A Revised Density Estimate for the Largest Known Exoplanet, HAT-P-67 b
Low-density ( ρ _p < 0.1 g cm ^−3 ) hot Saturns are expected to quickly (<100 Myr) lose their atmospheres owing to stellar irradiation, explaining their rarity. HAT-P-67 b seems to be an exception, with ρ _p < 0.09 g cm ^−3 and maintaining its atmosphere to well after 1 Gyr. We present a...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-3881/adcec9 |
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| author | Gavin Wang William O. Balmer Laurent Pueyo Daniel Thorngren Stephen P. Schmidt Le-Chris Wang Kevin C. Schlaufman Guðmundur Stefánsson Zafar Rustamkulov David K. Sing |
| author_facet | Gavin Wang William O. Balmer Laurent Pueyo Daniel Thorngren Stephen P. Schmidt Le-Chris Wang Kevin C. Schlaufman Guðmundur Stefánsson Zafar Rustamkulov David K. Sing |
| author_sort | Gavin Wang |
| collection | DOAJ |
| description | Low-density ( ρ _p < 0.1 g cm ^−3 ) hot Saturns are expected to quickly (<100 Myr) lose their atmospheres owing to stellar irradiation, explaining their rarity. HAT-P-67 b seems to be an exception, with ρ _p < 0.09 g cm ^−3 and maintaining its atmosphere to well after 1 Gyr. We present a photometric and spectroscopic follow-up of HAT-P-67 b to determine how it avoided mass loss. HAT-P-67 b orbits a V = 10.1 evolved F-type star in a 4.81-day orbit. We present new radial velocity observations of the system from the NEID spectrograph on the WIYN 3.5 m Telescope from a follow-up campaign robust to stellar activity. We characterize the activity using photometry and activity indicators, revealing a stellar rotation period (5.40 ± 0.09 days) near HAT-P-67 b’s orbital period. We mitigate the stellar activity using a constrained quasi-periodic Gaussian process through a joint fit of archival ground-based photometry, TESS photometry, and our NEID observations, obtaining a planetary mass of M _p = 0.45 M _J ± 0.15 M _J . Combined with a radius measurement of R _p = 2.140 R _J ± 0.025 R _J , this yields a density of ${\rho }_{p}=0.06{1}_{-0.021}^{+0.020}\,{\rm{g}}\,{{\rm{cm}}}^{-3}$ , making HAT-P-67 b the second-lowest-density hot giant known to date. We find that the recent evolution of the host star caused mass loss for HAT-P-67 b to only recently occur. The planet will be tidally disrupted/engulfed in ∼150–500 Myr, shortly after losing its atmosphere. With rapid atmospheric mass loss, a large helium leading tail, and upcoming observations with the Hubble Space Telescope, HAT-P-67 b is an exceptional target for future studies, for which an updated mass measurement provides important context. |
| format | Article |
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| institution | OA Journals |
| issn | 1538-3881 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| spelling | doaj-art-3a71cd92048a45f2aa5cedfd75deb4b22025-08-20T02:29:04ZengIOP PublishingThe Astronomical Journal1538-38812025-01-01169633610.3847/1538-3881/adcec9A Revised Density Estimate for the Largest Known Exoplanet, HAT-P-67 bGavin Wang0https://orcid.org/0000-0003-3092-4418William O. Balmer1https://orcid.org/0000-0001-6396-8439Laurent Pueyo2https://orcid.org/0000-0003-3818-408XDaniel Thorngren3https://orcid.org/0000-0002-5113-8558Stephen P. Schmidt4https://orcid.org/0000-0001-8510-7365Le-Chris Wang5https://orcid.org/0000-0002-6379-3816Kevin C. Schlaufman6https://orcid.org/0000-0001-5761-6779Guðmundur Stefánsson7https://orcid.org/0000-0001-7409-5688Zafar Rustamkulov8https://orcid.org/0000-0003-4408-0463David K. Sing9https://orcid.org/0000-0001-6050-7645William H. Miller III Department of Physics & Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; gwang59@jhu.eduWilliam H. Miller III Department of Physics & Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; gwang59@jhu.edu; Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USASpace Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USAWilliam