With next-generation astronomical facilities like WEAVE, 4MOST, and SDSS-V large datasets of high-quality stellar spectra will become available soon. The need for cutting edge 3D non-LTE radiative transfer codes is clear, but the demand for easy-to-use spectrum synthesis tools is even greater. We aim to provide both by supplying a non-LTE RT module based on the Multi3D code to the recently...
Late-type ultra metal-poor stars are thought to be formed from interstellar gas enriched by only one to few supernovae. As such, their elemental abundances and total metal content are important in understanding the limits of star formation in the early universe and the chemical evolution of the Milky Way. In this talk, I will present an updated chemical abundance analysis of the most...
Recent 3D simulations of cool giants and supergiants, specifically the asymptotic giant branch (AGB) and red supergiant (RSG) stars, with the CO5BOLD radiation-hydrodynamics code cover a wider range of stellar parameters and with greater temporal and spatial resolution than before. In these simulations, the hydrodynamical steps were handled straightforwardly with the Roe solver with 1D...
The albedo of a celestial body is the fraction of incident starlight reflected by it. The study of the albedos of Solar System objects is at least a century old, at least in the Western world. As examples: Bond (1861) speculated on the near-unity albedo of Jupiter, while Russell (1916) observed the opposition surge of the Moon near and at full phase. The light of a planet or moon varying with...
The helium line at 1083 nm is one of the strongest spectral features observable in transit spectroscopy of exoplanet atmospheres. As such, it is a powerful diagnostic of upper atmospheres of exoplanets, providing valuable insight into their dynamics and the process of atmospheric escape. Absorption in this line is caused by neutral helium atoms in an excited, metastable state. At low densities...
Ultra-hot Jupiters (UHJs) have become prime targets for atmospheric characterisation. KELT-9b is the hottest of the known UHJs and both hydrogen Balmer lines and metal line features have been detected in the planetary transmission spectrum. I will show how NLTE effects drive the temperature pressure structure of KELT-9b's atmosphere and that NLTE effects must be taken into account in order to...
Exoplanet atmospheres provide ideal atmospheric laboratories to explore atmospheres unlike anything in our Solar System. Atmosphere characterisation is also an important tool in understanding exoplanetary system formation and evolution. However, exoplanets are not globally homogeneous, as the light we observe must pass though many diverse regions any observations probe a wide variety of...
The center-to-limb variation (CLV) of the stellar lines across the stellar disk is an important effect for planetary transit spectroscopy. Indeed the variation of spectral line profiles when the planet transits different part of the stellar disk can affect the determination of elemental abundances in the planetary atmospheres, as shown by Yan et al. (2017). Accurately modeling the CLV effect...
High-quality transition probabilities (oscillator strengths, log(gf)) are of vital importance in the analysis of astronomical spectra. Along with spectral line wavelengths and widths, they allow astronomers not only to determine the chemical composition of stellar and exoplanetary atmospheres, but also to gain some insight into their temperature and electron density.
For more than 30 years,...
Recent direct evidence for ongoing accretion at gas giants such as PDS 70 b and c and Delorme 1 (AB)b make theoretical models of hydrogen-line emission timely. For the shock at the planet's surface, we present fluxes in the strongest indicators (H alpha, H beta, Pa beta, etc.) using the non-LTE, chemical-kinetics code of Aoyama et al. (2018). We consider the relevant large parameter space in...
Infall drives the growth of protostars in terms of their mass as well as the structural and chemical complexities. The rich spectra of molecules best probe the infall kinematics at a wide range of spatial scales and physical environments. Molecular emission highlights the infalling gas as specific patterns in position-velocity diagrams and streamers. Moreover, red-shifted absorption against...
The coupling between multi-species dust dynamics and radiative transfer is crucial for the realistic modeling of cold astrophysical environments such as star-forming regions, protoplanetary disks, and exoplanets atmospheres. At low temperatures, dust distribution plays a primordial role in shaping gas opacity, even when the dust mass fraction is negligible. Thus, in this talk, I will present a...
Radiative transfer modelling is an essential tool in star-forming studies, providing the connection between the complex physical reality within the interstellar medium and the radiation observed from it. Therefore, it is needed both in the analysis of observations and when predictions are made based on numerical simulations.
I will discuss the modelling of spectral lines and the dust...
Asymptotic giant branch (AGB) stars are agonising cool giants that lose mass through spectacular stellar winds. The gas and dust ejected through the winds create a chemically-rich expanding envelope around the star, namely the circumstellar envelope (CSE), and eventually enrich the interstellar medium. The mass loss is the most crucial process that determines the fate and the...
We present Quokka, a new subcycling-in-time, block-structured adaptive mesh refinement (AMR) radiation hydrodynamics code optimised for graphics processing units (GPUs). Quokka solves the equations of hydrodynamics with the piecewise parabolic method (PPM) in a method-of-lines formulation, and handles radiative transfer via the variable Eddington tensor (VET) radiation moment equations with a...
Understanding the processes that form stars and planets requires line observations of atoms and molecules at long (infrared and radio) wavelengths. Radiative transfer tools are essential for the step from observed line intensities to physical and chemical conditions such as cloud masses, kinetic temperatures, gas densities, and atomic & molecular abundances. This talk describes existing tools...
I will review methods for solving time-dependent radiation transfer in general relativistic spacetimes and described a new method for treating radiation transfer in a five or six dimensional finite volume approach. I will also describe our efforts to apply direct transfer solutions to simulations of black hole accretion and the driving of accretion disk winds via radiation pressure.
