Search

We present a chemo-dynamical analysis for 27 near main-sequence turnoff metal-poor stars, including 20 stars analysed for the first time. The sample spans a range in [Fe/H] from −2.5 to −3.6, with 44 per cent having [Fe/H]<−2.9. We derived chemical abundances for 17 elements, including strontium and barium. We derive Li abundances for the sample, which are in good agreement with the 'Spite Plateau' value. The lighter elements (Z < 30) generally agree well with those of other low-metallicity halo stars. This broadly indicates chemically homogeneous gas at the earliest times. We used the [Sr/Ba] versus [Ba/Fe] diagram to classify metal-poor stars into five populations based on their observed ratios. We find HE 0232 − 3755 to be a likely main r -process star, and HE 2214 − 6127 and HE 2332 − 3039 to be limited- r stars. CS30302-145, HE 2045 − 5057, and CD −24°17504 plausibly originated in long-disrupted early dwarf galaxies. We also find that the derived [Sr/H] and [Ba/H] values for CD −24°17504 are not inconsistent with the predicted yields of the s -process in massive rotating low-metallicity stars models. Further theoretical explorations will be helpful to better understand the earliest mechanisms and time scales of heavy element production for comparison with these and other observational abundance data. Finally, we investigate the orbital histories of our stars. Most display halo-like kinematics although three stars (CS 29504-018, HE 0223 − 2814, and HE 2133 − 0421) appear to be disc-like in nature. This confirms the extragalactic origin for CS 30302-145, HE 2045 − 5057, and, in particular, CD −24°17504 which likely originated from a small accreted stellar system as one of the oldest stars. [ABSTRACT FROM AUTHOR]

Background and Aims Germplasm with diverse, agronomically relevant traits forms the foundation of a successful plant breeding programme. Since 1993, the United Nations has been advocating the implementation of the Convention on Biological Diversity (CBD) and the subsequent 2002 Bonn Guidelines as international best practice on germplasm collection and use. In 2006, a European team made an expedition to Asia to collect wild germplasm of Miscanthus , a C4 perennial rhizomatous grass, for breeding an environmentally adaptable, resilient and high-yielding bioenergy crop. We outline general aspects of germplasm collection, conservation, breeding and biomass production evaluation while following the CBD's guidelines, respecting biodiversity and conservation needs, and the ethical use of genetic resources. Methods Effective protocols, quarantine, methods for collecting seed and rhizomes, and a genebank for conservation were established. Versatile informatics and database architecture were used to assist in selection, flowering synchronization, crossing, evaluation, phenotyping and data integration. Approaches were formulated to comply with the CBD guidelines. Key Results A total of 303 accessions of M. sinensis , M. sacchariflorus and M. floridulus were collected from 158 geographically and environmentally diverse locations. These species were shown to accumulate different amounts of aerial biomass due to combinations of stem count, height and thickness. Progeny from one interspecies cross accumulated more biomass in early trials and has shown double the yield performance in years 3–4 compared with the existing commercial cultivar M. × giganteus. An example of an F1 hybrid has already demonstrated the long-term potential of exploiting this collection for a breeding programme. Conclusions By conforming to the CBD principles, the authors' international collaboration provides a practical example of implementing the CBD. The collection widened the genetic diversity of Miscanthus available to allow for breeding of novel hybrids that exhibit more diverse traits to increase yield and resilience for growth on marginal land and in climate-challenged environments. [ABSTRACT FROM AUTHOR]

We present metallicities for red giant stars in the globular cluster NGC 6273 based on intermediate resolution GMOS-S spectra of the calcium triplet region. For the 42 radial velocity members with reliable calcium triplet line strength measurements, we obtain metallicities, [Fe/H], using calibrations established from standard globular clusters. We confirm the presence of an intrinsic abundance dispersion identified by Johnson et al. The total range in [Fe/H] is ~1.0 dex and after taking into account the measurement errors, the intrinsic abundance dispersion is σint[Fe/H] = 0.17 dex. Among the Galactic globular clusters, the abundance dispersion in NGC 6273 is only exceeded by ω Cen, which is regarded as the remnant of a disrupted dwarf galaxy, and M54, which is the nuclear star cluster of the Sagittarius dwarf galaxy. If these three globular clusters share the same formation mechanism, then NGC 6273 may also be the remnant nucleus of a disrupted dwarf galaxy. [ABSTRACT FROM AUTHOR]

