4,184 research outputs found
On the observability of bow shocks of Galactic runaway OB stars
Massive stars that have been ejected from their parent cluster and
supersonically sailing away through the interstellar medium (ISM) are
classified as exiled. They generate circumstellar bow shock nebulae that can be
observed. We present two-dimensional, axisymmetric hydrodynamical simulations
of a representative sample of stellar wind bow shocks from Galactic OB stars in
an ambient medium of densities ranging from n_ISM=0.01 up to 10.0/cm3.
Independently of their location in the Galaxy, we confirm that the infrared is
the most appropriated waveband to search for bow shocks from massive stars.
Their spectral energy distribution is the convenient tool to analyze them since
their emission does not depend on the temporary effects which could affect
unstable, thin-shelled bow shocks. Our numerical models of Galactic bow shocks
generated by high-mass (~40 Mo) runaway stars yield H fluxes which
could be observed by facilities such as the SuperCOSMOS H-Alpha Survey. The
brightest bow shock nebulae are produced in the denser regions of the ISM. We
predict that bow shocks in the field observed at Ha by means of
Rayleigh-sensitive facilities are formed around stars of initial mass larger
than about 20 Mo. Our models of bow shocks from OB stars have the emission
maximum in the wavelength range 3 <= lambda <= 50 micrometer which can be up to
several orders of magnitude brighter than the runaway stars themselves,
particularly for stars of initial mass larger than 20 Mo.Comment: 13 pages, 12 figures. Accepted to MNRAS (2016
Star forming regions of the southern galaxy
A catalog of southern dust cloud properties is being compiled to aid in the planning and analysis of radio spectral line surveys in the southern hemisphere. Ultimately, images of dust temperature and column density will be produced. For the interim, a list of the 60 and 100 micron fluxes was prepared for the cores and adjacent backgrounds of 65 prominent dust clouds. Dust temperatures and column densities were derived
Low frequency VLBI in space using GAS-Can satellites: Report on the May 1987 JPL Workshop
Summarized are the results of a workshop held at JPL on May 28 and 29, 1987, to study the feasibility of using small, very inexpensive spacecraft for a low-frequency radio interferometer array. Many technical aspects of a mission to produce high angular resolution images of the entire sky at frequencies from 2 to 20 MHz were discussed. The workshop conclusion was that such a mission was scientifically valuable and technically practical. A useful array could be based on six or more satellites no larger than those launched from Get-Away-Special canisters. The cost of each satellite could be $1-2M, and the mass less than 90 kg. Many details require further study, but as this report shows, there is good reason to proceed. No fundamental problems have been discovered involving the use of untraditional, very inexpensive spacecraft for this type of mission
Accreting millisecond X-ray pulsars: 10 years of INTEGRAL observations
During the last 10 years, INTEGRAL made a unique contribution to the study of
accreting millisecond X-ray pulsars (AMXPs), discovering three of the 14
sources now known of this class. Besides increasing the number of known AMXPs,
INTEGRAL also carried out observations of these objects above 20 keV,
substantially advancing our understanding of their behaviour. We present here a
review of all the AMXPs observed with INTEGRAL and discuss the physical
interpretation of their behaviour in the X-ray domain. We focus in particular
on the lightcurve profile during outburst, as well as the timing, spectral, and
thermonuclear type-I X-ray bursts properties.Comment: 8 pages, 8 figures. Proceedings of "An INTEGRAL view of the
high-energy sky (the first 10 years)" the 9th INTEGRAL Workshop, October
15-19, 2012, Paris, Franc
Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-layer- induced Octahedral Distortion
With reduced dimensionality, it is often easier to modify the properties of
ultra-thin films than their bulk counterparts. Strain engineering, usually
achieved by choosing appropriate substrates, has been proven effective in
controlling the properties of perovskite oxide films. An emerging alternative
route for developing new multifunctional perovskite is by modification of the
oxygen octahedral structure. Here we report the control of structural oxygen
octahedral rotation in ultra-thin perovskite SrRuO3 films by the deposition of
