5,470 research outputs found
Potential for Biodegradation of Contaminants of Emerging Concern in Stream Systems
2008 S.C. Water Resources Conference - Addressing Water Challenges Facing the State and Regio
Light Curve Patterns and Seismology of a White Dwarf with Complex Pulsation
The ZZ Ceti star KUV 02464+3239 was observed over a whole season at the
mountain station of Konkoly Observatory. A rigorous frequency analysis revealed
6 certain periods between 619 and 1250 seconds, with no shorter period modes
present. We use the observed periods, published effective temperature and
surface gravity, along with the model grid code of Bischoff-Kim, Montgomery and
Winget (2008) to perform a seismological analysis. We find acceptable model
fits with masses between 0.60 and 0.70 M_Sun. The hydrogen layer mass of the
acceptable models are almost always between 10^-4 and 10^-6 M_*. In addition to
our seismological results, we also show our analysis of individual light curve
segments. Considering the non-sinusoidal shape of the light curve and the
Fourier spectra of segments showing large amplitude variations, the importance
of non-linear effects in the pulsation is clearly seen.Comment: 5 pages, 6 figures, in "Stellar Pulsation: Challenges for Theory and
Observation", Eds. J. Guzik and P. A. Bradley, AIP
Deep Luminosity Functions of Old and Intermediate-Age Globular Clusters in NGC 1316: Evidence for Dynamical Evolution of Second-Generation Globular Clusters
The Advanced Camera for Surveys on board the Hubble Space Telescope has been
used to obtain deep high-resolution images of the giant early-type galaxy NGC
1316 which is an obvious merger remnant. These observations supersede previous,
shallower observations which revealed the presence of a population of
metal-rich globular clusters of intermediate age (~ 3 Gyr). We detect a total
of 1496 cluster candidates, almost 4 times as many as from the previous WFPC2
images. We confirm the bimodality of the color distribution of clusters, even
in V-I, with peak colors 0.93 and 1.06. The large number of detected clusters
allows us to evaluate the globular cluster luminosity functions as a function
of galactocentric radius. We find that the luminosity function of the inner 50%
of the intermediate-age, metal-rich (`red') population of clusters differs
markedly from that of the outer 50%. In particular, the luminosity function of
the inner 50% of the red clusters shows a clear flattening consistent with a
turnover that is about 1.0 mag fainter than the turnover of the blue clusters.
This constitutes the first direct evidence that metal-rich cluster populations
formed during major mergers of gas-rich galaxies can evolve dynamically
(through disruption processes) into the red, metal-rich cluster populations
that are ubiquitous in `normal' giant ellipticals.Comment: Accepted for publication in ApJ Letters; 4 pages in emulateapj style.
3 figure
Bounding the Moment Deficit Rate on Crustal Faults using Geodetic Data: Methods
The geodetically derived interseismic moment deficit rate (MDR) provides a first-order constraint on earthquake potential and can play an important role in seismic hazard assessment, but quantifying uncertainty in MDR is a challenging problem that has not been fully addressed. We establish criteria for reliable MDR estimators, evaluate existing methods for determining the probability density of MDR, and propose and evaluate new methods. Geodetic measurements moderately far from the fault provide tighter constraints on MDR than those nearby. Previously used methods can fail catastrophically under predictable circumstances. The bootstrap method works well with strong data constraints on MDR, but can be strongly biased when network geometry is poor. We propose two new methods: the Constrained Optimization Bounding Estimator (COBE) assumes uniform priors on slip rate (from geologic information) and MDR, and can be shown through synthetic tests to be a useful, albeit conservative estimator; the Constrained Optimization Bounding Linear Estimator (COBLE) is the corresponding linear estimator with Gaussian priors rather than point-wise bounds on slip rates. COBE matches COBLE with strong data constraints on MDR. We compare results from COBE and COBLE to previously published results for the interseismic MDR at Parkfield, on the San Andreas Fault, and find similar results; thus, the apparent discrepancy between MDR and the total moment release (seismic and afterslip) in the 2004 Parkfield earthquake remains
Cepheids and Long Period Variables in M33
We are conducting a long-term photometric survey of the nearby galaxy M33 to
discover Cepheids, eclipsing binaries, and long-period variables. The dataset
combines previously-obtained optical images from the DIRECT project with new
observations acquired at the WIYN 3.5m telescope. The entire data set spans
over 7 years with excellent synoptic coverage which will enable the discovery
and characterization of stars displaying variability over a wide range of
timescales (days, weeks, months, years). In this preliminary work we show
representative light curves of different variables we found so far in two
fields, color-magnitude diagrams, and optical Cepheid Period-Luminosity
relations for M33. The ultimate goal of the project is to provide an absolute
calibration of the Cepheid Period-Luminosity relation, and to study its
metallicity dependence at optical wavelengths.Comment: 3 pages, 6 figures. To appear in "Stellar Pulsation: Challenges for
Theory and Observation", Eds. J. Guzik and P. Bradle
Multiphase PC/PL Relations: Comparison between Theory and observations
Cepheids are fundamental objects astrophysically in that they hold the key to
a CMB independent estimate of Hubble's constant. A number of researchers have
pointed out the possibilities of breaking degeneracies between Omega_Matter and
H0 if there is a CMB independent distance scale accurate to a few percent (Hu
2005). Current uncertainties in the distance scale are about 10% but future
observations, with, for example, the JWST, will be capable of estimating H0 to
within a few percent. A crucial step in this process is the Cepheid PL
relation. Recent evidence has emerged that the PL relation, at least in optical
bands, is nonlinear and that neglect of such a nonlinearity can lead to errors
in estimating H0 of up to 2 percent. Hence it is important to critically
examine this possible nonlinearity both observationally and theoretically.
Existing PC/PL relations rely exclusively on evaluating these relations at mean
light. However, since such relations are the average of relations at different
phases. Here we report on recent attempts to compare theory and observation in
the multiphase PC/PL planes. We construct state of the art Cepheid pulsations
models appropriate for the LMC/Galaxy and compare the resulting PC/PL relations
as a function of phase with observations. For the LMC, the (V-I) period-color
relation at minimum light can have quite a narrow dispersion (0.2-0.3 mags) and
thus could be useful in placing constraints on models. At longer periods, the
models predict significantly redder (by about 0.2-0.3 mags) V-I colors. We
discuss possible reasons for this and also compare PL relations at various
phases of pulsation and find clear evidence in both theory and observations for
a nonlinear PL relation.Comment: 5 pages, 8 figures, proceeding for "Stellar Pulsation: Challenges for
Theory and Observation", Santa Fe 200
An Environmental Analysis of Illinois Coal Entry into the Transportation Market
Using Illinois coal in transportation has varied environmental consequences. This study calculated the total CO2 emissions from gasoline and eight other vehicle propulsion methods (VPMs) involving Illinois coal. VPMs of Ultra Super Critical electrical cycle (USC), Integrated Gasification Combined electrical Cycle (IGCC), Pulverized coal in a Sub-Critical electrical cycle (PSC), and electricity from a hydrogen fuel cell emitted the lowest CO2. VPMs using Illinois coal to produce ethanol, butanol, and IGCC/ethanol emitted CO2 comparable to gasoline. The VPM of Fischer-Tropsch (FT) diesel emitted the most CO2. It was concluded that energy efficiency and CO2 offset from agricultural growth and by-products were the most influential factors of CO2 emissions
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