217 research outputs found
Chemical and kinematical properties of Galactic bulge stars surrounding the stellar system Terzan 5
As part of a study aimed at determining the kinematical and chemical
properties of Terzan 5, we present the first characterization of the bulge
stars surrounding this puzzling stellar system. We observed 615 targets located
well beyond the tidal radius of Terzan 5 and we found that their radial
velocity distribution is well described by a Gaussian function peaked at
=+21.0\pm4.6 km/s and with dispersion sigma_v=113.0\pm2.7 km/s. This is
the one of the few high-precision spectroscopic survey of radial velocities for
a large sample of bulge stars in such a low and positive latitude environment
(b=+1.7{\deg}). We found no evidence for the peak at \sim+200 km/s found
in Nidever et al. 2012. The strong contamination of many observed spectra by
TiO bands prevented us from deriving the iron abundance for the entire
spectroscopic sample, introducing a selection bias. The metallicity
distribution was finally derived for a sub-sample of 112 stars in a magnitude
range where the effect of the selection bias is negligible. The distribution is
quite broad and roughly peaked at solar metallicity ([Fe/H]\simeq+0.05 dex)
with a similar number of stars in the super-solar and in the sub-solar ranges.
The population number ratios in different metallicity ranges agree well with
those observed in other low-latitude bulge fields suggesting (i) the possible
presence of a plateau for |b|<4{\deg} for the ratio between stars in the
super-solar (0<[Fe/H]<0.5 dex) and sub-solar (-0.5<[Fe/H]<0 dex) metallicity
ranges; (ii) a severe drop of the metal-poor component ([Fe/H]<-0.5) as a
function of Galactic latitude.Comment: 27 pages, 9 figures, accepted for publication by Ap
Ceci n'est pas a globular cluster: the metallicity distribution of the stellar system Terzan 5
We present new determinations of the iron abundance for 220 stars belonging
to the stellar system Terzan 5 in the Galactic bulge. The spectra have been
acquired with FLAMES at the Very Large Telescope of the European Southern
Observatory and DEIMOS at the Keck II Telescope. This is by far the largest
spectroscopic sample of stars ever observed in this stellar system. From this
dataset, a subsample of targets with spectra unaffected by TiO bands was
extracted and statistically decontaminated from field stars. Once combined with
34 additional stars previously published by our group, a total sample of 135
member stars covering the entire radial extent of the system has been used to
determine the metallicity distribution function of Terzan 5. The iron
distribution clearly shows three peaks: a super-solar component at
[Fe/H] dex, accounting for 29% of the sample, a dominant sub-solar
population at [Fe/H] dex, corresponding to 62% of the total, and a
minor (6%) metal-poor component at [Fe/H] dex. Such a broad,
multi-modal metallicity distribution demonstrates that Terzan 5 is not a
genuine globular cluster but the remnant of a much more complex stellar system.Comment: 29 pages, 10 figures. Accepted for publication by Ap
Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low Mass White Dwarfs
We present the first detailed study of the properties (temperatures,
gravities, and masses) of the NGC 6791 white dwarf population. This unique
stellar system is both one of the oldest (8 Gyr) and most metal-rich ([Fe/H] ~
0.4) open clusters in our Galaxy, and has a color-magnitude diagram (CMD) that
exhibits both a red giant clump and a much hotter extreme horizontal branch.
Fitting the Balmer lines of the white dwarfs in the cluster, using Keck/LRIS
spectra, suggests that most of these stars are undermassive, = 0.43 +/-
0.06 Msun, and therefore could not have formed from canonical stellar evolution
involving the helium flash at the tip of the red giant branch. We show that at
least 40% of NGC 6791's evolved stars must have lost enough mass on the red
giant branch to avoid the flash, and therefore did not convert helium into
carbon-oxygen in their core. Such increased mass loss in the evolution of the
progenitors of these stars is consistent with the presence of the extreme
horizontal branch in the CMD. This unique stellar evolutionary channel also
naturally explains the recent finding of a very young age (2.4 Gyr) for NGC
6791 from white dwarf cooling theory; helium core white dwarfs in this cluster
will cool ~3 times slower than carbon-oxygen core stars and therefore the
corrected white dwarf cooling age is in fact ~7 Gyr, consistent with the well
measured main-sequence turnoff age. These results provide direct empirical
evidence that mass loss is much more efficient in high metallicity environments
and therefore may be critical in interpreting the ultraviolet upturn in
elliptical galaxies.Comment: 15 pages, 9 figures, 2 tables. Accepted for publication in Astrophys.
