Physical Sciences and Mathematics | Open Access Articles

Branchings And Time Evolution Of Reaction Networks, Changyuan Wang

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In this thesis I analyze flows in reaction networks in terms of branchings
in a digraph. If the coupled differential equations governing the rate
of change of probabilities X of a state or species are finite-differenced in time, a matrix equation (I + Adt)X(t+dt) = X(t) results, where X(t) is a vector giving the probabilities at time t and X(t+dt) is a vector giving the probabilities at time t + dt. I demonstrate that the matrix (I + Adt) may be written as the product of an incidence matrix and a weight matrix for a directed graph (digraph) representing the …

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Observations Of Very High Energy Gamma-Ray Emission From Supernova Remnants With Veritas, Mark Theiling

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The nature and source of cosmic rays has been at the core of particle astrophysics since their discovery almost a century ago. The cosmic ray spectrum is best described by a broken power law, and can be better understood as three distinct parts. Theory holds that cosmic rays up to ∼1015 eV – those below the “knee” or steepening in the spectrum – are produced in the shocks of supernova remnants. Direct detection of cosmic rays produced in supernova remnant shocks is impossible, however, as cosmic rays below ∼1018 eV are deflected by the Galactic magnetic field and cannot be …

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Using Population Synthesis Of Massive Stars To Study The Interstellar Medium Near Ob Associations, R. Voss, R. Diehl, Dieter H. Hartmann, M. Cerviño, J. S. Vink, G. Meynet, M. Limongi, A. Chieffi

Publications

Aims. We study the massive stars in OB associations and their surrounding interstellar medium environment, using a population synthesis code. Methods. We developed a new population synthesis code for groups of massive stars, where we model the emission of diﬀerent forms of energy and matter from the stars of the association. In particular, the ejection of the two radioactive isotopes 26Al and 60Fe is followed, as well as the emission of hydrogen ionizing photons, and the kinetic energy of the stellar winds and supernova explosions. We investigate various alternative astrophysical inputs and the resulting output sensitivities, especially eﬀects due to …

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Weibel Instability And Associated Strong Fields In A Fully 3d Simulation Of A Relativistic Shock, K.-I. Nishikawa, J. Niemiec, P. E. Hardee, M. Medvedev, H. Sol, Y. Mizuno, B. Zhang, M. Pohl, M. Oka, Dieter H. Hartmann

Publications

Plasma instabilities (e.g., Buneman, Weibel and other two-stream instabilities) excited in collision-less shocks are responsible for particle (electron, positron, and ion) acceleration. Using a new 3-D relativistic particle-in-cell code, we have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. The simulation has been performed using a long simulation system in order to study the nonlinear stages of the Weibel instability, the particle acceleration mechanism, and the shock structure. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic …

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Tracing The Inner Edge Of The Disk Around Hd 100546 With Rovibrational Co Emission Lines, Sean D. Brittain, Joan R. Najita, John S. Carr

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In this paper we present high-resolution 4.7 μm spectra of the isolated Herbig Be star HD 100546. HD 100546 has been the subject of intense scrutiny because it is a young nearby star with a transitional disk. We observe the Δv = 1 rovibrational CO transitions in order to clarify the distribution of warm gas in the inner disk. Modeling of the CO spectrum indicates that the gas is vibrationally excited by collisions and UV fluorescence. The observed emission extends from 13 to 100 AU. The inner edge of the molecular gas emission is consistent with the inner edge of …

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A Spectroscopic Analysis Of V505 Persei And The Origin Of The Lithium Dip, Patrick Baugh

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We study the observed Li Dip in stellar clusters and field stars, testing Rotationally Induced Mixing (RIM) by measuring Li abundances in a middle-aged (1.1±0.15 Gyr), metal poor ([Fe/H]=-0.15±0.03), short period binary, V505 Per, finding Li abundances of Log N(Li)=2.67±0.1 and 2.42±0.2 from the primary and secondary components, respectively. These abundances are significantly higher than observed abundances from single stars of similar metallicity and ZAMS T_eff; as shown by comparison with NGC 752, and suggest that RIM may be a primary cause of the Li Dip.

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The Reality Of The Wolf 630 Moving Group, Eric Bubar

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The concept of relic kinematic assemblages from dispersed stellar clusters has
remained contentious since Eggen's initial formulation of moving groups in the
1960's. However, the availability of high quality parallaxes from the Hipparcos
space astrometry mission has resulted in distance measurements for thousands of
nearby, seemingly isolated stars. With these newly determined distances, a
high resolution spectroscopic abundance analysis can be brought to bear on many of the
alleged members of these relic associations. If a structure is a relic of
an open cluster, the members can be expected to be monolithic in age and abundance
inasmuch as homogeneity is …

