39,160 research outputs found
Period-luminosity relations in evolved red giants explained by solar-like oscillations
Solar-like oscillations in red giants have been investigated with CoRoT and
Kepler, while pulsations in more evolved M giants have been studied with
ground-based microlensing surveys. After 3.1 years of observation with Kepler,
it is now possible to make a link between these different observations of
semi-regular variables. We aim to identify period-luminosity sequences in
evolved red giants identified as semi-regular variables. Then, we investigate
the consequences of the comparison of ground-based and space-borne
observations. We have first measured global oscillation parameters of evolved
red giants observed with Kepler with the envelope autocorrelation function
method. We then used an extended form of the universal red giant oscillation
pattern, extrapolated to very low frequency, to fully identify their
oscillations. From the link between red giant oscillations observed by Kepler
and period-luminosity sequences, we have identified these relations in evolved
red giants as radial and non-radial solar-like oscillations. We were able to
expand scaling relations at very low frequency. This helped us to identify the
different sequences of period-luminosity relations, and allowed us to propose a
calibration of the K magnitude with the observed frequency large separation.
Interpreting period-luminosity relations in red giants in terms of solar-like
oscillations allows us to investigate, with a firm physical basis, the time
series obtained from ground-based microlensing surveys. This can be done with
an analytical expression that describes the low-frequency oscillation spectra.
The different behavior of oscillations at low frequency, with frequency
separations scaling only approximately with the square root of the mean stellar
density, can be used to address precisely the physics of the semi-regular
variables.Comment: Accepted in A&
Parametric high resolution techniques for radio astronomical imaging
The increased sensitivity of future radio telescopes will result in
requirements for higher dynamic range within the image as well as better
resolution and immunity to interference. In this paper we propose a new matrix
formulation of the imaging equation in the cases of non co-planar arrays and
polarimetric measurements. Then we improve our parametric imaging techniques in
terms of resolution and estimation accuracy. This is done by enhancing both the
MVDR parametric imaging, introducing alternative dirty images and by
introducing better power estimates based on least squares, with positive
semi-definite constraints. We also discuss the use of robust Capon beamforming
and semi-definite programming for solving the self-calibration problem.
Additionally we provide statistical analysis of the bias of the MVDR beamformer
for the case of moving array, which serves as a first step in analyzing
iterative approaches such as CLEAN and the techniques proposed in this paper.
Finally we demonstrate a full deconvolution process based on the parametric
imaging techniques and show its improved resolution and sensitivity compared to
the CLEAN method.Comment: To appear in IEEE Journal of Selected Topics in Signal Processing,
Special issue on Signal Processing for Astronomy and space research. 30 page
Free radially expanding liquid sheet in air: time- and space-resolved measurement of the thickness field
The collision of a liquid drop against a small target results in the
formation of a thin liquid sheet that extends radially until it reaches a
maximum diameter. The subsequent retraction is due to the air-liquid surface
tension. We have used a time- and space-resolved technique to measure the
thickness field of this class of liquid sheet, based on the grey level
measurement of the image of a dyed liquid sheet recorded using a fast camera.
This method enables a precise measurement of the thickness in the range
, with a temporal resolution equal to that of the
camera. We have measured the evolution with time since impact, , and radial
position, , of the thickness, , for various drop volumes and impact
velocities. Two asymptotic regimes for the expansion of the sheet are
evidenced. The scalings of the thickness with and measured in the two
regimes are those that were predicted in \citet{Rozhkov2004} fort the
short-time regime and \citet{Villermaux2011} for the long time regime, but
never experimentally measured before. Interestingly, our experimental data also
evidence the existence of a maximum of the film thickness at
a radial position corresponding to the crossover of these
two asymptotic regimes. The maximum moves with a constant velocity of the order
of the drop impact velocity, as expected theoretically. Thanks to our
visualization technique, we also evidence an azimuthal thickness modulation of
the liquid sheets.Comment: accepted for publication in Journal of Fluid Mechanic
Measurement of the Electric and Magnetic Polarizabilities of the Proton
The Compton scattering cross section on the proton has been measured at
laboratory angles of 90 and 135 using tagged photons in the
energy range 70--100 MeV and simultaneously using untagged photons in the range
100--148~MeV. With the aid of dispersion relations, these cross sections were
used to extract the electric and magnetic polarizabilities, and
respectively, of the proton. We find
in agreement with a model-independent dispersion sum rule, and
where the errors shown are statistical, systematic, and model-dependent,
respectively. A comparison with previous experiments is given and global values
for the polarizabilities are extracted.Comment: 35 pages, 11 PostScript figures, uses RevTex 3.
