206 research outputs found
Estimating hyperparameters and instrument parameters in regularized inversion. Illustration for SPIRE/Herschel map making
We describe regularized methods for image reconstruction and focus on the
question of hyperparameter and instrument parameter estimation, i.e.
unsupervised and myopic problems. We developed a Bayesian framework that is
based on the \post density for all unknown quantities, given the observations.
This density is explored by a Markov Chain Monte-Carlo sampling technique based
on a Gibbs loop and including a Metropolis-Hastings step. The numerical
evaluation relies on the SPIRE instrument of the Herschel observatory. Using
simulated and real observations, we show that the hyperparameters and
instrument parameters are correctly estimated, which opens up many perspectives
for imaging in astrophysics
Correlated Anisotropies in the Cosmic Far-Infrared Background Detected by MIPS/Spitzer: Constraint on the Bias
We report the detection of correlated anisotropies in the Cosmic Far-Infrared
Background at 160 microns. We measure the power spectrum in the Spitzer/SWIRE
Lockman Hole field. It reveals unambiguously a strong excess above cirrus and
Poisson contributions, at spatial scales between 5 and 30 arcminutes,
interpreted as the signature of infrared galaxy clustering. Using our model of
infrared galaxy evolution we derive a linear bias b=1.74 \pm 0.16. It is a
factor 2 higher than the bias measured for the local IRAS galaxies. Our model
indicates that galaxies dominating the 160 microns correlated anisotropies are
at z~1. This implies that infrared galaxies at high redshifts are biased
tracers of mass, unlike in the local Universe.Comment: ApJ Letters, in pres
Super-resolution in map-making based on a physical instrument model and regularized inversion. Application to SPIRE/Herschel
We investigate super-resolution methods for image reconstruction from data
provided by a family of scanning instruments like the Herschel observatory. To
do this, we constructed a model of the instrument that faithfully reflects the
physical reality, accurately taking the acquisition process into account to
explain the data in a reliable manner. The inversion, ie the image
reconstruction process, is based on a linear approach resulting from a
quadratic regularized criterion and numerical optimization tools. The
application concerns the reconstruction of maps for the SPIRE instrument of the
Herschel observatory. The numerical evaluation uses simulated and real data to
compare the standard tool (coaddition) and the proposed method. The inversion
approach is capable to restore spatial frequencies over a bandwidth four times
that possible with coaddition and thus to correctly show details invisible on
standard maps. The approach is also applied to real data with significant
improvement in spatial resolution.Comment: Astronomy & Astrophysic
Optical performance of the JWST MIRI flight model: characterization of the point spread function at high-resolution
The Mid Infra Red Instrument (MIRI) is one of the four instruments onboard
the James Webb Space Telescope (JWST), providing imaging, coronagraphy and
spectroscopy over the 5-28 microns band. To verify the optical performance of
the instrument, extensive tests were performed at CEA on the flight model (FM)
of the Mid-InfraRed IMager (MIRIM) at cryogenic temperatures and in the
infrared. This paper reports on the point spread function (PSF) measurements at
5.6 microns, the shortest operating wavelength for imaging. At 5.6 microns the
PSF is not Nyquist-sampled, so we use am original technique that combines a
microscanning measurement strategy with a deconvolution algorithm to obtain an
over-resolved MIRIM PSF. The microscanning consists in a sub-pixel scan of a
point source on the focal plane. A data inversion method is used to reconstruct
PSF images that are over-resolved by a factor of 7 compared to the native
resolution of MIRI. We show that the FWHM of the high-resolution PSFs were
5-10% wider than that obtained with Zemax simulations. The main cause was
identified as an out-of-specification tilt of the M4 mirror. After correction,
two additional test campaigns were carried out, and we show that the shape of
the PSF is conform to expectations. The FWHM of the PSFs are 0.18-0.20 arcsec,
in agreement with simulations. 56.1-59.2% of the total encircled energy
(normalized to a 5 arcsec radius) is contained within the first dark Airy ring,
over the whole field of view. At longer wavelengths (7.7-25.5 microns), this
percentage is 57-68%. MIRIM is thus compliant with the optical quality
requirements. This characterization of the MIRIM PSF, as well as the
deconvolution method presented here, are of particular importance, not only for
the verification of the optical quality and the MIRI calibration, but also for
scientific applications.Comment: 13 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes
and Instrumentation 2010: Optical, Infrared, and Millimeter Wav
Methodology of geoarchaeological prospections in a fluvial basin (example of the Peruaçu river basin, Minas Gerais, Brazil).
