The Detection of Wind Variability in Magellanic Cloud O Stars

We present Far Ultraviolet Explorer (FUSE) spectra for three Magellanic Cloud O stars (Sk 80, Sk -67 05 and Sk -67 111) with repeated observations. The data demonstrate the capabilities of FUSE to perform time-resolved spectroscopy on extragalactic stars. The wavelength coverage of FUSE provides access to resonance lines due to less abundant species, such as sulfur, which are unsaturated in O supergiants. This allows us to examine wind variability at all velocities in resonance lines for stars with higher mass loss rates than can be studied at longer (lambda > 1150 A) wavelengths. The FUSE wavelength range also includes resonance lines from ions which bracket the expected dominant ionization stage of the wind. Our observations span 1-4 months with several densely sampled intervals of 10 hours or more. These observations reveal wind variability in all of the program stars and distinctive differences in the ionization structure and time scales of the variability. Sk -67 111 demonstrates significant wind variability on a time scale less than 10 hours and the coolest O star (Sk -67 05) exhibits the largest variations in O VI.Comment: 3 pages of text and 3 JPG figures. To be included in the FUSE ApJ Letters special issu

Overview of the Far Ultraviolet Spectroscopic Explorer Mission

The Far Ultraviolet Spectroscopic Explorer satellite observes light in the far-ultraviolet spectral region, 905 - 1187 A with high spectral resolution. The instrument consists of four coaligned prime-focus telescopes and Rowland spectrographs with microchannel plate detectors. Two of the telescope channels use Al:LiF coatings for optimum reflectivity from approximately 1000 to 1187 A and the other two use SiC coatings for optimized throughput between 905 and 1105 A. The gratings are holographically ruled to largely correct for astigmatism and to minimize scattered light. The microchannel plate detectors have KBr photocathodes and use photon counting to achieve good quantum efficiency with low background signal. The sensitivity is sufficient to examine reddened lines of sight within the Milky Way as well as active galactic nuclei and QSOs for absorption line studies of both Milky Way and extra-galactic gas clouds. This spectral region contains a number of key scientific diagnostics, including O VI, H I, D I and the strong electronic transitions of H2 and HD.Comment: To appear in FUSE special issue of the Astrophysical Journal Letters. 6 pages + 4 figure

On-Orbit Performance of the Far Ultraviolet Spectroscopic Explorer (FUSE) Satellite

Launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed by an extensive period of calibration and characterization as part of the preparation for normal satellite operations. Major tasks carried out during this period include initial coalignment, focusing and characterization of the four instrument channels, and a preliminary measurement of the resolution and throughput performance of the instrument. We describe the results from this test program, and present preliminary estimates of the on-orbit performance of the FUSE satellite based on a combination of this data and prelaunch laboratory measurements.Comment: 8 pages, including 3 figures. This paper will appear in the FUSE special issue of ApJ Letter

A Second Chromatic Timing Event of Interstellar Origin toward PSR J1713+0747

The frequency dependence of radio pulse arrival times provides a probe of structures in the intervening media. Demorest et al. was the first to show a short-term (~100–200 days) reduction in the electron content along the line of sight to PSR J1713+0747 in data from 2008 (approximately MJD 54750) based on an apparent dip in the dispersion measure of the pulsar. We report on a similar event in 2016 (approximately MJD 57510), with average residual pulse-arrival times ≈−3.0, −1.3, and −0.7 μs at 820, 1400, and 2300 MHz, respectively. Timing analyses indicate possible departures from the standard ν −2 dispersive-delay dependence. We discuss and rule out a wide variety of potential interpretations. We find the likeliest scenario to be lensing of the radio emission by some structure in the interstellar medium, which causes multiple frequency-dependent pulse arrival-time delays

Pulsar Wind Nebulae with Bow Shocks: Non-thermal Radiation and Cosmic Ray Leptons

Pulsars with high spin-down power produce relativistic winds radiating a non-negligible fraction of this power over the whole electromagnetic range from radio to gamma-rays in the pulsar wind nebulae (PWNe). The rest of the power is dissipated in the interactions of the PWNe with the ambient interstellar medium (ISM). Some of the PWNe are moving relative to the ambient ISM with supersonic speeds producing bow shocks. In this case, the ultrarelativistic particles accelerated at the termination surface of the pulsar wind may undergo reacceleration in the converging flow system formed by the plasma outflowing from the wind termination shock and the plasma inflowing from the bow shock. The presence of magnetic perturbations in the flow, produced by instabilities induced by the accelerated particles themselves, is essential for the process to work. A generic outcome of this type of reacceleration is the creation of particle distributions with very hard spectra, such as are indeed required to explain the observed spectra of synchrotron radiation with photon indices Γ≲ 1.5. The presence of this hard spectral component is specific to PWNe with bow shocks (BSPWNe). The accelerated particles, mainly electrons and positrons, may end up containing a substantial fraction of the shock ram pressure. In addition, for typical ISM and pulsar parameters, the e+ released by these systems in the Galaxy are numerous enough to contribute a substantial fraction of the positrons detected as cosmic ray (CR) particles above few tens of GeV and up to several hundred GeV. The escape of ultrarelativistic particles from a BSPWN—and hence, its appearance in the far-UV and X-ray bands—is determined by the relative directions of the interstellar magnetic field, the velocity of the astrosphere and the pulsar rotation axis. In this respect we review the observed appearance and multiwavelength spectra of three different types of BSPWNe: PSR J0437-4715, the Guitar and Lighthouse nebulae, and Vela-like objects. We argue that high resolution imaging of such objects provides unique information both on pulsar winds and on the ISM. We discuss the interpretation of imaging observations in the context of the model outlined above and estimate the BSPWN contribution to the positron flux observed at the Earth

Hierarchies, markets and networks: ethnicity/race and drug distribution

Three models—hierarchies, markets, and networks—are used to explore the organization of drug distribution and the place of ethnicity/race in that. These models are well established as conceptual approaches to the coordination of social life. Each of them is employed in the analysis of drug distribution, though not always clearly. This paper aims to elucidate their key features as they bear on questions of ethnicity/race. In doing so, it problematizes the way that ethnicity/race is employed in research and policy circles and challenges naïve assumptions about ethnic sameness and ethnicity/race as bases for organizing drug distribution. Ethnicity may be a useful resource for criminal and legitimate enterprises but both comparisons between the two and details of what is specifically ethnic are generally lacking. Some avenues for future research and simple principles to guide such research are proposed