a SrTiO3 capping layer, which can be lithographically patterned to achieve
local control. Using a scanning Sagnac magnetic microscope, we show increase in
the Curie temperature of SrRuO3 due to the suppression octahedral rotations
revealed by the synchrotron x-ray diffraction. This capping-layer-based
technique may open new possibilities for developing functional oxide materials.Comment: Main-text 5 pages, SI 6 pages. To appear in Physical Review Letter
Hard X-ray timing and spectral characteristics of the energetic pulsar PSR J0205+6449 in supernova remnant 3C58
PSR J0205+6449 is a young rotation-powered pulsar in SNR 3C 58. It is one of
only three young (<10,000 year old) pulsars which are so far detected in the
radio and the classical X-ray bands, as well as at hard X-rays above 20 keV and
at high-energy (>100 MeV) -rays. The other two young pulsars are the
Crab and PSR B1509-58. Our aim is to derive the timing and spectral
characteristics of PSR J0205+6449 over the broad X-ray band from ~0.5 to ~270
keV. We used all publicly available RXTE observations of PSR J0205+6449 to
first generate accurate ephemerides over the period September 30, 2000 - March
18, 2006. Next, phase-folding procedures yielded pulse profiles using data from
RXTE PCA and HEXTE, and XMM-Newton EPIC PN. While our timing solutions are
consistent with earlier results, our work shows sharper structures in the PCA
X-ray profile. The X-ray pulse profile consists of two sharp pulses, separated
in phase by 0.488(2), which can be described with 2 asymmetric Lorentzians,
each with the rising wing steeper than the trailing wing, and
full-width-half-maximum 1.41(5) ms and 2.35(22) ms, respectively. We find an
indication for a flux increase by a factor ~2, about 3.5 sigma above the
time-averaged value, for the second, weaker pulse during a two-week interval,
while its pulse shape did not change. The spectrum of the pulsed X-ray emission
is of non-thermal origin, exhibiting a power-law shape with photon index Gamma
= 1.03(2) over the energy band ~0.5 to ~270 keV. In the energy band covered
with the PCA (~3-30 keV) the spectra of the two pulses have the same photon
index, namely, 1.04(3) and 1.10(8), respectively.Comment: 10 pages; 7 figures (2 in color), resubmitted to A&A, including
referee comment
INTEGRAL high energy detection of the transient IGR J11321-5311
Context: The transient hard X-ray source IGR J11321-5311 was discovered by
INTEGRAL on June 2005, during observations of the Crux spiral arm. To date,
this is the only detection of the source to be reported by any X/gamma-ray
mission. Aims: To characterize the behaviour and hence the nature of the source
through temporal and spectral IBIS analysis. Methods: Detailed spectral and
temporal analysis has been performed using standard INTEGRAL software OSA
v.5.1. Results: To date, IGR J11321-5311 has been detected only once. It was
active for about 3.5 hours, a short and bright flare lasting about 1.5 hours is
evident in the IBIS light curve. It reached a peak flux of about 80 mCrab or
2.2x10E-9 erg cmE-2 sE-1 (20--300 keV),corresponding to a peak luminosity of
1.1x10E37 erg sE-1 (assuming a distance of 6.5 kpc). During the outburst, the
source was detected with a significance of 18 sigma (20--300 keV) and 8 sigma
(100--300 keV). The spectrum of the total outburst activity (17--300 keV) is
best fitted by the sum of a power law (Gamma=0.55+/-0.18) plus a black body
(kT=1.0{+0.2}_{-0.3} keV), with no evidence for a break up to 300 keV. A
spectral analysis at Science Window level revealed an evident hardening of the
spectrum through the outburst. The IBIS data were searched for pulsations with
no positive result. Conclusions: The X-ray spectral shape and the flaring
behaviour favour the hypothesis that IGR J11321-5311 is an Anomalous X-ray
Pulsar, though a different nature can not be firmly rejected at the present
stage.Comment: accepted for publication in A&A letter, 4 pages, 6 figure
Omineca Herald, July, 10, 1914
Patients admitted to an intensive care unit after cardiac arrest often suffer from severe brain injury. This injury worsens further after restoration of circulation due to the cascade of reactions in the brain. Neuroprotective therapies aim to diminish this secondary brain injury, thereby targeting at a better outcome. Several new large international studies will start soon, next to two smaller national phase II studies. In this paper we describe the new studies and invite Dutch intensive care units to join
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