1,965 research outputs found
A new method of correcting radial velocity time series for inhomogeneous convection
Magnetic activity strongly impacts stellar RVs and the search for small
planets. We showed previously that in the solar case it induces RV variations
with an amplitude over the cycle on the order of 8 m/s, with signals on short
and long timescales. The major component is the inhibition of the convective
blueshift due to plages. We explore a new approach to correct for this major
component of stellar radial velocities in the case of solar-type stars. The
convective blueshift depends on line depths; we use this property to develop a
method that will characterize the amplitude of this effect and to correct for
this RV component. We build realistic RV time series corresponding to RVs
computed using different sets of lines, including lines in different depth
ranges. We characterize the performance of the method used to reconstruct the
signal without the convective component and the detection limits derived from
the residuals. We identified a set of lines which, combined with a global set
of lines, allows us to reconstruct the convective component with a good
precision and to correct for it. For the full temporal sampling, the power in
the range 100-500~d significantly decreased, by a factor of 100 for a RV noise
below 30 cm/s. We also studied the impact of noise contributions other than the
photon noise, which lead to uncertainties on the RV computation, as well as the
impact of the temporal sampling. We found that these other sources of noise do
not greatly alter the quality of the correction, although they need a better
noise level to reach a similar performance level. A very good correction of the
convective component can be achieved providing very good RV noise levels
combined with a very good instrumental stability and realistic granulation
noise. Under the conditions considered in this paper, detection limits at 480~d
lower than 1 MEarth could be achieved for RV noise below 15 cm/s.Comment: Accepted in A&A 18 July 201
Génération de données de carte
La présente invention concerne la génération de données cartographiques. Un instrument de mesure, mobile, mesure des distances entre une position courante du mobile et des obstacles dans un environnement du mobile. On prévoit en particulier de : a) effectuer au moins N mesures de distances entre le mobile et des obstacles dans ledit environnement, par pas angulaires successifs de A/N chacun, où A est un secteur angulaire prédéterminé définissant au moins partiellement ledit environnement du mobile, et associer lesdites distances aux pas angulaires respectifs dans une mémoire de travail, pour établir des données de carte, b) déplacer le mobile et réitérer l\u27étape a) pour une nouvelle position courante du mobile, et c) déterminer, en fonction des distances mesurées pour chaque pas angulaire de la position courante de l\u27étape b) et de la position précédente de l\u27étape a), à la fois, la position courante du mobile à l\u27étape b), sur ladite carte, par rapport à sa position initiale à l\u27étape a), et de nouvelles données de ladite carte
New constrains on Gliese 86 B
We present the results of multi epochs imaging observations of the companion
to the planetary host Gliese 86. Associated to radial velocity measurements,
this study aimed at characterizing dynamically the orbital properties and the
mass of this companion (here after Gliese 86 B), but also at investigating the
possible history of this particular system. We used the adaptive optics
instrument NACO at the ESO Very Large Telescope to obtain deep coronographic
imaging in order to determine new photometric and astrometric measurements of
Gliese 86 B. Part of the orbit is resolved. The photometry of Gliese B
indicates colors compatible with a ~70 Jupiter mass brown dwarf or a white
dwarf. Both types of objects allow to fit the available, still limited
astrometric data. Besides, if we attribute the long term radial velocity
residual drift observed for Gliese A to B, then the mass of the latter object
is ~0.5 Msun. We analyse both astrometric and radial velocity data to propose
first orbital parameters for Gliese B. Assuming Gliese B is a ~0.5 Msun white
dwarf, we explore the constraints induced by this hypothesis and refine the
parameters of the system.Comment: 10 pages, 18 figures, accepted in A&
A numerical approach to compute the topology of the Apparent Contour of a smooth mapping from R2 to R2
A rigorous algorithm for computing the topology of the Apparent Contour of a generic smooth map is designed and studied in this paper. The source set is assumed to be a simply connected compact subset of the plane and the target space is the plane. Whitney proved that, generically, critical points of a smooth map are folds or cusps (Whitney, 1955). The Apparent Contour is the set of critical values, that is, the image of the critical points. Generically speaking, the Apparent Contour does not have triple points and double points are normal crossings (i.e. crossing without tangency). Each of those particular cases, cusp and normal crossing, is described in order to be rigorously handled by an interval analysis based scheme. The first step of the presented method provides an enclosure of those particular points. The second part of the designed method is a computation of a graph which is homeomorphic to the Apparent Contour. Edges of this graph are computed by testing connectivity of those particular points in the source space. This paper also defines a concept called portrait. Relations between this notion and the more classical notion of Apparent Contour are discussed
Variability of stellar granulation and convective blueshift with spectral type and magnetic activity. I. K and G main sequence stars
In solar-type stars, the attenuation of convective blueshift by stellar
magnetic activity dominates the RV variations over the low amplitude signal
induced by low mass planets. Models of stars that differ from the Sun will
require a good knowledge of the attenuation of the convective blueshift to
estimate its impact on the variations. It is therefore crucial to precisely
determine not only the amplitude of the convective blueshift for different
types of stars, but also the dependence of this convective blueshift on
magnetic activity, as these are key factors in our model producing the RV. We
studied a sample of main sequence stars with spectral types from G0 to K2 and
focused on their temporally averaged properties: the activity level and a
criterion allowing to characterise the amplitude of the convective blueshift.
