Geometry of giant star model atmospheres: A consistency test

We investigate the effect of a geometric inconsistency in the calculation of synthetic spectra of giant stars. Spectra computed with model atmospheres calculated in spherical geometry while using the plane-parallel approximation for line formation calculations (s_p), as well as the fully plane-parallel case (p_p), are compared to the consistently spherical case (s_s). We present abundance differences for solar metallicity models with Teff ranging from 4000 to 6500 K and logg from 0.5 to 3.0 [cgs]. The effects are smaller for s_p calculations (-0.1 dex in the worst case) than for the p_p case (up to +0.35 dex for minority species and at most -0.04 dex for majority species), both with respect to the s_s case. In the s_p case the differences increase slightly with temperature, while in the p_p case they show a more complex behaviour. In both cases the effects decrease with increasing logg and increase with equivalent width. Thus, within the parameter range of F, G and K giants, consistency seems to be less important than using a spherical model atmosphere. The abundance differences due to sphericity effects presented here can be used for error estimation in abundance studies relying on plane-parallel modelling.Comment: 12 pages, including 10 figures and 1 table (A&A print format), accepted by A&

Chemical Inhomogeneities in the Milky Way Stellar Halo

We have compiled a sample of 699 stars from the recent literature with detailed chemical abundance information (spanning -4.2 < [Fe/H] < +0.3), and we compute their space velocities and Galactic orbital parameters. We identify members of the inner and outer stellar halo populations in our sample based only on their kinematic properties and then compare the abundance ratios of these populations as a function of [Fe/H]. In the metallicity range where the two populations overlap (-2.5 < [Fe/H] < -1.5), the mean [Mg/Fe] of the outer halo is lower than the inner halo by ~0.1 dex. For [Ni/Fe] and [Ba/Fe], the star-to-star abundance scatter of the inner halo is consistently smaller than in the outer halo. The [Na/Fe], [Y/Fe], [Ca/Fe], and [Ti/Fe] ratios of both populations show similar means and levels of scatter. Our inner halo population is chemically homogeneous, suggesting that a significant fraction of the Milky Way stellar halo originated from a well-mixed ISM. In contrast, our outer halo population is chemically diverse, suggesting that another significant fraction of the Milky Way stellar halo formed in remote regions where chemical enrichment was dominated by local supernova events. We find no abundance trends with maximum radial distance from the Galactic center or maximum vertical distance from the Galactic disk. We also find no common kinematic signature for groups of metal-poor stars with peculiar abundance patters, such as the alpha-poor stars or stars showing unique neutron-capture enrichment patterns. Several stars and dSph systems with unique abundance patterns spend the majority of their time in the distant regions of the Milky Way stellar halo, suggesting that the true outer halo of the Galaxy may have little resemblance to the local stellar halo.Comment: Accepted for publication in AJ. Full tables available upon reques

Detection of Elements at All Three r-process Peaks in the Metal-Poor Star HD 160617

We report the first detection of elements at all three r-process peaks in the metal-poor halo star HD 160617. These elements include arsenic and selenium, which have not been detected previously in halo stars, and the elements tellurium, osmium, iridium, and platinum, which have been detected previously. Absorption lines of these elements are found in archive observations made with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. We present up-to-date absolute atomic transition probabilities and complete line component patterns for these elements. Additional archival spectra of this star from several ground-based instruments allow us to derive abundances or upper limits of 45 elements in HD 160617, including 27 elements produced by neutron-capture reactions. The average abundances of the elements at the three r-process peaks are similar to the predicted solar system r-process residuals when scaled to the abundances in the rare earth element domain. This result for arsenic and selenium may be surprising in light of predictions that the production of the lightest r-process elements generally should be decoupled from the heavier r-process elements.Comment: Published in the Astrophysical Journal (22 pages, 12 figures

