In this paper we have inferred the magnetic shielding characteristics and space weather hazards of selected potentially habitable extrasolar planets using a dynamical geophysical model from calculations of internal heat, phases of volcanism and planetary magnetic moments. The space weather hazards on the extrasolar planet Kepler-452b orbiting around a Sun-like star are found to be a minimum which enhances the habitability probability of this planet.

One of the big challenges for 21st century stellar astrophysics is the impact of binary interactions on stellar evolution. Such interactions are believed to play a key role in the death throes of 1-8 M⊙ stars, as they evolve from the AGB stars into Planetary Nebulae. X-ray surveys of UV-emitting AGB stars show that ∼40% of objects with FUV emission and GALEX FUV/NUV flux ratios ≳0.2 have variable X-ray emission characterized by very high temperatures (Tx∼35-160 MK) and luminosities (Lx∼0.002-0.2L⊙). We hypothesize that such AGB stars have accretion and (accretion-powered) outflows associated with a close binary companion. UV spectroscopy with HST/STIS of our brightest object (Y Gem) shows the presence of infalling and outflowing gas, providing direct kinematic confirmation of this hypothesis. However, the UV-emitting AGB star population is dominated by objects with little or no FUV emission, and we do not know whether the UV emission from these is intrinsic to the AGB star or extrinsic (i.e., due to binarity). Here we present the first results from a large grid of simple chromospheric models to help discriminate between the intrinsic and extrinsic mechanisms of UV emission for AGB stars.

The INTEGRAL satellite, in orbit since October 2002, has significantly contributed to the study of magnetars and, thanks to its unique capabilities for the study of transient gamma-ray phenomena, it is now playing an important role in multimessenger astrophysics. The most recent results include the discovery of a peculiar burst from SGR J1935+2154, which gave the first observational evidence for the connection between magnetars and fast radio bursts, and extensive searches for bursting activity in peculiar sources, such as the repeating FRB 20200120E in M81 and the ultra-long period magnetar candidate GLEAMX J162759.5–523504.3.

A rich zoo of peculiar objects forms when Asymptotic Giant Branch (AGB) stars, undergo interactions in a binary system. For example, Barium (Ba) stars are main-sequence and red-giant stars that accreted mass from the outflows of a former AGB companion, which is now a dim white dwarf (WD). Their orbital properties can help us constrain AGB binary interaction mechanisms and their chemical abundances are a tracer of the nucleosynthesis processes that took place inside the former AGB star. The observational constraints concerning the orbital and stellar properties of Ba stars have increased in the past years, but important uncertainties remained concerning their WD companions. In this contribution, we used HD 76225 to demonstrate that by combining radial-velocity data with Hipparcos and Gaia astrometry, one can accurately constrain the orbital inclinations of these systems and obtain the absolute masses of these WDs, getting direct information about their AGB progenitors via initial-final mass relationships.

Accretion discs appear in many astrophysical systems. In most cases, these discs are probably not completely axisymmetric. Discs in binary systems are often found to be misaligned with respect to the binary orbit. In this case, the gravitational torque from a companion induces nodal precession in misaligned rings of gas. We first calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. For typical parameters, precession torque wins. To check this result, we perform numerical simulations using the Smoothed Particle Hydrodynamics code, PHANTOM, and confirm that sufficiently thin and sufficiently inclined discs can break into distinct planes that precess effectively independently. Disc tearing is widespread and severely changes the disc structure. It enhances dissipation and promotes stronger accretion onto the central object. We also perform a stability analysis on isolated warped discs to understand the physics of disc breaking and tearing observed in numerical simulations. The instability appears in the form of viscous anti-diffusion of the warp amplitude and the surface density. The discovery of disc breaking and tearing has revealed new physical processes that dramatically change the evolution of accretion discs, with obvious implications for observed systems.

The hot accretion flow around Kerr black holes is strongly magnetized. Magnetic field loops sustained by a surrounding accretion disk can close within the event horizon. We performed particle-in-cell simulations in Kerr metric to capture the dynamics of the electromagnetic field and of the ambient collisionless plasma in this coupled configuration. We find that a hybrid magnetic topology develops with a closed magnetosphere co-existing with open field lines threading the horizon reminiscent of the Blandford-Znajek solution. Further in the disk, highly inclined open magnetic field lines can launch a magnetically-driven wind. While the plasma is essentially force-free, a current sheet forms above the disk where magnetic reconnection produces macroscopic plasmoids and accelerates particles up to relativistic Lorentz factors. A highly dynamic Y-point forms on the furthest closed magnetic field line, with episodic reconnection events responsible for transient synchrotron emission and coronal heating.

The technetium-rich (Tc-rich) M stars reported in the literature (Little-Marenin & Little 1979; Uttenthaler et al. 2013) are puzzling objects since no isotope of technetium has a half-life longer than a few million years, and 9999Tc, the longest-lived isotope along the s-process path, is expected to be detected only in thermally-pulsing stars enriched with other s-process elements (like zirconium). Carbon should also be enriched, since it is dredged up at the same time, after each thermal pulse on the asymptotic giant branch (AGB). However, these Tc-enriched objects are classified as M stars, meaning that they neither have any significant zirconium enhancement (otherwise they would be tagged as S-type stars) nor any large carbon overabundance (in which case they would be carbon stars).

