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

Creators: Bayliss, D.; Howard, A. W.; Fulton, B. J.

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.

Additional Information

© 2015 American Astronomical Society. Received 2015 April 21. Accepted 2015 May 29. Published 2015 July 17. Development of the HATSouth project was funded by NSF MRI grant NSF/AST-0723074; operations have been supported by NASA grants NNX09AB29G/NNX12AH91H and internal Princeton funds. Follow-up observations receive partial support from grant NSF/AST-1108686. A.J. acknowledges support from FONDECYT project 1130857, BASAL CATA PFB-06, and project IC120009 "Millennium Institute of Astrophysics (MAS)" of the Millennium Science Initiative, Chilean Ministry of Economy. R.B. and N.E. are supported by CONICYT-PCHA/Doctorado Nacional. R.B. and N.E. acknowledge additional support from project IC120009 "Millennium Institute of Astrophysics (MAS)" of the Millennium Science Initiative, Chilean Ministry of Economy. V.S. acknowledges support form BASAL CATA PFB-06. K.P. acknowledges support from NASA grant NNX13AQ62G. B.J.F. acknowledges support from the NSF Graduate Research Fellowship grant No. 2014184874. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Operations at the MPG 2.2 m Telescope are jointly performed by the Max Planck Gesellschaft and the European Southern Observatory. This work is based on observations made with ESO Telescopes at the La Silla Observatory. Observations from the du Pont and Swope telescopes were taken as part of programs CN2012A-61, CN2013A-171, and CN2014A-104, awarded by the Chilean Telescope Allocation Committee (CNTAC). This paper also uses observations obtained using the facilities of the Las Cumbres Observatory Global Telescope. The radial velocity data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. Work at the Australian National University is supported by the ARC Laureate Fellowship grant FL0992131. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

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