astronomy

HD 15337

HD 15337 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 15337 rather than just read about it. In short: HD 15337 (TOI-402) is a binary star in the southern constellation of Fornax. It has an apparent magnitude of 9.09, making it too faint to be observed by the naked eye from Earth, but readily visible using a small telescope.

Key takeaways

HD 15337 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 15337 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 15337 from memory before moving on to harder problems.

Reference excerpt

HD 15337 (TOI-402) is a binary star in the southern constellation of Fornax. It has an apparent magnitude of 9.09, making it too faint to be observed by the naked eye from Earth, but readily visible using a small telescope. It is located 146 light-years (45 parsecs) distant based on stellar parallax, and is currently heading towards the Solar System with a radial velocity of −3.9 km/s.

Characteristics This is a relatively wide system with an orbital period that is thought to be 760 years. The semi-major axis is 88 AU, but the eccentricity of the orbit is high, at 0.75. The primary is about 15% smaller than the Sun in both mass and radius and radiates slightly less than half the Sun's luminosity from its photosphere. It has a spectral type of K1V and an effective temperature of 5,131 K (4,858 °C; 8,776 °F), giving the star an orange hue. It is 9.6+3.8−3.9 billion years old, making it much older than the Solar System. The star has a solar-like metallicity and displays similar amounts of stellar activity to the Sun, though when the star was only 150 million years old, it may have emitted between 3.7 and 127 times the high-energy luminosity of the Sun in the present day. The secondary has just 26% of the mass of the Sun.

Planetary system In May 2019, a pair of exoplanets were discovered to revolve around the primary star through transit observations by the TESS space telescope, namely HD 15337 b and c. The two planets are far closer to their host star than Mercury is to the Sun (0.3871 AU), which heats them up to equilibrium temperatures of 1,001 K (728 °C; 1,342 °F) and 642 K (369 °C; 696 °F), respectively, both of which are hot enough to melt lead (m.p. 327 °C). The inner planet, HD 15337 b, has a radius of 1.770 R🜨 and a mass of 6.519 M🜨. This places its density at 6.458 g/cm3, meaning it is denser than Earth (5.513 g/cm3) and very likely to be a rocky super-Earth. The outer planet, c, is only slightly more massive than b at 6.792 M🜨, but possesses a radius over 40% larger, which makes it much less dense at 2.303 g/cm3, suggesting a mini-Neptune-like composition with a thick (>0.01 M🜨) gaseous envelope probably consisting of hydrogen and helium. This striking difference in the structure of the two planets in spite of their similar masses implies that the two planets are on opposite sides of the small planet radius gap, making the HD 15337 system a prime target for research in planetary formation and evolution. In 2024, the planetary parameters of both planets were precisely gauged through photometric observations by CHEOPS and radial velocity measurements by HARPS. As a result, the uncertainties of HD 15337 b's mass and radius were each reduced to less than 2% and 7%, which put the planet among the most accurately characterized terrestrial exoplanets at the time. Additionally, the radius of HD 15337 c was constrained to within a 3% margin of error.

See also Kepler-93b: another precisely characterized hot super-Earth.

Notes

References

Illustrations

Worked examples

Example 1 — a first encounter with HD 15337

Start with the simplest possible case. Write down what HD 15337 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 15337 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 15337 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 15337

In research: HD 15337 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 15337 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 15337 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, Fornax, Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 15337 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 15337 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 15337 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 15337 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 15337 in simple terms?

Why does HD 15337 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 15337?

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 15337.