1,340 research outputs found
Redshifted emission lines and radiative recombination continuum from the Wolf-Rayet binary theta Muscae: evidence for a triplet system?
We present XMM-Newton observations of the WC binary Theta Muscae (WR 48), the
second brightest Wolf-Rayet binary in optical wavelengths. The system consists
of a short-period (19.1375 days) WC5/WC6 + O6/O7V binary and possibly has an
additional O supergiant companion (O9.5/B0Iab) which is optically identified at
a separation of ~46 mas. Strong emission lines from highly ionized ions of C,
O, Ne, Mg, Si, S, Ar, Ca and Fe are detected. The spectra are fitted by a
multi-temperature thin-thermal plasma model with an interstellar absorption N_H
= 2--3*10**21 cm**-2. Lack of nitrogen line indicates that the abundance of
carbon is at least an order of magnitude larger than that of nitrogen. A
Doppler shift of ~630 km/s is detected for the OVIII line, while similar shifts
are obtained from the other lines. The reddening strongly suggests that the
emission lines originated from the wind-wind shock zone, where the average
velocity is ~600 km/s. The red-shift motion is inconsistent with a scenario in
which the X-rays originate from the wind-wind collision zone in the
short-period binary, and would be evidence supporting the widely separated O
supergiant as a companion. This may make up the collision zone be lying behind
the short-period binary. In addition to the emission lines, we also detected
the RRC (radiative recombination continuum) structure from carbon around 0.49
keV. This implies the existence of additional cooler plasma.Comment: 6 pages, 4 figures, accepted to A&
Magnetosphere-Ionosphere Coupling Through E-region Turbulence 1: Energy Budget
During periods of intense geomagnetic activity, strong electric fields and
currents penetrate from the magnetosphere into high-latitude ionosphere where
they dissipate energy, form electrojets, and excite plasma instabilities in the
E-region ionosphere. These instabilities give rise to plasma turbulence which
induces non-linear currents and strong anomalous electron heating (AEH) as
observed by radars. These two effects can increase the global ionospheric
conductances. This paper analyzes the energy budget in the electrojet, while
the companion paper applies this analysis to develop a model of anomalous
conductivity and frictional heating useful in large-scale simulations and
models of the geospace environment. Employing first principles, this paper
proves for the general case an earlier conjecture that the source of energy for
plasma turbulence and anomalous heating equals the work by external field on
the non-linear current. Using a two-fluid model of an arbitrarily magnetized
plasma and the quasilinear approximation, this paper describes the energy
conversion process, calculates the partial sources of anomalous heating, and
reconciles the apparent contradiction between the inherently 2-D non-linear
current and the 3-D nature of AEH.Comment: 13 pages, 1 figure; 1st of two companion paper
Mass-Loss Rate Determination for the Massive Binary V444 Cyg using 3-D Monte-Carlo Simulations of Line and Polarization Variability
A newly developed 3-D Monte Carlo model is used, in conjunction with a
multi-line non-LTE radiative transfer model, to determine the mass-loss rate of
the Wolf-Rayet (W-R) star in the massive binary \object{V444 Cyg} (WN5+O6).
This independent estimate of mass-loss rate is attained by fitting the observed
\HeI (5876) \AA and \HeII (5412) \AA line profiles, and the continuum light
curves of three Stokes parameters ((I, Q, U)) in the (V) band simultaneously.
The high accuracy of our determination arises from the use of many
observational constraints, and the sensitivity of the continuum polarization to
the mass-loss rate. Our best fit model suggests that the mass-loss rate of the
system is (\dot{M}_{\WR}=0.6(\pm 0.2) \times 10^{-5} M_{\sun} \mathrm{yr}^{-1}
), and is independent of the assumed distance to \object{V444 Cyg}. The fits
did not allow a unique value for the radius of the W-R star to be derived. The
range of the volume filling factor for the W-R star atmosphere is estimated to
be in the range of 0.050 (for R_{\WR}=5.0 R_{\sun}) to 0.075 (for
R_{\WR}=2.5 R_{\sun}). We also found that the blue-side of \HeI (5876 ) \AA
and \HeII (5412) \AA lines at phase 0.8 is relatively unaffected by the
emission from the wind-wind interaction zone and the absorption by the O-star
atmosphere; hence, the profiles at this phase are suitable for spectral line
fittings using a spherical radiative transfer model.Comment: 18 pages, 17 figures: Accepeted for publication in A&
Individual variation in levels of haptoglobin-related protein in children from Gabon
Background: Haptoglobin related protein (Hpr) is a key component of trypanosome lytic factors (TLF), a subset of highdensity lipoproteins (HDL) that form the first line of human defence against African trypanosomes. Hpr, like haptoglobin (Hp) can bind to hemoglobin (Hb) and it is the Hpr-Hb complexes which bind to these parasites allowing uptake of TLF. This unique form of innate immunity is primate-specific. To date, there have been no population studies of plasma levels of Hpr, particularly in relation to hemolysis and a high prevalence of ahaptoglobinemia as found in malaria endemic areas. Methods and Principal Findings: We developed a specific enzyme-linked immunosorbent assay to measure levels of plasma Hpr in Gabonese children sampled during a period of seasonal malaria transmission when acute phase responses (APR), malaria infection and associated hemolysis were prevalent. Median Hpr concentration was 0.28 mg/ml (range 0.03-1.1). This was 5-fold higher than that found in Caucasian children (0.049 mg/ml, range 0.002-0.26) with no evidence of an APR. A general linear model was used to investigate associations between Hpr levels, host polymorphisms, parasitological factors and the acute phase proteins, Hp, C-reactive protein (CRP) and albumin. Levels of Hpr were associated with Hp genotype, decreased with age and were higher in females. Hpr concentration was strongly correlated with that of Hp, but not CRP