J. Very minor changes from first versio
Does a complex life cycle affect adaptation to environmental change? Genome-informed insights for characterizing selection across complex life cycle
Complex life cycles, in which discrete life stages of the same organism differ in form or function and often occupy different ecological niches, are common in nature. Because stages share the same genome, selective effects on one stage may have cascading consequences through the entire life cycle. Theoretical and empirical studies have not yet generated clear predictions about how life cycle complexity will influence patterns of adaptation in response to rapidly changing environments or tested theoretical predictions for fitness trade-offs (or lack thereof) across life stages. We discuss complex life cycle evolution and outline three hypotheses-ontogenetic decoupling, antagonistic ontogenetic pleiotropy and synergistic ontogenetic pleiotropy-for how selection may operate on organisms with complex life cycles. We suggest a within-generation experimental design that promises significant insight into composite selection across life cycle stages. As part of this design, we conducted simulations to determine the power needed to detect selection across a life cycle using a population genetic framework. This analysis demonstrated that recently published studies reporting within-generation selection were underpowered to detect small allele frequency changes (approx. 0.1). The power analysis indicates challenging but attainable sampling requirements for many systems, though plants and marine invertebrates with high fecundity are excellent systems for exploring how organisms with complex life cycles may adapt to climate change
A Chromosome-level genome assembly of the highly heterozygous sea urchin Echinometra sp. EZ reveals adaptation in the regulatory regions of stress response genes
Echinometra is the most widespread genus of sea urchin and has been the focus of a wide range of studies in ecology, speciation, and reproduction. However, available genetic data for this genus are generally limited to a few select loci. Here, we present a chromosome-level genome assembly based on 10x Genomics, PacBio, and Hi-C sequencing for Echinometra sp. EZ from the Persian/Arabian Gulf. The genome is assembled into 210 scaffolds totaling 817.8â
Mb with an N50 of 39.5â
Mb. From this assembly, we determined that the E. sp. EZ genome consists of 2nâ=â42 chromosomes. BUSCO analysis showed that 95.3% of BUSCO genes were complete. Ab initio and transcript-informed gene modeling and annotation identified 29,405 genes, including a conserved Hox cluster. E. sp. EZ can be found in high-temperature and high-salinity environments, and we therefore compared E. sp. EZ gene families and transcription factors associated with environmental stress response (âdefensomeâ) with other echinoid species with similar high-quality genomic resources. While the number of defensome genes was broadly similar for all species, we identified strong signatures of positive selection in E. sp. EZ noncoding elements near genes involved in environmental response pathways as well as losses of transcription factors important for environmental response. These data provide key insights into the biology of E. sp. EZ as well as the diversification of Echinometra more widely and will serve as a useful tool for the community to explore questions in this taxonomic group and beyond
The Star Formation History and Dust Content in the Far Outer Disc of M31
We present a detailed analysis of two fields located 26 kpc (~5 scalelengths)
from the centre of M31. One field samples the major axis populations--the Outer
Disc field--while the other is offset by ~18' and samples the Warp in the
stellar disc. The CMDs based on HST/ACS imaging reach old main-sequence
turn-offs (~12.5 Gyr). We apply the CMD-fitting technique to the Warp field to
reconstruct the star formation history (SFH). We find that after undergoing
roughly constant SF until about 4.5 Gyr ago, there was a rapid decline in
activity and then a ~1.5 Gyr lull, followed by a strong burst lasting 1.5 Gyr
and responsible for 25% of the total stellar mass in this field. This burst
appears to be accompanied by a decline in metallicity which could be a
signature of the inflow of metal-poor gas. The onset of the burst (~3 Gyr ago)
corresponds to the last close passage of M31 and M33 as predicted by detailed
N-body modelling, and may have been triggered by this event. We reprocess the
deep M33 outer disc field data of Barker et al. (2011) in order to compare
consistently-derived SFHs. This reveals a similar duration burst that is
exactly coeval with that seen in the M31 Warp field, lending further support to
the interaction hypothesis. The complex SFHs and the smoothly-varying
age-metallicity relations suggest that the stellar populations observed in the
far outer discs of both galaxies have largely formed in situ rather than
migrated from smaller galactocentric radii. The strong differential reddening
affecting the CMD of the Outer Disc field prevents derivation of the SFH.
