Everyday Magic: A Linguistic Analysis of Sarah Addison Allen’s “Just So You Know”

This project diagrams and analyzes Sarah Addison Allen’s magical realism essay, “Just So You Know,” which informs readers that, just as they fall in love with books, books fall in love with them, too. I focus on two defining features: (1) second person point of view (2) grammatical features from sentence structure and vocabular

Cost consideration for aircraft configuration changes, 1

The costs of improvements in aircraft drag reduction design changes are outlined in the context of production decisions. A drag reduction design with increased airframe weight requires cost increases for direct labor, overhead and direct expenses, plus general and administrative expenses

Propeller blockage research needs

The effect of mutual propeller/nacelle of fuselage interference on aircraft propulsive efficiency is studied in order to determine accurate drag levels from flight test data by accurately estimating installed thrust and drag and the resulting aircraft performance

Chemical Evolution in Hierarchical Models of Cosmic Structure II: The Formation of the Milky Way Stellar Halo and the Distribution of the Oldest Stars

This paper presents theoretical star formation and chemical enrichment histories for the stellar halo of the Milky Way based on new chemodynamical modeling. The goal of this study is to assess the extent to which metal-poor stars in the halo reflect the star formation conditions that occurred in halo progenitor galaxies at high redshift, before and during the epoch of reionization. Simple prescriptions that translate dark-matter halo mass into baryonic gas budgets and star formation histories yield models that resemble the observed Milky Way halo in its total stellar mass, metallicity distribution, and the luminosity function and chemical enrichment of dwarf satellite galaxies. These model halos in turn allow an exploration of how the populations of interest for probing the epoch of reionization are distributed in physical and phase space, and of how they are related to lower-redshift populations of the same metallicity. The fraction of stars dating from before a particular time or redshift depends strongly on radius within the galaxy, reflecting the "inside-out" growth of cold-dark-matter halos, and on metallicity, reflecting the general trend toward higher metallicity at later times. These results suggest that efforts to discover stars from z > 6 - 10 should select for stars with [Fe/H] <~ -3 and favor stars on more tightly bound orbits in the stellar halo, where the majority are from z > 10 and 15 - 40% are from z > 15. The oldest, most metal-poor stars - those most likely to reveal the chemical abundances of the first stars - are most common in the very center of the Galaxy's halo: they are in the bulge, but not of the bulge. These models have several implications for the larger project of constraining the properties of the first stars and galaxies using data from the local Universe.Comment: Submitted to ApJ, 22 pages emulateapj, 15 color figure

Carbon-Enhanced Hyper-metal-poor Stars and the Stellar IMF at Low Metallicity

The two known ``hyper-metal-poor'' (HMP) stars, HE0107-5240 and HE1327-2326, have extremely high enhancements of the light elements C, N, and O relative to Fe and appear to represent a statistically significant excess population relative to the halo metallicity distribution extrapolated from [Fe/H] > -3. This study weighs the available evidence for and against three hypothetical origins for these stars: (1) that they formed from gas enriched by a primordial ``faint supernova'', (2) that they formed from gas enriched by core-collapse supernovae and C-rich gas ejected in rotation-driven winds from massive stars, and (3) that they formed as the low-mass secondaries in binary systems at Z ~ 10^{-5.5} Zsun and acquired their light-element enhancements from an intermediate-mass companion as it passed through an AGB phase. The observations interpreted here, especially the depletion of lithium seen in HE1327-2326, favor the binary mass-transfer hypothesis. If HE0107-5240 and HE1327-2326 formed in binary systems, the statistically significant absence of isolated and/or C-normal stars at similar [Fe/H] implies that low-mass stars could form at that metallicity, but that masses M ~< 1.4 Msun were disfavored in the IMF. This result is also explained if the abundance-derived top-heavy IMF for primordial stars persists to [Fe/H] ~ -5.5. This finding indicates that low-mass star formation was possible at extremely low metallicity, and that the typical stellar mass may have had a complex dependence on metallicity rather than a sharp transition driven solely by gas cooling.Comment: 11 pages emulateapj text including three figures, accepted for publication in ApJ v666 (Sept 2007). A companion paper to 0706.290

Carbon-Enhanced Metal-Poor Stars, the Cosmic Microwave Background, and the Stellar IMF in the Early Universe

The characteristic mass of stars at early times may have been higher than today owing to the cosmic microwave background (CMB). This study proposes that (1) the testable predictions of this "CMB-IMF" hypothesis are an increase in the fraction of carbon-enhanced metal-poor (CEMP) stars with declining metallicity and an increase from younger to older populations at a single metallicity (e.g. disk to halo), and (2) these signatures are already seen in recent samples of CEMP stars and can be better tested with anticipated data. The expected spatial variation may explain discrepancies of CEMP frequency among published surveys. The ubiquity and time dependence of the CMB will substantially alter the reconstruction of star formation histories in the Local Group and early Universe.Comment: 7 pages emulateapj format, three figures, accepted for ApJ Letter

The Multiphase Intergalactic Medium towards PKS 2155-304

We study the cluster of H I and O VI absorption systems and the claimed detection of O VIII absorption from the intergalactic medium at z ~ 0.0567, associated with a group of galaxies toward the BL Lac object PKS 2155-304. As measured by spectrographs on the Hubble Space Telescope, Far Ultraviolet Spectroscopic Explorer, and Chandra, this system appears to contain gas at a variety of temperatures. We analyze this multi-phase gas in a clumpy-infall model. From the absence of C IV and Si III absorption in the Ly-alpha clouds, we infer metallicities less than 2.5-10% of solar values. The only metals are detected in two O VI absorption components, offset by +/- 400 km/s from the group barycenter (cz ~ 16,600 km/s). The O VI components may signify "nearside" and "backside" infall into the group potential well, which coincides with the claimed O VIII absorption. If the claimed O VIII detection is real, our analysis suggests that clusters of strong Ly-alpha and O VI absorbers, associated with groups of galaxies, may be the "signposts" of shock-heated, metal-enriched baryons. Through combined UV and X-ray spectra of H I and O VI, O VII, and O VIII, one may be able to clarify the heating mechanism of this multiphase gas.Comment: Accepted for ApJL (2003), 11 pages, 1 color figur