Stellar obliquity measurements of six gas giants

Orbital misalignment of WASP-101b and WASP-131b

¹ European Southern Observatory, Karl-Schwarzschild-str. 2, 85748 Garching, Germany
e-mail: jiri.zak@eso.org
² Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 25165 Ondřejov, Czech Republic
³ Faculty of Physics and Astronomy, Friedrich-Schiller-Universität, Fürstengraben 1, 07743 Jena, Germany
⁴ Dipartimento di Fisica, La Sapienza Università di Roma, Piazzale Aldo Moro 5, Roma 00185, Italy
⁵ European Southern Observatory, Casilla 13, Vitacura, Santiago, Chile
⁶ European Space Agency (ESA), ESA Office, Space Telescope Science Institute (STScI), Baltimore, MD 21218, USA
⁷ Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic
⁸ Thueringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany

Received: 22 December 2023
Accepted: 19 March 2024

Abstract

One can infer the orbital alignment of exoplanets with respect to the spin of their host stars using the Rossiter-McLaughlin effect, thereby giving us the chance to test planet formation and migration theories and improve our understanding of the currently observed population. We analyzed archival HARPS and HARPS-N spectroscopic transit time series of six gas giant exoplanets on short orbits, namely WASP-77 Ab, WASP-101b, WASP-103b, WASP-105b, WASP-120b, and WASP-131b. We find a moderately misaligned orbit for WASP-101b (λ = 34° ± 3) and a highly misaligned orbit for WASP-131b (λ = 161° ± 5), while the four remaining exoplanets appear to be aligned: WASP-77 Ab (λ = −8°₋₁₈⁺¹⁹), WASP-103b (λ = −2°₋₃₆⁺³⁵), WASP-105b (λ = −14°₋₂₄⁺²⁸), and WASP-120b (λ = −2° ± 4). For WASP-77 Ab, we are able to infer its true orbital obliquity (Ψ = 48°₋₂₁⁺²²). We additionally performed transmission spectroscopy of the targets in search of strong atomic absorbers in the exoatmospheres, but were unable to detect any features, most likely due to the presence of high-altitude clouds or Rayleigh scattering muting the strength of the features. Finally, we comment on future perspectives on studying these planets with upcoming space missions to investigate their evolution and migration histories.