148 research outputs found
Détection et caractérisation de naines brunes et exoplanètes avec un filtre accordable pour applications dans l'espace
Cette thèse porte sur la capacité à détecter des compagnons de faible intensité en présence de bruit de tavelures dans le contexte de l’imagerie à haute gamme dynamique pour l’astronomie spatiale. On s’intéressera plus particulièrement à l’imagerie spectrale différentielle (ISD) obtenue en utilisant un étalon Fabry-Pérot comme filtre accordable. Les performances d’un tel filtre accordable sont présentées dans le cadre du Tunable Filter Imager (TFI), instrument conçu pour le télescope spatial James Webb (JWST).
La capacité de l’étalon à supprimer les tavelures avec ISD est démontrée expérimentalement grâce à un prototype de l’étalon installé sur un banc de laboratoire. Les améliorations de contraste varient en fonction de la séparation, s’étendant d’un facteur 10 pour les séparations supérieures à 11 lambda/D jusqu’à un facteur 60 à 5 lambda/D. Ces résultats sont cohérents avec une étude théorique qui utilise un modèle basé sur la propagation de Fresnel pour montrer que les performances de suppression de tavelures sont limitées par le banc optique et non pas par l’étalon. De plus, il est démontré qu’un filtre accordable est une option séduisante pour l’imagerie à haute gamme dynamique combinée à la technique ISD. Une seconde étude basée sur la propagation de Fresnel de l’instrument TFI et du télescope, a permis de définir les performances de la technique ISD combinée avec un étalon pour l’astronomie spatiale. Les résultats prévoient une amélioration de contraste de l’ordre de 7 jusqu’à 100, selon la configuration de l’instrument. Une comparaison entre ISD et la soustraction par rotation a également été simulée. Enfin, la dernière partie de ce chapitre porte sur les performances de la technique ISD dans le cadre de l’instrument Near-Infrared Imager and Slitless Spectrograph (NIRISS), conçu pour remplacer TFI comme module scientifique à bord du Fine Guidance Sensor du JWST.
Cent quatre objets localisés vers la région centrale de la nébuleuse d’Orion ont été caractérisés grâce à un spectrographe multi-objet, de basse résolution et multi-bande (0.85-2.4 um). Cette étude a relevé 7 nouvelles naines brunes et 4 nouveaux candidats de masse planétaire. Ces objets sont utiles pour déterminer la fonction de masse initiale sous-stellaire et pour évaluer les modèles atmosphériques et évolutifs futurs des jeunes objets stellaires et sous-stellaires. Combinant les magnitudes en bande H mesurées et les valeurs d’extinction, les objets classifiés sont utilisés pour créer un diagramme de Hertzsprung-Russell de cet amas stellaire. En accord avec des études antérieures, nos résultats montrent qu’il existe une seule époque de formation d’étoiles qui a débuté il y a environ 1 million d’années. La fonction de masse initiale qui en dérive est en accord avec des études antérieures portant sur d’autres amas jeunes et sur le disque galactique.This thesis determines the capability of detecting faint companions in the presence of speckle noise when performing space-based high-contrast imaging through spectral differential imagery (SDI) using a low-order Fabry-Perot etalon as a tunable filter. The performance of such a tunable filter is illustrated through the Tunable Filter Imager (TFI), an instrument designed for the James Webb Space Telescope (JWST).
Using a TFI prototype etalon and a custom designed test bed, the etalon’s ability to perform speckle-suppression through SDI is demonstrated experimentally. Improvements in contrast vary with separation, ranging from a factor of 10 at working angles greater than 11 lambda/D and increasing up to a factor of 60 at 5 lambda/D. These measurements are consistent with a Fresnel optical propagation model which shows the speckle suppression capability is limited by the test bed and not the etalon. This result demonstrates that a tunable filter is an attractive option to perform high-contrast imaging through SDI. To explore the capability of space-based SDI using an etalon, we perform an end-to-end Fresnel propagation of JWST and TFI. Using this simulation, a contrast improvement ranging from a factor of 7 to 100 is predicted, depending on the instrument’s configuration. The performance of roll-subtraction is simulated and compared to that of SDI. The SDI capability of the Near-Infrared Imager and Slitless Spectrograph (NIRISS), the science instrument module to replace TFI in the JWST Fine Guidance Sensor is also determined.
