The Ever Changing Circumstellar Nebula Around UW Centauri

We present new images of the reflection nebula surrounding the R Coronae Borealis Star, UW Cen. This nebula, first detected in 1990, has changed its appearance significantly. At the estimated distance of UW Cen, this nebula is approximately 0.6 ly in radius so the nebula cannot have physically altered in only 8 years. Instead, the morphology of the nebula appears to change as different parts are illuminated by light from the central star modulated by shifting thick dust clouds near its surface. These dust clouds form and dissipate at irregular intervals causing the well-known declines in the R Coronae Borealis (RCB) stars. In this way, the central star acts like a lighthouse shining through holes in the dust clouds and lighting up different portions of the nebula. The existence of this nebula provides clues to the evolutionary history of RCB stars possibly linking them to the Planetary Nebulae and the final helium shell flash stars.Comment: To be published in ApJ Letters. 5 pages, 3 figures (2 in color

Field testing plan for unsaturated zone monitoring and field studies

The University of Arizona, in cooperation with the Bureau of Economic Geology at The University of Texas at Austin, and Stephens and Associates in Albuquerque, New Mexico has developed a field testing plan for evaluating subsurface monitoring systems. The U.S. Nuclear Regulatory Commission has requested development of these testing plans for low-level radioactive waste disposal sites (LLW) and for monitoring at decommissioned facilities designated under the {open_quotes}Site Decommissioning Management Plan{close_quotes} (SDMP). The tests are conducted on a 50 m by 50 m plot on the University of Arizona`s Maricopa Agricultural Center. Within the 50 m by 50 m plot one finds: (1) an instrumented buried trench, (2) monitoring islands similar to those proposed for the Ward Valley, California LLW Facility, (3) deep borehole monitoring sites, (4) gaseous transport monitoring, and (5) locations for testing non-invasive geophysical measurement techniques. The various subplot areas are instrumented with commercially available instruments such as neutron probes, time domain reflectometry probes, tensiometers, psychrometers, heat dissipation sensors, thermocouples, solution samplers, and cross-hole geophysics electrodes. Measurement depths vary from ground surface to 15 m. The data from the controlled flow and transport experiments, conducted over the plot, will be used to develop an integrated approach to long-term monitoring of the vadose zone at waste disposal sites. The data will also be used to test field-scale flow and transport models. This report describes in detail the design of the experiment and the methodology proposed for evaluating the data

Three-Dimensional Kinematics of Hummingbird Flight

Hummingbirds are specialized for hovering flight, and substantial research has explored this behavior. Forward flight is also important to hummingbirds, but the manner in which they perform forward flight is not well documented. Previous research suggests that hummingbirds increase flight velocity by simultaneously tilting their body angle and stroke-plane angle of the wings, without varying wingbeat frequency and upstroke: downstroke span ratio. We hypothesized that other wing kinematics besides stroke-plane angle would vary in hummingbirds. To test this, we used synchronized highspeed (500·Hz) video cameras and measured the threedimensional wing and body kinematics of rufous hummingbirds (Selasphorus rufus, 3·g, N=5) as they flew at velocities of 0–12·m·s–1 in a wind tunnel. Consistent with earlier research, the angles of the body and the stroke plane changed with velocity, and the effect of velocity on wingbeat frequency was not significant. However, hummingbirds significantly altered other wing kinematics including chord angle, angle of attack, anatomical strokeplane angle relative to their body, percent of wingbeat in downstroke, wingbeat amplitude, angular velocity of the wing, wingspan at mid-downstroke, and span ratio of the wingtips and wrists. This variation in bird-centered kinematics led to significant effects of flight velocity on the angle of attack of the wing and the area and angles of the global stroke planes during downstroke and upstroke. We provide new evidence that the paths of the wingtips and wrists change gradually but consistently with velocity, as in other bird species that possess pointed wings. Although hummingbirds flex their wings slightly at the wrist during upstroke, their average wingtip–span ratio of 93% revealed that they have kinematically ‘rigid’ wings compared with other avian species

Formation and evolution of E+A galaxies in dusty starburst galaxies

The formation and evolution of the ``E+A'' (also named ``k+a'' and ``a+k'' types by Dressler et al. 1999) galaxies found in significant numbers in the cores of intermediate redshift clusters has been extensively discussed by many authors. In this paper, we model the spectral, dynamical and morphological evolution of a prime candidate for producing this spectral signature: a dusty starburst associated with a major galaxy merger. We show that as this system evolves dynamically, its spectral type changes from and ``e(a)'' type (exhibiting strong H$\delta$ absorption and modest [OII] emission -- the identifying features of local dusty starburst galaxies) to a k+a type and then finally to a passive ``k'' type. This result shows that galaxies with an e(a) spectral type can be precursors to the k+a systems and that dynamical evolution greatly controls the spectral evolution in these merger cases. Our simulations also show that a merger with very high infrared luminosity ($L_{\rm IR}$ $>$ $10^{11}$ $L_{\odot}$) is more likely to show an e(a) spectrum, which implies that spectral types can be correlated with infrared fluxes in dusty starburst galaxies. Based on these results, we discuss the origin of the evolution of k+a/a+k galaxies in distant clusters and the role merging is likely to have.Comment: 14 pages 4 figures,2001,ApJL,in pres

The epsilon Chamaeleontis young stellar group and the characterization of sparse stellar clusters

