HD 217786

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HD 217786 is a binary star system in the Pisces constellation. With a visual magnitude of 7.78, it’s visible with binoculars or a small telescope and lies about 181 light-years away, drifting away from us at around 10 km/s. The system is part of the Milky Way’s thin disk.

The primary star is an F-type main-sequence star (F8V). It has about the Sun’s mass, a radius about 1.32 times larger than the Sun, and it shines with roughly 1.93 solar luminosities at a temperature of about 5,882 K. It’s much older than the Sun (around 9.4 billion years) and has lower metal content (about 65% of solar). It rotates slowly, at roughly 1.2 km/s.

A low-mass companion star, about 0.16 solar masses, orbits the primary at a projected distance of roughly 155 AU. The orbit is seen edge-on, and if it’s circular, the period would be about 6.2 million years.

The system shows ultraviolet flares. In 2010, a planet or brown dwarf, HD 217786 Ab, was found on a highly eccentric orbit, likely influenced by the secondary star. In 2022, astrometry measured the orbit and true mass, revealing a second planet closer to the star.