694 research outputs found
Their Old Kentucky Home: The Phenomenon of the Kentucky Burden in the Writing of James Still, Jesse Stuart, Allen Tate, and Robert Penn Warren
The focus of this project is to investigate the phenomenon of the Kentucky burden, and to explore the impact of that burden on four Vanderbilt-educated Kentucky authors of the early twentieth century. The works of James Still, Jesse Stuart, Allen Tate, and Robert Penn Warren reveal not only characteristics common to Southern regionalism in general but also traits radically particular to Kentucky. Through an exploration of the poetry and prose of these prominent Kentucky writers, we can gain a better understanding of the significance of their identities as Kentuckians and recognize the many obstacles and challenges the Kentucky burden posed for each of the four writers. I posit that the individual reactions of Still, Stuart, Tate, and Warren to the Kentucky burden dramatically affected their critical and popular success, thus deciding their place, or lack thereof, in the canon of American literature. By investigating this phenomenon, this project enters the debate concerning the existence of subregions within regionalism and further emphasizes the importance of the literature of the individual regions of this country which make up the whole American literature
Mean proton and alpha-particle reduced widths of the Porter-Thomas distribution and astrophysical applications
The Porter-Thomas distribution is a key prediction of the Gaussian orthogonal ensemble in random matrix theory. It is routinely used to provide a measure for the number of levels that are missing in a given resonance analysis. The Porter-Thomas distribution is also of crucial importance for estimates of thermonuclear reaction
rates where the contributions of certain unobserved resonances to the total reaction rate need to be taken into account. In order to estimate such contributions by randomly sampling over the Porter-Thomas distribution,
the mean value of the reduced width must be known. We present mean reduced width values for protons and α particles of compound nuclei in the A = 28–67 mass range. The values are extracted from charged-particle
elastic scattering and reaction data that weremeasured at the riangle Universities Nuclear Laboratory over several decades. Our new values differ significantly from those previously reported that were based on a preliminary analysis of a smaller data set. As an example for the application of our results, we present new thermonuclear rates for the 40Ca(α,γ)44Ti reaction, which is important for 44Ti production in core-collapse supernovae, and compare with previously reported results.Peer ReviewedPostprint (published version
The Origins of Blue Stragglers and Binarity in Globular Clusters
(abridged) We use newly available empirical binary fractions for globular
clusters to carry out a direct test of the binary evolution hypothesis, and of
collisional channels that involve binary stars. More specifically, using the
previously reported correlation between blue straggler numbers and core mass as
a benchmark, we test for correlations with the number of binary stars, as well
as with the rates of single-single, single-binary, and binary-binary
encounters. Surprisingly, we find that the simple correlation with core mass
remains by far the strongest predictor of blue straggler population size, even
in our joint models. This is despite the fact that the binary fractions
themselves strongly anti-correlate with core mass, just as expected in the
binary evolution model. At first sight, these results do not fit neatly with
either binary evolution or collisional models in their simplest forms. Arguably
the simplest and most intriguing possibility to explain this unexpected result
is that observational errors on the core binary fractions are larger than the
true intrinsic dispersion associated with their dependence on core mass. In the
context of the binary evolution model, this would explain why the combination
of binary fraction and core mass is a poorer predictor of blue straggler
numbers than core mass alone. It would also imply that core mass is a
remarkably clean predictor of core binary fractions. This would be of
considerable importance for the dynamical evolution of globular clusters, and
provides an important benchmark for models attempting to understand their
present-day properties.Comment: 10 pages, 9 figures, accepted for publication in MNRA
Implications for the Formation of Blue Straggler Stars from HST Ultraviolet Observations of NGC 188
We present results of a Hubble Space Telescope far-ultraviolet (FUV) survey
searching for white dwarf (WD) companions to blue straggler stars (BSSs) in
open cluster NGC 188. The majority of NGC 188 BSSs (15 of 21) are single-lined
binaries with properties suggestive of mass-transfer formation via Roche lobe
overflow, specifically through an asymptotic giant branch star transferring
mass to a main sequence secondary, yielding a BSS binary with a WD companion.
