247 research outputs found
High Resolution X-ray Spectra of the Brightest OB Stars in the Cygnus OB2 Association
The Cygnus OB2 Association contains some of the most luminous OB stars in our
Galaxy, the brightest of which are also among the most luminous in X-rays. We
have obtained a Chandra High Energy Transmission Grating Spectrometer (HETGS)
observation centered on Cyg OB2 No. 8a, the most luminous X-ray source in the
Association. Although our analysis will focus on the X-ray properties of Cyg
OB2 No. 8a, we also present limited analyses of three other OB stars (Cyg OB2
Nos. 5, 9, and 12). Applying standard diagnostic techniques as used in previous
studies of early-type stars, we find that the X-ray properties of Cyg OB2 No.
8a are very similar to those of other OB stars that have been observed using
high-resolution X-ray spectroscopy. From analyses of the He-like ion "fir"
emission lines, we derive radial distances of the He-like line emission sources
and find these fir-inferred radii are consistent with their corresponding X-ray
continuum optical depth unity radii. Contrary to other O-star results, the
emission lines of Cyg OB2 No. 8a show a large range in line centroid shifts
(roughly -800 to +250 km/s). We discuss the implications of our results in
light of the fact that Cyg OB2 No. 8a is a member of a rather tight stellar
cluster, and shocks could arise at interfaces with the winds of these other
stars.Comment: 36 pages (including 4 tables and 12 figures). LaTeX. Submitted to Ap
Inverse Compton Scattering as the Source of Diffuse EUV Emission in the Coma Cluster of Galaxies
We have examined the hypothesis that the majority of the diffuse EUV flux in
the Coma cluster is due to inverse Compton scattering of low energy cosmic ray
electrons (0.16 < epsilon < 0.31 GeV) against the 3K black-body background. We
present data on the two-dimensional spatial distribution of the EUV flux and
show that these data provide strong support for a non-thermal origin for the
EUV flux. However, we show that this emission cannot be produced by an
extrapolation to lower energies of the observed synchrotron radio emitting
electrons and an additional component of low energy cosmic ray electrons is
required.Comment: 11 pages, 5 figure
X-ray Point Sources in The Central Region of M31 as seen by Chandra
We report on \chandra observations of the central region of M31. By combining
eight \chandra ACIS-I observations taken between 1999 and 2001, we have
identified 204 X-ray sources within the central region of
M31, with a detection limit of \lum. Of these 204 sources,
22 are identified with globular clusters, 2 with supernova remnants, 9 with
planetary nebula, and 9 as supersoft sources. By comparing individual images,
about 50% of the sources are variable on time scales of months. We also found
13 transients, with light curves showing a variety of shapes. We also extracted
the energy spectra of the 20 brightest sources; they can be well fit by a
single power-law with a mean photon index of 1.8. The spectral shapes of 12
sources are shown to be variable, suggesting that they went through state
changes. The luminosity function of all the point sources is consistent with
previous observations (a broken power-law with a luminosity break at
\lum). However, when the X-ray sources in different regions
are considered separately, different luminosity functions are obtained. This
indicates that the star-formation history might be different in different
regions.Comment: 42 pages, 9 figures, ApJ, accepted, Higher-resolution figures
available on reques
X-ray Observations of the New Pulsar--Supernova Remnant System PSR J1119-6127 and SNR G292.2-0.5
PSR J1119-6127 is a recently discovered 1700-year-old radio pulsar that has a
very high inferred surface dipolar magnetic field. We present a detailed
analysis of a pointed ASCA observation and archival ROSAT data of J1119-6127
and its surroundings. Both data sets reveal extended emission coincident with
the newly-discovered radio supernova remnant G292.2-0.5, reported in a
companion paper by Crawford et al. (astro-ph/0012287).. A hard point source,
offset ~1.5' from the position of the radio pulsar, is seen with the ASCA GIS.
No pulsations are detected at the radio period with a pulsed fraction upper
limit of 61% (95% confidence). The limited statistics prevent a detailed
spectral analysis, although a power-law model with photon index (Gamma=~1-2)
describes the data well. Both the spectral model and derived X-ray luminosity
are consistent with those measured for other young radio pulsars, although the
spatial offset renders an identification of the source as the X-ray counterpart
of the pulsar uncertain.Comment: Accepted by ApJ; 12 Pages in emulated ApJ format with embedded tables
and color figure
Seal of transparency heritage in the CISMeF quality-controlled health gateway
BACKGROUND: It is an absolute necessity to continually assess the quality of health information on the Internet. Quality-controlled subject gateways are Internet services which apply a selected set of targeted measures to support systematic resource discovery. METHODS: The CISMeF health gateway became a contributor to the MedCIRCLE project to evaluate 270 health information providers. The transparency heritage consists of using the evaluation performed on providers that are referenced in the CISMeF catalogue for evaluating the documents they publish, thus passing on the transparency label from the publishers to their documents. RESULTS: Each site rated in CISMeF has a record in the CISMeF database that generates an RDF into HTML file. The search tool Doc'CISMeF displays information originating from every publisher evaluated with a specific MedCIRCLE button, which is linked to the MedCIRCLE central repository. Starting with 270 websites, this trust heritage has led to 6,480 evaluated resources in CISMeF (49.8% of the 13,012 resources included in CISMeF). CONCLUSION: With the MedCIRCLE project and transparency heritage, CISMeF became an explicit third party
A dependent nominal type theory
Nominal abstract syntax is an approach to representing names and binding
pioneered by Gabbay and Pitts. So far nominal techniques have mostly been
