astronomy

HD 98800

HD 98800 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 HD 98800 rather than just read about it. In short: HD 98800, also catalogued as TV Crateris (TV Crt), is a quadruple star system in the constellation of Crater (the cup). Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 150 light-years (45 parsecs) away.

Key takeaways

HD 98800 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HD 98800 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 98800 from memory before moving on to harder problems.

Reference excerpt

HD 98800, also catalogued as TV Crateris (TV Crt), is a quadruple star system in the constellation of Crater (the cup). Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 150 light-years (45 parsecs) away. The system is located within the TW Hydrae association (TWA), and has received the designation TWA 4. The system consists of HD 98800 A and HD 98800 B each of which contains two stars. In 2007, a debris disk was discovered orbiting HD 98800 B consisting of two rings which indicates there may be an extrasolar planet orbiting within a distance of 1.5 to 2 astronomical units.

Stellar system The system is a member of the TW Hydrae association, a group of young stars. Its membership was derived from the fact that its proper motion is similar to other stars in the group. The system itself is estimated to be around 7-10 million years old. HD 98800 is a quadruple system, with two pairs of stars orbiting each other. The two pairs are separated by over an arcsecond, so the wide visual orbit is poorly known. A preliminary range of orbits has been calculated, with an orbital period of 300 to 430 years, as well as a moderate eccentricity of 0.3 to 0.6. The primary component, HD 98800 A, is a K-type main-sequence star with a varying radial velocity. This indicates the presence of another star orbiting it, but light from that star cannot be detected, so the system is a single-lined spectroscopic binary. The secondary system, HD 98800 B, is another spectroscopic binary, but double-lined since both stars (another K-type star and a red dwarf) can be directly detected. The stars in the HD 98800 are much larger than would be expected from their masses: at such a young age, these stars have not condensed into their normal size yet.

Variability

The brightness of HD 98800 varies slightly between magnitudes 8.91 and 8.98, and it has been given the variable star designation TV Crateris. The designation TV Crateris includes all four stars and it appears that both components A and B are variable. Component A varies with a period of 2.521 days which is thought to be its rotation period and it is classified as an RS Canum Venaticorum variable, a dwarf star with an uneven surface brightness that changes brightness as it rotates. Component B is thought to be a T Tauri star, a pre-main-sequence star surrounded by a disk. It has been speculated that it is actually a post-T Tauri star and that the variations are caused by irregularities in the tilted disk intercepting the light from the star.

Planetary system

Debris disk

An infrared excess indicative of a debris disk was first discovered by IRAS. Further observations of the system have been made using Keck and the Spitzer Space Telescope. The disk consists of two separate belts. The inner ring extends from a distance of 1.5 to 2 astronomical units from the barycenter of the central binary. The outer ring begins at approximately 5.9 astronomical units from the central binary, and extends out an undetermined distance. The gap between the two rings is ~3 astronomical units. The inner ring is thin, while the inner portion of the outer ring is dense. Dr. Elise Furlan, leader of the Spitzer team that imaged this disk, concludes that the dust generated from the collision of rocky objects in the outer belt should eventually migrate toward the inner disk. But because the system is a double binary system, the dust particles do not evenly fill out the inner disk as expected. The disk was imaged with ALMA and the high resolution image showed that the disk is likely misaligned with the orbit of the inner binary. The long period of the orbiting inner binary could be responsible for this misalignment and any circumbinary planet forming in this disk would be misaligned with the orbit of the inner binary. Based on VLA observations the disk extends from 3 to 5 astronomical units. The disk is more similar to a massive gas-rich protoplanetary disks than to a debris disks, which is unusual for this kind of age of a circumbinary disk.

Possible planets Debris disks are thought to constitute a phase in planetary formation. Because of the gap within the debris disk, the possibility of a planet within the system becomes even more likely. The detected gap could be caused by a unique gravitational relationship between the disk and a possible planet already begun to form, carving out a clear space in the disk. However, the gap could also be gravitational resonance effects of the four stars.

Gallery

See also 2M1207 HD 188753 UX Tauri V4046 Sagittarii

References

External links "HD 98800". Jumk.de. Retrieved 2008-06-20. Vu, Linda (2007-07-24). "Planets with Four Parents? Spitzer Finds Evidence for Strange Stellar Family". NASA. Spitzer Space Telescope. Retrieved 2010-06-18.

Illustrations

Worked examples

Example 1 — a first encounter with HD 98800

Start with the simplest possible case. Write down what HD 98800 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 HD 98800 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 HD 98800 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 HD 98800

In research: HD 98800 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 HD 98800 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: HD 98800 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Circumstellar disks, Crater (constellation), Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 98800 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 HD 98800 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 98800 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 HD 98800 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 98800 in simple terms?

Why does HD 98800 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 HD 98800?

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 HD 98800.