High precision transit observations of the exoplanet WASP-13b with the RISE instrument

TL;DR

This study used high-precision transit observations with the RISE instrument to refine the system parameters of exoplanet WASP-13b, revealing its low density, evolved host star, and suitability for atmospheric follow-up.

Contribution

First high-precision transit data for WASP-13b obtained with RISE, leading to improved system parameters and insights into the host star's evolutionary state.

Findings

Orbital inclination of 85.2 ± 0.3 degrees.

Stellar radius 1.56 ± 0.04 R⊙ and planetary radius 1.39 ± 0.05 RJup.

WASP-13b is a low-density planet with a density of 0.17ρJ.

Abstract

WASP-13b is a sub-Jupiter mass exoplanet orbiting a G1V type star with a period of 4.35 days. The current uncertainty in its impact parameter (0 < b < 0.46) resulted in poorly defined stellar and planetary radii. To better constrain the impact parameter we have obtained high precision transit observations with the RISE instrument mounted on 2.0 m Liverpool Telescope. We present four new transits which are fitted with an MCMC routine to derive accurate system parameters. We found an orbital inclination of 85.2 \pm 0.3 degrees resulting in stellar and planetary radii of 1.56 \pm 0.04 R\odot and 1.39 \pm 0.05 RJup, respectively. This suggests that the host star has evolved off the main-sequence and is in the shell hydrogen-burning phase. We also discuss how the limb darkening affects the derived system parameters. With a density of 0.17{\rho}J, WASP-13b joins the group of low density planets whose radii are too large to be explained by standard irradiation models. We derive a new ephemeris for the system, T0 = 2455575.5136 \pm 0.0016 (HJD) and P = 4.353011 \pm 0.000013 days. The planet equilibrium temperature (Tequ = 1500 K) and the bright host star (V = 10.4 mag) make it a good candidate for follow-up atmospheric studies.