752 research outputs found
Segue 1: An Unevolved Fossil Galaxy from the Early Universe
We present Magellan/MIKE and Keck/HIRES high-resolution spectra of six red
giant stars in the dwarf galaxy Segue 1. Including one additional Segue 1 star
observed by Norris et al. (2010), high-resolution spectra have now been
obtained for every red giant in Segue 1. Remarkably, three of these seven stars
have metallicities below [Fe/H] = -3.5, suggesting that Segue 1 is the least
chemically evolved galaxy known. We confirm previous medium-resolution analyses
demonstrating that Segue 1 stars span a metallicity range of more than 2 dex,
from [Fe/H] = -1.4 to [Fe/H] = -3.8. All of the Segue 1 stars are
alpha-enhanced, with [alpha/Fe] ~ 0.5. High alpha-element abundances are
typical for metal-poor stars, but in every previously studied galaxy [alpha/Fe]
declines for more metal-rich stars, which is typically interpreted as iron
enrichment from supernova Ia. The absence of this signature in Segue 1
indicates that it was enriched exclusively by massive stars. Other light
element abundance ratios in Segue 1, including carbon-enhancement in the three
most metal-poor stars, closely resemble those of metal-poor halo stars.
Finally, we classify the most metal-rich star as a CH star given its large
overabundances of carbon and s-process elements. The other six stars show
remarkably low neutron-capture element abundances of [Sr/H] < -4.9 and [Ba/H] <
-4.2, which are comparable to the lowest levels ever detected in halo stars.
This suggests minimal neutron-capture enrichment, perhaps limited to a single
r-process or weak s-process synthesizing event. Altogether, the chemical
abundances of Segue 1 indicate no substantial chemical evolution, supporting
the idea that it may be a surviving first galaxy that experienced only one
burst of star formation.Comment: ApJ, accepted, 20 pages (emulateapj), 9 figure
Impacts of Reduced Water Availability on Lower Murray Irrigation, Australia
This article evaluates irrigated agriculture sector response and resultant economic impacts of climate change for a part of the Murray Darling Basin in Australia. A water balance model is used to predict reduced basin inflows for mild, moderate and severe climate change scenarios involving 10, 20, 40 Celcius warming, and predict 13%, 38% and 63% reduced inflows. Impact on irrigated agricultural production and profitability are estimated with a mathematical programming model using a two-stage approach that simultaneously estimates short and long-run adjustments. The model accounts for a range of adaptive responses including: deficit irrigation, temporarily fallowing some areas, and permanently reducing irrigated area and changing the mix of crops. The results suggest that relatively low cost adaptation strategies are available for moderate reduction in water availability and thus costs of such reduction are likely to be relatively small. In more severe climate change scenarios greater costs are estimated, adaptations predicted include a reduction in total area irrigated, investments in efficient irrigation, and a shift away from perennial to annual crops as the latter can be managed more profitably when water allocations in some years are very low.water availability, irrigation, Murray Darling Basin, climate change
Uncovering Extremely Metal-Poor Stars in the Milky Way's Ultra-Faint Dwarf Spheroidal Satellite Galaxies
We present new metallicity measurements for 298 individual red giant branch
stars in eight of the least luminous dwarf spheroidal galaxies (dSphs) in the
Milky Way (MW) system. Our technique is based on medium resolution Keck/DEIMOS
spectroscopy coupled with spectral synthesis. We present the first
spectroscopic metallicities at [Fe/H] < -3.0 of stars in a dwarf galaxy, with
individual stellar metallicities as low as [Fe/H] = -3.3. Because our [Fe/H]
measurements are not tied to empirical metallicity calibrators and are
sensitive to arbitrarily low metallicities, we are able to probe this extremely
metal-poor regime accurately. The metallicity distribution of stars in these
dSphs is similar to the MW halo at the metal-poor end. We also demonstrate that
the luminosity-metallicity relation previously seen in more luminous dSph
galaxies (M_V = -13.4 to -8.8) extends smoothly down to an absolute magnitude
of M_V = -3.7. The discovery of extremely metal-poor stars in dSphs lends
support to the LCDM galaxy assembly paradigm wherein dwarf galaxies dissolve to
form the stellar halo of the MW.Comment: 5 pages, 5 figures, accepted for publication in ApJ
High-resolution Spectroscopy of Extremely Metal-poor Stars in the Least Evolved Galaxies: Leo IV
We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H] = â3.2, adding to the rapidly growing sample of extremely metal-poor (EMP) stars being identified in Milky Way satellite galaxies. The star is enhanced in the α elements Mg, Ca, and Ti by ~0.3 dex, very similar to the typical Milky Way halo abundance pattern. All of the light and iron-peak elements follow the trends established by EMP halo stars, but the neutron-capture elements Ba and Sr are significantly underabundant. These results are quite similar to those found for stars in the ultra-faint dwarfs Ursa Major II, Coma Berenices, Boötes I, and Hercules, suggesting that the chemical evolution of the lowest-luminosity galaxies may be universal. The abundance pattern we observe is consistent with predictions for nucleosynthesis from a Population III supernova explosion. The extremely low metallicity of this star also supports the idea that a significant fraction (âł10%) of the stars in the faintest dwarfs have metallicities below [Fe/H] = â3.0
Association between Practice Participation in a Pediatric-focused Medical Home Learning Collaborative and Reduction of Preventable Emergency Department Visits by Publicly-insured Children in Massachusetts
Introduction: This study evaluates the impact of practice participation in a pediatric patient-centered medical home learning collaborative on preventable emergency department (ED) visits among children in MassHealth (Massachusetts Medicaid/Children\u27s Health Insurance Program).
