Nick L. J. Cox

Aims . The planetary nebula Tc 1 (PN G345.2–08.8), one of the rare group of Galactic PNe showing fullerene emission in the infrared, is spatially extended with high a surface brightness. Optical imaging spectroscopy enables the line and continuum structure and diagnostics to be examined, and permits a search for any correlations to the presence of fullerene dust. Methods . Tc 1 was observed with MUSE wide field mode with adaptive optics, wavelength range 4700–9300 Å, at three exposure levels to ensure unsaturated emission lines. Extinction, electron temperature ( T _e ), and density ( N _e ) diagnostic images are presented from collisionally excited and recombination line ratios. Results . The nebula has a high surface brightness core, with a diameter 12″, an elliptical ring of major axis 2.8″ around the central star and some low ionization knots, and an extended halo of 55″ in diameter; between the core and halo is an annulus with intermediate properties, including a higher T _e and a lower N _e than in the core. The spectrum of the central star was extracted and fitted by a 31 000 K model atmosphere and is of type O7.5I(f). The image of optical extinction from H Balmer line ratios is highly structured, and shows an annulus, which is adjacent to the core, of low extinction, with values lower than the line-of-sight interstellar extinction. Instrumental effects to account for this anomalously low extinction area were investigated and intrinsic effects from the scattering properties of the nebular dust; neither can entirely explain the low-extinction region and the most likely cause is a local non-standard dust reddening law. This low extinction region additionally shows an anomalously high He I 7281/6678 Å line ratio, possibly caused by a contaminating line, but none have been conclusively identified; its origin remains unresolved. Spectra over extended regions were also analysed and distinct enhancement of the continuum above the expected nebular continuum (as also seen in some other PNe observed with MUSE) was found. Conclusions . The annulus of low extinction occurs outside the region of strongest fullerene emission, in the zone where N _e declines and T _e rises. A change in dust properties linked to conditions in this transition region between the higher density core nebula and lower density halo is deduced.

Context . Hyperspectral-multispectral fusion enhances low-resolution hyperspectral images so that they match high-resolution multi-spectral data. For JWST astronomical imaging, this is challenging because the data dimensionality is extreme, the resolution varies spectrally, the sampling is limited, and there is high noise. Combining an imager and an integral field spectrometer, the MIRI midinfrared instrument on board the JWST creates opportunities for high-definition spectral mapping, but requires joint super-resolution, denoising, and deconvolution. Aims . We developed a simulation pipeline that models the full JWST instrument responses to enable supervised training on realistic synthetic datasets. This framework trains a deep-learning architecture for joint fusion, denoising, and deconvolution of the MIRI imager and Medium Resolution Spectrometer data to reconstruct spatially super-resolved hyperspectral images with full spectral fidelity. Methods . The training relied on synthetic data generated by simulating complete JWST MIRI instrument responses. We then introduced an innovative two-branch neural architecture estimating compact parametric correction functions per pixel. A spline-based branch modeled smooth spectral continua, while a high-frequency branch restored the spectral lines. Results . The method achieves stable optimization on thousands of spectral channels, enables super-resolution beyond the guiding images, and reconstructs broad continua and narrow features under high noise. We report the first deep-learning deconvolution of real JWST MIRI multispectral and hyperspectral images on the reflexion nebula NGC 7023. Conclusions . These results demonstrate the effectiveness of compact parametric fusion for astronomical multispectral and hyperspectral imaging and establish deep learning as a practical tool for JWST data fusion and deconvolution.

We report the detection of a set of new near-infrared emission features between 3.5 and 5.2 μ m in JWST/NIRSpec observations of Tc 1, the planetary nebula known for displaying the cleanest and most prominent mid-infrared cosmic fullerene spectrum. These broad features share the same spatial distribution as the well-known C ₆₀ and C ₇₀ mid-infrared emission bands, peaking in an asymmetric ring approximately 5″–6″ from the central star. Through comparison with new anharmonic quantum chemical calculations, we demonstrate that these features arise from C ₆₀ combination bands, marking their first detection in an astrophysical environment. The total energy radiated in the combination bands amounts to ∼17% of the total energy emitted from all C ₆₀ modes, with direct implications for fullerene cooling models. These near-infrared combination bands offer a promising new window for identifying and studying the molecular astrophysics of C ₆₀ in sources where mid-infrared spectra are more complex.

