Luhman 16

Coordinates: 10^h 49^m 18.723^s, −53° 19′ 09.86″

Luhman 16

The Luhman 16 binary brown dwarf is the yellow disc at the center of this 7 January 2010 WISE image. The individual brown dwarfs are not resolved.
Observation data Epoch J2000[ 1]      Equinox J2000[ 1]
Constellation	Vela
Right ascension	10h 49m 18.723s[ 1]
Declination	−53° 19′ 09.86″[ 1]
Characteristics
Spectral type	A: L8±1[1] B: T1±2[1]
Apparent magnitude (i (DENIS filter system))	14.94 ± 0.03[ 1]
Apparent magnitude (J (2MASS filter system))	10.73 ± 0.03[ 1]
Apparent magnitude (J (DENIS filter system))	10.68 ± 0.05[ 1]
Apparent magnitude (H (2MASS filter system))	9.56 ± 0.03[ 1]
Apparent magnitude (KS (2MASS filter system))	8.84 ± 0.02[ 1]
Apparent magnitude (KS (DENIS filter system))	8.87 ± 0.08[ 1]
Astrometry
Proper motion (μ)	RA: −2759 ± 6[ 1] mas/yr Dec.: 354 ± 6[ 1] mas/yr
Parallax (π)	495 ± 5[1] mas
Distance	6.59 ± 0.07 ly (2.02 ± 0.02 pc)
Orbit[ 1]
Period (P)	~ 25 yr
Details[1]
Luhman 16A
Mass	0.04–0.05 M☉
Luhman 16B
Mass	0.03–0.05 M☉
Position (relative to A)[ 1]
Component	B
Angular distance	1.5″
Observed separation (projected)	3 AU
Other designations
Whole system: LUH 16,[ 1] Luhman-WISE 1,[ 1] WISE J104915.57-531906.1,[ 1] WISE J104915.57-531906,[ 1] WISE J1049-5319,[ 1] WISE 1049-5319,[ 1] WISE 1049-53,[ 1] WISE J1049,[ 1] WISE 1049,[ 1] DENIS-P J104919.0-531910,[2] 2MASS J10491891-5319100,[ 1] IRAS Z10473-5303,[ 1] AKARI J1049166-531907,[ 1] GSC2.2 S11132026703,[ 1] GSC2.3 S4BM006703[ 1] Component A: Luhman 16A[ 1] Component B: Luhman 16B[ 1]

Luhman 16 (WISE 1049-5319, WISE J104915.57–531906.1) is a binary brown-dwarf system in the southern constellation Vela at a distance of approximately 6.6 light-years from the Sun. They are the closest known brown dwarfs, and the closest system found since the measurement of the proper motion of Barnard's Star in 1916.^{[ 1][ 1]} The primary is of spectral type L8±1,^{[ 1][1]} and the secondary of type T1±2^[1] (and is hence near the L–T transition). Luhman 16 A and B orbit each other at a distance of about 3 AU^{[ 1]} with an orbital period of approximately 25 years.^{[ 1]}

Discovery

WISE image of Luhman 16. In the inset, it is resolved into a pair.

The brown dwarfs were discovered by Kevin Luhman, astronomer from Pennsylvania State University and a researcher in Penn State's Center for Exoplanets and Habitable Worlds,^{[ 1]} 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 is 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.^{[ 1][ 1]}

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.^{[ 1]}

Discovery of companion

The second component of the system was discovered also 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 arcsecond, corresponding to a projected separation of 3 AU; and magnitude difference of 0.45 mag.^{[ 1]}

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)),^{[ 1]} Infrared Astronomical Satellite (IRAS) (1983),^{[ 1]} ESO Schmidt (Red), 1984),^{[ 1]} Guide Star Catalog (GCS) (1995),^{[ 1]} Deep Near-Infrared Survey of the Southern Sky (DENIS) (1999),^{[ 1]} Two Micron All-Sky Survey (2MASS) (1999),^{[ 1]} AKARI satellite (2007).^{[ 1]}

On the ESO Schmidt Telescope image, taken in 1984, the source looks elongated with position angle 138°.^{[ 1]} The similarity of this position angle with that of the resolved pair in the GMOS image (epoch 2013) in Fig. 1 of Luhman (2013) may suggest 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)^{[ 1]}).^{[ 1]}

Possible detection of a planetary-mass object

In December 2013, perturbations of the orbital motions in the system were detected using astrometric measurements. The period of the possible companion is about a few months, indicating that it orbits around one of the brown dwarfs. This companion is expected to be below the brown-dwarf mass limit, because it would otherwise have been detected through direct imaging. High-accuracy radial-velocity measurements are expected to be taken to confirm the existence of the planet.^[1]

Name

Eric E. Mamajek proposed the name Luhman 16 for the system, hence the components could be called Luhman 16A and Luhman 16B. The name originates from the frequently updated Washington Double Star Catalog (WDS): Luhman has already published several new binary star discoveries which are compiled in WDS with discovery identifier "LUH". The WDS catalog now lists this system with the identifier 10493-5319 and discoverer designation LUH 16.^[3]

The rationale is that Luhman 16 is easier than WISE J104915.57-531906 and that "it seems silly to call this object by a 22-character name (space included)".^{[ 1][note 1]} The "phone number names" also include WISE J1049-5319 and WISE 1049-5319, and “Luhman-WISE 1” was also proposed.^{[ 1]}

As a binary object it is also called Luhman 16AB.

