11,573 research outputs found
The use of Planetary Nebulae precursors in the study of Diffuse Interstellar Bands
We present the first results of a systematic search for Diffuse Interstellar
Bands in a carefully selected sample of post-AGB stars observed with high
resolution optical spectroscopy. These stars are shown to be ideal targets to
study this old, intriguing astrophysical problem. Our results suggest that the
carrier(s) of these bands may not be present in the circumstellar environments
of these evolved stars. The implications of the results obtained on the
identification of the still unknown carrier(s) are discussed.Comment: 4 pages, 2 figures, proceedings of the conference 'Planetary Nebulae
as Astrophysical Tools', held in Gdansk, Poland (June 28 - July 2, 2005
Topological Vertex, String Amplitudes and Spectral Functions of Hyperbolic Geometry
We discuss the homological aspects of the connection between quantum string
generating function and the formal power series associated to the dimensions of
chains and homologies of suitable Lie algebras. Our analysis can be considered
as a new straightforward application of the machinery of modular forms and
spectral functions (with values in the congruence subgroup of ) to the partition functions of Lagrangian branes, refined vertex and open
string partition functions, represented by means of formal power series that
encode Lie algebra properties. The common feature in our examples lies in the
modular properties of the characters of certain representations of the
pertinent affine Lie algebras and in the role of Selberg-type spectral
functions of an hyperbolic three-geometry associated with -series in the
computation of the string amplitudes.Comment: Revised version. References added, results remain unchanged. arXiv
admin note: text overlap with arXiv:hep-th/0701156, arXiv:1105.4571,
arXiv:1206.0664 by other author
Magneto-seismology of solar atmospheric loops by means of longitudinal oscillations
There is increasingly strong observational evidence that slow magnetoacoustic
modes arise in the solar atmosphere. Solar magneto-seismology is a novel tool
to derive otherwise directly un-measurable properties of the solar atmosphere
when magnetohydrodynamic (MHD) wave theory is compared to wave observations.
Here, MHD wave theory is further developed illustrating how information about
the magnetic and density structure along coronal loops can be determined by
measuring the frequencies of the slow MHD oscillations. The application to
observations of slow magnetoacoustic waves in coronal loops is discused.Comment: 4 pages, 2 figures, to appear in Proceedings of IAU Symp 286,
Comparative Magnetic Minima, C. H. Mandrini, ed
High-Energy Proton-Proton Forward Scattering and Derivative Analyticity Relations
We present the results of several parametrizations to two different ensemble
of data on total cross sections at the highest
center-of-mass energies (including cosmic-ray information). The results are
statistically consistent with two distinct scenarios at high energies. From one
ensemble the prediction for the LHC ( TeV) is mb and from the other, mb. From each
parametrization, and making use of derivative analyticity relations (DAR), we
determine (ratio between the forward real and imaginary parts of the
elastic scattering amplitude). A discussion on the optimization of the DAR in
terms of a free parameter is also presented.In all cases good descriptions of
the experimental data are obtained.Comment: One formula added, one unit changed, small misprints corrected, final
version to be published in Brazilian Journal of Physics; 13 pages, 8 figures,
aps-revte
High-resolution X-ray Spectra Of The Symbiotic Star SS73 17
SS73 17 was an innocuous Mira-type symbiotic star until Integral and Swift
discovered its bright hard X-ray emission, adding it to the small class of
"hard X-ray emitting symbiotics." Suzaku observations in 2006 then showed it
emits three bright iron lines as well, with little to no emission in the 0.3-2
keV bandpass. We present here followup observations with the Chandra HETG and
Suzaku that confirm the earlier detection of strong emission lines of Fe Kalpha
fluorescence, Fe XXV and Fe XXVI but also show significantly more soft X-ray
emission. The high resolution spectrum also shows emission lines of other
highly ionized ions as Si XIV and possibly S XVI. In addition, a reanalysis of
the 2006 Suzaku data using the latest calibration shows that the hard (15-50
keV) X-ray emission is brighter than previously thought and remains constant in
both the 2006 and 2008 data.