We present the outcomes of a Chandra X-ray Observatory snapshot study of five nearby Herbig Ae/Be (HAeBe) stars which are kinematically linked with the Oph-Sco-Cen Association (OSCA). Optical photometric and spectroscopic followup was conducted for the HD 104237 field. The principal result is the discovery of a compact group of pre-main sequence (PMS) stars associated with HD 104237 and its codistant, comoving B9 neighbor epsilon Chamaeleontis AB. We name the group after the most massive member. The group has five confirmed stellar systems ranging from spectral type B9-M5, including a remarkably high degree of multiplicity for HD 104237 itself. The HD 104237 system is at least a quintet with four low mass PMS companions in nonhierarchical orbits within a projected separation of 1500 AU of the HAeBe primary. Two of the low-mass members of the group are actively accreting classical T Tauri stars. The Chandra observations also increase the census of companions for two of the other four HAeBe stars, HD 141569 and HD 150193, and identify several additional new members of the OSCA. We discuss this work in light of several theoretical issues: the origin of X-rays from HAeBe stars; the uneventful dynamical history of the high-multiplicity HD 104237 system; and the origin of the epsilon Cha group and other OSCA outlying groups in the context of turbulent giant molecular clouds. Together with the similar eta Cha cluster, we paint a portrait of sparse stellar clusters dominated by intermediate-mass stars 5-10 Myr after their formation.Comment: Accepted for publication in the Astrophysical Journal. 32 pages and 7 figure

Morphological and kinematic basis of the hummingbird flight stroke: scaling of flight muscle transmission ratio

Hummingbirds (Trochilidae) are widely known for their insect-like flight strokes characterized by high wing beat frequency, small muscle strains and a highly supinated wing orientation during upstroke that allows for lift production in both halves of the stroke cycle. Here, we show that hummingbirds achieve these functional traits within the limits imposed by a vertebrate endoskeleton and muscle physiology by accentuating a wing inversion mechanism found in other birds and using long-axis rotational movement of the humerus. In hummingbirds, long-axis rotation of the humerus creates additional wing translational movement, supplementing that produced by the humeral elevation and depression movements of a typical avian flight stroke. This adaptation increases the wing-to-muscle-transmission ratio, and is emblematic of a widespread scaling trend among flying animals whereby wing-to-muscle-transmission ratio varies inversely with mass, allowing animals of vastly different sizes to accommodate aerodynamic, biomechanical and physiological constraints on muscle-powered flapping flight

V838 Mon: light echo evolution and distance estimate

Following its 2002 February eruption, V838 Mon developed a light echo that continues to expand and evolve as light from the outburst scatters off progressively more distant circumstellar and/or interstellar material. Multi-filter images of the light echo, obtained with the South African Astronomical Observatory (SAAO) 1.0-m telescope between 2002 May and 2004 December, are analysed and made available electronically. The expansion of the light echo is measured from the images and the data compared with models for scattering by a thin sheet and a thin shell of dust. From these model results we infer that the dust is likely in the form of a thin sheet distant from the star, suggesting that the material is of interstellar origin, rather than being from earlier stages in the star's evolution. Although the fit is uncertain, we derive a stellar distance of ~ 9 kpc and a star-dust distance of ~ 5 pc, in good agreement with recent results reported from other methods. We also present JHKL and Cousins UBVRI photometry obtained at the SAAO during the star's second, third and fourth observing seasons post-outburst. These data show complex infrared colour behaviour while V838 Mon is slowly brightening in the optical.Comment: 9 pages, 6 figures - accepted for publication in MNRA

The fall and rise of V854 Centauri: long-term ultraviolet spectroscopy of a highly-active R Coronae Borealis star

We examine long-term low-dispersion IUE, SWP and LWP spectroscopy of the R Coronae Borealis (RCB) star V854 Cen, obtained across the deep 1991, 1992-1993 and 1994 declines. We also report the optical light curve for the star in the interval 1987-1998, including multi-color photometry obtained during 1989-1998. Analysis of the UV emission line spectra indicates most lines decay during the deep declines on characteristic timescales comparable to that reported for optical features. Fe, Mg and neutral C lines decay on timescales of typically 50-100 d. Other lines, notably ionized C lines, decay on longer timescales (> 200 d) or appear to be unaffected by the declines. The general nature of the UV emission lines and other UV features during the declines is consistent with the E1/E2/BL line-region model developed from the behavior of optical spectral features during declines. However, the detailed line-behavior indicates large intrinsic variability between decline events inconsistent with the simple E1/E2/BL model. Limited temporal coverage prevents detailed examination of the geometry of the emission line region or the obscuring dust. We also report the first detection of the transition-region line C IV 1550 in the spectrum of an RCB star.Comment: AJ in press (June), 7 figures, 4 table

Opportunities for improving irrigation efficiency with quantitative models, soil water sensors and wireless technology

Increasingly serious shortages of water make it imperative to improve the efficiency of irrigation in agriculture, horticulture and in the maintenance of urban landscapes. The main aim of the current review is to identify ways of meeting this objective. After reviewing current irrigation practices, discussion is centred on the sensitivity of crops to water deficit, the finding that growth of many crops is unaffected by considerable lowering of soil water content and, on this basis, the creation of improved means of irrigation scheduling. Subsequently, attention is focused on irrigation problems associated with spatial variability in soil water and the often slow infiltration of water into soil, especially the subsoil. As monitoring of soil water is important for estimating irrigation requirements, the attributes of the two main types of soil water sensors and their most appropriate uses are described. Attention is also drawn to the contribution of wireless technology to the transmission of sensor outputs. Rapid progress is being made in transmitting sensor data, obtained from different depths down the soil profile across irrigated areas, to a PC that processes the data and on this basis automatically commands irrigation equipment to deliver amounts of water, according to need, across the field. To help interpret sensor outputs, and for many other reasons, principles of water processes in the soil–plant system are incorporated into simulation models that are calibrated and tested in field experiments. Finally, it is emphasized that the relative importance of the factors discussed in this review to any particular situation varies enormously