Using JWST/MIRI observations, we report the detection of CO2 ice in the dusty torus of the planetary nebula NGC 6302, an environment generally considered hostile to fragile molecular species and ices due to intense UV irradiation. This detection accompanies cold (20-50 K) gas-phase CO(2 )along the same sightlines. The ice absorption profile exhibits a double-peak profile, which is characteristic of pure crystalline CO(2 )ice. The CO(2 )gas-to-ice ratio is higher by more than an order of magnitude than in young stellar objects, which indicates distinct ice formation or processing mechanisms in evolved stellar environments. This discovery demonstrates that the dusty torus provides sufficient shielding to harbor ice chemistry, and that ice-mediated surface reactions must be incorporated into chemical models of planetary nebulae.

We investigate the evolution of the PAH population's charge state and size across key physical zones in the Orion Bar, which include the HII region, the atomic PDR (APDR), and three HI/H2 dissociation fronts (DF1, DF2, and DF3). Utilising the NASA Ames PAH Infrared Spectroscopic Database (PAHdb) and the pyPAHdb spectral modelling tool, we analysed the MIRI-MRS observations of the Orion Bar from the "PDRs4All" ERS Program. pyPAHdb modelling reveals the fractional contribution of the different PAH charge states and sizes to the total PAH emission across the Orion Bar. Cationic PAH emission peaks in the APDR region, where neutral PAHs have minimal contribution. Emission from neutral PAHs peaks in the HII region that consists of emission from a face-on PDR associated to the background OMC-1 molecular cloud, and in the molecular cloud regions past DF2. PAH anions are observed deep within the DF2 and DF3 zones. The average PAH size ranges between 60-74 Nc. The modelling reveals regions of top-down PAH formation at the ionisation front, and bottom-up PAH formation within the molecular cloud region. The PAH ionisation parameter γ ranges between 2-9 x 10^4. Intensity ratios tracing PAH ionisation scale well with γ in regions encompassing edge-on or face-on PDR emission, but their correlation weakens within the molecular cloud zone. Modelling of the 5-15 μm PAH spectrum with pyPAHdb achieves comprehensive characterization of the net contribution of neutral and cationic PAHs across different environments, whereas empirical PAH proxy intensity ratio tracers can be highly variable and unreliable outside regions dominated by PDR emission. The derived average PAH size in the different physical zones is consistent with a view of PAHs being more extensively subjected to ultraviolet processing closer to the ionisation front, and less affected within the molecular cloud.

Context. Infrared emission from polycyclic aromatic hydrocarbons (PAHs) plays a major role in determining the charge balance of their host environments that include photodissociation regions (PDRs) in galaxies, planetary nebulae, and rims of molecular clouds.Aims. We aim to investigate the distribution and sizes of charged PAHs across the key zones of the Orion Bar PDR, i.e., the ionization front, the atomic PDR, and the dissociation fronts. Methods. We employed JWST MIRI-MRS observations of the Orion Bar from the Early Release Science program "PDRs4All" and synthetic images in the JWST MIRI filters. We investigated the spatial morphology of the aromatic infrared bands (AIBs) at 6.2, 7.7, 8.6, and 11.0 mu m (commonly tracing PAH cations) and the neutral PAH-tracing 11.2 mu m AIB, their (relative) correlations, and their relationship with existing empirical prescriptions for AIBs. Results. The 6.2, 7.7, 8.6, 11.0, and 11.2 mu m AIBs are similar in spatial morphology on larger scales. Aside from the 11.0 mu m AIB, these AIBs exhibit enhanced intensities at the dissociation fronts. Analyzing three-feature intensity correlations, two distinct groups emerge: the 8.6 and 11.0 mu m AIBs versus the 6.2 and 7.7 mu m AIBs. We attribute these correlations to PAH size. The 6.2 and 7.7 mu m AIBs trace cationic, medium-sized PAHs. Quantum chemical calculations reveal that the 8.6 mu m AIB is carried by large, compact, cationic PAHs, and the 11.0 mu m AIB's correlation with it implies that this band is as well. The 6.2/8.6 and 7.7/8.6 PAH band ratios thus probe PAH size. We conclude that the 6.2/11.2 AIB ratio is the most reliable proxy for charged PAHs within the cohort. We outline JWST MIRI imaging prescriptions that serve as effective tracers of the PAH ionization fraction, as traced by the 7.7/11.2 PAH emission. Conclusions. This study showcases the efficacy of the 6-9 mu m AIBs in probing the charge state and size distribution of emitting PAHs, offering insights into the physical conditions of their host environments. JWST MIRI photometry offers a viable alternative to IFU spectroscopy for characterizing this emission in extended objects.

