33,952 research outputs found
Bayesian least squares deconvolution
Aims. To develop a fully Bayesian least squares deconvolution (LSD) that can
be applied to the reliable detection of magnetic signals in noise-limited
stellar spectropolarimetric observations using multiline techniques. Methods.
We consider LSD under the Bayesian framework and we introduce a flexible
Gaussian Process (GP) prior for the LSD profile. This prior allows the result
to automatically adapt to the presence of signal. We exploit several linear
algebra identities to accelerate the calculations. The final algorithm can deal
with thousands of spectral lines in a few seconds. Results. We demonstrate the
reliability of the method with synthetic experiments and we apply it to real
spectropolarimetric observations of magnetic stars. We are able to recover the
magnetic signals using a small number of spectral lines, together with the
uncertainty at each velocity bin. This allows the user to consider if the
detected signal is reliable. The code to compute the Bayesian LSD profile is
freely available.Comment: 8 pages, accepted for publication in A&
An approach for the detection of point-sources in very high resolution microwave maps
This paper deals with the detection problem of extragalactic point-sources in
multi-frequency, microwave sky maps that will be obtainable in future cosmic
microwave background radiation (CMB) experiments with instruments capable of
very high spatial resolution. With spatial resolutions that can be of order of
0.1-1.0 arcsec or better, the extragalactic point-sources will appear isolated.
The same holds also for the compact structures due to the Sunyaev-Zeldovich
(SZ) effect (both thermal and kinetic). This situation is different from the
maps obtainable with instruments as WMAP or PLANCK where, because of the
smaller spatial resolution (approximately 5-30 arcmin), the point-sources and
the compact structures due to the SZ effect form a uniform noisy background
(the "confusion noise"). Hence, the point-source detection techniques developed
in the past are based on the assumption that all the emissions that contribute
to the microwave background can be modeled with homogeneous and isotropic
(often Gaussian) random fields and make use of the corresponding spatial
power-spectra. In the case of very high resolution observations such an
assumption cannot be adopted since it still holds only for the CMB. Here, we
propose an approach based on the assumption that the diffuse emissions that
contribute to the microwave background can be locally approximated by
two-dimensional low order polynomials. In particular, two sets of numerical
techniques are presented containing two different algorithms each. The
performance of the algorithms is tested with numerical experiments that mimic
the physical scenario expected for high Galactic latitude observations with the
Atacama Large Millimeter/Submillimeter Array (ALMA).Comment: Accepted for publication on "Astronomy & Astrophysics". arXiv admin
note: substantial text overlap with arXiv:1206.4536 Replaced version is the
accepted one and published in A&
D Mesons in Nuclear Matter: A DN Coupled-Channel Equations Approach
A set of coupled two-body scattering equations is solved for the DN system
embedded in an iso-symmetric nuclear matter. The in-medium behavior of charmed
D mesons: (D^+,D^0), is investigated from the self-consistent solution within
this scheme. The effective meson-baryon Lagrangian in charm quantum number one
sector, the key ingredient in the present study, is adopted from a recent model
by Hofmann and Lutz which has aimed at combining the charmed meson degree of
freedom in a consistent manner with chiral unitary models. After a critical
examination, the original model is modified in several important aspects, such
as the method of regularization, in order to be more consistent and practical
for our objective. The resultant interaction is used to reproduce the position
and width of the s-wave \Lambda_c(2593) resonance in the isospin zero DN
channel. In the isospin one channel, it generates a rather wide resonance at
\~2770 MeV. The corresponding in-medium solution is then sought by
incorporating Pauli blocking and the D- and \pi-meson dressing
self-consistently. At normal nuclear matter density, the resultant \Lambda_c
(2593) is found to stay narrow and shifted at a lower energy, while the I=1
resonance is lowered in position as well and broadened considerably. The
possible implication of our findings on the J/\Psi suppression, etc. in
relativistic heavy ion collisions is briefly discussed.Comment: 30 pages, 8 eps figures, some typos and coefficients corrected,
published in Phys. Rev.
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