Maser properties can be measured with milli-arcsec precision over multiple epochs using ALMA, cm- and mm-wave VLBI and e-MERLIN. This allows: (i) Tracing SiO maser proper motions in the pulsation-dominated zone; (ii) Quantifying clumpiness, variability and asymmetry of the wind traced by masers; (iii) Contrasting behaviour from OH masers even at similar distances from the star; (iv) Measuring magnetic fields. Mass lost from the star, traced by SiO masers, is likely to take decades to reach ∼5 stellar radii. At 5–50 stellar radii, once dust is well formed, 22-GHz H2O masers show the wind accelerating through the escape velocity; its overall direction is away from the star but the velocity field is complex. In a few cases (so far), highly-directed, localised ejecta are seen. Magnetic fields appear to be stellar-centred and strong enough to influence wind kinematics. Recent ALMA and other observations have shown that otherwise inconspicuous companions shape a majority of evolved star winds, whilst advanced models demonstrate how, for some situations, this is compatible with masers showing negligible rotation proper motions. The long-term monitoring achievable at radio frequencies complements the multi-transition maser studies and analysis of thermal lines and dust at shorter wavelengths.

Auroral events are the prominent manifestation of solar/stellar forcing on planetary atmospheres and are closely related to the energy deposition by and evolution of planetary atmospheres. Observations of auroras are widely used to analyze the composition, structure, and chemistry of the atmosphere under study, as well as charged particle and energy fluxes that affect the atmosphere. Numerical kinetic Monte Carlo models had been developed allowing us to study the processes of precipitation of high-energy electrons, protons and hydrogen atoms into the planetary atmospheres on molecular level of description, taking into account the stochastic nature of collisional scattering at high kinetic energies. Such models are used to study auroras at both magnetized and non-magnetized planets in the Solar and extrasolar planetary systems. The current status of the kinetic model is illustrated in application to the auroral events at Mars.

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M 33 (Triangulum). In this paper, we present the dust and gas mass-loss rates by the pulsating Asymptotic Giant Branch (AGB) stars and red supergiants (RSGs) across the stellar disc of M 33.

On August 17, 2017, the LIGO/VIRGO collaboration detected the first gravitational wave signal coming from the merger of two neutron stars. This groundbreaking discovery, referred to as GW170817, revealed to us how heavy elements, such as gold and platinum, are synthesized through a mechanism known as rapid neutron capture (r-process). In order to fully understand these signals, we need to simulate the resulting accretion disk around a black hole, and its outflows. This task requires efficient computing codes that include general relativity magnetohydrodynamics (GRMHD), neutrino physics, and a model for matter at high densities. We present the implementation of a tabulated equation of state that takes care of matter at high densities and a neutrino leakage scheme that considers the impact of neutrinos into HARM3D, a GRMHD parallelized code. We also apply the tools to a magnetized torus.

Transit observations have revealed the existence of atmospheric escape in several hot Jupiters. High energy photons from the host star heat the upper atmosphere and drive the hydrodynamic escape. The escaping atmosphere can interact with the stellar wind from the host star. We run radiation hydrodynamics simulations with non-equilibrium chemistry to investigate the wind effects on the escape and the transit signature. Our simulations follow the planetary outflow driven by the photoionization heating and the wind interaction in a dynamically coupled, self-consistent manner. We show that the planetary mass-loss rate is almost independent of the wind strength, which however affects the Ly-α transit depth considerably. But the Hα transit depth is almost independent of the wind strength because it is largely caused by the lower hot layer. We argue that observations of both lines can solve the degeneracy between the EUV flux from the host and the wind strength.

In the neutron-star mergers, the radioactive decay of freshly synthesized heavy elements produces emissions in the ultraviolet-optical-infrared range, producing a transient called kilonova. The observational properties of the kilonova depend on the bound-bound opacity of the heavy elements, which was largely unavailable for the conditionssuitable at an early time (t < day). In this article, I share some of our recent progress on modeling the early kilonova light curve, focusing on the atomic opacity calculation.

A recent analysis of a few carbon-oxygen white dwarfs in old open clusters of the Milky Way (MW) identified a kink in the initial-final mass relation (IFMR), located over a range of initial masses, 1.65 ≲ Mi/M⊙ ≲ 2.10, which unexpectedly interrupts the commonly assumed monotonic trend. The proposed interpretation links this observational fact to the formation of carbon stars and the modest outflows (with mass loss rate < 10−7 M⊙/yr) that are expected as long as the carbon excess remains too low to produce dust grains in sufficient amount. Under these conditions the mass of the carbon-oxygen core can grow more than is generally predicted by stellar models. We discuss these new findings also in light of a new systematic follow-up investigation, based on Gaia EDR3, of evolved giants (13 carbon stars, 3 S stars and 4 M stars) belonging to intermediate-age open clusters.

