Ultraviolet properties of individual hot stars in globular cluster cores. 1: NGC 1904 (M 79)

As part of an observing program using the International Ultraviolet Explorer (IUE) satellite to investigate the ultraviolet properties of stars found within the cores of galactic globular clusters with blue horizontal branches (HBs), we obtained three spectra of the cluster NGC 1904 (M 79). All three were long integration-time, short-wavelength (SWP) spectra obtained at the so called 'center of light' and all three showed evidence of sources within the IUE large aperture (21.4 in. by 10 in.). In this paper we shall describe the analysis of these spectra and present evidence that the UV sources represent individual hot stars in the post-HB stage of evolution

Intra-household use and acceptability of Ready-to-Use-Supplementary-Foods distributed in Niger between July and December 2010.

Few studies have looked at consumption of Ready-to-Use-Supplementary-Foods (RUSFs) during a nutritional emergency. Here, we describe the use and acceptability of RUSF within households in four districts of the region of Maradi, Niger during large scale preventive distributions with RUSF in 2010 targeted at children 6-35months of age. Our study comprised both quantitative and qualitative components to collect detailed information and to allow in-depth interviews. We performed a cross-sectional survey in 16 villages between two monthly distributions of RUSF (October-November 2010). All households with at least one child who received RUSF were included and a total of 1842 caregivers were interviewed using a structured questionnaire. Focus groups and individual interviews of 128 caregivers were conducted in eight of the selected villages. On average, 24.7% of households reported any sharing of RUSF within the household. Sharing practices outside the household remained rare. Most of the sharing reported occurred among children under 5years of age living in the household. On average, 91% of caregivers in all districts rated the child's appreciation of the products as good or very good. Program planning may need to explicitly accounting for the sharing of products among children under 5 within household

The Observations Of The X-Ray Source Hz Herculis-Hercules X-1

NASAESASRCAstronom

The stellar thermal wind as a consequence of oblateness

In many rotating fluids, the lowest-order force balance is between gravity, pressure, and rotational acceleration ('GPR' balance). Terrestrial GPR balance takes the form of geostrophy and hydrostasy, which together yield the terrestrial thermal wind equation. By contrast, stellar GPR balance is an oblateness equation, which determines the departures of the thermal variables from spherical symmetry; its curl yields the 'stellar thermal wind equation.' In this sense, the stellar thermal wind should be viewed not as a consequence of geostrophy, but of baroclinicity in the oblateness. Here we treat the full stellar oblateness, including the thermal wind, using pressure coordinates. We derive the generalised stellar thermal wind equation and identify the parameter regime for which it holds. In the case of the Sun, not considering the full oblateness has resulted in conflicting calculations of the theoretical aspherical temperature anomaly. We provide new calculation here and find that the baroclinic anomaly is ~3-60 times smaller than the barotropic anomaly. Thus, the anomaly from the thermal wind may not be measurable helioseismically; but if measurement were possible, this would potentially yield a new way to bracket the depth of the solar tachocline.Comment: 5 pages, accepted for publication in MNRAS

Dynamics of Rotation and Magnetism in the Sun's Convection Zone and Tachocline

In this thesis, we assess the theoretical dynamics achieved in the solar interior, with particular focus on the solar tachocline. We use the open-source Rayleigh code on parallel supercomputers to simulate 3-D, rotating spherical shells of convection. These shells cover much of the solar convection zone and in the tachocline models, a portion of the underlying radiative interior. This thesis divides solar dynamics into two distinct classes: The hydrodynamic (HD) Sun (which explores convection in the presence of differential rotation) and the magnetohydrodynamic (MHD) Sun (which explores how a self-excited solar dynamo interacts with convection and rotation). In the HD Sun, we discuss how the Near-Surface Shear Layer (NSSL) might be generated by fast downflow plumes. We also identify a physical mechanism whereby the Sun might establish an internal latitudinal temperature gradient and thus achieve isorotation contours significantly tilted with respect to the rotation axis. In the MHD Sun, we focus on the global magnetism and rotation profiles achieved in self-excited dynamo simulations. We first describe how dynamos in convection-zone-only shells display remarkable bistability: Two distinct magnetic cycles---each reminiscent of observed behavior in the solar cycle---are supported by the convection simultaneously. Finally, we present an MHD simulation achieving a solid-body-rotating radiative interior and differentially rotating convection zone. This shear layer, similar to the solar tachocline, is dynamically maintained by magnetic torques acting against viscous torques. Our work is thus the first to identify a ``magnetic tachocline confinement scenario" operating in a fully 3-D, nonlinear global simulation. Furthermore, the magnetism is produced by dynamo action, even below the region of convective overshoot. Rather than the classical ``abyssal deep''---i.e., a largely motion-free reservoir that accumulates magnetism pumped in from above---we argue that the Sun's radiative interior may contain inertial oscillations that couple to the dynamo.</p

A0620-00 revisited: a black-hole transient case-study

For the first time we have performed a detailed study of the X-ray, optical and infra-red light curves of the 1975/1976 outburst of the famous black-hole transient A0620-00 (Nova Mon 1975, V616 Mon). During the various stages of its outburst the X-rays lag the optical by ~5-20 days. Moreover, the activity associated with the secondary maximum started even earlier in the infra-red. This suggests that most of the outburst processes occur in the outer parts of the disk. We also find various drops in the X-ray intensity (lasting ~1 day or more). Near one of these a local maximum in the optical light curve occurs. This maximum appears ~30 days after the secondary maximum, i.e. close to the viscous time scale of an irradiated disk. We suggest this feature to be an `echo' of the secondary maximum. At the end of the outburst a similar local optical maximum occurs, which might be an `echo' of the tertiary maximum. We find that the drops in the optical and X-rays near the tertiary maximum are also present in other SXTs. They always occur ~150 days after the start of the outburst. We find for the first time that the X-ray spectrum of A0620-00 starts to harden ~100-150 days after the start of its outburst, similar to GS2000+25 and GS1124-68. This suggests we witness the transition from the so-called high to low state at that time. We show that the optical outburst light curve of A0620-00 closely resembles that of the cataclysmic variable AL Com. This strengthens the similarity in the properties of the SXTs and TOADs (or WZ Sge stars), and shows that the optical outburst light curves of both groups are governed by the disk properties and not by the compact object. Since irradiation provides a natural mechanism to prolong the outburst of SXTs, we suggest this could be of influence as well during TOAD outbursts.Comment: 38 pages, 10 figures, accepted for New Astronomy Review