HAT-P-4b: A metal-rich low-density transiting hot Jupiter

TL;DR

HAT-P-4b is a low-density, metal-rich hot Jupiter with a large radius, challenging existing theories of planetary inflation, discovered through combined photometric and spectroscopic analysis.

Contribution

This paper reports the discovery and detailed characterization of HAT-P-4b, a low-density hot Jupiter around a metal-rich star, highlighting its inflated radius and implications for planetary formation theories.

Findings

Planet has a mass of 0.68 MJ and radius of 1.27 RJ.

Density is unusually low at 0.41 g/cm^3.

The planet's large radius challenges existing inflation models.

Abstract

We describe the discovery of HAT-P-4b, a low-density extrasolar planet transiting BD+36 2593, a V = 11.2 mag slightly evolved metal-rich late F star. The planet's orbital period is 3.056536+/-0.000057 d with a mid-transit epoch of 2,454,245.8154 +/- 0.0003 (HJD). Based on high-precision photometric and spectroscopic data, and by using transit light curve modeling, spectrum analysis and evolutionary models, we derive the following planet parameters: Mp= 0.68 +/- 0.04 MJ, Rp= 1.27 +/- 0.05 RJ, rho = 0.41 +/- 0.06 g cm-3 and a = 0.0446 +/- 0.0012 AU. Because of its relatively large radius, together with its assumed high metallicity of that of its parent star, this planet adds to the theoretical challenges to explain inflated extrasolar planets.