Context. Infrared emission from polycyclic aromatic hydrocarbons (PAHs) plays a major role in determining the charge balance of their host environments that include photodissociation regions (PDRs) in galaxies, planetary nebulae, and rims of molecular clouds. Aims. We aim to investigate the distribution and sizes of charged PAHs across the key zones of the Orion Bar PDR, i.e., the ionization front, the atomic PDR, and the dissociation fronts. Methods. We employed JWST MIRI-MRS observations of the Orion Bar from the Early Release Science program “PDRs4All” and synthetic images in the JWST MIRI filters. We investigated the spatial morphology of the aromatic infrared bands (AIBs) at 6.2, 7.7, 8.6, and 11.0 μm (commonly tracing PAH cations) and the neutral PAH-tracing 11.2 μm AIB, their (relative) correlations, and their relationship with existing empirical prescriptions for AIBs. Results. The 6.2, 7.7, 8.6, 11.0, and 11.2 μm AIBs are similar in spatial morphology on larger scales. Aside from the 11.0 μm AIB, these AIBs exhibit enhanced intensities at the dissociation fronts. Analyzing three-feature intensity correlations, two distinct groups emerge: the 8.6 and 11.0 μm AIBs versus the 6.2 and 7.7 μm AIBs. We attribute these correlations to PAH size. The 6.2 and 7.7 μm AIBs trace cationic, medium-sized PAHs. Quantum chemical calculations reveal that the 8.6 μm AIB is carried by large, compact, cationic PAHs, and the 11.0 μm AIB's correlation with it implies that this band is as well. The 6.2/8.6 and 7.7/8.6 PAH band ratios thus probe PAH size. We conclude that the 6.2/11.2 AIB ratio is the most reliable proxy for charged PAHs within the cohort. We outline JWST MIRI imaging prescriptions that serve as effective tracers of the PAH ionization fraction, as traced by the 7.7/11.2 PAH emission. Conclusions. This study showcases the efficacy of the 6−9 μm AIBs in probing the charge state and size distribution of emitting PAHs, offering insights into the physical conditions of their host environments. JWST MIRI photometry offers a viable alternative to IFU spectroscopy for characterizing this emission in extended objects.

Conspicuous excess emission is present in the near-infrared (NIR) region in various objects, including reflection nebulae, planetary nebulae, and nearby galaxies. However, the spatial distribution and spectral shape of the excess emission remain poorly understood. We studied the NIR continuum emission spectroscopically and obtained its spatial distribution relative to the aromatic infrared band (AIB) at 3.3um in the Orion Bar prototypical photodissociation region (PDR). We aim to characterize its spectral shape and discuss its origin. We employed 3D spectroscopic data of the Orion Bar taken with the integrated field unit of NIRSpec on JWST from the Early Release Science program "PDRs4All." Contribution from the foreground ionized gas was estimated using the Cloudy code and subtracted. The observed regions were divided into nine physically distinct regions and an average spectrum was derived for each region. The nine regions, including the ionized gas, atomic PDR, and molecular PDR, clearly show remaining continuum in the region 1–4.5um. The continuum at wavelengths longer than 2.7um shows good correlations with the 3.3um AIB, while the correlation of the continuum at 1.2um is not significant. We further find that the NIR continuum in the Orion Bar can be approximated by a summation of two blackbodies. The low-temperature component correlates with the AIB well, while the high-temperature component does not. The average spectra also show absorption features at 3.0 and 4.27um, which are attributed to the presence in the spectra of water ice and CO2 ice. We discuss possible origins of the NIR continuum, among which recurrent fluorescence from carbon clusters better explains the observed low-temperature component. The presence of ice species suggests a contribution from a deeper layer of the PDR along the line of sight producing characteristic ice absorption features.

