Supernova Remnants and Plerions in the Compton Gamma-Ray Observatory Era

Due to observations made by the Compton Gamma-Ray Observatory over the last six years, it appears that a number of galactic supernova remnants may be candidates for sources of cosmic gamma-rays. These include shell-type remnants such as IC443 and $\gamma$ Cygni, which have no known parent pulsars, but have significant associations with unidentified EGRET sources, and others that appear to be composite, where a pulsar is embedded in a shell (e.g. W44 and Vela), or are purely pulsar-driven, such as the Crab Nebula. This review discusses our present understanding of gamma-ray production in plerionic and non-plerionic supernova remnants, and explores the relationship between such emission and that in other wavebands. Focuses include models of the Crab and Vela nebulae, the composite nature of W44, the relationship of shell-type remnants to cosmic ray production, the relative importance of shock-accelerated protons and electrons, constraints on models placed by TeV, X-ray and radio observations, and the role of electrons injected directly into the remnants by parent pulsars.Comment: 21 pages, including 4 eps figures, invited review, to appear in Proc. 4th Compton Symposium, (1997) ed. Dermer, C. D. & Kurfess, J. D. (AIP, New York

Flavor decomposition of the elastic nucleon electromagnetic form factors

The u- and d-quark contributions to the elastic nucleon electromagnetic form factors have been determined using experimental data on GEn, GMn, GpE, and GpM. Such a flavor separation of the form factors became possible up to 3.4 GeV2 with recent data on GEn from Hall A at JLab. At a negative four-momentum transfer squared Q2 above 1 GeV2, for both the u- and d-quark components, the ratio of the Pauli form factor to the Dirac form factor, F2/F1, was found to be almost constant, and for each of F2 and F1 individually, the d-quark portions of both form factors drop continuously with increasing Q2.Comment: 4 pages, 3 figure

Periodic Modulations in an X-ray Flare from Sagittarius A*

We present the highly significant detection of a quasi-periodic flux modulation with a period of 22.2 min seen in the X-ray data of the Sgr A* flare of 2004 August 31. This flaring event, which lasted a total of about three hours, was detected simultaneously by EPIC on XMM-Newton and the NICMOS near-infrared camera on the HST. Given the inherent difficulty in, and the lack of readily available methods for quantifying the probability of a periodic signal detected over only several cycles in a data set where red noise can be important, we developed a general method for quantifying the likelihood that such a modulation is indeed intrinsic to the source and does not arise from background fluctuations. We here describe this Monte Carlo based method, and discuss the results obtained by its application to a other XMM-Newton data sets. Under the simplest hypothesis that we witnessed a transient event that evolved, peaked and decayed near the marginally stable orbit of the supermassive black hole, this result implies that for a mass of 3.5 x 10^{6} Msun, the central object must have an angular momentum corresponding to a spin parameter of a=0.22.Comment: 4 pages, 6 figures, submitted to ApJ

The Inhomogeneous Wind of the LBV Candidate CygOB2-No.12

We present the results of high-resolution spectroscopy of the extremely luminous star CygOB2-No.12. We identified about 200 spectral features in the range 4552-7939 AA, including the interstellar NaI, KI lines and numerous very strong DIBs, along with the HeI, CII, and SiII lines. An MK spectral type we derived for the object is B4.5Ia+. Our analysis of the radial velocity data shows the presence of a gradient in the stellar atmosphere, caused by both atmospheric expansion and matter infall onto the star. The Halpha emission displays broad Thompson wings, a slightly blue-shifted PCyg type absorption component and a time-variable core absorption. We conclude that the wind is variable in time.Comment: 3 pages, 2 figures, IAU Symposium No.272 "Active OB stars: structure, evolution, mass loss and critical limits", 201

The yellow hypergiants HR 8752 and rho Cassiopeiae near the evolutionary border of instability

High-resolution near-ultraviolet spectra of the yellow hypergiants HR 8752 and rho Cassiopeiae indicate high effective temperatures placing both stars near the T_eff border of the ``yellow evolutionary void''. At present, the temperature of HR 8752 is higher than ever. For this star we found Teff=7900+-200 K, whereas rho Cassiopeiae has Teff=7300+-200 K. Both, HR 8752 and rho Cassiopeiae have developed strong stellar winds with Vinf ~ 120 km/s and Vinf ~ 100 km/s, respectively. For HR 8752 we estimate an upper limit for the spherically symmetric mass-loss of 6.7X10^{-6}M_solar/yr. Over the past decades two yellow hypergiants appear to have approached an evolutionary phase, which has never been observed before. We present the first spectroscopic evidence of the blueward motion of a cool super/hypergiant on the HR diagram.Comment: 13 pages including 3 figures. Accepted for publication in ApJ Letter