Distance and proper motion

Trigonometric parallax of Luhman 16, published in 2013 in its discovery paper, is 0.496 ± 0.037 arcsec, corresponding to a distance 2.02+0.16
−0.14 pc, or 6.58+0.53
−0.46 ly.^{[ 1]} The proper motion published in the same paper is about 2.8″/year, which is relatively large due to proximity of Luhman 16.^{[ 1]}

The best estimate is marked in bold.

Proximity

Currently Luhman 16 is the third closest known star/brown-dwarf system to the Sun after the triple Alpha Centauri system (4.37 ly) and Barnard's Star (5.98 ly), pushing Wolf 359 (7.78 ly) to the fourth place. Also it 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).

Proximity to Alpha Centauri

Luhman 16 is also the nearest known star/brown-dwarf system to Alpha Centauri, located 3.63 ly from it.^{[note 2]} This is due to both systems being located in neighboring constellations, in the same part of the sky as seen from Earth but Luhman 16 is a bit farther away. Before the discovery of Luhman 16, the Solar System was the nearest known system to Alpha Centauri.

Atmosphere

On 5 May 2013, Crossfield, et al., used the European Southern Observatory's Very Large Telescope (VLT) to directly observe the Luhman 16 system for five hours, the equivalent of a full rotation of Luhman 16B.^[4][5] A study by Gillon, et al., found that Luhman 16B exhibited uneven surface illumination during its rotation.^[6] The research by Crossfield, et al., confirmed this observation, finding a large, dark region at the middle latitudes, a bright area near its upper pole, and mottled illumination elsewhere. They suggest this variant illumination indicates "patchy global clouds", where darker areas represent thick clouds and brighter areas are holes in the cloud layer permitting light from the interior.^[4][5] Gillon, et al., determined that Luhman 16B's illumination patterns change rapidly, on a day-to-day basis.^[6]

Although Luhman 16A has also been observed in the same fashion as 16B, no similar variance in illumination was found.^[5][6]

•  

  Surface map of Luhman 16B recreated from VLT observations

•  

  Artist's impression of Luhman 16B based on the VLT observations

Notes

References

Further reading

• Kniazev, A. Y.; Vaisanen, P.; Mužić, K.; Mehner, A.; Boffin, H. M. J. et al. (June 2013). "Characterization of the nearby L/T Binary Brown Dwarf WISE J104915.57-531906.1 at 2 Pc from the Sun". The Astrophysical Journal 770 (2): 124. arXiv:1303.7171. Bibcode:2013ApJ...770..124K. doi:10.1088/0004-637X/770/2/124. 

• Burgasser, Adam J.; Sheppard, Scott S.; Luhman, K. L. (2013). "Resolved Near-Infrared Spectroscopy of WISE J104915.57-531906.1AB: A Flux-Reversal Binary at the L dwarf/T dwarf Transition". arXiv:1303.7283 [astro-ph.SR].

• Gillon, M.; Triaud, A. H. M. J.; Jehin, E.; Delrez, L.; Opitom, C.; et al. (2013). "Fast-evolving weather for the coolest of our two new substellar neighbours". arXiv:1304.0481 [astro-ph.SR].

• Gandhi, P.; Done, C.; Ivanov, V. D.; Huelamo, N. (26 April 2013). "X-ray non-detection of the nearest brown dwarf binary WISE 1049-5319". The Astronomer's Telegram (5012). Bibcode:2013ATel.5012....1G. 

• Burgasser, A. J.; Faherty, J.; Beletsky, Y.; Plavchan, P.; Gillon, M. et al. (2013). "Luhman 16AB: A Remarkable, Variable L/T Transition Binary 2 pc from the Sun". Memorie della Societa Astronomica Italiana 84 (4): 1017. arXiv:1307.6916. Bibcode:2013MmSAI..84.1017B. 

• Burgasser, Adam J.; Faherty, Jacqueline; Beletsky, Yuri; Radigan, Jacqueline; Gillon, Michael et al. (2013). "Luhman 16AB: A Remarkable, Variable, L/T Transition Binary at 2 pc" (Slideshow). IAC.es. 

• Biller, Beth A.; Crossfield, Ian J. M.; Mancini, Luigi; Ciceri, Simona; Southworth, John et al. (November 2013). "Weather on the Nearest Brown Dwarfs: Resolved Simultaneous Multi-Wavelength Variability Monitoring of WISE J104915.57-531906.1AB". The Astrophysical Journal Letters 778 (1): L10. arXiv:1310.5144. Bibcode:2013ApJ...778L..10B. doi:10.1088/2041-8205/778/1/L10. 

External links

Wikimedia Commons has media related to Luhman 16.

• WISE Nabs the Closest Brown Dwarfs Yet Discovered (Universe Today 13 March 2013)
• The closest star system found in a century (phys.org 11 March 2013)
• WISE 1049-5319 ab (Solstation.com)
• Checking Out Our New Neighbors, astrobites.org, 5 April 2013