The Volatility Trend of Protosolar and Terrestrial Elemental Abundances

We present new estimates of protosolar elemental abundances based on an improved combination of solar photospheric abundances and CI chondritic abundances. These new estimates indicate CI chondrites and solar abundances are consistent for 60 elements. We compare our new protosolar abundances with our recent estimates of bulk Earth composition (normalized to aluminium), thereby quantifying the devolatilization in going from the solar nebula to the formation of the Earth. The quantification yields a linear trend $\log(f) = \alpha\log(T_C) + \beta$, where $f$ is the Earth-to-Sun abundance ratio and $T_C$ is the 50$\%$ condensation temperature of elements. The best fit coefficients are: $\alpha = 3.676\pm 0.142$ and $\beta = -11.556\pm 0.436$. The quantification of these parameters constrains models of devolatilization processes. For example, the coefficients $\alpha$ and $\beta$ determine a critical devolatilization temperature for the Earth $T_{\mathrm{D}}(\mathrm{E}) = 1391 \pm 15$ K. The terrestrial abundances of elements with $T_{C} < T_{\mathrm{D}}(\mathrm{E})$ are depleted compared with solar abundances, whereas the terrestrial abundances of elements with $T_{C} > T_{\mathrm{D}}(\mathrm{E})$ are indistinguishable from solar abundances. The terrestrial abundance of Hg ($T_C$ = 252 K) appears anomalously high under the assumption that solar and CI chondrite Hg abundances are identical. To resolve this anomaly, we propose that CI chondrites have been depleted in Hg relative to the Sun by a factor of $13\pm7$. We use the best-fit volatility trend to derive the fractional distribution of carbon and oxygen between volatile and refractory components ($f_\mathrm{vol}$, $f_\mathrm{ref}$). We find ($0.91\pm 0.08$, $0.09 \pm 0.08$) for carbon and ($0.80 \pm 0.04$, $0.20 \pm 0.04$) for oxygen.Comment: Accepted for publication in Icarus. 28 pages, 12 figures, 5 tables. Compared to v1, the results and conclusion are the same, while discussion of results and implications is expanded considerabl

A close halo of large transparent grains around extreme red giant stars

Intermediate-mass stars end their lives by ejecting the bulk of their envelope via a slow dense wind back into the interstellar medium, to form the next generation of stars and planets. Stellar pulsations are thought to elevate gas to an altitude cool enough for the condensation of dust, which is then accelerated by radiation pressure from starlight, entraining the gas and driving the wind. However accounting for the mass loss has been a problem due to the difficulty in observing tenuous gas and dust tens of milliarcseconds from the star, and there is accordingly no consensus on the way sufficient momentum is transferred from the starlight to the outflow. Here, we present spatially-resolved, multi-wavelength observations of circumstellar dust shells of three stars on the asymptotic giant branch of the HR diagram. When imaged in scattered light, dust shells were found at remarkably small radii (<~ 2 stellar radii) and with unexpectedly large grains (~300 nm radius). This proximity to the photosphere argues for dust species that are transparent to starlight and therefore resistant to sublimation by the intense radiation field. While transparency usually implies insufficient radiative pressure to drive a wind, the radiation field can accelerate these large grains via photon scattering rather than absorption - a plausible mass-loss mechanism for lower-amplitude pulsating stars.Comment: 13 pages, 1 table, 6 figure

Differential cross section analysis in kaon photoproduction using associated legendre polynomials

Angular distributions of differential cross sections from the latest CLAS data sets \cite{bradford}, for the reaction ${\gamma}+p {\to} K^{+} + {\Lambda}$ have been analyzed using associated Legendre polynomials. This analysis is based upon theoretical calculations in Ref. \cite{fasano} where all sixteen observables in kaon photoproduction can be classified into four Legendre classes. Each observable can be described by an expansion of associated Legendre polynomial functions. One of the questions to be addressed is how many associated Legendre polynomials are required to describe the data. In this preliminary analysis, we used data models with different numbers of associated Legendre polynomials. We then compared these models by calculating posterior probabilities of the models. We found that the CLAS data set needs no more than four associated Legendre polynomials to describe the differential cross section data. In addition, we also show the extracted coefficients of the best model.Comment: Talk given at APFB08, Depok, Indonesia, August, 19-23, 200

Midwives' competence : is it affected by working in a rural location?

