3,926 research outputs found
Probing the evolving massive star population in Orion with kinematic and radioactive tracers
We assemble a census of the most massive stars in Orion, then use stellar
isochrones to estimate their masses and ages, and use these results to
establish the stellar content of Orion's individual OB associations. From this,
our new population synthesis code is utilized to derive the history of the
emission of UV radiation and kinetic energy of the material ejected by the
massive stars, and also follow the ejection of the long-lived radioactive
isotopes 26Al and 60Fe. In order to estimate the precision of our method, we
compare and contrast three distinct representations of the massive stars. We
compare the expected outputs with observations of 26Al gamma-ray signal and the
extent of the Eridanus cavity. We find an integrated kinetic energy emitted by
the massive stars of 1.8(+1.5-0.4)times 10^52 erg. This number is consistent
with the energy thought to be required to create the Eridanus superbubble. We
also find good agreement between our model and the observed 26Al signal,
estimating a mass of 5.8(+2.7-2.5) times 10^-4 Msol of 26Al in the Orion
region. Our population synthesis approach is demonstrated for the Orion region
to reproduce three different kinds of observable outputs from massive stars in
a consistent manner: Kinetic energy as manifested in ISM excavation, ionization
as manifested in free-free emission, and nucleosynthesis ejecta as manifested
in radioactivity gamma-rays. The good match between our model and the
observables does not argue for considerable modifications of mass loss. If
clumping effects turn out to be strong, other processes would need to be
identified to compensate for their impact on massive-star outputs. Our
population synthesis analysis jointly treats kinematic output and the return of
radioactive isotopes, which proves a powerful extension of the methodology that
constrains feedback from massive stars.Comment: Accepted for publication in A&A, 10 page
An explanation for the curious mass loss history of massive stars: from OB stars, through Luminous Blue Variables to Wolf-Rayet stars
The stellar winds of massive stars show large changes in mass-loss rates and
terminal velocities during their evolution from O-star through the Luminous
Blue Variable phase to the Wolf-Rayet phase. The luminosity remains
approximately unchanged during these phases. These large changes in wind
properties are explained in the context of the radiation driven wind theory, of
which we consider four different models. They are due to the evolutionary
changes in radius, gravity and surface composition and to the change from
optically thin (in continuum) line driven winds to optically thick radiation
driven winds.Comment: Accepted for publication in Astronomy and Astrophysics (Letter to the
Editor
Cooling curves for neutron stars with hadronic matter and quark matter
The thermal evolution of isothermal neutron stars is studied with matter both
in the hadronic phase as well as in the mixed phase of hadronic matter and
strange quark matter. In our models, the dominant early-stage cooling process
is neutrino emission via the direct Urca process. As a consequence, the cooling
curves fall too fast compared to observations. However, when superfluidity is
included, the cooling of the neutron stars is significantly slowed down.
Furthermore, we find that the cooling curves are not very sensitive to the
precise details of the mixing between the hadronic phase and the quark phase
and also of the pairing that leads to superfluidity.Comment: 19 pages, 25 figure
First-order phase transitions in two-dimensional off-lattice liquid crystals
We consider an off-lattice liquid crystal pair potential in strictly two
dimensions. The potential is purely repulsive and short-ranged. Nevertheless,
by means of a single parameter in the potential, the system is shown to undergo
a first-order phase transition. The transition is studied using mean-field
density functional theory, and shown to be of the isotropic-to-nematic kind. In
addition, the theory predicts a large density gap between the two coexisting
phases. The first-order nature of the transition is confirmed using computer
simulation and finite-size scaling. Also presented is an analysis of the
interface between the coexisting domains, including estimates of the line
tension, as well as an investigation of anchoring effects.Comment: 12 pages, 17 figures, submitted to J. Phys.: Condens. Matte
The VLT-FLAMES Tarantula Survey
We present a number of notable results from the VLT-FLAMES Tarantula Survey
(VFTS), an ESO Large Program during which we obtained multi-epoch
medium-resolution optical spectroscopy of a very large sample of over 800
massive stars in the 30 Doradus region of the Large Magellanic Cloud (LMC).
