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We describe the design and performance of the Engineering Development Array, which is a low-frequency radio telescope comprising 256 dual-polarisation dipole antennas working as a phased array. The Engineering Development Array was conceived of, developed, and deployed in just 18 months via re-use of Square Kilometre Array precursor technology and expertise, specifically from the Murchison Widefield Array radio telescope. Using drift scans and a model for the sky brightness temperature at low frequencies, we have derived the Engineering Development Array’s receiver temperature as a function of frequency. The Engineering Development Array is shown to be sky-noise limited over most of the frequency range measured between 60 and 240 MHz. By using the Engineering Development Array in interferometric mode with the Murchison Widefield Array, we used calibrated visibilities to measure the absolute sensitivity of the array. The measured array sensitivity matches very well with a model based on the array layout and measured receiver temperature. The results demonstrate the practicality and feasibility of using Murchison Widefield Array-style precursor technology for Square Kilometre Array-scale stations. The modular architecture of the Engineering Development Array allows upgrades to the array to be rolled out in a staged approach. Future improvements to the Engineering Development Array include replacing the second stage beamformer with a fully digital system, and to transition to using RF-over-fibre for the signal output from first stage beamformers.

Our ROSAT observations of γ Velorum obtained over several binary cycles reveal substantial, and repeatable phase-dependent X-ray (0.1—2.5 keV) variations. The derived X-ray light-curve shows a 4 x increase in flux at phase ∼ 0.5, which is shown to arise in shocked gas formed in the collison of the two stellar winds, viewed through a cavity in the WC8 wind with an observed opening angle of ∼ 50°. This colliding-wind X-ray emission has L x ≥ 1032 ergs−1 and kT ≥ 2 keV. Our 2-D hydrodynamical models of the system predict copious X-ray emission from the wind-collision region, at a level and spectrum similar to that observed. Harder (1—10 kev) X-ray observations with the ASCA satellite are being sought to provide improved constraints on the luminosity, spectrum and absorption of the wind-collision emission, and the complex theoretical models involved.

We describe some of the observational phenomena associated with colliding stellar winds, focussing especially on close WR+O binaries. In particular, we report some new ultraviolet observations of CQ Cep and V444 Cyg. We also discuss some of the general theory of such wind collisions.

We present the results of fitting an ionization nonequilibrium (NIE) model to the high energy (> 5 keV) X-ray spectra of the young supernova remnants Cas A and Tycho. As an additional constraint, we demand that the models simultaneously fit lower energy, higher resolution data. For Cas A, a single NIE component can not adequately reproduce the features for the entire X-ray spectrum because 1) the ionization structure of iron ions responsible for the K emission is inconsistent with that of the ions responsible for the lower energy lines, and 2) the flux of the highest energy X-rays is underestimated. The iron K line and the high energy continuum could arise from the same NIE component but the identification of this component with either the blast wave or the ejecta in the “standard” model is difficult. In Tycho, the high energy data rule out a class of models for the lower energy data which have too large a continuum contribution.

NGC 1365 is a galaxy which has lately received a lot of attention from people studying the structure and dynamics of barred galaxies. This is not surprising since it is one of the best suited objects in the sky. We have obtained a number of long-slit spectra in the red region (Hα, [NII], [SII]) with the ESO 3.6 m (Lindblad and Jörsäter) and with the CTIO 4 m (Peterson) telescopes. In addition, a couple of Fabry-Perot Hα interferograms have kindly been given to us by G. Comte and Y. Georgelin. Some preliminary results are presented here. Fig. 1 shows the positions of measured velocity points. The digits along the vertical axis indicate distance from the nucleus in seconds of arc. The dashed line at P.A. 48 deg indicates the line of nodes as determined from photometry of the outer features of the galaxy (Lindblad 1978). An arbitrary isophote has been sketched to aid the orientation. The emission lines in the bar are surprisingly weak which is the reason for the scarcity of velocity points there. Fig. 2 shows a rotation curve based on the P.A. of the line of nodes of 48 deg and an inclination of 55 deg (Lindblad 1978). Only velocity measurements within 50 deg of the line of nodes have been used in this diagram in order to avoid large projection errors. The distance used is 20 Mpc. The spread is quite large indicating a significant amount of non-circular motion.

We have obtained estimates of the solar internal rotational velocity from measurements of the frequency splittings of p-mode oscillations. Specifically, we have analyzed a 10-day time series of full-disk Dopplergrams obtained during July and August 1984 at the 60-Foot Tower Telescope of the Mt. Wilson Observatory. The Dopplergrams were obtained with a Na magneto-optical filter and a 244 × 248-pixel CID camera. From the time series we computed power spectra for all of the prograde and retrograde sectoral p-modes from ℓ = 0 to 200 and for all of the tessaral harmonics up to ℓ = 89. We then applied a cross-correlation analysis to the resulting sectoral power spectra to obtain estimates of the frequency splittings. From ℓ = 4 to ℓ = 30 we obtained a mean value of the frequency spitting of roughly 450 nHz (sidereal) in close agreement with most previously published results, while from ℓ = 40 to ℓ = 140 we obtained a mean value of about 470 nHz. We believe that the latter value is slightly higher than the surface rotational splitting of 461 nHz because of possible confusion due to the temporal sidelobes introduced by the day/night observing cycle. Confirmation of this possibility will have to await our computation of tesseral power spectra for degrees greater than our current limit of 89. Finally, for degrees between 140 and 200, the frequency splittings are indistinguishable from the surface rotation rate.

We present here the first full-disk solar Dopplergram obtained with the new 1024 × 1024-pixel CCD camera which has recently been installed at the 60-Foot Tower Telescope of the Mt. Wilson Observatory. This Dopplergram has a spatial resolution of 2.2 arcseconds and was obtained in less than one minute of time. The Dopplergram was obtained with a magneto-optical filter which was designed to obtain images in the two Na D lines. The filter and the camera were operated together as part of the development of a Solar Oscillations Imager (SOI) esperiment which is currently being designed at JPL for the joint NASA/ESA Solar and Heliospheric Observatory (SOHO) mission.

We report on progress in the theoretical modelling of colliding winds in WR binary systems, concentrating on two WR+O systems, namely V444 Cygni, and HD 193793.

Prior to the Syrian civil war, access and delivery of health care and health care information over the past 4 decades had steadily improved. The life expectancy of the average Syrian in 2012 was 75.7 years, compared to 56 years in 1970. As a result of the civil war, this trend has reversed, with the life expectancy reduced by 20 years from the 2012 level. The Syrian government and its allies have specifically targeted the health care infrastructure not under government control. (Disaster Med Public Health Preparedness. 2015;page 1 of 3)