Multi-frequency Study of the LMC Supernova Remnant (SNR) B0513-692 and New SNR Candidate J051327-6911

We present a new multi-wavelength study of supernova remnant (SNR) B0513-692 in the Large Magellanic Cloud (LMC). The remnant also has a strong, superposed, essentially unresolved, but unrelated radio source at its north-western edge, J051324-691049. This is identified as a likely compact HII region based on related optical imaging and spectroscopy. We use the Australia Telescope Compact Array (ATCA) at 4790 and 8640 MHz to determine the large scale morphology, spectral index and polarization characteristics of B0513-692 for the first time. We detect a strongly polarized region (49%) in the remnant's southern edge. Interestingly we also detect a small (~40 arcsec) moderately bright, but distinct optical, circular shell in our Halpha imagery which is adjacent to the compact HII region and just within the borders of the NE edge of B0513-692. We suggest this is a separate new SNR candidate based on its apparently distinct character in terms of optical morphology in 3 imaged emission lines and indicative SNR optical spectroscopy (including enhanced optical [SII] emission relative to Halpha).Comment: 12 page

Metal Abundances in the Magellanic Stream

We report on the first metallicity determination for gas in the Magellanic Stream, using archival HST GHRS data for the background targets Fairall 9, III Zw 2, and NGC 7469. For Fairall 9, using two subsequent HST revisits and new Parkes Multibeam Narrowband observations, we have unequivocally detected the MSI HI component of the Stream (near its head) in SII1250,1253 yielding a metallicity of [SII/H]=-0.55+/-0.06(r)+/-0.2(s), consistent with either an SMC or LMC origin and with the earlier upper limit set by Lu et al. (1994). We also detect the saturated SiII1260 line, but set only a lower limit of [SiII/H]>-1.5. We present serendipitous detections of the Stream, seen in MgII2796,2803 absorption with column densities of (0.5-1)x10^13 cm^-2 toward the Seyfert galaxies III Zw 2 and NGC 7469. These latter sightlines probe gas near the tip of the Stream (80 deg down-Stream of Fairall 9). For III Zw 2, the lack of an accurate HI column density and the uncertain MgIII ionization correction limits the degree to which we can constrain [Mg/H]; a lower limit of [MgII/HI]>-1.3 was found. For NGC 7469, an accurate HI column density determination exists, but the extant FOS spectrum limits the quality of the MgII column density determination, and we conclude that [MgII/HI]>-1.5. Ionization corrections associated with MgIII and HII suggest that the corresponding [Mg/H] may range lower by 0.3-1.0 dex. However, an upward revision of 0.5-1.0 dex would be expected under the assumption that the Stream exhibits a dust depletion pattern similar to that seen in the Magellanic Clouds. Remaining uncertainties do not allow us to differentiate between an LMC versus SMC origin to the Stream gas.Comment: 30 pages, 8 figures, LaTeX (aaspp4), also available at http://casa.colorado.edu/~bgibson/publications.html, accepted for publication in The Astronomical Journa

Evidence for Extremely High Dust Polarization Efficiency in NGC 3184

Recent studies have found the Type II-plateau supernova (SN) 1999gi to be highly polarized (p_max = 5.8%, where p_max is the highest degree of polarization measured in the optical bandpass; Leonard & Filippenko 2001) and minimally reddened (E[B-V] = 0.21 +/- 0.09 mag; Leonard et al. 2002). From multiple lines of evidence, including the convincing fit of a ``Serkowski'' interstellar polarization (ISP) curve to the continuum polarization shape, we conclude that the bulk of the observed polarization is likely due to dust along the line of sight (l-o-s), and is not intrinsic to SN 1999gi. We present new spectropolarimetric observations of four distant Galactic stars close to the l-o-s to SN 1999gi (two are within 0.02 degrees), and find that all are null to within 0.2%, effectively eliminating Galactic dust as the cause of the high polarization. The high ISP coupled with the low reddening implies an extraordinarily high polarization efficiency for the dust along this l-o-s in NGC 3184: ISP / E(B-V) = 31^{+22}_{-9} % mag^{-1}. This is inconsistent with the empirical Galactic limit (ISP / E[B-V] < 9% mag^{-1}), and represents the highest polarization efficiency yet confirmed for a single sight line in either the Milky Way or an external galaxy.Comment: 27 pages, accepted for publication by the Astronomical Journa

