Figure 1: Artist’s impression of a gas giant planet.
Ciceri et al. (2015) present the discovery of two massive hot-Jupiters in close-in orbits around old Sun-like stars. The two planets are identified as HATS-15b and HATS-16b. HATS-15b has 2.17 ± 0.15 times the mass of Jupiter, 1.105 ± 0.040 times the radius of Jupiter and it orbits a G9V star in 1.75 days. HATS-16b has 3.27 ± 0.19 times the mass of Jupiter, 1.30 ± 0.15 times the radius of Jupiter and it orbits a G3V star in 2.69 days. For comparison, the Sun is a G2V star.
With the masses and radii of both planets known, the density of HATS-15b is 1.97 g/cm³ and the density of HATS-16b is 1.86 g/cm³. Interior models suggest that HATS-15b does not possess a core while HATS-16b probably has a low-mass core. Being so close to their parent stars, both planets have very high equilibrium temperatures and are classified as hot-Jupiters. HATS-15b has a temperature of 1500 K and HATS-16b has a temperature of 1600 K.
The parent star of HATS-16b has a relatively short rotation period of just 12 days. Such a short rotation period might be the result of tidal interactions between HATS-16b and its parent star, whereby the star has been tidally spun up by the planet. The parent star of HATS-15b is estimated to be ~11 billion years old and the parent star of HATS-16b is estimated to be ~9.5 billion years old. Both stars are relatively old. For comparison, the Sun is only 4.6 billion years old.
Figure 2: Transit light curves indicating the presence of HATS-15b (left) and HATS-16b (right). The transit depths indicate that HATS-15b and HATS-16b have 1.105 ± 0.040 and 1.30 ± 0.15 times the radius of Jupiter, respectively. Ciceri et al. (2015)
Figure 3: Radial velocity measurements for HATS-15b (left) and HATS-16b (right). The radial velocity amplitudes indicate that HATS-15b and HATS-16b have 2.17 ± 0.15 and 3.27 ± 0.19 times the radius of Jupiter, respectively. Ciceri et al. (2015)
Figure 4: HATS-15b and HATS-16b (highlighted in orange) are presented in the mass-density diagram showing the known transiting planets for which the mass is measured. The superimposed lines represent the expected density of planets having an inner core of 0, 25 and 50 Earth masses, and calculated for 10 bullion year old planets at 0.02 AU (solid lines), and 0.045 AU (dashed lines) from their parent stars. It can be seen in the diagram that planets with ~2 to 3 times the mass of Jupiter are much rarer than planets with ~0.1 to 1 times the mass of Jupiter. Ciceri et al. (2015)
Ciceri et al. (2015), “HATS-15 b and HATS-16 b: Two massive planets transiting old G dwarf stars”, arXiv:1511.06305 [astro-ph.EP]