Figure 1: Artist's impression of a gas giant planet.
Santos et al. (2016) present the discovery of a
super-Jupiter in a very eccentric long-period orbit around a host star that
also has a hot-Neptune in a close-in orbit around it. The super-Jupiter is
identified as HD 219828 c. Its orbital period is 13.1 years and it is estimated
to have at least 15.1 times the mass of Jupiter. It also has a highly eccentric
orbit with eccentricity 0.81. In the same planetary system, but much close to
the host star, lies the hot-Neptune HD 219828 b. The orbital period of HD
219828 b is 3.83 days and it is estimated to have at least 21 times the mass of
Earth.
The host star in this planetary system is a G0IV star that
has evolved slightly beyond the main sequence. It has 3.08 times the Sun's
luminosity, 1.23 ± 0.10 times the Sun's mass, 1.69 times the Sun's radius and
an estimated effective temperature of 5891 ± 18 K. This extreme planetary
system is estimated to be ~250 light years away. Dynamical simulations show
that the orbits of HD 219828 b and HD 219828 c are both stable in the long run.
Additionally, the large mass of HD 219828 c places it at the mass boundary
between gas giant planets and brown dwarfs.
Figure 2: Top and middle plots: phase-folded radial-velocity
curves and data for the planets HD 219828 b and HD 219828 c, respectively.
Santos et al. (2016)
Reference:
Santos et al. (2016), "An extreme planetary system
around HD219828. One long-period super Jupiter to a hot-neptune host
star", arXiv:1605.06942 [astro-ph.EP]