Figure 1: Artist’s impression of a gas giant planet.
HD 33844 is a metal-rich, evolved giant star with almost twice the Sun’s metallicity, 1.78 times the Sun’s mass and 5.29 times the Sun’s radius. The effective temperature of HD 33844 is 4861 K, much cooler than the Sun. Nevertheless, due to the large physical size of the star, HD 33844 has 14 times the Sun’s luminosity. HD 33844 hosts a planetary system consisting of two gas giant plants that are each more massive than Jupiter. Both planets were found using the radial velocity method which involves measuring the “wobbling” motion of the host star due to the presence of the two planets.
The two planets are identified as HD 33844b and HD 33844c, and they induce radial velocity amplitude of 33.5 ± 2.0 m/s and 25.4 ± 2.9 m/s on their host star, respectively. HD 33844b has at least 1.96 ± 0.12 times the mass of Jupiter and it orbits its host star at 1.60 ± 0.02 AU. HD 33844c has at least 1.75 ± 0.18 times the mass of Jupiter and it orbits its host star at 2.24 ± 0.05 AU. The orbital periods of HD 33844b and HD 33844c are 551.4 days and 916.0 days, respectively. Both HD 33844b and HD 33844c are likely trapped in a 3:5 orbital resonance. For every 3 times HD 33844c goes around its host star, HD 33844b goes around 5 times.
Figure 2: Radial velocity curve indicating the presence of the inner planet HD 33844b. Wittenmyer et al. (2015)
Figure 3: Radial velocity curve indicating the presence of the outer planet HD 33844c. Wittenmyer et al. (2015)
Wittenmyer et al. (2015), “The Pan-Pacific Planet Search. IV. Two super-Jupiters in a 3:5 resonance orbiting the giant star HD 33844”, arXiv:1512.07316 [astro-ph.EP]