12,337 research outputs found
Stellar over-densities in the halo: the extent of the Virgo over-density
We map the three dimensional extent of the Virgo Over-density by combining
distance information from RR Lyrae variables and projected spatial information
from SEKBO (Keller et al. 2008) and Sloan Digital Sky Survey (SDSS) DR6
photometry. The Virgo Over-density is seen to comprise two filaments 14.5 x 3
degrees and 10 x 3 degrees and a circular structure 3 degrees in diameter.
Together the three features span 38 degrees of right ascension and declinations
of +2 to -15 degrees. RR Lyrae variables place the two filamentary features at
heliocentric distances of 20 and 17 kpc respectively, with projected dimensions
of 5 x 1 kpc and 3 x 1 kpc.Comment: 6 pages, 5 figures, MNRAS accepte
Gemini/GMOS photometry of intermediate-age star clusters in the Large Magellanic Cloud
We present Gemini South GMOS g,i photometry of 14 intermediate-age Large
Magellanic Cloud (LMC) star clusters, namely: NGC 2155, 2161, 2162, 2173, 2203,
2209, 2213, 2231, 2249, Hodge 6, SL 244, 505, 674, and 769, as part of a
continuing project to investigate the extended Main Sequence Turnoff (EMSTO)
phenomenon. Extensive artificial star tests were made over the observed field
of view. These tests reveal the observed behaviour of photometric errors with
magnitude and crowding. The cluster stellar density radial profiles were traced
from star counts over the extent of the observed field. We adopt clus- ter
radii and build colour-magnitude diagrams (CMDs) with cluster features clearly
identified. We used the cluster (g,g-i) CMDs to estimate ages from the matching
of theoretical isochrones. The studied LMC clusters are confirmed to be
intermediate-age clusters, which range in age 9.10 < log(t) < 9.60. NGC 2162
and NGC 2249 look like new EMSTO candidates, in addition to NGC 2209, on the
basis of having dual red clumps.Comment: MNRAS, accepte
Genomic blueprints of sponge-prokaryote symbiosis are shared by low abundant and cultivatable Alphaproteobacteria
Marine sponges are early-branching, filter-feeding metazoans that usually host complex microbiomes comprised of several, currently uncultivatable symbiotic lineages. Here, we use a low-carbon based strategy to cultivate low-abundance bacteria from Spongia officinalis. This approach favoured the growth of Alphaproteobacteria strains in the genera Anderseniella, Erythrobacter, Labrenzia, Loktanella, Ruegeria, Sphingorhabdus, Tateyamaria and Pseudovibrio, besides two likely new genera in the Rhodobacteraceae family. Mapping of complete genomes against the metagenomes of S. officinalis, seawater, and sediments confirmed the rare status of all the above-mentioned lineages in the marine realm. Remarkably, this community of low-abundance Alphaproteobacteria possesses several genomic attributes common to dominant, presently uncultivatable sponge symbionts, potentially contributing to host fitness through detoxification mechanisms (e.g. heavy metal and metabolic waste removal, degradation of aromatic compounds), provision of essential vitamins (e.g. B6 and B12 biosynthesis), nutritional exchange (especially regarding the processing of organic sulphur and nitrogen) and chemical defence (e.g. polyketide and terpenoid biosynthesis). None of the studied taxa displayed signs of genome reduction, indicative of obligate mutualism. Instead, versatile nutrient metabolisms along with motility, chemotaxis, and tight-adherence capacities - also known to confer environmental hardiness - were inferred, underlying dual host-associated and free-living life strategies adopted by these diverse sponge-associated Alphaproteobacteria.PTDC/MAR-BIO/1547/2014; full PhD scholarship from the
Erasmus Mundus Programme/SALAM EMA2 lot7/SALA1206422info:eu-repo/semantics/publishedVersio
Metagenome-assembled genome sequences of three uncultured planktomarina sp. strains from the Northeast Atlantic Ocean
We report three metagenome-assembled genomes (MAGs) of Planktomarina strains from coastal seawater (Portugal) to help illuminate the functions of understudied Rhodobacteraceae bacteria in marine environments. The MAGs encode proteins involved in aerobic anoxygenic photosynthesis and a versatile carbohydrate metabolism, strengthening the role of Planktomarina species in oceanic carbon cycling.Portuguese Foundation for Science and Technology: EXPL/MAR-EST/1664/2013
PTDC/MAR-BIO/1547/2014, UIDB/04565/2020, PD/BD/143029/2018, CEECIND/00788/2017,PTDC/BIA-MIC/31996/2017;Institute of Bioengineering and Biosciences (iBB) by the Programa Operacional Regional de Lisboa 007317; Helmholtz Association VH-NG-1248.info:eu-repo/semantics/publishedVersio
Finding RR Lyrae Stars with SkyMapper: an Observational Test
One of the major science goals of the SkyMapper Survey of the Southern
Hemisphere sky is the determination of the shape and extent of the halo of the
