Transmission Spectroscopy of the Lowest-density Gas Giant: Metals and a Potential Extended Outflow in HAT-P-67b
Extremely low-density exoplanets are tantalizing targets for atmospheric characterization because of their promisingly large signals in transmission spectroscopy. We present the first analysis of the atmosphere of the lowest-density gas giant currently known, HAT-P-67b. This inflated Saturn-mass exo...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astronomical Journal |
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| Online Access: | https://doi.org/10.3847/1538-3881/acd935 |
| _version_ | 1797694747288010752 |
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| author | Aaron Bello-Arufe Heather A. Knutson João M. Mendonça Michael M. Zhang Samuel H. C. Cabot Alexander D. Rathcke Ana Ulla Shreyas Vissapragada Lars A. Buchhave |
| author_facet | Aaron Bello-Arufe Heather A. Knutson João M. Mendonça Michael M. Zhang Samuel H. C. Cabot Alexander D. Rathcke Ana Ulla Shreyas Vissapragada Lars A. Buchhave |
| author_sort | Aaron Bello-Arufe |
| collection | DOAJ |
| description | Extremely low-density exoplanets are tantalizing targets for atmospheric characterization because of their promisingly large signals in transmission spectroscopy. We present the first analysis of the atmosphere of the lowest-density gas giant currently known, HAT-P-67b. This inflated Saturn-mass exoplanet sits at the boundary between hot and ultrahot gas giants, where thermal dissociation of molecules begins to dominate atmospheric composition. We observed a transit of HAT-P-67b at high spectral resolution with CARMENES and searched for atomic and molecular species using cross-correlation and likelihood mapping. Furthermore, we explored potential atmospheric escape by targeting H α and the metastable helium line. We detect Ca ii and Na i with significances of 13.2 σ and 4.6 σ , respectively. Unlike in several ultrahot Jupiters, we do not measure a day-to-night wind. The large line depths of Ca ii suggest that the upper atmosphere may be more ionized than models predict. We detect strong variability in H α and the helium triplet during the observations. These signals suggest the possible presence of an extended planetary outflow that causes an early ingress and late egress. In the averaged transmission spectrum, we measure redshifted absorption at the ∼3.8% and ∼4.5% level in the H α and He i triplet lines, respectively. From an isothermal Parker wind model, we derive a mass-loss rate of $\dot{M}\sim {10}^{13}\,{\rm{g}}\,{{\rm{s}}}^{-1}$ and an outflow temperature of T ∼ 9900 K. However, due to the lack of a longer out-of-transit baseline in our data, additional observations are needed to rule out stellar variability as the source of the H α and He signals. |
| first_indexed | 2024-03-12T03:01:17Z |
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| id | doaj.art-93603824381d4862b400f75a1165f725 |
| institution | Directory Open Access Journal |
| issn | 1538-3881 |
| language | English |
| last_indexed | 2024-03-12T03:01:17Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astronomical Journal |
| spelling | doaj.art-93603824381d4862b400f75a1165f7252023-09-03T14:43:41ZengIOP PublishingThe Astronomical Journal1538-38812023-01-0116626910.3847/1538-3881/acd935Transmission Spectroscopy of the Lowest-density Gas Giant: Metals and a Potential Extended Outflow in HAT-P-67bAaron Bello-Arufe0https://orcid.org/0000-0003-3355-1223Heather A. Knutson1https://orcid.org/0000-0002-5375-4725João M. Mendonça2https://orcid.org/0000-0002-6907-4476Michael M. Zhang3https://orcid.org/0000-0002-0659-1783Samuel H. C. Cabot4https://orcid.org/0000-0001-9749-6150Alexander D. Rathcke5https://orcid.org/0000-0002-4227-4953Ana Ulla6https://orcid.org/0000-0001-6424-5005Shreyas Vissapragada7https://orcid.org/0000-0003-2527-1475Lars A. Buchhave8https://orcid.org/0000-0003-1605-5666National Space Institute, Technical University of Denmark , Elektrovej, DK-2800 Kgs. Lyngby, Denmark ; aaron.bello.arufe@jpl.nasa.gov; Division of Geological and Planetary Sciences, California Institute of Technology , 1200 East California Boulevard, Pasadena, CA 91125, USA; Jet Propulsion Laboratory, California Institute of