615 research outputs found
Study of a Strategy for Parallax Microlensing Detection Towards the Magellanic Clouds
In this article, we have investigated the possibility to distinguish between
different galactic models through the microlensing parallax studies. We show
that a systematic search for parallax effects can be done using the currently
running alert systems and complementary photometric telescopes, to distinguish
between different lens distance distributions. We have considered two galactic
dark compact objects distributions, with total optical depths corresponding to
the EROS current upper limits. These models correspond to two extreme
hypothesis on a three component galactic structure made of a thin disc, a thick
disc, and a spherically symmetric halo. Our study shows that for sub-solar mass
lenses, an exposure of staryr toward LMC should allow to
distinguish between these two extreme models. In addition the self-lensing
hypothesis (lensing by LMC objects) can efficiently be tested through the
method proposed here.Comment: 10 pages, 12 eps figures. To be published in A&A (accepted version).
Minor changes: - Discussion added on the differential velocity of the thick
galactic disk with respect to the thin disk. - Quality and lisibility of
figures improved. - Typo errors correcte
Possible use of the dedicated MARLY one meter telescope for intensive supernovae studies
The EROS2 microlensing search will end at the end of 2002. Apart of this
microlensing search, EROS has discovered ~70 supernovae during 8 periods
partially dedicated to a SN search. In this document, we investigated a new way
of using the EROS telescope (The MARLY) after this date, as a dedicated nearby
supernovae photometer. The performance of a set-up with two cameras allowing to
simultaneously perform BVRI and U photometry have been estimated. Each year, of
order of 100 type Ia supernovae at z ~0.05 should be photometrically
followed-up during 80 days with a precision of 2% in BVRI and ~3,5% in U.Comment: You can find the full resolution of this report at
http://www.lal.in2p3.fr/presentation/bibliotheque/publications/
publicationsLAL01.html/LAL0171.p
Agnostic cosmology in the CAMEL framework
Cosmological parameter estimation is traditionally performed in the Bayesian
context. By adopting an "agnostic" statistical point of view, we show the
interest of confronting the Bayesian results to a frequentist approach based on
profile-likelihoods. To this purpose, we have developed the Cosmological
Analysis with a Minuit Exploration of the Likelihood ("CAMEL") software.
Written from scratch in pure C++, emphasis was put in building a clean and
carefully-designed project where new data and/or cosmological computations can
be easily included.
CAMEL incorporates the latest cosmological likelihoods and gives access from
the very same input file to several estimation methods: (i) A high quality
Maximum Likelihood Estimate (a.k.a "best fit") using MINUIT ; (ii) profile
likelihoods, (iii) a new implementation of an Adaptive Metropolis MCMC
algorithm that relieves the burden of reconstructing the proposal distribution.
We present here those various statistical techniques and roll out a full
use-case that can then used as a tutorial. We revisit the CDM
parameters determination with the latest Planck data and give results with both
methodologies. Furthermore, by comparing the Bayesian and frequentist
approaches, we discuss a "likelihood volume effect" that affects the optical
reionization depth when analyzing the high multipoles part of the Planck data.
The software, used in several Planck data analyzes, is available from
http://camel.in2p3.fr. Using it does not require advanced C++ skills.Comment: Typeset in Authorea. Online version available at:
https://www.authorea.com/users/90225/articles/104431/_show_articl
Relieving tensions related to the lensing of CMB temperature power spectra
The angular power spectra of the cosmic microwave background (CMB)
temperature anisotropies reconstructed from Planck data seem to present too
much gravitational lensing distortion. This is quantified by the control
parameter that should be compatible with unity for a standard cosmology.
With the Class Boltzmann solver and the profile-likelihood method, for this
parameter we measure a 2.6 shift from 1 using the Planck public
likelihoods. We show that, owing to strong correlations with the reionization
optical depth and the primordial perturbation amplitude , a
tension on also appears between the results obtained with
the low () and high () multipoles
likelihoods. With Hillipop, another high- likelihood built from Planck
data, this difference is lowered to . In this case, the value
is still in disagreement with unity by , suggesting a non-trivial
effect of the correlations between cosmological and nuisance parameters. To
better constrain the nuisance foregrounds parameters, we include the very high
measurements of the Atacama Cosmology Telescope (ACT) and South Pole
Telescope (SPT) experiments and obtain . The
Hillipop+ACT+SPT likelihood estimate of the optical depth is
which is now fully compatible with the low
likelihood determination. After showing the robustness of our results with
various combinations, we investigate the reasons for this improvement that
results from a better determination of the whole set of foregrounds parameters.