studied using classical logic or model theory, not type theory. Nominal
extensions to simple, dependent and ML-like polymorphic languages have been
studied, but decidability and normalization results have only been established
for simple nominal type theories. We present a LF-style dependent type theory
extended with name-abstraction types, prove soundness and decidability of
beta-eta-equivalence checking, discuss adequacy and canonical forms via an
example, and discuss extensions such as dependently-typed recursion and
induction principles
A Chandra Study of the Rosette Star-Forming Complex. I. The Stellar Population and Structure of the Young Open Cluster NGC 2244
We present the first high spatial resolution Chandra X-ray study of NGC 2244,
the 2 Myr old stellar cluster immersed in the Rosette Nebula. Over 900 X-ray
sources are detected; 77% have optical or FLAMINGOS near-infrared (NIR) stellar
counterparts and are mostly previously uncatalogued young stellar cluster
members. All known OB stars with spectral type earlier than B1 are detected and
the X-ray selected stellar population is estimated to be nearly complete
between 0.5 and 3 Msun. The X-ray luminosity function (XLF) ranges from
29.4<logLx<32 ergs/s in the hard (2-8keV) band. By comparing the NGC 2244 and
Orion Nebula Cluster XLFs, we estimate a total population of 2000 stars in NGC
2244. A number of further results emerge from our analysis: The XLF and the
associated K-band luminosity function indicate a normal Salpeter initial mass
function (IMF) for NGC 2244. This is inconsistent with the top-heavy IMF
reported from earlier optical studies that lacked a good census of <4Msun
stars. The spatial distribution of X-ray stars is strongly concentrated around
the central O5 star, HD 46150. The other early O star, HD 46223, has few
companions. The cluster's stellar radial density profile shows two distinctive
structures. This double structure, combined with the absence of mass
segregation, indicates that this cluster is not in dynamical equilibrium. The
spatial distribution of X-ray selected K-excess disk stars and embedded stars
is asymmetric with an apparent deficit towards the north. The fraction of
X-ray-selected cluster members with K-band excesses caused by inner
protoplanetary disks is 6%, slightly lower than the 10% disk fraction estimated
from the FLAMINGOS study based on the NIR-selected sample. This is due to the
high efficiency of X-ray surveys in locating disk-free T Tauri stars.[Abridged]Comment: Accepted for publication in ApJ (March 1, 2008 v675 issue). 61 pages,
20 figures, 7 tables. Updated a statement on NGC 2244-334 and added a
referenc
An X-ray investigation of the NGC346 field in the SMC (1) : the LBV HD5980 and the NGC346 cluster
We present results from a Chandra observation of the NGC346 cluster. This
cluster contains numerous massive stars and is responsible for the ionization
of N66, the most luminous HII region and the largest star formation region in
the SMC. In this first paper, we will focus on the characteristics of the main
objects of the field. The NGC346 cluster itself shows only relatively faint
X-ray emission (with L_X^{unabs} ~ 1.5 times 10^{34} erg s^{-1}), tightly
correlated with the core of the cluster. In the field also lies HD5980, a LBV
star in a binary (or possibly a triple system) that is detected for the first
time at X-ray energies. The star is X-ray bright, with an unabsorbed luminosity
of L_X^{unabs} ~ 1.7 times 10^{34} erg s^{-1}, but needs to be monitored
further to investigate its X-ray variability over a complete 19d orbital cycle.
The high X-ray luminosity may be associated either with colliding winds in the
binary system or with the 1994 eruption. HD5980 is surrounded by a region of
diffuse X-ray emission, which is a supernova remnant. While it may be only a
chance alignment with HD5980, such a spatial coincidence may indicate that the
remnant is indeed related to this peculiar massive star.Comment: 12 pages, 9 figures (3 in jpg and 6 in ps), to be published in Ap
First Midwives in the Town of Bjelovar, Croatia 1756-1856
Prve izučene (aprobirane) primalje dolaze u novoosnovani Bjelovar, jako vojno središte Vojne krajine početkom druge polovice XVIII. stoljeća zajedno s vojnim liječnicima, kirurzima i ljekarnicima, a većina njih je germanskoga podrijetla. U do sada neistraženom arhivskom materijalu za razdoblje 1756.-1856. pronađeni su podaci o 23 izučene primalje, od kojih je 14 bilo pukovnijskih i 9 gradskih primalja. Visok perinatalni pomor djece i majki i kriminalni pobačaji karakteristike su toga razdoblja. Uz model domicilnoga primaljstva: skrb za trudnice, rodilje, babinjače, novorođenčad i dojenčad, primalje u teškim porodima obavljaju krštenje iz nužde ugroženoj novorođenčadi ili su pak krsne kume zdravoj dojenčadi. Premda je u samom gradu Bjelovaru ustrojeno stručno primaljstvo, u okolici grada i dalje se porodi obavljaju bez stručne pomoći. Za razliku od većine tadašnjih gradova kontinentalne Hrvatske, pa i Dalmacije, u Bjelovaru postoji kontinuirano izučeno primaljstvo i zaštita materinstva od polovice XVIII. stoljeća.The first trained (certified) midwives came to the newly founded town of Bjelovar, a strong military centre of Vojna Krajina (Croatian province bordering Ottoman Empire), at the beginning of the 1750s, along with army physicians, surgeons, and pharmacists. Most were of German origin. The archival material investigated for the period 1756-1856 speaks of 23 certified midwives, of whom 14 were regimental and nine municipal. This period was characterised by high neonatal and maternal mortality rates and criminal abortions. Within the scope of the domiciliary midwifery model that included care for pregnant women, parturient women, neonates, and infants, midwives used to act as godmothers to newborns at risk, in periculo, or to healthy newborns. Although Bjelovar had professional midwifery service, the practice of unassisted childbirths continued in the town surroundings. Unlike other inland and coastal (Dalmatian) towns of the time, Bjelovar has had a continuous tradition of training midwives and maternal health care since the 1750s
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