An absolute mass, precise age, and hints of planetary winds for WASP-121 A and b from a JWST NIRSpec phase curve
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| Format: | Preprint |
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2025
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| _version_ | 1866913639261274112 |
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| author | Sing, David K. Evans-Soma, Thomas M. Rustamkulov, Zafar Lothringer, Joshua D. Mayne, Nathan J. Schlaufman, Kevin C. |
| author_facet | Sing, David K. Evans-Soma, Thomas M. Rustamkulov, Zafar Lothringer, Joshua D. Mayne, Nathan J. Schlaufman, Kevin C. |
| contents | We have conducted a planetary radial velocity measurement of the ultra-hot Jupiter WASP-121b using JWST NIRSpec phase curve data. Our analysis reveals the Doppler shift of the planetary spectral lines across the full orbit, which shifts considerably across the detector ($\sim$ 10 pixels). Using cross-correlation techniques, we have determined an overall planetary velocity amplitude of $K_{\rm p}=215.7\pm1.1$ km/s, which is in good agreement with the expected value. We have also calculated the dynamical mass for both components of the system by treating it as an eclipsing double-line spectroscopic binary, with WASP-121A having a mass of M$_{\star}$=1.330 $\pm$ 0.019 M$_{\odot}$, while WASP-121b has a mass of M$_{\rm p}$= 1.170 $\pm$ 0.043 M$_{\rm Jup}$. These dynamical measurements are $\sim3\times$ more precise than previous estimates and do not rely on any stellar modeling assumptions which have a $\sim$5\% systematic floor mass uncertainty. Additionally, we used stellar evolution modeling constrained with a stellar density and parallax measurement to determine a precise age for the system, found to be 1.11 $\pm$ 0.14 Gyr. Finally, we observed potential velocity differences between the two NIRSpec detectors, with NRS1 lower by 5.5$\pm$2.2 km/s. We suggest that differences can arise from day/night asymmetries in the thermal emission, which can lead to a sensitivity bias favoring the illuminated side of the planet, with planetary rotation and winds both acting to lower a measured $K_{\rm P}$. The planet's rotation can account for 1 km/s of the observed velocity difference, with 4.5$\pm$2.2 km/s potentially attributable to vertical differences in wind speeds. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2501_03844 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | An absolute mass, precise age, and hints of planetary winds for WASP-121 A and b from a JWST NIRSpec phase curve Sing, David K. Evans-Soma, Thomas M. Rustamkulov, Zafar Lothringer, Joshua D. Mayne, Nathan J. Schlaufman, Kevin C. Earth and Planetary Astrophysics Solar and Stellar Astrophysics We have conducted a planetary radial velocity measurement of the ultra-hot Jupiter WASP-121b using JWST NIRSpec phase curve data. Our analysis reveals the Doppler shift of the planetary spectral lines across the full orbit, which shifts considerably across the detector ($\sim$ 10 pixels). Using cross-correlation techniques, we have determined an overall planetary velocity amplitude of $K_{\rm p}=215.7\pm1.1$ km/s, which is in good agreement with the expected value. We have also calculated the dynamical mass for both components of the system by treating it as an eclipsing double-line spectroscopic binary, with WASP-121A having a mass of M$_{\star}$=1.330 $\pm$ 0.019 M$_{\odot}$, while WASP-121b has a mass of M$_{\rm p}$= 1.170 $\pm$ 0.043 M$_{\rm Jup}$. These dynamical measurements are $\sim3\times$ more precise than previous estimates and do not rely on any stellar modeling assumptions which have a $\sim$5\% systematic floor mass uncertainty. Additionally, we used stellar evolution modeling constrained with a stellar density and parallax measurement to determine a precise age for the system, found to be 1.11 $\pm$ 0.14 Gyr. Finally, we observed potential velocity differences between the two NIRSpec detectors, with NRS1 lower by 5.5$\pm$2.2 km/s. We suggest that differences can arise from day/night asymmetries in the thermal emission, which can lead to a sensitivity bias favoring the illuminated side of the planet, with planetary rotation and winds both acting to lower a measured $K_{\rm P}$. The planet's rotation can account for 1 km/s of the observed velocity difference, with 4.5$\pm$2.2 km/s potentially attributable to vertical differences in wind speeds. |
| title | An absolute mass, precise age, and hints of planetary winds for WASP-121 A and b from a JWST NIRSpec phase curve |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2501.03844 |