Investigating dusty red supergiant outflows in Westerlund 1 with 3D hydrodynamic simulations

Context. Recent JWST observations towards Westerlund 1 have revealed extensive nebular emission associated with the cluster. Given the age of the region and the proximity of that material to massive stars, it cannot be primordial star-forming gas and the origin is uncertain. Aims. We aim to determine whether the nebular emission in Westerlund 1 is due to ablation flows from red supergiant (RSG) stars embedded in the cluster wind driven by the Wolf-Rayet stars in the cluster core. We also aim to explore the efficiency of mass loading for the RSG wind in this scenario. Methods. We used 3D hydrodynamic simulations with the PION code to study the interaction between the cluster and RSG winds. We compared our simulations with the JWST observations by generating synthetic dust-emission maps. Results. We find that the ablation flow morphology – which shows clumps and instabilities – is consistent with the observations towards Westerlund 1. Synthetic observations at 11 µm predict fluxes in the ablation flow of ~1000–6000 MJy ster−1, which is consistent with the unsaturated components of the JWST F1130W observations in the vicinity of the RSGs in the region. This good agreement is achieved without any consideration of polycyclic aromatic hydrocarbons (PAHs), which have a known 11.3 µm feature that appears in the F1130W band. This suggests that the environment is not conducive to PAH formation and/or the ablation flow is PAH-depleted by wind and radiation action. Conclusions. Ablation of RSG winds can explain the observed nebulosity in Westerlund 1, at least in the vicinity of the RSGs. Further observations are encouraged to enable detailed studies of these interactions

Seismic Velocity Structure of the Irish Crust from Quarry Blasts

Travel-time tomography uses the travel times of seismic waves between pairs of sources and receivers to constrain the elastic properties of the subsurface. However, the low rate of natural seismicity in Ireland limits the application of standard local earthquake tomography. This study uses seismic wave arrival times from controlled explosions generated during quarry and mining activities to refine the constraints on the velocity structure of the Irish crust. Previous seismic studies have utilised (i) surface wave dispersion from teleseismic earthquakes, providing broad insights into the lithospheric structure, and (ii) spatially sparse seismic reflection and refraction profiles. While these studies have delineated major tectonic features, such as the late-Caledonian Leinster Granite and a crustal boundary linked to the closure of the Iapetus Ocean, the precise boundaries of these features remain unresolved. Subašić (2021) employed the FMTOMO package to compute a preliminary 3D travel-time tomography model of the Irish crust based on quarry blast data. FMTOMO (Rawlinson et al., 2006) uses a gradient-based subspace inversion scheme to derive a seismic velocity model from observed travel times. In this study, we re-evaluate and expand the input dataset used by Subašić (2021) and focus on optimising the regularisation parameters of the tomographic inversion. Event classification into natural earthquakes and quarry explosions is performed using the spectral ratio method applied to S-wave trains, a procedure developed and routinely applied by the Irish National Seismic Network (INSN). The updated dataset includes 1,411 quarry blast events with P- and S-wave travel-time measurements from 2013–2014, a period of increased station density due to temporary seismic deployments. Quarry blasts, being surface explosions, are assumed to have well-constrained surface locations. A catalogue of 234 quarry sites in Ireland was initially compiled from satellite imagery by the INSN. Hypocentre locations for each event are first calculated from phase arrival times and subsequently relocated to the nearest quarry. Given that quarry mines in Ireland typically range from hundreds of metres to a maximum of ~1.5 km in length, most events fall within the error margin of the initial locations. For events located beyond a 3 km radius of known quarries, additional searches for unrecorded sites were conducted. Satellite imagery inspections of these unclassified events identified 25 additional quarries. The operational status of these quarries during the study period was confirmed using historical imagery from Google Earth by comparing quarry areas before and after the analysed time frame

