ABSTRACT Wrapping around the Milky Way, the Sagittarius stream is the dominant substructure in the halo. Our statistical selection method has allowed us to identify 106 highly likely members of the ...Sagittarius stream. Spectroscopic analysis of metallicity and kinematics of all members provides us with a new mapping of the Sagittarius stream. We find correspondence between the velocity distribution of stream stars and those computed for a triaxial model of the Milky Way dark matter halo. The Sagittarius trailing arm exhibits a metallicity gradient, ranging from −0.59 to −0.97 dex over 142°. This is consistent with the scenario of tidal disruption from a progenitor dwarf galaxy that possessed an internal metallicity gradient. We note high metallicity dispersion in the leading arm, causing a lack of detectable gradient and possibly indicating orbital phase mixing. We additionally report on a potential detection of the Sextans dwarf spheroidal in our data.
The Delaware Bay ecosystem has been the focus of extensive habitat restoration efforts to offset finfish losses due to mortality associated with power plant water intake. As a result, a 45
km
2 or a ...3% increase in total marsh area was achieved by 1996–1997 through the restoration efforts of the Public Service Enterprise Group (PSEG). To quantify the impact of restoration efforts on system productivity, an Ecopath with Ecosim model was constructed that represented all major components of the ecosystem. The model consisted of 47 functional groups including: 27 fish species, 5 invertebrate groups, 4 multi-species benthic groups, 6 multi-species fish groups, 3 plankton groups, 1 shorebird group and 1 marine mammal group. Biomass, abundance, catch, and demographic data were obtained from the literature or from individual stock assessments conducted for principal ecosystem components. A base Ecosim model was fitted to time series of key species in the Bay representing the period 1966–2003. To access the gains from marsh restoration, model simulations reflecting no restoration were conducted to estimate the productivity that would have been lost if restoration efforts had not occurred. The results indicated that restoration increased total ecosystem biomass by 47.7
t
km
−2
year
−1. Simulations indicated increased biomasses across a wide range of species including important forage and commercially important species. The marsh restoration also significantly impacted ecosystem structure increasing the ratio of production-to-respiration, increasing system path length and decreasing the ratio of production-to-biomass.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Context. Binary stellar systems form a large fraction of the Galaxy’s stars. They are useful as laboratories for studying the physical processes taking place within stars, and must be correctly taken ...into account when observations of stars are used to study the structure and evolution of the Galaxy. The advent of large-scale spectroscopic and photometric surveys allows us to obtain large samples of binaries that permit characterising their populations. Aims. We aim to obtain a large sample of double-lined spectroscopic binaries (SB2s) by analysis of spectra from the GALAH survey in combination with photometric and astrometric data. A combined analysis will provide stellar parameters of thousands of binary stars that can be combined to form statistical observables of a given population. We aim to produce a catalogue of well-characterised systems, which can in turn be compared to models of populations of binary stars, or to follow-up individual systems of interest. Methods. We obtained a list of candidate SB2 systems from a t-distributed stochastic neighbour embedding (t-SNE) classification and a cross-correlation analysis of GALAH spectra. To compute parameters of the primary and secondary star, we used a Bayesian approach that includes a parallax prior from Gaia DR2, spectra from GALAH, and apparent magnitudes from APASS, Gaia DR2, 2MASS, and WISE. We used a Markov chain Monte Carlo approach to sample the posterior distributions of the following model parameters for the two stars: Teff1,2, logg1,2, Fe/H, Vr1,2, vmic1,2, vbroad1,2, R1,2, and E(B−V). Results. We present results for 12 760 binary stars detected as SB2s. We construct the statistical observables T1∕T2, ΔVr, and R1∕R2, which demonstrate that our sample mostly consists of dwarfs, with a significant fraction of evolved stars and several dozen members of the giant branch. The majority of these binary stars is concentrated at the lower boundary of the ΔVr distribution, and the R1∕R2 ratio is mostly close to unity. The derived metallicity of our binary stars is statistically lower than that of single dwarf stars from the same magnitude-limited sample. Conclusions. Our sample of binary stars represents a large population of well-characterised double-lined spectroscopic binaries that are appropriate for statistical studies of the binary populations. The derived stellar properties and their distributions show trends that are expected for a population of close binary stars (a < 10 AU) detected through double lines in their spectra. Our detection technique allows us to probe binary systems with mass ratios 0.5 ≤q ≤ 1.