H. Miller III Department of Physics & Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; gwang59@jhu.eduWilliam H. Miller III Department of Physics & Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; gwang59@jhu.eduWilliam H. Miller III Department of Physics & Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; gwang59@jhu.eduWilliam H. Miller III Department of Physics & Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; gwang59@jhu.eduAnton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, 1098 XH Amsterdam, The NetherlandsMorton K. Blaustein Department of Earth & Planetary Sciences, Johns Hopkins University , Baltimore, MD 21218, USAWilliam H. Miller III Department of Physics & Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; gwang59@jhu.edu; Morton K. Blaustein Department of Earth & Planetary Sciences, Johns Hopkins University , Baltimore, MD 21218, USALow-density ( ρ _p < 0.1 g cm ^−3 ) hot Saturns are expected to quickly (<100 Myr) lose their atmospheres owing to stellar irradiation, explaining their rarity. HAT-P-67 b seems to be an exception, with ρ _p < 0.09 g cm ^−3 and maintaining its atmosphere to well after 1 Gyr. We present a photometric and spectroscopic follow-up of HAT-P-67 b to determine how it avoided mass loss. HAT-P-67 b orbits a V = 10.1 evolved F-type star in a 4.81-day orbit. We present new radial velocity observations of the system from the NEID spectrograph on the WIYN 3.5 m Telescope from a follow-up campaign robust to stellar activity. We characterize the activity using photometry and activity indicators, revealing a stellar rotation period (5.40 ± 0.09 days) near HAT-P-67 b’s orbital period. We mitigate the stellar activity using a constrained quasi-periodic Gaussian process through a joint fit of archival ground-based photometry, TESS photometry, and our NEID observations, obtaining a planetary mass of M _p = 0.45 M _J ± 0.15 M _J . Combined with a radius measurement of R _p = 2.140 R _J ± 0.025 R _J , this yields a density of ${\rho }_{p}=0.06{1}_{-0.021}^{+0.020}\,{\rm{g}}\,{{\rm{cm}}}^{-3}$ , making HAT-P-67 b the second-lowest-density hot giant known to date. We find that the recent evolution of the host star caused mass loss for HAT-P-67 b to only recently occur. The planet will be tidally disrupted/engulfed in ∼150–500 Myr, shortly after losing its atmosphere. With rapid atmospheric mass loss, a large helium leading tail, and upcoming observations with the Hubble Space Telescope, HAT-P-67 b is an exceptional target for future studies, for which an updated mass measurement provides important context.https://doi.org/10.3847/1538-3881/adcec9Exoplanet astronomyExoplanet tidesExoplanetsExtrasolar gaseous giant planetsRadial velocityStellar activity |
| spellingShingle | Gavin Wang William O. Balmer Laurent Pueyo Daniel Thorngren Stephen P. Schmidt Le-Chris Wang Kevin C. Schlaufman Guðmundur Stefánsson Zafar Rustamkulov David K. Sing A Revised Density Estimate for the Largest Known Exoplanet, HAT-P-67 b The Astronomical Journal Exoplanet astronomy Exoplanet tides Exoplanets Extrasolar gaseous giant planets Radial velocity Stellar activity |
| title | A Revised Density Estimate for the Largest Known Exoplanet, HAT-P-67 b |
| title_full | A Revised Density Estimate for the Largest Known Exoplanet, HAT-P-67 b |
| title_fullStr | A Revised Density Estimate for the Largest Known Exoplanet, HAT-P-67 b |
| title_full_unstemmed | A Revised Density Estimate for the Largest Known Exoplanet, HAT-P-67 b |
| title_short | A Revised Density Estimate for the Largest Known Exoplanet, HAT-P-67 b |
| title_sort | revised density estimate for the largest known exoplanet hat p 67 b |
| topic | Exoplanet astronomy Exoplanet tides Exoplanets Extrasolar gaseous giant planets Radial velocity Stellar activity |
| url | https://doi.org/10.3847/1538-3881/adcec9 |
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