Polarization of Broad Absorption Line QSOs I. A Spectropolarimetric Atlas

We present a spectropolarimetric survey of 36 broad absorption line quasi-stellar objects (BAL QSOs). The continuum, absorption trough, and emission line polarization of BAL QSOs yield clues about their structure. We confirm that BAL QSOs are in general more highly polarized than non-BAL QSOs, consistent with a more equatorial viewing direction for the former than the latter. We have identified two new highly-polarized QSOs in our sample (1232+1325 and 1333+2840). The polarization rises weakly to the blue in most objects, perhaps due to scattering and absorption by dust particles. We find that a polarization increase in the BAL troughs is a general property of polarized BAL QSOs, indicating an excess of scattered light relative to direct light, and consistent with the unification of BAL QSOs and non-BAL QSOs. We have also discovered evidence of resonantly scattered photons in the red wing of the C IV broad emission lines of a few objects. In most cases, the broad emission lines have lower polarization and a different position angle than the continuum. The polarization characteristics of low-ionization BAL QSOs are similar to those of high-ionization BAL QSOs, suggesting a similar BAL wind geometry.Comment: 39 pages, 6 figures (20 .gif files), accepted for publication in The Astrophysical Journal Supplement

On the Exchange of Kinetic and Magnetic Energy Between Clouds and the Interstellar Medium

We investigate, through 2D MHD numerical simulations, the interaction of a uniform magnetic field oblique to a moving interstellar cloud. In particular we explore the transformation of cloud kinetic energy into magnetic energy as a result of field line stretching. Some previous simulations have emphasized the possible dynamical importance of a ``magnetic shield'' formed around clouds when the magnetic field is perpendicular to the cloud motion (Jones et al. 1996, Miniati et al. 1998). It was not clear, however, how dependent those findings were to the assumed field configuration and cloud properties. To expand our understanding of this effect, we examine several new cases by varing the magnetic field orientation angle with respect to the cloud motion (\theta), the cloud-background density contrast, and the cloud Mach number. We show that in 2D and with \theta large enough, the magnetic field tension can become dominant in the dynamics of the motion of high density contrast, low Mach number clouds. In such cases a significant fraction of cloud kinetic energy can be transformed into magnetic energy with the magnetic pressure at the cloud nose exceeding the ram pressure of the impinging flow. We derive a characteristic timescale for this process of energy ``conversion''. We find also that unless the cloud motion is highly aligned to the magnetic field, reconnection through tearing mode instabilities in the cloud wake limit the formation of a strong flux rope feature following the cloud. Finally we attempt to interpret some observational properties of the magnetic field in view of our results.Comment: 24 pages in aaspp4 Latex and 7 figures. Accepted for publication in The Astrophysical Journa

Automated Fabrication ofCeramic Components from Tape-Cast Ceramic

This paper describes a machine and process for automated fabrication of functional 3-D laminated engineering components, ceramics in the present example. A laser cuts successive layers of a part derived from a CAD model description out of unfired tape-cast ceramic sheets vacuum-clamped to an x-y sled. A material-handling robot uses a selective-area gripper to extract only the desired part outlines from the surrounding waste material, then stacks the slices to build the part. This system design enables rapid manufacture of functional engineering components with arbitrarily complex internal and external geometries from virtually any material available in sheet form.Mechanical Engineerin

A Search for Intrinsic Polarization in O Stars with Variable Winds

New observations of 9 of the brightest northern O stars have been made with the Breger polarimeter on the 0.9~m telescope at McDonald Observatory and the AnyPol polarimeter on the 0.4~m telescope at Limber Observatory, using the Johnson-Cousins UBVRI broadband filter system. Comparison with earlier measurements shows no clearly defined long-term polarization variability. For all 9 stars the wavelength dependence of the degree of polarization in the optical range can be fit by a normal interstellar polarization law. The polarization position angles are practically constant with wavelength and are consistent with those of neighboring stars. Thus the simplest conclusion is that the polarization of all the program stars is primarily interstellar. The O stars chosen for this study are generally known from ultraviolet and optical spectroscopy to have substantial mass loss rates and variable winds, as well as occasional circumstellar emission. Their lack of intrinsic polarization in comparison with the similar Be stars may be explained by the dominance of radiation as a wind driving force due to higher luminosity, which results in lower density and less rotational flattening in the electron scattering inner envelopes where the polarization is produced. However, time series of polarization measurements taken simultaneously with H-alpha and UV spectroscopy during several coordinated multiwavelength campaigns suggest two cases of possible small-amplitude, periodic short-term polarization variability, and therefore intrinsic polarization, which may be correlated with the more widely recognized spectroscopic variations.Comment: LaTeX2e, 22 pages including 11 tables; 12 separate gif figures; uses aastex.cls preprint package; accepted by The Astronomical Journa

Setting targets for HIV/AIDS-What lessons can be learned from other disease control programmes?

