HD 106315, or K2-109, is a single star with a pair of close-orbiting exoplanets, located in the constellation of Virgo. Based on parallax measurements, this system lies at a distance of 356 light years from the Sun.^[2] At that range, the star is too faint to be seen with the naked eye, as it has an apparent visual magnitude of 8.95.^[3] But it is slowly drifting closer with a radial velocity of −3 km/s.^[2] As of 2020^[update], multiplicity surveys have not detected any stellar companions to HD 106315.^[6]

The spectrum of HD 106315 presents as an ordinary F-type main-sequence star with a stellar classification of F5V,^[4] indicating it is generating energy through hydrogen fusion at its core. It is estimated to be roughly four^[5] billion years old but is spinning quickly with a rotation period of 5 days. The star is relatively metal-poor, having 60% of solar concentration of iron. It has only a low level of magnetic activity in its chromosphere, showing a minimal level of star spot coverage.^[6] The star has 11% more mass and a 29% larger radius than the Sun. It is radiating 2.4 times the luminosity of the Sun from its photosphere at an effective temperature of 6,300 K.^[5]

Planetary system

Two planets were detected by the transit method in 2017,^[5] using data from the extended Kepler mission (K2). Their large planetary radii imply both planets have a massive steam atmosphere for planet b and hydrogen-helium atmosphere for planet c.^[6] The planetary system of HD 106315 is rather unstable and current planetary orbits are the outcome of violent dynamical history,^[8] strongly affected by relativistic effects.^[9] The orbits of planets are nearly coplanar, and orbit of c is well aligned with the equatorial plane of the star, misalignment been equal to -10^+3.6
_−3.8°.^[10]

Since 2017, a third outer planet with mass above 45M_🜨 is suspected to exist in the system.^[3]

References