The highly inflated giant planet WASP-174b

Mancini, L. and Sarkis, P. and Henning, Th. and Bakos, G. A. and Bayliss, D. and Bento, J. and Bhatti, W. and Brahm, R. and Csubry, Z. and Espinoza, N. and Hartman, J. and Jordan, A. and Penev, K. and Rabus, M. and Suc, V. and de Val-Borro, M. and Zhou, G. ORCID: and Chen, G. and Damasso, M. and Southworth, J. and Tan, T. G. (2020) The highly inflated giant planet WASP-174b. Astronomy and Astrophysics, 633:A30. pp. 1-12. ISSN 0004-6361

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Context. The transiting exoplanetary system WASP-174 was reported to be composed by a main-sequence F star (V = 11.8 mag) and a giant planet, WASP-174b (orbital period Porb = 4.23 days). However only an upper limit was placed on the planet mass (<1.3 MJup), and a highly uncertain planetary radius (0.7-1.7 RJup) was determined. Aims. We aim to better characterise both the star and the planet and precisely measure their orbital and physical parameters. Methods. In order to constrain the mass of the planet, we obtained new measurements of the radial velocity of the star and joined them with those from the discovery paper. Photometric data from the HATSouth survey and new multi-band, high-quality (precision reached up to 0.37 mmag) photometric follow-up observations of transit events were acquired and analysed for getting accurate photometric parameters. We fit the model to all the observations, including data from the TESS space telescope, in two different modes: incorporating the stellar isochrones into the fit, and using an empirical method to get the stellar parameters. The two modes resulted to be consistent with each other to within 2σ. Results. We confirm the grazing nature of the WASP-174b transits with a confidence level greater than 5σ, which is also corroborated by simultaneously observing the transit through four optical bands and noting how the transit depth changes due to the limb-darkening effect. We estimate that ≈76% of the disk of the planet actually eclipses the parent star at mid-transit of its transit events. We find that WASP-174b is a highly-inflated hot giant planet with a mass of Mp = 0.330 ± 0.091 MJup and a radius of Rp = 1.435 ± 0.050 RJup, and is therefore a good target for transmission-spectroscopy observations. With a density of ρp = 0.135 ± 0.042 g cm-3, it is amongst the lowest-density planets ever discovered with precisely measured mass and radius.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 07 Feb 2022 03:41
Last Modified: 14 Feb 2022 02:18
Uncontrolled Keywords: planetary systems; stars: fundamental parameters; stars: individual:; WASP-174; techniques: photometric; techniques: radial velocities; methods: data analysis; Astrophysics - Earth and Planetary Astrophysics
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
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