Using low resolution, multi-band (0.85-2.4 um) multi-object spectroscopy, 104 objects towards the central region of the Orion Nebular Cluster have been assigned spectral types including 7 new brown dwarfs, and 4 new planetary mass candidates. These objects are useful for determining the substellar initial mass function and for testing evolutionary and atmospheric models of young stellar and substellar objects. Using the measured H band magnitudes, combined with our determined extinction values, the classified objects are used to create an Hertzsprung-Russell diagram for the cluster. Our results indicate a single epoch of star formation beginning 1 Myr ago. The initial mass function of the cluster is derived and found to be consistent with the values determined for other young clusters and the galactic disk
GPI PSF subtraction with TLOCI: the next evolution in exoplanet/disk high-contrast imaging
To directly image exoplanets and faint circumstellar disks, the noisy stellar
halo must be suppressed to a high level. To achieve this feat, the angular
differential imaging observing technique and the least-squares Locally
Optimized Combination of Images (LOCI) algorithm have now become the standard
in single band direct imaging observations and data reduction. With the
development and commissioning of new high-order high-contrast adaptive optics
equipped with integral field units, the image subtraction algorithm needs to be
modified to allow the optimal use of polychromatic images, field-rotated images
and archival data. A new algorithm, TLOCI (for Template LOCI), is designed to
achieve this task by maximizing a companion signal-to-noise ratio instead of
simply minimizing the noise as in the original LOCI algorithm. The TLOCI
technique uses an input spectrum and template Point Spread Functions (PSFs,
generated from unocculted and unsaturated stellar images) to optimize the
reference image least-squares coefficients to minimize the planet
self-subtraction, thus maximizing its throughput per wavelength, while
simultaneously providing a maximum suppression of the speckle noise. The new
algorithm has been developed using on-sky GPI data and has achieved impressive
contrast. This paper presents the TLOCI algorithm, on-sky performance, and will
discuss the challenges in recovering the planet spectrum with high fidelity.Comment: 13 pages, 8 figures, to appear in Proceedings of SPIE 914
Gemini Planet Imager Observational Calibrations III: Empirical Measurement Methods and Applications of High-Resolution Microlens PSFs
The newly commissioned Gemini Planet Imager (GPI) combines extreme adaptive
optics, an advanced coronagraph, precision wavefront control and a
lenslet-based integral field spectrograph (IFS) to measure the spectra of young
extrasolar giant planets between 0.9-2.5 um. Each GPI detector image, when in
spectral model, consists of ~37,000 microspectra which are under or critically
sampled in the spatial direction. This paper demonstrates how to obtain
high-resolution microlens PSFs and discusses their use in enhancing the
wavelength calibration, flexure compensation and spectral extraction. This
method is generally applicable to any lenslet-based integral field spectrograph
including proposed future instrument concepts for space missions.Comment: 10 pages, 6 figures. Proceedings of the SPIE, 9147-282 v2: reference
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Microfabricated pinholes for high contrast imaging testbeds
In order to reach contrast ratios of and beyond, coronagraph
testbeds need source optics that reliably emulate nearly-point-like starlight,
with microfabricated pinholes being a compelling solution. To verify, a
physical optics model of the Space Coronagraph Optical Bench (SCoOB) source
optics, including a finite-difference time-domain (FDTD) pinhole simulation,
was created. The results of the FDTD simulation show waveguide-like behavior of
pinholes. We designed and fabricated microfabricated pinholes for SCoOB made
from an aluminum overcoated silicon nitride film overhanging a silicon wafer
substrate, and report characterization of the completed pinholes.Comment: Submitted to SPIE Optical Engineering + Applications (OP23O
Gemini Planet Imager Observational Calibrations VI: Photometric and Spectroscopic Calibration for the Integral Field Spectrograph
The Gemini Planet Imager (GPI) is a new facility instrument for the Gemini
Observatory designed to provide direct detection and characterization of
planets and debris disks around stars in the solar neighborhood. In addition to
its extreme adaptive optics and corona graphic systems which give access to
high angular resolution and high-contrast imaging capabilities, GPI contains an
integral field spectrograph providing low resolution spectroscopy across five
bands between 0.95 and 2.5 m. This paper describes the sequence of
processing steps required for the spectro-photometric calibration of GPI
science data, and the necessary calibration files. Based on calibration
observations of the white dwarf HD 8049B we estimate that the systematic error
in spectra extracted from GPI observations is less than 5%. The flux ratio of
the occulted star and fiducial satellite spots within coronagraphic GPI
observations, required to estimate the magnitude difference between a target
and any resolved companions, was measured in the -band to be in laboratory measurements and using
on-sky observations. Laboratory measurements for the , , and
filters are also presented. The total throughput of GPI, Gemini South and the
atmosphere of the Earth was also measured in each photometric passband, with a
typical throughput in -band of 18% in the non-coronagraphic mode, with some
variation observed over the six-month period for which observations were
available. We also report ongoing development and improvement of the data cube
extraction algorithm.Comment: 15 pages, 6 figures. Proceedings of the SPIE, 9147-30
Constraints on the architecture of the HD 95086 planetary system with the Gemini Planet Imager
We present astrometric monitoring of the young exoplanet HD 95086 b obtained
with the Gemini Planet Imager between 2013 and 2016. A small but significant
position angle change is detected at constant separation; the orbital motion is
confirmed with literature measurements. Efficient Monte Carlo techniques place
preliminary constraints on the orbital parameters of HD 95086 b. With 68%
confidence, a semimajor axis of 61.7^{+20.7}_{-8.4} au and an inclination of
153.0^{+9.7}_{-13.5} deg are favored, with eccentricity less than 0.21. Under
the assumption of a co-planar planet-disk system, the periastron of HD 95086 b
is beyond 51 au with 68% confidence. Therefore HD 95086 b cannot carve the
entire gap inferred from the measured infrared excess in the SED of HD 95086.