The role of academic libraries in the enhancement of information literacy: A study of the Fort Hare Library

Students today are faced with many difficulties in finding information, because new technology makes information available in different, mainly electronic, formats. For this information to be accessed and used properly, students are required to be information literate. It is a duty of today’s libraries to equip students with the necessary information skills to function effectively and to meet challenges of the information age. This paper reports on an investigation into the role of the University of Fort Hare Library in the enhancement of students’ information literacy. A survey was conducted among both undergraduate and postgraduate students and results of a total of 246 responses were analysed. Findings show that while there is some evidence that the University of Fort Hare Library is engaging in information literacy activities, students still have difficulty in finding, critically evaluating and using information

Crossing the `Yellow Void' -- Spatially Resolved Spectroscopy of the Post- Red Supergiant IRC+10420 and Its Circumstellar Ejecta

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the HR diagram. During their post--RSG evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semi--forbidden region, that de Jager and his collaborators have called the `yellow void'. We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double--peaked Halpha emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a `rain' model in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass loss rate, IRC +10420 may be about to shed its opaque wind, cross the `yellow void', and emerge as a hotter star.Comment: To appear in the Astronomical Journal, August 200

Ratchet-induced variations in bulk states of an active ideal gas

We study the distribution of active, noninteracting particles over two bulk states separated by a ratchet potential. By solving the steady-state Smoluchowski equations in a flux-free setting, we show that the ratchet potential affects the distribution of particles over the bulks, and thus exerts an influence of infinitely long range. As we show, crucial for having such a long-range influence is an external potential that is nonlinear. We characterize how the difference in bulk densities depends on activity and on the ratchet potential, and we identify power law dependencies on system parameters in several limiting cases. While weakly active systems are often understood in terms of an effective temperature, we present an analytical solution that explicitly shows that this is not possible in the current setting. Instead, we rationalize our results by a simple transition state model, that presumes particles to cross the potential barrier by Arrhenius rates modified for activity. While this model does not quantitatively describe the difference in bulk densities for feasible parameter values, it does reproduce - in its regime of applicability - the complete power law behavior correctly.Comment: 11 pages, 6 figure

Use of traditional medicine versus use of the community-based primary health care clinic by the San community at Platfontein

Introduction: Working amongst a San community led to the observation that, despite the availability of modern healthcare, high mortality and morbidity associated with disease, such as dehydration, malnutrition and tuberculosis, still prevailed.This study aimed to determine how traditional beliefs and customs influenced the utilisation of Western medicine. Methods: An observational-descriptive study was conducted. Consenting patients, facilitated by interpreters, completed questionnaires during consultations conducted by nurses and the principal investigator at the Platfontein primary healthcare (PHC) clinic. Results: Of the 113 participants, two-thirds were female. The median age was 40 years; 56.7% lacked formal education; 42.5% conversed only in their native tongue. The initial use of the PHC facility was high (71.4%), even though 37% of the participants visited a traditional healer in the preceding year. Circumcision was the condition for which traditional healers were consulted most commonly (28.8%). Conditions preferably requiring clinic visitation were coughing (51.4%), pain (35.1%) and diarrhoea (34.2%). Of the participants leading mostly a traditional lifestyle (n = 48), 30.6 % indicated that they did not use traditional medicine or healers; 72.9% indicated that illness could be caused by a spell. Of the participantsnot leading a traditional lifestyle (n = 41), 85.4% indicated that they did not use traditional medicine; 41.4% indicated that illness could be caused by a spell.Conclusion: The assumption that the mortality and morbidity observed for certain conditions were due to the preference for traditional medicine in this community could not be confirmed. Doctors working amongst isolated communities or in multicultural environments, however, should recognise that traditional medicine still plays a role in the health care of their patients.Keywords: assumptions; perceptions; modern medicine; Western medicine; traditional healers; San community; Khoisa