Cooling fractures found within impact melt deposits have been manually mapped within several craters on the Moon and Mercury, as their distribution can indicate which heat‐loss processes were most significant in the periods after impact. However, due to the discovery of melt deposits in Lunar impact craters with sub‐km diameters, it is unlikely that the complete mapping of these impact melt fractures (IMFs) on the Moon will be achievable without automation. As such, we have trained a DeepLabV3 semantic segmentation deep convolutional neural network, called IMFMapper, to detect IMFs within Lunar Reconnaissance Orbiter Narrow Angle Camera (LROC NAC) satellite imagery. As a means of maximizing the size of the training data set, “weak” pixel‐level labels were generated by buffering line annotations. In testing upon the IMFs found within Ohm crater, IMFMapper achieved an average ‐score of 69.3%. IMFMapper has also been deployed to map IMFs within the previously surveyed Crookes crater, where we have found new candidate melt deposits within the crater's western and southern walls. In addition, IMFMapper has produced the first map of IMFs within Schomberger A crater, in which IMFs may act as permanently shadowed regions due to the crater's proximity to the Lunar South Pole. The successful mapping of IMFs in Schomberger A also signifies IMFMapper's robustness to extreme solar incidence angles. We also demonstrate that IMFMapper could be implemented for automated mapping of IMFs on Mercury upon the commencement of BepiColombo's science operations.

The planetary nebula NGC 6720, also known as the “Ring Nebula,” is one of the most iconic examples of nearby planetary nebulae whose morphologies present a challenge to our theoretical understanding of the processes that govern the deaths of most stars in the Universe that evolve on a Hubble time. We present new imaging with JWST of the central star of this planetary nebula (CSPN) and its close vicinity, in the near-to-mid-IR wavelength range. We find the presence of a dust cloud around the CSPN, both from the spectral energy distribution at wavelengths ≳5 μm as well as from radially extended emission in the 7.7, 10, and 11.3 μm images. From the modeling of these data, we infer that the CSPN has a luminosity of 310 L _⊙ and is surrounded by a dust cloud with a size of ∼2600 au, consisting of relatively small amorphous silicate dust grains (radius ∼0.01 μm) with a total mass of 1.9 × 10⁻⁶ M _⊕. However, our best-fit model shows a significant lack of extended emission at 7.7 μm—we show that such emission can arise from a smaller (7.3 × 10⁻⁷ M _⊕) but uncertain mass of (stochastically heated) ionized polycyclic aromatic hydrocarbon (PAHs). However, the same energetic radiation also rapidly destroys PAH molecules, suggesting that these are most likely being continuously replenished, via the outgassing of cometary bodies and/or the collisional grinding of planetesimals. We also find significant photometric variability of the central source that could be due to the presence of a close dwarf companion of mass ≤0.1 M _⊙.

Context. Numerous studies of diffuse interstellar band (DIB) profiles have detected substructures, which in turn suggests that large molecules are acting as their carriers. However, some of the narrowest DIBs generally do not show such substructures, suggesting the possibility of very small carriers. Aims. Based on the previously found tight correlation of the three narrow DIBs at 6196, 6440, and 6623 Å and the present detection of weaker side DIBs to each of them in the extensive dataset from the ESO Diffuse Interstellar Bands Large Exploration Survey, we investigated whether they may stem from small linear carrier molecules. This approach can lead to concrete DIB carrier suggestions, which can be tested in laboratory measurements in future studies. Methods. We suggest that the DIBs we studied here represent individual rotational transitions of a small molecule. We determined the molecular constants from observations and compared them with data from a large set of quantum-chemical calculations to constrain possible carrier candidates. Furthermore, we determined the rotational temperatures by fitting line ratios using the fitted molecular models. Results. We determined molecular constants for three DIB systems and the corresponding transition types. The fitted rotational temperatures lie within the range of known interstellar diatomic molecules. We identified several DIB carrier candidates, almost all of them molecular ions. Some of them are metastable species, indicating the possibility of collision complexes as DIB carriers. Conclusions. If our hypothesis holds, this would be a major step towards the identification of a carrier molecule of the 6196 Å DIB, the strongest among the narrow DIBs.

