7,240 research outputs found
A Sino-German 6cm polarisation survey of the Galactic plane - VIII. Small-diameter sources
Information of small-diameter sources is extracted from the Sino-German 6cm
polarisation survey of the Galactic plane carried out with the Urumqi 25-m
telescope. We performed two-dimensional elliptical Gaussian fits to the 6cm
maps to obtain a list of sources with total-intensity and polarised flux
densities. The source list contains 3832 sources with a fitted diameter smaller
than 16 arcmin and a peak flux density exceeding 30 mJy, so about 5 times the
rms noise, of the total-intensity data. The cumulative source count indicates
completeness for flux densities exceeding about 60 mJy. We identify 125
linearly polarised sources at 6cm with a peak polarisation flux density greater
than 10 mJy, so about 3 times the rms noise, of the polarised-intensity data.
Despite lacking compact steep spectrum sources, the 6cm catalogue lists about
20 percent more sources than the Effelsberg 21cm source catalogue at the same
angular resolution and for the same area. Most of the faint 6cm sources must
have a flat spectrum and are either HII regions or extragalactic. When compared
with the Green Bank 6cm (GB6) catalogue, we obtain higher flux densities for a
number of extended sources with complex structures. Polarised 6cm sources
density are uniformly distributed in Galactic latitude. Their number density
decreases towards the inner Galaxy. More than 80 percent of the polarised
sources are most likely extragalactic. With a few exceptions, the sources have
a higher percentage polarisation at 6cm than at 21cm. Depolarisation seems to
occur mostly within the sources with a minor contribution from the Galactic
foreground emission.Comment: A&A accepted, 9 pages, 5 figures, Tables 1 and 2 are accessible from
http://zmtt.bao.ac.cn/6cm
The sino-german 6cm polarization survey of the galactic plane: A summary
We have finished the 6cm polarization survey of the Galactic plane using the
Urumqi 25m radio telescope. It covers 10deg<l<230deg in Galactic longitude and
|b| <5deg in Galactic latitude. The new polarization maps not only reveal new
properties of the diffuse magnetized interstellar medium, but also are very
useful for studying individual objects such as Hii regions, which may act as
Faraday screens with strong regular magnetic fields inside, and supernova
remnants for their polarization properties and spectra. The high sensitivity of
the survey enables us to discover two new SNRs G178.2-4.2 and G25.3-2.1 and a
number of Hii regions.Comment: 10 pages, 1 figure. International Journal of Modern Physics:
Conference Series (IJMPCS) for Proceedings of 3rd Galileo-Xu Guangqi meetin
HI ``Tails'' from Cometary Globules in IC1396
IC 1396 is a relatively nearby (750 pc), large (>2 deg), HII region ionized
by a single O6.5V star and containing bright-rimmed cometary globules. We have
made the first arcmin resolution images of atomic hydrogen toward IC 1396, and
have found remarkable ``tail''-like structures associated with some of the
globules and extending up to 6.5 pc radially away from the central ionizing
star. These HI ``tails'' may be material which has been ablated from the
globule through ionization and/or photodissociation and then accelerated away
from the globule by the stellar wind, but which has since drifted into the
``shadow'' of the globules.
This report presents the first results of the Galactic Plane Survey Project
recently begun by the Dominion Radio Astrophysical Observatory.Comment: 11 pages, 5 postscript figures, uses aaspp4.sty macros, submitted in
uuencoded gzipped tar format, accepted for publication in Astrophysical
Journal Letters, colour figures available at
http://www.drao.nrc.ca/~schieven/news_sep95/ic1396.htm
Processes, Roles and Their Interactions
Taking an interaction network oriented perspective in informatics raises the
challenge to describe deterministic finite systems which take part in networks
of nondeterministic interactions. The traditional approach to describe
processes as stepwise executable activities which are not based on the
ordinarily nondeterministic interaction shows strong centralization tendencies.
As suggested in this article, viewing processes and their interactions as
complementary can circumvent these centralization tendencies.
The description of both, processes and their interactions is based on the
same building blocks, namely finite input output automata (or transducers).
Processes are viewed as finite systems that take part in multiple, ordinarily
nondeterministic interactions. The interactions between processes are described
as protocols.
