3,167 research outputs found
Formation and evolution of planetary systems: the impact of high angular resolution optical techniques
The direct images of giant extrasolar planets recently obtained around
several main sequence stars represent a major step in the study of planetary
systems. These high-dynamic range images are among the most striking results
obtained by the current generation of high angular resolution instruments,
which will be superseded by a new generation of instruments in the coming
years. It is therefore an appropriate time to review the contributions of high
angular resolution visible/infrared techniques to the rapidly growing field of
extrasolar planetary science. During the last 20 years, the advent of the
Hubble Space Telescope, of adaptive optics on 4- to 10-m class ground-based
telescopes, and of long-baseline infrared stellar interferometry has opened a
new viewpoint on the formation and evolution of planetary systems. By spatially
resolving the optically thick circumstellar discs of gas and dust where planets
are forming, these instruments have considerably improved our models of early
circumstellar environments and have thereby provided new constraints on planet
formation theories. High angular resolution techniques are also directly
tracing the mechanisms governing the early evolution of planetary embryos and
the dispersal of optically thick material around young stars. Finally, mature
planetary systems are being studied with an unprecedented accuracy thanks to
single-pupil imaging and interferometry, precisely locating dust populations
and putting into light a whole new family of long-period giant extrasolar
planets.Comment: 71 pages, published in Astronomy and Astrophysics Review, online at
http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s00159-009-0028-
The Structure of the {\beta} Leonis Debris Disk
We combine nulling interferometry at 10 {\mu}m using the MMT and Keck
Telescopes with spectroscopy, imaging, and photometry from 3 to 100 {\mu}m
using Spitzer to study the debris disk around {\beta} Leo over a broad range of
spatial scales, corresponding to radii of 0.1 to ~100 AU. We have also measured
the close binary star o Leo with both Keck and MMT interferometers to verify
our procedures with these instruments. The {\beta} Leo debris system has a
complex structure: 1.) relatively little material within 1 AU; 2.) an inner
component with a color temperature of ~600 K, fitted by a dusty ring from about
2 to 3 AU; and 3.) a second component with a color temperature of ~120 K fitted
by a broad dusty emission zone extending from about ~5 AU to ~55 AU. Unlike
many other A-type stars with debris disks, {\beta} Leo lacks a dominant outer
belt near 100 AU.Comment: 14 page body, 3 page appendix, 15 figure
PIONIER: a visitor instrument for the VLTI
PIONIER is a 4-telescope visitor instrument for the VLTI, planned to see its
first fringes in 2010. It combines four ATs or four UTs using a pairwise ABCD
integrated optics combiner that can also be used in scanning mode. It provides
low spectral resolution in H and K band. PIONIER is designed for imaging with a
specific emphasis on fast fringe recording to allow closure-phases and
visibilities to be precisely measured. In this work we provide the detailed
description of the instrument and present its updated status.Comment: Proceedings of SPIE conference Optical and Infrared Interferometry II
(Conference 7734) San Diego 201
A near-infrared interferometric survey of debris disk stars. I. Probing the hot dust content around epsilon Eridani and tau Ceti with CHARA/FLUOR
We probed the first 3AU around tau Ceti and epsilon Eridani with the CHARA
array (Mt Wilson, USA) in order to gauge the 2micron excess flux emanating from
possible hot dust grains in the debris disks and to also resolve the stellar
photospheres. High precision visibility amplitude measurements were performed
with the FLUOR single mode fiber instrument and telescope pairs on baselines
ranging from 22 to 241m of projected length. The short baseline observations
allow us to disentangle the contribution of an extended structure from the
photospheric emission, while the long baselines constrain the stellar diameter.
