538 research outputs found
A Proposal to Search for Transparent Hidden Matter Using Optical Scintillation
It is proposed to search for scintillation of extragalactic sources through
the last unknown baryonic structures. Appropriate observation of the
scintillation process described here should allow one to detect column density
stochastic variations in cool Galactic molecular clouds of order of -- that is
-- per transverse distance
Positioning and orienting a static cylindrical radio-reflector for wide field surveys
Several projects in radioastronomy plan to use large static cylindrical
reflectors with an extended lobe sampling a sector of the rotating sky. This
study provides the exact mathematical expression of the transit time of a
celestial object within the acceptance lobe of such a cylindrical device. The
mathematical approach, based on the stereographic projection, allows one to
study the optimisation of the position and orientation of the radio-reflector,
and should provide exact coefficients for the spatial Fourier Transform of the
radio signal along the cylinder axis.Comment: 15 pages, 13 figure
Simulation of optical interstellar scintillation
Stars twinkle because their light propagates through the atmosphere. The same
phenomenon is expected on a longer time scale when the light of remote stars
crosses an interstellar turbulent molecular cloud, but it has never been
observed at optical wavelengths. The aim of the study described in this paper
is to fully simulate the scintillation process, starting from the molecular
cloud description as a fractal object, ending with the simulations of
fluctuating stellar light curves. Fast Fourier transforms are first used to
simulate fractal clouds. Then, the illumination pattern resulting from the
crossing of background star light through these refractive clouds is calculated
from a Fresnel integral that also uses fast Fourier transform techniques.
Regularisation procedure and computing limitations are discussed, along with
the effect of spatial and temporal coherency (source size and wavelength
passband). We quantify the expected modulation index of stellar light curves as
a function of the turbulence strength --characterised by the diffraction radius
-- and the projected source size, introduce the timing aspects, and
establish connections between the light curve observables and the refractive
cloud. We extend our discussion to clouds with different structure functions
from Kolmogorov-type turbulence. Our study confirms that current telescopes of
~4m with fast-readout, wide-field detectors have the capability of discovering
the first interstellar optical scintillation effects. We also show that this
effect should be unambiguously distinguished from any other type of variability
through the observation of desynchronised light curves, simultaneously measured
by two distant telescopes.Comment: 11 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Final results from EROS Microlensing search for Massive Compact Halo Objects
International audienceWe present the results of the EROS2 search for the hidden galactic matter of the halo through the gravitational microlensing of stars in the Magellanic clouds. Microlensing was also searched for and found in the Milky-Way plane, where foreground faint stars are expected to lens background stars. A total of 67 million of stars were monitored over a period of about 7 years. Hundreds of microlensing candidates have been found in the galactic plane, but only one was found towards the subsample of bright --well measured-- Magellanic stars. This result implies that massive compact halo objects (machos) in the mass range $10^{-7}M_\odo
Cosmology with Wide Field Astronomy
PoS(ICHEP 2010)441International audienceWide field astronomy has recently produced important results for the dark matter and dark energy problematics. I will summarize the scientific impact of the ongoing wide field surveys and focus on the future LSST program (Large Synoptic Survey Telescope). This program will use a 8.4 m diameter telescope, equipped with a 3.2 Gpixel wide field camera. Cosmological studies is one of his main objectives
Search for hidden turbulent gas through interstellar scintillation
Stars twinkle because their light propagates through the atmosphere. The same
phenomenon is expected when the light of remote stars crosses a Galactic - disk
or halo - refractive medium such as a molecular cloud. We present the promising
results of a test performed with the ESO-NTT and the perspectives of detection.Comment: Structure and dynamics of disk galaxies, Petit Jean Mountain : United
States (2013). arXiv admin note: substantial text overlap with
arXiv:1208.637
The OSER project
The OSER project (Optical Scintillation by Extraterrestrial Refractors) is
proposed to search for scintillation of extragalactic sources through the
galactic -- disk or halo -- transparent clouds, the last
unknown baryonic structures. This project should allow one to detect column
density stochastic variations in cool Galactic molecular clouds of order of
per transverse
distance.Comment: 6 pages, 9 figures, 1 tabl
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
Search for Turbulent Gas through Interstellar Scintillation
Stars twinkle because their light propagates through the atmosphere. The same
phenomenon is expected when the light of remote stars crosses a Galactic - disk
or halo - refractive medium such as a molecular cloud.We present the promising
results of a test performed with the ESO-NTT and the perspectives.Comment: Tenth Symposium on Sources and Detection of Dark Matter and Dark
Energy in the Universe, Los-Angeles : \'Etats-Unis (2012
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