Radiation Hydrodynamics of Line-Driven Winds

Dimtri Mihalas' textbooks in the 70's and 80's on "Stellar Atmospheres" and "Foundations of Radiation Hydrodynamics" helped lay the early groundwork for understanding the moving atmospheres and winds of massive, luminous stars. Indeed, the central role of the momentum of stellar radiation in driving the mass outflow makes such massive-star winds key prototypes for radiation hydrodynamical processes. This paper reviews the dynamics of such radiative driving, building first upon the standard CAK model, and then discussing subtleties associated with the development and saturation of instabilities, and wind initiation near the sonic point base. An overall goal is to illuminate the rich physics of radiative driving and the challenges that lie ahead in developing dynamical models that can explain the broad scaling of mass loss rate and flow speed with stellar properties, as well as the often complex structure and variability observed in massive-star outflows.Comment: 14 pages. to appear in "Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics

Including All the Lines

I present a progress report on including all the lines in the linelists, including all the lines in the opacities, including all the lines in the model atmosphere and spectrum synthesis calculations, producing high-resolution, high-signal-to-noise atlases that show (not quite) all the lines, so that finally we can determine the properties of stars from a few of the lines.Comment: 9 pages, no figures. Presented at "Dimitrifest" conference in Boulder, Colorado, March 30 - April 3, 200

Calculation of the Solar UV/EUV Spectrum in Spherical Symmetry

We present work in progress concerning spectral synthesis calculations of the solar UV/EUV in spherical symmetry carried out with the Solar Radiation Physical Modeling (SRPM) project. We compare the synthetic irradiance spectrum for the quiet Sun with the recent solar minimum spectrum taken with the EVE rocket instrument. The good agreement of the synthetic spectrum with the observation shows that the employed atmosphere structures are suitable for irradiance calculations.Comment: to appear in: Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics, edited by I. Hubeny, K. Macgregor, and K. Werner, AIP Conference Proceeding

Formation of helium lines in solar prominences

We summarize the results on the formation of the helium spectrum in solar prominences obtained over recent years. The radiative transfer problem under non-LTE conditions is solved to compute the profiles of the lines of He I and He II. The structure of the prominence-to-corona transition region (PCTR) has a major influence on the resulting spectrum of the resonance lines since they are formed mostly in this part of the prominence. However, subordinate lines are also affected by the structure of the PCTR. We pay particular attention to the formation of the He II 304 Å resonance line which is routinely observed from space, but yet not fully understood. Future steps in the modelling will be addressed

Radiation-Driven Outflows in Active Galactic Nuclei

We review the results from multi-dimensional, time-dependent simulations of gas dynamics in AGN. We will focus on two types of outflows powered by radiation emitted from the AGN central engine: (i) outflows driven from the innermost part of an accretion disk and (2) outflows driven from a large-scale inflow that is likely the main supplier of material to the central engine. We discuss the relevance of both types of outflows to the so-called AGN feedback problem. However, the AGN feedback should not be considered separately from the AGN physics. Therefore, we also discuss the issue whether the properties of the same outflows are consistent with the gas properties in broad- and narrow-line regions.Comment: 9 pages, 5 figures, in Recent Directions In Astrophysical Quantitative Spectroscopy And Radiation Hydrodynamics: Proceedings of the International Conference in Honor of Dimitri Mihalas for His Lifetime Scientific Contributions on the Occasion of His 70th Birthday (AIP Conference Proceedings 1171

