76 research outputs found
Studies of regular and random magnetic fields in the ISM: statistics of polarization vectors and the Chandrasekhar-Fermi technique
Polarimetry is extensively used as a tool to trace the interstellar magnetic
field projected on the plane of sky. Moreover, it is also possible to estimate
the magnetic field intensity from polarimetric maps based on the
Chandrasekhar-Fermi method. In this work, we present results for turbulent,
isothermal, 3-D simulations of sub/supersonic and sub/super-Alfvenic cases.
With the cubes, assuming perfect grain alignment, we created synthetic
polarimetric maps for different orientations of the mean magnetic field with
respect to the line of sight (LOS). We show that the dispersion of the
polarization angle depends on the angle of the mean magnetic field regarding
the LOS and on the Alfvenic Mach number. However, the second order structure
function of the polarization angle follows the relation , being dependent exclusively on the Alfvenic Mach number.
The results show an anti-correlation between the polarization degree and the
column density, with exponent , in agreement with
observations, which is explained by the increase in the dispersion of the
polarization angle along the LOS within denser regions. However, this effect
was observed exclusively on supersonic, but sub-Alfvenic, simulations. For the
super-Alfvenic, and the subsonic model, the polarization degree showed to be
intependent on the column density. Our major quantitative result is a
generalized equation for the CF method, which allowed us to determine the
magnetic field strength from the polarization maps with errors . We also
account for the role of observational resolution on the CF method.Comment: submitted to ApJ, 42 page
The mortality rates and the space-time patterns of John Snow’s cholera epidemic map
Background Snow’s work on the Broad Street map is widely known as a pioneering example of spatial epidemiology. It lacks, however, two significant attributes required in contemporary analyses of disease incidence: population at risk and the progression of the epidemic over time. Despite this has been repeatedly suggested in the literature, no systematic investigation of these two aspects was previously carried out. Using a series of historical documents, this study constructs own data to revisit Snow’s study to examine the mortality rate at each street location and the space-time pattern of the cholera outbreak. Methods This study brings together records from a series of historical documents, and prepares own data on the estimated number of residents at each house location as well as the space-time data of the victims, and these are processed in GIS to facilitate the spatial-temporal analysis. Mortality rates and the space-time pattern in the victims’ records are explored using Kernel Density Estimation and network-based Scan Statistic, a recently developed method that detects significant concentrations of records such as the date and place of victims with respect to their distance from others along the street network. The results are visualised in a map form using a GIS platform. Results Data on mortality rates and space-time distribution of the victims were collected from various sources and were successfully merged and digitised, thus allowing the production of new map outputs and new interpretation of the 1854 cholera outbreak in London, covering more cases than Snow’s original report and also adding new insights into their space-time distribution. They confirmed that areas in the immediate vicinity of the Broad Street pump indeed suffered from excessively high mortality rates, which has been suspected for the past 160 years but remained unconfirmed. No distinctive pattern was found in the space-time distribution of victims’ locations. Conclusions The high mortality rates identified around the Broad Street pump are consistent with Snow’s theory about cholera being transmitted through contaminated water. The absence of a clear space-time pattern also indicates the water-bourne, rather than the then popular belief of air bourne, nature of cholera. The GIS data constructed in this study has an academic value and would cater for further research on Snow’s map
Observed Consequences of Presupernova Instability in Very Massive Stars
This chapter concentrates on the deaths of very massive stars, the events
leading up to their deaths, and how mass loss affects the resulting death. The
previous three chapters emphasized the theory of wind mass loss, eruptions, and
core collapse physics, but here we emphasize mainly the observational
properties of the resulting death throes. Mass loss through winds, eruptions,
and interacting binaries largely determines the wide variety of different types
of supernovae that are observed, as well as the circumstellar environments into
which the supernova blast waves expand. Connecting these observed properties of
the explosions to the initial masses of their progenitor stars is, however, an
enduring challenge and is especially difficult for very massive stars.
Superluminous supernovae, pair instability supernovae, gamma ray bursts, and
"failed" supernovae are all end fates that have been proposed for very massive
stars, but the range of initial masses or other conditions leading to each of
these (if they actually occur) are still very certain. Extrapolating to infer
the role of very massive stars in the early universe is essentially
unencumbered by observational constraints and still quite dicey.Comment: 39 pages, 5 figures, to appear as chapter in the book "Very Massive
Stars in the Local Universe", ed. J. Vin
First Results from the Lick AGN Monitoring Project: The Mass of the Black Hole in Arp 151
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7 M_sun. We present here the first results from
this project -- the mass of the central black hole in Arp 151. Strong
variability throughout the campaign led to an exceptionally clean Hbeta lag
measurement in this object of 4.25(+0.68/-0.66) days in the observed frame.
