2,617 research outputs found
Phase-dependent X-ray observations of the beta Lyrae system: No eclipse in the soft band
We report on observations of the eclipsing and interacting binary beta Lyrae
from the Suzaku X-ray telescope. This system involves an early B star embedded
in an optically and geometrically thick disk that is siphoning atmospheric
gases from a less massive late B II companion. Motivated by an unpublished
X-ray spectrum from the Einstein X-ray telescope suggesting unusually hard
emission, we obtained time with Suzaku for pointings at three different phases
within a single orbit. From the XIS detectors, the softer X-ray emission
appears typical of an early-type star. What is surprising is the remarkably
unchanging character of this emission, both in luminosity and in spectral
shape, despite the highly asymmetric geometry of the system. We see no eclipse
effect below 10 keV. The constancy of the soft emission is plausibly related to
the wind of the embedded B star and Thomson scattering of X-rays in the system,
although it might be due to extended shock structures arising near the
accretion disk as a result of the unusually high mass-transfer rate. There is
some evidence from the PIN instrument for hard emission in the 10-60 keV range.
Follow-up observations with the RXTE satellite will confirm this preliminary
detection.Comment: to appear in A&A Letter
The Correlation between X-Ray Line Ionization and Optical Spectral Types of the OB Stars
Marked correlations are reported between the ionization of the X-ray line
spectra of normal OB stars, as observed by the Chandra X-Ray Observatory, and
their optical spectral types. These correlations include the progressive
weakening of the higher ionization relative to the lower ionization X-ray lines
with advancing spectral type, and the similarly decreasing intensity ratios of
the H-like to He-like lines of the alpha ions. These relationships were not
predicted by models, nor have they been clearly evident in astrophysical
studies of a few objects; rather, they have emerged from morphological analysis
of an adequate (albeit still small) sample, from which known peculiar objects
such as magnetic stars and very rapid rotators have been isolated to reveal the
normal trends. This process is analogous to that which first demonstrated the
strong relationships between the UV wind profiles and the optical spectral
types of normal OB stars, which likely bear a physical as well as a historical
connection to the present X-ray results. Since the optical spectral types are
calibrated in terms of fundamental stellar parameters, it follows that the
winds and X-ray spectra are determined by the latter. These observations
provide strong guidance for further astrophysical modeling of these phenomena.Comment: 19 pages, 7 figures, 2 tables; ApJ accepte
Complex microwave conductivity of PrCeCuO thin films using a cavity perturbation method
We report a study of the microwave conductivity of electron-doped
PrCeCuO superconducting thin films using a
cavity perturbation technique. The relative frequency shifts obtained for the
samples placed at a maximum electric field location in the cavity are treated
using the high conductivity limit presented recently by Peligrad
Using two resonance modes, TE (16.5 GHz) and TE
(13 GHz) of the same cavity, only one adjustable parameter is needed
to link the frequency shifts of an empty cavity to the ones of a cavity loaded
with a perfect conductor. Moreover, by studying different sample
configurations, we can relate the substrate effects on the frequency shifts to
a scaling factor. These procedures allow us to extract the temperature
dependence of the complex penetration depth and the complex microwave
conductivity of two films with different quality. Our data confirm that all the
physical properties of the superconducting state are consistent with an order
parameter with lines of nodes. Moreover, we demonstrate the high sensitivity of
these properties on the quality of the films
Mode Bifurcation and Fold Points of Complex Dispersion Curves for the Metamaterial Goubau Line
In this paper the complex dispersion curves of the four lowest-order
transverse magnetic modes of a dielectric Goubau line () are
compared with those of a dispersive metamaterial Goubau line. The vastly
different dispersion curve structure for the metamaterial Goubau line is
characterized by unusual features such as mode bifurcation, complex fold
points, both proper and improper complex modes, and merging of complex and real
modes
Gravity Drip Irrigation System
