Tighter constraints on the atmosphere of GJ 436 b from combined high-resolution CARMENES and CRIRES$^+$ observations
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Peláez-Torres, A. Sánchez-López, A. Nortmann, L. López-Puertas, M. González-Álvarez, E. Tabernero, H. M. Jiang, C. Revilla, D. Morello, G. Orell-Miquel, J. Pallé, E. Amado, P. J. Caballero, J. A. Ribas, I. Reiners, A. Quirrenbach, A. Cont, D. Dreizler, S. Fernández-Martín, A. Hatzes, A. P. Henning, Th. Lesjak, F. Montes, D. Schweizer, A. Trifonov, T. Yan, F. |
| author_facet | Peláez-Torres, A. Sánchez-López, A. Nortmann, L. López-Puertas, M. González-Álvarez, E. Tabernero, H. M. Jiang, C. Revilla, D. Morello, G. Orell-Miquel, J. Pallé, E. Amado, P. J. Caballero, J. A. Ribas, I. Reiners, A. Quirrenbach, A. Cont, D. Dreizler, S. Fernández-Martín, A. Hatzes, A. P. Henning, Th. Lesjak, F. Montes, D. Schweizer, A. Trifonov, T. Yan, F. |
| contents | We aim to study the atmospheric properties of the warm Neptune GJ 436 b by combining a set of five transit events observed with the CARMENES spectrograph with one transit from CRIRES$^+$ so as to provide the most constrained results possible at high resolution. We removed telluric and stellar signals from the data using SysRem and potential planetary signals were investigated using the cross-correlation technique. Following standard procedures for undetected species, we performed injection recovery tests and Bayesian retrievals to place constraints on the detectability of the main near-infrared absorbers. In addition, we simulated ELT/ANDES observations by computing end-to-end in silico datasets with EXoPLORE. No molecular signals were detected in the atmosphere of GJ 436 b, which is consistent with previous studies. Combined CARMENES-CRIRES$^+$ injection-recovery and Bayesian retrieval analyses show that the atmosphere is likely covered by high-altitude clouds ($\sim$ $1$ mbar) at low and intermediate metallicities or, alternatively, is very metal-rich ($\gtrsim$ $900\times$ solar), which would suppress spectral features without invoking clouds. Simulations of ELT/ANDES observations suggest a boost by nearly an order of magnitude to the upper limit in the photon-limited regime, reaching $0.1$ mbar at $10$-$300\times$ solar metallicities. The joint analysis of all useful transit observations from CARMENES and CRIRES$^+$ provides the most stringent constraints to date on the atmospheric properties of GJ 436 b. Complementary CCF-based and retrieval approaches consistently indicate that the atmosphere is either cloudy or highly metal enriched. Any weak near-infrared absorption lines, if present, are likely to be below current detection limits. However, according to our simulations, these features may be revealed with ELT/ANDES even in single-transit observations. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2512_04161 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Tighter constraints on the atmosphere of GJ 436 b from combined high-resolution CARMENES and CRIRES$^+$ observations Peláez-Torres, A. Sánchez-López, A. Nortmann, L. López-Puertas, M. González-Álvarez, E. Tabernero, H. M. Jiang, C. Revilla, D. Morello, G. Orell-Miquel, J. Pallé, E. Amado, P. J. Caballero, J. A. Ribas, I. Reiners, A. Quirrenbach, A. Cont, D. Dreizler, S. Fernández-Martín, A. Hatzes, A. P. Henning, Th. Lesjak, F. Montes, D. Schweizer, A. Trifonov, T. Yan, F. Earth and Planetary Astrophysics We aim to study the atmospheric properties of the warm Neptune GJ 436 b by combining a set of five transit events observed with the CARMENES spectrograph with one transit from CRIRES$^+$ so as to provide the most constrained results possible at high resolution. We removed telluric and stellar signals from the data using SysRem and potential planetary signals were investigated using the cross-correlation technique. Following standard procedures for undetected species, we performed injection recovery tests and Bayesian retrievals to place constraints on the detectability of the main near-infrared absorbers. In addition, we simulated ELT/ANDES observations by computing end-to-end in silico datasets with EXoPLORE. No molecular signals were detected in the atmosphere of GJ 436 b, which is consistent with previous studies. Combined CARMENES-CRIRES$^+$ injection-recovery and Bayesian retrieval analyses show that the atmosphere is likely covered by high-altitude clouds ($\sim$ $1$ mbar) at low and intermediate metallicities or, alternatively, is very metal-rich ($\gtrsim$ $900\times$ solar), which would suppress spectral features without invoking clouds. Simulations of ELT/ANDES observations suggest a boost by nearly an order of magnitude to the upper limit in the photon-limited regime, reaching $0.1$ mbar at $10$-$300\times$ solar metallicities. The joint analysis of all useful transit observations from CARMENES and CRIRES$^+$ provides the most stringent constraints to date on the atmospheric properties of GJ 436 b. Complementary CCF-based and retrieval approaches consistently indicate that the atmosphere is either cloudy or highly metal enriched. Any weak near-infrared absorption lines, if present, are likely to be below current detection limits. However, according to our simulations, these features may be revealed with ELT/ANDES even in single-transit observations. |
| title | Tighter constraints on the atmosphere of GJ 436 b from combined high-resolution CARMENES and CRIRES$^+$ observations |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2512.04161 |