Our analysis of experience from programmes targeting malaria, leprosy and TB shows the importance of drawing broadly on research and implementation expertise, and civil society more broadly, when setting targets for HIV control. The engagement of stakeholders from the highest burden settings, including affected populations, is crucial, to ensure that disease control efforts uphold human rights and tackle HIV-related stigma and discrimination. An appropriate balance is needed between ambitious, galvanising global targets that drive funding and political/public engagement, and targets that reflect the complexities and local epidemiological variations in disease profile. Ethical issues and unintended consequences need to be considered when setting targets—particularly around local effects and opportunity costs of having foregone other areas of disease control and public health. Intermediate and adaptable targets are needed that allow for course corrections to programmes. Overly burdensome reporting requirements for individual local programmes and countries should be avoided, as well as potential for overlapping and sometimes conflicting targets both within and across vertical disease programmes. Process targets should be distinguished from outcome targets, which should be measurable and based on high-quality data. Retention of expert healthcare worker skills and specialist services is vital, while moving towards integrated health systems if effective disease control programmes are to be maintained. Target development should seek areas of programme delivery where an opportunity to codevelop targets and integrate services exists. Global efforts to move to universal health coverage (UHC), for example, could be factored in when developing targets. Sustaining investment and continuing political interest in the end phase of any elimination or eradication strategy, once incidence and prevalence are low, are critical to achieve success. Equity- and access-based service delivery targets become increasingly important as the elimination strategy nears its end and should be factored into planning. Achieving disease elimination and/or eradication is only possible with sufficient investment in research to develop new prevention tools such as vaccines, point-of-care diagnostics, and treatments to counteract the effects of increasing drug resistance and the challenging latency period of diseases; public health infrastructure upgrades that address wider determinants of health; and health and surveillance systems that allow for equitable delivery and access to services

The mysterious HI deficiency of NGC 3175

Australia Telescope Compact Array HI observations reveal the existence of 5.8x10^8 M_sun of HI gas in the central 7 kpc of the edge-on spiral galaxy NGC 3175. The detected HI and CO gas can explain why star formation, as traced by other emission processes, is going on in the inner part of its disk. On the other hand, the entire outer disk, beyond 3.5 kpc radius, shows no HI emission, has a very red colour and exhibits neither radio continuum nor H-alpha emission. This indicates that the outer part of NGC 3175 is quiescent, i.e. not forming stars at a measurable rate. Its HI deficiency and the small extent of the HI layer, which is confined to the boundaries of the optically visible disk, make NGC 3175 a peculiar spiral galaxy. No intergalactic HI gas in the NGC 3175 group was detected in our interferometric observations. Earlier Parkes telescope single dish HI observations put an upper limit on the amount of diffuse gas that might have been missed by the interferometer at 2x10^8 M_sun. On DSS plates no galaxy in the NGC 3175 group of galaxies (Garcia 1993) is close enough to it and none exhibits disturbances that could indicate a close interaction which might have led to the stripping of large parts of its HI gas. Thus, despite an extensive multi-wavelength investigation, the reason for the unusual absence of HI and star formation activity in the outer disk of NGC 3175 remains an intriguing mystery.Comment: 8 pages, 6 figures, uses aa.cls. Accepted for publication in Astronomy & Astrophysic

Observational Constraints on the Ages of Molecular Clouds and the Star-Formation Timescale: Ambipolar-Diffusion--Controlled or Turbulence-Induced Star Formation?

We revisit the problem of the star formation timescale and the ages of molecular clouds. The apparent overabundance of star-forming molecular clouds over clouds without active star formation has been thought to indicate that molecular clouds are "short-lived" and that star formation is "rapid". We show that this statistical argument lacks self-consistency and, even within the rapid star-formation scenario, implies cloud lifetimes of approximately 10 Myr. We discuss additional observational evidence from external galaxies that indicate lifetimes of molecular clouds and a timescale of star formation of approximately 10 Myr . These long cloud lifetimes in conjunction with the rapid (approximately 1 Myr) decay of supersonic turbulence present severe difficulties for the scenario of turbulence-controlled star formation. By contrast, we show that all 31 existing observations of objects for which the linewidth, the size, and the magnetic field strength have been reliably measured are in excellent quantitative agreement with the predictions of the ambipolar-diffusion theory. Within the ambipolar-diffusion-controlled star formation theory the linewidths may be attributed to large-scale non-radial cloud oscillations (essentially standing large-amplitude, long-wavelength Alfven waves), and the predicted relation between the linewidth, the size, and the magnetic field is a natural consequence of magnetic support of self-gravitating clouds.Comment: 7 pages, 2 figures, uses emulateapj; accepted for publication in Ap