Abundances of metal-weak thick-disc candidates

High resolution spectra of 5 candidate metal-weak thick-disc stars suggested by Beers & Sommer-Larsen (1995) are analyzed to determine their chemical abundances. The low abundance of all the objects has been confirmed with metallicity reaching [Fe/H]=-2.9. However, for three objects, the astrometric data from the Hipparcos catalogue suggests they are true halo members. The remaining two, for which proper-motion data are not available, may have disc-like kinematics. It is therefore clear that it is useful to address properties of putative metal-weak thick-disc stars only if they possess full kinematic data. For CS 22894-19 the abundance pattern similar to those of typical halo stars is found, suggesting that chemical composition is not a useful discriminant between thick-disc and halo stars. CS 29529-12 is found to be C enhanced with [C/Fe]=+1.0; other chemical peculiarities involve the s process elements: [Sr/Fe]=-0.65 and [Ba/Fe]=+0.62, leading to a high [Ba/Sr] considerably larger than what is found in more metal-rich carbon-rich stars, but similar to LP 706-7 and LP 625-44 discussed by Norris et al (1997a). Hipparcos data have been used to calculate the space velocities of 25 candidate metal-weak thick-disc stars, thus allowing us to identify 3 bona fide members, which support the existence of a metal-poor tail of the thick-disc, at variance with a claim to the contrary by Ryan & Lambert (1995).Comment: to be published in MNRA

Measuring children’s involvement as an indicator of curriculum effectiveness : a curriculum evaluation of a selected child study centre in Singapore

This paper presents one aspect of a research project evaluating a curriculum model of a selected child study centre in Singapore. An issue of worldwide interest and concern is the &lsquo;quality of learning&rsquo; debate as it relates to early childhood centres. In Singapore, the government is focusing on expansion in child care settings and increases in the amount of funded training. One of the issues surrounding prior-to-school education raises the question of how one measures the quality of teaching and learning, to describe the value of using, funding and promoting early education. The research reported in this study used a quasi experimental research paradigm to assess one aspect of the quality of a curriculum programme in a child study centre in Singapore. Children aged between 18 months and 6 years (N = 81) participated in the research. Using the observation scale of Laevers&rsquo; Child Involvement Scale, the active involvement of children in learning experiences was measured. The findings are presented and discussed

‘Inspired and assisted’, or ‘berated and destroyed’? Research leadership, management and performativity in troubled times

Research leadership in Australian universities takes place against a backdrop of policy reforms concerned with measurement and comparison of institutional research performance. In particular, the Excellence in Research in Australian initiative undertaken by the Australian Research Council sets out to evaluate research quality in Australian universities, using a combination of expert review process, and assessment of performance against &lsquo;quality indicators&rsquo;. Benchmarking exercises of this sort continue to shape institutional policy and practice, with inevitable effects on the ways in which research leadership, mentoring and practice are played out within university faculties and departments. In an exploratory study that interviewed 32 Australian academics in universities in four Australian states, we asked participants, occupying formal or informal research leadership roles, to comment on their perceptions of research leadership as envisioned and enacted in their particular workplaces. We found a pervasive concern amongst participants that coalesced around binaries characterized in metaphoric terms of &lsquo;carrots and whips&rsquo;. Research leadership was seen by many as managerial in nature, and as such, largely tethered to instrumentalist notions of productivity and performativity, while research cultures were seen as languishing under the demoralizing weight of reward and punishment systems. Here, we consider what is at stake for the future of the academic workforce under such conditions, arguing that new models of visionary research leadership are urgently needed in the &lsquo;troubled times&rsquo; of techno-bureaucratic university reforms.<br /

The impact of an updated 14N(p,γ)15O^{14}N(p,\gamma)^{15}O reaction rate on advanced evolutionary stages of low-mass stellar models

We have investigated the impact of the $^{14}N(p,\gamma)^{15}O$ reaction rate recently redetermined by the LUNA experiment, on the shell H-burning and core He-burning phases of low-mass, metal poor stellar models. The new reaction rate has small but noticeable effects, the largest one being a $\sim$7-8\% reduction of the red giant branch lifetimes. To different degrees, the lifetimes and luminosities of horizontal branch models, the mass of the stellar models evolving within the RR Lyrae instability strip, the luminosity of the red giant branch luminosity function bump, the theoretical calibrations of the R-parameter and tip of the red giant branch luminosity are also affected. Predictions for the tip of the red giant branch luminosity, in particular, are in very good agreement with the currently available empirical constraints.Comment: 8 pages, accepted for publication in A&