We measure the C+N+O abundance sum in red giant stars in two Galactic globular clusters, NGC 1851 and NGC 6752. NGC 1851 has a split subgiant branch which could be due to different ages or C+N+O content while NGC 6752 is representative of the least complex globular clusters. For NGC 1851 and NGC 6752, we obtain average values of A(C+N+O) = 8.16 ± 0.10 (σ = 0.34) and 7.62 ± 0.02 (σ = 0.06), respectively. When taking into account the measurement errors, we find a constant C+N+O abundance sum in NGC 6752. The C+N+O abundance dispersion is only 0.06 dex, and such a result requires that the source of the light element abundance variations does not increase the C+N+O sum in this cluster. For NGC 1851, we confirm a large spread in C+N+O. In this cluster, the anomalous RGB has a higher C+N+O content than the canonical RGB by a factor of 4 (∼0.6 dex). This result lends further support to the idea that the two subgiant branches in NGC 1851 are roughly coeval, but with different CNO abundances. [ABSTRACT FROM AUTHOR]

We present CN and CH indices and Ca ii triplet metallicities for 34 giant stars and chemical abundances for 33 elements in 14 giants in the globular cluster M2. Assuming that the programme stars are cluster members, our analysis reveals (i) an extreme variation in CN and CH line strengths, (ii) a metallicity dispersion with a dominant peak at [Fe/H] ≈ −1.7 and smaller peaks at −1.5 and −1.0, (iii) star-to-star abundance variations and correlations for the light elements O, Na, Al and Si and (iv) a large (and possibly bimodal) distribution in the abundances of all elements produced mainly via the s-process in Solar system material. Following Roederer, Marino & Sneden, we define two groups of stars, ‘r + s’ and ‘r-only’, and subtract the average abundances of the latter from the former group to obtain an ‘s-process residual’. This s-process residual is remarkably similar to that found in M22 and in M4 despite the range in metallicity covered by these three systems. With recent studies identifying a double subgiant branch in M2 and a dispersion in Sr and Ba abundances, our spectroscopic analysis confirms that this globular cluster has experienced a complex formation history with similarities to M22, NGC 1851 and ω Centauri. [ABSTRACT FROM AUTHOR]

We analyse a 10 000 star spectroscopic survey, focused on Galactic thick disc stars typically 2–5 kpc from the Sun, carried out using the AAOmega Spectrograph on the Anglo-Australian Telescope (AAT). We develop methods for completeness correction of the survey based on Sloan Digital Sky Survey (SDSS) photometry, and we derive star distances using an improved isochrone fitting method with accuracies better than 10 per cent. We determine the large-scale kinematic [Vϕ = 172 km s−1 and σ(ϕ, r, z) = (49,51,40) km s−1], and abundance properties of the thick disc, showing these representative values are a fair description within about 3 kpc of the Sun, and in the range 1–3 kpc from the Galactic plane. We identify a substantial overdensity in lines of sight towards the inner Galaxy, with metallicity [Fe/H] ∼ −1 dex, and higher line of sight velocities than the thick disc, localized along the direction (ℓ, b) = (48°, −26°). This overdensity appears to be towards, but closer than, the known Hercules-Aquila halo overdensity and may be related to the Humphreys–Larsen inner Galaxy thick disc asymmetry. [ABSTRACT FROM AUTHOR]

Miscanthus sacchariflorus is a fast-growing C4 perennial grass that can naturally hybridize with M. sinensis to produce interspecific hybrids, such as the sterile triploid M.× giganteus. The creation of such hybrids is essential for the rapid domestication of this novel bioenergy crop. However, progress has been hindered by poor understanding of the environmental cues promoting floral transition in M. sacchariflorus, which flowers less readily than M. sinensis. The purpose of this work was to identify the flowering requirements of M. sacchariflorus genotypes in order to expedite the introduction of new germplasm optimized to different environments. Six M. sacchariflorus accessions collected from a range of latitudes were grown under controlled photoperiod and temperature conditions, and flowering, biomass, and morphological phenotypic data were captured. Results indicated that M. sacchariflorus, irrespective of origin, is a quantitative short-day plant. Flowering under static long days (15.3h daylength), compared with shorter photoperiods, was delayed by an average 61 d, with an average associated increase of 52% of above-ground biomass (DM plant–1). Timing of floral initiation occurred between photoperiods of 14.2h and 12.1h, and accumulated temperatures of 553–1157 °C above a base temperature of 10 °C. Miscanthus sacchariflorus flowering phenology closely resembles that of Sorghum and Saccharum, indicating potentially similar floral pathways and suggesting that determination of the underlying genetic mechanisms will be facilitated by the syntenic relationships existing between these important C4 grasses. [ABSTRACT FROM AUTHOR]

