Kappa Andromedae

In traditional Arabic astronomy, the stars ι Andromedae, κ Andromedae, and λ Andromedae were known as Kaff al-Musalsala, the hand of the chained woman (i.e. Andromeda), and as Ra’s al-Nāqa, the head of the she-camel. ==Properties==

The stellar classification of Kappa Andromedae is B9 IVn, indicating that it is a subgiant star in the process of evolving away from the main sequence. The star has an estimated 2.8 times the mass of the Sun and is radiating 62.6 times the Sun's luminosity. It is spinning rapidly, with a projected rotational velocity of 162 km/s. Its true rotational velocity is 283.8 km/s, which is about 85% of its critical rotation rate (the rate at which it would break up). With such a rapid rotation rate, the star is deformed into an oblate spheroid, such that while the polar radius is , the equatorial radius is significantly larger, at . The outer envelope of the star is radiating energy into space with an effective temperature of at the equator and at its poles, producing a blue-white hue. The age of Kappa Andromedae has been the subject of debate. The discovery paper for Kappa Andromedae b argued that the primary's kinematics are consistent with membership in the Columba Association, which would imply a system age of 20-50 million years, while a subsequent work derived an older age of million years based on the star's position on the Hertzsprung-Russell diagram position assuming that the star is not a fast rotator viewed pole-on. Direct measurements of the star later showed that Kappa Andromedae A is in fact a rapid rotator viewed nearly pole-on and yield a best-estimated age of 47 million years. ==Planetary system==

In November 2012, members of the Strategic Explorations of Exoplanets and Disks with Subaru (SEEDS) survey reported the discovery of a faint, directly-imaged companion Kappa Andromedae b. Follow-up photometry and spectroscopy of kappa And b with the Subaru Telescope, Keck Observatory, and Large Binocular Telescope constrained its mass to be about 13 Jupiter masses, temperature to be between 1700 K and 2150 K, and orbit to be highly eccentric with a semimajor axis likely greater than about 75 AU. The companion's spectrum shows evidence for water and carbon monoxide molecules and suggests the object has a low surface gravity. ==See also==