HR 7907 Delphini

(The Planet Project)

Del HR 7907 is classed as a wide double star, which would make it odd as a planet host. True companionship, however, is unlikely.


The lower circle shows the location of the class F subgiant star HR 7907, found in the constellation Delphinus. The planet, whose mass is at least 1.84 times that of Jupiter, orbits with a period of 386 days at an average distance of 1.12 Astronomical Units (168 million kilometers, 104 million miles), just 12 percent greater than the Earth's orbital size. A significant orbital eccentricity causes it to range between 1.46 and 0.78 AU from the star (the latter just nine percent greater than the diameter of the Venusian orbit).


HR 7907, also known as HD 196885, is a sixth magnitude (6.40) star in Delphinus that is near the limit of naked eye vision (though easily accessible with binoculars) and is classed as an F8 subgiant implying that it is has given up (or is close to giving up) core hydrogen fusion. Too faint to have a proper or Greek letter name, or even Flamsteed number, it is known best by its numbers in the Bright Star(HR) and the Henry Draper (HD) Catalogues. From a distance of 108 light years, the star shines with a luminosity 2.47 times that of the Sun with a surface temperature of 6040 Kelvin (260 degrees warmer than the Sun), from which we derive a mass near 1.10 solar and a radius of 1.44 solar. The high luminosity for its mass shows that HR 7907 is older then the Sun and may be a true subgiant. The metal content is uncertain, two studies giving very divergent results, and may be close to solar. A tenth (10.4) magnitude "companion" lies over 3 minutes of arc away. If HR 7907 is a real double star, the companion is roughly an M0 dwarf at least 6300 AU away with a huge period of at least 400,000 years. Such a separation makes real duplicity highly unlikely, the "companion" probably a line-of-sight coincidence.

HD 195019 Delphini, toward upper left in the picture, also has an orbiting planet.
Written by Jim Kaler. Return to The Planet Project or go to STARS.