objects are physically bound to it. HIP 81208 B is a high-mass (67 MJ) brown dwarf with an effective temperature of 2,900 K (2,630 °C; 4,760 °F), mostly due to residual heat from formation. It orbits the primary star at a distance of 54 AU (8.1 billion km) once every 247 years (albeit with a large margin of error), close to the orbital period of Pluto (247.94 years). HIP 81208 C orbits the star much farther at 234 AU (35.0 billion km) with a 2,242-year period, though its orbital parameters are also poorly constrained. It has a temperature of 3,165 K (2,892 °C; 5,237 °F), only slightly hotter than the brown dwarf. Curiously, the orbits of the two companions are almost orthogonal to one another, and are probably in a Kozai resonance with the host star.

Possible fourth star The 15th-magnitude star Gaia DR3 6020420074469092608 (2MASS J16360769-3543514), located at a separation of 0.1823°, shares a similar parallax and proper motion with HIP 81208, and is potentially located within the Hill sphere of the system. This hints at the possibility of a fourth stellar component even farther from the primary star than the confirmed two.

Planetary system

In 2023, a previously unresolved object was identified in orbit of HIP 81208 C. The object, with a mass of 14.8 MJ, is right at the boundary between exoplanets and brown dwarfs, as it is close to the threshold for deuterium fusion (~13 MJ). This made the HIP 81208 system the first binary between two stars (A, C) discovered by imaging where both stars are orbited by substellar companions (B, Cb). It orbits the red dwarf host somewhere around 23 AU (3.4 billion km) distant with a period of roughly 285 years. HIP 81208 Cb is also unique in that it is unusually close to its host star for being a giant planet or brown dwarf companion to a late M-type star. Other objects of a similar nature, at least those that have been directly imaged, usually have a mass similar to that of the host star that a binary-like formation is likely, but HIP 81208 Cb is light enough that such a formation mode can be ruled out. The true formation of the object, however, remains inconclusive.

Footnotes

References

Illustrations

Worked examples

Example 1 — a first encounter with HIP 81208

Start with the simplest possible case. Write down what HIP 81208 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 HIP 81208 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 HIP 81208 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 HIP 81208

In research: HIP 81208 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 HIP 81208 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: HIP 81208 is common in secondary-school and first-year university syllabi. It links to neighbouring topics B-type main-sequence stars, Brown dwarfs, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for HIP 81208 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 HIP 81208 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HIP 81208 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 HIP 81208 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HIP 81208 in simple terms?

Why does HIP 81208 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 HIP 81208?

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 HIP 81208.