Bloodstream form pre-adaptation to the tsetse fly in Trypanosoma brucei

African trypanosomes are sustained in the bloodstream of their mammalian hosts by their extreme capacity for antigenic variation. However, for life cycle progression, trypanosomes also must generate transmission stages called stumpy forms that are pre-adapted to survive when taken up during the bloodmeal of the disease vector, tsetse flies. These stumpy forms are rather different to the proliferative slender forms that maintain the bloodstream parasitaemia. Firstly, they are non proliferative and morphologically distinct, secondly, they show particular sensitivity to environmental cues that signal entry to the tsetse fly and, thirdly, they are relatively robust such that they survive the changes in temperature, pH and proteolytic environment encountered within the tsetse midgut. These characteristics require regulated changes in gene expression to pre-adapt the parasite and the use of environmental sensing mechanisms, both of which allow the rapid initiation of differentiation to tsetse midgut procyclic forms upon transmission. Interestingly, the generation of stumpy forms is also regulated and periodic in the mammalian blood, this being governed by a density-sensing mechanism whereby a parasite-derived signal drives cell cycle arrest and cellular development both to optimise transmission and to prevent uncontrolled parasite multiplication overwhelming the host.In this review we detail recent developments in our understanding of the molecular mechanisms that underpin the production of stumpy forms in the mammalian bloodstream and their signal perception pathways both in the mammalian bloodstream and upon entry into the tsetse fly. These discoveries are discussed in the context of conserved eukaryotic signalling and differentiation mechanisms. Further, their potential to act as targets for therapeutic strategies that disrupt parasite development either in the mammalian bloodstream or upon their transmission to tsetse flies is also discussed

Teff and log g dependence of velocity fields in M-stars

We present an investigation of velocity fields in early to late M-type hydrodynamic stellar atmosphere models. These velocities will be expressed in classical terms of micro- and macro-turbulent velocities for usage in 1D spectral synthesis. The M-star model parameters range between log g of 3.0 - 5.0 and Teff of 2500 K - 4000 K. We characterize the Teff- and log g-dependence of the hydrodynamical velocity fields in these models with a binning method, and for the determination of micro-turbulent velocities, the Curve of Growth method is used. The macro-turbulent velocities are obtained by convolutions with Gaussian profiles. Velocity fields in M-stars strongly depend on log g and Teff. Their velocity amplitudes increase with decreasing log g and increasing Teff. The 3D hydrodynamical and 1D macro-turbulent velocities range from ~100 m/s for cool high gravity models to ~ 800 m/s - 1000 m/s for hot models or models with low log g. The micro-turbulent velocities range in the order of ~100 m/s for cool models, to ~600 m/s for hot or low log g models. Our M-star structure models are calculated with the 3D radiative-hydrodynamics (RHD) code CO5BOLD. The spectral synthesis on these models is performed with the line synthesis code LINFOR3D.Comment: 8 pages, 6 Figures, Proceeding fot the "Recent directions in astrophysical quantitative spectroscopy and radiation hydrodynamics" conferenc

3D Radiative Transfer with PHOENIX

Using the methods of general relativity Lindquist derived the radiative transfer equation that is correct to all orders in v/c. Mihalas developed a method of solution for the important case of monotonic velocity fields with spherically symmetry. We have developed the generalized atmosphere code PHOENIX, which in 1-D has used the framework of Mihalas to solve the radiative transfer equation (RTE) in 1-D moving flows. We describe our recent work including 3-D radiation transfer in PHOENIX and particularly including moving flows exactly using a novel affine method. We briefly discuss quantitative spectroscopy in supernovae.Comment: 13 pages, 9 figures, to appear in Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics, Ed. I. Hubeny, American Institute of Physics (2009

Cosmological Radiation Hydrodynamics with ENZO

We describe an extension of the cosmological hydrodynamics code ENZO to include the self-consistent transport of ionizing radiation modeled in the flux-limited diffusion approximation. A novel feature of our algorithm is a coupled implicit solution of radiation transport, ionization kinetics, and gas photoheating, making the timestepping for this portion of the calculation resolution independent. The implicit system is coupled to the explicit cosmological hydrodynamics through operator splitting and solved with scalable multigrid methods. We summarize the numerical method, present a verification test on cosmological Stromgren spheres, and then apply it to the problem of cosmological hydrogen reionization.Comment: 14 pages, 3 figures, to appear in Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics, Ed. I. Hubeny, American Institute of Physics (2009