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

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.

11 pages, 7 figures, accepted for publication in AJ

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• HAT-P-65b and HAT-P-66b: Two Transiting Inflated Hot Jupiters and Observational Evidence for the Re-Inflation of Close-In Giant Planets
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• HATS-17b: A Transiting Compact Warm Jupiter in a 16.3 Days Circular Orbit
• The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert
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• Evidence of a Sub-Saturn around EPIC~211945201
• HATS-22b, HATS-23b and HATS-24b: Three new transiting Super-Jupiters from the HATSouth Project
• EPIC 201498078b: A low density Super Neptune on an eccentric orbit
• Characterization of the K2-19 Multiple-Transiting Planetary System via High-Dispersion Spectroscopy, AO Imaging, and Transit Timing Variations
• HATS-43b, HATS-44b, HATS-45b, and HATS-46b: Four Short Period Transiting Giant Planets in the Neptune-Jupiter Mass Range
• HATS-39b, HATS-40b, HATS-41b, and HATS-42b: Three Inflated Hot Jupiters and a Super-Jupiter Transiting F Stars
• Measuring Tidal Dissipation in Giant Planets from Tidal Circularization
• HATS-50b through HATS-53b: four transiting hot Jupiters orbiting G-type stars discovered by the HATSouth survey
• The architecture and formation of the Kepler-30 planetary system
• The HATNet and HATSouth Exoplanet Surveys
• A Holistic and Probabilistic Approach to the Ground-based Data of HAT-P-19 System
• HATS-15 b and HATS-16 b: Two massive planets transiting old G dwarf stars