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GD 165

Star in the constellation Boötes

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GD 165 is a binary white dwarf and brown dwarf system located in the Boötes constellation, roughly 109 light-years from Earth.^[7] Neither of the stars have any known exoplanets.

The system GD 165 is named after Henry L. Giclas, an American Astronomer who lived throughout the 20th century.^[9]

GD 165 B was discovered in 1988 by Becklin and Zuckerman at the University of California, Los Angeles.^[10] GD 165 B was the first brown dwarf discovered to be cooler than M-Type stars^[11] and was initially assigned the spectral type ≥M10. It would not be recognized as a brown dwarf until 1999, when new spectral types L-Type and T-Type for objects cooler than M-type stars were established, reclassifying GD 165 B as L4.^[3]

GD 165 A is a pulsating white dwarf with a temperature of about 12,100 K, a mass of 0.64 M_☉, and a radius of 0.0124 R_☉.^[6] GD 165 A has an extremely dim luminosity of 0.0030L_☉,^[6] making it completely invisible to the naked eye.

GD 165 B is an L-Type Brown Dwarf with a temperature of about 1,750 K, a mass of about 63 M_J, and a radius of 1.00 R_J.^[8] GD 165B is separated by 123±12 astronomical units from its host white dwarf. It is the second closest spacially resolved brown dwarf after PHL 5038, which has a separation of around 69 AU.^[12] It produces almost no light and is completely invisible to the naked eye.

Other cooler than M brown dwarfs, discovered before 1998:

• Gliese 229 B - T6.5^[13][14]
• 2MASP J0345432+254023 - L0 (first isolated L-dwarf)^[3]
• DENIS-P J020529.0-115925 - L7^[3][15]
• DENIS-P J1058.7-1548 - L3^{[3] [15]}
• DENIS-P J1228.2-1547 - L5^[3][15]
• Kelu-1 - L2^[3][16]