Binary star in the constellation Ophiuchi
! style="text-align: center; background-color: #FFFFC0;" colspan="2" | Observation dataEpoch J2000      Equinox J2000
! style="text-align:left" | Constellation
! style="text-align:left" | Right ascension
! style="text-align:left" | Declination
! style="text-align:left" | Apparent magnitude (V)
! style="background-color: #FFFFC0; text-align: center;" colspan="2"| Characteristics
! style="text-align:left" | Evolutionary stage
! style="text-align:left" | Spectral type
! style="text-align:left" | B−V 
! style="text-align:left" | J−H 
! style="text-align:left" | J−K 
! style="text-align:left" | Variable type
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HD 164509 is a binary star system in the constellation of Ophiuchus. The primary component has an orbiting exoplanet companion. This system is located at a distance of 175 light years based on parallax measurements, and is drifting further away with a radial velocity of 13.7 km/s. It has an absolute magnitude of 4.64, but at that distance the system has an apparent visual magnitude of 8.10, which is too faint to be seen with the naked eye.
The primary component is a Sun-like G-type main-sequence star with a stellar classification of G2V. It is young and metal rich, having heavy elements abundance 160% of solar. The star has a modest level of magnetic activity in its chromosphere. It has 1.10 times the mass of the Sun and 1.04 times the Sun's radius. This star is radiating 1.15 times the luminosity of the Sun from its photosphere at an effective temperature of 5,865 K.
Initially it was thought the system consisted of a single star, but in 2016 it was discovered the primary is accompanied by the M-class red dwarf star at a projected separation of . The evidence for this stellar companion being on a bound orbit was further fortified in 2017.
Planetary system.
In 2011, a gas giant, HD 164509 Ab, was discovered orbiting the primary of HD 164509 using Doppler spectroscopy. Given the binary nature of this system, the planet HD 164509 Ab could not have formed on the current orbit, which is unstable in long term. Instead, it may be a captured body formed elsewhere.
! align=center| Companion
! align=center| Mass
! align=center| Semimajor axis
! align=center| Orbital period
! align=center| Eccentricity
! align=center| Inclination
! align=center| Radius
References.
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