Context. JWST observations of the Orion Bar have revealed rich and diverse polycyclic aromatic hydrocarbon (PAH) emission. These observations allow for the first time a comprehensive characterisation of the charge state and size of the PAH population on morphologically resolved photodissociation regions (PDR) scales, properties closely linked to physical conditions of their inhabiting environments. Aims. We investigate the evolution of the PAH population's charge state and size across key physical zones in the Orion Bar, which include the H ii region, the atomic PDR (APDR), and three bright H I/H-2 dissociation fronts (DF1, DF2, and DF3). We connect changes in the PAH charge and size as probed by empirical emission proxies with the varying physical properties of their surrounding environments. Methods. Utilising the NASA Ames PAH Infrared Spectroscopic Database (PAHdb) and the pyPAHdb spectral modelling tool, we analysed the MIRI-MRS observations of the Orion Bar from the 'PDRs4All' JWST Early Release Science Program. Decomposition and modelling were performed on the 5-15 mu m spectrum across the entire JWST mosaic, as well as on the weighted average spectra of the five key physical zones. Results. pyPAHdb modelling reveals the fractional contribution of the different PAH charge states and sizes to the total PAH emission across the Orion Bar. Cationic PAH emission peaks in the APDR region, where neutral PAHs make a minimal contribution. Emission from neutral PAHs peaks in the H ii region that consists of emission from a face-on PDR associated with the background OMC-1 molecular cloud, and in the molecular cloud regions past DF2. The PAH anions are observed deep within the DF2 and DF3 zones. Small and medium-sized PAHs make up similar to 70% of the PAH emission across the mosaic, with the peak of the small PAH emission found between the DF2 and DF3 zones. The average PAH size in the Orion Bar ranges between similar to 60-74 N-C. The modelling reveals regions of top-down PAH formation at the ionisation front, and bottom-up PAH formation within the molecular cloud region. The PAH ionisation parameter, gamma, ranges between similar to 2-9 & times; 10(4). Intensity ratios that are empirical tracers of PAH ionisation (I-6.2/I-11.2, I-7.7/I-11.2, I-8.6/I-11.2) scale well with gamma in regions encompassing edge-on or face-on PDR emission, but their correlation weakens within the molecular cloud zone. Conclusions. Modelling of the 5-15 mu m PAH spectrum with pyPAHdb achieves a comprehensive characterisation of the net contribution of neutral and cationic PAHs across different environments, whereas empirical PAH proxy intensity ratio tracers can be highly variable and unreliable outside regions dominated by PDR emission. The derived average PAH size in the different physical zones is consistent with a view of PAHs being more extensively subjected to ultraviolet processing closer to the ionisation front, and less affected within the molecular cloud.

We report the detection of a set of new near-infrared emission features between 3.5 and 5.2 mu 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 C60 and C70 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 C60 combination bands, marking their first detection in an astrophysical environment. The total energy radiated in the combination bands amounts to similar to 17% of the total energy emitted from all C60 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 C60 in sources where mid-infrared spectra are more complex.