This unprecedented data-set has enabled us to address some key questions
regarding atmospheres and winds, as well as the evolution of (very) massive
stars. Here we focus on O-type runaways, the width of the main sequence, and
the mass-loss rates for (very) massive stars. We also provide indications for
the presence of a top-heavy initial mass function (IMF) in 30 Dor.Comment: 7 Figures, 8 pages. Invited talk: IAUS 329: "The Lives and
Death-Throes of Massive Stars
On the influence of shock-cloud interactions on the nonthermal X-ray emission from the supernova remnant RCW 86
The effect of the surrounding environment of supernova remnant shocks on nonthermal X-rays from accelerated electrons, with or without interacting dense material, is an open issue. We conduct spatially resolved X-ray spectroscopy of the shock–cloud interacting region of RCW 86 with XMM–Newton. It is found that bright soft X-ray filaments surround the dense cloud, observed with 12CO and H I emission lines. These filaments are brighter in thermal X-ray emission, and fainter and possibly softer in synchrotron X-rays, compared to those without interaction. Our results show that the shock decelerates due to the interaction with clouds, which results in an enhancement of thermal X-ray emission. This could possibly also explain the softer X-ray synchrotron component, because it implies that those shocks that move through a low-density environment, and therefore decelerate much less, can be more efficient accelerators. This is similar to SN 1006 and Tycho, and is in contrast to RX J1713.7−3946. This difference among remnants may be due to the clumpiness of dense material interacting with the shock, which should be examined in future observations
Implications of the lowest frequency detection of the persistent counterpart of FRB121102
Context. The repeating FRB121102 is so far the only extra-galactic Fast Radio
Burst found to be associated with a counterpart, a steady radio source with a
nearly flat spectral energy distribution (SED) in centimeter wavelengths.
Aims. Previous observations of the persistent source down to ~GHz has
shown no sign of a spectral turn-over. Absorption is expected to eventually
cause a turn-over at lower frequencies. Better constraints on the physical
parameters of the emitting medium can be derived by detecting the
self-absorption frequency.
Methods. We used the Giant Metre-Wave Radio Telescope (GMRT) during the
period of July to December 2017 to observe the source at low radio frequencies
down to ~MHz.
Results. The spectral energy distribution of the source remains optically
thin even at ~MHz, with a spectral index of
similar to what is seen in Galactic plerions. Using a generic synchrotron
radiation model, we obtain constraints on properties of the non-thermal plasma
and the central engine powering it.
Conclusions. We present low-frequency detections of the persistent source
associated with FRB121102. Its characteristic flat SED extends down to
~MHz. Like Galactic plerions, the energy in the persistent source is
carried predominantly by leptons. The emitting plasma has a ~G, and
its age is . We show that
the energetics of the persistent source requires an initial spin period shorter
than 36~ms, and the magnetic field of the neutron star must exceed ~G. This implies that the persistent source does not necessarily
require energetic input from a magnetar.Comment: Submitted to A&A, 8 pages, 4 figure
The Extraordinarily Rapid Expansion of the X-ray Remnant of Kepler's Supernova (SN1604)
Four individual high resolution X-ray images from ROSAT and the Einstein
Observatory have been used to measure the expansion rate of the remnant of
Kepler's supernova (SN 1604). Highly significant measurements of the expansion
have been made for time baselines varying from 5.5 yrs to 17.5 yrs. All
measurements are consistent with a current expansion rate averaged over the
entire remnant of 0.239 (+/-0.015) (+0.017,-0.010) % per yr, which, when
combined with the known age of the remnant, determines the expansion parameter
m, defined as , to be 0.93 (+/-0.06) (+0.07,-0.04). The error
bars on these results include both statistical (first set of errors) and
systematic (second set) uncertainty. According to this result the X-ray remnant
is expanding at a rate that is remarkably close to free expansion and nearly
twice as fast as the mean expansion rate of the radio remnant. The expansion
rates as a function of radius and azimuthal angle are also presented based on
two ROSAT images that were registered to an accuracy better than 0.5
arcseconds. Significant radial and azimuthal variations that appear to arise
from the motion of individual X-ray knots are seen. The high expansion rate of
the X-ray remnant appears to be inconsistent with currently accepted dynamical
models for the evolution of Kepler's SNR.Comment: 14 pages, including 7 postscript figs, LaTeX, emulateapj. Accepted by
Ap
A 3D extinction map of the northern Galactic plane based on IPHAS photometry
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2014 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present a 3D map of extinction in the northern Galactic plane derived using photometry from the INT/WFC Photometric Hα Survey of the northern Galactic plane. The map has fine angular (~10 arcmin) and distance (100 pc) sampling allied to a significant depth (≳5 kpc). We construct the map using a method based on a hierarchical Bayesian model described in a previous article by Sale. In addition to mean extinction, we also measure differential extinction, which arises from the fractal nature of the interstellar medium, and show that it will be the dominant source of uncertainty in estimates of extinction to some arbitrary position. The method applied also furnishes us with photometric estimates of the distance, extinction, effective temperature, surface gravity, and mass for ~38 million stars. Both the extinction map and the catalogue of stellar parameters are made publicly available via http://www.iphas.org/extinction.Peer reviewe
Critical behavior of colloid-polymer mixtures in random porous media
We show that the critical behavior of a colloid-polymer mixture inside a
random porous matrix of quenched hard spheres belongs to the universality class
of the random-field Ising model. We also demonstrate that random-field effects
in colloid-polymer mixtures are surprisingly strong. This makes these systems
attractive candidates to study random-field behavior experimentally.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
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