GD 165

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.