Here we present the first detailed chemical analysis of a Tc-rich M-type star, namely S Her. We first confirm the detection of the Tc lines, and then analyze its carbon and s-process abundances, and draw conclusions on its evolutionary status. Understanding these Tc-rich M stars is an important step to constrain the threshold luminosity for the first occurrence of the third dredge-up and the composition of s-process ejecta during the very first thermal pulses on the AGB.

Pulsating Ultra Luminous X-ray sources (PULXs) are thought to be X-ray bright, accreting, magnetized neutron stars, and could be the first and only evidence for the existence of magnetars in binary systems. Their apparent soft (< 20 keV) X-ray luminosity can exceed the Eddington luminosity for a neutron star (NS) by a few orders of magnitude. Although several scenarios have been proposed to explain the different components observed in the X-ray spectra and the characteristics of the X-ray lightcurve of these system, detailed quantitative calculations are still missing. In particular, the observed soft X-ray lightcurves are almost sinuosidal and show an increase in the pulsed fraction (from 8% up to even 30%) with increasing energy. Here, we present how emission originating from an optically thick envelope, expected to be formed during super-Eddington accretion, can result in pulsed fractions similar to observations.

Broadband X-ray data of five magnetars show that their hard X-ray pulses suffer periodic phase modulations, at a period ∼ 104 times their pulse period. The phenomenon is interpreted as a result of free precession of neutron stars that are prolately deformed to an asphericity of ∼ 10−4, by the magnetic stress of toroidal fields reaching ∼ 1016 G. The behavior is absent in their soft X-ray pulses, probably due to a higher emission symmetry. The ultra-high toroidal fields, considered common to magnetars, may persist longer than their dipole fields.

Merger of binary neutron stars and black hole-neutron star binaries is the promising source of short-hard gamma-ray bursts, the most promising site for the r-process nucleosynthesis, and the source of kilonovae. To theoretically predict the merger and mass ejection processes and resulting electromagnetic emission, numerical simulation in full general relativity (numerical relativity) is the unique approach. We summarize our current understanding for the processes of neutron-star mergers and subsequent mass ejection based on the results of long-term numerical-relativity simulations. We pay particular attention to the electron fraction of the ejecta.

Binary interaction with a stellar or planetary companion has been proposed to be the driving mechanism behind large-scale asymmetries, such as spirals and disks, observed within AGB outflows. We developed the first chemical kinetics model that takes the effect of a stellar companions’s UV radiation into account. The presence of a stellar companion can initiate a rich photochemistry in the inner wind. Its impact is determined by the intensity of the UV radiation and the extinction the radiation experiences. The outcome of the inner wind photochemistry depends on the balance between two-body reactions and photoreactions. If photoreactions dominate, the outflow can appear molecule-poor. If two-body reactions dominate, chemical complexity within the outflow can increase, yielding daughter species with a large inner wind abundance. A comprehensive view on the molecular content of the outflow, especially combined with abundance profiles, can point towards the presence of a stellar companion.

Boasting supreme magnetic strengths, magnetars are among the prime candidates to generate fast radio bursts. Several theories have been proposed for the formation mechanism of magnetars, but have not yet been fully tested. As different magnetar formation theories expect distinct magnetar space velocity distributions, high-precision astrometry of Galactic magnetars can serve as a probe for the formation theories. In addition, magnetar astrometry can refine the understanding of the distribution of Galactic magnetars. This distribution can be compared against fast radio bursts (FRBs) localized in spiral galaxies, in order to test the link between FRBs and magnetars. Swift J1818.0–1607 is the hitherto fastest-spinning magnetar and the fifth discovered radio magnetar. In an ongoing astrometric campaign, we have observed Swift J1818.0–1607 for one year using the Very Long Baseline Array, and have determined a precise proper motion as well as a tentative parallax for the magnetar.

Based on our current high resolution direct N-body modelling of the Milky Way typical Star Cluster systems dynamical evolution we try to numerically estimate the influence of individual spin values and orientations on gravitational wave (GW) waveforms and observed time-frequency maps during multiple cycles for binary black hole (BBH) mergers. In our up to date N-body dynamical simulations we use the high order relativistic post-Newtonian corrections for the BH binary particles (3.5 post-Newtonian (PN) terms including spin-spin and spin-orbit terms). In the current work, we present the GW waveforms catalogue which covers the large parameter space in mass ratios 0.05 - 0.82 and extreme possible individual spin cases.

Astrochemical models treat dust surfaces as ice covered. We investigate the effects of implementing increased bare dust binding energies of CO and S-bearing species on the chemistry in the outflows of asymptotic giant branch (AGB) stars. We demonstrate the potential for improving agreement with observations in the outflow of IK Tau.

