astronomy

Luhman 16

Luhman 16 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 Luhman 16 rather than just read about it. In short: Luhman 16 (also designated WISE 1049−5319 or WISE J104915.57−531906.1) is a binary system of two brown dwarfs, located in the southern constellation Vela at a distance of 6.51 light-years (2.00 parsecs) from the Sun. These are the closest-known brown dwarfs and the closest system found since the measurement of the proper motion of Barnard's Star in 1916, and the third-closest-known system to the Sun (after the Alpha…

Key takeaways

Luhman 16 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Luhman 16 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Luhman 16 from memory before moving on to harder problems.

Reference excerpt

Luhman 16 (also designated WISE 1049−5319 or WISE J104915.57−531906.1) is a binary system of two brown dwarfs, located in the southern constellation Vela at a distance of 6.51 light-years (2.00 parsecs) from the Sun. These are the closest-known brown dwarfs and the closest system found since the measurement of the proper motion of Barnard's Star in 1916, and the third-closest-known system to the Sun (after the Alpha Centauri system and Barnard's Star). The primary is of spectral type L7.5 and the secondary of type T0.5±1 (and is hence near the L–T transition). The masses of Luhman 16 A and B are 35.4 and 29.4 Jupiter masses, respectively, and their ages are estimated to be 400–800 million years. Luhman 16 A and B orbit each other at a distance of about 3.5 astronomical units with an orbital period of approximately 26.6 years.

Discovery

This system was discovered by Kevin Luhman, astronomer from Pennsylvania State University and a researcher at Penn State's Center for Exoplanets and Habitable Worlds, from images made by the Wide-field Infrared Survey Explorer (WISE) Earth-orbiting satellite—NASA infrared-wavelength 40 cm (16 in) space telescope, a mission that lasted from December 2009 to February 2011; the discovery images were taken from January 2010 to January 2011, and the discovery was announced in 2013 (the pair are the only two objects announced in the discovery paper). The system was found by comparing WISE images at different epochs to reveal objects that have high proper motions. Luhman 16 appears in the sky close to the galactic plane, which is densely populated by stars; the abundance of light sources makes it difficult to spot faint objects. This explains why an object so near to the Sun was not discovered in earlier searches.

Discovery of companion

The second component of the system was also discovered by Luhman in 2013, and was announced in the same article as the primary. Its discovery image in the i-band was taken on the night of 23 February 2013 with the Gemini Multi-Object Spectrograph (GMOS) at the Gemini South telescope, Chile. The components of the system were resolved with an angular distance of 1.5 arcseconds, corresponding to a projected separation of 3 AU, and a magnitude difference of 0.45 mag.

Precovery Although the system was first found on images taken by WISE in 2010–2011, afterwards it was precovered from the Digitized Sky Survey (DSS, 1978 (IR) & 1992 (red)), Infrared Astronomical Satellite (IRAS, 1983), ESO Schmidt telescope (1984 (red)), Guide Star Catalog (GSC, 1995), Deep Near Infrared Survey of the Southern Sky (DENIS, 1999), Two Micron All-Sky Survey (2MASS, 1999), and the AKARI satellite (2007). On the ESO Schmidt telescope image, taken in 1984, the source looks elongated with a position angle of 138°. The similarity of this position angle with that of the resolved pair in the GMOS image (epoch 2013) in Fig. 1 of Luhman (2013) suggests that the time period between 1984 and 2013 may be close to the orbital period of the system (not far from original orbital period estimate by Luhman (2013)).

Name Eric E. Mamajek proposed the name Luhman 16 for the system, with the components called Luhman 16A and Luhman 16B. The name originates from the frequently updated Washington Double Star Catalog (WDS). Kevin Luhman had already published several new discoveries of binary stars that have been compiled in the WDS with discovery identifier "LUH". The WDS catalog now lists this system with the identifier 10493−5319 and discoverer designation LUH 16. The rationale given by Mamajek is that Luhman 16 is easier to remember than WISE J104915.57−531906.1 and "it seems silly to call this object by a 24-character name (space included)". The "phone number names" also include WISE J1049−5319 and WISE 1049−5319. Luhman–WISE 1 was proposed as another alternative. As a binary object it is also called Luhman 16AB.

Astrometry

Position in the sky

Luhman 16 is located in the southern celestial hemisphere in the constellation Vela. As of July 2015, its components are the nearest-known celestial objects in this constellation outside the Solar System. Its celestial coordinates: RA = 10h 49m 18.723s, Dec = −53° 19′ 09.86″.

Distance The trigonometric parallax of Luhman 16 as published by Sahlmann & Lazorenko (2015) is 0.50051±0.00011 arcsec, corresponding to a distance of 6.5166 ± 0.0013 light-years (1.998 ± 0.0004 parsecs). Subsequent observations with Hubble and Gaia improved the parallax to 500.993+0.059−0.048 mas, corresponding to a distance of 1.996036+0.00019−0.00024 pc, which is accurate to about 50 astronomical units.

Proximity to the Solar System

Currently Luhman 16 is the third-closest-known star/brown-dwarf system to the Sun after the triple Alpha Centauri system (4.344 ly) and Barnard's Star (5.98 ly), pushing Wolf 359 (7.78 ly) to the fifth place, along with the discovery of WISE 0855−0714. It also holds several records: the nearest brown dwarf, the nearest L-type dwarf, and possibly the nearest T-type dwarf (if component B is of T-type).

Proper motion The proper motion of Luhman 16 as published by Garcia et al. (2017), is about 2.79″/year, which is relatively large due to the proximity of Luhman 16.

Radial velocity The radial velocity of component A is 23.1 ± 1.1 km/s (14.35 ± 0.68 mi/s), and the radial velocity of component B is 19.5 ± 1.2 km/s (12.12 ± 0.75 mi/s). Since values of the radial velocity are positive, the system currently is moving away from the Solar System. Assuming these values for the components, and a mass ratio of Luhman 16 from Sahlmann & Lazorenko (2015) of 0.78, the system's barycentre radial velocity is about 21.5 km/s (13.4 mi/s). This implies that Luhman 16 passed by the Solar System around 36,000 years ago at a minimal distance of about 5.05 ly (1.55 pc).

Orbit and masses

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Luhman 16

Start with the simplest possible case. Write down what Luhman 16 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 Luhman 16 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 Luhman 16 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 Luhman 16

In research: Luhman 16 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 Luhman 16 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: Luhman 16 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 2013, Binary stars, L-type brown dwarfs, so understanding it makes those chapters shorter.
In everyday life: Look for Luhman 16 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 Luhman 16 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Luhman 16 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 Luhman 16 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Luhman 16 in simple terms?

Why does Luhman 16 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 Luhman 16?

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 Luhman 16.