GD 165 is a binary white dwarf and brown dwarf system located in the Boötes constellation, roughly 109 light-years from Earth.
Nomenclature and observation The system GD 165 is named after Henry L. Giclas, an American Astronomer who lived throughout the 20th century.
In 1990, GD 165 A was discovered to be a variable star by Pierre Bergeron and John Thomas McGraw. It was given its variable star designation, CX Boötis, in 1993.
GD 165 B was discovered in 1988 by Eric Becklin and Benjamin Zuckerman at the University of California, Los Angeles. GD 165 B was the first dwarf discovered to be cooler than M-Type stars and was initially assigned the spectral type ≥M10. It would not be regarded 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.
Physical properties GD 165 A is a pulsating white dwarf with a temperature of about 12,100 K, a mass of 0.64 , and a radius of 0.0124 .
GD 165 B is an L-Type brown dwarf with a temperature of about 1,750 K, a mass of about 63 , and a radius of 1.00 . 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.
See also Other cooler than M brown dwarfs, discovered before 1998: Gliese 229 B – T6.5 2MASP J0345432+254023 – L0 (first isolated L-dwarf) DENIS-P J020529.0-115925 – L7 DENIS-P J1058.7-1548 – L3 DENIS-P J1228.2-1547 – L5 Kelu-1 – L2
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