593 research outputs found
2D non-LTE Modeling for Axi-symmetric Winds. II. A Short Characteristic Solution for Radiative Transfer in Rotating Winds
We present a new radiative transfer code for axi-symmetric stellar
atmospheres and compare test results against 1D and 2D models with and without
velocity fields. The code uses the short characteristic method with
modifications to handle axi-symmetric and non-monotonic 3D wind velocities, and
allows for distributed calculations. The formal solution along a characteristic
is evaluated with a resolution that is proportional to the velocity gradient
along the characteristic. This allows us to accurately map the variation of the
opacities and emissivities as a function of frequency and spatial coordinates,
but avoids unnecessary work in low velocity regions. We represent a
characteristic with an impact-parameter vector p (a vector that is normal to
the plane containing the characteristic and the origin) rather than the
traditional unit vector in the direction of the ray. The code calculates the
incoming intensities for the characteristics by a single latitudinal
interpolation without any further interpolation in the radiation angles. Using
this representation also provides a venue for distributed calculations since
the radiative transfer can be done independently for each p.Comment: 18 pages, 12 figures, accepted for publication in A&
Time Dependent Monte Carlo Radiative Transfer Calculations For 3-Dimensional Supernova Spectra, Lightcurves, and Polarization
We discuss Monte-Carlo techniques for addressing the 3-dimensional
time-dependent radiative transfer problem in rapidly expanding supernova
atmospheres. The transfer code SEDONA has been developed to calculate the
lightcurves, spectra, and polarization of aspherical supernova models. From the
onset of free-expansion in the supernova ejecta, SEDONA solves the radiative
transfer problem self-consistently, including a detailed treatment of gamma-ray
transfer from radioactive decay and with a radiative equilibrium solution of
the temperature structure. Line fluorescence processes can also be treated
directly. No free parameters need be adjusted in the radiative transfer
calculation, providing a direct link between multi-dimensional hydrodynamical
explosion models and observations. We describe the computational techniques
applied in SEDONA, and verify the code by comparison to existing calculations.
We find that convergence of the Monte Carlo method is rapid and stable even for
complicated multi-dimensional configurations. We also investigate the accuracy
of a few commonly applied approximations in supernova transfer, namely the
stationarity approximation and the two-level atom expansion opacity formalism.Comment: 16 pages, ApJ accepte
XMM-Newton observations of the nitrogen-rich Wolf-Rayet star WR 1
We present XMM-Newton results for the X-ray spectrum from the N-richWolf-Rayet (WR) star WR1. The EPIC instrument was used to obtain a medium-resolution spectrum. The following features characterize this spectrum: ( a) significant emission "bumps" appear that are coincident with the wavelengths of typical strong lines, such as MgXI, SiXIII, and SXV; (b) little emission is detected above 4 keV, in contrast to recent reports of a hard component in the stars WR 6 and WR 110 which are of similar subtype; and ( c) evidence for sulfur K-edge absorption at about 2.6 keV, which could only arise from absorption of X- rays by the ambient stellar wind. The lack of hard emission in our dataset is suggestive that WR 1 may truly be a single star, thus representing the first detailed X-ray spectrum that isolates the WR wind alone ( in contrast to colliding wind zones). Although the properties of the S-edge are not well- constrained by our data, it does appear to be real, and its detection indicates that at least some of the hot gas in WR 1 must reside interior to the radius of optical depth unity for the total absorptive opacity at the energy of the edge
Bioplastic (PHBV) addition to soil alters microbial community structure and negatively affects plant-microbial metabolic functioning in maize
Near-Infrared Spectroscopy of Low Mass X-ray Binaries : Accretion Disk Contamination and Compact Object Mass Determination in V404 Cyg and Cen X-4
We present near-infrared (NIR) broadband (0.80--2.42 m) spectroscopy of
two low mass X-ray binaries: V404 Cyg and Cen X-4. One important parameter
required in the determination of the mass of the compact objects in these
systems is the binary inclination. We can determine the inclination by modeling
the ellipsoidal modulations of the Roche-lobe filling donor star, but the
contamination of the donor star light from other components of the binary,
particularly the accretion disk, must be taken into account. To this end, we
determined the donor star contribution to the infrared flux by comparing the
spectra of V404 Cyg and Cen X-4 to those of various field K-stars of known
spectral type. For V404 Cyg, we determined that the donor star has a spectral
type of K3 III. We determined the fractional donor contribution to the NIR flux
in the H- and K-bands as and , respectively. We
remodeled the H-band light curve from \citet{sanwal1996} after correcting for
the donor star contribution to obtain a new value for the binary inclination.
