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HD 96700

HD 96700 is the Henry Draper Catalogue designation for a star in the equatorial constellationofHydra. It has an apparent visual magnitude of 6.51,^[2] which puts it below the limit that can be seen with the naked eye by a typical observer.^[8] (According to the Bortle scale, it is possible for some observers to see it from dark rural skies.) Based upon parallax measurements, this star is around 83 light years away from the Sun.^[1] It is drifting further away with a radial velocity of 12.8 km/s.^[2]

This is considered a high proper motion star, shifting its position across the celestial sphere at a rate of 0.52 arc seconds per year, along a position angle of 255.21°.^[9] It is a member of the thin disk population of stars and is orbiting the galactic core at a mean galactocentric distance of 23.4 kly (7.17 kpc) with an orbital eccentricity 0.16. The inclination of its galactic orbit carries it no more than 950 ly (290 pc) away from the galactic plane.^[10]

HD 96700 is a G-type main sequence star with a stellar classification of G0 V.^[3] It has a slightly lower mass than the Sun^[4] and a lower metallicity.^[3] The estimated size is similar to the Sun, ranging from 96% to 110% depending on the method used.^[5] The effective temperature of the star's outer atmosphere is 5,879 K,^[3] giving it the yellow-hued glow of a G-type star.^[11] It appears to be much older than the Sun, with age estimates ranging up to 11.9 billion years.^[6]

A 2015 survey ruled out the existence of any additional stellar companions at projected distances from 7 to 209 astronomical units.^[12]

Planetary system[edit]

Two planetary companions have been discovered by the HARPS instrument, which measures variations in the star's radial velocity that are presumed to be caused by gravitational perturbations from orbiting objects. The innermost planet, HD 96700 b, is orbiting close to the star at a distance of roughly 0.08 AU with a brief orbital period of 8.13 days. It has at least nine times the mass of the Earth, and so may be a Neptune-like planet. But until astronomers can determine the orbital inclination or directly image the planet, there is no way to know for certain its actual mass.^[13]

The second companion, HD 96700 c, is orbiting at roughly the same distance as Mercury from the Sun, with a semimajor axis of 0.42 AU and a period of around 103 days. It may have a relatively high eccentricity of 0.4. This object has at least 13 times the mass of the Earth.^[13] A 2017 study found that HD 96700 b does not transit its host star.^[14] The existence of both planets was confirmed in 2021, and an additional planetary companion orbiting between them was found.^[15]

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