The effects of communication between processes as well as the necessary
coordination of different interactions within a processes are both based on the
restriction of the transition relation of product automata. The channel based
outer coupling represents the causal relation between the output and the input
of different systems. The coordination condition based inner coupling
represents the causal relation between the input and output of a single system.
All steps are illustrated with the example of a network of resource
administration processes which is supposed to provide requesting user processes
exclusive access to a single resource.Comment: In Proceedings IWIGP 2012, arXiv:1202.422
DA495 - an aging pulsar wind nebula
We present a radio continuum study of the pulsar wind nebula (PWN) DA 495
(G65.7+1.2), including images of total intensity and linear polarization from
408 to 10550 MHz based on the Canadian Galactic Plane Survey and observations
with the Effelsberg 100-m Radio Telescope. Removal of flux density
contributions from a superimposed \ion{H}{2} region and from compact
extragalactic sources reveals a break in the spectrum of DA 495 at 1.3 GHz,
with a spectral index below the break and
above it (). The
spectral break is more than three times lower in frequency than the lowest
break detected in any other PWN. The break in the spectrum is likely the result
of synchrotron cooling, and DA 495, at an age of 20,000 yr, may have
evolved from an object similar to the Vela X nebula, with a similarly energetic
pulsar. We find a magnetic field of 1.3 mG inside the nebula. After
correcting for the resulting high internal rotation measure, the magnetic field
structure is quite simple, resembling the inner part of a dipole field
projected onto the plane of the sky, although a toroidal component is likely
also present. The dipole field axis, which should be parallel to the spin axis
of the putative pulsar, lies at an angle of {\sim}50\degr east of the North
Celestial Pole and is pointing away from us towards the south-west. The upper
limit for the radio surface brightness of any shell-type supernova remnant
emission around DA 495 is OAWatt
m Hz sr (assuming a radio spectral index of ), lower than the faintest shell-type remnant known to date.Comment: 25 pages, accepted by Ap
Combined cerebellar and bilateral cervical posterior spinal artery stroke demonstrated on MRI
Combined cerebellar and spinal ischemic stroke is a rare, critical condition. We report a patient with combined cerebellar and bilateral posterolateral cervical spinal cord infarction due to bilateral stenosis of the vertebral arteries. MRI is the method of choice for imaging this condition; diffusion-weighted imaging of the spinal cord gives reliable results
A Sino-German 6\ cm polarization survey of the Galactic plane VI. Discovery of supernova remnants G178.2-4.2 and G25.1-2.3
Supernova remnants (SNRs) were often discovered in radio surveys of the
Galactic plane. Because of the surface-brightness limit of previous surveys,
more faint or confused SNRs await discovery. The Sino-German 6\ cm
Galactic plane survey is a sensitive survey with the potential to detect new
low surface-brightness SNRs. We want to identify new SNRs from the 6\
cm survey map of the Galactic plane. We searched for new shell-like objects in
the 6\ cm survey maps, and studied their radio emission, polarization,
and spectra using the 6\ cm maps together with the 11\ cm and
21\ cm Effelsberg observations. Extended polarized objects with
non-thermal spectra were identified as SNRs. We have discovered two new, large,
faint SNRs, G178.2-4.2 and G25.1-2.3, both of which show shell structure.
G178.2-4.2 has a size of 72 arcmin x 62 arcmin with strongly polarized emission
being detected along its northern shell. The spectrum of G178.2-4.2 is
non-thermal, with an integrated spectral index of . Its
surface brightness is , which makes G178.2-4.2 the second faintest known Galactic SNR.
G25.1-2.3 is revealed by its strong southern shell which has a size of 80
arcmin x 30\arcmin. It has a non-thermal radio spectrum with a spectral index
of . Two new large shell-type SNRs have been detected at
6\ cm in an area of 2200 deg^2 along the the Galactic plane. This
demonstrates that more large and faint SNRs exist, but are very difficult to
detect.Comment: 8 pages, 8 figures, accepted by Astronomy and Astrophysics. For the
version with high resolution figures, please go to
http://zmtt.bao.ac.cn/6cm/papers/2newSNR.pd
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