We find the differential velocity shifts of spectral lines due to convection to
depend on the spectral type, the wavelength (this dependence is correlated with
the Teff and activity level), and on the activity level. This allows us to
quantify the dependence of granulation properties on magnetic activity for
stars other than the Sun. The attenuation factor of the convective blueshift
appears to be constant over the considered range of spectral types. We derive a
convective blueshift which decreases towards lower temperatures, with a trend
in close agreement with models for Teff lower than 5800 K, but with a
significantly larger global amplitude. We finally compare the observed RV
variation amplitudes with those that could be derived from our convective
blueshift using a simple law and find a general agreement on the amplitude. Our
results are consistent with previous results and provide, for the first time,
an estimation of the convective blueshift as a function of Teff, magnetic
activity, and wavelength, over a large sample of G and K main sequence stars
Recommended from our members
Characterisation of acoustic scenes using a temporally-constrained shift-invariant model
International audienceIn this paper, we propose a method for modeling and classifying acoustic scenes using temporally-constrained shift-invariant probabilistic latent component analysis (SIPLCA). SIPLCA can be used for extracting time-frequency patches from spectrograms in an unsupervised manner. Component-wise hidden Markov models are incorporated to the SIPLCA formulation for enforcing temporal constraints on the activation of each acoustic component. The time-frequency patches are converted to cepstral coefficients in order to provide a compact representation of acoustic events within a scene. Experiments are made using a corpus of train station recordings, classified into 6 scene classes. Results show that the proposed model is able to model salient events within a scene and outperforms the non-negative matrix factorization algorithm for the same task. In addition, it is demonstrated that the use of temporal constraints can lead to improved performance
Comment on "Large energy gaps in CaC6 from tunneling spectroscopy: possible evidence of strong-coupling superconductivity"
Comment on "Large energy gaps in CaC6 from tunneling spectroscopy: possible
evidence of strong-coupling superconductivity
Multiple spiral patterns in the transitional disk of HD 100546
Protoplanetary disks around young stars harbor many structures related to
planetary formation. Of particular interest, spiral patterns were discovered
among several of these disks and are expected to be the sign of gravitational
instabilities leading to giant planets formation or gravitational perturbations
caused by already existing planets. In this context, the star HD100546 presents
some specific characteristics with a complex gas and dusty disk including
spirals as well as a possible planet in formation. The objective of this study
is to analyze high contrast and high angular resolution images of this
emblematic system to shed light on critical steps of the planet formation. We
retrieved archival images obtained at Gemini in the near IR (Ks band) with the
instrument NICI and processed the data using advanced high contrast imaging
technique taking advantage of the angular differential imaging. These new
images reveal the spiral pattern previously identified with HST with an
unprecedented resolution, while the large-scale structure of the disk is mostly
erased by the data processing. The single pattern at the southeast in HST
images is now resolved into a multi-armed spiral pattern. Using two models of a
gravitational perturber orbiting in a gaseous disk we attempted to bring
constraints on the characteristics of this perturber assuming each spiral being
independent and we derived qualitative conclusions. The non-detection of the
northeast spiral pattern observed in HST allows to put a lower limit on the
intensity ratio between the two sides of the disk, which if interpreted as
forward scattering yields a larger anisotropic scattering than derived in the
visible. Also, we found that the spirals are likely spatially resolved with a
thickness of about 5-10AU. Finally, we did not detect the candidate forming
planet recently discovered in the Lp band, with a mass upper limit of 16-18 MJ.Comment: Accepted for publication in Astronomy and Astrophysics, 10 pages, 8
figure
- …