Young (≲ 10 Myr) planetary-mass companions (PMCs) provide valuable insights into the formation and early evolution of planetary systems. To date, only a dozen such objects have been identified through direct imaging. Using JWST/NIRCam observations towards the Orion Nebula, obtained as part of the PDRs4All Early Release Science program, we have identified a faint point source near the M-type star V2376 Ori. Follow-up spectroscopic observations with the MUSE instrument on the VLT confirm that the source, V2376 Ori b, is indeed a young planetary-mass companion. It is a member of Orion D, around 80 pc in the foreground of the Trapezium cluster of Orion and with an age of approximately 7 ± 3 Myr. We fit the SED of V2376 Ori b to infer a mass of ∼ 20 M_ Jup. The MUSE spectrum reveals several accretion tracers. Based on the Hα line intensity, we estimate an accretion rate of ∼10^-6.5 ± 0.7 M_Jup yr^-1, which is comparable to that of young PMCs such as PDS 70b. In addition, the MUSE data cube reveals extended emission in the [O ii] doublet at 7320 and 7330 Å, which is interpreted as evidence of a dynamical interaction between the two sources that, potentially, involves mass transfer between their individual accretion disks. These results demonstrate that JWST/NIRCam imaging surveys of young stellar associations can uncover new PMCs, which can then be confirmed and characterized through ground-based spectroscopic follow-up.

The chemical composition of exoplanets is thought to be influenced by the composition of the disks in which they form. JWST observations have unveiled a variety of chemical species in numerous nearby disks, which show substantial variations in the C/O abundance ratio. However, little is known about the composition and C/O ratio of disks around young stars in clusters exposed to strong ultraviolet radiation from nearby massive stars, which are representative of the environments where most planetary systems form, including ours. Here we present JWST spectroscopy of d203-504, a young 0.7 M circle dot star in the Orion nebula with a 30 au disk irradiated by nearby massive stars. These observations reveal spectroscopic signatures of CO, H2O, CH3+ and polycyclic aromatic hydrocarbons. Water and CO are detected in absorption in the inner disk (r less than or similar to 1 au), where the estimated gas-phase C/O ratio is 0.48, consistent with the solar value and that of the Orion nebula. By contrast, CH3+ and polycyclic aromatic hydrocarbons are found in the extended surface layers of the disk. These results suggest that gas in the inner disk is chemically shielded from ultraviolet radiation, whereas the surface layers of the disk experience ultraviolet-induced chemistry, potentially depleting their carbon content.

Context. JWST continues to deliver incredibly detailed infrared (IR) images of star-forming regions in the Milky Way and beyond. IR emission from star-forming regions is very spectrally rich due to emission from gas-phase atoms, ions, and polycyclic aromatic hydrocarbons (PAHs). Physically interpreting IR images of these regions relies on assumptions about the underlying spectral energy distribution in the imaging bandpasses. Aims. We aim to provide empirical prescriptions to derive line, PAH, and continuum intensities from JWST images. These prescriptions will facilitate the interpretation of images in a wide variety of astrophysical contexts. We also measure the level of agreement between JWST imaging and integral field spectroscopy. Methods. We use JWST PDRs4All Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) imaging and Near-Infrared Spectrograph (NIRSpec) integral field unit (IFU) and MIRI Medium Resolution Spectrograph (MRS) spectroscopic observations of the Orion Bar, the prototypical photodissociation region (PDR), to directly compare and cross-calibrate imaging and IFU data at ~100 AU resolution over a region where the radiation field and ISM environment evolves from hot ionized gas to warm neutral gas followed by cold molecular gas. We study the relative contributions of line, PAH, and continuum emission to the NIRCam and MIRI filters as functions of local physical conditions, and investigate filter combinations that represent selected line and PAH emission. Results. We provide empirical prescriptions based on NIRCam and MIRI images that may be used to derive intensities of strong emission lines and PAH features. Within the range of the environments probed in this study, these prescriptions accurately predict Pa α, Brα, and PAH 3.3 μm and 11.2 μm intensities, while those for [Fe II] 1.644 μm, H2 1–0 S(1) 2.12 μm and 0–0 S(9) 4.69 μm, and PAH 7.7 μm show more complicated environmental dependencies. Conclusions. Linear combinations of JWST NIRCam and MIRI images provide effective tracers of ionized gas, H2, and PAH emission in PDRs. We expect these recipes to be useful for both the Galactic and extragalactic communities. The flux calibration between imaging and spectroscopy is found to agree within 1–20% for NIRCam and NIRSpec, and 2–7% for MIRI Imager and MRS.

