astronomy

HD 146389

HD 146389 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 146389 rather than just read about it. In short: HD 146389, also known as WASP-38 and named Irena, is a star with a yellow-white hue in the northern constellation of Hercules. It is invisible to the naked eye with an apparent visual magnitude of 9.4 The star is located at a distance of approximately 445 light-years from the Sun based on parallax, but is drifting closer with a radial velocity of −9 km/s.

Key takeaways

HD 146389 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 146389 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 146389 from memory before moving on to harder problems.

Reference excerpt

HD 146389, also known as WASP-38 and named Irena, is a star with a yellow-white hue in the northern constellation of Hercules. It is invisible to the naked eye with an apparent visual magnitude of 9.4 The star is located at a distance of approximately 445 light-years from the Sun based on parallax, but is drifting closer with a radial velocity of −9 km/s. The star is known to host one exoplanet, designated WASP-38b or formally named Iztok.

Nomenclature The designation HD 146389 comes from the Henry Draper Catalogue, while WASP-38 comes from the Wide Angle Search for Planets. This was one of the systems selected to be named in the 2019 NameExoWorlds campaign during the 100th anniversary of the IAU, which assigned each country a star and planet to be named. This system was assigned to Slovenia. The approved names were Irena for the star and Iztok for the planet, named after characters from the Slovenian novel Pod svobodnim soncem.

Characteristics The stellar classification of HD 146389 is F8, which is an F-type star of uncertain luminosity class. The age of the star is uncertain. It shows a low lithium abundance, which suggests an age of more than 5 billion years. However, the rotation rate indicates an age closer to one billion. The study in 2015 utilizing Chandra X-ray Observatory, have failed to detect any X-ray emissions from the star during planetary eclipse, which may indicate an unusually low coronal activity or the presence of absorbing gas ring formed by atmosphere escaping planet WASP-38 b. The star is 33% larger and 20% more massive than the Sun. It is radiating nearly three times the luminosity of the Sun at an effective temperature of 6,150 K.

Planetary system The hot Jupiter class planet WASP-38 b, later named Iztok, was discovered around HD 146389 in 2010. The planet is losing significant amounts of gas, estimated to be 0.023 Earth masses per billion years. In 2013, it was found the planetary orbit is surprisingly well aligned with the rotational axis of the parent star, despite the noticeable orbital eccentricity. A 2012 study, utilizing the Rossiter–McLaughlin effect, have determined the orbital plane of WASP-38b is poorly constrained but probably aligned with the equatorial plane of the star, misalignment equal to 15+33−43°.

References

Worked examples

Example 1 — a first encounter with HD 146389

Start with the simplest possible case. Write down what HD 146389 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 146389 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 146389 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 146389

In research: HD 146389 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 146389 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 146389 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, F-type main-sequence stars, Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 146389 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 146389 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 146389 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 146389 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 146389 in simple terms?

Why does HD 146389 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 146389?

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 146389.