How to turn a supernova into a PeVatron

Context. It is important to determine which Galactic cosmic-ray (CR) sources have the ability to accelerate particles to the knee of the CR spectrum at a few peta-electronvolt (PeV). In particular, we need to consider whether supernova remnants (SNRs) could also be contributors to this process. Current models for particle acceleration in very young remnants assume the circumstellar material (CSM) consists of smooth, freely expanding winds. There is strong evidence that some supernovae (SNs) expand into much denser CSM, including dense shells ejected by eruptions shortly before explosion. Aims. We investigate the effects of dense circumstellar shells on particle acceleration in SN shocks during the first few years post-explosion to quantify whether SNs resulting from interactions may act as PeVatrons. Methods. We used the PION code to model the CSM around luminous blue variables (LBVs) after having a brief episode with a mass-loss rate of up to 2 Solar Masses per year. Consequently, we performed spherically symmetric 1D simulations using our time-dependent acceleration code RATPAC, where we simultaneously solved the transport equations for CRs, magnetic turbulence, and the hydrodynamical flow of the thermal plasma in the test-particle limit. Results. We find that the interaction with the circumstellar shells can significantly boost the maximum energy by enhancing particle escape during the onset of the shock-shell interaction, followed by the reacceleration of the shock propagating into a medium with a preamplified field. Early interactions boost the maximum energy to a greater degree and interactions within the first five months after explosion can increase Emax to levels over 1 PeV

Leveraging Social Media for Geoscience Communication: Insights from the British Geological Survey's Multi-Hazard and Resilience Campaigns

Social media offers a unique avenue for scientific communication; however, it remains underutilised by many scientific organisations. This study examines the social media strategy of the British Geological Survey (BGS), the UK’s leading geoscience organisation, to assess its effectiveness in engaging the public with research on Multi-Hazard and Resilience. We investigate two key research questions; 1. how effectively does BGS engage the public through its social media efforts, and 2. what challenges does BGS face in using these social media platforms to enhance public understanding? Scientific organisations often rely on the deficit model of communication, characterised by a one-way transfer of knowledge. Yet, emerging studies suggest that a dialogue-based approach, tailored to different social media platforms and formats, may foster better public engagement. This paper provides a framework for assessing social media activity that can be applied to scientific organisations worldwide. To address research question 1, we conduct content and sentiment analysis on BGS social media posts – including X, Facebook, LinkedIn, Instagram, YouTube, and BlueSky – from May 2023 to March 2024. A systematic codebook is developed to categorise descriptive and interpretive variables for any social media output. To answer research question 2, we conduct semi-structured interviews with five BGS employees who manage departmental social media accounts to understand their attitudes towards social media engagement. Our findings suggest several actionable strategies, such as streamlining communication across platforms, maximising the reach of ‘Multi-Hazard and Resilience’ themes, increasing video content output, and better incorporating public feedback. Although focused on BGS, our mixed-methods approach and methodology offer a valuable template for other scientific organisations seeking to enhance their online presence and science communication efforts. This study highlights BGS’s successful establishment of a multi-platform online presence, showcasing a range of content formats that effectively engage audiences

EWOCS-IV: 1Ms ACIS Chandra observation of the supergiant B[e] star Wd1-9

Context. Supergiant B[e] (sgB[e]) stars are exceptionally rare objects, with only a select number of confirmed examples in the Milky Way. The evolutionary pathways leading to the sgB[e] phase remain largely debated, highlighting the need for additional observations. The sgB[e] star Wd1-9, located in the massive cluster Westerlund 1 (Wd1), is enshrouded in a dusty cocoon – likely the result of past eruptive activity – leaving its true nature enigmatic. Aims. We present the most detailed X-ray study of Wd1-9 to date, using X-rays that pierce through its cocoon with the aim of uncovering its nature and evolutionary state. Methods. We utilised 36 Chandra observations of Wd1 from the ‘Extended Westerlund 1 and 2 Open Clusters Survey’ (EWOCS), plus eight archival datasets, totalling 1.1 Ms. We used this dataset to investigate long-term variability and periodicity in Wd1-9, and analysed X-ray colours and spectra over time to uncover patterns that shed light on its nature. Results. Wd1-9 exhibits significant long-term X-ray variability, within which we identify a strong ∼14-day periodic signal. We interpret this as the orbital period, marking the first period determination for the system. The X-ray spectrum of Wd1-9 is thermal and hard (kT ∼ 3.0 keV), resembling the spectra of bright Wolf-Rayet (WR) binaries in Wd1, while a strong Fe emission line at 6.7 keV indicates hot plasma from a colliding-wind X-ray binary. Conclusions. Wd1-9, with evidence of past mass loss, circumbinary material, a hard X-ray spectrum, and a newly detected 14-day period, displays all the hallmarks of a binary – likely a WR+OB – that recently underwent early Case B mass transfer. Its sgB[e] classification is likely phenomenological, reflecting emission from the dense circumbinary material. This places Wd1-9 in a rarely observed phase, possibly revealing a newly formed WN star, bridging the gap between immediate precursors and later evolutionary stages in Wd1