The G ratio calculated from the Fe XXV lines shows that these lines are
thermal, not photoionized, in origin. With the exception of the hard X-ray
emission, the spectra from both epochs can be fit using thermal radiation
assuming a differential emission measure based on a cooling flow model combined
with a full and partial absorber. We show that acceptable fits can be obtained
for all the data in the 1-10 keV band varying only the partial absorber. Based
on the temperature and accretion rate, the thermal emission appears to be
arising from the boundary layer between the accreting white dwarf and the
accretion disk.Comment: 7 pages, 5 figures. Accepted by the Astrophysical Journa
Transverse oscillations of a multi-stranded loop
We investigate the transverse oscillations of a line-tied multi-stranded
coronal loop composed of several parallel cylindrical strands. First, the
collective fast normal modes of the loop are found with the T-matrix theory.
There is a huge quantity of normal modes with very different frequencies and a
complex structure of the associated magnetic pressure perturbation and velocity
field. The modes can be classified as bottom, middle, and top according to
their frequencies and spatial structure. Second, the temporal evolution of the
velocity and magnetic pressure perturbation after an initial disturbance are
analyzed. We find complex motions of the strands. The frequency analysis
reveals that these motions are a combination of low and high frequency modes.
The complexity of the strand motions produces a strong modulation of the whole
tube movement. We conclude that the presumed internal fine structure of a loop
influences its transverse oscillations and so its transverse dynamics cannot be
properly described by those of an equivalent monolithic loop.Comment: Accepted in Ap
Transverse oscillations of two coronal loops
We study transverse fast magnetohydrodynamic waves in a system of two coronal
loops modeled as smoothed, dense plasma cylinders in a uniform magnetic field.
The collective oscillatory properties of the system due to the interaction
between the individual loops are investigated from two points of view. Firstly,
the frequency and spatial structure of the normal modes are studied. The system
supports four trapped normal modes in which the loops move rigidly in the
transverse direction. The direction of the motions is either parallel or
perpendicular to the plane containing the axes of the loops. Two of these modes
correspond to oscillations of the loops in phase, while in the other two they
move in antiphase. Thus, these solutions are the generalization of the kink
mode of a single cylinder to the double cylinder case. Secondly, we analyze the
time-dependent problem of the excitation of the pair of tubes. We find that
depending on the shape and location of the initial disturbance, different
normal modes can be excited. The frequencies of normal modes are accurately
recovered from the numerical simulations. In some cases, because of the
simultaneous excitation of several eigenmodes, the system shows beating and the
phase lag between the loops is .Comment: Accepted for publication in The Astrophysical Journa
A conjecture on the infrared structure of the vacuum Schrodinger wave functional of QCD
The Schrodinger wave functional for the d=3+1 SU(N) vacuum is a partition
function constructed in d=4; the exponent 2S in the square of the wave
functional plays the role of a d=3 Euclidean action. We start from a
gauge-invariant conjecture for the infrared-dominant part of S, based on
dynamical generation of a gluon mass M in d=4. We argue that the exact leading
term, of O(M), in an expansion of S in inverse powers of M is a d=3
gauge-invariant mass term (gauged non-linear sigma model); the next leading
term, of O(1/M), is a conventional Yang-Mills action. The d=3 action that is
the sum of these two terms has center vortices as classical solutions. The d=3
gluon mass, which we constrain to be the same as M, and d=3 coupling are
related through the conjecture to the d=4 coupling strength, but at the same
time the dimensionless ratio in d=3 of mass to coupling squared can be
estimated from d=3 dynamics. This allows us to estimate the QCD coupling
in terms of this strictly d=3 ratio; we find a value of about
0.4, in good agreement with an earlier theoretical value but a little low
compared to QCD phenomenology. The wave functional for d=2+1 QCD has an
exponent that is a d=2 infrared-effective action having both the
gauge-invariant mass term and the field strength squared term, and so differs
from the conventional QCD action in two dimensions, which has no mass term.
This conventional d=2 QCD would lead in d=3 to confinement of all color-group
representations. But with the mass term (again leading to center vortices),
N-ality = 0 mod N representations are not confined.Comment: 15 pages, no figures, revtex
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