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Revealing The Structure Of A Pre-Transitional Disk: The Case Of The Herbig F Star Sao 206462 (Hd 135344b), C A. Grady, G Schneider, M L. Sitko, G M. Williger, K Hamaguchi, Sean D. Brittain, K Ablordeppey, D Apai, L Beerman, W J. Carpenter

Publications

SAO 206462 (HD 135344B) has previously been identified as a Herbig F star with a circumstellar disk with a dip in its infrared excess near 10 mum. In combination with a low accretion rate estimated from Br gamma, it may represent a gapped, but otherwise primordial or "pre-transitional" disk. We test this hypothesis with Hubble Space Telescope coronagraphic imagery, FUV spectroscopy and imagery and archival X-ray data, and spectral energy distribution (SED) modeling constrained by the observed system inclination, disk outer radius, and outer disk radial surface brightness (SB) profile using the Whitney Monte Carlo Radiative Transfer Code. The essentially …

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The First Two Transient Supersoft X-Ray Sources In M31 Globular Clusters And The Connection To Classical Novae, M. Henze, W. Pietsch, F. Haberl, G. Sala, R. Quimby, M. Hernanz, M. Della Valle, P. Milne, G. G. Williams, V Burwitz, J Greiner, H Stiele, Dieter H. Hartmann, A.K.H. Dong, K Hornoch

Publications

Context. Classical novae (CNe) have been found to represent the major class of supersoft X-ray sources (SSSs) in our neighbour galaxy M 31. Aims. We determine the properties and evolution of the two ﬁrst SSSs ever discovered in the M 31 globular cluster (GC) system. Methods. We have used XMM-Newton, Chandra and Swift observations of the centre region of M 31 to discover both SSSs and to determine their X-ray light curves and spectra. We performed detailed analysis of XMM-Newton EPIC PN spectra of the source in Bol 111 (SS1) using blackbody and NLTE white dwarf (WD) atmosphere models. For …

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The Very Short Supersoft X-Ray State Of The Classical Nova M31n 2007-11a, M. Henze, W. Pietsch, G. Sala, M. Della Valle, M. Hernanz, J. Greiner, V. Burwitz, M. J. Freyberg, F. Haberl, Dieter H. Hartmann, P Milne, G G. Williams

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Context. Short supersoft X-ray source (SSS) states (durations ≤100 days) of classical novae (CNe) indicate massive white dwarfs that are candidate progenitors of supernovae type Ia. Aims. We carry out a dedicated optical and X-ray monitoring program of CNe in the bulge of M 31. Methods. We discovered M31N 2007-11a and determined its optical and X-ray light curve. We used the robotic Super-LOTIS tele-scope to obtain the optical data and XMM-Newton and Chandra observations to discover an X-ray counterpart to that nova. Results. Nova M31N 2007-11a is a very fast CN, exhibiting a very short SSS state with an appearance …

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Grb 080913 At Redshift 6.7, J. Greiner, T. Krühler, J. P. U. Fynbo, A. Rossi, R. Schwarz, S. Klose, S. Savaglio, N. R. Tanvir, S. Mcbreen, T Totani, B B. Zhang, X F. Wu, D Watson, S D. Barthelmy, A P. Beardmore, P Ferrero, N Gehrels, D A. Kann, N Kawai, A Küpcü Yoldaş, P Mészáros, B Milvang-Jensen, S R. Oates, D Pierini, P Schady, K Toma, P M. Vreeswijk, A Yoldas, B Zhang, P Afonso, K Aoki, D N. Burrows, C Clemens, R Filgas, Z Haiman, Dieter H. Hartmann

Publications

We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND, which led to the discovery of its optical/NIR afterglow and the recognition of its high-z nature via the detection of a spectral break between the i and z bands. Spectroscopy obtained at the ESO-VLT revealed a continuum extending down to λ = 9400 Å, and zero ﬂux for 7500 Å<λ< 9400 Å, which we interpret as the onset of a Gunn–Peterson trough at z = 6.695± 0.025 (95.5% conﬁdence level), making GRB 080913 the highest-redshift gamma-ray burst (GRB) to date, and more distant than the highest-redshift QSO. We note that many redshift indicators that are based on promptly available burst or afterglow properties have failed for GRB 080913. We report on our follow-up campaign and compare the properties of GRB 080913 with bursts at lower redshift. In particular, since the afterglow of this burst is fainter than typical for GRBs, we show that 2 m class telescopes can identify most high-redshift GRBs.

