2,604 research outputs found
Probing Electron-Capture Supernovae: X-Ray Binaries in Starbursts
Presenting population models of high-mass X-ray binaries (HMXBs) formed after
bursts of star formation, we investigate the effect of electron-capture
supernovae (ECS) of massive ONeMg white dwarfs and the hypothesis that ECS
events are associated with typically low supernova kicks imparted to the
nascent neutron stars. We identify an interesting ECS bump in the time
evolution of HMXB numbers; this bump is caused by significantly increased
production of wind-fed HMXBs 20-60 Myr post starburst. The amplitude and age
extent of the ECS bump depend on the strength of ECS kicks and the mass range
of ECS progenitors. We also find that ECS-HMXBs form through a specific
evolutionary channel that is expected to lead to binaries with Be donors in
wide orbits. These characteristics, along with their sensitivity to ECS
properties, provide us with an intriguing opportunity to probe ECS physics and
progenitors through studies of starbursts of different ages. Specifically, the
case of the Small Magellanic Cloud, with a significant observed population of
Be HMXBs and starburst activity 30-60 Myr ago, arises as a promising laboratory
for understanding the role of electron-capture supernovae in neutron star
formation.Comment: 5 pages, 3 figures, Published by ApJ in 07/0
Sustainable Performance Optimization for Digital Housing
With natural resources depleting, sustainable solutions are becoming more and more a necessity. To deal with the depleting resources, the Dutch government aims to generate 14% of countryâs energy consumption through natural resources by 2020. The Dutch built environment is estimated to be responsible for 38.1% of the total energy consumption. This means that investments and innovation within this area have high potential.
However, there are some indications that these goals cannot be met. New houses often meet these requirements but, with a growth of 0.8% per year, these only make up for a small portion of all projects. As a result, a strong focus lays on improving and renovating the existing housing market towards a sustainable and low energy environment. For this transition, information on the current housing market, possible renovation options and insight on the investments costs are required.
Within this PDEng-project the aim is to further develop WoonConnect, a digital tool that can help to speed up this transition for both renovation projects and new buildings
An Unusual Spectral State of an Ultra-luminous Very Soft X-ray Source during Outburst
We report the results of Chandra and XMM-Newton observations of a new
outburst of an ultra-luminous X-ray source in M101. During a Chandra monitoring
observation of M101, M101 ULX-1 was found to be in outburst in 2004 December,
the second outburst in 2004. The peak bolometric luminosity is about 3e40 erg/s
(7e39 erg/s in 0.3-7 keV). The outburst spectra are very soft and can generally
be fitted with a blackbody model with temperatures of 40-80 eV, similar to
supersoft X-ray sources in the Milky Way and in the Magellanic Clouds. In one
Chandra observation, the source spectrum appears to be harder with a
temperature of 150 eV. Such a spectral state is rarely seen in M101 ULX-1 and
no X-ray source in the Milky Way shows this kind of spectrum. However, such an
unusual spectral state very likely belongs to a new class of X-ray sources,
quasisoft X-ray sources, recently discovered in nearby galaxies. M101 ULX-1
returned to supersoft state in a subsequent XMM-Newton observation. Based on
the two outbursts in 2004, the extremely high luminosity (L_bol=1e40-1e41
erg/s), very soft X-ray spectra (kT=40-150 eV), transient behavior, and state
transition provide strong evidence that M101 ULX-1 harbors an intermediate-mass
black hole.Comment: 4 pages, 2 figures, accepted for publication in ApJ
T Pyxidis: The First Cataclysmic Variable with a Collimated Jet
We present the first observational evidence for a collimated jet in a
cataclysmic variable system; the recurrent nova T Pyxidis. Optical spectra show
bipolar components of H with velocities , very similar
to those observed in the supersoft X-ray sources and in SS 433. We argue that a
key ingredient of the formation of jets in the supersoft X-ray sources and T
Pyx (in addition to an accretion disk threaded by a vertical magnetic field),
is the presence of nuclear burning on the surface of the white dwarf.Comment: 10 pages 2 figures to appear in ApJ Letter
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Properties of Deflagration Fronts and Models for Type Ia Supernovae
Detailed models of the explosion of a white dwarf, which include
self-consistent calculations of the light curve and spectra, provide a link
between observational quantities and the underlying explosion.These
calculations assume spherical geometry and are based on parameterized
descriptions of the burning front during the deflagration phase. Recently,
first multi-dimensional calculations for nuclear burning fronts have been
performed. Although a fully consistent treatment of the burning fronts is
beyond the current state of the art, these calculations provided a new and
better understanding of the physics, and new descriptions for the flame
propagation have been proposed. Here, we have studied the influence on the
results of previous analyses of Type Ia Supernovae, namely, the nucleosynthesis
and structure of the expanding envelope. Our calculations are based on a set of
delayed detonation models with parameters that give a good account of the
optical and infrared light curves, and of the spectral evolution. In this
