Wednesday, December 23, 2015

Grazing Transit by a Hot-Jupiter

Figure 1: Artist’s impression of a hot-Jupiter.

Grziwa et al. (2015) present the detection of EPIC 204129699b, the first hot-Jupiter found using data from NASA’s K2 mission. The orbit of EPIC 204129699b is such that it transits its host star in a grazing fashion, which means the planet does not entirely pass in front of its host star. EPIC 204129699b orbits around a G7V star with 91 percent the mass and 78 percent the radius of the Sun. The periodicity of the planet’s grazing transits indicates that the planet’s orbital period is 1.26 days. This makes EPIC 204129699b a short-period hot-Jupiter. The dayside of EPIC 204129699b is estimated to have a temperature of roughly 1750 K.

The size of EPIC 204129699b can only be weakly constrained due to the grazing nature of the planet’s transits and it lies somewhere between 0.7 to 1.4 times the size of Jupiter.  Follow-up radial velocity observations indicate that EPIC 204129699b has 1.774 ± 0.079 times the mass of Jupiter. A search for reflected light from EPIC 204129699b yielded no reliable detection, placing an upper limit on the planet-to-star surface-brightness ratio at around 0.01. This means the planet has an albedo of less than 0.4, indicating that it has a low-reflectivity that is consistent with most hot-Jupiters. EPIC 204129699b is an important addition to the small number of short-period hot-Jupiters detected to date.

Figure 2: Phase-folded transit light curve indicating the presence of EPIC 204129699b and the V-shaped curve is caused by a grazing transit. Grziwa et al. (2015)

Grziwa et al. (2015), “EPIC 204129699b, a grazing transiting hot Jupiter on an 1.26-day orbit around a bright solar like star”, arXiv:1510.09149 [astro-ph.EP]