Increasing the binding energies to measured and computationally derived values in high mass-loss AGB outflows increased the production of daughter species. Switching from a high binding energy on bare dust to weaker binding to ice, the gas phase abundance increased at a radius in agreement with observations of IK Tau, suggesting that displacement of bound species could contribute to this observational puzzle. Using a strong binding to bare dust, a gas phase increase was not observed, however parent species concentrations had to be increased by around a factor of four to explain observed concentrations.

Post-Asymptotic Giant Branch (post-AGB) binary systems are binary interaction products. These stars have recently undergone a strong, but not well understood, binary interaction phase, leading to the formation of stable, compact circumbinary discs. These circumbinary discs are found to show many similar properties to protoplanetary discs around young stars. Here, we focus on one such system, namely IRAS 08544-4431 and resolve the inner regions of the complex circumstellar environment using multi-wavelength infrared interferometric techniques. The visibility data of PIONIER (H-band), GRAVITY (K-band), and MATISSE (L and N band) are analysed together using two families of geometric models, giving a good fit to all data.

Anomalous X-ray pulsars (AXPs) and Soft gamma repeaters (SGRs) form together a single class of astrophysical sources, commonly associated to magnetars. New-generation X-ray polarimeters will play a key role in assessing the nature of these sources by directly probing the star magnetic field. In the highly magnetized environment radiation is expected to be strongly polarized and such a measure will be easily within reach of IXPE and eXTP. Polarization measurements will eventually confirm the presence of ultra-strong magnetic fields, probing the magnetar scenario. In this work we will discuss theoretical expectations for the polarization signature of AXPs and SGRs and present numerical simulations for the detector response of the polarimeters currently under construction. We will also show how these sources can be used to test vacuum birefringence, a QED effect predicted by Heisemberg and Euler in the Thirties and not experimentally verified as yet.

The load imbalance and communication overhead of parallel computing are crucial bottlenecks for galaxy simulations. A successful way to improve the scalability of astronomical simulations is a Hamiltonian splitting method, which needs to identify such regions integrated with smaller timesteps than the global timestep for integrating the entire galaxy. In the case of galaxy simulations, the regions inside supernova (SN) shells require the smallest steps. We developed the deep learning model to forecast the region affected by the SN shell’s expansion during one global step. In addition, we identified the particles with small timesteps using image processing. We can identify target particles using our method with a higher identification rate (88 % to 98 % on average) and lower “non-target”-to-“target” fraction (6.4 to 5.5 on average) compared to the analytic approach with the Sedov-Taylor solution. Our method using Hamiltonian splitting and deep learning will improve the performance of extremely high-resolution galaxy simulations.

The observational properties of isolated NSs are shaped by their magnetic field and surface temperature. They evolve in a strongly coupled fashion, and modelling them is key in understanding the emission properties of NSs. Much effort was put in tackling this problem in the past but only recently a suitable 3D numerical framework was developed. We present a set of 3D simulations addressing both the long-term evolution (≈ 104–106 yrs) and short-lived outbursts (≲ 1 yr). Not only a 3D approach allows one to test complex field geometries, but it is absolutely key to model magnetar outbursts, which observations associate to the appearance of small, inherently asymmetric hot regions. Even though the mechanism that triggers these phenomena is not completely understood, following the evolution of a localised heat injection in the crust serves as a model to study the unfolding of the event.

Motivated by their role as the direct or indirect source of many of the elements in the Universe, numerical modeling of core collapse supernovae began more than five decades ago. Progress toward ascertaining the explosion mechanism(s) has been realized through increasingly sophisticated models, as physics and dimensionality have been added, as physics and numerical modeling have improved, and as the leading computational resources available to modelers have become far more capable. The past five to ten years have witnessed the emergence of a consensus across the core collapse supernova modeling community that had not existed in the four decades prior. For the majority of progenitors – i.e., slowly rotating progenitors – the efficacy of the delayed shock mechanism, where the stalled supernova shock wave is revived by neutrino heating by neutrinos emanating from the proto-neutron star, has been demonstrated by all core collapse supernova modeling groups, across progenitor mass and metallicity. With this momentum, and now with a far deeper understanding of the dynamics of these events, the path forward is clear. While much progress has been made, much work remains to be done, but at this time we have every reason to be optimistic we are on track to answer one of the most important outstanding questions in astrophysics: How do massive stars end their lives?

Astrophysical outflows treated initially as spherically symmetric often show evidence for asymmetry once seen at higher resolution. The preponderance of aspherical and multipolar planetary nebulae (PN) and pre-planetary nebulae (PPN) was evident after many observations from the Hubble Space Telescope. Binary interactions have long been thought to be essential for shaping asymmetric PN/PPN, but how? PPN are the more kinematically demanding of the two, and warrant particular focus. I address how progress from observation and theory suggests two broad classes of accretion driven PPN jets: one for wider binaries (PPN-W) where the companion is outside the outer radius of the giant and accretes via Roche lobe overflow, and the other which occurs in the later stages of CE for close binaries (PPN-C). The physics within these scenarios connects to progress and open questions about the role and origin of magnetic fields in the engines and in astrophysical jets more generally.