Context. Three-dimensional (3D) distributions of the 862 nm diffuse interstellar band (DIB) carrier have been computed based on Gaia parallaxes and DIB catalogues, in parallel with 3D maps of dust extinction density. Three-dimensional maps provide local diagnostics and information on the distribution of structures in addition to line-of-sight (LOS) integrated quantities, and allow us to focus on poorly studied low-extinction areas. They make cross-matching with other catalogues possible through estimates of the DIB and extinction along any given path. Aims. We re-examined the relationships between the density of DIB carriers and the absorption and emission properties of spatially co-located dust. Along with laboratory identifications of carriers, these properties may shed light on the formation and evolution of this organic matter. They may also help to model dust emission and absorption properties in a more detailed way. Methods. We used the 3D maps of 862 nm DIBs and of dust extinction, as well as available DIB equivalent width (EW) catalogues and published measurements of parameters characterizing the dust extinction law and the dust emission. We studied the relationships between the extinction-normalized 862 nm DIB EW and the extinction level, the total-to-selective extinction ratio R_V, and the dust far-IR emission spectral index β. We re-visited the link between several DIBs and the UV absorption bump at 220 nm. Results. The ratio of the 862 nm DIB carrier density to the optical extinction density (DIB_norm⁸⁶²) is increasing in low-density clouds, confirming with local values the trend seen in the LOS data. In both cases, the coefficients of a fitted power law fall within the range of those measured towards SDSS high-latitude targets for 20 different bands, ranking this DIB among those with a high increase, above that of the broad 4430 Å DIB. This is consistent with the recent measurement of a larger scale height above the Plane for the 862 nm DIB compared to that of the 4430 Å DIB. Using map-integrated 862 nm DIB EWs and extinctions along the paths to APOGEE targets with published proxies R′_V for the total-to-selective extinction ratio, we found that, despite a large scatter, DIB_norm⁸⁶² is positively correlated with R′_V for those stars with low to moderate extinctions (A_V = 0.2 to 2–3 mag). Independently, using stars from the 862 nm DIB catalogue located outside the disk and for the same regime of extinction, DIB_norm⁸⁶² is found to be globally anti-correlated with the Planck opacity spectral index β. This is consistent with the observed anti-correlation between β and R′_V. In the light of a recent result on the variability of the carbon/silicate ratio in dust grains as a source of this anti-correlation, it suggests that DIB_norm⁸⁶² increases with the fraction of carbonaceous to silicate grains in the co-located dust, in agreement with the carbonaceous nature of DIB carriers and recent evidences for a spatial correlation between DIB_norm⁸⁶² and the fluxes of carbon-rich ejecta of asymptotic giant branch (AGB) stars. At higher extinction both trends disappear, and there is evidence for a trend reversal. Regarding the link between the height of the 220 nm UV absorption bump and extinction-normalized EWs of DIBs, we found that two factors explain the absence of previous clear results: the correlation disappears when we move from σ-type to ζ-type DIBs and/or from single-cloud LOSs to paths crossing multiple clouds distant from each other; ζ-type bands can be used to predict low and high values of the bump height, provided one adds a correcting factor linked to the ambient radiation field (e.g. the 5780/5797 DIB ratio). We show examples of simple models of the bump height based on the 5780 Å band, the 5850 Å band and the 5780/5797 DIB ratio. We also found an anti-correlation between DIB_norm and the width of the bump, which similarly disappears from σ-type to ζ-type DIBs. This suggests that a fraction of the bump is generated outside the dense molecular clouds. Conclusions. There are complex relationships between DIBs and dust; however, massive measurements of DIBs and extinction and the derived 3D maps may provide some constraints on the density, the nature, and the contribution to extinction and emission of the co-located dust. This requires large stellar spectroscopic surveys and space-based measurements of UV extinction.