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FMFMET, NUK, UL, UM, UPUK
LoTr 1 is a planetary nebula thought to contain an intermediate-period binary central star system (that is, a system with an orbital period, P, between 100 and, say, 1500 d). The system shows the ...signature of a K type, rapidly rotating giant and most likely constitutes an accretion-induced post-mass-transfer system similar to other PNe, such as LoTr 5, WeBo 1 and A70. Such systems represent rare opportunities to further the investigation into the formation of barium stars and intermediate-period post-asymptotic giant branch systems - a formation process still far from being understood. Here, we present the first detailed analyses of both the central star system and the surrounding nebula of LoTr 1 using a combination of spectra obtained with Very Large Telescope-Focal Reducer and low dispersion Spectrograph, Anglo-Australian Telescope-UCL Coudé Echelle Spectrograph and New Technology Telescope-European Southern Observatory Multi-Mode Instrument, as well as SuperWASP (Wide Angle Search for Planets) photometry. We confirm the binary nature of the central star of LoTr 1 that consists of a K1 III giant and a hot white dwarf. The cool giant does not present any sign of s-process enhancement but is shown to have a rotation period of 6.4 d, which is a possible sign of mass accretion. LoTr 1 also presents broad double-peaked Hα emission lines, whose origin is still unclear. The nebula of LoTr 1 consists in two slightly elongated shells, with ages of 17 000 and 35 000 yr, respectively, and with different orientations. As such, LoTr 1 present a very different nebular morphology than A70 and WeBo 1, which may be an indication of difference in the mass-transfer episodes.
A stock synthesis model was used to assess effects of experimental flows on early life stages of nonnative rainbow trout (Oncorhynchus mykiss) in the Colorado River below Glen Canyon Dam (Arizona, ...USA). The model estimated time-varying survival rates while correcting for entry of new recruits to the age-0 population and changes in vulnerability to capture associated with growth and ontogenetic habitat shifts. A controlled flood, designed in part to enhance native fish habitat, led to an 11-fold increase in early survival rates (fertilization to ~1 month from emergence) of weekly cohorts of trout fertilized after the flood. Effects of increased flow fluctuations during incubation, designed to reduce trout abundance, were not apparent. Age-0 mortality between August and September was over twofold higher in years when there was a 50% reduction in the minimum flow compared with years when flow was stable. There was strong support for models that simulated an ontogenetic shift to deeper habitat in four of five study years. The integration of detailed field information in a stock synthesis model to describe early life history dynamics is a valuable approach that can be applied in a wide range of systems.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Ecosim models have been fitted to time-series data for a wide variety of ecosystems for which there are long-term data that confirm the models' ability to reproduce past responses of many species to ...harvesting. We subject these model ecosystems to a variety of harvest policies, including options based on harvesting each species at its maximum sustainable yield (MSY) fishing rate. We show that widespread application of single-species MSY policies would in general cause severe deterioration in ecosystem structure, in particular the loss of top predator species. This supports the long-established practice in fisheries management of protecting at least some smaller “forage” species specifically for their value in supporting larger piscivores.
