Saturday, July 9, 2016

Giant Planets and the Core Accretion Mass Limit

As part of the Calan-Hertfordshire Extrasolar Planet Search, Jenkins et al. (2016) present the discovery of eight giant planets. The planets have masses between 1.1 to 5.4 times the mass of Jupiter, and orbital periods ranging from 40 to 2900 days. The study also show a sharp decline in the number of planets with more than 3 times the mass of Jupiter, suggesting that the core accretion model of planet formation is efficient at forming giant planets with up to a few times the mass of Jupiter, but has problems forming super-Jupiters (i.e. planets with several times the mass of Jupiter).

This sample of newly discovered planets includes a planetary system, located ~340 light years away, consisting of two giant planets identified as HD 147873b and HD 147873c. Both planets orbit a host star with ~1.38 times the mass and ~2.29 times the radius of the Sun. The host star also has ~6 times the Sun's luminosity and its effective temperature is ~5972 K. HD 147873b and HD 147873c have at least ~5.14 and ~2.30 times the mass of Jupiter, and their orbital periods are 116.6 and 491.5 days, respectively.

Another notable planet is HD 224538b. It is a giant planet with at least ~5.97 times the mass of Jupiter and its orbital period around its host star is ~1200 days. The orbit of HD 224538b has a large eccentricity of about 0.46. The host star of HD 224538b is an F-type star with ~1.34 times the mass, ~1.54 times the radius and ~2.95 times the luminosity of the Sun. Furthermore, the star's effective temperature is ~6097 K and it is a metal-rich star with almost twice the Sun's metallicity. HD 224538b is basically a massive eccentric giant planet orbiting a super metal-rich star, a relatively rare type of planet.

Jenkins et al. (2016), "New Planetary Systems from the Calan-Hertfordshire Extrasolar Planet Search and the Core Accretion Mass Limit", arXiv:1603.09391 [astro-ph.EP]