Context. The carbonaceous macromolecules imprinting the numerous absorptions called diffuse interstellar bands (DIBs) in astronomical spectra are omnipresent in the Galaxy and beyond. They represent a considerable reservoir of organic matter. However, their chemical formulae, formation, and destruction sites remain unknown. Their spatial distribution and the local relation to other interstellar species is key to tracing their role in the lifecycle of organic matter. Aims. Volume density maps bring local instead of line-of-sight distributed information and allow for new diagnostics to be captured. We present the first large-scale volume (3D) density map of a DIB carrier and compare it with an equivalent map of interstellar dust. Methods. The DIB carrier map was obtained through hierarchical inversion of ~202 000 measurements of the 8621 nm DIB obtained with the Gaia-RVS instrument. It covers about 4000 pc around the Sun in the Galactic plane. We built a dedicated interstellar dust map based on the extinction towards the same target stars. Results. At the ≃50 pc resolution of the maps, the shape of the 3D DIB distribution is found to be remarkably similar to the 3D distribution of dust. On the other hand, the DIB-to-dust local density ratio increases in low-dust areas. It is also increasing away from the disk, however, the minimum ratio is found to be shifted above the Galactic plane to Z=≃+50pc. Finally, the average ratio is also surprisingly found to increase away from the Galactic Center. We suggest that the three latter trends may be indications of a dominant contribution of material from the carbon-rich category of dying giant stars to the formation of the carriers. Our suggestion is based on recent catalogs of asymptotic giant branch (AGB) stars and estimates of the mass fluxes of their C-rich and O-rich ejecta.

Background Identifying stars belonging to different classes is vital in order to build up statistical samples of different phases and pathways of stellar evolution. In the era of surveys covering billions of stars, an automated method of identifying these classes becomes necessary. Methods Many classes of stars are identified based on their emitted spectra. In this paper, we use a combination of the multi-class multi-label Machine Learning (ML) method XGBoost and the PySSED spectral-energy-distribution fitting algorithm to classify stars into nine different classes, based on their photometric data. The classifier is trained on subsets of the SIMBAD database. Particular challenges are the very high sparsity (large fraction of missing values) of the underlying data as well as the high class imbalance. We discuss the different variables available, such as photometric measurements on the one hand, and indirect predictors such as Galactic position on the other hand. Results We show the difference in performance when excluding certain variables, and discuss in which contexts which of the variables should be used. Finally, we show that increasing the number of samples of a particular type of star significantly increases the performance of the model for that particular type, while having little to no impact on other types. The accuracy of the main classifier is ∼0.7 with a macro F1 score of 0.61. Conclusions While the current accuracy of the classifier is not high enough to be reliably used in stellar classification, this work is an initial proof of feasibility for using ML to classify stars based on photometry.

With the increasing number of ongoing space missions for Earth Observation (EO), there is a need to enhance data products by combining observations from various remote sensing instruments. We introduce a new Transformer-based approach for data fusion, achieving up to a 10- to-30-fold increase in the spatial resolution of our hyperspectral data. We trained the network on a synthetic set of Sentinel-2 (S2) and Sentinel-3 (S3) images, simulated from the hyperspectral mission EnMAP (30 m resolution), leading to a fused product of 21 bands at a 30 m ground resolution. The performances were calculated by fusing original S2 (12 bands, 10, 20, and 60 m resolutions) and S3 (21 bands, 300 m resolution) images. To go beyond EnMap’s ground resolution, the network was also trained using a generic set of non-EO images from the CAVE dataset. However, we found that training the network on contextually relevant data is crucial. The EO-trained network significantly outperformed the non-EO-trained one. Finally, we observed that the original network, trained at 30 m ground resolution, performed well when fed images at 10 m ground resolution, likely due to the flexibility of Transformer-based networks.