677 research outputs found
Impact of micro-telluric lines on precise radial velocities and its correction
Context: In the near future, new instruments such as ESPRESSO will arrive,
allowing us to reach a precision in radial-velocity measurements on the order
of 10 cm/s. At this level of precision, several noise sources that until now
have been outweighed by photon noise will start to contribute significantly to
the error budget. The telluric lines that are not neglected by the masks for
the radial velocity computation, here called micro-telluric lines, are one such
noise source. Aims: In this work we investigate the impact of micro-telluric
lines in the radial velocities calculations. We also investigate how to correct
the effect of these atmospheric lines on radial velocities. Methods: The work
presented here follows two parallel lines. First, we calculated the impact of
the micro-telluric lines by multiplying a synthetic solar-like stellar spectrum
by synthetic atmospheric spectra and evaluated the effect created by the
presence of the telluric lines. Then, we divided HARPS spectra by synthetic
atmospheric spectra to correct for its presence on real data and calculated the
radial velocity on the corrected spectra. When doing so, one considers two
atmospheric models for the synthetic atmospheric spectra: the LBLRTM and TAPAS.
Results: We find that the micro-telluric lines can induce an impact on the
radial velocities calculation that can already be close to the current
precision achieved with HARPS, and so its effect should not be neglected,
especially for future instruments such as ESPRESSO. Moreover, we find that the
micro-telluric lines' impact depends on factors, such as the radial velocity of
the star, airmass, relative humidity, and the barycentric Earth radial velocity
projected along the line of sight at the time of the observation.Comment: Accepted in A&
The HARPS search for southern extra-solar planets. XXIV. Companions to HD 85390, HD 90156 and HD 103197: A Neptune analogue and two intermediate mass planets
We report the detection of three new extrasolar planets orbiting the solar
type stars HD 85390, HD 90156 and HD 103197 with the HARPS spectrograph mounted
on the ESO 3.6-m telescope at La Silla observatory. HD 85390 has a planetary
companion with a projected intermediate mass (42.0 Earth masses) on a 788-day
orbit (a=1.52 AU) with an eccentricity of 0.41, for which there is no analogue
in the solar system. A drift in the data indicates the presence of another
companion on a long period orbit, which is however not covered by our
measurements. HD 90156 is orbited by a warm Neptune analogue with a minimum
mass of 17.98 Earth masses (1.05 Neptune masses), a period of 49.8 days (a=0.25
AU) and an eccentricity of 0.31. HD 103197 has an intermediate mass planet on a
circular orbit (P=47.8 d, Msini=31.2 Earth masses). We discuss the formation of
planets of intermediate mass (about 30-100 Earth masses) which should be rare
inside a few AU according to core accretion formation models.Comment: 9 pages, 5 figures. Accepted to A&
The HARPS search for southern extra-solar planets. XXVII. Up to seven planets orbiting HD 10180: probing the architecture of low-mass planetary systems
Context. Low-mass extrasolar planets are presently being discovered at an
increased pace by radial velocity and transit surveys, opening a new window on
planetary systems. Aims. We are conducting a high-precision radial velocity
survey with the HARPS spectrograph which aims at characterizing the population
of ice giants and super-Earths around nearby solar-type stars. This will lead
to a better understanding of their formation and evolution, and yield a global
picture of planetary systems from gas giants down to telluric planets. Methods.
