HATS-7b: A HOT SUPER NEPTUNE TRANSITING A QUIET K DWARF STAR

Gaspar Aron Bakos, K. Penev, D. Bayliss, J. D. Hartman, G. Zhou, R. Brahm, L. Mancini, M. De Val-Borro, W. Bhatti, A. Jordán, M. Rabus, N. Espinoza, Z. Csubry, A. W. Howard, B. J. Fulton, L. A. Buchhave, S. Ciceri, T. Henning, B. Schmidt, H. IsaacsonR. W. Noyes, G. W. Marcy, V. Suc, A. R. Howe, Adam S. Burrows, J. Lázár, I. Papp, P. Sári

Research output: Contribution to journalArticle

14 Scopus citations

Abstract

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).

Original languageEnglish (US)
Article number111
JournalAstrophysical Journal
Volume813
Issue number2
DOIs
StatePublished - Nov 10 2015

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • stars: individual (HATS-7)
  • techniques: photometric
  • techniques: radial velocities
  • techniques: spectroscopic

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    Bakos, G. A., Penev, K., Bayliss, D., Hartman, J. D., Zhou, G., Brahm, R., Mancini, L., De Val-Borro, M., Bhatti, W., Jordán, A., Rabus, M., Espinoza, N., Csubry, Z., Howard, A. W., Fulton, B. J., Buchhave, L. A., Ciceri, S., Henning, T., Schmidt, B., ... Sári, P. (2015). HATS-7b: A HOT SUPER NEPTUNE TRANSITING A QUIET K DWARF STAR. Astrophysical Journal, 813(2), [111]. https://doi.org/10.1088/0004-637X/813/2/111