HD 217107

HD 217 107 is a yellow subgiant, which can be found in the constellation Pisces. Although the star is much older than the sun, he has roughly the same mass. The star is orbited by two planets, one of which only seven days to orbit its sun needs while the other requires eight years for an orbit.

The Star

The star is from an astronomical point of view considered very close to our sun. Its distance is only 64 light years, which can be regarded as closer around our sun. Since its apparent brightness but only 6.17 is like, it is only possible under optimal conditions, to see it with the naked eye.

Spectroscopic studies show that the star of spectral type G7 or G8 is and thus has a surface temperature of about 5000 Kelvin. The age of the star is estimated to 7.7 billion years, which is relatively large compared to the 4.6 billion years the sun. The star has now merged most of its hydrogen and moves away from the main sequence.

Planetary system

Through measurements of the radial velocity was found in 1998 that there is a variation with a 7.1 - day period. This was attributed to the presence of an orbital companion, who had to have a minimum mass, which is just above the mass of Jupiter. This companion was designated HD 217 107 b. Planet with such a short orbital period usually have nearly circular orbits for HD 217 107 b, however, an eccentricity was found, the cause could be a second companion of the star, which had to orbit the star at a distance of a few AU. Through long-term observations was found that the star has a further variation in the radial velocity, which shows a period of eight years. This observation confirmed the assumption of a second planet, its minimum mass could be limited to two times Jupiter's mass, the radius of its semimajor axis is four AU. This second Planet HD 217 107 was called c.

Credentials

• Individual star fifth size and darker
• Subgiant
• Pisces ( constellation )
• Star with exoplanet