We use our sensitivity to additional planets to discuss specific scenarios
presented in the literature to explain the geometry of the debris belts. We
suggest that either two planets on moderately eccentric orbits or three to four
planets with inhomogeneous masses and orbital properties are possible. The
sensitivity to additional planetary companions within the observations
presented in this study can be used to help further constrain future dynamical
simulations of the planet-disk system.Comment: Accepted for publication in ApJ
The Peculiar Debris Disk of HD 111520 as Resolved by the Gemini Planet Imager
Using the Gemini Planet Imager (GPI), we have resolved the circumstellar
debris disk around HD 111520 at a projected range of ~30-100 AU in both total
and polarized -band intensity. The disk is seen edge-on at a position angle
of ~165 along the spine of emission. A slight inclination or
asymmetric warping are covariant and alters the interpretation of the observed
disk emission. We employ 3 point spread function (PSF) subtraction methods to
reduce the stellar glare and instrumental artifacts to confirm that there is a
roughly 2:1 brightness asymmetry between the NW and SE extension. This specific
feature makes HD 111520 the most extreme examples of asymmetric debris disks
observed in scattered light among similar highly inclined systems, such as HD
15115 and HD 106906. We further identify a tentative localized brightness
enhancement and scale height enhancement associated with the disk at ~40 AU
away from the star on the SE extension. We also find that the fractional
polarization rises from 10 to 40% from 0.5" to 0.8" from the star. The
combination of large brightness asymmetry and symmetric polarization fraction
leads us to believe that an azimuthal dust density variation is causing the
observed asymmetry.Comment: 9 pages, 8 Figures, 1 table, Accepted to Ap
Automated data processing architecture for the Gemini Planet Imager Exoplanet Survey
The Gemini Planet Imager Exoplanet Survey (GPIES) is a multi-year direct
imaging survey of 600 stars to discover and characterize young Jovian
exoplanets and their environments. We have developed an automated data
architecture to process and index all data related to the survey uniformly. An
automated and flexible data processing framework, which we term the Data
Cruncher, combines multiple data reduction pipelines together to process all
spectroscopic, polarimetric, and calibration data taken with GPIES. With no
human intervention, fully reduced and calibrated data products are available
less than an hour after the data are taken to expedite follow-up on potential
objects of interest. The Data Cruncher can run on a supercomputer to reprocess
all GPIES data in a single day as improvements are made to our data reduction
pipelines. A backend MySQL database indexes all files, which are synced to the
cloud, and a front-end web server allows for easy browsing of all files
associated with GPIES. To help observers, quicklook displays show reduced data
as they are processed in real-time, and chatbots on Slack post observing
information as well as reduced data products. Together, the GPIES automated
data processing architecture reduces our workload, provides real-time data
reduction, optimizes our observing strategy, and maintains a homogeneously
reduced dataset to study planet occurrence and instrument performance.Comment: 21 pages, 3 figures, accepted in JATI
Dynamical Mass Measurement of the Young Spectroscopic Binary V343 Normae AaAb Resolved With the Gemini Planet Imager
We present new spatially resolved astrometry and photometry from the Gemini
Planet Imager of the inner binary of the young multiple star system V343
Normae, which is a member of the beta Pictoris moving group. V343 Normae
comprises a K0 and mid-M star in a ~4.5 year orbit (AaAb) and a wide 10" M5
companion (B). By combining these data with archival astrometry and radial
velocities we fit the orbit and measure individual masses for both components
of M_Aa = 1.10 +/- 0.10 M_sun and M_Ab = 0.290 +/- 0.018 M_sun. Comparing to
theoretical isochrones, we find good agreement for the measured masses and JHK
band magnitudes of the two components consistent with the age of the beta Pic
moving group. We derive a model-dependent age for the beta Pic moving group of
26 +/- 3 Myr by combining our results for V343 Normae with literature
measurements for GJ 3305, which is another group member with resolved binary
components and dynamical masses.Comment: 12 pages, 7 figures. Accepted to A
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