177 research outputs found
A needlet ILC analysis of WMAP 9-year polarisation data: CMB polarisation power spectra
We estimate Cosmic Microwave Background (CMB) polarisation power spectra, and
temperature-polarisation cross-spectra, from the 9-year data of the Wilkinson
Microwave Anisotropy Probe (WMAP). Foreground cleaning is implemented using
minimum variance linear combinations of the coefficients of needlet
decompositions of sky maps for all WMAP channels, to produce maps for CMB
temperature anisotropies (T-mode) and polarisation (E-mode and B-mode), for 9
different years of observation. The final power spectra are computed from
averages of all possible cross-year power spectra obtained using
foreground-cleaned maps for the different years. Our analysis technique yields
a measurement of the EE spectrum that is in excellent agreement with
theoretical expectations from the current cosmological model. By comparison,
the publicly available WMAP EE power spectrum is higher on average (and
significantly higher than the predicted EE spectrum from the current best fit)
at scales larger than about a degree, an excess that is not confirmed by our
analysis.Comment: 13 pages, 7 figures, Significantly changed version accepted for
publication in MNRA
Equilibrium and equivariant triangulations of some small covers with minimum number of vertices
Small covers were introduced by Davis and Januszkiewicz in 1991. We introduce
the notion of equilibrium triangulations for small covers. We study equilibrium
and vertex minimal -equivariant triangulations of
-dimensional small covers. We discuss vertex minimal equilibrium
triangulations of ,
and a nontrivial bundle over . We construct some nice
equilibrium triangulations of the real projective space with
vertices. The main tool is the theory of small covers.Comment: 15 pages, 10 figures, minor changes, accepted for publication in
Journal of the Ramanujan Mathematical Societ
Statistical Isotropy of CMB Polarization Maps
We formulate statistical isotropy of CMB anisotropy maps in its most general
form. We also present a fast and orientation independent statistical method to
determine deviations from statistical isotropy in CMB polarization maps.
Importance of having statistical tests of departures from SI for CMB
polarization maps lies not only in interesting theoretical motivations but also
in testing cleaned CMB polarization maps for observational artifacts such as
residuals from polarized foreground emission. We propose a generalization of
the Bipolar Power Spectrum (BiPS) to polarization maps. Application to the
observed CMB polarization maps will be soon possible after the release of WMAP
three year data. As a demonstration we show that for E-polarization this test
can detect breakdown of statistical isotropy due to polarized synchrotron
foreground.Comment: 6 pages, 2 figures, Conclusions & results unchanged; Extension to
cutsky included (discussion & references added); Matches version accepted to
Phys. Rev. D Rapid Com
Radius measurement in binary stars: simulations of intensity interferometry
Mass and radius measurements of stars are important inputs for models of stellar structure. Binary stars are of particular interest in this regard, because astrometry and spectroscopy of a binary together provide the masses of both stars as well as the distance to the system, while interferometry can both improve the astrometry and measure the radii of the stars. In this work, we simulate parameter recovery from intensity interferometry, especially the challenge of disentangling the radii of two stars from their combined interferometric signal. Two approaches are considered: separation of the visibility contributions of each star with the help of differing brightness ratios at different wavelengths, and direct fitting of the intensity correlation to a multiparameter model. Full image reconstructions is not attempted. Measurement of angular radii, angular separation, and first-order limb-darkening appears readily achievable for bright binary stars with current instrumentation
Reflection coefficient for superresonant scattering
We investigate superresonant scattering of acoustic disturbances from a
rotating acoustic black hole in the low frequency range. We derive an
expression for the reflection coefficient, exhibiting its frequency dependence
in this regime.Comment: 7 page
Importance of high-frequency bands for thermal dust removal in ECHO
The Indian Consortium of Cosmologists has proposed a cosmic microwave
background (CMB) space mission, Exploring Cosmic History and Origin (ECHO). A
major scientific goal of the mission is to detect the primordial B-mode signal
of CMB polarization. The detection of the targeted signal is very challenging
as it is deeply buried under the dominant astrophysical foreground emissions of
the thermal dust and the Galactic synchrotron. To facilitate the adequate
subtraction of thermal dust, the instrument design of ECHO has included nine
dust-dominated high-frequency bands over the frequency range of 220-850 GHz. In
this work, we closely reexamine the utility of the high-frequency ECHO bands in
foreground subtraction using the Needlet Internal Linear Combination component
separation method. We consider three dust models: a physical dust model, a dust
spectral energy distribution (SED) with a single modified black body (MBB)
emission law and a multilayer dust model with frequency-frequency
decorrelation. We consider eleven ECHO bands in the 28-190 GHz range as our
baseline configuration and investigate the changes in the level foreground and
noise residuals as subsequent dust-dominated high-frequency bands are added. We
find that adding the high-frequency bands leads to a consistent decrease in the
level of residual foreground and noise, and the sensitivity of r measurement
improves. Most of the reduction in both residual levels and enhancement in the
sensitivity is achieved in the 28-600 GHz frequency range. Negligible change in
residual levels is seen by extending the frequency range from 600 GHz to 850
GHz.Comment: 8 figures; changed the title of the paper, made revisions in abstract
and text, result and conclusion unchange
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