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

• Main Authors: Bakos, G. Á., 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., Isaacson, H., Noyes, R. W., Marcy, G. W., Suc, V., Howe, A. R., Burrows, A. S., Lázár, J., Papp, I., Sári, P.
• Format: Text
• Language: unknown
• Published: arXiv 2015
• Subjects: Earth and Planetary Astrophysics astro-ph.EP; FOS Physical sciences; ice core
• Online Access: https://dx.doi.org/10.48550/arxiv.1507.01024; https://arxiv.org/abs/1507.01024

IW ../submit_V2/abstract.txt ( Row 1 Col 1 6:48 Ctrl-K H for help We report the discovery by the HATSouth network of HATS-7b, a transiting Super-Neptune with a mass of 0.120+/-0.012MJ, a radius of 0.563+/-(0.046,0.034)RJ, and an orbital period of 3.1853days. The host star is a moderately bright (V=13.340+/-0.010mag, K_S=10.976+/-0.026mag) K dwarf star with a mass of 0.849+/-0.027Msun , a radius of 0.815+/-(0.049,-0.035)Rsun, and a metallicity of [Fe/H]=+0.250+/-0.080. The star is photometrically quiet to within the precision of the HATSouth measurements and has low RV jitter. 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 power-law 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 : 11 pages, accepted for publication by ApJ