283 research outputs found
Ethnic Identity of Older Chinese in Canada
In Canada’s multicultural society, ethnic identity is important to the elderly and can influence areas such as access to services, health promotion and care. Often, the complex nature of ethnic identity is underestimated when looking at cultural groups. This study aims to: (a) validate the factor structure of a Chinese ethnic identity measure for older Chinese in Canada, (b) examine the level of ethnic identity of the participants, and (c) examine the correlates of ethnic identity in these older individuals. Using data from a large, national research project on the elderly Chinese in Canada, this study analyzed the results gathered from a total of 2,272 participants. Principal component analysis, maximum-likelihood confirmatory factor analysis, and multiple regression analysis were performed. The results indicated that ethnic identity of the older Chinese is a multi-dimensional construct made up of three factors: (a) culture related activities, (b) community ties, (c) linkage with country of origin, and (d) cultural identification. The findings have provided a better understanding of how ethnic identity can be measured among the aging Chinese population in Canada
Monte Carlo Simulations of Star Clusters - VII. The globular cluster 47 Tuc
We describe Monte Carlo models for the dynamical evolution of the massive
globular cluster 47 Tuc (NGC 104). The code includes treatments of two-body
relaxation, most kinds of three- and four-body interactions involving
primordial binaries and those formed dynamically, the Galactic tide, and the
internal evolution of both single and binary stars. We arrive at a set of
initial parameters for the cluster which, after 12Gyr of evolution, gives a
model with a fairly satisfactory match to surface brightness and density
profiles, the velocity dispersion profile, the luminosity function in two
fields, and the acceleration of pulsars. Our models appear to require a
relatively steep initial mass function for stars above about turnoff, with an
index of about 2.8 (where the Salpeter mass function has an index of 2.35), and
a relatively flat initial mass function (index about 0.4) for the lower main
sequence. According to the model, the current mass is estimated at 0.9 million
solar masses, of which about 34% consists of remnants. We find that primordial
binaries are gradually taking over from mass loss by stellar evolution as the
main dynamical driver of the core. Despite the high concentration of the
cluster, core collapse will take at least another 20Gyr.Comment: 16 pages, 16 figures, revised version submitted to MNRA
Electromagnetic Counterparts of Compact Object Mergers Powered by the Radioactive Decay of R-process Nuclei
The most promising astrophysical sources of kHz gravitational waves (GWs) are
the inspiral and merger of binary neutron star(NS)/black hole systems.
Maximizing the scientific return of a GW detection will require identifying a
coincident electro-magnetic (EM) counterpart. One of the most likely sources of
isotropic EM emission from compact object mergers is a supernova-like transient
powered by the radioactive decay of heavy elements synthesized in ejecta from
the merger. We present the first calculations of the optical transients from
compact object mergers that self-consistently determine the radioactive heating
by means of a nuclear reaction network; using this heating rate, we model the
light curve with a one dimensional Monte Carlo radiation transfer calculation.
For an ejecta mass ~1e-2 M_sun[1e-3 M_sun] the resulting light curve peaks on a
timescale ~ 1 day at a V-band luminosity nu L_nu ~ 3e41[1e41] ergs/s (M_V =
-15[-14]); this corresponds to an effective "f" parameter ~3e-6 in the
Li-Paczynski toy model. We argue that these results are relatively insensitive
to uncertainties in the relevant nuclear physics and to the precise early-time
dynamics and ejecta composition. Due to the rapid evolution and low luminosity
of NS merger transients, EM counterpart searches triggered by GW detections
will require close collaboration between the GW and astronomical communities.
NS merger transients may also be detectable following a short-duration
Gamma-Ray Burst or "blindly" with present or upcoming optical transient
surveys. Because the emission produced by NS merger ejecta is powered by the
formation of rare r-process elements, current optical transient surveys can
directly constrain the unknown origin of the heaviest elements in the Universe.Comment: 14 pages, 7 figures; accepted to MNRAS; title changed to highlight
r-process connection and new figure added
Searches for Gravitational Waves from Binary Neutron Stars: A Review
A new generation of observatories is looking for gravitational waves. These
waves, emitted by highly relativistic systems, will open a new window for ob-
servation of the cosmos when they are detected. Among the most promising
sources of gravitational waves for these observatories are compact binaries in
the final min- utes before coalescence. In this article, we review in brief
interferometric searches for gravitational waves emitted by neutron star
binaries, including the theory, instru- mentation and methods. No detections
have been made to date. However, the best direct observational limits on
coalescence rates have been set, and instrumentation and analysis methods
continue to be refined toward the ultimate goal of defining the new field of
gravitational wave astronomy.Comment: 30 pages, 5 Figures, to appear in "Short-Period Binary Stars:
Observations, Analyses, and Results", Ed.s Eugene F. Milone, Denis A. Leahy,
David W. Hobil
Discovery of a Radio Source following the 27 December 2004 Giant Flare from SGR 1806-20
Over a decade ago it was established that the remarkable high energy
transients, known as soft gamma-ray repeaters (SGRs), are a Galactic population
and originate from neutron stars with intense (<~ 10^15 G) magnetic fields
("magnetars"). On 27 December 2004 a giant flare (fluence >~ 0.3 erg/cm^2) was
detected from SGR 1806-20. Here we report the discovery of a fading radio
counterpart. We began a monitoring program from 0.2GHz to 250GHz and obtained a
high resolution 21-cm radio spectrum which traces the intervening interstellar
neutral Hydrogen clouds. Analysis of the spectrum yields the first direct
distance measurement of SGR 1806-20. The source is located at a distance
