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Proposal Number: 10200640

Title: Towards a Better Understanding of the X-Ray Emission from Wind-Blown Bubbles around Massive Stars

PI Name: Vikram Dwarkadas

Stellar mass-loss leads to the formation of circumstellar wind-blown bubbles (WBB) around the star, with a low density, high pressure, extremely hot interior that should be observable as diffuse hard X-ray emission. Instead, if diffuse X-ray emission is detected at all, both the luminosity and temperature are orders of magnitude lower than expected. Herein we propose to carry out three-dimensional simulations to model the complex structure of WBBs around massive stars. We will take into account the variation in mass loss properties over the star's lifetime, ionization from the star, thermal conduction and interior turbulence. We will compute the X-ray emission and compare to observations. Realistic simulations will go a long way towards addressing the observed discrepancies with data.

Proposal Number: 10400359

Title: From hot spots to shocked shells: The interaction of microquasars with the ISM

PI Name: Sebastian Heinz

We propose to develop a comprehensive set of numerical simulations of microuasar interactions with the ISM. We will incorporate characteristics of the ISM (such as multi-phase gas and Galactic shear) that make this interaction qualitatively different from what we have already studied in AGNs. The goal of these simulations is to directly model observations of this interaction in the form of X-ray hot spots, shocked shells, and radio cavities and to investigate the impact microquasars have on their surroundings.

Proposal Number: 10400811

Title: K-Shell Photoabsorption Studies for Modeling Interstellar Medium Spectra

PI Name: Thomas Gorczyca

Proper modeling of the interstellar medium (ISM) is crucial to identify intrinsic line features from any object, and this modeling in turn relies on knowledge of the photoabsorption cross sections of the constituent elements in the ISM. In the past, we have computed atomic data which were then used within ISM models to determine elemental abundances of oxygen and neon ions in the ISM by X-ray astronomer colleagues from Chandra observations of X-ray binaries. We propose to complete state-of-the-art photoabsorption calculations for all carbon ions, and to begin similar investigations of nitrogen and magnesium ions. These data will be provided to our colleagues interpreting Chandra spectra.

Proposal Number: 10500791

Title: Understanding the X-ray emission from SN 1987A via Multi-Dimensional Simulations

PI Name: Vikram Dwarkadas

SN 1987A, probably the best observed supernova (SN) ever, shows linearly increasing hard X-ray emission from day 1200, with soft Xrays increasing more rapidly, as a result of the SN shock impacting a dense and complicated circumstellar medium (CSM). The observations can only be understood via detailed, and equally high-resolution, numerical modeling that takes the pre-SN CSM into account. Using 3D hydrodynamic simulations. I propose a two-year study to investigate the interaction of the SN shock wave with the ambient medium formed by the pre-SN star in SN 1987A. We will aim to create a model that is consistent with the morphology, dynamics, kinematics and emission structures from the remnant. The results will also be applicable to objects where shock wave interaction is predominant.

Proposal Number: 10700397

Title: The Nature and Origin of Quasar Outflows

PI Name: Frederick Hamann

We propose a theoretical study of quasar outflows using a unique combination of micro-physics, radiative gas dynamics and spectral synthesis. We will make the first thorough examination of quasar/outflow properties to address these questions: What physical circumstances can radiatively drive different types of outflows? Where do the flows originate? What is the physical relationship between the high column density X-ray absorber and the outflowing BAL gas? Is an X-ray absorber required as a radiative "shield"? What are the mass loss rates and kinetic energy yields? We will test our results based on comparisons to existing Chandra and UV data, and advance Chandra science by making testable predictions, including a catalog of predicted spectra and observable outflow/spectral parameters.

Proposal Number: 10700443

Title: Modeling quasars in the young Universe

PI Name: Marta Volonteri

We propose to study, by means of dedicated simulations of massive black hole (MBH) build-up, the possibility to constrain the existence and nature of the AGN population at z>4-6 with deep Chandra observations. This proposal aims at extending the predictive power of available models, focussing on the z=4-6 range, where data is becoming available. We will address (i) MBHs formation, (ii) MBHs dynamics, (iii) MBH feeding, (iv) MBH radiative output, taking into consideration small scale physical processes, and large scale environment. We will make publicly available the model results (luminosity functions, number counts, mass functions, redshift distributions, column density statistics) which can contribute to the interpretation of archival, ongoing and future deep observations.

Proposal Number: 10800390

Title: Shaken, then stirred: The interaction of sound waves with X-ray cavities and bubbles in galaxy clusters

PI Name: Sebastian Heinz

We propose to investigate the complex interaction of sound waves with bubbles and filaments of radio plasma in the inhomogeneous intracluster medium. This interaction is important for dissipating wave energy (thus heating cooling flow atmospheres) and creating a complex, turbulent, multiphase mixture of gas in the wake of the waves that can severely affect the X-ray appearance of clusters. Our planned program of 3D hydro and MHD simulations will investigate the role that shock wave/bubble interactions play in shaping the X-ray emitting atmospheres of galaxy clusters observed with Chandra.

Proposal Number: 10800396

Title: Conduction and Multiphase Structure in the ICM

PI Name: Mark Voit

Recent observations of H-alpha emission and blue light from brightest cluster galaxies are suggesting that star formation happens only if radiative cooling is more efficient than thermal conduction, allowing a multiphase medium to be present. We are proposing to perform hydrodynamical adaptive mesh refinement simulations of cooling, conduction, and condensation in cluster cores to test this hypothesis, representing the first detailed simulations to focus on a conduction-related transition to multiphase structure in the intracluster medium.

Proposal Number: 10800516

Title: A Study of Ram Pressure Stripping with Numerical Simulations of the Merging Galaxy Group M86

PI Name: Scott Randall

X-ray observations of the elliptical galaxy M86, which is currently merging with the Virgo cluster, show several interesting features in the diffuse emission, including a long ram pressure stripped tail. As Virgo is the nearest rich cluster, M86 provides the most detailed view of ram pressure stripping possible. Our recent analysis of Chandra observations revealed detailed structure, derived the length of the stripped tail, which is the longest presently known, and tightly constrained the orbit of M86. We propose to use these constraints to perform accurate N-body/hydrodynamical simulations of this system, which are required to fully interpret its complex structure. By comparing simulations with observations, we can study the stripping process and physical conditions in the ICM.

Proposal Number: 10910235

Title: The OVI Mystery

PI Name: Smita Mathur

Chandra observations have uncovered an extraordinary problem: the O VI column densities derived from X-ray and UV absorption lines do not match. Obvious possible solutions to this problem such as X-ray data quality, saturation effects, and known atomic physics uncertainties do not work in all cases. Astrophysical scenarios also fail to provide a global solution to the O VI problem. We propose a theoretical investigation with the aim of resolving the O VI mystery. This would have a far-reaching impact on our understanding of warm-hot plasma systems such as hot stars, the hot interstellar medium, AGN outflows, and the warm-hot intergalactic medium. Resolving the O VI mystery is thus important to astronomy in general, Chandra science in particular, and possibly to atomic physics as well.

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