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Grieves, N., Nielsen, L. D., Vines, J. I., Bryant, E. M., Gill, S., Bouchy, F., et al. (2021). NGTS-13b: a hot 4.8 Jupiter-mass planet transiting a subgiant star. Astron. Astrophys., 647, A180.
Abstract: We report the discovery of the massive hot Jupiter NGTS-13b by the Next Generation Transit Survey (NGTS). The V = 12.7 host star is likely in the subgiant evolutionary phase with logg(*) = 4.04 +/- 0.05, T-eff = 5819 +/- 73 K, M-* = 1.30(-0.18)(+0.11) M-circle dot, and R-* = 1.79 +/- 0.06 R-circle dot. The NGTS detected a transiting planet with a period of P = 4.12 days around the star, which was later validated with the Transiting Exoplanet Survey Satellite (TESS; TIC 454069765). We confirm the planet using radial velocities from the CORALIE spectrograph. Using NGTS and TESS full-frame image photometry combined with CORALIE radial velocities, we determine NGTS-13b to have a radius of R-P = 1.142 +/- 0.046 R-Jup, a mass of M-P = 4.84 +/- 0.44 M-Jup, and an eccentricity of e = 0.086 +/- 0.034. Previous studies have suggested that similar to 4 M-Jup may be the border separating two formation scenarios (e.g., core accretion and disk instability) and that massive giant planets share similar formation mechanisms as lower-mass brown dwarfs. NGTS-13b is just above 4 M-Jup, making it an important addition to the statistical sample needed to understand the differences between various classes of substellar companions. The high metallicity of NGTS-13, [Fe/H] = 0.25 +/- 0.17, does not support previous suggestions that massive giants are found preferentially around lower metallicity host stars, but NGTS-13b does support findings that more massive and evolved hosts may have a higher occurrence of close-in massive planets than lower-mass unevolved stars.
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Smith, A. M. S., Acton, J. S., Anderson, D. R., Armstrong, D. J., Bayliss, D., Belardi, C., et al. (2021). NGTS-14Ab: a Neptune-sized transiting planet in the desert. Astron. Astrophys., 646, A183.
Abstract: Context. The sub-Jovian, or Neptunian, desert is a previously identified region of parameter space where there is a relative dearth of intermediate-mass planets with short orbital periods.Aims. We present the discovery of a new transiting planetary system within the Neptunian desert, NGTS-14.Methods. Transits of NGTS-14Ab were discovered in photometry from the Next Generation Transit Survey (NGTS). Follow-up transit photometry was conducted from several ground-based facilities, as well as extracted from TESS full-frame images. We combine radial velocities from the HARPS spectrograph with the photometry in a global analysis to determine the system parameters.Results. NGTS-14Ab has a radius that is about 30 per cent larger than that of Neptune (0.444 +/- 0.030 R-Jup) and is around 70 per cent more massive than Neptune (0.092 +/- 0.012 M-Jup). It transits the main-sequence K1 star, NGTS-14A, with a period of 3.54 days, just far away enough to have maintained at least some of its primordial atmosphere. We have also identified a possible long-period stellar mass companion to the system, NGTS-14B, and we investigate the binarity of exoplanet host stars inside and outside the Neptunian desert using Gaia.
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