Multi-band, Multi-epoch Photometry of the Spot-crossing System TOI-3884: Refined System Geometry and Spot Properties
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2025
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| author | Mori, Mayuko Fukui, Akihiko Hirano, Teruyuki Narita, Norio Livingston, John H. Barkaoui, Khalid Collins, Karen A. de Leon, Jerome P. Ikuta, Kai Kawai, Yugo Schwarz, Richard P. Shporer, Avi Srdoc, Gregor |
| author_facet | Mori, Mayuko Fukui, Akihiko Hirano, Teruyuki Narita, Norio Livingston, John H. Barkaoui, Khalid Collins, Karen A. de Leon, Jerome P. Ikuta, Kai Kawai, Yugo Schwarz, Richard P. Shporer, Avi Srdoc, Gregor |
| contents | Spot-crossing transits offer a unique opportunity to probe spot properties such as temperature, size, and surface distribution. TOI-3884 is a rare system in which spot-crossing features are persistently observed during every transit. This is due to its unusual configuration: a nearly poler orbit super-Neptune transits a pole-on mid-M dwarf, repeatedly crossing a polar spot. However, previous studies have reported discrepant values in key system parameters, such as stellar inclination and obliquity. To address this, we conducted multi-band, multi-epoch transit observations of TOI-3884b using the MuSCAT instrument series, along with photometric monitoring with the LCO 1m telescopes/Sinistro. We detected time-dependent variations in the spot-crossing signals, indicating that the spot is not exactly on the pole. From the monitoring data, we measured a stellar rotation period of $11.043~_{-0.053}^{+0.054}$ days with a modulation amplitude of $\sim$5% in the r-band, consistent with the time variability in the spot-crossing features. Our analysis reconciles previous discrepancies and improves the constraints on the parameters of the system geometry ($i_\star = 139.9~^{+1.2}_{-2.0}$ deg and $λ=41.0~^{+3.7}_{-9.0}$ deg) and those of the spot properties (spot radius of $0.425~_{-0.011}^{+0.018}~R_\star$ and spot-photosphere temperature difference of $200~_{-9}^{+11}$ K). These results provide a critical context for interpreting upcoming transmission spectroscopy of TOI-3884b, as well as yielding new insights into the magnetic activity and spin-orbit geometry of M dwarfs. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_06445 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Multi-band, Multi-epoch Photometry of the Spot-crossing System TOI-3884: Refined System Geometry and Spot Properties Mori, Mayuko Fukui, Akihiko Hirano, Teruyuki Narita, Norio Livingston, John H. Barkaoui, Khalid Collins, Karen A. de Leon, Jerome P. Ikuta, Kai Kawai, Yugo Schwarz, Richard P. Shporer, Avi Srdoc, Gregor Earth and Planetary Astrophysics Solar and Stellar Astrophysics Spot-crossing transits offer a unique opportunity to probe spot properties such as temperature, size, and surface distribution. TOI-3884 is a rare system in which spot-crossing features are persistently observed during every transit. This is due to its unusual configuration: a nearly poler orbit super-Neptune transits a pole-on mid-M dwarf, repeatedly crossing a polar spot. However, previous studies have reported discrepant values in key system parameters, such as stellar inclination and obliquity. To address this, we conducted multi-band, multi-epoch transit observations of TOI-3884b using the MuSCAT instrument series, along with photometric monitoring with the LCO 1m telescopes/Sinistro. We detected time-dependent variations in the spot-crossing signals, indicating that the spot is not exactly on the pole. From the monitoring data, we measured a stellar rotation period of $11.043~_{-0.053}^{+0.054}$ days with a modulation amplitude of $\sim$5% in the r-band, consistent with the time variability in the spot-crossing features. Our analysis reconciles previous discrepancies and improves the constraints on the parameters of the system geometry ($i_\star = 139.9~^{+1.2}_{-2.0}$ deg and $λ=41.0~^{+3.7}_{-9.0}$ deg) and those of the spot properties (spot radius of $0.425~_{-0.011}^{+0.018}~R_\star$ and spot-photosphere temperature difference of $200~_{-9}^{+11}$ K). These results provide a critical context for interpreting upcoming transmission spectroscopy of TOI-3884b, as well as yielding new insights into the magnetic activity and spin-orbit geometry of M dwarfs. |
| title | Multi-band, Multi-epoch Photometry of the Spot-crossing System TOI-3884: Refined System Geometry and Spot Properties |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2506.06445 |