WD 0806−661

WD 0806−661 (L 97-3, GJ 3483), formally named Maru, is a DQ white dwarf with an extremely cold Y-type substellar companion (designated "B"), located in the constellation Volans at 62.7 ly 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 B
Component WD 0806-661 B was discovered in 2011 with the Spitzer Space Telescope. Its discovery paper is Luhman et al., 2011. The secondary has a mass between 7 and 9 and a temperature between 325 and 350 K. At the time of its discovery, WD 0806−661 B was the coldest "brown dwarf" that has ever been found. 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. 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. Hydrogen-deficient AGB stars might evolve into DB white dwarfs and then into DQ white dwarfs as they cool down.

In August 2022, WD 0806-661 and its planetary-mass companion were included among 20 systems to be named by the third NameExoWorlds project. The approved names, proposed by a team from South Korea, were announced in June 2023. WD 0806-661 is named Maru and its companion is named Ahra, after Korean words meaning "sky" and "ocean".