Planetary nebulae are sites where ejected stellar material evolves into complex molecules, but the precise physical conditions and chemical routes that govern these processes are unclear. The presence of abundant carbon-rich molecules in O-rich environments poses particular challenges. Here we report the first detection of methyl cation (CH 3 + ) in any planetary nebula, observed in the O-rich nebula NGC 6302 using JWST MIRI/Medium Resolution Spectrometer observations. CH 3 + is a key driver of organic chemistry in UV-irradiated environments. Spatially resolved observations reveal that CH 3 + is colocated with 12 CO, H 2 , H ii , HCO + , and polycyclic aromatic hydrocarbons. LTE modeling of the CH 3 + emission yields excitation temperatures of 500–800 K in the inner bubble and torus, rising to 1000–2000 K in the outer bubble of NGC 6302, with column densities ranging from ∼10 11 to 10 13 cm −2 . This detection suggests that hydrocarbon radical chemistry must be incorporated into planetary nebulae chemical models. Further near-IR observations are crucial to map different chemical networks operating in these environments.

Planetary nebulae are sites where ejected stellar material evolves into complex molecules, but the precise physical conditions and chemical routes that govern these processes are unclear. The presence of abundant carbon-rich molecules in O-rich environments poses particular challenges. Here we report the first detection of methyl cation (CH ${}_{3}^{+}$ ) in any planetary nebula, observed in the O-rich nebula NGC 6302 using JWST MIRI/Medium Resolution Spectrometer observations. CH ${}_{3}^{+}$ is a key driver of organic chemistry in UV-irradiated environments. Spatially resolved observations reveal that CH ${}_{3}^{+}$ is colocated with ^12 CO, H _2 , H ii , HCO ^+ , and polycyclic aromatic hydrocarbons. LTE modeling of the CH ${}_{3}^{+}$ emission yields excitation temperatures of 500–800 K in the inner bubble and torus, rising to 1000–2000 K in the outer bubble of NGC 6302, with column densities ranging from ∼10 ^11 to 10 ^13 cm ^−2 . This detection suggests that hydrocarbon radical chemistry must be incorporated into planetary nebulae chemical models. Further near-IR observations are crucial to map different chemical networks operating in these environments.

Polycyclic aromatic hydrocarbons (PAHs) are responsible for strong mid-IR emission features near star-forming regions. It is well known that low-metallicity environments exhibit weaker PAH emission, but it is not clear how metallicity affects the properties of the emitting PAH population. We present a detailed study of the PAH emission in a region of 30 Doradus (30 Dor), a well-known low-metallicity star-forming environment in the Large Magellanic Cloud and we compare it to PAH emission in the Orion Bar to investigate the characteristics of the PAH population and how the environments affect the resulting IR emission. We analyze JWST observations of 30 Dor that include imaging (NIRCam and MIRI) and spectroscopy (NIRSpec integral-field unit (IFU) and MIRI Medium Resolution Spectroscopy (MRS)). We extracted NIRSpec/IFU and MIRI/MRS spectra from 18 apertures that cover the morphological structures present within the observed region of 30 Dor. We characterize the profiles and relative intensities of PAH emission in these apertures. The detailed profiles of the PAH emission bands in 30 Dor are all similar and match with one of the dissociation fronts (DF2) in the Orion Bar, but their relative band ratios show a much larger range than in the Orion Bar. The PAH emission in 30 Dor originates from a population with a lower or similar ionization fraction than in the Orion Bar, and a size distribution that has more small-sized PAHs. Since smaller PAHs typically photofragment before larger PAHs, our findings support the hypothesis that the lower PAH emission due to lower metallicities is the result of the inhibition of growth toward larger PAHs rather than photofragmentation.