Methods: Claims and enrollment data were extracted for child MassHealth members (aged 3â18) comprising 2 groups: members enrolled in a group of 13 child-serving practices that participated in an intensive, 29-month long patient-centered medical home learning collaborative (intervention group), and members enrolled in a group of 12 comparison practices with roughly similar panel size, type, and geographic location (comparison group). Preventable ED visits were identified using a modified version of the New York University ED algorithm. Two analyses were then conducted: (1) a repeat cross-sectional analysis among children enrolled in intervention or comparison group practices during baseline (first half of 2011) and follow-up (second half of 2013) periods; and (2) a longitudinal analysis among a subset of children enrolled for the full study period (2011â2013). Both analyses tested whether the effect of the intervention differed for children with versus without chronic conditions (effect modification).
Results: Preventable ED visits declined from baseline to follow-up among children in both intervention and comparison practices. In the cross-sectional analysis, the decrease was the same in both practice groups, and for children with versus without chronic conditions. The longitudinal analysis shows a statistically significantly greater decrease among children with chronic conditions enrolled in the intervention practices (P = 0.02).
Conclusion: Children with chronic conditions might receive the greatest benefit from receiving care in a medical home setting
The University of Michiganâs Department of Human Genetics and its Impact on Medical Education
This poster was presented at the University of Michigan's2012 Medical Education Day held on June 5. It highlights the University of Michigan's Department of Human Genetics and the role that it has played and continues to play in medical education and genetic research.http://deepblue.lib.umich.edu/bitstream/2027.42/91296/1/Merle_TimeLine_Template2.pd
Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor
Current cosmological models indicate that the Milky Way's stellar halo was
assembled from many smaller systems. Based on the apparent absence of the most
metal-poor stars in present-day dwarf galaxies, recent studies claimed that the
true Galactic building blocks must have been vastly different from the
surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in
the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt
on this conclusion. However, verification of the iron-deficiency and
measurements of additional elements, such as the alpha-element Mg, are
mandatory for demonstrating that the same type of stars produced the metals
found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars
be conclusively linked to early stellar halo assembly. Here we report
high-resolution spectroscopic abundances for 11 elements in S1020549,
confirming the iron abundance of less than 1/4000th that of the Sun, and
showing that the overall abundance pattern mirrors that seen in low-metallicity
halo stars, including the alpha-elements. Such chemical similarity indicates
that the systems destroyed to form the halo billions of years ago were not
fundamentally different from the progenitors of present-day dwarfs, and
suggests that the early chemical enrichment of all galaxies may be nearly
identical.Comment: 16 pages, including 2 figures. Accepted for publication in Nature. It
is embargoed for discussion in the press until formal publication in Natur
Designing for palliative care: Three ideas toward an architecture of generosity
Palliative care has a distinct philosophy that is not always reflected in the architecture created for it. From a study conducted to better understand the relationship of the built environment to patient and family experiences of palliative care, this article discusses the benefits of access to nature, the provision of semi-private spaces beyond the patient room, and environments that support the rituals of home. Research methods included semi-structured interviews, an online survey, and an architectural precedent study
The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z_* â M_*^(0.30±0.02). The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M_* = 10^(12) M_â. Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type. The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions. Furthermore, the metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the sudden truncation of star formation due to ram pressure stripping
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