The ExoMol database (www.exomol.com) provides extensive line lists of molecular transitions which are valid over extended temperature ranges. The status of the current release of the database is reviewed and a new data structure is specified. This structure augments the provision of energy levels (and hence transition frequencies) and Einstein A coefficients with other key properties, including lifetimes of individual states, temperature-dependent cooling functions, Land? g-factors, partition functions, cross sections, k-coefficients and transition dipoles with phase relations. Particular attention is paid to the treatment of pressure broadening parameters. The new data structure includes a definition file which provides the necessary information for utilities accessing ExoMol through its application programming interface (API). Prospects for the inclusion of new species into the database are discussedPeer reviewe

The study of exoplanetary atmospheres relies on detecting minute changes in the transit depth at different wavelengths. To date, a number of ground- and space-based instruments have been used to obtain transmission spectra of exoplanets in different spectral bands. One common practice is to combine observations from different instruments in order to achieve a broader wavelength coverage. We present here two inconsistent observations of WASP-96 b, one by the Hubble Space Telescope (HST) and the other by the Very Large Telescope (VLT). We present two key findings in our investigation: (1) a strong water signature is detected via the HST WFC3 observations and (2) a notable offset in transit depth (>1100 ppm) can be seen when the ground-based and space-based observations are combined. The discrepancy raises the question of whether observations from different instruments could indeed be combined. We attempt to align the observations by including an additional parameter in our retrieval studies but are unable to definitively ascertain that the aligned observations are indeed compatible. The case of WASP-96 b signals that compatibility of instruments should not be assumed. While wavelength overlaps between instruments can help, it should be noted that combining data sets remains risky business. The difficulty of combining observations also strengthens the need for next-generation instruments that possess broader spectral coverage.

Rotation-vibration energy levels are determined for the electronic ground state of the acetylene molecule, $^{12}$C$_2$H$_2$, using the Measured Active Rotational-Vibrational Energy Levels (MARVEL) technique. 37,813 measured transitions from 61 publications are considered. The distinct components of the spectroscopic network linking ortho and para states are considered separately. The 20,717 ortho and 17,096 para transitions measured experimentally are used to determine 6013 ortho and 5200 para energy levels. The MARVEL results are compared with alternative compilations based on the use of effective Hamiltonians.Comment: 55 pages, 8 figures, JQSRT, 201

For solar system objects, ultraviolet spectroscopy has been critical in identifying sources of stratospheric heating and measuring the abundances of a variety of hydrocarbon and sulfur-bearing species, produced via photochemical mechanisms, as well as oxygen and ozone. To date, fewer than 20 exoplanets have been probed in this critical wavelength range (0.2–0.4 μm). Here we use data from Hubble’s newly implemented WFC3 UVIS G280 grism to probe the atmosphere of the hot Jupiter HAT-P-41b in the ultraviolet through optical in combination with observations at infrared wavelengths. We analyze and interpret HAT-P-41b’s 0.2–5.0 μm transmission spectrum using a broad range of methodologies including multiple treatments of data systematics as well as comparisons with atmospheric forward, cloud microphysical, and multiple atmospheric retrieval models. Although some analysis and interpretation methods favor the presence of clouds or potentially a combination of Na, VO, AlO, and CrH to explain the ultraviolet through optical portions of HAT-P-41b’s transmission spectrum, we find that the presence of a significant H⁻ opacity provides the most robust explanation. We obtain a constraint for the abundance of H⁻, , in HAT-P-41b’s atmosphere, which is several orders of magnitude larger than predictions from equilibrium chemistry for a ∼1700–1950 K hot Jupiter. We show that a combination of photochemical and collisional processes on hot hydrogen-dominated exoplanets can readily supply the necessary amount of H⁻ and suggest that such processes are at work in HAT-P-41b and the atmospheres of many other hot Jupiters.

We present a new optical transmission spectrum of the hot Jupiter WASP-79b. We observed three transits with the STIS instrument mounted on the Hubble Space Telescope (HST), spanning 0.3–1.0 μm. Combining these transits with previous observations, we construct a complete 0.3–5.0 μm transmission spectrum of WASP-79b. Both HST and ground-based observations show decreasing transit depths toward blue wavelengths, contrary to expectations from Rayleigh scattering or hazes. We infer atmospheric and stellar properties from the full near-UV to infrared transmission spectrum of WASP-79b using three independent retrieval codes, all of which yield consistent results. Our retrievals confirm previous detections of H₂O (at 4.0σ confidence) while providing moderate evidence of H⁻ bound–free opacity (3.3σ) and strong evidence of stellar contamination from unocculted faculae (4.7σ). The retrieved H₂O abundance (∼1%) suggests a superstellar atmospheric metallicity, though stellar or substellar abundances remain consistent with present observations (O/H = 0.3–34× stellar). All three retrieval codes obtain a precise H⁻ abundance constraint: log( X H − ) ≈ −8.0 ± 0.7. The potential presence of H⁻ suggests that James Webb Space Telescope observations may be sensitive to ionic chemistry in the atmosphere of WASP-79b. The inferred faculae are ∼500 K hotter than the stellar photosphere, covering ∼15% of the stellar surface. Our analysis underscores the importance of observing UV–optical transmission spectra in order to disentangle the influence of unocculted stellar heterogeneities from planetary transmission spectra.

Aims. Our goal is to create a retrieval framework which encapsulates the three-dimensional (3D) nature of exoplanet atmospheres, and to apply it to observed emission phase curve and transmission spectra of the ‘hot Jupiter’ exoplanet WASP-43b. Methods. We present our 3D framework, which is freely available as a stand-alone module from GitHub. We use the atmospheric modelling and Bayesian retrieval package ARCiS (ARtful modelling Code for exoplanet Science) to perform a series of eight 3D retrievals on simultaneous transmission (HST/WFC3) and phase-dependent emission (HST/WFC3 and Spitzer/IRAC) observations of WASP-43b as a case study. Via these retrieval setups, we assess how input assumptions affect our retrieval outcomes. In particular we look at constraining equilibrium chemistry vs. a free molecular retrieval, the case of no clouds vs. parametrised clouds, and using Spitzer phase data that have been reduced from two different literature sources. For the free chemistry retrievals, we retrieve abundances of H₂O, CH₄, CO, CO₂, AlO, and NH₃ as a function of phase, with many more species considered for the equilibrium chemistry retrievals. Results. We find consistent super-solar C/O (0.6–0.9) and super-solar metallicities (1.7–2.9 dex) for all retrieval setups that assume equilibrium chemistry. We find that atmospheric heat distribution, hotspot shift (≈15.6° vs. 4.5° for the different Spitzer datasets), and temperature structure are very influenced by the choice of Spitzer emission phase data. We see some trends in molecular abundances as a function of phase, in particular for CH₄ and H₂O. Comparisons are made with other studies of WASP-43b, including global climate model (GCM) simulations, available in the literature. Conclusions. The parametrised 3D setup we have developed provides a valuable tool to analyse extensive observational datasets such as spectroscopic phase curves. We conclude that further near-future observations with missions such as the James Webb Space Telescope and Ariel will greatly improve our understanding of the atmospheres of exoplanets such as WASP-43b. This is particularly evident from the effect that the current phase-dependent Spitzer emission data has on retrieved atmospheres.