Binary neutron star (NS) mergers have been expected to synthesize r-process elements and cause electromagnetic radiation called kilonovae. Although r-process nucleosynthesis was confirmed by the observations of GW170817/AT2017gfo, individual elements have not been identified except for strontium. Toward identification of elements in kilonova spectra, we perform radiative transfer simulations in NS merger ejecta. We find that Sr II triplet lines appear in the spectrum, which is consistent with the absorption feature observed in GW170817/AT2017gfo. The synthetic spectrum also shows the strong Ca II triplet lines. Absence of the Ca II line features in GW170817/AT2017gfo implies that the Ca/Sr ratio is < 0.002 in mass fraction, which is consistent with nucleosynthesis for electron fraction ≥ 0.40 and entropy per nucleon (in units of Boltzmann constant) ≥ 25. Identification of absorption lines in near-infrared wavelengths which have not yet been decoded may lead to clarify the abundances synthesized in NS merger ejecta.

We have studied the input of the exothermic photochemistry into the formation of the non-thermal escape flux in the transition H2 − H region of the extended upper atmosphere of the hot exoplanet - the sub-neptune π Men c. The formation rate and the energy spectrum of hydrogen atoms formed with an excess of kinetic energy due to the exothermic photochemistry forced by the stellar XUV radiation were calculated using a numerical kinetic Monte Carlo model of a hot planetary corona. The escape flux was estimated to be equal to 2.5×1012 cm−2s−1 for the mean level of stellar activity in the XUV radiation flux. This results in the mean estimate of the atmospheric loss rate due to the exothermic photochemistry equal to 6.7×108 g s−1. The calculated estimate is close to the observational estimates of the possible atmospheric loss rate for the exoplanet π Men c in the range less than 1.0×109 gs−1.

The origin of chemically peculiar stars and nonzero eccentricity in evolved close binaries have been long-standing problems in binary stellar evolution. Answers to these questions may trace back to an intense mass transfer during the asymptotic-giant-branch (AGB) binary phase. We use AstroBEAR to solve the 3D radiation hydrodynamic equations and calculate the mass transfer rate in AGB binaries that undergo the wind-Roche-lobe overflow or Bondi-Hoyle-Lyttleton (BHL) accretion. One of the goals of this work is to illustrate the transition from the wind- Roche-lobe overflow to BHL accretion. Both circumbinary disks and spiral structure outflows can appear in the simulations. As a result of enhanced mass transfer and angular momentum transfer, some AGB binaries may undergo orbit shrinkage, and some will expand. The high mass transfer efficiency is closely related to the presence of the circumbinary disks.

The detection of an electromagnetic counterpart to the gravitational-wave source GW 170817 marked year zero of the multi-messenger gravitational-wave era. This event was generated by the merger of two neutron stars and gave rise to an electromagnetic transient, dubbed a “kilonova”. In this proceeding article, I will show how radiative transfer simulations can illuminate neutron star mergers and provide a connection between numerical models and observational data. I will present viewing-angle dependent kilonova predictions made with the Monte Carlo radiative transfer code POSSIS and show how these can be used to interpret data, place constraints on models and guide future follow-up campaigns of gravitational-wave triggers.

Low- and intermediate mass stars experience a significant mass loss during the last phases of their evolution, which obscures them in a vast, dusty envelope. Although it has long been thought this envelope is generally spherically symmetric in shape, recent high-resolution observations find that most of these stars exhibit complex and asymmetrical morphologies, most likely resulting from binary interaction. In order to improve our understanding about these systems, theoretical studies are needed in the form of numerical simulations. Currently, a handful of simulations exist, albeit they mainly focus on the hydrodynamics of the outflow. Hence, we here present the pathway to more detailed and accurate modelling of companion-perturbed outflows with, by discussing the missing but crucial physical and chemical processes. With these state-of-the-art simulations we aim to make a direct comparison with observations to unveil the true identity on the embedded systems.

We describe a numerical model of hot Jupiter extended envelope that interacts with stellar wind. Our model is based on approximation of multi-component magnetic hydrodynamic. The processes of ionization, recombination, dissosiation and chemical reactions in hydrogen-helium envelope are taken into account. In particular, the ionization of neutral hydrogen atoms takes place due to processes of photo-ionization, charge-exchange and thermal collisions. Further, this model is supposed to be used for research on biomarkers’ dynamics in extended envelopes of hot Jupiters.