Knowledge about the prehistoric occupancy of a region depends obviously on the method of data acquisition based on a systematic methodology. The recent introduction of the multidisciplinary approach in modem studies allows the elaboration of a systemic methodology of location of the archeological sites, based on the basic geomorphological unit, the hydrographical basin. The methodology elaborated and developed in the Rio Perua§u basin, in northern Minas Gerais, area studied since 1980, is founded on the morphogenesis and evolution of the landscape. Its goal is to help the understanding of the human colonization of a definite geomorphological unity.O conhecimento da ocupação pré-histórica de uma região depende dos métodos de aquisição de dados que devem se apoiar sobre uma metodologia sistemática. A introdução de uma abordagem interdisciplinar para as pesquisas modernas permite a elaboração de uma metodologia sistêmica de localização de sítios arqueológicos, a partir de uma unidade geomorfológica básica, a saber, a bacia hidrográfica. A metodologia elaborada e desenvolvida na bacia do rio Peruaçu, região norte do estado de Minas Gerais, estudada desde o início dos anos 1980, é fundada na análise morfogenética da paisagem. Ela tem por objetivo facilitar a compreensão da ocupação humana dentro de uma unidade geomorfológica definida
DATA INVERSION FOR HYPERSPECTRAL OBJECTS IN ASTRONOMY
ABSTRACT We present an original method for reconstruction of hyperspectral objects (two spatial and one spectral dimensions) from data provided by the infrared slit spectrograph on board the Spitzer Space Telescope. The originality of the work lies in the fact that both measurement model and inversion method are tackled in continuous (spatial and spectral) variables. The method is built in a deterministic regularization framework and enable to achieve both deconvolution and over-resolution. Results show that the method is able to evidence spatial structures not detectable by means of conventional methods. The spatial resolution is shown to be improved by a factor 1.5. We discuss our data processing approach for the new generation of infrared to millimeter space observatories launched in 2009 (Herschel and Planck)
Peering into the Young Planetary System AB Pic. Atmosphere, Orbit, Obliquity & Second Planetary Candidate
We aim to revisit the system AB Pic which has a known companion at the
exoplanet/ brown-dwarf boundary. We based this study on a rich set of
observations to investigate the companion's orbit and atmosphere. We composed a
spectrum of AB Pic b merging archival VLT/SINFONI K-band data, with published
spectra at J and H-band (SINFONI) and Lp-band (Magellan-AO), and photometric
measurements (HST and Spitzer). We modeled the spectrum with ForMoSA, based on
two atmospheric models: ExoREM and BT-SETTL13. We determined the orbital
properties of b fitting the astrometric measurements from NaCo (2003 and 2004)
and SPHERE (2015). The orbital solutions favor a semi-major axis of 190au
viewed edge-on. With Exo-REM, we derive a T of 170050K and surface
gravity of 4.50.3dex, consistent with previous works, and we report for
the first time a C/O ratio of 0.580.08 (solar). The posteriors are
sensitive to the wavelength interval and the family of models used. Given the
2.1hr rotation period and our vsin(i) of 73km/s, we estimate for the
first time the true obliquity to be 45 or 135deg, indicating a
significant misalignment between the planet's spin and orbit orientations.
