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

August 2015 • 2015AJ....150...49B

Authors • Bayliss, D. • Hartman, J. D. • Bakos, G. Á. • Penev, K. • Zhou, G. • Brahm, R. • Rabus, M. • Jordán, A. • Mancini, L. • de Val-Borro, M. • Bhatti, W. • Espinoza, N. • Csubry, Z. • Howard, A. W. • Fulton, B. J. • Buchhave, L. A. • Henning, T. • Schmidt, B. • Ciceri, S. • Noyes, R. W. • Isaacson, H. • Marcy, G. W. • Suc, V. • Lázár, J. • Papp, I. • Sári, P.

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+/- 0.10, {T}{eff} = 5679+/- 50 K) with a period of 3.5839 days. 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+/- 0.019 {M}{{J}} it is approximately halfway between the masses of Neptune and Saturn. However, HATS-8b has a radius of {0.873}-0.075+0.123 {R}{{J}}, resulting in a bulk density of just 0.259+/- 0.091 {{g}} {{cm}}-3. The metallicity of the host star is super-solar ([{Fe}/{{H}}] = 0.210+/- 0.080), providing evidence 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 nearly equal magnitude at just 19″ separation in the sky. These factors make HATS-8b an exciting target for future atmospheric characterization studies, particularly for long-slit transmission spectroscopy.

The HATSouth network is operated by a collaboration consisting of Princeton University (PU), the Max Planck Institute für Astronomie (MPIA), the Australian National University (ANU), and the Pontificia Universidad Católica de Chile (PUC). The station at Las Campanas Observatory (LCO) of the Carnegie Institute is operated by PU in conjunction with PUC, the station at the High Energy Spectroscopic Survey site is operated in conjunction with MPIA, and the station at Siding Spring Observatory is operated jointly with ANU. This paper includes data gathered with the 6.5 m Magellan Telescopes located in LCO, Chile. The work is based in part on observations made with the MPG 2.2 m Telescope and the ESO 3.6 m Telescope at the ESO Observatory in La Silla. This paper uses observations obtained using the facilities of the Las Cumbres Observatory Global Telescope.


IPAC Authors


Benjamin Fulton

Assistant Scientist