We finally provide estimates of the CDM parameters with our combined
CMB data likelihood.Comment: accepted by A&
About the connection between the power spectrum of the Cosmic Microwave Background and the Fourier spectrum of rings on the sky
In this article we present and study a scaling law of the CMB
Fourier spectrum on rings which allows us (i) to combine spectra corresponding
to different colatitude angles (e.g. several detectors at the focal plane of a
telescope), and (ii) to recover the power spectrum once the
coefficients have been measured. This recovery is performed numerically below
the 1% level for colatitudes degrees. In addition, taking
advantage of the smoothness of the and of the , we provide
analytical expressions which allow to recover one of the spectrum at the 1%
level, the other one being known.Comment: 8 pages, 8 figure
HFI L2 DPC destripping and mapmaking modules
PoS(CMB2006)049International audienceThe data processing of the data from the High Frequency Instrument (HFI) of the Planck mission will use several modules. Destriping is expected to play a central role in the mapmaking stage. This paper outlines two existing HFI l2 DPC destriping modules together with estimations of their performances. MOKAPIX is a temperature data destriping tool based on scanning redundancies on the sky. We have developped another modules, BOGOPIX , based on the same philosophy, to perform simultaneously destriping and relative intercalibration
Iterative destriping and photometric calibration for Planck-HFI, polarized, multi-detector map-making
We present an iterative scheme designed to recover calibrated I, Q, and U
maps from Planck-HFI data using the orbital dipole due to the satellite motion
with respect to the Solar System frame. It combines a map reconstruction, based
on a destriping technique, juxtaposed with an absolute calibration algorithm.
We evaluate systematic and statistical uncertainties incurred during both these
steps with the help of realistic, Planck-like simulations containing CMB,
foreground components and instrumental noise, and assess the accuracy of the
sky map reconstruction by considering the maps of the residuals and their
spectra. In particular, we discuss destriping residuals for polarization
sensitive detectors similar to those of Planck-HFI under different noise
hypotheses and show that these residuals are negligible (for intensity maps) or
smaller than the white noise level (for Q and U Stokes maps), for l > 50. We
also demonstrate that the combined level of residuals of this scheme remains
comparable to those of the destriping-only case except at very low l where
residuals from the calibration appear. For all the considered noise hypotheses,
the relative calibration precision is on the order of a few 10e-4, with a
systematic bias of the same order of magnitude.Comment: 18 pages, 21 figures. Match published versio
Determination of the branching ratios and
Improved branching ratios were measured for the decay in a
neutral beam at the CERN SPS with the NA31 detector: and .
From the first number an upper limit for and transitions in neutral kaon decay is derived. Using older results for the
Ke3/K3 fraction, the 3 branching ratio is found to be , about a factor three more
precise than from previous experiments
Observational Limits on Machos in the Galactic Halo
We present final results from the first phase of the EROS search for
gravitational microlensing of stars in the Magellanic Clouds by unseen
deflectors (machos: MAssive Compact Halo Objects). The search is sensitive to
events with time scales between 15 minutes and 200 days corresponding to
deflector masses in the range 1.e-7 to a few solar masses. Two events were
observed that are compatible with microlensing by objects of mass of about 0.1
Mo. By comparing the results with the expected number of events for various
models of the Galaxy, we conclude that machos in the mass range [1.e-7, 0.02]
Mo make up less than 20% (95% C.L.) of the Halo dark matter.Comment: 4 pages, 3 Postscript figures, to be published in Astronomy &
Astrophysic
Galactic Bulge Microlensing Optical Depth from EROS-2
We present a new EROS-2 measurement of the microlensing optical depth toward
the Galactic Bulge. Light curves of clump-giant stars
distributed over of the Bulge were monitored during seven Bulge
seasons. 120 events were found with apparent amplifications greater than 1.6
and Einstein radius crossing times in the range 5 {\rm d}.
This is the largest existing sample of clump-giant events and the first to
include northern Galactic fields. In the Galactic latitude range
1.4\degr<|b|<7.0\degr, we find with . These results are in good
agreement with our previous measurement, with recent measurements of the MACHO
and OGLE-II groups, and with predictions of Bulge models.Comment: accepted A&A, minor revision
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