Michael J. Barlow

Polycyclic aromatic hydrocarbons (PAHs) and carbonaceous dust have been observed in oxygen-rich planetary nebulae (PNe), yet their formation and evolution in these environments is an open question. We aim to study the formation and evolution of the PAHs in the O-rich PN NGC 6302 (the Butterfly Nebula), by characterizing the PAH emission throughout this object. We obtained James Webb Space Telescope Mid-Infrared Instrument (MIRI) Integral Field Unit (IFU) spectroscopic observations of NGC 6302 pointed at its central source. From these, we extract four template spectra that are representative of the variation in PAH emission throughout NGC 6302. We detect the major PAH features at 6.2, 7.7, 8.6, 11.2, and 12.7 μm, and several minor PAH features. The template spectra vary in terms of their PAH feature widths, peak wavelengths, and relative intensities. The 11.2 μm PAH feature is class B, typical for PNe. The 6–9 μm PAH features are class A, which is less common for PNe. We estimate the PAH charge to be 75 per cent cations on average, based on the 7.7/11.2 PAH feature ratio. The relative strengths of the 11–15 μm PAH features indicate a range of PAH edge structures. To ensure consistency in our observations and explain variable PAH feature widths, we propose a variation in the size of the PAHs throughout NGC 6302, and suggest variation in the shielding of these PAHs. The PAHs range from large and non-compact, to small and compact. We find that NGC 6302 formed PAHs in situ in the current PN phase, likely from small hydrocarbons formed by the photodissociation of CO.

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.

We present high angular resolution observations of the HCO+ emission in the central ejecta of the supernova remnant SN 1987A using the Atacama Large Millimeter Array (ALMA). We use this to infer the degree and type of mixing required within the ejecta in order to form HCO+. The distribution of the J = 3 − 2 HCO+ emission is co-spatial with that of the J = 2 − 1 CO emission, with an overlap between their brightest peaks. The correlation between the two molecules is strong and suggests that HCO+ could form from reactions involving CO. We obtain additional observations of the J = 4 − 3 HCO+ emission to calculate the mass of HCO+. The estimated HCO+ mass is 3–9 × 10−6 M⊙. The relatively large fractional abundance of HCO+ with respect to CO ($M_{\mathrm{HCO}^+}/M_{\mathrm{CO}} = 3 \times 10^{-6}\textrm{--}3 \times 10^{-4}$) suggests that a moderate amount of hydrogen was mixed into the carbon- and oxygen-rich nuclear zones of the ejecta prior to and during the supernova explosion, in addition to large-scale macroscopic mixing.

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.

Supernova (SN) 1987A provides a unique laboratory for investigating many aspects of SN physics and evolution. An observation at Day 12927 (35.4 yr) since the explosion with the Mid-Infrared Instrument (MIRI) Medium Resolution Spectrometer (MRS) on the James Webb Space Telescope provided the first spatially resolved spectroscopic study of SN 1987A in the mid-infrared (mid-IR), yielding insights into the evolution of dust, the ejecta, the equatorial ring (ER), and shocks in the system. Here we present a second epoch with MIRI/MRS at Day 13311 (36.4 yr), allowing the mid-IR spatially resolved spectroscopic temporal evolution of SN 1987A to be probed for the first time. Analysis of the ER-dominated dust continuum showed little evolution between Days 12927 and 13311. However, spatial analysis reveals that the inner ER is fading while the outermost regions are brightening. Broad ejecta emission lines detected at Day 12927 are evolving rapidly, driven by the recent onset of ejecta–ER interaction in the northeast and southwest portions of the ER. Most lines from the ER show no change during the 384 days between epochs, although some, such as [Ne ii ] and [Ar ii ], have faded. We identify mid-IR H ₂ emission associated with the ejecta for the first time. Using near- and mid-IR [Fe ii ] lines as density and temperature diagnostics of the ejecta in the interaction region, we find it likely that the dense, inner Fe-rich ejecta has now reached the reverse shock. Continued monitoring of SN 1987A is essential to observe the evolving ejecta–ER interaction and dust components.

Using JWST/MIRI observations, we report the detection of CO ₂ 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.

Context . While supernova remnants (SNRs) have been observed to produce up to 1 M _⊙ of dust, the amount of dust destroyed by the forward shock is poorly constrained, raising the question of whether they are net dust producers or destroyers. Aims . Our aim was to estimate the dust destruction efficiency of SNR forward shocks in a realistically turbulent interstellar medium (ISM) during their most destructive phase, and to assess dust shielding by high-density filaments during this period. Methods . We ran 3D high-resolution turbulence simulations for different turbulent Mach numbers (0–3) and average ISM densities (1–100 cm ⁻³ ) to resemble observations of the turbulent ISM. We then set off a supernova explosion to trace its 3D magnetohydrodynamic evolution for the first 10 kyr. Finally, we ran post-processing simulations to investigate the dust transport and destruction by the SNR forward shock, taking into account gas and plasma drag, kinetic and thermal sputtering, and grain–grain collisions, and considering either silicates or carbonaceous dust. Results . The dust destruction rate of the forward shock strongly depends on the average ISM density and turbulence strength, varying in the range 27–92% (0.85–11.0 M _⊙ ) in the studied 10 kyr. Overall, dust is less efficiently destroyed in a low-density medium (1 cm ⁻³ , 27–57%) than in intermediate-density (10 cm ⁻³ , 46–92%) and high-density (100 cm ⁻³ , 73–87%) cases. The forward shock is found to destroy 8–34% less dust in high Mach turbulence compared to a homogeneous medium. Furthermore, carbonaceous grains are up to 21% more robust than silicates. Conclusions . Filaments can partly shield dust from destruction in the first 10 kyr; however, always more than 0.85 M _⊙ of dust is destroyed, making most SNRs dust sinks under the conditions explored in this work. The destruction efficiency of the SNRs with less than 1 M _⊙ of destroyed dust has not yet plateaued, so that they are most likely also net dust destroyers by the end of their lifetimes.

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.

The first JWST observations of SN 1987A provided clear evidence that a compact object is ionizing the innermost ejecta. Here, we analyze a second epoch of JWST NIRSpec and MIRI/Medium-Resolution Spectrometer observations to better characterize the properties of this region, aided by a higher spectral resolving power for the new NIRSpec data. We confirm the presence of the previously identified narrow lines from the central region, i.e., ([Ar vi] 4.5292 μm, [Ar ii] 6.9853 μm, [S iv] 10.5105 μm, and [S iii] 18.7130 μm), and also identify similar components in [Ca v] 4.1585 μm, [Cl ii] 14.3678 μm, and possibly [Fe ii] 1.6440 μm. These lines are blueshifted by ∼−250 km s⁻¹, while the emission region is spatially unresolved and located southeast of the center. The offset and blueshift could imply a kick velocity of 510 ± 55 km s⁻¹ for the neutron star. We also identify [Ca iv] 3.2068 μm near the center, but it is displaced to the north and has a redshift of ∼700 km s⁻¹. We find that scattering by dust in the ejecta with a typical grain size ∼0.3 μm can explain the [Ca iv] properties and the absence of other narrow lines at shorter wavelengths, while dust absorption is important at λ ≳ 8 μm. Photoionization models for a pulsar wind nebula and a cooling neutron star are both compatible with the observations, with the exception of the [Fe ii] feature. The two models primarily differ at short wavelengths, where new lines are expected to emerge over time as the optical depth of dust in the expanding ejecta decreases.