890 research outputs found
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IV. Helium content and relative age of multiple stellar populations within NGC 6352
In this paper we combine WFC3/UVIS F275W, F336W, and F438W data from the "UV
Legacy Survey of Galactic Globular Clusters: Shedding Light on Their
Populations and Formation" (GO-13297) HST Treasury program with F606W, F625W,
F658N, and F814W ACS archive data for a multi-wavelength study of the globular
cluster NGC 6352. In the color-magnitude and two-color diagrams obtained with
appropriate combination of the photometry in the different bands we separate
two distinct stellar populations and trace them from the main sequence to the
subgiant, red giant, horizontal and asymptotic giant branches. We infer that
the two populations differ in He by Delta Y=0.029+/-0.006. With a new method,
we also estimate the age difference between the two sequences. Assuming no
difference in [Fe/H] and [alpha/Fe], and the uncertainties on Delta Y, we found
a difference in age between the two populations of 10+/-120 Myr. If we assume
[Fe/H] and [alpha/Fe] differences of 0.02 dex (well within the uncertainties of
spectroscopic measurements), the total uncertainty in the relative age rises to
~300 Myr.Comment: 12 pages, 6 figures (3 at low resolution), 3 tables. Accepted for
publication in MNRAS on April 29, 201
The New Science of Complexity
Deterministic chaos, and even maximum computational complexity, have been discovered within Newtonian dynamics. Economists assume that prices and price changes can also obey abstract mathematical laws of motion. Sociologists and other postmodernists advertise that physics and chemistry have outgrown their former limitations, that chaos and complexity provide new holistic paradigms for science, and that the boundaries between the hard and soft sciences, once impenetrable, have disappeared like the Berlin Wall. Three hundred years after the deaths of Galileo, Descartes, and Kepler, and the birth of Newton, reductionism appears to be on the decline, with holistic approaches to science on the upswing. We therefore examine the evidence that dynamical laws of motion may be discovered from empirical studies of chaotic or complex phenomena, and also review the foundation of reductionism in invariance principle
Making dynamic modelling effective in economics
Mathematics has been extremely effective in physics, but not in economics beyond finance. To establish economics as science we should follow the Galilean method and try to deduce mathematical models of markets from empirical data, as has been done for financial markets. Financial markets are nonstationary. This means that 'value' is subjective. Nonstationarity also means that the form of the noise in a market cannot be postulated a priroi, but must be deduced from the empirical data. I discuss the essence of complexity in a market as unexpected events, and end with a biological speculation about market growth.Economics; fniancial markets; stochastic process; Markov process; complex systems
Multi-wavelength Hubble Space Telescope photometry of stellar populations in NGC288
We present new UV observations for NGC288, taken with the WFC3 detector on
board the Hubble Space Telescope, and combine them with existing optical data
from the archive to explore the multiple-population phenomenon in this globular
cluster (GC). The WFC3's UV filters have demonstrated an uncanny ability to
distinguish multiple populations along all photometric sequences in GCs, thanks
to their exquisite sensitivity to the atmospheric changes that are tell-tale
signs of second-generation enrichment. Optical filters, on the other hand, are
more sensitive to stellar-structure changes related to helium enhancement. By
combining both UV and optical data we can measure helium variation. We quantify
this enhancement for NGC288 and find that its variation is typical of what we
have come to expect in other clusters.Comment: 15 pages, 5 figures, accepted for publication in Ap
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Development and Demonstration of a TDOA-Based GNSS Interference Signal Localization System
Background theory, a reference design, and demonstration
results are given for a Global Navigation Satellite
System (GNSS) interference localization system comprising a
distributed radio-frequency sensor network that simultaneously
locates multiple interference sources by measuring their signals’
time difference of arrival (TDOA) between pairs of nodes in
the network. The end-to-end solution offered here draws from
previous work in single-emitter group delay estimation, very long
baseline interferometry, subspace-based estimation, radar, and
passive geolocation. Synchronization and automatic localization
of sensor nodes is achieved through a tightly-coupled receiver
architecture that enables phase-coherent and synchronous sampling
of the interference signals and so-called reference signals
which carry timing and positioning information. Signal and crosscorrelation
models are developed and implemented in a simulator.
Multiple-emitter subspace-based TDOA estimation techniques
are developed as well as emitter identification and localization
algorithms. Simulator performance is compared to the CramérRao
lower bound for single-emitter TDOA precision. Results are
given for a test exercise in which the system accurately locates
emitters broadcasting in the amateur radio band in Austin, TX.Aerospace Engineering and Engineering Mechanic
Carbon and nitrogen abundances of stellar populations in the globular cluster M 2
We present CH and CN index analysis and C and N abundance calculations based
on the low-resolution blue spectra of red giant branch (RGB) stars in the
Galactic globular cluster NGC 7089 (M 2). Our main goal is to investigate the
C-N anticorrelation for this intermediate metallicity cluster. The data were
collected with DOLORES, the multiobject, low-resolution facility at the
Telescopio Nazionale Galileo. Spectroscopic data were coupled with UV
photometry obtained during the spectroscopic run. We found a considerable
star-to-star variation in both A(C) and A(N) at all luminosities for our sample
of 35 targets. These abundances appear to be anticorrelated, with a hint of
bimodality in the C content for stars with luminosities below the RBG bump
(V~15.7), while the range of variations in N abundances is very large and spans
almost ~ 2 dex. We find additional C depletion as the stars evolve off the RGB
bump, in fairly good agreement with theoretical predictions for metal-poor
stars in the course of normal stellar evolution. We isolated two groups with
N-rich and N-poor stars and found that N abundance variations correlate with
the (U-V) color in the DOLORES color-magnitude diagram (CMD). The V, (U-V) CMD
for this cluster shows an additional RGB sequence, located at the red of the
main RGB and amounting to a small fraction of the total giant population. We
identified two CH stars detected in previous studies in our U, V images. These
stars, which are both cluster members, fall on this redder sequence, suggesting
that the anomalous RGB should have a peculiar chemical pattern. Unfortunately,
no additional spectra were obtained for stars in this previously unknown RGB
branch.Comment: 15 pages, 14 figures; accepted for publication in A&
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