HST Observations of Gravitationally Lensed Features in the Rich Cluster Ac114

Deep Hubble Space Telescope images of superlative resolution obtained for the distant rich cluster AC114 (z=0.31) reveal a variety of gravitational lensing phenomena for which ground-based spectroscopy is available. We present a luminous arc which is clearly resolved by HST and appears to be a lensed z=0.64 sub-L star spiral galaxy with a detected rotation curve. Of greatest interest is a remarkably symmetrical pair of compact blue images separated by 10 arcsec and lying close to the cluster cD. We propose that these images arise from a single very faint background source gravitationally lensed by the cluster core. Deep ground-based spectroscopy confirms the lensing hypothesis and suggests the source is a compact star forming system at a redshift z=1.86. Taking advantage of the resolved structure around each image and their very blue colours, we have identified a candidate third image of the same source roughly 50 arcsec away. The angular separation of the three images is much larger than previous multiply-imaged systems and indicates a deep gravitational potential in the cluster centre. Resolved multiply-imaged systems, readily recognised with HST, promise to provide unique constraints on the mass distribution in the cores of intermediate redshift clusters.Comment: submitted to ApJ, 6 pages (no figures), uuencoded Postscript, compressed TAR of Postscript figures available via anonymous ftp in users/irs/figs/ac114_figs.tar.gz on astro.caltech.edu. PAL-IRS-

The use of slips in scientific correspondence

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Design and experimental evaluation of a test rig for ultrasonic monitoring of sccelerated corrosion

The design of a test rig for ultrasonic monitoring of corroding steel samples and results of its experimental evaluation are presented. In order to accelerate and quantify corrosion, the monitored sample acts as an anode in a typical constant current electroplating setup. An Arduino-powered microcontroller is used to log the relevant voltage and current values on an SD card, and a high accuracy ultrasonic waveform acquisition instrument is employed to record the ultrasonic waveforms reflected form the corroding surface. Experimental assessment of the designed rig confirmed that it met the design objectives and could be used for experimental studies of accelerated corrosion in steel samples

Air Pollution and Daylight Availability in Urban Areas: Dynamic Simulation in an Office

The deposition of air pollutants on glazing can significantly affect the daylight transmittance of building fenestration systems in urban areas. This study presents a simulation analysis of the impact of air pollution and glazing visual transmittance on indoor daylight availability in an open-plan office in London. First, the direct links between glazing visual transmittance and daylighting conditions were developed and assessed. Second, several simple algorithms were established to estimate the loss of daylight availability due to the pollutant deposition at the external surface of vertical glazing. Finally, some conclusions and design strategies to support façade strategies at the early design stage of an urban building project were developed

Ground Factors and Lighting Design in an Urban Area: Daylighting and Light Pollution

In urban areas the daylight available to a building directly from the sky may be compromised, and the contribution from reflected daylight can become more significant. The influence of external obstructions and façade configurations has received some attention, but the impact of daylight reflected from the external ground surrounding an urban building has not been widely examined. This study implemented a lighting simulation analysis of the influence of ground reflection configurations on the daylight availability and the light pollution risk in a typical urban courtyard in Beijing, China. Based on the simulated data, some design strategies are suggested to support landscape and lighting design in a similar urban context

Evidence of a Metal Rich Galactic Bar from the Vertex Deviation of the Velocity Ellipsoid

We combine radial velocities, proper motions, and low resolution abundances for a sample of 315 K and M giants in the Baade's Window (l,b)=(0.9,-4) Galactic bulge field. The velocity ellipsoid of stars with [Fe/H]>-0.5 dex shows a vertex deviation in the plot of radial versus transverse velocity, consistent with that expected from a population with orbits supporting a bar. We demonstrate that the significance of this vertex deviation using non-parametric rank correlation statistic is >99%. The velocity ellipsoid for the metal poor ([FeH]<-0.5) part of the population shows no vertex deviation and is consistent with an isotropic, oblate rotating population. We find no evidence for kinematic subgroups, but there is a mild tendency for the vertical velocity dispersion sigma_b to decrease with increasing metallicity.Comment: 4 pages, ApJ Letters, submitte

Capture of field stars by globular clusters in dense bulge regions

The recent detection of a double Red Giant Branch in the optical color-magnitude diagram (CMD) of the bulge globular cluster HP1 (Ortolani et al. 1997), a more populated metal-poor steep one corresponding to the cluster itself, and another metal-rich curved, led us to explore in the present Letter the possibility of capture of field stars by a globular cluster orbiting in dense bulge regions over several gigayears. Analytical arguments, as well as N-body calculations for a cluster model of 10^5 solar masses in a bulge-like environment, suggest that a significant fraction of cluster stars may consist of captures. Metal-poor globular clusters in the inner bulge, like HP1, contrasting at least in Delta [Fe/H] = 1.0 dex with respect to the surrounding metal-rich stars, are ideal probes to further test the capture scenario. In turn, if this scenario is confirmed, the double RGB of HP1 could provide direct estimates of blanketing amounts, which is fundamental for the photometric calibration of metal-rich stellar populations.Comment: 6 pages, 2 included figures, aas2pp4,sty Latex style. To be published in Astrophysical Journal Letter