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In Situ Probes Of The First Galaxies And Reionization: Gamma-Ray Bursts, Matthew Mcquinn, Joshua S. Bloom, Jonathan Grindlay, David Band, S. D. Barthemy, E. Berger, A. Corsi, S. Covino, G. J. Fishman, Steven R. Furlanetto, Neil Gehrels, Dieter H. Hartmann, Chryssa Kouveliotou, A S. Kutyrev, Abraham Loeb, S Harvard Moseley, Tsvi Piran, L Piro, J X. Prochaska, R Salvaterra, P Schady, A M. Soderberg, G Tagliaferri

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The ﬁrst structures in the Universe formed at z > 7, at higher redshift than all currently known galaxies. Since GRBs are brighter than other cosmological sources at high redshift and exhibit simple power-law afterglow spectra that is ideal for absorption studies, they serve as powerful tools for studying the early universe. New facilities planned for the coming decade will be able to obtain a large sample of high-redshift GRBs. Such a sample would constrain the nature of the ﬁrst stars, galaxies, and the reionization history of the Universe.

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Hd 100453: A Link Between Gas-Rich Protoplanetary Disks And Gas-Poor Debris Disks, K A. Collins, C A. Grady, K Hamaguchi, J P. Wisniewski, Sean D. Brittain, M Sitko, W J. Carpenter, J P. Williams, G S. Mathews, G M. Williger, R Van Boekel, A Carmona, Th. Henning, M E. Van Den Ancker, G Meeus, X P. Chen, R Petre, B E. Woodgate

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HD 100453 has an IR spectral energy distribution (SED) which can be fit with a power law plus a blackbody. Previous analysis of the SED suggests that the system is a young Herbig Ae star with a gas-rich, flared disk. We reexamine the evolutionary state of the HD 100453 system by refining its age (based on a candidate low-mass companion) and by examining limits on the disk extent, mass accretion rate, and gas content of the disk environment. We confirm that HD 100453B is a common proper motion companion to HD 100453A, with a spectral type of M4.0V-M4.5V, and derive …

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Nuclear Resonances: The Quest For Large Column Densities And A New Tool, J. Greiner, S. Boggs, G. Dicocco, K. T. Freese, N. Gehrels, Dieter H. Hartmann, A. Iyudin, G. Kanbach, A. A. Zdziarski

Publications

Nuclear physics offers us a powerful tool: using nuclear resonance absorption lines to infer the physical conditions in astrophysical settings which are otherwise diffcult to deduce. Present-day technology provides an increase in sensitivity over previous gamma-ray missions large enough to utilize this tool for the ﬁrst time. The most exciting promise is to measure gamma-ray bursts from the ﬁrst star(s) at redshifts 20–60, but also active galactic nuclei are promising targets.

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Physical Sciences and Mathematics Commons^™

Full-Text Articles in Physical Sciences and Mathematics

Branchings And Time Evolution Of Reaction Networks, Changyuan Wang

All Dissertations

Observations Of Very High Energy Gamma-Ray Emission From Supernova Remnants With Veritas, Mark Theiling

All Dissertations

Using Population Synthesis Of Massive Stars To Study The Interstellar Medium Near Ob Associations, R. Voss, R. Diehl, Dieter H. Hartmann, M. Cerviño, J. S. Vink, G. Meynet, M. Limongi, A. Chieffi

Publications

Weibel Instability And Associated Strong Fields In A Fully 3d Simulation Of A Relativistic Shock, K.-I. Nishikawa, J. Niemiec, P. E. Hardee, M. Medvedev, H. Sol, Y. Mizuno, B. Zhang, M. Pohl, M. Oka, Dieter H. Hartmann

Publications

Tracing The Inner Edge Of The Disk Around Hd 100546 With Rovibrational Co Emission Lines, Sean D. Brittain, Joan R. Najita, John S. Carr

Publications

A Spectroscopic Analysis Of V505 Persei And The Origin Of The Lithium Dip, Patrick Baugh

All Theses

The Reality Of The Wolf 630 Moving Group, Eric Bubar

All Dissertations

Revealing The Structure Of A Pre-Transitional Disk: The Case Of The Herbig F Star Sao 206462 (Hd 135344b), C A. Grady, G Schneider, M L. Sitko, G M. Williger, K Hamaguchi, Sean D. Brittain, K Ablordeppey, D Apai, L Beerman, W J. Carpenter

Publications

The First Two Transient Supersoft X-Ray Sources In M31 Globular Clusters And The Connection To Classical Novae, M. Henze, W. Pietsch, F. Haberl, G. Sala, R. Quimby, M. Hernanz, M. Della Valle, P. Milne, G. G. Williams, V Burwitz, J Greiner, H Stiele, Dieter H. Hartmann, A.K.H. Dong, K Hornoch

Publications

The Very Short Supersoft X-Ray State Of The Classical Nova M31n 2007-11a, M. Henze, W. Pietsch, G. Sala, M. Della Valle, M. Hernanz, J. Greiner, V. Burwitz, M. J. Freyberg, F. Haberl, Dieter H. Hartmann, P Milne, G G. Williams

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Nuclear Resonances: The Quest For Large Column Densities And A New Tool, J. Greiner, S. Boggs, G. Dicocco, K. T. Freese, N. Gehrels, Dieter H. Hartmann, A. Iyudin, G. Kanbach, A. A. Zdziarski

Publications