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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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Hobson, M. J., Brahm, R., Jordan, A.., Espinoza, N., Kossakowski, D., Henning, T., et al. (2021). A Transiting Warm Giant Planet around the Young Active Star TOI-201. Astron. J., 161(5), 235.
Abstract: We present the confirmation of the eccentric warm giant planet TOI-201 b, first identified as a candidate in Transiting Exoplanet Survey Satellite photometry (Sectors 1-8, 10-13, and 27-28) and confirmed using groundbased photometry from Next Generation Transit Survey and radial velocities from FEROS, HARPS, CORALIE, and MINERVA-Australis. TOI-201 b orbits a young (0.87(-0.49)(+0.46)) and bright (V = 9.07 mag) F-type star with a 52.9781 day period. The planet has a mass of 0.42(-0.03)(+0.05) M-J, a radius of 1.008(-0.015)(+0.012) R-J, and an orbital eccentricity of 0.28(-0.09)(+0.06); it appears to still be undergoing fairly rapid cooling, as expected given the youth of the host star. The star also shows long-term variability in both the radial velocities and several activity indicators, which we attribute to stellar activity. The discovery and characterization of warm giant planets such as TOI-201 b are important for constraining formation and evolution theories for giant planets.
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Nowak, G., Palle, E., Gandolfi, D., Deeg, H. J., Hirano, T., Barragan, O., et al. (2020). K2-280 b – a low density warm sub-Saturn around a mildly evolved star. Mon. Not. Roy. Astron. Soc., 497(4), 4423–4435.
Abstract: We present an independent discovery and detailed characterization of K2-280 b, a transiting low density warm sub-Saturn in a 19.9-d moderately eccentric orbit (e = 0.35(-0.04)(+0.05)) from K2 campaign 7. A joint analysis of high precision HARPS, HARPS-N, and FIES radial velocity measurements and K2 photometric data indicates that K2-280 b has a radius of R-b = 7.50 +/- 0.44 R-circle plus and a mass of M-b = 37.1 +/- 5.6 M-circle plus, yielding a mean density of rho(b) = 0.48(-0.10)(+0.13) g cm(-3). The host star is a mildly evolved G7 star with an effective temperature of T-eff = 5500 +/- 100 K, a surface gravity of log g(star) = 4.21 +/- 0.05 (cgs), and an iron abundance of [Fe/H] = 0.33 +/- 0.08 dex, and with an inferred mass of M-star = 1.03 +/- 0.03 M-circle dot and a radius of R-star = 1.28 +/- 0.07 R-circle dot. We discuss the importance of K2-280 b for testing formation scenarios of sub-Saturn planets and the current sample of this intriguing group of planets that are absent in the Solar system.
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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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