HD 205739 b

Lore & Background

The discovery of HD 205739 b began when the N2K Consortium extended its search for planets around 300 stars not typically targeted by Doppler spectroscopy surveys. The star HD 205739 was selected primarily because it was metal-rich, as the collaboration biased its search toward metal-rich stars with closely orbiting Jupiter-size planets, hoping to find a connection between a star's metallicity and its planets' masses. The star was observed using the Magellan Telescopes at Las Campanas Observatory in Chile, and studied through the Magellan Inamori Kyocera Echelle spectrograph's (MIKE) ability to use Doppler spectroscopy to measure radial velocity. Twenty-four measurements were recorded and analyzed for accuracy, leading to the planet's confirmation.

HD 205739 b is a Jupiter-size planet with an estimated minimum mass of 1.37 times the mass of Jupiter. It orbits its host star every 279.8 days at a distance of 0.896 AU, approximately 89.6% of the mean distance between the Sun and Earth. The planet has a mildly elliptical orbit with an eccentricity of 0.27, which is typical for discovered planets with orbits longer than twenty days that have not grown circular because of tidal forces. According to its discoverers, the elongated orbit causes the planet's surface temperature to fluctuate by up to 100 K.

The host star, HD 205739 (also named Sāmaya), is an F-type star with a mass 1.22 times that of the Sun and a radius 1.33 times the Sun's radius. It has an effective temperature of 6176 K and an estimated age of 2.84 billion years. The star is rich in iron, with a measured metallicity of [Fe/H] = 0.19, or 1.55 times the iron detected in the Sun. Its chromosphere is not active, and the star cannot be seen from Earth with the naked eye due to its apparent magnitude of 8.56.

Reader's Guide

HD 205739 b holds significance as a product of the N2K Consortium's targeted search for planets around metal-rich stars, aiming to explore the relationship between stellar metallicity and planetary mass. The planet's discovery, based on twenty-four radial velocity measurements from the Magellan Telescopes, contributed to the understanding of gas giants with moderately long orbital periods. Its mildly elliptical orbit (eccentricity 0.27) and the resulting temperature fluctuation of up to 100 K provide insight into the dynamics of planets that have not been circularized by tidal forces.

The planet's name, Samagiya, meaning togetherness and unity in Sinhalese, was selected by Sri Lanka during the NameExoWorlds campaign on the 100th anniversary of the IAU, adding a cultural dimension to its legacy. The discovery was published in the Astronomical Journal after being accepted following submission by a team of astronomers from the United States, Chile, and the Vatican City. The host star's high metallicity and the planet's characteristics continue to inform models of planetary formation and orbital evolution.