In NGC 188, a BSS formed by this mechanism within the past 400 Myr will have a
WD companion hot and luminous enough to be directly detected as a FUV
photometric excess with HST. Comparing expected BSS FUV emission to observed
photometry reveals four BSSs with WD companions above 12,000 K (younger than
250 Myr) and three WD companions with temperatures between 11,000-12,000 K.
These BSS+WD binaries all formed through recent mass transfer. The location of
the young BSSs in an optical color-magnitude diagram (CMD) indicates that
distance from the zero-age main sequence does not necessarily correlate with
BSS age. There is no clear CMD separation between mass transfer-formed BSSs and
those likely formed through other mechanisms, such as collisions. The seven
detected WD companions place a lower limit on the mass-transfer formation
frequency of 33%. We consider other possible formation mechanisms by comparing
properties of the BSS population to theoretical predictions. We conclude that
14 BSS binaries likely formed from mass transfer, resulting in an inferred
mass-transfer formation frequency of approximately 67%.Comment: 13 pages, 6 figures, accepted to the Astrophysical Journa
Detection of white dwarf companions to blue stragglers in the open cluster NGC 188: direct evidence for recent mass transfer
Several possible formation pathways for blue straggler stars have been
developed recently, but no one pathway has yet been observationally confirmed
for a specific blue straggler. Here we report the first findings from a Hubble
Space Telescope ACS/SBC far-UV photometric program to search for white dwarf
companions to blue straggler stars. We find three hot and young white dwarf
companions to blue straggler stars in the 7-Gyr open cluster NGC 188,
indicating that mass transfer in these systems ended less than 300 Myr ago.
These companions are direct and secure observational evidence that these blue
straggler stars were formed through mass transfer in binary stars. Their
existence in a well-studied cluster environment allows for observational
constraints of both the current binary system and the progenitor binary system,
mapping the entire mass transfer history.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
An Analytic Model for Blue Straggler Formation in Globular Clusters
We present an analytic model for blue straggler formation in globular
clusters. We assume that blue stragglers are formed only through stellar
collisions and binary star evolution, and compare our predictions to observed
blue straggler numbers taken from the catalogue of Leigh, Sills & Knigge
(2011). We can summarize our key results as follows: (1) Binary star evolution
consistently dominates blue straggler production in all our best-fitting
models. (2) In order to account for the observed sub-linear dependence of blue
straggler numbers on the core masses (Knigge, Leigh & Sills 2009), the core
binary fraction must be inversely proportional to the total cluster luminosity
and should always exceed at least a few percent. (3) In at least some clusters,
blue straggler formation must be enhanced by dynamical encounters (either via
direct collisions or by stimulating mass-transfer to occur by altering the
distribution of binary orbital parameters) relative to what is expected by
assuming a simple population of binaries evolving in isolation. (4) The
agreement between the predictions of our model and the observations can be
improved by including blue stragglers that form outside the core but later
migrate in due to dynamical friction. (5) Longer blue straggler lifetimes are
preferred in models that include blue stragglers formed outside the core since
this increases the fraction that will have sufficient time to migrate in via
dynamical friction.Comment: 11 pages, 4 figures, accepted for publication in MNRA
European Union Forest Law Enforcement, Governance and Trade (FLEGT) Voluntary Partnership Agreement in Ghana:Introducing needed change or reinforcing business as usual?
Dissecting the Colour-Magnitude Diagram: A Homogeneous Catalogue of Stellar Populations in Globular Clusters
We present a homogeneous catalogue for blue straggler, red giant branch,
horizontal branch and main-sequence turn-off stars in a sample of 35 clusters
taken from the ACS Survey for Globular Clusters. As a result of the superior
photometry and relatively large field of view offered by the ACS data, this new
catalogue is a significant improvement upon the one presented in Leigh, Sills &
knigge (2007). Using our catalogue, we study and compare the radial
distributions of the different stellar populations.
We have confirmed our previous result (Knigge, Leigh & Sills 2009) that there
is a clear, but sub-linear, correlation between the number of blue stragglers
found in the cluster core and the total stellar mass contained within it. By
considering a larger spatial extent than just the core, our results suggest
that mass segregation is not the dominant effect contributing to the observed
sub-linearity. We also investigate the radial distributions of the different
stellar populations in our sample of clusters. Our results are consistent with
a linear relationship between the number of stars in these populations and the
total mass enclosed within the same radius. Therefore, we conclude that the
cluster dynamics does not significantly affect the relative distributions of
these populations in our sample.Comment: 14 pages, 5 figures, accepted for publication in MNRA
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