Progress has been possible in this field thanks in particular to the sub-m/s
radial velocity precision achieved by HARPS. We present here new high-quality
measurements from this instrument. Results. We report the discovery of a
planetary system comprising at least five Neptune-like planets with minimum
masses ranging from 12 to 25 M_Earth, orbiting the solar-type star HD 10180 at
separations between 0.06 and 1.4 AU. A sixth radial velocity signal is present
at a longer period, probably due to a 65-M_Earth object. Moreover, another body
with a minimum mass as low as 1.4 M_Earth may be present at 0.02 AU from the
star. This is the most populated exoplanetary system known to date. The planets
are in a dense but still well-separated configuration, with significant secular
interactions. Some of the orbital period ratios are fairly close to integer or
half-integer values, but the system does not exhibit any mean-motion
resonances. General relativity effects and tidal dissipation play an important
role to stabilize the innermost planet and the system as a whole. Numerical
integrations show long-term dynamical stability provided true masses are within
a factor ~3 from minimum masses. We further note that several low-mass
planetary systems exhibit a rather "packed" orbital architecture with little or
no space left for additional planets. (Abridged)Comment: 20 pages, 15 figures, accepted for publication in A&
Parameterized maximum likelihood method (PML): application to space-time radar localization
We present a maximum likelihood method for the localization of sources with known waveforms . It's a joint space time
radar localization which is a generalisation of recent methods to coherent signal . The obtained results are usefull in wireless
communications for the identification of propagation channel with a pilot signal . An exact maximum likelihood method is presented .
Variances of estimation and related Cramer Rao Bound are established . Simulations results illustrate the behaviour of the algorithm.Nous présentons une technique du maximum de vraisemblance qui localise des sources dont les formes d'ondes sont identiques et connues. Il s'agit d'une localisation radar conjointe direction-retard qui est une extension aux cas de signaux cohérents des méthodes actuellement utilisées et exploitant la connaissance des signaux émis. Les résultats obtenus s'appliquent de la même manière aux cas des communications mobiles pour lesquelles on veut identifier le canal de propagation à l'aide d'un signal connu. Un estimateur exact du maximum de vraisemblance est présenté. Les variances d'estimation ainsi que les bornes de Cramer-Rao sont établies. Des résultats de simulations viennent illustrer le comportement des algorithmes pour lesquels les performances sont comparées à la borne de Cramer-Rao
Localisation 2D à l'aide d'un réseau phasé très perturbé.
Dans cet article nous proposons d'améliorer la robustesse des algorithmes d'autocalibration en 2D (gisement et site) à l'aide d'une régularisation. Nous avons introduit un a priori sur le module des gains des capteurs. En effet, lorsque l'on utilise une antenne omnidirectionnelle, nous montrons que l'estimée des gains des obtenue à l'aide des éléments diagonaux de la matrice de corrélation est une information très précieuse. Nous proposons alors deux techniques de régularisation qui exploitent ces résultats. La première, grà ce à une contrainte sur la somme des modules exhibe une vitesse de convergence élevée. La seconde exploite chaque contrainte de gain simultanément et nécessite la mise en oeuvre d'une optimisation itérative. De nombreuses simulations viennent confirmer les résultats attendus et montrent les améliorations apportées
Turbulent Diffusion and Turbulent Thermal Diffusion of Aerosols in Stratified Atmospheric Flows
The paper analyzes the phenomenon of turbulent thermal diffusion in the Earth
atmosphere, its relation to the turbulent diffusion and its potential impact on
aerosol distribution. This phenomenon was predicted theoretically more than 10
years ago and detected recently in the laboratory experiments. This effect
causes a non-diffusive flux of aerosols in the direction of the heat flux and
results in formation of long-living aerosol layers in the vicinity of
temperature inversions. We demonstrated that the theory of turbulent thermal
diffusion explains the GOMOS aerosol observations near the tropopause (i.e.,
the observed shape of aerosol vertical profiles with elevated concentrations
located almost symmetrically with respect to temperature profile). In
combination with the derived expression for the dependence of the turbulent
thermal diffusion ratio on the turbulent diffusion, these measurements yield an
independent method for determining the coefficient of turbulent diffusion at
the tropopause. We evaluated the impact of turbulent thermal diffusion to the
lower-troposphere vertical profiles of aerosol concentration by means of
numerical dispersion modelling, and found a regular upward forcing of aerosols
with coarse particles affected stronger than fine aerosols.Comment: 19 pages, 10 figure
