WD 0806−661

WD 0806−661 (L 97-3, GJ 3483), formally named Maru,^[10] is a DQ white dwarf with an extremely cold Y-type substellar companion (designated "B"), located in the constellation Volans at 62.7 light-years (19.2 parsecs) from Earth. The companion was discovered in 2011, and is the only known Y-type companion to a star or stellar remnant. At the time of its discovery WD 0806-661 B had the largest actual (2500 AU) and apparent separation (more than 2 arcminutes) of any known planetary-mass object, as well as being the coldest directly imaged substellar object then known.

WD 0806−661 / Maru

The right side shows an image taken by ESO's VLT HAWK-I in near-infrared. The white dwarf is marked with an arrow. The left side shows an image taken by the NASA/ESA HST WFC3 also in near-infrared wavelengths. The sub-brown dwarf appears as green pixels (2014) and purple pixels (2015) in an inset.
Observation data Epoch J2000[1]      Equinox J2000[1]
Constellation	Volans
Right ascension	08h 06m 53.75366s[2]
Declination	−66° 18′ 16.7011″[2]
Characteristics
Spectral type	DQ4.2[3][4] + Y1[5]
Apparent magnitude (B)	13.74[6] / -
Apparent magnitude (V)	13.71[6] / -
Apparent magnitude (R)	13.64[6] / -
Apparent magnitude (I)	13.60[6] / -
Apparent magnitude (J)	13.704 ± 0.023[1] / ~25.42[7]
Apparent magnitude (H)	13.739 ± 0.025[1] / ~25.29[7]
Apparent magnitude (K)	13.781 ± 0.043[1] / -
Astrometry
Proper motion (μ)	RA: 335.519(16) mas/yr[2] Dec.: −288.994(17) mas/yr[2]
Parallax (π)	51.9970±0.0141 mas[2]
Distance	62.73 ± 0.02 ly (19.232 ± 0.005 pc)
Absolute magnitude (MV)	12.30[6] / -
Details
Component A
Mass	0.562±0.005[8] M☉
Radius	0.0129[8][a] R☉
Luminosity	0.015[8] L☉
Surface gravity (log g)	7.969±0.006[8] cgs
Temperature	10029±41[8] K
Age	1.5–2.7[7] Gyr
Component B
Mass	7–9[7] MJup
Surface gravity (log g)	4.2–4.3[7] cgs
Temperature	325–350[7] K
Metallicity	<0[7]
Position (relative to A)
Component	B
Angular distance	130.2 ± 0.2″ [9]
Position angle	104.2 ± 0.2° [9]
Projected separation	2500 AU [9]
Other designations
Maru, GJ 3483, BPM 4834, L 97-3, LAWD 27, LTT 3059, NLTT 19008, WD 0806-661, WD 0806−66, GSC 08936−01284, 2MASS J08065373−6618167, GEN# +6.00204834, uvby98 986097003, WG 12[1]
Database references
SIMBAD	data

WD 0806-661 B

Main article: WD 0806−661 B

Component WD 0806-661 B was discovered in 2011 with the Spitzer Space Telescope. Its discovery was announced in the paper Luhman et al., 2011. The secondary has a mass between 7 and 9 M_J and a temperature between 325 and 350 kelvins (52 and 77 °C; 125 and 170 °F).^[7] At the time of its discovery, WD 0806−661 B was the coldest "brown dwarf" that has ever been found.^[9] The object is too faint to acquire a spectrum even with the Hubble Space Telescope, however the spectral type of this object was estimated to be Y1 based on its detection in Hubble images at near-infrared wavelengths.^[5] The photometric colors of this object suggest that it is metal-poor. The metal-poor composition of the companion could explain the DQ spectral type of the primary white dwarf.^[7] Hydrogen-deficient AGB stars might evolve into DB white dwarfs and then into DQ white dwarfs as they cool down.^[11]

In August 2022, WD 0806-661 and its planetary-mass companion were included among 20 systems to be named by the third NameExoWorlds project.^[12] The approved names, proposed by a team from South Korea, were announced in June 2023. WD 0806-661 and its companion are named after the Korean words Maru (마루) and Ahra (아라).^[10]

See also

• List of exoplanets and planetary debris around white dwarfs
• WISE 0146+4234 – a Y0 companion to a T9 brown dwarf
• WISE 1217+1626 B – another Y0 companion to a T9 brown dwarf
• DT Virginis
• HD 106906 b
• GU Piscium b

Notes

1. Calculated, using the Stefan-Boltzmann law and the star's effective temperature and luminosity, with respect to the solar nominal effective temperature of 5,772 K:$${\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{10,029}}{\biggr )}^{4}\cdot 10^{-2.8207}}}=0.0129\ R_{\odot }.}$$