Instead, we quantify this reddening and find that the fine-scale distribution
of dust precisely follows that of the HI gas. This indicates that the outer HI
disc of M31 contains a substantial amount of dust and therefore suggests
significant metal enrichment in these parts, consistent with inferences from
our CMD analysis.Comment: Abstract shortened. 17 pages, 12 figures (+ 6 pages & 5 figures in
Appendix). MNRAS, in pres
A tidally distorted dwarf galaxy near NGC 4449
NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band
absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at
a distance from Earth of 3.8 megaparsecs. It is wreathed in an extraordinary
neutral hydrogen (H I) complex, which includes rings, shells and a
counter-rotating core, spanning 90 kiloparsecs. NGC 4449 is relatively
isolated, although an interaction with its nearest known companion-the galaxy
DDO 125, some 40 kpc to the south-has been proposed as being responsible for
the complexity of its HI structure. Here we report the presence of a dwarf
galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band
absolute magnitude of -13.4 and a half-light radius of 2.7 kpc, with a full
extent of around 8 kpc. It is in a transient stage of tidal disruption, similar
to that of the Sagittarius dwarf near the Milky Way. NGC 4449B exhibits a
striking S-shaped morphology that has been predicted for disrupting galaxies
but has hitherto been seen only in a dissolving globular cluster. We also
detect an additional arc or disk ripple embedded in a two-component stellar
halo, including a component extending twice as far as previously known, to
about 20 kpc from the galaxy's centre.Comment: Published in Nature, February 9, 2012. Nature, 482, 192-194 Published
article available at
http://www.nature.com/nature/journal/v482/n7384//full/nature10837.htm
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A comparison of blood pressure reductions following 12-weeks of isometric exercise training either in the laboratory or at home
Purpose:
Isometric exercise training (IET) induced reductions in resting blood pressure (RBP) have been achieved in laboratory environments, but data in support of IET outside the lab is scarce. The aim of this study was to compare 12-weeks of home-based (HOM) IET with laboratory-based, face-to-face (LAB) IET in hypertensive adults.
Methods:
22 hypertensive participants (24-60 years) were randomized to three conditions; HOM, LAB or control (CON). IET involved isometric handgrip training (4 x 2-minutes at 30% maximum voluntary contraction, 3 days per week). RBP was measured every 6-weeks (0, 6 and 12 weeks) during training and 6-weeks post-training (18 weeks).
Results:
Clinically meaningful, but not statistically significant reductions RBP were observed following 12 weeks of LAB IET (SBP -9.1±4.1; DBP-2.8±2.1 P>0.05), which was sustained for 6 weeks of detraining (SBP -8.2±2.9; DBP -4±2.9 P>0.05). RBP was reduced in the HOM group after 12 weeks of training (SBP -9.7±3.4; DBP - 2.2±2.0 P>0.05) which was sustained for an additional 6 weeks of detraining (SBP -5.5±3.4;
DBP -4.6±1.8, P>0.05).
Conclusions:
Unsupervised home-based IET programs present an exciting opportunity for community-based strategies to combat hypertension but additional work is needed if IET is to be employed routinely outside the laboratory
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