greater than 6.4 kpc and we argue that it is nearer than 9.8 kpc. If true, our
distance estimate lowers the total energy of the explosion and relaxes the
demands on theoretical models. The energetics and the rapid decay of the radio
source are not compatible with the afterglow model that is usually invoked for
gamma-ray bursts. Instead we suggest that the rapidly decaying radio emission
arises from the debris ejected during the explosion.Comment: 16 pages, 2 figures, submitted to Nature (substantial revisions
The Spectacular Ultraviolet Flash from the Peculiar Type Ia Supernova 2019yvq
Early observations of Type Ia supernovae (SNe Ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. We present exquisite observations of SN 2019yvq, the second observed SN Ia, after iPTF 14atg, to display an early flash of emission in the ultraviolet (UV) and optical. Our analysis finds that SN 2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for an SN Ia ( mag at peak) yet featured very high absorption velocities ( km s−1 for Si ii λ6355 at peak). We find that many of the observational features of SN 2019yvq, aside from the flash, can be explained if the explosive yield of radioactive 56Ni is relatively low (we measure ) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. To explain both the UV/optical flash and peak properties of SN 2019yvq we consider four different models: interaction between the SN ejecta and a nondegenerate companion, extended clumps of 56Ni in the outer ejecta, a double-detonation explosion, and the violent merger of two white dwarfs. Each of these models has shortcomings when compared to the observations; it is clear additional tuning is required to better match SN 2019yvq. In closing, we predict that the nebular spectra of SN 2019yvq will feature either H or He emission, if the ejecta collided with a companion, strong [Ca ii] emission, if it was a double detonation, or narrow [O i] emission, if it was due to a violent merger
AT2018cow: A Luminous Millimeter Transient
We present detailed submillimeter- through centimeter-wave observations of the extraordinary extragalactic transient AT2018cow. The apparent characteristics—the high radio luminosity, the rise and long-lived emission plateau at millimeter bands, and the sub-relativistic velocity—have no precedent. A basic interpretation of the data suggests coupled to a fast but sub-relativistic () shock in a dense () medium. We find that the X-ray emission is not naturally explained by an extension of the radio-submm synchrotron spectrum, nor by inverse Compton scattering of the dominant blackbody UV/optical/IR photons by energetic electrons within the forward shock. By , the X-ray emission shows spectral softening and erratic inter-day variability. Taken together, we are led to invoke an additional source of X-ray emission: the central engine of the event. Regardless of the nature of this central engine, this source heralds a new class of energetic transients shocking a dense medium, which at early times are most readily observed at millimeter wavelengths
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
The afterglow and elliptical host galaxy of the short gamma-ray burst GRB 050724
Despite a rich phenomenology, gamma-ray bursts (GRBs) are divided into two
classes based on their duration and spectral hardness -- the long-soft and the
short-hard bursts. The discovery of afterglow emission from long GRBs was a
watershed event, pinpointing their origin to star forming galaxies, and hence
the death of massive stars, and indicating an energy release of about 10^51
erg. While theoretical arguments suggest that short GRBs are produced in the
coalescence of binary compact objects (neutron stars or black holes), the
progenitors, energetics, and environments of these events remain elusive
despite recent localizations. Here we report the discovery of the first radio
afterglow from a short burst, GRB 050724, which unambiguously associates it
with an elliptical galaxy at a redshift, z=0.257. We show that the burst is
powered by the same relativistic fireball mechanism as long GRBs, with the
ejecta possibly collimated in jets, but that the total energy release is
10-1000 times smaller. More importantly, the nature of the host galaxy
demonstrates that short GRBs arise from an old (>1 Gyr) stellar population,
strengthening earlier suggestions, and providing support for coalescing compact
object binaries as the progenitors.Comment: Accepted to Nature; revisions include broad-band afterglow mode
Self-Reported Health Status in Primary Health Care: The Influence of Immigration and Other Associated Factors
OBJECTIVE: The aims of this study are to compare self-reported health status between Spanish-born and Latin American-born Spanish residents, adjusted by length of residence in the host country; and additionally, to analyse sociodemographic and psychosocial variables associated with a better health status. DESIGN: This is a cross-sectional population based study of Latin American-born (n = 691) and Spanish-born (n = 903) in 15 urban primary health care centres in Madrid (Spain), carried out between 2007 and 2009. The participants provided information, through an interview, about self-reported health status, socioeconomic characteristics, psychosocial factors and migration conditions. Descriptive and multiple logistic regression analyses were conducted. RESULTS: The Spanish-born participants reported a better health status than the Latin America-born participants (79.8% versus 69.3%, p<0.001). Different patterns of self-reported health status were observed depending on the length of residence in the host country. The proportion of immigrants with a better health status is greater in those who have been in Spain for less than five years compared to those who have stayed longer. Better health status is significantly associated with being men, under 34 years old, being Spanish-born, having a monthly incomes of over 1000 euros, and having considerable social support and low stress. CONCLUSIONS: Better self-reported health status is associated with being Spanish-born, men, under 34 years old, having an uppermiddle-socioeconomic status, adequate social support, and low stress. Additionally, length of residence in the host country is seen as a related factor in the self-reported health status of immigrants
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