From this, we determined the mass of the black hole in V404 Cyg to be . We performed the same spectral analysis for Cen X-4
and found the spectral type of the donor star to be in the range K5 -- M1V. The
donor star contribution in Cen X-4 is in the H-band while in the
K-band, the accretion disk can contribute up to 10% of the infrared flux. We
remodeled the H-band light curve from \citet{shahbaz1993}, again correcting for
the fractional contribution of the donor star to obtain the inclination. From
this, we determined the mass of the neutron star as . However, the masses obtained for both systems should
be viewed with some caution since contemporaneous light curve and spectral data
are required to obtain definitive masses
The conspicuous absence of X-ray emission from carbon-enriched Wolf-Rayet stars
The carbon-rich WC5 star WR 114 was not detected during a 15.9 ksec XMM-Newton observation, implying an upper limit to the X- ray luminosity of L-X less than or similar to 2.5 x 10(30) erg s(-1) and to the X-ray to bolometric luminosity ratio of L- X/L(bo)l less than or similar to 4 x 10(-9). This confirms indications from earlier less sensitive measurements that there has been no convincing X-ray detection of any single WC star. This lack of detections is reinforced by XMM-Newton and Chandra observations of WC stars. Thus the conclusion has to be drawn that the stars with radiatively-driven stellar winds of this particular class are insignificant X-ray sources. We attribute this to photoelectronic absorption by the stellar wind. The high opacity of the metal-rich and dense winds from WC stars puts the radius of optical depth unity at hundreds or thousands of stellar radii for much of the X-ray band. We believe that the essential absence of hot plasma so far out in the wind exacerbated by the large distances and correspondingly high ISM column densities makes the WC stars too faint to be detectable with current technology. The result also applies to many WC stars in binary systems, of which only about 20% are identified X-ray sources, presumably due to colliding winds
Development of the multidimensional peer victimization scale–revised (MPVS-R) and the multidimensional peer bullying scale (MPVS-RB)
Peer victimization is a frequent occurrence for many adolescents; however, some of the psychometric properties of self-report scales assessing these experiences remain unclear. Furthermore, with an increase in access to technology, electronic aggression should also be considered. The study examined the psychometric properties of the Multidimensional Peer Victimization Scale (MPVS, Mynard & Joseph, 2000), and developed versions to include the assessment of electronic aggression according to whether the adolescent was the target or perpetrator of peer victimization. Three hundred and 71 (191 girls and 180 boys Mage = 13 years 4 months, SDage= 1 year 2 months) adolescents in the UK completed the MPVS including 5 newly developed items assessing electronic aggression, a version of the MPVS designed to assess victimization perpetration, and a measure of self-esteem. Confirmatory factor analyses yielded a five-factor structure comprising: Physical, social manipulation, verbal, attacks on property, and electronic for both scales. Convergent validity was established through negative associations between the victimization scales and self-esteem. Sex differences also emerged. One revised scale and one new scale are subsequently proposed: The Multidimensional Peer Victimization Scale - Revised (MPVS-R) and the Multidimensional Peer Bullying Scale (MPVS-RB)
Detection of broad functional gag-specific CD4+ T cell responses in HIV-1-infected subjects following therapeutic immunization with rMVA expressing an HIV-1 gag immunogen
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