In this article, we examine current practices in the measurement of syntactic complexity to illustrate the need for more organic and sustainable practices in the measurement of complexity, accuracy, and fluency (CAF) in second language production. Through in-depth review of examples drawn from research on instructed second language acquisition, we identify and discuss challenges to the evidentiary logic that underlies current approaches. We also illuminate critical mismatches between the interpretations that researchers want to make and the complexity measures that they use to make them. Building from the case of complexity, we point to related concerns with impoverished operationalizations of multidimensional CAF constructs and the lack of attention to CAF as a dynamic and interrelated set of constantly changing subsystems. In conclusion, we offer suggestions for addressing these challenges, and we call for much closer articulation between theory and measurement as well as more central roles for multidimensionality and dynamicity in future CAF research. [ABSTRACT FROM PUBLISHER]

We present results of an analysis of high-resolution spectra ( R∼ 50 000), obtained with the Subaru Telescope High Dispersion Spectrograph, of two carbon-enhanced metal-poor (CEMP) stars selected from the Hamburg/European Southern Observatory prism survey, HE 1305+0007 and HE 1152−0355, and of the classical CH star HD 5223. All these stars have relatively low effective temperatures (4000–4750 K) and high carbon abundances, which result in the presence of very strong molecular carbon bands in their spectra. The stellar atmospheric parameters for these stars indicate that they all have surface gravities consistent with a present location on the red giant branch, and metallicities of (HE 1305+0007, HD 5223) and (HE 1152−0355). In addition to their large enhancements of carbon ( and +0.6, respectively), all three stars exhibit strong enhancements of the s-process elements relative to iron. HE 1305+0007 exhibits a large enhancement of the third-peak s-process element, lead, with , as well as a high abundance of the r-process element europium, . The second-peak s-process elements, Ba, La, Ce, Nd and Sm, are found to be more enhanced than the first-peak s-process elements Zr, Sr and Y. Thus, HE 1305+0007 joins the growing class of the so-called ‘Lead stars’, and also the class of objects that exhibit the presence of both r- and s-process elements, the CEMP- r/ s stars. The large enhancements of neutron-capture ( n-capture) elements exhibited by HE 1152−0355 and HD 5223 are more consistent with the abundance patterns generally noticed in CH stars, essentially arising from pure s-process nucleosynthesis. The elemental abundance distributions observed in these stars are discussed in light of existing theories of CH star formation, as well as the suggested formation scenarios of the CEMP- r/ s group. [ABSTRACT FROM AUTHOR]

We have compiled a new sample of 240 halo objects with accurate distance and radial velocity measurements, including globular clusters, satellite galaxies, field blue horizontal branch (FHB) stars and red giant stars from the Spaghetti survey. The new data lead to a significant increase in the number of known objects for Galactocentric radii beyond 50 kpc, which allows a reliable determination of the radial velocity dispersion profile out to very large distances. The radial velocity dispersion shows an almost constant value of 120 km s−1 out to 30 kpc and then continuously declines down to 50 km s−1 at about 120 kpc. This fall-off puts important constraints on the density profile and total mass of the dark matter halo of the Milky Way. For a constant velocity anisotropy, the isothermal profile is ruled out, while both a dark halo following a truncated flat (TF) model of mass and a Navarro, Frenk & White (NFW) profile of mass are consistent with the data. The significant increase in the number of tracers combined with the large extent of the region probed by these has allowed a more precise determination of the Milky Way mass in comparison to previous works. We also show how different assumptions for the velocity anisotropy affect the performance of the mass models. [ABSTRACT FROM AUTHOR]

