astronomy

HD 155358

HD 155358 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 155358 rather than just read about it. In short: HD 155358 is a low metallicity yellow dwarf star 44 pc away in the constellation Hercules. This star is known to be orbited by two extrasolar planets.

Key takeaways

HD 155358 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 155358 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 155358 from memory before moving on to harder problems.

Reference excerpt

HD 155358 is a low metallicity yellow dwarf star 44 pc away in the constellation Hercules. This star is known to be orbited by two extrasolar planets. The star is 11.9 billion years old and has a mass 0.85 times that of the Sun. At the time of the planets' discoveries, it was notable for being the lowest metallicity planet-bearing star known, with an iron-to-hydrogen ratio 21% of the solar value.

Observation With a visual magnitude of 7.5, this star can not be observed with the unaided eye. Hence it was discovered only after the introduction of the telescope. In 1859 it was catalogued in the Bonner Durchmusterung by the Prussian astronomer F. W. Argelander, who listed an estimated visual magnitude of 7.2. In 1958 it was identified as a star with a relatively large proper motion by the Nizamiah Observatory, Hyderabad. It was suggested in 1979 that this star may lie within 25 parsecs of the Sun. (Up to that time it had never been catalogued as a nearby star.) Beginning in 2001, this star underwent observation using the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. Changes were observed in the radial velocity motion of the star, indicating a gravitational influence from orbiting objects. Based on the motion of the star over time, astronomers were able to deduce that there are at least two planets in orbit around HD 155358.

Planetary system On 10 May 2007, astronomers included Cochran from the University of Texas announced two mass type II planets orbiting the same star with the lowest metal content than any planetary host stars. Its discoveries were made by using the Hobby-Eberly Telescope, which used radial velocity to monitor the change of line of sight motion of the star caused by gravity of the planets. These two planets gravitationally interact: modelling the planets assuming their masses are the same as the empirically-determined lower limits, they exchange eccentricities on a timescale of 2700 years, and their arguments of periastron precess on a timescale of 2300 years. HD 155358 b has mass little bit less than Jupiter but more than Saturn. HD 155358 c has 0.8 the mass of Jupiter. HD 155358 b orbits at 0.64 AU while c orbits at 1.02 AU. These two planets are near exact mutual 2:1 mean motion resonance (MMR).

References

External links The Extrasolar Planet Encyclopedia: HD 155358 Extrasolar Planet Interactions Archived 2016-05-05 at the Wayback Machine by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona

Worked examples

Example 1 — a first encounter with HD 155358

Start with the simplest possible case. Write down what HD 155358 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 155358 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 155358 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 155358

In research: HD 155358 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 155358 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 155358 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, G-type main-sequence stars, Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 155358 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 155358 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 155358 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 155358 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 155358 in simple terms?

HD 155358 is a low metallicity yellow dwarf star 44 pc away in the constellation Hercules. This star is known to be orbited by two extrasolar planets.

Why does HD 155358 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 155358?

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 155358.