Figure 1: Artist’s impression of an exoplanet.
Combining data from ground-based observations with the exquisite photometric precision of NASA’s re-purposed Kepler space telescope as part of the K2 mission, Huang et al. (2015) present the discovery of HAT-P-56b, an inflated massive hot-Jupiter transiting a bright F-type star. HAT-P-56b has roughly 2.18 times the mass and roughly 1.47 times the radius of Jupiter. It orbits its host star in a close-in orbit with a period of 2.79 days. Due to its proximity to its host star, the dayside of HAT-P-56b is predicted to be intensely irradiated to a temperature of over 1,800 K.
The radius of HAT-P-56b is among the largest known for a planet with more than twice the mass of Jupiter. In general, hot-Jupiters with more than twice the mass of Jupiter are less likely to be inflated by the intense irradiation from their host stars. HAT-P-56b does not follow this trend and is one of the few known inflated massive hot-Jupiters. In fact, HAT-P-56b is currently the most inflated hot-Jupiter that is between 1.5 to 4 times the mass of Jupiter.
Figure 2: Radial velocity curve of the host star of HAT-P-56b. The amplitude of the radial velocity curve indicates that HAT-P-56b has roughly 2.18 times the mass of Jupiter. Huang et al. (2015).
Figure 3: Transit light curve of HAT-P-56b. The transit depth (i.e. the amount of starlight the planet blocks when it transits in front of its host star) indicates that HAT-P-56b has roughly 1.47 times the radius of Jupiter and the shape of the light curve indicates that it is a grazing transit. Huang et al. (2015).
Figure 4: Mass-radius diagram for HAT-P-56b (big square) compared to the full sample of confirmed hot-Jupiters (circles). The points are colour coded with their equilibrium temperature (cooler planets have darker colours). Huang et al. (2015).
Huang et al. (2015), “An inflated massive Hot Jupiter transiting a bright F star followed up with K2.0 observations”, arXiv:1506.01776 [astro-ph.EP]