HATS-8b: A Low-Density Transiting Super-Neptune

TL;DR

HATS-8b is a low-density super-Neptune exoplanet with a large atmosphere, making it an ideal candidate for atmospheric studies, discovered through the HATSouth ground-based survey.

Contribution

This paper reports the discovery and characterization of HATS-8b, a low-density super-Neptune, highlighting its suitability for atmospheric analysis and its significance among ground-based exoplanet discoveries.

Findings

HATS-8b has a mass of 0.138 M_J and a radius of 0.873 R_J.

The planet's density is 0.259 g/cm^3, indicating a low-density composition.

The host star has a super-Solar metallicity ([Fe/H]=0.210).

Abstract

HATS-8b is a low density transiting super-Neptune discovered as part of the HATSouth project. The planet orbits its solar-like G dwarf host (V=14.03 $\pm$ 0.10 and T$_{eff}$ =5679 $\pm$ 50 K) with a period of 3.5839 d. HATS-8b is the third lowest mass transiting exoplanet to be discovered from a wide-field ground based search, and with a mass of 0.138 $\pm$ 0.019 M$_J$ it is approximately half-way between the masses of Neptune and Saturn. However HATS-8b has a radius of 0.873 (+0.123,-0.075) R$_J$, resulting in a bulk density of just 0.259 $\pm$ 0.091 g.cm$^{-3}$. The metallicity of the host star is super-Solar ([Fe/H]=0.210 $\pm$ 0.080), arguing against the idea that low density exoplanets form from metal-poor environments. The low density and large radius of HATS-8b results in an atmospheric scale height of almost 1000 km, and in addition to this there is an excellent reference star of near equal magnitude at just 19 arcsecond separation on the sky. These factors make HATS-8b an exciting target for future atmospheric characterization studies, particularly for long-slit transmission spectroscopy.