astronomy

TOI-1338

TOI-1338 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 TOI-1338 rather than just read about it. In short: TOI-1338 (also known as BEBOP-1 or EBLM J0608-59) is an eclipsing binary star system located in the constellation Pictor, about 1,300 light-years (400 pc) from Earth. The binary system consists of a large, F-type main-sequence star, and a small, red dwarf star.

Key takeaways

TOI-1338 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect TOI-1338 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TOI-1338 from memory before moving on to harder problems.

Reference excerpt

TOI-1338 (also known as BEBOP-1 or EBLM J0608-59) is an eclipsing binary star system located in the constellation Pictor, about 1,300 light-years (400 pc) from Earth. The binary system consists of a large, F-type main-sequence star, and a small, red dwarf star. Viewed from Earth, TOI-1338 appears at an apparent magnitude of 11.7, which is too faint to be seen with the naked eye. It is known for hosting two circumbinary exoplanets: TOI-1338 b, a Saturn-sized super-puff planet, and TOI-1338 c, a Saturn-mass gas giant planet.

Location and brightness TOI-1338 is located in the constellation Pictor, about 59 and a half degrees south of the celestial equator. When viewed from Earth in visible light, it appears as a single star with an apparent magnitude of 11.7—too faint to be seen with the naked eye or a small telescope. According to the latest parallax measurements by the Gaia satellite (as of 2020), the distance of TOI-1338 from Earth 1,318 ± 5 light-years (404 ± 2 parsecs). The NASA Exoplanet Archive gives a slightly smaller distance of 1,302 ± 10 ly (399 ± 3 pc). The star system does not appear reddened (very low extinction of E(B–V)=0.0036±0.0018), which implies there is very little interstellar dust between it and Earth. As of 2026, TOI-1338 is the brightest star system known to have at least two transiting circumbinary planets. For this reason, astronomers consider TOI-1338 a favorable target for observing its planet's transits via transmission spectroscopy, which would enable the determination of the planet's atmospheric composition.

Observational history TOI-1338 was first catalogued by the Hipparcos satellite during the 1990s, and published in the Tycho-2 (TYC) Catalogue in 2000. The star was found to be periodically eclipsing when it was observed by the Wide Angle Search for Planets (WASP) during the 2000s. However, the star's eclipses were initially mistaken for transits by a hot Jupiter exoplanet. Upon further examination by the Eclipsing Binary, Low Mass (EBLM) project in 2009, the star became recognized as an eclipsing binary system and was given the designation EBLM J0608-59. Under the EBLM project, the star system received extensive observations from telescopes in Chile during 2009–2022, with the goal of characterizing the physical properties of its two stars. During that time, two other independent projects had begun observing the star system: the Binaries Escorted By Orbiting Planets (BEBOP) project in 2014, and the Transiting Exoplanet Survey Satellite (TESS) in 2018. The star system became known as TOI-1338 ("TOI" standing for "TESS Object of Interest") in 2020, when astronomers announced the discovery of the first exoplanet orbiting it. The other designation, BEBOP-1, was given to the star system in 2023, when astronomers of the BEBOP project announced the discovery of a second planet orbiting it. The James Webb Space Telescope (JWST) is scheduled to observe TOI-1338 on 24 and 25 September 2026, when the inner planet of TOI-1338 is predicted to transit both stars. JWST will observe the transit using transmission spectroscopy, which could determine the composition of the planet's atmosphere. If successful, these observations will provide the first characterization of a circumbinary exoplanet's atmosphere.

Binary system

Physical characteristics TOI-1338 is a single-lined spectroscopic binary system, consisting of an F-type star and a red dwarf of spectral type M. The red dwarf is about nine magnitudes fainter than the primary star and cannot be detected in the spectrum. The primary star of the binary system, A, is hotter (temperature 6031 K), brighter (luminosity 2.1 L☉), larger (radius 1.32 R☉, and more massive (1.1 M☉) than the Sun. The secondary, B, is cooler (temperature 3300 K), dimmer (luminosity 0.009 L☉),smaller (radius 0.31 R☉, and less massive (0.31 M☉) than the Sun. The system has an age of six billion years.

Orbit The two stars orbit each other every 14.6 days and are mutually separated by an average distance of about 0.13 astronomical units (20 million km or 12 million mi). The orbit of the two stars is inclined at 89.7° to the plane of the sky (so edge-on) and both primary and secondary eclipses can be observed, although the brightness changes are very small. The primary eclipse occurs when the hotter primary star is partially occulted by the cooler secondary. It lasts about five hours and the brightness decreases by about 4%. The secondary eclipses occur when the cooler star is occulted by the hotter star. They also last about five hours but the brightness drops by less than half a percent.

Planetary system

The planet TOI-1338 b is between Neptune and Saturn in size, and has an orbit that is within ~1° coplanar with the binary. Its mass is estimated to be roughly 11 times that of Earth, indicating a low density similar to that of circumbinary planet Kepler-47c. The spin of the primary star aligns with the orbits of the binary and the planet (spin-orbit angle β = 2.8°±17.1°). This is the second time the Rossiter–McLaughlin effect was measured for a star hosting a circumbinary planet. Kepler-16 was the first system with such a measurement. The measurement of the alignment for TOI-1338 suggests that the planet formed from a single circumbinary disk. TOI-1338 c, or BEBOP-1c, is a gas giant about 75 times the mass of Earth. It is also coplanar (or nearly so) with the binary stars and planet b.

See also Circumbinary planet Kepler-16 – eclipsing binary star with the first discovered circumbinary exoplanet Kepler-47 – an eclipsing binary star system with multiple circumbinary gas giant planets Kepler-64 – a quadruple star system with a circumbinary gas giant

Notes

References

External links

TOI 1338 at ExoFOP TESS

Illustrations

Worked examples

Example 1 — a first encounter with TOI-1338

Start with the simplest possible case. Write down what TOI-1338 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 TOI-1338 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 TOI-1338 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 TOI-1338

In research: TOI-1338 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 TOI-1338 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: TOI-1338 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Eclipsing binaries, F-type main-sequence stars, M-type main-sequence stars, so understanding it makes those chapters shorter.
In everyday life: Look for TOI-1338 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 TOI-1338 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TOI-1338 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 TOI-1338 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TOI-1338 in simple terms?

Why does TOI-1338 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 TOI-1338?

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 TOI-1338.