Context. Photodissociation regions (PDRs) exhibit strong emission bands between 3–20 μm known as the aromatic infrared bands (AIBs), and they originate from small carbonaceous species such as polycyclic aromatic hydrocarbons (PAHs) excited by UV radiation. The AIB spectra observed in Galactic PDRs are considered a local analog for those seen in extragalactic star-forming regions. Recently, the PDRs4All JWST program observed the Orion Bar PDR, revealing the subcomponents and profile variations of the AIBs in very high detail. Aims. We present the Python version of PAHFIT, a spectral decomposition tool that separates the contributions by AIB subcomponents, thermal dust emission, gas lines, stellar light, and dust extinction. We aim to provide a configuration that enables highly detailed decompositions of JWST spectra of PDRs (3.1–26 μm) and to test if the same configuration is suitable to characterize AIB emission in extragalactic star forming regions. Methods. We determined the central wavelength and FWHM of the AIB subcomponents by fitting selected segments of the Orion Bar spectra and compiled them into a “PDR pack” for PAHFIT. We tested the PDR pack by applying PAHFIT to the full 3.1–26 μm PDRs4All templates. We applied PAHFIT with this PDR pack and the default continuum model to seven spectra extracted from the central star forming ring of the galaxy NGC7469. Results. We introduce an alternate dust continuum model to fit the Orion Bar spectra, as the default PAHFIT continuum model mismatches the intensity at 15–26 μm. Using the PDR pack and the alternate continuum model, PAHFIT reproduces the Orion Bar template spectra with residuals of a few percent. A similar performance is achieved when applying the PDR pack to the NGC7469 spectra. We provide PAHFIT-based diagnostics that trace the profile variations of the 3.3, 3.4, 5.7, 6.2, and 7.7 μm AIBs and thus the photochemical evolution of the AIB carriers. The 5.7 μm AIB emission originates from at least two subpopulations, one more prominent in highly irradiated environments and one preferring more shielded environments. Smaller PAHs as well as very small grains or PAH clusters both thrive in the more shielded environments of the molecular zone in the Orion Bar. Based on these new diagnostics, we show and quantify the strong similarity of the AIB profiles observed in NGC7469 to the Orion Bar template spectra.

Polycyclic Aromatic Hydrocarbons (PAHs) are organic molecules responsible for the Aromatic Infrared Bands (AIBs), observed across a multitude of astrophysical environments. Despite their ubiquity, the precise formation mechanisms of PAHs remain unclear. One of the possible way for PAHs to form is in the outflows of evolved stars, such as HD 44179, which produces the Red Rectangle nebula a known emitter of AIBs. However, no specific PAH molecules have been detected in such environments, complicating the understanding of PAH formation and evolution. This study aimed to detect the PAH molecule corannulene (C20H10), a viable candidate for radio detection due to its large dipole moment of 2.07 D. We analysed high-resolution band 4 ALMA observations of the Red Rectangle nebula, collected over almost 9 h. Although corannulene emission was not detected, we estimated a firm upper limit on its abundance compared to hydrogen (5 x10( - 13)) and we discuss the lack of detection in the context of our current understanding of PAH formation and destruction mechanisms. Additionally, we report tentative detection of signals at 139.612, 139.617, and 139.621 GHz, potentially originating from cyclopropenyledine (c-C3H2) and the 140 GHz H2O maser.

The profiles of several diffuse interstellar bands (DIBs) show substructures that resemble unresolved rotational bands of the electronic transitions of large molecules. Their profiles show clear variations along the lines of sight, probing different physical conditions. Analysis of variations in such profiles can constrain the sizes and geometries of the DIB carriers and the physical conditions of the interstellar environments in which they reside. We investigate the properties of rotational band contours for perpendicular transitions in planar, oblate symmetric top molecules and compare such contours to the observed profile of the lambda 6614 DIB. We examine the shapes of the profiles as a function of the model parameters: the rotational constant B in the ground state, the relative change in the rotational constant of the excited state Delta B, the Coriolis coupling constant zeta, the rotational excitation temperature T rot, and line width sigma. We determine which parameters can reproduce the overall triple-peak profile of the lambda 6614 DIB and the variations across different lines of sight. We find that the substructures in the lambda 6614 DIB can be reproduced with an oblate top with rotational constant B = (2.2 +/- 1.8) x 10-3 cm-1, Delta B = (-7.2 +/- 0.4) x 10-2%, and Coriolis coupling constant zeta = (2.9 +/- 0.1) x 10-1 cm-1. Thus, if the lambda 6614 DIB carrier conforms to an oblate symmetric top geometry, it is most likely to be a similar to 54C atom molecule. The profile variations correspond to changes in the rotational temperature from 81 to 92 K. We furthermore find that the intrinsic line width is a key parameter for each sightline and requires a range from 0.14 to 0.21 cm-1 (or 2.8 to 4.2 km s-1) across our sample to reproduce the observations. The intrinsic line width of the lambda 6614 DIB correlates with the width of the CH+ lines, suggesting an origin in the same environment. We conclude that the lambda 6614 DIB carrier resides in the same hot gas at low density that is probed by CH+.

