Tuesday, January 5, 2016

HD 20794 is Host to Three Rocky Super-Earths

HD 20794 is a Sun-like star located ~20 light years away. It has 70 percent the Sun’s mass and 0.656 ± 0.003 times the Sun’s luminosity. Its surface temperature is estimated to be 5401 ± 17 K and it is a middle-age star about 5.76 ± 0.66 billion years old. High precision radial velocity observations of HD 20794 by the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph reveal the presence of three planets orbiting the star. The three planets are identified as HD 20794b, HD 20794c, and HD 20794d; hereafter referred to as planets “b”, “c”, and “d”.

Figure 1: Artist’s impression of a rocky planet.

Gravitation tugging from planets “b”, “c”, and “d” cause their host star to wobble by 0.83 ± 0.09 m/s, 0.56 ± 0.10 m/s, and 0.85 ± 0.10 m/s, respectively. The strength and periodicity of the wobbling indicates that planets “b”, “c”, and “d” have 2.68, 2.38, and 4.73 times the mass of Earth, and their orbital periods are 18.3, 40.1, and 90.3 days, respectively. Furthermore, planets “b”, “c”, and “d” orbit 0.12 AU, 0.20 AU, and 0.35 AU from their host star, and their estimated equilibrium temperatures are 660 K, 508 K, and 388 K, respectively. All three planets around HD 20794 have masses in the super-Earth regime, and they are probably rocky worlds.

Figure 2: Phase-folded radial velocity curve for the three planetary components “b”, “c”, and “d” around HD 20794. F. Pepe et al. (2011)

F. Pepe et al. (2011), “The HARPS search for Earth-like planets in the habitable zone: I -- Very low-mass planets around HD 20794, HD 85512 and HD 192310”, arXiv:1108.3447 [astro-ph.EP]