HD 188753

HD 188753 is a hierarchical triple star system approximately 151 light-years away in the constellation of Cygnus, the Swan. In 2005, an extrasolar planet was announced to be orbiting the primary star (designated HD 188753 A) in the system. Follow-up measurements by an independent group in 2007 did not confirm the planet's existence.

The primary star, HD 188753 A, is similar to the Sun with a mass only 6% larger and a stellar classification of G8V. Orbiting this primary at a distance of 12.3 AU is a pair of smaller stars that orbit each other with a period of 156.0 ± 0.1 days, a semi-major axis of 0.67 AU, and eccentricity of 0.1 ± 0.03. The pair have estimated masses of 0.96 and 0.67 solar masses. They orbit the primary with a period of about 25.7 years and an orbital eccentricity of about 0.50. The periastron distance of this orbit is 6.2 AU. The distance between the parent star and HD 188753 AB is 0.0446 AU, or 6.7 million miles.

In 2005 the discovery of a candidate planet orbiting the primary star of the triple star system was announced. This planet, which received the designation HD 188753 Ab, was announced by a Polish astronomer working in the United States, Dr. Maciej Konacki. This would not be the first known planet in a triple star system – for example, the planet 16 Cygni Bb had been discovered earlier, orbiting one of the components of a wide triple system also in the constellation of Cygnus.

Since HD 188753 Ab was believed to be orbiting in a multi-star system, Konacki referred to planets of this type as "Tatooine planets" after Luke Skywalker's home world. The detection of this planet has been challenged by Eggenberger et al.