Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

A possible misaligned orbit for the young planet AU Mic c

Yu, H. ; Davies, M.B. LU ; Korth, J. LU and Wheatley, P.J. (2025) In Monthly Notices of the Royal Astronomical Society 536(3). p.2046-2063
Abstract
The AU Microscopii planetary system is only 24 Myr old, and its geometry may provide clues about the early dynamical history of planetary systems. Here, we present the first measurement of the Rossiter–McLaughlin effect for the warm sub-Neptune AU Mic c, using two transits observed simultaneously with the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT)/Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), CHaracterising ExOPlanet Satellite (CHEOPS), and Next-Generation Transit Survey (NGTS). After correcting for flares and for the magnetic activity of the host star, and accounting for transit-timing variations, we find the sky-projected spin–orbit angle of planet c to be in the range... (More)
The AU Microscopii planetary system is only 24 Myr old, and its geometry may provide clues about the early dynamical history of planetary systems. Here, we present the first measurement of the Rossiter–McLaughlin effect for the warm sub-Neptune AU Mic c, using two transits observed simultaneously with the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT)/Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), CHaracterising ExOPlanet Satellite (CHEOPS), and Next-Generation Transit Survey (NGTS). After correcting for flares and for the magnetic activity of the host star, and accounting for transit-timing variations, we find the sky-projected spin–orbit angle of planet c to be in the range λc = 67.8+31.7-49.0 degrees (1σ). We examine the possibility that planet c is misaligned with respect to the orbit of the inner planet b (λb = −2.96 +10.44-10.30), and the equatorial plane of the host star, and discuss scenarios that could explain both this and the planet’s high density, including secular interactions with other bodies in the system or a giant impact. We note that a significantly misaligned orbit for planet c is in some degree of tension with the dynamical stability of the system, and with the fact that we see both planets in transit, though these arguments alone do not preclude such an orbit. Further observations would be highly desirable to constrain the spin–orbit angle of planet c more precisely. © 2024 The Author(s). (Less)
Please use this url to cite or link to this publication:
author
; ; and
author collaboration
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
planets and satellites: dynamical evolution and stability, planets and satellites: formation, stars: activity, stars: individual: AU Microscopii, techniques: photometric, techniques: radial velocities, Giant stars, Interplanetary flight, Satellite observatories, Spectrographs, Tropics, Exo-planets, Planet-C, Planetary system, Planets and satellites: dynamical evolution and stabilities, Planets and satellites: formation, Star: activity, Star: individual: AU microscopii, Stars: individual: proxima Centauri, Techniques: photometric, Techniques: radial velocities, Exoplanets
in
Monthly Notices of the Royal Astronomical Society
volume
536
issue
3
pages
18 pages
publisher
Oxford University Press
external identifiers
  • scopus:85215549660
ISSN
0035-8711
DOI
10.1093/mnras/stae2655
language
English
LU publication?
yes
id
38be5a32-1cdb-4836-8326-7c3804469395
date added to LUP
2025-12-17 09:25:42
date last changed
2025-12-19 14:38:29
@article{38be5a32-1cdb-4836-8326-7c3804469395,
  abstract     = {{The AU Microscopii planetary system is only 24 Myr old, and its geometry may provide clues about the early dynamical history of planetary systems. Here, we present the first measurement of the Rossiter–McLaughlin effect for the warm sub-Neptune AU Mic c, using two transits observed simultaneously with the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT)/Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), CHaracterising ExOPlanet Satellite (CHEOPS), and Next-Generation Transit Survey (NGTS). After correcting for flares and for the magnetic activity of the host star, and accounting for transit-timing variations, we find the sky-projected spin–orbit angle of planet c to be in the range λc = 67.8+31.7-49.0 degrees (1σ). We examine the possibility that planet c is misaligned with respect to the orbit of the inner planet b (λb = −2.96 +10.44-10.30), and the equatorial plane of the host star, and discuss scenarios that could explain both this and the planet’s high density, including secular interactions with other bodies in the system or a giant impact. We note that a significantly misaligned orbit for planet c is in some degree of tension with the dynamical stability of the system, and with the fact that we see both planets in transit, though these arguments alone do not preclude such an orbit. Further observations would be highly desirable to constrain the spin–orbit angle of planet c more precisely. © 2024 The Author(s).}},
  author       = {{Yu, H. and Davies, M.B. and Korth, J. and Wheatley, P.J.}},
  issn         = {{0035-8711}},
  keywords     = {{planets and satellites: dynamical evolution and stability; planets and satellites: formation; stars: activity; stars: individual: AU Microscopii; techniques: photometric; techniques: radial velocities; Giant stars; Interplanetary flight; Satellite observatories; Spectrographs; Tropics; Exo-planets; Planet-C; Planetary system; Planets and satellites: dynamical evolution and stabilities; Planets and satellites: formation; Star: activity; Star: individual: AU microscopii; Stars: individual: proxima Centauri; Techniques: photometric; Techniques: radial velocities; Exoplanets}},
  language     = {{eng}},
  number       = {{3}},
  pages        = {{2046--2063}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{A possible misaligned orbit for the young planet AU Mic c}},
  url          = {{http://dx.doi.org/10.1093/mnras/stae2655}},
  doi          = {{10.1093/mnras/stae2655}},
  volume       = {{536}},
  year         = {{2025}},
}