The Event Horizon Telescope is a global effort to construct an
Earth-sized virtual radio telescope array, with the goal to make pictures and movies of two nearby supermassive black holes. A detailed theoretical understanding of black hole accretion is now crucial to interpret these observations. I will review our current efforts to model polarimetric properties of light produced in...
Emission from the Broad-line regions (BLR) in active galaxies are produced primarily by photoionization processes, driven by the continuum arising from an underlying, complex structure circumscribing the black hole. Modelling the broad-band spectral energy distribution (SED) that ionizes these gas-rich BLRs is key to understanding the various radiative processes leading to the emission...
A binary neutron star merger (BNS) is expected to produce supernova-like radioactively powered transient known as a kilonova (KN), which enters the nebular phase several days after the merger. Modelling of the ejecta in this phase has often been approached under the assumption that local thermodynamic equilibrium (LTE) is applicable. In order to test the validity of this assumption, we compare...
We present a new algorithm for radiative transfer, based on a statistical Monte-Carlo approach, that does not suffer from teleportation effects and yields smooth results. Implicit-Monte-Carlo (IMC) techniques for modelling radiative transfer exist from the 70's. However, in optically thick problems, the basic algorithm suffers from ‘teleportation’ errors, where the photons propagate faster...
Nebular [Ca II] emission can show up in the spectra of just about every type of supernovae (SNe): SNe Type Ia, core collapse SNe and of course the elusive Ca-rich transients. But what this emission can tell us, beyond there being some (how much?) calcium in the ejecta, is not well understood. I will present the early results of ongoing work to quantify this phenomena using NLTE radiative...
Tidal disruption events, in which stars are torn apart by massive black holes, are ideal laboratories for studying the accretion and emission physics around black holes. In this talk, we will show some of our recent general relativistic magnetohydrodynamic simulations of super-Eddington disks formed in tidal disruptions and their spectra obtained via Monte Carlo radiative transfer codes. We...
After the tidal disruption event (TDE) of a star around a supermassive black hole (SMBH), if the stellar debris stream rapidly circularizes and forms a compact disc, the TDE emission is expected to peak in the soft X-ray or far ultraviolet (UV). The fact that many TDE candidates are observed to peak in the near UV and optical has challenged conventional TDE emission models. By idealizing a...
We present, for the first time, a fully self-consistent radiation hydrodynamic simulation of a realistic tidal disruption event (TDE). TDEs are highly luminous, multiwavelength astrophysical transients that carry great promise for measuring the properties of supermassive black holes, but the complex physics and large dynamic range of the problem has until now prevented self-consistent...
When a star comes too close to a supermassive black hole, it gets torn apart by strong tidal forces in a tidal disruption event. The emitted signal represents a powerful probe of these compact objects, the large majority being otherwise starved of gas and therefore undetectable. Exploiting this potential requires a precise characterization of the electromagnetic signatures from these phenomena...
A wealth of spectral data now exists for the flares that follow the tidal disruptions of stars by supermassive black holes, over a wide range of wavelengths. The information encoded in these spectra will be essential to uncovering the dynamical process by which the disruption unfolds and the radiation is generated, which remains intensely debated. However, the theoretical interpretation of...
Considerable progress has been made towards modeling supernova (SN) spectra using a variety of codes and techniques. The codes broadly fall into three categories - hydro codes that treat the hydrodynamics but approximate the radiative transfer and the properties of the gas; transfer codes that treat the radiative transfer and gas properties (e.g., temperature, ionization structure)...
It is widely accepted that Type Ia supernovae (SNe Ia) are thermonuclear explosions of a CO white dwarf in a binary system, but it is still unknown how the explosive nucleosynthesis proceeds during the explosion. Thanks to the recent technological development of the transient observations, many supernovae are now detected shortly after the explosion, followed by quick spectroscopic...
A kilonova in the first neutron star merger GW170817 provided us with evidence that the merger ejects a large amount of neutron rich material. Despite the success of the very detailed observations, there remain unanswered questions. Non-LTE modelings of kilonovae likely play key roles to fully understand kilonovae. I will talk about the recent progress in non-LTE kilonova and discuss the...
It has long since been established that observable actinides in the universe originate from the r-process. In 2017, the electromagnetic counterpart to the gravitational wave detection of two merging neutron stars was observed. From the light curve alone it was possible to characterise two ejecta components: one that contains low-Ye material such as lanthanides and possibly actinides, and a...
We use the 3D radiative transfer code ARTIS to predict light curves and spectra for hydrodynamic explosion models. We first present radiative transfer simulations of the ‘double detonation’ scenario, which is a promising explosion mechanism to explain Type Ia supernovae from sub-Chandrasekhar mass white dwarfs. The synthetic spectra and light curves from our approximate non-LTE calculations...
Exoplanet atmospheres provide ideal atmospheric laboratories to explore atmospheres unlike anything in our Solar System. Atmosphere characterisation is also an important tool in understanding exoplanetary system formation and evolution. However, exoplanets are not globally homogeneous, as the light we observe must pass though many diverse regions any observations probe a wide variety of...
Measuring the driving mode of turbulence is important for characterizing its role in the ISM. The driving mode of turbulence is parameterized by b, the ratio of the width of the gas density PDF to the turbulent Mach number. b ~ 1/3, 1, and 0.4 correspond to turbulence driving that is purely solenoidal, purely compressive, and a natural mixture of the two, respectively. We use high-resolution...