A gravity-fed, drip irrigation system prototype has been developed for use in raised garden beds and other small-scale crop irrigation applications. The original developer of the prototype and sponsor of the project, Tina Creel, is seeking to refine it into a functional consumer product through the implementation of technical engineering and standard manufacturing processes. The scope of the project includes the tank support system and supply of water to the sponsors current piping subsystem. It does not include any modifications to the bed, piping system or water tank itself. The target specifications of the system include its load capacity, dimensions, susceptibility to leakage, durability, and assembly time. Numerous potential design concepts were ideated and compared so that a design direction could be established. This document serves as a complete outline of the project and includes the initial design/research proceedings, concept design process, explanation of the chosen design, and the manufacturing process as well as the testing results for the prototype design
Signature of wide-spread clumping in B supergiant winds
We seek to establish additional observational signatures of the effects of
clumping in OB star winds. The action of clumping on strategic wind-formed
spectral lines is tested to steer the development of models for clumped winds
and thus improve the reliability of mass-loss determinations for massive
stars.The SiIV 1400 resonance line doublets of B0 to B5 supergiants are
analysed using empirical line-synthesis models. The focus is on decoding
information on wind clumping from measurements of ratios of the radial optical
depths (tau_(rad)(w)) of the red and blue components of the SiIV doublet. We
exploit in particular the fact that the two doublet components are decoupled
and formed independently for targets with relatively low wind terminal
velocities. Line-synthesis analyses reveal that the mean ratio of tau_(rad)(w)
of the blue to red SiIV components are rarely close to the canonical value of ~
2 (expected from atomic constants), and spread instead over a range of values
between ~1 and 2. These results are interpreted in terms of a photosphere that
is partially obscured by optically thick structures in the outflowing gas.The
spectroscopic signatures established in this study demonstrate the wide-spread
existence of wind clumping in B supergiants. The additional information in
unsaturated doublet profiles provides a means to quantify the porosity of the
winds.Comment: Accepted for publication in A&A Letter
X-ray emission from the double-binary OB-star system QZ Car (HD 93206)
X-ray observations of the double-binary OB-star system QZ Car (HD 93206)
obtained with the Chandra X-ray Observatory over a period of roughly 2 years
are presented. The orbit of systems A (O9.7 I+b2 v, PA = 21 d) and B (O8 III+o9
v, PB = 6 d) are reasonably well sampled by the observations, allowing the
origin of the X-ray emission to be examined in detail. The X-ray spectra can be
well fitted by an attenuated three temperature thermal plasma model,
characterised by cool, moderate, and hot plasma components at kT ~ 0.2, 0.7,
and 2 keV, respectively, and a circumstellar absorption of ~ 0.2 x 10^22 cm-2.
Although the hot plasma component could be indicating the presence of wind-wind
collision shocks in the system, the model fluxes calculated from spectral fits,
with an average value of ~ 7 x 10^-13 erg s-1 cm-2, do not show a clear
correlation with the orbits of the two constituent binaries. A semi-analytical
model of QZ Car reveals that a stable momentum balance may not be established
in either system A or B. Yet, despite this, system B is expected to produce an
observed X-ray flux well in excess of the observations. If one considers the
wind of the O8 III star to be disrupted by mass transfer the model and
observations are in far better agreement, which lends support to the previous
suggestion of mass-transfer in the O8 III + o9 v binary. We conclude that the
X-ray emission from QZ Car can be reasonably well accounted for by a
combination of contributions mainly from the single stars and the mutual
wind-wind collision between systems A and B.Comment: 11 pages, 7 figures. Accepted for the ApJS Special Issue on the
Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011.
All 16 CCCP Special Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
leas
Ab-initio GMR and current-induced torques in Au/Cr multilayers
We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and
current-induced-torques (CITs) in Cr/Au multilayers that is based on
non-equilibrium Green's functions and spin density functional theory. We find
substantial GMR due primarily to a spin-dependent resonance centered at the
Cr/Au interface and predict that the CITs are strong enough to switch the
antiferromagnetic order parameter at current-densities times smaller
than typical ferromagnetic metal circuit switching densities.Comment: 8 pages, 6 figure
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