North American Ospreys (Pandion haliaetus) typically migrate long distances to their wintering grounds in the tropics. Beyond the general distribution of their wintering range (i.e., the Caribbean, ...South America, and Central America), very little is known about the wintering ecology of these birds. We used satellite telemetry to determine the duration of wintering period, to examine the characteristics of wintering areas used by Ospreys, and to quantify space use and activity patterns of wintering Ospreys. Adult Ospreys migrated to wintering sites and exhibited high wintering site fidelity among years. Overall, Ospreys wintered on river systems (50.6%) more than on lakes (19.0%), and use of coastal areas was (30.4%) intermediate. Ospreys remained on their wintering grounds for an average of 154 d for males and 167 d for females. Locations of wintering Ospreys obtained via GPS-capable satellite telemetry suggest these birds move infrequently and their movements are very localized (i.e., <5 km from selected roosting areas). Sizes of home ranges and core-use areas for wintering Ospreys averaged 12.7 km2 and 1.4 km2, respectively. Overall, our findings suggest wintering adult North American Ospreys are very sedentary, demonstrating a pattern of limited daily movements and high fidelity to a few select locations (presumably roosts). We suggest this wintering strategy might be effective for reducing the risk of mortality and maximizing energy conservation. Pandion haliaetus típicamente migra grandes distancias hacia sus sitios de invernada en los trópicos. Más allá de la distribución general del rango de invernada (i.e., el Caribe, América del Sur y América Central), se sabe muy poco sobre la ecología de invernada de esta especie. Utilizamos telemetría satelital para determinar la duración del periodo de invernada, examinar las características de las áreas de invernada utilizadas por P. haliaetus y cuantificar el uso del espacio y los patrones de actividad de individuos de esta especie. Los individuos adultos de P. haliaetus migraron hacia los sitios de invernada y exhibieron una elevada fidelidad por el sitio de invernada entre años. En general, P. haliaetus invernó en sistemas riparios (50.6%) más que en lagos (19.0%) y el uso de zonas costeras fue (30.4%) intermedio. Los individuos de P. haliaetus permanecieron en sus áreas de invernada un promedio de 154 días para los machos y 167 días para las hembras. Las ubicaciones de individuos de P. haliaetus obtenidas vía telemetría satelital GPS sugieren que estas aves se mueven con poca frecuencia y que sus movimientos son muy localizados (i.e., <5 km de las áreas de dormideros seleccionadas). El tamaño de las áreas de hogar y áreas núcleo de uso para invernada en P. haliaetus promedió 12.7 km2 y 1.4 km2 respectivamente. En general, estos hallazgos sugieren que los individuos adultos de P. haliaetus invernantes son muy sedentarios, demostrando un patrón de movimientos diarios limitado y una elevada fidelidad a las ubicaciones seleccionadas (presumiblemente dormideros). Sugerimos que esta estrategia de invernada puede ser efectiva para reducir el riesgo de mortalidad y maximizar la conservación de energía.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The Galactic globular cluster NGC 1851 has raised much interest since Hubble Space Telescope photometry revealed that it hosts a double subgiant branch. Here we report on our homogeneous study into ...the cyanogen (CN) band strengths in the red giant branch (RGB) population (17 stars) and asymptotic giant branch (AGB) population (21 stars) using AAOmega/2dF spectra with R ~ 3000. We discover that NGC 1851 hosts a quadrimodal distribution of CN band strengths in its RGB and AGB populations. This result supports the merger formation scenario proposed for this cluster, such that the CN quadrimodality could be explained by the superposition of two "normal" bimodal populations. A small sample overlap with an abundance catalog allowed us to tentatively explore the relationship between our CN populations and a range of elemental abundances. We found a striking correlation between CN and O/Na. We also found that the four CN peaks may be paired-the two CN-weaker populations being associated with low Ba and the two CN-stronger populations with high Ba. If true, then s-process abundances would be a good diagnostic for disentangling the two original clusters in the merger scenario. More observations are needed to confirm the quadrimodality and also the relationship between the subpopulations. We also report CN results for NGC 288 as a comparison. Our relatively large samples of AGB stars show that both clusters have a bias toward CN-weak AGB populations.
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