Spot-Crossing Variations Confirm a Misaligned Orbit for a Planet Transiting an M Dwarf

2025/06/13 by Patrick Tamburo, Tamburo, Patrick, Samuel W. Yee +12 · 2 voices · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph.EP #astro-ph.SR

paper · pdf · doi:10.48550/arxiv.2506.11998

openalex publication_date 2025/06/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

TOI-3884~b is an unusual 6.4~R_⊕ planet orbiting an M4 host, whose transits display large and persistent spot-crossing events. We used the Tierras Observatory to monitor both the long-term photometric variability of TOI-3884 and changes in the spot-crossing events across multiple transits of the planet. We show that the star rotates with a period of 11.020 ± 0.015~days. We simultaneously model the rotational modulation of the star and variations in transit shapes that arise due to rotation of the spot, allowing us to determine the true stellar obliquity, ψ_⋆. The data are best described by a planet on a misaligned orbit around a highly inclined star (ψ_⋆ = 77.4^∘ ^{+2.3^∘}_-2.5^∘; i_⋆ = 22.3^∘^{+1.8^∘}_-1.6^∘) that hosts a large polar starspot (r_spot = 31.2^∘^{+2.4^∘}_-1.9^∘; λ_spot = 80.5^∘±1.2^∘). Archival photometry from the Zwicky Transient Facility suggests that this polar spot has persisted on TOI-3884 for at least seven years. The TOI-3884 system provides a benchmark for studying the evolution of a polar spot on an M dwarf.

Citations

• Quantifying the Limits of TESS Stellar Rotation Measurements with the K2-TESS Overlap
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities
• ASTROIMAGEJ: IMAGE PROCESSING AND PHOTOMETRIC EXTRACTION FOR ULTRA-PRECISE ASTRONOMICAL LIGHT CURVES
• emcee : The MCMC Hammer

Cited by

• NASA’s Pandora SmallSat Mission: Simulating the Impact of Stellar Photospheric Heterogeneity and Its Correction
• A Panchromatic JWST Spectrum of a Giant Starspot on the Fully Convective M Dwarf TOI-3884
• The Polar Orbit of TOI-2374 b, a Planet in the Neptunian Ridge

Discussions

• TOI-3884 b is a planet around an M dwarf whose transits show persistent spot crossings. We show that the star's rotational and spot-crossing variations can be modeled with a misaligned planet transiti [bsky, 47 points, 3 comments]
• @tamburo.bsky.social is on a roll. 👏 #stellarastro 🔭 Measuring planetary orbital obliquity from spot crossings, using the same system as M. Mori et al. from last week: arxiv.org/abs/2506.11998 bsky. [bsky, 20 points, 0 comments]

Related

• Multi-band, Multi-epoch Photometry of the Spot-crossing System TOI-3884: Refined System Geometry and Spot Properties
• An In-Depth Look at TOI-3884b: a Super-Neptune Transiting a M4 Dwarf with Persistent Star Spot Crossings
• The changing transit shape of TOI-3884 b
• A Panchromatic JWST Spectrum of a Giant Starspot on the Fully Convective M Dwarf TOI-3884
• The Polar Orbit of TOI-2374 b, a Planet in the Neptunian Ridge