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astronomy

HD 9289

HD 9289 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 9289 rather than just read about it. In short: HD 9289 is a white-hued variable star in the constellation of Cetus. It has the variable-star designation BW Ceti (abbreviated to BW Cet).

HD 9289 — main illustration
HD 9289 — illustration

Key takeaways

  • HD 9289 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 9289 to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of HD 9289 from memory before moving on to harder problems.

Reference excerpt

HD 9289 is a white-hued variable star in the constellation of Cetus. It has the variable-star designation BW Ceti (abbreviated to BW Cet). With an apparent magnitude of 9.38, it is too faint to be observed by the naked eye from Earth. It is located at a distance of approximately 1,000 light-years (310 parsecs) according to Gaia EDR3 parallax measurements, and is moving away from the Solar System at a heliocentric radial velocity of 11.352 km/s.

Stellar properties HD 9289 is an A-type main-sequence star with the spectral type A3 SrEuCr. The suffix indicates that the star shows strong spectral lines of strontium, europium, and chromium, characteristic of an Ap star. The star radiates roughly 8.7 times the luminosity of the Sun from its photosphere. It possesses a magnetic field with a strength of 2.0 kG, which is 3,000–9,000 times stronger than Earth's magnetic field (0.22–0.67 G).

The star was first classified as a rapidly oscillating Ap star (roAp) in 1993 by Kurtz et al. when it was found to pulsate at multiple periods, all clustered around 10.5 minutes (1585.06 μHz). Additional observations confirmed the presence of rotational amplitude modulation, similar to that of the well-studied roAp star HR 1217. In 2011, a new set of pulsation frequencies were discovered, the strongest of them being at 1585.936 μHz with an amplitude of 0.63 mmag. Few of them were consistent with the initial reports, however, which was explained by the fact that the measurements by Kurtz et al. were affected by aliasing that caused misidentifications, though an innate shift in the star's pulsation behavior could not be ruled out. In 2012, the rotational period of HD 9289 was constrained to 8.55±0.08 d through differential photometry observations. This was revised slightly upward in 2021 to 8.660±0.006 d.

Binary companion In 2012, a previously undetected visual companion was discovered at a separation of 0.441 arcseconds to the east-northeast of HD 9289. The probability that the two stars are unrelated and aligned by chance is very low (2.16×10−4 %), therefore the pair are most certainly part of a wide binary system. The secondary star is about 1.70 magnitudes fainter than the primary when observed in the K band.

References

Illustrations

HD 9289 illustration
HD 9289: Light curves for BW Ceti. The upper plot, adapted from Gruberbauer et al.[12] shows the short timescale variability, and the lower plot of TESS data[13] shows the longer timescale variability, with the rotation period marked in red.
Light curves for BW Ceti. The upper plot, adapted from Gruberbauer et al.[12] shows the short timescale variability, and the lower plot of TESS data[13] shows the longer timescale variability, with the rotation period marked in red.

Worked examples

Example 1 — a first encounter with HD 9289

Start with the simplest possible case. Write down what HD 9289 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 9289 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 9289 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 9289

In research
HD 9289 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 9289 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 9289 is common in secondary-school and first-year university syllabi. It links to neighbouring topics A-type main-sequence stars, Cetus (constellation), Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life
Look for HD 9289 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 9289 in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what HD 9289 means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain HD 9289 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 9289 in simple terms?

HD 9289 is a white-hued variable star in the constellation of Cetus. It has the variable-star designation BW Ceti (abbreviated to BW Cet).

Why does HD 9289 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 9289?

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 9289.

Tags

  • A-type main-sequence stars
  • Cetus (constellation)
  • Durchmusterung objects
  • Henry Draper Catalogue objects
  • Objects with variable star designations
  • Rapidly oscillating Ap stars

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