Technology , Pasadena, CA 91109, USADivision of Geological and Planetary Sciences, California Institute of Technology , 1200 East California Boulevard, Pasadena, CA 91125, USANational Space Institute, Technical University of Denmark , Elektrovej, DK-2800 Kgs. Lyngby, Denmark ; aaron.bello.arufe@jpl.nasa.govDepartment of Astronomy, California Institute of Technology , Pasadena, CA 91125, USAYale University , 52 Hillhouse Avenue, New Haven, CT 06511, USACenter for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USAApplied Physics Department, Universidade de Vigo , Campus Lagoas-Marcosende, s/n, E-36310 Vigo, SpainDivision of Geological and Planetary Sciences, California Institute of Technology , 1200 East California Boulevard, Pasadena, CA 91125, USANational Space Institute, Technical University of Denmark , Elektrovej, DK-2800 Kgs. Lyngby, Denmark ; aaron.bello.arufe@jpl.nasa.govExtremely low-density exoplanets are tantalizing targets for atmospheric characterization because of their promisingly large signals in transmission spectroscopy. We present the first analysis of the atmosphere of the lowest-density gas giant currently known, HAT-P-67b. This inflated Saturn-mass exoplanet sits at the boundary between hot and ultrahot gas giants, where thermal dissociation of molecules begins to dominate atmospheric composition. We observed a transit of HAT-P-67b at high spectral resolution with CARMENES and searched for atomic and molecular species using cross-correlation and likelihood mapping. Furthermore, we explored potential atmospheric escape by targeting H α and the metastable helium line. We detect Ca ii and Na i with significances of 13.2 σ and 4.6 σ , respectively. Unlike in several ultrahot Jupiters, we do not measure a day-to-night wind. The large line depths of Ca ii suggest that the upper atmosphere may be more ionized than models predict. We detect strong variability in H α and the helium triplet during the observations. These signals suggest the possible presence of an extended planetary outflow that causes an early ingress and late egress. In the averaged transmission spectrum, we measure redshifted absorption at the ∼3.8% and ∼4.5% level in the H α and He i triplet lines, respectively. From an isothermal Parker wind model, we derive a mass-loss rate of $\dot{M}\sim {10}^{13}\,{\rm{g}}\,{{\rm{s}}}^{-1}$ and an outflow temperature of T ∼ 9900 K. However, due to the lack of a longer out-of-transit baseline in our data, additional observations are needed to rule out stellar variability as the source of the H α and He signals.https://doi.org/10.3847/1538-3881/acd935Exoplanet atmospheric compositionExoplanet atmospheric dynamicsExoplanet atmospheric evolutionHot JupitersHigh resolution spectroscopy |
| spellingShingle | Aaron Bello-Arufe Heather A. Knutson João M. Mendonça Michael M. Zhang Samuel H. C. Cabot Alexander D. Rathcke Ana Ulla Shreyas Vissapragada Lars A. Buchhave Transmission Spectroscopy of the Lowest-density Gas Giant: Metals and a Potential Extended Outflow in HAT-P-67b The Astronomical Journal Exoplanet atmospheric composition Exoplanet atmospheric dynamics Exoplanet atmospheric evolution Hot Jupiters High resolution spectroscopy |
| title | Transmission Spectroscopy of the Lowest-density Gas Giant: Metals and a Potential Extended Outflow in HAT-P-67b |
| title_full | Transmission Spectroscopy of the Lowest-density Gas Giant: Metals and a Potential Extended Outflow in HAT-P-67b |
| title_fullStr | Transmission Spectroscopy of the Lowest-density Gas Giant: Metals and a Potential Extended Outflow in HAT-P-67b |
| title_full_unstemmed | Transmission Spectroscopy of the Lowest-density Gas Giant: Metals and a Potential Extended Outflow in HAT-P-67b |
| title_short | Transmission Spectroscopy of the Lowest-density Gas Giant: Metals and a Potential Extended Outflow in HAT-P-67b |
| title_sort | transmission spectroscopy of the lowest density gas giant metals and a potential extended outflow in hat p 67b |
| topic | Exoplanet atmospheric composition Exoplanet atmospheric dynamics Exoplanet atmospheric evolution Hot Jupiters High resolution spectroscopy |
| url | https://doi.org/10.3847/1538-3881/acd935 |
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