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Full-Text Articles in Physical Sciences and Mathematics
Analysis Of Doppler-Broadened X-Ray Emission Line Profiles From Hot Stars, David H. Cohen, Roban Hultman Kramer , '03, S. P. Owocki
Analysis Of Doppler-Broadened X-Ray Emission Line Profiles From Hot Stars, David H. Cohen, Roban Hultman Kramer , '03, S. P. Owocki
Physics & Astronomy Faculty Works
We show how X-ray emission arising within an accelerating, expanding medium that also contains a source of continuum absorption generates line profiles of a characteristic shape. A simple, spherical wind model based on this picture provides good fits to the Chandra HETGS spectrum of the prototypical O star, Zeta Pup. We discuss the model, the fitting procedure and the determination of confidence limits on the model parameters, and our initial results for this star. The derived fit parameters are consistent with a generic wind-shock scenario for Zeta Pup, but there are several surprising aspects of the results, including a lower-than-expected …
New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis, N. A. Miller, J. P. Cassinelli, W. L. Waldron, J. J. Macfarlane, David H. Cohen
New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis, N. A. Miller, J. P. Cassinelli, W. L. Waldron, J. J. Macfarlane, David H. Cohen
Physics & Astronomy Faculty Works
The Chandra spectrum of delta Ori A shows emission lines from hydrogen- and helium-like states of Si, Mg, Ne, and O, along with N VII Lyalpha and lines from ions in the range Fe XVII-Fe XXI In contrast to the broad lines seen in zeta Pup and zeta Ori (850 +/- 40 and 1000 +/- 240 km s(-1) half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 +/- 60 km s(-1) HWHM. This is much lower than the measured wind terminal velocity of 2000 km s(-1). The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate …
Experimental Observation Of Energetic Ions Accelerated By Three-Dimensional Magnetic Reconnection In A Laboratory Plasma, Michael R. Brown, C. D. Cothran, Matthew Joseph Landreman , '03, David J. Schlossberg , '01, W. H. Matthaeus
Experimental Observation Of Energetic Ions Accelerated By Three-Dimensional Magnetic Reconnection In A Laboratory Plasma, Michael R. Brown, C. D. Cothran, Matthew Joseph Landreman , '03, David J. Schlossberg , '01, W. H. Matthaeus
Physics & Astronomy Faculty Works
Magnetic reconnection is widely believed responsible for heating the solar corona as well as for generating X-rays and energetic particles in solar flares. On astrophysical scales, reconnection in the intergalactic plasma is a prime candidate for a local source (Mpc) of cosmic rays exceeding the Greisen-Zatsepin-Kuzmin cutoff (∼10(19) eV). In a laboratory astrophysics experiment, we have made the first observation of particles accelerated by magnetic reconnection events to energies significantly above both the thermal and the characteristic magnetohydrodynamic energies. These particles are correlated temporally and spatially with the formation of three-dimensional magnetic structures in the reconnection region.
Energetic Particles From Three-Dimensional Magnetic Reconnection Events In The Swarthmore Spheromak Experiment, Michael R. Brown, C. D. Cothran, Matthew J. Landreman , '03, David J. Schlossberg , '01
Energetic Particles From Three-Dimensional Magnetic Reconnection Events In The Swarthmore Spheromak Experiment, Michael R. Brown, C. D. Cothran, Matthew J. Landreman , '03, David J. Schlossberg , '01
Physics & Astronomy Faculty Works
Measurements are presented from the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] showing a population of superthermal, super-Alfvénic ions with Ē≅90 eV and Emax⩾200 eV accelerated by reconnection activity in three-dimensional magnetic structures. These energetic ions are temporally and spatially correlated with three-dimensional magnetic reconnection events (measured with a 3D probe array) and are accelerated along the X-line normal to the local 2D plane of reconnection. In a typical SSX discharge, the peak reconnection electromotive force ℰ=vBL⩽(105 m/s)(0.05 T)(0.1 m)=500 V consistent with our observations. In addition, test particle simulations using magnetohydrodynamic (MHD) data from …
Radiation Science Using Z-Pinch X-Rays, J. E. Bailey, G. A. Chandler, David H. Cohen, M. E. Cuneo, M. E. Foord, R. F. Heeter, D. Jobe, P. W. Lake, J. J. Macfarlane, T. J. Nash, D. S. Nielson, R. Smelser, J. Torres
Radiation Science Using Z-Pinch X-Rays, J. E. Bailey, G. A. Chandler, David H. Cohen, M. E. Cuneo, M. E. Foord, R. F. Heeter, D. Jobe, P. W. Lake, J. J. Macfarlane, T. J. Nash, D. S. Nielson, R. Smelser, J. Torres
Physics & Astronomy Faculty Works
Present-day Z-pinch experiments generate 200 TW peak power, 5–10 ns duration x-ray bursts that provide new possibilities to advance radiation science. The experiments support both the underlying atomic and plasma physics, as well as inertial confinement fusion and astrophysics applications. A typical configuration consists of a sample located 1–10 cm away from the pinch, where it is heated to 10–100 eV temperatures by the pinch radiation. The spectrally-resolved sample-plasma absorption is measured by aiming x-ray spectrographs through the sample at the pinch. The pinch plasma thus both heats the sample and serves as a backlighter. Opacitymeasurements with this source are …
Effective Index Of Refraction, Optical Rotation, And Circular Dichroism In Isotropic Chiral Liquid Crystals, D. Lacoste, Peter J. Collings, T. C. Lubensky
Effective Index Of Refraction, Optical Rotation, And Circular Dichroism In Isotropic Chiral Liquid Crystals, D. Lacoste, Peter J. Collings, T. C. Lubensky
Physics & Astronomy Faculty Works
This paper concerns optical properties of the isotropic phase above the isotropic-cholesteric transition and of the blue phase BP III. We introduce an effective index, which describes spatial dispersion effects such as optical rotation, circular dichroism, and the modification of the average index due to the fluctuations. We derive the wavelength dependence of these spatial dispersion effects quite generally without relying on an expansion in powers of the chirality and without assuming that the pitch of the cholesteric P is much shorter than the wavelength of the light lambda, an approximation that has been made in previous studies of this …
Mass-Loss And Magnetospheres: X-Rays From Hot Stars And Young Stellar Objects, M. Gagné, David H. Cohen, S. P. Owocki, A. Ud-Doula
Mass-Loss And Magnetospheres: X-Rays From Hot Stars And Young Stellar Objects, M. Gagné, David H. Cohen, S. P. Owocki, A. Ud-Doula
Physics & Astronomy Faculty Works
High-resolution X-ray spectra of high-mass stars and low-mass T-Tauri stars obtained during the first year of the Chandra mission are providing important clues about the mechanisms which produce X-rays on very young stars. For zeta Puppis (O4 If) and zeta Ori (O9.5 I), the broad, blue-shifted line profiles, line ratios, and derived temperature distribution suggest that the X-rays are produced throughout the wind via instability-driven wind shocks. For some less luminous OB stars, like theta^1 Ori C (O7 V) and tau Sco (B0 V), the line profiles are symmetric and narrower. The presence of time-variable emission and very high-temperature lines …
Liquid Crystals: Nature's Delicate Phase Of Matter, Peter J. Collings
Liquid Crystals: Nature's Delicate Phase Of Matter, Peter J. Collings
Physics & Astronomy Faculty Works
No abstract provided.