HATS-7b: A Hot Super Neptune Transiting a Quiet K Dwarf Star

Bakos, G. A. and Penev, K. and Bayliss, D. and Hartman, J. D. and Zhou, G. ORCID: https://orcid.org/0000-0002-4891-3517 and Brahm, R. and Mancini, L. and de Val-Borro, M. and Bhatti, W. and Jordan, A. and Rabus, M. and Espinoza, N. and Csubry, Z. and Howard, A. W. and Fulton, B. J. and Buchhave, L. A. and Ciceri, S. and Henning, T. and Schmidt, B. and Isaacson, H. and Noyes, R. W. and Marcy, G. W. and Suc, V. and Howe, A. R. and Burrows, A. S. and Lazar, J. and Papp, I. and Sari, P. (2015) HATS-7b: A Hot Super Neptune Transiting a Quiet K Dwarf Star. The Astrophysical Journal, 813 (2):111. pp. 1-10. ISSN 1538-4357

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We report the discovery by the HATSouth network of HATS-7b, a transiting Super-Neptune with a mass of 0.120 ± 0.012 MJ, a radius of 0.563-0.034 +0.046 RJ, and an orbital period of 3.1853 days. The host star is a moderately bright (V = 13.340 ± 0.010 mag, KS = 10.976 ± 0.026 mag) K dwarf star with a mass of 0.849 ± 0.027 M⊙, a radius of 0.815-0.035+0.049 R⊙, and a metallicity of [Fe H] = +0.250 ± 0.080. The star is photometrically quiet to within the precision of the HATSouth measurements, has low RV jitter, and shows no evidence for chromospheric activity in its spectrum. HATS-7b is the second smallest radius planet discovered by a wide-field ground-based transit survey, and one of only a handful of Neptune-size planets with mass and radius determined to 10% precision. Theoretical modeling of HATS-7b yields a hydrogen-helium fraction of 18 ± 4% (rock-iron core and H2-He envelope), or 9 ± 4% (ice core and H2-He envelope), i.e., it has a composition broadly similar to that of Uranus and Neptune, and very different from that of Saturn, which has 75% of its mass in H2-He. Based on a sample of transiting exoplanets with accurately (<20%) determined parameters, we establish approximate powerlaw relations for the envelopes of the mass-density distribution of exoplanets. HATS-7b, which, together with the recently discovered HATS-8b, is one of the first two transiting super-Neptunes discovered in the Southern sky, is a prime target for additional follow-up observations with Southern hemisphere facilities to characterize the atmospheres of Super-Neptunes (which we define as objects with mass greater than that of Neptune, and smaller than halfway between that of Neptune and Saturn, i.e., 0.054 MJ < Mp < 0.18 MJ).

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 25 Jan 2022 05:33
Last Modified: 25 Jan 2022 05:33
Uncontrolled Keywords: stars: individual: HATS-7; techniques: photometric; techniques:; radial velocities; techniques: spectroscopic; Astrophysics - Earth; Planetary Astrophysics
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
Identification Number or DOI: https://doi.org/10.1088/0004-637x/813/2/111
URI: http://eprints.usq.edu.au/id/eprint/44963

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