We present FOcal Reducer/low dispersion Spectrograph-1 spectra (from the European Southern Observatory's Very Large Telescope) of a sample of 34 faint A-type stars selected from the Sloan Digital Sky Survey Early Data Release, with the goal of measuring the velocity dispersion of blue horizontal branch (BHB) stars in the remote Galactic halo, . We show that colour selection with and minimizes contamination of the sample by less luminous blue stragglers. In classifying the stars we confine our attention to the 20 stars with spectra of signal-to-noise ratio >15 Å−1. Classification produces a sample of eight BHB stars at distances from the Sun (mean 80 kpc), which represents the most distant sample of Galactic stars with measured radial velocities. The dispersion of the measured radial component of the velocity with respect to the centre of the Galaxy is . This value is anomalously low in comparison with measured values for stars at smaller distances, as well as for satellites at similar distances. Seeking an explanation for the low measured velocity dispersion, further analysis reveals that six of the eight remote BHB stars are plausibly associated with a single orbit. Three previously known outer halo carbon stars also appear to belong to this stream. The velocity dispersion of all nine stars relative to the orbit is only . Further observations along the orbit are required to trace the full extent of this structure on the sky. [ABSTRACT FROM AUTHOR]

This is the second in a series of papers presenting a new calculation of the mass of the Galaxy based on radial velocities and distances for a sample of faint field blue horizontal-branch (BHB) stars. We present accurate BV CCD photometry and spectra for 142 candidate A-type stars selected from photometry of UK Schmidt telescope plates in six high-Galactic-latitude fields. Classification of these candidates produces a sample of 60 BHB stars at distances of 11–52 kpc from the Sun (mean 28 kpc), with heliocentric line-of-sight velocities accurate to 15 km s−1, and distance errors <10 per cent. We provide a summary table listing coordinates and velocities of these stars. The measured dispersion of the radial component of the Galactocentric velocity for this sample is 108 ± 10 km s−1, in agreement with a recent study of the distant halo by Sirko and coworkers. Measurements of the Ca ii K line indicate that nearly all the stars are metal-poor with a mean with dispersion 0.5. Subsequent papers will describe a second survey of BHBs to heliocentric distances and present a new estimate of the mass of the Galaxy. [ABSTRACT FROM AUTHOR]

This is the first in a series of three papers presenting a new calculation of the mass of the Galaxy based on radial velocities and distances measured for a sample of some 100 faint 16 < B < 20 field blue horizontal branch (BHB) stars. This study aims to reduce the uncertainty in the measured mass of the Galaxy by increasing the number of halo objects at Galactocentric distances r > 30 kpc with measured radial velocities by a factor of 5. Faint A-type stars in the Galactic halo have been identified from ub[sub j]r photometry in six UK Schmidt fields. These samples include field BHB stars as well as less luminous stars of main-sequence surface gravity, which are predominantly field blue stragglers. We obtain accurate charge-coupled device photometry and spectra to classify these stars. This paper describes our methods for separating out clean samples of BHB stars in a way that is efficient in terms of telescope time required. We use the high signal-to-noise (S/N) ratio spectra of A-type stars of Kinman, Suntzeff & Kraft (published in 1994), and their definitive spectrophotometric A classifications, to assess the reliability of two methods, and to quantify the S/N ratio requirements. First we revisit, refine and extend the hydrogen linewidth versus colour relation as a classifier (here called the D[sub 0.15]-colour method). The second method is new and compares the shapes of the Balmer lines. With this method (here called the scale-width-shape method) there is no need for colours or spectrophotometry. Using the equivalent width of the Ca II K line as an additional filter we find we can reproduce Kinman, Suntzeff & Kraft's Λ classifications with both methods. In a sample of stars with strong Balmer lines, equivalent width Hγ > 13 Å [equivalent to the colour range 0 ≤ (B - V)[sub 0] ≤ 0.2], halo BHB stars can be separated from halo blue stragglers reliably. For the spectroscopy (i.e. both classification methods) the minimum required... [ABSTRACT FROM AUTHOR]

A correction to the article "The Radial Velocity Dispersion Profile of the Galactic Halo: Constraining the Density Profile of the Dark Halo of the Milky Way," in the previous issue is presented.