In the first observed neutron star merger, GW170817, two dynamical components, mildly- and ultra-relativistic outflows were detected independently. The first component triggered a rapidly evolving thermal transient named macronova (kilonova), while the second caused an observed short GRB where the early gamma-ray signal was followed by a multi-wavelength afterglow. These two distinct components are typically modelled independently and the observational consequences of their interplay are hardly explored. Here we summarize the results of 3D special-relativistic simulations that we have used to investigate the consequences of jet propagation through a realistic environment. We show how the presence of a jet can lead to the macronova being brighter and bluer for on-axis observers in the first few days. Then we show the consequences on the interaction on the shape of the emerging jet. Finally, we will discuss how small scale features in the emerging jet structure can impact the best-fit afterglow parameters.

The detection of Earth-size exoplanets is a technological and data analysis challenge. Future progress in Earth-mass exoplanet detection is expected from the development of extreme precision radial velocity measurements. Increasing radial velocity precision requires developing a new physics-based data analysis methodology to discriminate planetary signals from host-star-related effects, taking stellar variability and instrumental uncertainties into account. In this work, we investigate and quantify stellar disturbances of the planet-hosting solar-type star HD121504 (G2V spectral type) from 3D radiative modeling obtained with the StellarBox code. The model has been used for determining statistical properties of the turbulent plasma and obtaining synthetic spectroscopic observations for several Fe I lines at different locations on the stellar disk to mimic high-resolution spectroscopic observations.

With the use of high-resolution ALMA observations, complex structures that resemble those observed in post-AGB stars and planetary nebulae are detected in the circumstellar envelopes of low-mass evolved stars. These deviations from spherical symmetry are believed to be caused primarily by the interaction with a companion star or planet. With the use of three-dimensional hydrodynamic simulations, we study the impact of a binary companion on the wind morphology and dynamics of an AGB outflow. We classifiy the wind structures and morphology that form in these simulations with the use of a classification parameter, constructed with characteristic parameters of the binary configuration. Finally we conclude that the companion alters the wind expansion velocity through the slingshot mechanism, if it is massive enough.

In this work we applied the previously developed self-consistent 1D model of hydrogen-helium atmosphere with suprathermal electrons to close-in hot neptune GJ 436 b. The obtained height profile of density shows the two-scale structure of the planetary atmosphere. The mass-loss rate is found to be about .

Because they lose tremendous amounts of mass, cool evolved stars are major sources of dust and molecules for the interstellar medium. Spectro-imaging of the dust-driven winds around these stars has enabled us to identify recurring nonspherical patterns (e.g. spirals, arcs, compressed wind). We use radiative-hydrodynamic simulations of dust-driven winds to study the imprints left in the wind by an orbiting stellar or sub-stellar companion. We designed 3D numerical setup to solve the wind dynamics beyond the dust condensation radius and follow the flow up to several hundreds of stellar radii. Non-uniform grids enable us to capture small scale features such as shocks or disks forming around the orbiting object. Depending on its mass and orbital parameters, we reproduced typical non-spherical features such as arcs, spirals, petals and orbital density enhancements, and identified patterns associated to eccentric orbits.

The LIGO-Virgo gravitational wave detectors have confidently observed 4 events involving neutron stars: two binary neutron star (BNS) mergers (GW170817 and GW190425), and two neutron star-black hole mergers (GW200105 and GW200115). However, our theoretical understanding of the remnant properties of such systems is incomplete due to the complexities related to the modeling of matter effects and the very high computational cost of corresponding numerical relativity simulations. An important such property is the recoil velocity, which is imparted onto the remnant due to the anisotropic emission of gravitational radiation and the dynamical ejection of matter in the kilonova. In this work, we combine gravitational radiation as well as dynamical ejecta distributions, computed by the Computational Relativity numerical simulations, to get accurate estimates for BNS remnant recoil velocities. We find that recoils due to ejection of matter dominate those caused by gravitational wave emission. Knowledge of BNS remnant recoil velocities is important in determining if the remnant is retained by its environment for future hierarchical mergers which, in turn, can form binaries with black holes in the so-called lower mass gap of ∼ 3 – 5M⊙.

The nuclear equation-of-state (EOS) describing newly formed proto-neutron stars (PNSs) in core-collapse supernovae (CCSNe) is yet uncertain, and varying its prescription affects multimessenger signatures in CCSN simulations. Focusing on the gravitational wave (GW) signal, we demonstrate the effect of varying parameter values in the EOS. We conclude that an especially important parameter is the effective mass of nucleons which affect thermal properties and subsequently the PNS compactness, regulating the GW signal in both amplitude and frequency. By radially decomposing the GW emission, we show where in the PNS the GWs originate from.