RR-Lyrae-type pulsations from a 0.26-solar-mass star in a binary system

RR Lyrae pulsating stars have been extensively used as tracers of old stellar populations for the purpose of determining the ages of galaxies, and as tools to measure distances to nearby galaxies. There was accordingly considerable interest when the RR Lyr star OGLE-BLG-RRLYR-02792 was found to be a member in an eclipsing binary system4, as the mass of the pulsator (hitherto constrained only by models) could be unambiguously determined. Here we report that RRLYR-02792 has a mass of 0.26 M_sun and therefore cannot be a classical RR Lyrae star. Through models we find that its properties are best explained by the evolution of a close binary system that started with 1.4 M_sun and 0.8 M_sun stars orbiting each other with an initial period of 2.9 days. Mass exchange over 5.4 Gyr produced the observed system, which is now in a very short-lived phase where the physical properties of the pulsator happen to place it in the same instability strip of the H-R diagram occupied by RR Lyrae stars. We estimate that samples of RR Lyr stars may contain a 0.2 percent contamination with systems similar to this one, implying that distances measured with RR Lyrae stars should not be significantly affected by these binary interlopers

Chemically consistent evolution of galaxies: II. Spectrophotometric evolution from zero to high redshift

We present a new generation of chemically consistent evolutionary synthesis models for galaxies of various spectral types from E through Sd. The models follow the chemical enrichment of the ISM and take into account the increasing initial metallicity of successive stellar generations using recently published metallicity dependent stellar evolutionary isochrones, spectra and yields. Our first set of closed-box 1-zone models does not include any spatial resolution or dynamics. For a Salpeter initial mass function (IMF) the star formation rate(SFR) and its time evolution are shown to successfully parameterise spectral galaxy types E, ..., Sd. We show how the stellar metallicity distribution in various galaxy types build up with time to yield after $\sim 12$ Gyr agreement with stellar metallicity distributions observed in our and other local galaxies. The models give integrated galaxy spectra over a wide wavelength range (90.9\AA - 160$\mu$m), which for ages of $\sim 12$ Gyr are in good agreement not only with observed broad band colours but also with template spectra for the respective galaxy types. Using filter functions for Johnson-Cousins, as well as for HST broad band filters in the optical and Bessel & Brett's NIR filter system, we calculate the luminosity and colour evolution of model galaxies over a Hubble time. Including a standard cosmological model and the attenuation by intergalactic hydrogen we present evolutionary and cosmological corrections as well as apparent luminosities in various filters over the redshift range from z $\sim 5$ to the present for our galaxy types and compare to earlier models using single (=solar) metallicity input physics only. We also present a first comparison of our cc models to HDF data.(Abridged abstract)Comment: 13 pages, accepted for publication in Astronomy and Astrophysic

Mobilising knowledge between practitioners and researchers to iteratively refine a complex intervention (DAFNEplus) pre-trial: protocol for a structured, collaborative working group process.

Background: Randomised controlled trials (RCTs) of complex interventions often begin with a pilot phase to test the proposed methods and refine the intervention before it is trialled. Although the Medical Research Council (MRC) recommends regular communication between the practitioners delivering the intervention and the researchers evaluating it during the pilot phase, there is a lack of practical guidance about how to undertake this aspect of pre-trial work. This paper describes a novel structured process for collaborative working, which we developed to iteratively refine a complex intervention prior to an RCT. We also describe an in-built qualitative study to learn lessons about how this approach could be used by future study teams. Methods: This work forms part of a broader research programme to develop and trial a complex intervention for people with type 1 diabetes, called DAFNEplus. The intervention is being piloted in three National Health Service (NHS) diabetes centres in two waves, with refinements being incrementally implemented between each wave in response to real-time, collective learning (combining practitioner experience, process evaluation data and patient and public involvement via an advisory group). A structured 'Collaborative Working Group' (CWG) process, comprising monthly teleconferences and four strategically timed face-to-face meetings, is being used to identify and respond systematically to emerging implementation challenges and research findings. The group involves 25 members of the study team, including the multi-disciplinary practitioners delivering the intervention, the research teams conducting the process evaluation, the study manager and Chief Investigator. An in-built qualitative study comprising documentary analysis of meeting materials, discourse analysis of meeting transcripts, reflexive note taking, and thematic analysis of focus groups and interviews with CWG members is being undertaken to explore how the CWG works and how its processes and procedures might be improved. Discussion: The CWG process offers a potential model for collaborative working in future pre-trial pilot phases and intervention development studies that operationalises MRC guidance to progressively develop a complex intervention and foster shared ownership through genuine collaboration. The findings from the qualitative study will provide insight into how to best support collaborative working to achieve optimal intervention design