X-ray Emission from Nitrogen-Type Wolf-Rayet Stars
We summarize new X-ray detections of four nitrogen-type Wolf-Rayet (WR) stars
obtained in a limited survey aimed at establishing the X-ray properties of WN
stars across their full range of spectral subtypes. None of the detected stars
is so far known to be a close binary. We report Chandra detections of WR 2
(WN2), WR 18 (WN4), and WR 134 (WN6), and an XMM-Newton detection of WR79a
(WN9ha). These observations clearly demonstrate that both WNE and WNL stars are
X-ray sources. We also discuss Chandra archive detections of the WN6h stars WR
20b, WR 24, and WR 136 and ROSAT non-detections of WR 16 (WN8h) and WR 78
(WN7h). The X-ray spectra of all WN detections show prominent emission lines
and an admixture of cool (kT 2 keV) plasma. The hotter
plasma is not predicted by radiative wind shock models and other as yet
unidentified mechanisms are at work. Most stars show X-ray absorption in excess
of that expected from visual extinction (Av), likely due to their strong winds
or cold circumstellar gas. Existing data suggest a falloff in X-ray luminosity
toward later WN7-9 subtypes, which have higher Lbol but slower, denser winds
than WN2-6 stars. This provides a clue that wind properties may be a more
crucial factor in determining emergent X-ray emission levels than bolometric
luminosity.Comment: 42 pages, 5 tables, 10 figure
Electronic Structure and Valence Band Spectra of Bi4Ti3O12
The x-ray photoelectron valence band spectrum and x-ray emission valence-band
spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented
(analyzed in the common energy scale) and interpreted on the basis of a
band-structure calculation for an idealized I4/mmm structure of this material.Comment: 6 pages + 7 PostScript figures, RevTex3.0, to be published in
Phys.Rev.B52 (Oct.95). Figures also available via anonymous ftp at
ftp://ftp.physik.uni-osnabrueck.de/pub/apostnik/BiTiO
Two new rapid SNP-typing methods for classifying Mycobacterium tuberculosis complex into the main phylogenetic lineages
There is increasing evidence that strain variation in Mycobacterium tuberculosis complex (MTBC) might influence the outcome of tuberculosis infection and disease. To assess genotype-phenotype associations, phylogenetically robust molecular markers and appropriate genotyping tools are required. Most current genotyping methods for MTBC are based on mobile or repetitive DNA elements. Because these elements are prone to convergent evolution, the corresponding genotyping techniques are suboptimal for phylogenetic studies and strain classification. By contrast, single nucleotide polymorphisms (SNP) are ideal markers for classifying MTBC into phylogenetic lineages, as they exhibit very low degrees of homoplasy. In this study, we developed two complementary SNP-based genotyping methods to classify strains into the six main human-associated lineages of MTBC, the 'Beijing' sublineage, and the clade comprising Mycobacterium bovis and Mycobacterium caprae. Phylogenetically informative SNPs were obtained from 22 MTBC whole-genome sequences. The first assay, referred to as MOL-PCR, is a ligation-dependent PCR with signal detection by fluorescent microspheres and a Luminex flow cytometer, which simultaneously interrogates eight SNPs. The second assay is based on six individual TaqMan real-time PCR assays for singleplex SNP-typing. We compared MOL-PCR and TaqMan results in two panels of clinical MTBC isolates. Both methods agreed fully when assigning 36 well-characterized strains into the main phylogenetic lineages. The sensitivity in allele-calling was 98.6% and 98.8% for MOL-PCR and TaqMan, respectively. Typing of an additional panel of 78 unknown clinical isolates revealed 99.2% and 100% sensitivity in allele-calling, respectively, and 100% agreement in lineage assignment between both methods. While MOL-PCR and TaqMan are both highly sensitive and specific, MOL-PCR is ideal for classification of isolates with no previous information, whereas TaqMan is faster for confirmation. Furthermore, both methods are rapid, flexible and comparably inexpensive
Initiator Elements Function to Determine the Activity State of BX-C Enhancers
A >300 kb cis-regulatory region is required for the proper expression of the three bithorax complex (BX-C) homeotic genes. Based on genetic and transgenic analysis, a model has been proposed in which the numerous BX-C cis-regulatory elements are spatially restricted through the activation or repression of parasegment-specific chromatin domains. Particular early embryonic enhancers, called initiators, have been proposed to control this complex process. Here, in order to better understand the process of domain activation, we have undertaken a systematic in situ dissection of the iab-6 cis-regulatory domain using a new method, called InSIRT. Using this method, we create and genetically characterize mutations affecting iab-6 function, including mutations specifically modifying the iab-6 initiator. Through our mutagenesis of the iab-6 initiator, we provide strong evidence that initiators function not to directly control homeotic gene expression but rather as domain control centers to determine the activity state of the enhancers and silencers within a cis-regulatory domain
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