The NUV transit of XO-3 b
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| Main Authors: | , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866913153718157312 |
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| author | Cilley, Raven Corrales, Lia King, George W. Dong, Jiayin Frazier, Robert Miyakawa, Kohei Fukui, Akihiko Hirano, Teruyuki Becker, Juliette Sikora, James T. Dang, Lisa |
| author_facet | Cilley, Raven Corrales, Lia King, George W. Dong, Jiayin Frazier, Robert Miyakawa, Kohei Fukui, Akihiko Hirano, Teruyuki Becker, Juliette Sikora, James T. Dang, Lisa |
| contents | Near-UV (NUV) measurements of exoplanet transits offer a means to probe atmospheric escape, cloud formation, and planetary magnetic fields. We examine a 2024 XMM-Newton Optical Monitor NUV observation of the transit of XO-3~b, a massive hot Jupiter on an eccentric orbit with a previously observed abnormally large NUV-absorbing atmosphere. We analyze this NUV data jointly with a concurrent ground-based optical observation and all TESS transit observations, and find a NUV transit depth of $R_{p,NUV}/R_{\star} = 0.1371^{+0.016}_{-0.019}$, which is 30-70% deeper than the optical transit. Although the optical transits do not show signs of transit timing variations, the transit center in the NUV is $22^{+13}_{-11}$ minutes late compared to the optical ephemeris. We investigate atmospheric escape as a potential explanation of the properties of this NUV transit by examining X-ray data from XMM-Newton, characterizing the X-ray luminosity of XO-3 for the first time and estimating an extremely small mass-loss rate of $\sim10^4$ g/s ($\sim10^{-19}$ M$_{\text{jup}}$/yr). Finally, we investigate the likelihood of an NUV-absorbent bow-shock by estimating the magnetic field of the planet. While such a mechanism is capable of producing NUV transit offsets on the order of tens of minutes, our analytic approximations predict an early rather than late transit, indicating a need for further magnetohydrodynamic simulations. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_05068 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The NUV transit of XO-3 b Cilley, Raven Corrales, Lia King, George W. Dong, Jiayin Frazier, Robert Miyakawa, Kohei Fukui, Akihiko Hirano, Teruyuki Becker, Juliette Sikora, James T. Dang, Lisa Earth and Planetary Astrophysics Near-UV (NUV) measurements of exoplanet transits offer a means to probe atmospheric escape, cloud formation, and planetary magnetic fields. We examine a 2024 XMM-Newton Optical Monitor NUV observation of the transit of XO-3~b, a massive hot Jupiter on an eccentric orbit with a previously observed abnormally large NUV-absorbing atmosphere. We analyze this NUV data jointly with a concurrent ground-based optical observation and all TESS transit observations, and find a NUV transit depth of $R_{p,NUV}/R_{\star} = 0.1371^{+0.016}_{-0.019}$, which is 30-70% deeper than the optical transit. Although the optical transits do not show signs of transit timing variations, the transit center in the NUV is $22^{+13}_{-11}$ minutes late compared to the optical ephemeris. We investigate atmospheric escape as a potential explanation of the properties of this NUV transit by examining X-ray data from XMM-Newton, characterizing the X-ray luminosity of XO-3 for the first time and estimating an extremely small mass-loss rate of $\sim10^4$ g/s ($\sim10^{-19}$ M$_{\text{jup}}$/yr). Finally, we investigate the likelihood of an NUV-absorbent bow-shock by estimating the magnetic field of the planet. While such a mechanism is capable of producing NUV transit offsets on the order of tens of minutes, our analytic approximations predict an early rather than late transit, indicating a need for further magnetohydrodynamic simulations. |
| title | The NUV transit of XO-3 b |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2605.05068 |