VLT/CRIRES+ observations of warm Neptune WASP-107 b: Challenges in detecting molecules with ground-based transmission spectroscopy of cooler and cloudy exoplanets
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| Main Authors: | , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866917435321352192 |
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| author | Boldt-Christmas, Linn Rains, Adam D. Piskunov, Nikolai Nortmann, Lisa Lesjak, Fabio Cont, David Kochukhov, Oleg Hahlin, Axel Lavail, Alexis Marquart, Thomas Heiter, Ulrike Rengel, Miriam Shulyak, Denis Yan, Fei Hatzes, Artie Nagel, Evangelos Reiners, Ansgar Seemann, Ulf |
| author_facet | Boldt-Christmas, Linn Rains, Adam D. Piskunov, Nikolai Nortmann, Lisa Lesjak, Fabio Cont, David Kochukhov, Oleg Hahlin, Axel Lavail, Alexis Marquart, Thomas Heiter, Ulrike Rengel, Miriam Shulyak, Denis Yan, Fei Hatzes, Artie Nagel, Evangelos Reiners, Ansgar Seemann, Ulf |
| contents | Atmospheres of transiting exoplanets can be studied spectroscopically using space-based or ground-based observations. Each has its own strengths and weaknesses, so there are benefits to both approaches. This is especially true for challenging targets such as cooler, smaller exoplanets whose atmospheres likely contain many molecular species and cloud decks.
We aim to study the atmosphere of the warm Neptune-like exoplanet WASP-107 b (Teq~740 K). Several molecular species have been detected in this exoplanet in recent space-based JWST studies, and we aim to confirm and expand upon these detections using ground-based VLT, evaluating how well our findings agree with previously retrieved atmospheric parameters.
We observe two transits of WASP-107 b with VLT/CRIRES+ and create cross-correlation templates of the target atmosphere based on retrieval results from JWST studies. We create different templates to investigate the impact of varying volume mixing ratios of species and inclusion or exclusion of clouds. Considering this target's observational challenges, we create simulated observations prior to evaluating real data to assess expected detection significances.
We report detections of two molecular species, CO (~6 S/N) and H2O (~4.5 S/N). This confirms previous space-based detections and demonstrates, for the first time, the capability of VLT/CRIRES+ to detect species in targets cooler than hot Jupiters using transmission spectroscopy. We show our analysis is sensitive to cloud inclusion, but less so to different volume mixing ratios. Interestingly, our detection deviates from its expected location in our Kp-vsys diagrams, and we speculate on possible reasons for this. We demonstrate that the error budget for relatively cooler exoplanets is severely reduced in comparison to hotter exoplanets, and underline need for further work in context of high-resolution spectroscopy. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_18964 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | VLT/CRIRES+ observations of warm Neptune WASP-107 b: Challenges in detecting molecules with ground-based transmission spectroscopy of cooler and cloudy exoplanets Boldt-Christmas, Linn Rains, Adam D. Piskunov, Nikolai Nortmann, Lisa Lesjak, Fabio Cont, David Kochukhov, Oleg Hahlin, Axel Lavail, Alexis Marquart, Thomas Heiter, Ulrike Rengel, Miriam Shulyak, Denis Yan, Fei Hatzes, Artie Nagel, Evangelos Reiners, Ansgar Seemann, Ulf Earth and Planetary Astrophysics Atmospheres of transiting exoplanets can be studied spectroscopically using space-based or ground-based observations. Each has its own strengths and weaknesses, so there are benefits to both approaches. This is especially true for challenging targets such as cooler, smaller exoplanets whose atmospheres likely contain many molecular species and cloud decks. We aim to study the atmosphere of the warm Neptune-like exoplanet WASP-107 b (Teq~740 K). Several molecular species have been detected in this exoplanet in recent space-based JWST studies, and we aim to confirm and expand upon these detections using ground-based VLT, evaluating how well our findings agree with previously retrieved atmospheric parameters. We observe two transits of WASP-107 b with VLT/CRIRES+ and create cross-correlation templates of the target atmosphere based on retrieval results from JWST studies. We create different templates to investigate the impact of varying volume mixing ratios of species and inclusion or exclusion of clouds. Considering this target's observational challenges, we create simulated observations prior to evaluating real data to assess expected detection significances. We report detections of two molecular species, CO (~6 S/N) and H2O (~4.5 S/N). This confirms previous space-based detections and demonstrates, for the first time, the capability of VLT/CRIRES+ to detect species in targets cooler than hot Jupiters using transmission spectroscopy. We show our analysis is sensitive to cloud inclusion, but less so to different volume mixing ratios. Interestingly, our detection deviates from its expected location in our Kp-vsys diagrams, and we speculate on possible reasons for this. We demonstrate that the error budget for relatively cooler exoplanets is severely reduced in comparison to hotter exoplanets, and underline need for further work in context of high-resolution spectroscopy. |
| title | VLT/CRIRES+ observations of warm Neptune WASP-107 b: Challenges in detecting molecules with ground-based transmission spectroscopy of cooler and cloudy exoplanets |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2508.18964 |