Coupled with the width of the Hbeta emission line in the variable spectrum, we
determine a black hole mass of (7.1 +/- 1.2)x10^6 M_sun, assuming the Onken et
al. normalization for reverberation-based virial masses. We also find
velocity-resolved lag information within the Hbeta emission line which clearly
shows infalling gas in the Hbeta-emitting region. Further detailed analysis may
lead to a full model of the geometry and kinematics of broad line region gas
around the central black hole in Arp 151.Comment: 4 pages, 4 figures and 2 tables, accepted for publication in ApJ
Letter
The Exceptionally Luminous Type II-L SN 2008es
We report on our early photometric and spectroscopic observations of the
extremely luminous Type II supernova (SN) 2008es. With an observed peak optical
magnitude of m_V = 17.8 and at a redshift z = 0.213, SN 2008es had a peak
absolute magnitude of M_V = -22.3, making it the second most luminous SN ever
observed. The photometric evolution of SN 2008es exhibits a fast decline rate
(~0.042 mag d^-1), similar to the extremely luminous Type II-L SN 2005ap. We
show that SN 2008es spectroscopically resembles the luminous Type II-L SN
1979C. Although the spectra of SN 2008es lack the narrow and intermediate-width
line emission typically associated with the interaction of a SN with the
circumstellar medium of its progenitor star, we argue that the extreme
luminosity of SN 2008es is powered via strong interaction with a dense,
optically thick circumstellar medium. The integrated bolometric luminosity of
SN 2008es yields a total radiated energy at ultraviolet and optical wavelengths
of >10^51 ergs. Finally, we examine the apparently anomalous rate at which the
Texas Supernova Search has discovered rare kinds of supernovae, including the
five most luminous supernovae observed to date, and find that their results are
consistent with those of other modern SN searches.Comment: accepted to ApJ, 10 pages, 7 figures, 6 tables. Minor revisions,
conclusions remain unchange
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
CVIT expert consensus document on primary percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI) in 2018
While primary percutaneous coronary intervention (PCI) has significantly contributed to improve the mortality in patients with ST segment elevation myocardial infarction even in cardiogenic shock, primary PCI is a standard of care in most of Japanese institutions. Whereas there are high numbers of available facilities providing primary PCI in Japan, there are no clear guidelines focusing on procedural aspect of the standardized care. Whilst updated guidelines for the management of acute myocardial infarction were recently published by European Society of Cardiology, the following major changes are indicated; (1) radial access and drug-eluting stent over bare metal stent were recommended as Class I indication, and (2) complete revascularization before hospital discharge (either immediate or staged) is now considered as Class IIa recommendation. Although the primary PCI is consistently recommended in recent and previous guidelines, the device lag from Europe, the frequent usage of coronary imaging modalities in Japan, and the difference in available medical therapy or mechanical support may prevent direct application of European guidelines to Japanese population. The Task Force on Primary Percutaneous Coronary Intervention of the Japanese Association of Cardiovascular Intervention and Therapeutics (CVIT) has now proposed the expert consensus document for the management of acute myocardial infarction focusing on procedural aspect of primary PCI
The visualization and analysis of urban facility pois using network kernel density estimation constrained by multi-factors
The urban facility, one of the most important service providers is usually represented by sets of points in GIS applications using POI (Point of Interest) model associated with certain human social activities. The knowledge about distribution intensity and pattern of facility POIs is of great significance in spatial analysis, including urban planning, business location choosing and social recommendations. Kernel Density Estimation (KDE), an efficient spatial statistics tool for facilitating the processes above, plays an important role in spatial density evaluation, because KDE method considers the decay impact of services and allows the enrichment of the information from a very simple input scatter plot to a smooth output density surface. However, the traditional KDE is mainly based on the Euclidean distance, ignoring the fact that in urban street network the service function of POI is carried out over a network-constrained structure, rather than in a Euclidean continuous space. Aiming at this question, this study proposes a computational method of KDE on a network and adopts a new visualization method by using 3-D "wall" surface. Some real conditional factors are also taken into account in this study, such as traffic capacity, road direction and facility difference. In practical works the proposed method is implemented in real POI data in Shenzhen city, China to depict the distribution characteristic of services under impacts of multi-factors
PTF13efv - An Outburst 500 Days Prior to the SNHUNT 275 Explosion and Its Radiative Efficiency
The American Astronomical Society. All rights reserved..The progenitors of some supernovae (SNe) exhibit outbursts with super-Eddington luminosities prior to their final explosions. This behavior is common among SNe IIn, but the driving mechanisms of these precursors are not yet well-understood. SNHunt 275 was announced as a possible new SN during 2015 May. Here we report on pre-explosion observations of the location of this event by the Palomar Transient Factory (PTF) and report the detection of a precursor about 500 days prior to the 2015 May activity (PTF 13efv). The observed velocities in the 2015 transient and its 2013 precursor absorption spectra are low (1000-2000 km s-1), so it is not clear yet if the recent activity indeed marks the final disruption of the progenitor. Regardless of the nature of this event, we use the PTF photometric and spectral observations, as well as Swift-UVOT observations, to constrain the efficiency of the radiated energy relative to the total kinetic energy of the precursor. We find that, using an order-of-magnitude estimate and under the assumption of spherical symmetry, the ratio of the radiated energy to the kinetic energy is in the range of 4 x 10-2 to 3.4 x 103. © 2016
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