NGC 6302 is a spectacular bipolar planetary nebula (PN) whose spectrum exhibits fast outflows and highly ionized emission lines, indicating the presence of a very hot central star (similar to 220 000 K). Its infrared spectrum reveals a mixed oxygen and carbon dust chemistry, displaying both silicate and polycyclic aromatic hydrocarbon (PAH) features. Using the James Webb Space Telescope Mid-Infrared Instrument and Medium Resolution Spectrometer, a mosaic map was obtained over the core of NGC 6302, covering the wavelength range of 5-28 mu m and spanning an area of similar to 18.5 arcsec x 15arcsec. The spatially resolved spectrum reveals similar to 200 molecular and ionized lines from species requiring ionization potentials of up to 205 eV. The spatial distributions highlight a complex structure at the nebula's centre. Highly ionized species such as [Mg VII ] and [Si VII ] show compact structures, while lower ionization species such as H+ extend much farther outwards, forming filament-defined rims that delineate a bubble. Within the bubble, the H+ and H-2 emission coincide, while the PAH emission appears farther out, indicating an ionization structure distinct from typical photodissociation regions, such as the Orion Bar. This may be the first identification of a PAH formation site in a PN. This PN appears to be shaped not by a steady, continuous outflow, but by a series of dynamic, impulsive bubble ejections, creating local conditions conducive to PAH formation. A dusty torus surrounds the core, primarily composed of large (mu m-sized) silicate grains with crystalline components. The long-lived torus contains a substantial mass of material, which could support an equilibrium chemistry and a slow dust-formation process.

Context. Photodissociation regions (PDRs) exhibit strong emission bands between 3-20 mu m known as the aromatic infrared bands (AIBs), and they originate from small carbonaceous species such as polycyclic aromatic hydrocarbons (PAHs) excited by UV radiation. The AIB spectra observed in Galactic PDRs are considered a local analog for those seen in extragalactic star-forming regions. Recently, the PDRs4All JWST program observed the Orion Bar PDR, revealing the subcomponents and profile variations of the AIBs in very high detail. Aims. We present the Python version of PAHFIT, a spectral decomposition tool that separates the contributions by AIB subcomponents, thermal dust emission, gas lines, stellar light, and dust extinction. We aim to provide a configuration that enables highly detailed decompositions of JWST spectra of PDRs (3.1-26 mu m) and to test if the same configuration is suitable to characterize AIB emission in extragalactic star forming regions. Methods. We determined the central wavelength and FWHM of the AIB subcomponents by fitting selected segments of the Orion Bar spectra and compiled them into a "PDR pack" for PAHFIT. We tested the PDR pack by applying PAHFIT to the full 3.1-26 mu m PDRs4All templates. We applied PAHFIT with this PDR pack and the default continuum model to seven spectra extracted from the central star forming ring of the galaxy NGC7469. Results. We introduce an alternate dust continuum model to fit the Orion Bar spectra, as the default PAHFIT continuum model mismatches the intensity at 15-26 mu m. Using the PDR pack and the alternate continuum model, PAHFIT reproduces the Orion Bar template spectra with residuals of a few percent. A similar performance is achieved when applying the PDR pack to the NGC7469 spectra. We provide PAHFIT-based diagnostics that trace the profile variations of the 3.3, 3.4, 5.7, 6.2, and 7.7 mu m AIBs and thus the photochemical evolution of the AIB carriers. The 5.7 mu m AIB emission originates from at least two subpopulations, one more prominent in highly irradiated environments and one preferring more shielded environments. Smaller PAHs as well as very small grains or PAH clusters both thrive in the more shielded environments of the molecular zone in the Orion Bar. Based on these new diagnostics, we show and quantify the strong similarity of the AIB profiles observed in NGC7469 to the Orion Bar template spectra.

