Based on the radial velocity method, a group of Japanese astronomers have discovered three new exoplanets – gas giants – evolving around two advanced stars: 24 Booties and Gamma Librae.
It is extremely difficult to observe an exoplanet directly. The radiation of the planet is indeed too weak compared to that of its star. As a result, astronomers rely on indirect observations and focus on the spectrum of light emitted by the star. Variations in this spectrum can be detected when the wavelength of certain spectral absorption lines increases and decreases steadily over a given time interval. These variations may be indicative of changes in radial velocity, which can be altered by the presence of a planet orbiting the star.
The radial velocity technique has so far allowed the discovery of more than 600 exoplanets. More recently, a team of Japanese astronomers led by Takuya Takarada, of the Tokyo Institute of Technology, reported the discovery through this same method of three new exoplanets. The three gaseous giants were spotted from the Okayama Astrophysical Observatory (OAO) in Japan. One of them orbits around the star 24 Booties and the other two observe the same movement around Gamma Librae.
24 Booties is a star similar in mass to our Sun, but almost 11 times larger. Its designated planet 24 Boo b orbits around the star every 30.35 days at a distance of about 0.19 AU (one AU equals the Earth-Sun distance, about 150 million km). The researchers estimate that the minimum mass of the newly discovered planet is about 0.91 mass of Jupiter.
For its part, Gamma Librae is about 11 times larger than the Sun for a mass of about 1.47 solar mass. The two gaseous giant planets – γ Lib b and γ Lib c, have respective minimum masses of 1.02 and 4.58 masses of Jupiter. Located at about 1.24 AU of the parent star, γ Lib b needs about 415 days to completely orbit its host, while γ Lib c is located at about 2.17 AU from its star and orbits it at nearly 965 days.