Extended Modified Observable Technique for a Multi-Parametric Trilinear Gauge Coupling Estimation at LEP II
This paper describes the extension of the Modified Observables technique in
estimating simultaneously more than one Trilinear Gauge Couplings. The optimal
properties, unbiasedness and consistent error estimation of this method are
demonstrated by Monte Carlo experimentation using four-fermion
final state topologies. Emphasis is given in the determination of the expected
sensitivities in estimating the and
pair of couplings with data from the 183
GeV LEPII run.Comment: (17 pages, 8 figures
A model independent safeguard for unbinned Likelihood
We present a universal method to include residual un-modeled background shape
uncertainties in likelihood based statistical tests for high energy physics and
astroparticle physics. This approach provides a simple and natural protection
against mismodeling, thus lowering the chances of a false discovery or of an
over constrained confidence interval, and allows a natural transition to
unbinned space. Unbinned likelihood allows optimal usage of information for the
data and the models, and enhances the sensitivity.
We show that the asymptotic behavior of the test statistic can be regained in
cases where the model fails to describe the true background behavior, and
present 1D and 2D case studies for model-driven and data-driven background
models. The resulting penalty on sensitivities follows the actual discrepancy
between the data and the models, and is asymptotically reduced to zero with
increasing knowledge
Analysis of the TOF resolution: a "tomography" study of the time of flight detector of the ALICE experiment at the LHC
Questa tesi presenta uno studio dettagliato della risoluzione del rilevatore a tempo
di volo TOF dellâesperimento ALICE, utilizzando dati di collisioni Pb-Pb del RUN 2
dellâacceleratore LHC del CERN.
Ă stata effettuata unâanalisi dei profili della risoluzione temporale lungo i principali
assi di simmetria del rivelatore (lâasse del fascio e quelli che definiscono il piano
trasverso), cosĂŹ da evidenziare discontinuitĂ date dalla struttura del rivelatore.
Le strutture osservate corrispondono in larga parte a effetti previsti. Le dipendenze
previste sono quelle date dalla presenza di materiale, modulate dalla distanza
media di traccia, che sono state confermate da una correlazione statisticamente significativa
con la risoluzione. Sono anche state osservate alcune strutture impreviste,
probabilmente derivanti da malfunzionamenti nellâoperativitĂ e nellâelettronica del
rivelatore, che saranno oggetto di studi futuri
Radial distribution of stars, gas and dust in SINGS galaxies. I. Surface photometry and morphology
We present ultraviolet through far-infrared surface brightness profiles for
the 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS). The
imagery used to measure the profiles includes GALEX UV data, optical images
from KPNO, CTIO and SDSS, near-IR data from 2MASS, and mid- and far-infrared
images from Spitzer. Along with the radial profiles, we also provide
multi-wavelength asymptotic magnitudes and several non-parametric indicators of
galaxy morphology: the concentration index (C_42), the asymmetry (A), the Gini
coefficient (G) and the normalized second-order moment of the brightest 20% of
the galaxy's flux (M_20). Our radial profiles show a wide range of morphologies
and multiple components (bulges, exponential disks, inner and outer disk
truncations, etc.) that vary not only from galaxy to galaxy but also with
wavelength for a given object. In the optical and near-IR, the SINGS galaxies
occupy the same regions in the C_42-A-G-M_20 parameter space as other normal
galaxies in previous studies. However, they appear much less centrally
concentrated, more asymmetric and with larger values of G when viewed in the UV
(due to star-forming clumps scattered across the disk) and in the mid-IR (due
to the emission of Polycyclic Aromatic Hydrocarbons at 8.0 microns and very hot
dust at 24 microns).Comment: 66 pages in preprint format, 14 figures, published in ApJ. The
definitive publisher authenticated version is available online at
http://dx.doi.org/10.1088/0004-637X/703/2/156
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