HD 233731

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HD 233731, also known as HAT-P-22, is a star system in the Ursa Major constellation. It is too faint to see without a telescope (apparent magnitude about 9.7) and lies roughly 270 light-years away. The primary star is a sun-like G-type star with about the Sun’s mass and similar size, shining at around 0.77 times the Sun’s brightness. It has a surface temperature near 5,314 K and rotates slowly, taking about 28.7 days for a full spin. The star is metal-rich, with roughly twice the Sun’s metal content.

A faint red companion star, 2MASS J10224397+5007504, sits about 9 arcseconds away. Spectroscopic data from around 2015 suggest another close stellar companion with an orbit shorter than about 33 AU.

In 2010, a planet was discovered orbiting the star: HAT-P-22b, a hot Jupiter with an estimated equilibrium temperature near 1,460 K, likely with a cloudy atmosphere. Measurements in 2018 of the Rossiter–McLaughlin effect indicate the planet’s orbit is fairly well aligned with the star’s equator, within about 25 degrees. In 2017, analysis of additional data hinted at a possible second planet, HAT-P-22c, further influencing the star’s motion.