Rosanna H. Tilbrook and colleagues reported the discovery of four new hot Jupiters: NGTS-15b, NGTS-16b, NGTS-17b, and NGTS-18b. All four planets are short-period (𝑃 < 5d) planets orbiting G-type main sequence stars, with radii and masses between 1.10 − 1.30 𝑅𝐽 (1.10-1.30 times that of the radius of Jupiter) and 0.41 − 0.76 𝑀𝐽 (0.41–0.76 times that of the mass of Jupiter).
Each planet was originally identified from photometry from the Next Generation Transit Survey (NGTS), and was confirmed through follow-up observations carried out at the South African Astronomical Observatory (SAAO) with the 1.0 m and Lesedi telescopes, and radial velocity measurements made with the HARPS, CORALIE and FEROS spectrographs. Additional photometry from the Transiting Exoplanet Survey Satellite (TESS) was also acquired for three of the four targets.
Global fits to these data were produced using the open-source astronomy software package ALLESFITTER, and yielded masses, radii, and orbital periods consistent with hot Jupiter planets (see Table 1). Spectral analysis via iSPEC and SED fitting via ARIADNE revealed the properties of the host stars in each system, which were all found to be main-sequence G-type stars (see Tables 2, 3, 4, and 5).
By considering the host star luminosities and the planets’ small orbital separations (0.039 − 0.052 AU), they found that all four hot Jupiters are highly irradiated and therefore occupy a region of parameter space in which planetary inflation mechanisms become effective. Comparison with statistical studies and a consideration of the planets’ high incident fluxes reveals that NGTS-16b, NGTS-17b, and NGTS-18b are indeed likely inflated, although some disparities arise upon analysis with current Bayesian inflationary models. While, they were unable to draw any firm conclusions on the nature of inflation for NGTS-15b due to the poorly constrained age for this system resulting in a broad range of non-inflated radius values.
“We found that two of the planets are likely inflated when compared with non-inflationary models, and it is reasonable to assume that NGTS-18b, although consistent with both inflated and non-inflated solutions, is also inflated due to its high incident flux. We were unable to draw any firm conclusions on the nature of inflation for NGTS-15b due to the poorly constrained age for this system resulting in a broad range of non-inflated radius values.”— told Rosanna Tilbrook, first author of the study
Furthermore, they note some disparity between the radii derived from global modelling and those predicted by the inflationary forward model of Sestovic et al. (2018), although all four planets were found to fit within the general hot Jupiter population (see Featured image & Figure 1). They suggested that the inclusion of both new hot Jupiter data and additional hyperparameters which describe latent parameters, such as system age, into the Bayesian model may refine the relations further.
Featured image: Exoplanets with confirmed masses and radii (grey points) from the NASA Exoplanet Archive (https://exoplanetarchive.ipac.caltech.edu/). The background and the dotted black contour lines highlight the point density per grid element of their sample. The hot Jupiters presented in this paper are plotted with error bars, and can be seen to lie comfortably within the general population of hot Jupiters. NGTS-15b to NGTS-18b are labeled with coloured circles on the plot with associated uncertainties. © Tilbrook et al.
Reference: Rosanna H. Tilbrook, Matthew R. Burleigh, Jean C. Costes, Samuel Gill, Louise D. Nielsen, José I. Vines, Didier Queloz, Simon T. Hodgkin, Hannah L. Worters, Michael R. Goad, Jack S. Acton, Beth A. Henderson, David J. Armstrong, David R. Anderson, Daniel Bayliss, François Bouchy, Joshua T. Briegal, Edward M. Bryant, Sarah L. Casewell, Alexander Chaushev, Benjamin F. Cooke, Philipp Eigmüller, Edward Gillen, Maximilian N. Günther, Aleisha Hogan, James S. Jenkins, Monika Lendl, James McCormac, Maximiliano Moyano, Liam Raynard, Alexis M. S. Smith, Stéphane Udry, Christopher A. Watson, Richard G. West, Peter J. Wheatley, Hannes Breytenbach, Ramotholo R. Sefako, Jessymol K. Thomas, Douglas R. Alves, “NGTS 15b, 16b, 17b and 18b: four hot Jupiters from the Next Generation Transit Survey”, pp. 1-17, ArXiv, 18 March 2021. https://arxiv.org/abs/2103.10302
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