Friday, July 8, 2016

Five Planets Transiting a Bright Star

HIP 41378 is a relatively bright, slightly metal-poor F-type star located ~380 light years away. It has ~1.15 times the mass and ~1.4 times the radius of the Sun, and its effective temperature is ~6200 K. Using new data from the K2 mission, Vanderburg et al. (2016) present the discovery of a planetary system consisting of five transiting planets around HIP 41378.

Figure 1: Artist's impression of an exoplanet.

The two innermost planets are sub-Neptune-sized planets with 2.90 ± 0.44 and 2.56 ± 0.40 times the size of Earth, and their orbital periods are 15.57 and 31.70 days, respectively. The three outer planets each transit once during the 75 days of K2 observations. One is a sub-Saturn-sized planet with 5.51 ± 0.77 times the size of Earth in a ~131 day orbit; one is a Neptune-sized planet with 3.96 ± 0.59 times the size of Earth in a ~156 day orbit; and one is a Jupiter-sized planet with 10.2 ± 1.4 times the size of Earth in a ~324 day orbit.

HIP 41378 is a good target for future radial velocity measurements to determine the masses of its five transiting planets. Furthermore, the outer Jovian planet, identified as HIP 41378 f, is one of the first known gas giant planets with a relatively cool equilibrium temperature that transits a star that is sufficiently bright for transit transmission spectroscopy. HIP 41378 f is an excellent candidate for follow-up transit observations to characterise its atmosphere and measure its oblateness.

Figure 2: Phase-folded light curve for each of the five transiting planets in the HIP 41378 system. Vanderburg et al. (2016)

Vanderburg et al. (2016), "Five Planets Transiting a Ninth Magnitude Star", arXiv:1606.08441 [astro-ph.EP]