Detection of Lowermost Mantle Heterogeneity Using Seismic Migration of Diffracted S‐Waves

The bottom of Earth's mantle hosts strong seismic wave speed heterogeneities. These are commonly detected via forward modeling of seismic waveforms, which can include time‐consuming waveform synthesis and visual inspection. Furthermore, such imaging has been most commonly carried out with waves that have limited global coverage. In this work, we investigate the efficacy of the diffracted S (Sdiff) wavefield, which has global coverage to map core‐mantle boundary heterogeneity. We implement a Kirchhoff migration algorithm to objectively investigate the presence or absence of postcursors to Sdiff, caused by ultralow velocity zones (ULVZs) and other sharp velocity contrasts. Our approach makes use of the expected moveout of ULVZ‐ generated Sdiff postcursors as a function of distance from great‐circle path at the base of the mantle. We investigate epicentral distances >95°, where Sdiff includes asymptotic S/ScS up to diffraction. We test the algorithm using synthetic waveforms calculated for models that include lowermost mantle wavespeed heterogeneity via a recently proposed hybrid simulation approach. Our results demonstrate that the migration approach, when applied to a single event, can well resolve the location of heterogeneity structures in the azimuthal direction, but is less accurate at constraining the along‐great circle path location. To locate ULVZ structure accurately, heterogeneity maps from different earthquakes with crisscrossing raypaths are combined. Lastly, we provide real‐data proof‐of‐concept examples which detect ULVZs with different sizes that have been proposed in past work. These include the Hawaiian ULVZ, which is roughly 1,000 km across and a ULVZ beneath the Himalayas with a lateral extent of only 200 km

The lithosphere of South America from seismic tomography: Structure, evolution, and control on tectonics and magmatism

The thickness, temperature and mechanical strength of the lithosphere vary greatly across South America and have controlled tectonic and magmatic processes during its evolution. Here, we introduce a new tomographic model of South America’s lithosphere and underlying mantle, SACI-24, and analyse this and other state-of-the-art models together with other geological and geophysical data. The new model is obtained by waveform inversion of surface, S and multiple S waveforms globally, but is optimised for South America and the surrounding oceans. SACI-24 is constrained by ∼ 970,000 seismograms from 9259 stations and maps detailed structure of cratonic lithosphere across the continent, highlighting previously unknown complexities and fragmentation. Within the Amazon Craton, the Guiana and Central Brazil blocks show high Vs exceeding 4.8 km/s in the 80–150 km depth range but are separated by lower velocities below the Amazon Basin, matching the locations of ancient rifting and the flood basalts of the Central Atlantic Magmatic Province. In the São Francisco Craton, high velocities extend north and southwest beyond the previously proposed boundaries. Warmer, thinner lithosphere underlies the Paramirim and Pirapora aulacogens, locations of magmatic and rifting cycles. A fragmented cratonic root underlies the Paraná Basin, with thinner lithosphere along its central rift. High velocities south of the Paraná Block indicate the northern Rio de la Plata Craton’s thick root. The Cenozoic intraplate basalts in the Borborema province, along the southern Atlantic coast and in Paraguay occurred in areas of thin lithosphere and near thick-thin lithospheric boundaries. Most flood basalts of the Phanerozoic large igneous provinces also map on low velocity areas. Smaller flood-basalt portions sit atop cratonic lithosphere and offer new evidence on lateral flow of flood-basalt lava and magma within the crust. About 80 % of known diamondiferous kimberlites are on thick lithosphere, with the exceptions indicating cratonic erosion and thinning since their emplacement

Thermal emission from bow shocks III: Variable diffuse X-ray emission from stellar-wind bow shocks driven by dynamical instabilities,

Context. X-ray emission from wind-driven bow shocks is both difficult to measure and predict, but may give important insights into the energy budget of the hot phase of the interstellar medium (ISM) by quantifying mixing at the interface between hot and warm gas phases. Aims. We investigate the effect of magnetic fields and numerical resolution on predicted X-ray emission and other observable properties of bow shocks, to study convergence properties and assess robustness of predicted observables from simulations. Methods. A suite of 2D and 3D hydrodynamic and magnetohydrodynamic simulations of bow shocks were run and analysed to generate synthetic emission maps and light curves in X-ray and infrared emission. Results. Resolving the Kelvin-Helmholtz (KH) instability at the wind-ISM contact discontinuity is crucial for obtaining converged results and for predicting X-ray emission and the properties of the hot shocked wind. When sufficient spatial resolution is used, we measure time variation of X-ray emission of at least an order of magnitude on a timescale comparable to the advection timescale of the wake downstream from the bow shock. Good correspondence is found between 2D and 3D simulations with comparable resolution, and 3D simulations can achieve the required resolution with reasonable computing resources. Development of the KH instability is inhibited for shear flows parallel to the ISM magnetic field, compared with what is seen in the perpendicular direction, resulting in synthetic IR emission maps of bow shocks that are smooth when seen from one perspective but show strong distortions from another. Conclusions. Measuring the X-ray morphology and luminosity in bow shocks may be useful for constraining mixing and energytransfer rates between hot and warm gas phases of the ISM. Dynamical instabilities at the wind-ISM interface are a crucial ingredient in determining the properties of the hot-gas phase in stellar bow-shocks, in particular to capture its time dependence