Polycyclic aromatic hydrocarbons (PAHs) and carbonaceous dust have been observed in clumpy circumstellar environments, yet their formation and evolutionary pathways in such environments remain elusive. We aim to characterize the PAH emission in a clumpy planetary nebula to decipher their formation and evolution pathways. We obtained JWST Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) integral field unit spectroscopic observations of two individual knots in the Ring Nebula (NGC 6720), a clumpy planetary nebula, and determine the PAH spectral characteristics. We detect the 3.3 and 11.2 mu m PAH emission bands in both knots but do not detect PAH emission in the 6-9 mu m range. We supplement our data with Spitzer Infrared Spectrograph (IRS) Short-Low 1 (SL1) and SL2 data, containing 11.2, weak 6.2, and weak 7.7 mu m PAH emission bands. The JWST data confirm the unusual profile of the 11.2 mu m band, which is very broad and redshifted with respect to typical 11.2 mu m PAH profiles. We estimate the PAH population to be largely neutral. The relative integrated surface brightness of the 3.3 and 11.2 mu m bands indicates the presence of small-sized PAHs, consisting of 35 +/- 6 carbon atoms. We find that the PAH emission is concentrated outside of the clumps, in the inter-clump medium, and confirm the existence of enhanced PAH emission in a narrow 'PAH ring' centred on the central star. This morphology suggests that PAHs formed during the Ring Nebula's asymptotic giant branch phase, in the central star's dust-driven wind.

Context. JWST continues to deliver incredibly detailed infrared (IR) images of star-forming regions in the Milky Way and beyond. IR emission from star-forming regions is very spectrally rich due to emission from gas-phase atoms, ions, and polycyclic aromatic hydrocarbons (PAHs). Physically interpreting IR images of these regions relies on assumptions about the underlying spectral energy distribution in the imaging bandpasses. Aims. We aim to provide empirical prescriptions to derive line, PAH, and continuum intensities from JWST images. These prescriptions will facilitate the interpretation of images in a wide variety of astrophysical contexts. We also measure the level of agreement between JWST imaging and integral field spectroscopy. Methods. We use JWST PDRs4All Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) imaging and Near-Infrared Spectrograph (NIRSpec) integral field unit (IFU) and MIRI Medium Resolution Spectrograph (MRS) spectroscopic observations of the Orion Bar, the prototypical photodissociation region (PDR), to directly compare and cross-calibrate imaging and IFU data at similar to 100 AU resolution over a region where the radiation field and ISM environment evolves from hot ionized gas to warm neutral gas followed by cold molecular gas. We study the relative contributions of line, PAH, and continuum emission to the NIRCam and MIRI filters as functions of local physical conditions, and investigate filter combinations that represent selected line and PAH emission. Results. We provide empirical prescriptions based on NIRCam and MIRI images that may be used to derive intensities of strong emission lines and PAH features. Within the range of the environments probed in this study, these prescriptions accurately predict Pa alpha, Br alpha, and PAH 3.3 mu m and 11.2 mu m intensities, while those for [Fe II] 1.644 mu m, H-2 1-0 S(1) 2.12 mu m and 0-0 S(9) 4.69 mu m, and PAH 7.7 mu m show more complicated environmental dependencies. Conclusions. Linear combinations of JWST NIRCam and MIRI images provide effective tracers of ionized gas, H2, and PAH emission in PDRs. We expect these recipes to be useful for both the Galactic and extragalactic communities. The flux calibration between imaging and spectroscopy is found to agree within 1-20% for NIRCam and NIRSpec, and 2-7% for MIRI Imager and MRS.