Shape modeling technique KOALA validated by ESA Rosetta at (21) Lutetia
We present a comparison of our results from ground-based observations of
asteroid (21) Lutetia with imaging data acquired during the flyby of the
asteroid by the ESA Rosetta mission. This flyby provided a unique opportunity
to evaluate and calibrate our method of determination of size, 3-D shape, and
spin of an asteroid from ground-based observations. We present our 3-D
shape-modeling technique KOALA which is based on multi-dataset inversion. We
compare the results we obtained with KOALA, prior to the flyby, on asteroid
(21) Lutetia with the high-spatial resolution images of the asteroid taken with
the OSIRIS camera on-board the ESA Rosetta spacecraft, during its encounter
with Lutetia. The spin axis determined with KOALA was found to be accurate to
within two degrees, while the KOALA diameter determinations were within 2% of
the Rosetta-derived values. The 3-D shape of the KOALA model is also confirmed
by the spectacular visual agreement between both 3-D shape models (KOALA pre-
and OSIRIS post-flyby). We found a typical deviation of only 2 km at local
scales between the profiles from KOALA predictions and OSIRIS images, resulting
in a volume uncertainty provided by KOALA better than 10%. Radiometric
techniques for the interpretation of thermal infrared data also benefit greatly
from the KOALA shape model: the absolute size and geometric albedo can be
derived with high accuracy, and thermal properties, for example the thermal
inertia, can be determined unambiguously. We consider this to be a validation
of the KOALA method. Because space exploration will remain limited to only a
few objects, KOALA stands as a powerful technique to study a much larger set of
small bodies using Earth-based observations.Comment: 15 pages, 8 figures, 2 tables, accepted for publication in P&S
The HARPS search for southern extra-solar planets. IX. mu Ara, a system with four planets
The mu Ara planetary system is rather complex: It contains two already known
planets, mu Ara b with P=640 days and mu Ara c with P=9.64 days, and a third
companion on a wide but still poorly defined orbit. Even with three planets in
the system, the data points keep anomalously high dispersion around the fitted
solution. The high residuals are only partially due to the strong p-mode
oscillations of the host star. We have therefore studied in this paper the
possible presence of a fourth planet in the system. During the past years we
have carried out additional and extremely precise radial-velocity measurements
with the HARPS spectrograph. We provide in this paper a full orbital solution
of the planetary system around mu Ara. It turns out to be the second system
known to harbor 4 planetary companions. Thanks to the new data points acquired
with HARPS we can confirm the presence of mu Ara c at P=9.64 days, which
produces a coherent RV signal over more than two years. The new orbital fit
sets the mass of mu Ara c to 10.5 M_Earth. Furthermore, we present the
discovery of mu Ara d, a new planet on an almost circular 310 days-period and
with a mass of 0.52 M_Jup. Finally, we give completely new orbital parameters
for the longest-period planet, mu Ara e. It is the first time that this
companion is constrained by radial-velocity data into a dynamical stable orbit,
which leaves no doubt about its planetary nature. (Abridged).Comment: 11 pages, 8 low-resolution figures. Submitted to A&A on August 5,
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A global climatology of the mesospheric sodium layerfrom GOMOS data during the 2002-2008 period
This paper presents a climatology of the mesospheric sodium layer built from the processing of 7 years of GOMOS data. With respect to preliminary results already published for the year 2003, a more careful analysis was applied to the averaging of occultations inside the climatological bins (10° in latitude-1 month). Also, the slant path absorption lines of the Na doublet around 589 nm shows evidence of partial saturation that was responsible for an underestimation of the Na concentration in our previous results. The sodium climatology has been validated with respect to the Fort Collins lidar measurements and, to a lesser extent, to the OSIRIS 2003–2004 data. Despite the important natural sodium variability, we have shown that the Na vertical column has a marked semi-annual oscillation at low latitudes that merges into an annual oscillation in the polar regions, a spatial distribution pattern that was unreported so far. The sodium layer seems to be clearly influenced by the mesospheric global circulation and the altitude of the layer shows clear signs of subsidence during polar winter. The climatology has been parameterized by time-latitude robust fits to allow for easy use. Taking into account the non-linearity of the transmittance due to partial saturation, an experimental approach is proposed to derive mesospheric temperatures from limb remote sounding measurements
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