Finally, the existence of a proper motion anomaly between the Hipparcos and
Gaia eDR3 compared to our SPHERE detection limits and adapted radial velocity
limits indicate the existence of a 6M inner planet orbiting from
2 to 10au (40-200mas). The possible existence of an inner companion, together
with the likely miss-alignment of the spin axis orientation, strongly favor a
formation path by gravitational instability or core accretion within a disk
closer inside followed by dynamical interactions. Confirmation and
characterization of planet c and access to a broader wavelength coverage for
planet b will be essential to probe the uncertainties associated with the
parameters.Comment: 17 pages, 13 Figures, 6 Tables. Accepted for publication in A&A (31
of October
In-depth study of moderately young but extremely red, very dusty substellar companion HD206893B
Accepted for publication in Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.The substellar companion HD206893b has recently been discovered by direct imaging of its disc-bearing host star with the SPHERE instrument. We investigate the atypical properties of the companion, which has the reddest near-infrared colours among all known substellar objects, either orbiting a star or isolated, and we provide a comprehensive characterisation of the host star-disc-companion system. We conducted a follow-up of the companion with adaptive optics imaging and spectro-imaging with SPHERE, and a multiinstrument follow-up of its host star. We obtain a R=30 spectrum from 0.95 to 1.64 micron of the companion and additional photometry at 2.11 and 2.25 micron. We carried out extensive atmosphere model fitting for the companions and the host star in order to derive their age, mass, and metallicity. We found no additional companion in the system in spite of exquisite observing conditions resulting in sensitivity to 6MJup (2MJup) at 0.5" for an age of 300 Myr (50 Myr). We detect orbital motion over more than one year and characterise the possible Keplerian orbits. We constrain the age of the system to a minimum of 50 Myr and a maximum of 700 Myr, and determine that the host-star metallicity is nearly solar. The comparison of the companion spectrum and photometry to model atmospheres indicates that the companion is an extremely dusty late L dwarf, with an intermediate gravity (log g 4.5-5.0) which is compatible with the independent age estimate of the system. Though our best fit corresponds to a brown dwarf of 15-30 MJup aged 100-300 Myr, our analysis is also compatible with a range of masses and ages going from a 50 Myr 12MJup planetary-mass object to a 50 MJup Hyades-age brown dwarf...Peer reviewedFinal Accepted Versio
Direct Discovery of the Inner Exoplanet in the Hd 206893 System: Evidence for Deuterium Burning in a Planetary-Mass Companion
Aims. HD 206893 is a nearby debris disk star that hosts a previously identified brown dwarf companion with an orbital separation of ~ 10 au. Long-Term precise radial velocity (RV) monitoring, as well as anomalies in the system proper motion, has suggested the presence of an additional, inner companion in the system. Methods. Using information from ongoing precision RV measurements with the HARPS spectrograph, as well as Gaia host star astrometry, we have undertaken a multi-epoch search for the purported additional planet using the VLTI/GRAVITY instrument. Results. We report a high-significance detection over three epochs of the companion HD 206893c, which shows clear evidence for Keplerian orbital motion. Our astrometry with ~ 50-100 µarcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7MJup and an orbital separation of 3.53 au for HD 206893c. Our fits to the orbits of both companions in the system use both Gaia astrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore allow us to derive an age of 155 ± 15 Myr for the system. We find that theoretical atmospheric and evolutionary models that incorporate deuterium burning for HD 206893c, parameterized by cloudy atmosphere models as well as a hybrid sequence (encompassing a transition from cloudy to cloud-free), provide a good simultaneous fit to the luminosity of both HD 206893B and c. Thus, accounting for both deuterium burning and clouds is crucial to understanding the luminosity evolution of HD 206893c. Conclusions. In addition to using long-Term RV information, this effort is an early example of a direct imaging discovery of a bona fide exoplanet that was guided in part by Gaia astrometry. Utilizing Gaia astrometry is expected to be one of the primary techniques going forward for identifying and characterizing additional directly imaged planets. In addition, HD 206893c is an example of an object narrowly straddling the deuterium-burning limit but unambiguously undergoing deuterium burning. Additional discoveries like this may therefore help clarify the discrimination between a brown dwarf and an extrasolar planet. Lastly, this discovery is another example of the power of optical interferometry to directly detect and characterize extrasolar planets where they form, at ice-line orbital separations of 2-4 au
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