The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant Exoplanets
Recent studies revealed viewing-angle-dependent color and spectral trends in brown dwarfs, as well as long-term photometric variability (∼100 hr). The origins of these trends are yet unexplained. Here, we propose that these seemingly unrelated sets of observations stem from the same phenomenon: the...
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IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/ad87e9 |
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| author | Nguyen Fuda Dániel Apai |
| author_facet | Nguyen Fuda Dániel Apai |
| author_sort | Nguyen Fuda |
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| description | Recent studies revealed viewing-angle-dependent color and spectral trends in brown dwarfs, as well as long-term photometric variability (∼100 hr). The origins of these trends are yet unexplained. Here, we propose that these seemingly unrelated sets of observations stem from the same phenomenon: the polar regions of brown dwarfs and directly imaged exoplanets are spectrally different from lower-latitude regions, and they evolve over longer timescales, possibly driven by polar vortices. We explore this hypothesis via a spatiotemporal atmosphere model capable of simulating time series and disk-integrated spectra of ultracool atmospheres. We study three scenarios with different spectral and temporal components: a null hypothesis without polar vortex, and two scenarios with polar vortices. We find that the scenarios with polar vortex can explain the observed infrared color–inclination trend and the variability amplitude–inclination trend. The presence of spectrally distinct, time-evolving polar regions in brown dwarfs and giant exoplanet atmospheres raises the possibility that one-dimensional static atmospheric models may be insufficient for reproducing ultracool atmospheres in detail. |
| format | Article |
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| issn | 2041-8205 |
| language | English |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal Letters |
| spelling | doaj-art-22ab875f78e1434d84f1cd634636bfbf2025-08-20T02:18:58ZengIOP PublishingThe Astrophysical Journal Letters2041-82052024-01-019752L3210.3847/2041-8213/ad87e9The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant ExoplanetsNguyen Fuda0https://orcid.org/0000-0002-6372-8395Dániel Apai1https://orcid.org/0000-0003-3714-5855Lunar and Planetary Laboratory, University of Arizona , 1629 E. University Boulevard, Tucson, AZ 85721, USA ; fudanguyen@arizona.eduLunar and Planetary Laboratory, University of Arizona , 1629 E. University Boulevard, Tucson, AZ 85721, USA ; fudanguyen@arizona.edu; Steward Observatory, University of Arizona , 933 N. Cherry Avenue, Tucson, AZ 85721, USARecent studies revealed viewing-angle-dependent color and spectral trends in brown dwarfs, as well as long-term photometric variability (∼100 hr). The origins of these trends are yet unexplained. Here, we propose that these seemingly unrelated sets of observations stem from the same phenomenon: the polar regions of brown dwarfs and directly imaged exoplanets are spectrally different from lower-latitude regions, and they evolve over longer timescales, possibly driven by polar vortices. We explore this hypothesis via a spatiotemporal atmosphere model capable of simulating time series and disk-integrated spectra of ultracool atmospheres. We study three scenarios with different spectral and temporal components: a null hypothesis without polar vortex, and two scenarios with polar vortices. We find that the scenarios with polar vortex can explain the observed infrared color–inclination trend and the variability amplitude–inclination trend. The presence of spectrally distinct, time-evolving polar regions in brown dwarfs and giant exoplanet atmospheres raises the possibility that one-dimensional static atmospheric models may be insufficient for reproducing ultracool atmospheres in detail.https://doi.org/10.3847/2041-8213/ad87e9Brown dwarfsExoplanet atmospheresTime series analysisPlanetary polar regions |
| spellingShingle | Nguyen Fuda Dániel Apai The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant Exoplanets The Astrophysical Journal Letters Brown dwarfs Exoplanet atmospheres Time series analysis Planetary polar regions |
| title | The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant Exoplanets |
| title_full | The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant Exoplanets |
| title_fullStr | The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant Exoplanets |
| title_full_unstemmed | The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant Exoplanets |
| title_short | The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant Exoplanets |
| title_sort | polar vortex hypothesis evolving spectrally distinct polar regions explain short and long term light curve evolution and color inclination trends in brown dwarfs and giant exoplanets |
| topic | Brown dwarfs Exoplanet atmospheres Time series analysis Planetary polar regions |
| url | https://doi.org/10.3847/2041-8213/ad87e9 |
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