Introduction: Rising health care costs and the need to consolidate expertise in tertiary services have led to the centralisation of services. In the UK, the result has been that many rural maternity units have become midwife-led. A key consideration is that midwives have the skills to competently and confidently provide maternity services in rural areas, which may be geographically isolated and where the midwife may only see a small number of pregnant women each year. Our objective was to compare the views of midwives in rural and urban settings, regarding their competence and confidence with respect to ‘competencies’ identified as being those which all professionals should have in order to provide effective and safe care for low-risk women. Method: This was a comparative questionnaire survey involving a stratified sample of remote and rural maternity units and an ad hoc comparison group of three urban maternity units in Scotland. Questionnaires were sent to 82 midwives working in remote and rural areas and 107 midwives working in urban hospitals with midwife-led units. Results: The response rate from midwives in rural settings was considerably higher (85%) than from midwives in the urban areas (60%). Although the proportion of midwives who reported that they were competent was broadly similar in the two groups, there were some significant differences regarding specific competencies. Midwives in the rural group were more likely to report competence for breech delivery (p = 0.001), while more urban midwives reported competence in skills such as intravenous fluid replacement (p <0.001) and initial and discharge examination of the newborn (p <0.001). Both groups reported facing barriers to continuing professional development; however, more of the rural group had attended an educational event within the last month (p <0.001). Lack of time was a greater barrier for urban midwives (p = 0.02), whereas distance to training was greater for rural midwives (p = 0.009). Lack of motivation or interest was significantly higher in urban units (p = 0.006). Conclusion: It is often assumed that midwives in rural areas where there are fewer deliveries, will be less competent and confident in their practice. Our exploratory study suggests that the issue of competence is far more complex and deserves further attention.NHS Education Scotlan

The Radiated Energy Budget of Chromospheric Plasma in a Major Solar Flare Deduced From Multi-Wavelength Observations

This paper presents measurements of the energy radiated by the lower solar atmosphere, at optical, UV, and EUV wavelengths, during an X-class solar flare (SOL2011-02-15T01:56) in response to an injection of energy assumed to be in the form of nonthermal electrons. Hard X-ray observations from RHESSI were used to track the evolution of the parameters of the nonthermal electron distribution to reveal the total power contained in flare accelerated electrons. By integrating over the duration of the impulsive phase, the total energy contained in the nonthermal electrons was found to be $>2\times10^{31}$ erg. The response of the lower solar atmosphere was measured in the free-bound EUV continua of H I (Lyman), He I, and He II, plus the emission lines of He II at 304\AA\ and H I (Ly$\alpha$) at 1216\AA\ by SDO/EVE, the UV continua at 1600\AA\ and 1700\AA\ by SDO/AIA, and the WL continuum at 4504\AA, 5550\AA, and 6684\AA, along with the Ca II H line at 3968\AA\ using Hinode/SOT. The summed energy detected by these instruments amounted to $\sim3\times10^{30}$ erg; about 15% of the total nonthermal energy. The Ly$\alpha$ line was found to dominate the measured radiative losses. Parameters of both the driving electron distribution and the resulting chromospheric response are presented in detail to encourage the numerical modelling of flare heating for this event, to determine the depth of the solar atmosphere at which these line and continuum processes originate, and the mechanism(s) responsible for their generation.Comment: 14 pages, 18 figures. Accepted for publication in Astrophysics Journa

The radius and mass of the subgiant star bet Hyi from interferometry and asteroseismology

We have used the Sydney University Stellar Interferometer (SUSI) to measure the angular diameter of beta Hydri. This star is a nearby G2 subgiant whose mean density was recently measured with high precision using asteroseismology. We determine the radius and effective temperature of the star to be 1.814+/-0.017 R_sun (0.9%) and 5872+/-44 K (0.7%) respectively. By combining this value with the mean density, as estimated from asteroseismology, we make a direct estimate of the stellar mass. We find a value of 1.07+/-0.03 M_sun (2.8%), which agrees with published estimates based on fitting in the H-R diagram, but has much higher precision. These results place valuable constraints on theoretical models of beta Hyi and its oscillation frequencies.Comment: 3 figures, 3 tables, to appear in MNRAS Letter