Galaxy. In this paper we quantify the likely efficiency and completeness of the
survey as regards the detection of RR Lyrae variable stars, which are excellent
tracers of the halo stellar population. We have accomplished this via
observations of the RR Lyrae-rich globular cluster NGC 3201. We find that for
single epoch uvgri observations followed by two further epochs of g, r imaging,
as per the intended three-epoch survey strategy, we recover known RR Lyraes
with a completeness exceeding 90%. We also investigate boundaries in the
gravity-sensitive single-epoch two-color diagram that yield high completeness
and high efficiency (i.e., minimal contamination by non-RR Lyraes) and the
general usefulness of this diagram in separating populations.Comment: 10 pages, 5 figures, to appear in the Publications of the
Astronomical Society of Australia (PASA), published by Cambridge University
Pres
Revisiting Clifford algebras and spinors III: conformal structures and twistors in the paravector model of spacetime
This paper is the third of a series of three, and it is the continuation of
math-ph/0412074 and math-ph/0412075. After reviewing the conformal spacetime
structure, conformal maps are described in Minkowski spacetime as the twisted
adjoint representation of the group Spin_+(2,4), acting on paravectors.
Twistors are then presented via the paravector model of Clifford algebras and
related to conformal maps in the Clifford algebra over the lorentzian R{4,1}$
spacetime. We construct twistors in Minkowski spacetime as algebraic spinors
associated with the Dirac-Clifford algebra Cl(1,3)(C) using one lower spacetime
dimension than standard Clifford algebra formulations, since for this purpose
the Clifford algebra over R{4,1} is also used to describe conformal maps,
instead of R{2,4}. Although some papers have already described twistors using
the algebra Cl(1,3)(C), isomorphic to Cl(4,1), the present formulation sheds
some new light on the use of the paravector model and generalizations.Comment: 17 page
Extended star formation in the intermediate-age large magellanic cloud star cluster NGC 2209
We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters
The Extended Main-Sequence Turn-off Clusters of the Large Magellanic Cloud - Missing links in Globular Cluster Evolution
Recent observations of intermediate age (1 - 3 Gyr) massive star clusters in
the Large Magellanic Cloud (LMC) have revealed that the majority possess
bifurcated or extended main-sequence turn-off (EMSTO) morphologies. This effect
can be understood to arise from subsequent star formation amongst the stellar
population with age differences between constituent stars amounting to 50 - 300
Myr. Age spreads of this order are similarly invoked to explain the light
element abundance variations witnessed in ancient globular clusters. In this
paper we explore the proposition that the clusters exhibiting the EMSTO
phenomenon are a general phase in the evolution of massive clusters, one that
naturally leads to the particular chemical properties of the ancient globular
cluster population.
We show that the isolation of EMSTO clusters to intermediate ages is the
consequence of observational selection effects. In our proposed scenario, the
EMSTO phenomenon is identical to that which establishes the light element
abundance variations that are ubiquitous in the ancient globular cluster
population. Our scenario makes a strong prediction: EMSTO clusters will exhibit
abundance variations in the light elements characteristic of the ancient GC
population.Comment: ApJ accepted. 33 pages, 5 figure
Metallicity gradients in the Sagittarius dwarf spheroidal Galaxy
Metallicity gradients in the Sagittarius dwarf Galaxy (Sgr) are investigated
by using infrared photometric data from the 2MASS survey. To search for
metallicity effects, the giant branch in a field situated near the Center of
the Sgr is compared to the giant branch in a field situated near its southern
edge. The contamination of Sgr giant branch by foreground Galactic stars is
canceled by statistical subtraction of diagrams symmetrical in Galactic
latitude. After subtraction it is possible to reconstruct the Sgr giant branch
with excellent accuracy. The giant branch in the two fields have similar slopes
but are shifted in color. Even after correction for the differential reddening
between the fields, the shift in color between the branch remains, and is very
significant. This variation in the color of the giant branch corresponds to a
metallicity variation of about -0.25 Dex. The existence of a metallicity
gradient in Sgr may indicate that there are two different stellar population in
Sgr. One has low metallicity, and another one of higher metallicity has a
smaller spatial extension.Comment: 7 pages, 8 figures, A&A in pres
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