Saturday, January 30, 2016

The Properties of Two Bloated Hot-Jupiters

Figure 1: Artist’s impression of a gas giant planet.

Lillo-Box et al. (2016) present the discovery of two bloated hot-Jupiters in close-in orbits around stars similar to the Sun. The two hot-Jupiters are identified as EPIC210957318b and EPIC212110888b, hereafter referred to as EPIC318b and EPIC888b. Both planets were first detected using data from NASA's K2 mission which hunts for planets around other stars via the transit method. Based on how much light from the host star each planet obscures as it transits, EPIC318b and EPIC888b were found to have, respectively, 1.196 ± 0.060 and 0.0905 ± 0.0017 times the radius of Jupiter. Subsequent ground-based radial velocity measurements with SOPHIE, HARPS-N and CAFE indicate that EPIC318b and EPIC888b have 0.623 ± 0.031 and 1.76 ± 0.13 times the mass of Jupiter, respectively.

With the sizes and masses known, the densities of EPIC318b and EPIC888b are 0.364 ± 0.058 and 0.71 ± 0.11 times the average density of Jupiter, respectively. The relatively low densities indicate that both planets are somewhat inflated. Both EPIC318b and EPIC888b orbit very close to their host stars. The orbital period of EPIC318b is 4.099 days, while the orbital period of EPIC888b is 2.996 days. The close proximity to their host stars means that EPIC318b is heated to almost ~1200 K, while EPIC888b is heated to temperatures exceeding ~1700 K. The inflated radii of EPIC318b and EPIC888b is probably due to the high amount of insolation they receive from their host stars, although tidal heating can also play a significant role.

Figure 2: Transit light curve (top) and radial velocity curve (bottom) indicating the presence of EPIC318b. Lillo-Box et al. (2016)

Figure 3: Transit light curve (top) and radial velocity curve (bottom) indicating the presence of EPIC888b. Lillo-Box et al. (2016)

Lillo-Box et al. (2016), "EPIC210957318b and EPIC212110888b: two inflated hot-Jupiters around Solar-type stars", arXiv:1601.07635 [astro-ph.EP]