scenario, the burning front propagates first in a deflagration mode and,
subsequently, turns into a detonation. The explosions and light curves are
calculated using a one-dimensional Lagrangian radiation-hydro code, including a
detailed nuclear network.Comment: 9 pages, 4 figures, macros 'crckapb.sty'. The Astrophysical Journal
(accepted
The Physics of Supernova Remnant Blast Waves. I. Kinematics of DEM L71 in the Large Magellanic Cloud
We present the results from Fabry-Perot imaging spectroscopy of the
Balmer-dominated supernova remnant DEM L71 (0505-67.9) in the LMC. Spectra
extracted from the entire circumference of the blast wave reveal the broad and
narrow component H-alpha line emission characteristic of non-radiative shocks
in partially neutral gas. The new spectra of DEM L71 include portions of the
rim that have not been previously observed. We find that the broad component
width varies azimuthally along the edge of DEM L71, ranging from 450+/-60 km/s
along the eastern edge to values as high as 985 (+210)(-165) km/s along the
faint western edge. In part of the faint northern rim the broad component is
not detected, possibly indicating a lower density in these regions and/or a
broad component width in excess of 1000 km/s. Between the limits of zero and
full electron-ion temperature equilibration at the shock front, the allowed
range of shock velocities is 430-560 km/s along the east rim and 700-1250 km/s
along other parts of the blast wave. The H-alpha broad-to-narrow flux ratios
vary considerably around the remnant, ranging from 0.4 to 0.8. These ratios lie
below the values predicted by our shock models. We find that narrow component
H-alpha emission from a cosmic ray precursor may be the cause of the
discrepancy. The least decelerated portions of the blast wave (i.e., regions
excluding the brightest filaments) are well characterized by Sedov models with
a kinetic energy E_51= (0.37+/-0.06)*D_50**(5/2), where D_50 is the LMC
distance in units of 50 kpc. The corresponding age for DEM L71 is
(4360+/-290)*D_50 yr. This is the first time that velocity information from the
entire blast wave has been utilized to study the global kinematics of a
non-radiative SNR at a known distance.Comment: 21 pages, including 8 postscript figures and 4 tables, LaTeX,
accepted to ApJ; see companion pape
The Possible White Dwarf-Neutron Star Connection
The current status of the problem of whether neutron stars can form, in close
binary systems, by accretion-induced collapse (AIC) of white dwarfs is
examined. We find that, in principle, both initially cold C+O white dwarfs in
the high-mass tail of their mass distribution in binaries and O+Ne+Mg white
dwarfs can produce neutron stars. Which fractions of neutron stars in different
types of binaries (or descendants from binaries) might originate from this
process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and
E. Garcia-Berro (Dordrecht: Kluwer
Thermal Timescale Mass Transfer and the Evolution of White Dwarf Binaries
The evolution of binaries consisting of evolved main sequence stars (1 <
M_d/Msun < 3.5) with white dwarf companions (0.7 < M_wd/Msun < 1.2) is
investigated through the thermal mass transfer phase. Taking into account the
stabilizing effect of a strong, optically thick wind from the accreting white
dwarf surface, we have explored the formation of several evolutionary groups of
systems for progenitors with initial orbital periods of 1 and 2 days. The
numerical results show that CO white dwarfs can accrete sufficient mass to
evolve to a Type Ia supernova and ONeMg white dwarfs can be built up to undergo
accretion induced collapse for donors more massive than about 2 Msun. For
donors less massive than ~2 Msun the system can evolve to form a He and CO or
ONeMg white dwarf pair. In addition, sufficient helium can be accumulated (~0.1
Msun) in systems characterized by 1.6 < M_d/Msun < 1.9 and 0.8 < M_wd/Msun < 1
such that sub Chandrasekhar mass models for Type Ia supernovae, involving off
center helium ignition, are possible for progenitor systems evolving via the
Case A mass transfer phase. For systems characterized by mass ratios > 3 the
system likely merges as a result of the occurrence of a delayed dynamical mass
transfer instability. A semi-analytical model is developed to delineate these
phases which can be easily incorporated in population synthesis studies of
these systems.Comment: 9 pages, 6 figures, Latex, emulateapj style, ApJ accepte
Lifting the Shroud: Government, Investment Banks and Power in Post Financial Crisis United Kingdom - A critical deconstruction of the relationship between government and investment banks in the United Kingdom post global financial crisis (2007 â 2011)
The late 2000s Global Financial Crisis swept the advanced world and spilled into the developing, creating chaos in its wake. At the crux of the crisis were the high-risk activities of investment banks in the developed world â and especially United Kingdom. Since then, academic and public discussion has revolved around the questionable relationship between investment banks and government that resulted in subpar regulation and the costly bank âbailoutsâ of 2008 and 2009. What this thesis will to do is holistically assess how the power relationship between British investment banks and the United Kingdom government has evolved since the crisis, utilising Doris Fuchsâ Three Dimensional Approach to Business Power and Governance and a wide array of research to address those structural, instrumental and discursive elements of business power
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