HD 195019 Delphini

(The Planet Project)

Del HD 195019 is a double star, which makes it unusual for a planet host. The planet orbits the brighter primary star, the fainter companion at least 150 AU away.


The upper circle shows the location of the class G subgiant-dwarf star HD 195019, found in the constellation Delphinus. The planet, whose mass is at least 3.43 times that of Jupiter, orbits with a very short period of only 18.3 days at an average distance of just 0.14 Astronomical Units (21 million kilometers, 13 million miles, 36 percent the distance of Mercury from the Sun), the proximity to its star making it a "hot Jupiter." Consistently, the orbit is close to circular, the eccentricity only about 5 percent.


HD 195019 is a seventh magnitude (6.91) star in Delphinus that is below naked eye vision (though easily accessible with binoculars) and classed as a G3 subgiant-dwarf (implying that it is close to giving up core hydrogen fusion). Much too faint to have a proper or Greek letter name, or even Flamsteed number, it is known best by its number in the Henry Draper (HD) Catalogue. From a distance of 122 light years, the star shines with a luminosity 2.0 times that of the Sun with a surface temperature of 5840 Kelvin (only 60 degrees warmer than the Sun), from which we derive a mass of 1.06 solar and a radius of 1.4 solar (after adjusting for the light from the faint companion). The relatively high luminosity for a near-solar-mass star shows that HD 195019 is older then the Sun, is nearing the end of its hydrogen-fusing life, and may indeed be close to true subgiant status. Typical of stars with planets, the iron abundance higher than normal, 20 percent greater than solar. HD 195019 seems to be a true binary. Four seconds of arc away (3.5" as of 1988) is an 11th magnitude (10.6) class K3 companion. While little orbital motion is seen, the two are moving together, implying real association. The two are at least 150 AU apart and orbit with a period of at least 1500 years. From HD 195019's planet, the companion would shine with the brightness of three full Moons. A bit over a minute of arc away lie two other stars of tenth magnitude, one of which is clearly just a line-of- sight coincidence. The status of the other one is not known. HD 195019 is "high velocity star" that speeds along at 112 kilometers per second relative to the Sun, some 7 times higher than average, suggesting that it is a visitor from a different part of the Galaxy.

HR 7907 Delphini, just below the center of the picture, also has an orbiting planet.
Written by Jim Kaler. Return to The Planet Project or go to STARS.