Improving passive reflection seismic imaging in complex geological settings through site effect reduction: application to Krafla volcano, Iceland

Reflection imaging at volcanoes presentssignificant challenges due to the highly heterogeneous subsurface, which generates complex wavefields characterized by substantial wave scattering. These scattered waves obscure coherent energy, such as reflections from geological structures in the subsurface. In this study, we develop processing strategies to address the limitations of high-frequency (5–20 Hz) passive reflection imaging at Krafla, a volcanic caldera in NE Iceland. Krafla is among the few locations worldwide where magma has been encountered at 2.1 km depth when drilling the IDDP1 borehole. We analyse over 300 local microearthquakes and industrial noise recorded during five weeksin the summer of 2022. We show that wavefields lack coherency even between stations spaced at 30-m intervals due to the dominance of site effects beneath the stations. However, data coherency improvesin the common-station domain, where different earthquakes recorded by a fixed station are analysed, thereby stabilizing the site effect. Spectral analyses in this domain reveal that site effects are partly due to resonances at the stations, likely caused by lava flows and cavities in the heterogeneous near-surface. By constructing a resonance removal filter, we successfully deconvolve resonance effects from the data, revealing previously masked coherent energy. We further reduce site effects by applying linear stacking of clustered earthquake traces and nonlinear amplitude weighting. Our approach significantly enhances coherency between stations and enables the identification of reflections in microearthquakes likely originating from the known magma–rock interface beneath the IDDP1 borehole

A new subsurface temperature model for Ireland from joint geophysical–petrological inversion of seismic, surface heat flow and petrophysical data

High-quality maps of subsurface temperature and the geothermal gradient are useful when assessing the geothermal potential of a region. However, determining geothermal potential is a challenge when direct measurements of in-situ temperature and thermal property information are sparse and indirect geophysical methods are sensitive to a range of parameters, not just temperature. Here, we produce subsurface temperature maps of Ireland using a joint geophysical–petrological inversion, where seismic and other geophysical and petrophysical data are inverted directly for temperature in 1-D columns and are collated into a pseudo 3-D temperature volume. Additionally, the inversion produces new models for Moho and LAB depth and for the average crustal radiogenic heat production. To assess the robustness of the resulting temperature model, an uncertainty analysis has been performed by inverting all of the 1-D columns for a range of reasonable input parameters applicable to the Irish crust (rather than the ‘best’ input parameters). The resulting uncertainty model suggests temperature estimates at 2 km depth in our model could vary by ± 2 to 5 °C with an average of 3.5 °C in most locations. The uncertainty model can be used to assess confidence in different regions of the temperature model. In addition, 3-D forward modelling was performed to assess the lateral heat flow variations when compared to the purely 1-D inversion. The upper-crustal geothermal gradient ranges from 20 to 40 °C km−1 indicating a higher geothermal gradient for Ireland than previously reported with subsurface temperatures at 2 km depth > 60 °C everywhere, sufficient for residential and industrial heating purposes. The temperature gradient is typically higher in areas with thinner lithosphere. However, in some locations, the observed geotherms are elevated further due to high radiogenic heat production in granitic rocks. In Northern Ireland, a thin lithosphere, coupled with a weakly conductive basalt layer overlying warm crust, results in elevated temperatures. These are the first temperature maps for Ireland that include uncertainty estimates, providing ranges for the subsurface temperature values, and demonstrate that the maps are comparable to direct independent borehole temperature measurements, which are observed to fall within the model uncertainty. Our new methodology provides workflows for determining the geothermal potential in areas with limited direct temperature measurements. The final temperature model with uncertainty provides useful constraints for geothermal exploration and utilization on the island of Ireland