We have detected a resolved emission around tau Cet, corresponding to a
spatially integrated, fractional excess flux of 0.98 +/- 0.21 x 10^{-2} with
respect to the photospheric flux in the K'-band. Around eps Eri, our
measurements can exclude a fractional excess of greater than 0.6x10^{-2}
(3sigma). We interpret the photometric excess around tau Cet as a possible
signature of hot grains in the inner debris disk and demonstrate that a faint,
physical or background, companion can be safely excluded. In addition, we
measured both stellar angular diameters with an unprecedented accuracy:
Theta_LD(tau Cet)= 2.015 +/- 0.011 mas and Theta_LD(eps Eri)=2.126 +/- 0.014
mas.Comment: 8 pages, 5 figures, to appear in Astronomy and Astrophysic
Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
We present a review of the interplay between the evolution of circumstellar
disks and the formation of planets, both from the perspective of theoretical
models and dedicated observations. Based on this, we identify and discuss
fundamental questions concerning the formation and evolution of circumstellar
disks and planets which can be addressed in the near future with optical and
infrared long-baseline interferometers. Furthermore, the importance of
complementary observations with long-baseline (sub)millimeter interferometers
and high-sensitivity infrared observatories is outlined.Comment: 83 pages; Accepted for publication in "Astronomy and Astrophysics
Review"; The final publication is available at http://www.springerlink.co
Asteroid Belts in Debris Disk Twins: VEGA and FOMALHAUT
Vega and Fomalhaut, are similar in terms of mass, ages, and global debris
disk properties; therefore, they are often referred as "debris disk twins". We
present Spitzer 10-35 um spectroscopic data centered at both stars, and
identify warm, unresolved excess emission in the close vicinity of Vega for the
first time. The properties of the warm excess in Vega are further characterized
with ancillary photometry in the mid infrared and resolved images in the
far-infrared and submillimeter wavelengths. The Vega warm excess shares many
similar properties with the one found around Fomalhaut. The emission shortward
of ~30 um from both warm components is well described as a blackbody emission
of ~170 K. Interestingly, two other systems, eps Eri and HR 8799, also show
such an unresolved warm dust using the same approach. These warm components may
be analogous to the solar system's zodiacal dust cloud, but of far greater. The
dust temperature and tentative detections in the submillimeter suggest the warm
excess arises from dust associated with a planetesimal ring located near the
water-frost line and presumably created by processes occurring at similar
locations in other debris systems as well. We also review the properties of the
2 um hot excess around Vega and Fomalhaut, showing that the dust responsible
for the hot excess is not spatially associated with the dust we detected in the
warm belt. We suggest it may arise from hot nano grains trapped in the magnetic
field of the star. Finally, the separation between the warm and cold belt is
rather large with an orbital ratio >~10 in all four systems. In light of the
current upper limits on the masses of planetary objects and the large gap, we
discuss the possible implications for their underlying planetary architecture,
and suggest that multiple, low-mass planets likely reside between the two belts
in Vega and Fomalhaut.Comment: 14 pages, accepted for publication in Ap
A near-infrared interferometric survey of debris-disc stars. IV. An unbiased sample of 92 southern stars observed in H-band with VLTI/PIONIER
Context. Detecting and characterizing circumstellar dust is a way to study
the architecture and evolution of planetary systems. Cold dust in debris disks
only traces the outer regions. Warm and hot exozodiacal dust needs to be
studied in order to trace regions close to the habitable zone.
Aims. We aim to determine the prevalence and to constrain the properties of
hot exozodiacal dust around nearby main-sequence stars.
Methods. We search a magnitude limited (H < 5) sample of 92 stars for bright
exozodiacal dust using our VLTI visitor instrument PIONIER in the H-band. We
derive statistics of the detection rate with respect to parameters such as the
stellar spectral type and age or the presence of a debris disk in the outer
regions of the systems. We derive more robust statistics by combining our
sample with the results from our CHARA/FLUOR survey in the K-band. In addition,
our spectrally dispersed data allows us to put constraints on the emission
mechanism and the dust properties in the detected systems.
Results. We find an over-all detection rate of bright exozodiacal dust in the
H-band of 11% (9 out of 85 targets) and three tentative detections. The
detection rate decreases from early type to late type stars and increases with
the age of the host star. We do not confirm the tentative correlation between
the presence of cold and hot dust found in our earlier analysis of the FLUOR
sample alone. Our spectrally dispersed data suggest that either the dust is
extremely hot or the emission is dominated by the scattered light in most
cases. The implications of our results for the target selection of future
terrestrial planet finding missions using direct imaging are discussed.Comment: 20 pages, 16 figures, 4 tables, updated references and minor changes
to the text, accepted for publication in A&
L'-band AGPM vector vortex coronagraph's first light on LBTI/LMIRCam
We present the first observations obtained with the L'-band AGPM vortex
coronagraph recently installed on LBTI/LMIRCam. The AGPM (Annular Groove Phase
Mask) is a vector vortex coronagraph made from diamond subwavelength gratings.
It is designed to improve the sensitivity and dynamic range of high-resolution
imaging at very small inner working angles, down to 0.09 arcseconds in the case
of LBTI/LMIRCam in the L' band. During the first hours on sky, we observed the
young A5V star HR\,8799 with the goal to demonstrate the AGPM performance and
assess its relevance for the ongoing LBTI planet survey (LEECH). Preliminary
analyses of the data reveal the four known planets clearly at high SNR and
provide unprecedented sensitivity limits in the inner planetary system (down to
the diffraction limit of 0.09 arcseconds).Comment: 9 pages, 4 figures, SPIE proceeding
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