84,844 research outputs found
137Cs measurement uncertainties and detection limits for airborne gamma spectrometry (AGS) data analysed using a spectral windows method
The uncertainties associated with airborne gamma spectrometry (AGS) measurements analysed using a spectral windows method, and associated detection limits, have been investigated. For individual short measurements over buried 137Cs activity detection limits of are achieved. These detection limits are reduced for superficial activity and longer integration times. For superficial activity, detection limits below are achievable. A comparison is made with the detection limits for other data processing methods
Comparison of different exoplanet mass detection limit methods using a sample of main-sequence intermediate-type stars
The radial velocity (RV) technique is a powerful tool for detecting
extrasolar planets and deriving mass detection limits that are useful for
constraining planet pulsations and formation models. Detection limit methods
must take into account the temporal distribution of power of various origins in
the stellar signal. These methods must also be able to be applied to large
samples of stellar RV time series We describe new methods for providing
detection limits. We compute the detection limits for a sample of ten main
sequence stars, which are of G-F-A type, in general active, and/or with
detected planets, and various properties. We use them to compare the
performances of these methods with those of two other methods used in the
litterature. We obtained detection limits in the 2-1000 day period range for
ten stars. Two of the proposed methods, based on the correlation between
periodograms and the power in the periodogram of the RV time series in specific
period ranges, are robust and represent a significant improvement compared to a
method based on the root mean square of the RV signal. We conclude that two of
the new methods (correlation-based method and local power analysis, i.e. LPA,
method) provide robust detection limits, which are better than those provided
by methods that do not take into account the temporal sampling.Comment: 18 pages, 15 figures Accepted in Astronomy & Astrophysic
Sparse aperture masking at the VLT II. Detection limits for the eight debris disks stars Pic, AU Mic, 49 Cet, Tel, Fomalhaut, g Lup, HD181327 and HR8799
Context. The formation of planetary systems is a common, yet complex
mechanism. Numerous stars have been identified to possess a debris disk, a
proto-planetary disk or a planetary system. The understanding of such formation
process requires the study of debris disks. These targets are substantial and
particularly suitable for optical and infrared observations. Sparse Aperture
masking (SAM) is a high angular resolution technique strongly contributing to
probe the region from 30 to 200 mas around the stars. This area is usually
unreachable with classical imaging, and the technique also remains highly
competitive compared to vortex coronagraphy. Aims. We aim to study debris disks
with aperture masking to probe the close environment of the stars. Our goal is
either to find low mass companions, or to set detection limits. Methods. We
observed eight stars presenting debris disks ( Pictoris, AU
Microscopii, 49 Ceti, Telescopii, Fomalhaut, g Lupi, HD181327 and
HR8799) with SAM technique on the NaCo instrument at the VLT. Results. No close
companions were detected using closure phase information under 0.5 of
separation from the parent stars. We obtained magnitude detection limits that
we converted to Jupiter masses detection limits using theoretical isochrones
from evolutionary models. Conclusions. We derived upper mass limits on the
presence of companions in the area of few times the diffraction limit of the
telescope around each target star.Comment: 7 pages, All magnitude detection limits maps are only available in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5
Detection Limits for Super-Hubble Suppression of Causal Fluctuations
We investigate to what extent future microwave background experiments might
be able to detect a suppression of fluctuation power on large scales in flat
and open universe models. Such suppression would arise if fluctuations are
generated by causal processes, and a measurement of a small suppression scale
would be problematic for inflation models, but consistent with many defect
models. More speculatively, a measurement of a suppression scale of the order
of the present Hubble radius could provide independent evidence for a
fine-tuned inflation model leading to a low-density universe. We find that,
depending on the primordial power spectrum, a suppression scale modestly larger
than the visible Horizon can be detected, but that the detectability drops very
rapidly with increasing scale. For models with two periods of inflation, there
is essentially no possibility of detecting a causal suppression scale.Comment: 8 pages, 4 figures, revtex, In Press Physical Review D 200
Detection limits of organic compounds achievable with intense, short-pulse lasers
Many organic molecules have strong absorption bands which can be accessed by ultraviolet short pulse lasers to produce efficient ionization. This resonant multiphoton ionization scheme has already been exploited as an ionization source in time-of-flight mass spectrometers used for environmental trace analysis. In the present work we quantify the ultimate potential of this technique by measuring absolute ion yields produced from the interaction of 267 nm femtosecond laser pulses with the organic molecules indole and toluene, and gases Xe, N2 and O2. Using multiphoton ionization cross sections extracted from these results, we show that the laser pulse parameters required for real-time detection of aromatic molecules at concentrations of one part per trillion in air and a limit of detection of a few attomoles are achievable with presently available commercial laser systems. The potential applications for the analysis of human breath, blood and tissue samples are discussed
First Direct Detection Limits on sub-GeV Dark Matter from XENON10
The first direct detection limits on dark matter in the MeV to GeV mass range
are presented, using XENON10 data. Such light dark matter can scatter with
electrons, causing ionization of atoms in a detector target material and
leading to single- or few-electron events. We use 15 kg-days of data acquired
in 2006 to set limits on the dark-matter-electron scattering cross section. The
strongest bound is obtained at 100 MeV where sigma_e < 3 x 10^{-38} cm^2 at 90%
CL, while dark matter masses between 20 MeV and 1 GeV are bounded by sigma_e <
10^{-37} cm^2 at 90% CL. This analysis provides a first proof-of-principle that
direct detection experiments can be sensitive to dark matter candidates with
masses well below the GeV scale.Comment: Submitted to PR
Planetary detection limits taking into account stellar noise. I. Observational strategies to reduce stellar oscillation and granulation effects
The radial velocity signature of stellar noise is small, around the
meter-per-second, but already too much for the detection of Earth mass planets
in habitable zones. In this paper, we address the important role played by
observational strategies in averaging out the radial velocity signature of
stellar noise. We also derive the planetary mass detection limits expected in
presence of stellar noise. We start with HARPS asteroseismology measurements
for 4 stars (beta Hyi, alpha Cen A, mu Ara and tau Ceti) available in the ESO
archive plus very precise measurements of alpha Cen B. This sample covers
different spectral types, from G2 to K1 and different evolutionary stage, from
subgiant to dwarf stars. Since the span of our data ranges between 5 to 8 days,
we will have access to oscillation modes and granulation phenomena, without
important contribution of activity noise which is present at larger time
scales. For those 5 stars, we generate synthetic radial velocity measurements
after fitting corresponding models of stellar noise in Fourier space. These
measurements allows us to study the radial velocity variation due to stellar
noise for different observational strategies as well as the corresponding
planetary mass detection limits. Applying 3 measurements per night of 10
minutes exposure each, 2 hours apart, seems to average out most efficiently the
stellar noise considered. For quiet K1V stars as alpha Cen B, such a strategy
allows us to detect planets of ~3 times the mass of Earth with an orbital
period of 200 days, corresponding to the habitable zone of the star. Since
activity is not yet included in our simulation, these detection limits
correspond to a case, which exist, where the host star has few magnetic
features. In this case stellar noise is dominated by oscillation modes and
granulation phenomena.Comment: 12 pages, 6 figures, Accepted for publication in A&
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