The Best and Brightest Metal-Poor Stars

The chemical abundances of large samples of extremely metal-poor (EMP) stars can be used to investigate metal-free stellar populations, supernovae, and nucleosynthesis as well as the formation and galactic chemical evolution of the Milky Way and its progenitor halos. However, current progress on the study of EMP stars is being limited by their faint apparent magnitudes. The acquisition of high signal-to-noise spectra for faint EMP stars requires a major telescope time commitment, making the construction of large samples of EMP star abundances prohibitively expensive. We have developed a new, efficient selection that uses only public, all-sky APASS optical, 2MASS near-infrared, and WISE mid-infrared photometry to identify bright metal-poor star candidates through their lack of molecular absorption near 4.6 microns. We have used our selection to identify 11,916 metal-poor star candidates with V < 14, increasing the number of publicly-available candidates by more than a factor of five in this magnitude range. Their bright apparent magnitudes have greatly eased high-resolution follow-up observations that have identified seven previously unknown stars with [Fe/H] <~ -3.0. Our follow-up campaign has revealed that 3.8^{+1.3}_{-1.1}% of our candidates have [Fe/H] <~ -3.0 and 32.5^{+3.0}_{-2.9}% have -3.0 <~ [Fe/H] <~ -2.0. The bulge is the most likely location of any existing Galactic Population III stars, and an infrared-only variant of our selection is well suited to the identification of metal-poor stars in the bulge. Indeed, two of our confirmed metal-poor stars with [Fe/H] <~ -2.7 are within about 2 kpc of the Galactic Center. They are among the most metal-poor stars known in the bulge.Comment: 28 pages, 6 figures, and 4 tables in emulateapj format; accepted for publication in Ap

Chemistry of the Most Metal-poor Stars in the Bulge and the z > 10 Universe

Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies. However, a low metallicity does not prove that a star formed in this ancient era, as metal-poor stars form over a range of redshift in different environments. Theoretical models of Milky Way formation have shown that at constant metallicity, the oldest stars are those closest to the center of the Galaxy on the most tightly-bound orbits. For that reason, the most metal-poor stars in the bulge of the Milky Way provide excellent tracers of the chemistry of the high-redshift universe. We report the dynamics and detailed chemical abundances of three stars in the bulge with [Fe/H] $\lesssim-2.7$, two of which are the most metal-poor stars in the bulge in the literature. We find that with the exception of scandium, all three stars follow the abundance trends identified previously for metal-poor halo stars. These three stars have the lowest [Sc II/Fe] abundances yet seen in $\alpha$-enhanced giant stars in the Galaxy. Moreover, all three stars are outliers in the otherwise tight [Sc II/Fe]-[Ti II/Fe] relation observed among metal-poor halo stars. Theoretical models predict that there is a 30% chance that at least one of these stars formed at $z\gtrsim15$, while there is a 70% chance that at least one formed at $10 \lesssim z \lesssim 15$. These observations imply that by $z\sim10$, the progenitor galaxies of the Milky Way had both reached [Fe/H] $\sim-3.0$ and established the abundance pattern observed in extremely metal-poor stars.Comment: Submitted to ApJ on 2014 December 23, accepted 2015 May 4th after minor revisions. ArXiv tarball includes referee report and respons

Computing Fast and Reliable Gravitational Waveforms of Binary Neutron Star Merger Remnants

Gravitational waves have been detected from the inspiral of a binary neutron-star, GW170817, which allowed constraints to be placed on the neutron star equation of state. The equation of state can be further constrained if gravitational waves from a post-merger remnant are detected. Post-merger waveforms are currently generated by numerical-relativity simulations, which are computationally expensive. Here we introduce a hierarchical model trained on numerical-relativity simulations, which can generate reliable post-merger spectra in a fraction of a second. Our spectra have mean fitting factors of 0.95, which compares to fitting factors of 0.76 and 0.85 between different numerical-relativity codes that simulate the same physical system. This method is the first step towards generating large template banks of spectra for use in post-merger detection and parameter estimation.Comment: Submitted to PRL. 6 pages, 4 figure

Exposure to the Dental Environment and Prevalence of Respiratory Illness in Dental Student Populations

Objective: To determine if the prevalence of respiratory disease among dental students and dental residents varies with their exposure to the clinical dental environment. Methods: A detailed questionnaire was administered to 817 students at 3 dental schools. The questionnaire sought information concerning demographic characteristics, school year, exposure to the dental environment and dental procedures, and history of respiratory disease. The data obtained were subjected to bivariate and multiple logistic regression analysis. Results: Respondents reported experiencing the following respiratory conditions during the previous year: asthma (26 cases), bronchitis (11 cases), chronic lung disease (6 cases), pneumonia (5 cases) and streptococcal pharyngitis (50 cases). Bivariate statistical analyses indicated no significant associations between the prevalence of any of the respiratory conditions and year in dental school, except for asthma, for which there was a significantly higher prevalence at 1 school compared to the other 2 schools. When all cases of respiratory disease were combined as a composite variable and subjected to multivariate logistic regression analysis controlling for age, sex, race, dental school, smoking history and alcohol consumption, no statistically significant association was observed between respiratory condition and year in dental school or exposure to the dental environment as a dental patient. Conclusion: No association was found between the prevalence of respiratory disease and a student\u27s year in dental school or previous exposure to the dental environment as a patient. These results suggest that exposure to the dental environment does not increase the risk for respiratory infection in healthy dental health care workers

Rethinking Tiebout: The Contribution of Political Fragmentation and Racial/Economic Segregation to the Flint Water Crisis

The water crisis that has embroiled Flint, Michigan, since 2014 is often explained via the proximate causes of government oversight and punitive emergency management. While these were critical elements in the decision to switch the city's water source, many other forces helped precipitate the crisis. One such force has been an enduring support for Charles Tiebout's model of interlocal competition, through which a region is presumed stronger when fragmented, independent municipalities compete for residents and investment. However, the Tiebout model fails to account for spillover effects, particularly regarding questions of social and regional equity. In this sense, the fragmentation of the Flint metropolitan region?supported through a variety of housing and land use policies over many decades?created the conditions through which suburbs were absolved of responsibility for Flint's decades-long economic crisis. Because of the Tiebout model's inability to address imbalances in population shifts arising from disparities in municipal services, Flint's more affluent suburbs continued to prosper, while Flint grew poorer and experienced infrastructure decline. Underlying this pattern of inequality has been a long history of racial segregation and massive deindustrialization, which concentrated the region's black population in the economically depressed central city. The Flint Water Crisis is thus a classic example of an environmental injustice, as policies were set in motion, which led to the creation of a politically separate and majority-black municipality with concentrated poverty, while nearby municipalities?most of them overwhelmingly white?accepted little responsibility for the legacy costs created by the region's starkly uneven patterns of metropolitan development.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140089/1/env.2016.0015.pd