Letter to the Editor

HD 110067 c has an aligned orbit

Measuring the Rossiter–McLaughlin effect inside a resonant multi-planet system with ESPRESSO

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 European Southern Observatory, Casilla 13, Vitacura, Santiago, Chile
⁵ Dipartimento di Fisica, La Sapienza Università di Roma, Piazzale Aldo Moro 5, Roma 00185, Italy
⁶ European Space Agency (ESA), ESA Office, Space Telescope Science Institute (STScI), Baltimore, MD 21218, USA
⁷ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
⁸ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁹ Thueringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁰ Department of Physics and Astronomy, Valparaiso University, Valparaiso, IN 46383, USA
¹¹ Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA
¹² Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹³ Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, 38711 Breña Baja, Spain
¹⁴ Department of Multi-Disciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
¹⁵ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
¹⁶ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁷ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
¹⁸ Department of Physics, Ludwig-Maximilian University of Munich, Geschwister-Scholl-Platz 1, 80539 Munich, Germany
¹⁹ Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, UK
²⁰ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
²¹ American Association of Variable Star Observers, Cambridge, USA

Received: 30 April 2024
Accepted: 24 May 2024

Abstract

Planetary systems in mean motion resonances hold a special place among the planetary population. They allow us to study planet formation in great detail as dissipative processes are thought to have played an important role in their existence. Additionally, planetary masses in bright resonant systems can be independently measured via both radial velocities and transit timing variations. In principle, they also allow us to quickly determine the inclination of all planets in the system since, for the system to be stable, they are likely all in coplanar orbits. To describe the full dynamical state of the system, we also need the stellar obliquity, which provides the orbital alignment of a planet with respect to the spin of its host star and can be measured thanks to the Rossiter–McLaughlin effect. It was recently discovered that HD 110067 harbors a system of six sub-Neptunes in resonant chain orbits. We here analyze an ESPRESSO high-resolution spectroscopic time series of HD 110067 during the transit of planet c. We find the orbit of HD 110067 c to be well aligned, with a sky-projected obliquity of λ =6⁺²⁴_-26 deg. This result indicates that the current architecture of the system was reached through convergent migration without any major disruptive events. Finally, we report transit-timing variation in this system as we find a significant offset of 19 ± 4 min in the center of the transit compared to the published ephemeris.