427 research outputs found
Signatures of massive collisions in debris discs
Violent stochastic collisional events have been invoked as a possible
explanation for some debris discs displaying pronounced asymmetries or having a
great luminosity excess. So far, no thorough modelling of the consequences of
such events has been carried out, mainly because of the extreme numerical
challenge of coupling the dynamical and collisional evolution of dust.
We perform the first fully self-consistent modelling of the aftermath of
massive breakups in debris discs. We follow the collisional and dynamical
evolution of dust released after the breakup of a Ceres-sized body at 6 AU from
its central star. We investigate the duration, magnitude and spatial structure
of the signature left by such a violent event, as well as its observational
detectability.
We use the recently developed LIDT-DD code (Kral et al., 2013), which handles
the coupled collisional and dynamical evolution of debris discs. The main focus
is placed on the complex interplay between destructive collisions, Keplerian
dynamics and radiation pressure forces. We use the GRaTer package to estimate
the system's luminosity at different wavelengths.
The breakup of a Ceres-sized body at 6 AU creates an asymmetric dust disc
that is homogenized, by the coupled action of collisions and dynamics, on a
timescale of a few years. The luminosity excess in the breakup's
aftermath should be detectable by mid-IR photometry, from a 30 pc distance,
over a period of years that exceeds the duration of the asymmetric
phase of the disc (a few years). As for the asymmetric structures, we
derive synthetic images for the SPHERE/VLT and MIRI/JWST instruments, showing
that they should be clearly visible and resolved from a 10 pc distance. Images
at 1.6m (marginally), 11.4 and 15.5m would show the inner disc
structures while 23m images would display the outer disc asymmetries.Comment: 16 pages, 14 figures, abstract shortened, accepted for publication in
A&
Independent confirmation of {\beta} Pictoris b imaging with NICI
Context. {\beta} Pictoris b is one of the most studied objects nowadays since
it was identified with VLT/NaCo as a bona-fide exoplanet with a mass of about 9
times that of Jupiter at an orbital separation of 8-9 AU. The link between the
planet and the dusty disk is unambiguously attested and this system provides an
opportunity to study the disk/planet interactions and to constrain formation
and evolutionary models of gas giant planets. Still, {\beta} Pictoris b had
never been confirmed with other telescopes so far. Aims. We aimed at an
independent confirmation using a different instrument. Methods. We retrieved
archive images from Gemini South obtained with the instrument NICI, which is
designed for high contrast imaging. The observations combine coronagraphy and
angular differential imaging and were obtained at three epochs in Nov. 2008,
Dec. 2009 and Dec. 2010. Results. We report the detection with NICI of the
planet {\beta} Pictoris b in Dec. 2010 images at a separation of 404 \pm 10 mas
and P A = 212.1 \pm 0.7{\deg} . It is the first time this planet is observed
with a telescope different than the VLT.Comment: Letter accepted for publication in Astronomy and Astrophysics on Feb.
21, 2013. 4 pages, 2 figure
Fast-moving features in the debris disk around AU Microscopii
In the 1980s, excess infrared emission was discovered around main-sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source. These ‘debris disks’ were thought to be by-products of planet formation because they often exhibited morphological and brightness asymmetries that may result from gravitational perturbation by planets. This was proved to be true for the β Pictoris system, in which the known planet generates an observable warp in the disk. The nearby, young, unusually active late-type star AU Microscopii hosts a well-studied edge-on debris disk; earlier observations in the visible and near-infrared found asymmetric localized structures in the form of intensity variations along the midplane of the disk beyond a distance of 20 astronomical units. Here we report high-contrast imaging that reveals a series of five large-scale features in the southeast side of the disk, at projected separations of 10–60 astronomical units, persisting over intervals of 1–4 years. All these features appear to move away from the star at projected speeds of 4–10 kilometres per second, suggesting highly eccentric or unbound trajectories if they are associated with physical entities. The origin, localization, morphology and rapid evolution of these features are difficult to reconcile with current theories
Near-Infrared Detection and Characterization of the Exoplanet HD 95086 b with the Gemini Planet Imager
HD 95086 is an intermediate-mass debris-disk-bearing star. VLT/NaCo observations revealed it hosts a companion (HD
95086 b) at AU. Follow-up observations at 1.66 and 2.18
yielded a null detection, suggesting extremely red colors for the planet and
the need for deeper direct-imaging data. In this Letter, we report H- () and - () band detections of HD 95086 b from
Gemini Planet Imager (GPI) commissioning observations taken by the GPI team.
The planet position in both spectral channels is consistent with the NaCo
measurements and we confirm it to be comoving. Our photometry yields colors of
H-L'= mag and K-L'= mag, consistent with
previously reported 5- upper limits in H and Ks. The photometry of HD
95086 b best matches that of 2M 1207 b and HR 8799 cde. Comparing its spectral
energy distribution with the BT-SETTL and LESIA planet atmospheric models
yields T600-1500 K and log g2.1-4.5. Hot-start
evolutionary models yield M= M. Warm-start models reproduce the
combined absolute fluxes of the object for M=4-14 M for a wide range of
plausible initial conditions (S=8-13 k/baryon). The
color-magnitude diagram location of HD 95086 b and its estimated
T and log g suggest that the planet is a peculiar L-T
transition object with an enhanced amount of photospheric dust.Comment: 4 pages, 4 figures, 3 tables, accepted on April, 15th, 201
Spectral signatures from super-Earths, warm and hot-Neptunes
ESA's and NASA's planet characterization missions, will allow us to explore the diversity
of planets around stars of different spectral type, and will expand the existing field of
comparative planetology beyond our Solar System. In particular, terrestrial planets
greater than one Earth mass are not represented in our Solar System, but may occur in
others (Beaulieu et al., 2006; Rivera et al. 2005). The next generation of space telescopes,
the James Webb Space Telescope (2013), will have the capability of acquiring
transmission and emission spectra in the infrared of these extrasolar worlds. Further into
the future, the direct imaging of exoplanets, both in the optical and infrared, will extend
our understanding to extrasolar bodies orbiting few Astronomical Units from their parent
star and expand our knowledge to smaller-size objects
Fundamental limitations of high contrast imaging set by small sample statistics
In this paper, we review the impact of small sample statistics on detection
thresholds and corresponding confidence levels (CLs) in high contrast imaging
at small angles. When looking close to the star, the number of resolution
elements decreases rapidly towards small angles. This reduction of the number
of degrees of freedom dramatically affects CLs and false alarm probabilities.
Naively using the same ideal hypothesis and methods as for larger separations,
which are well understood and commonly assume Gaussian noise, can yield up to
one order of magnitude error in contrast estimations at fixed CL. The
statistical penalty exponentially increases towards very small inner working
angles. Even at 5-10 resolution elements from the star, false alarm
probabilities can be significantly higher than expected. Here we present a
rigorous statistical analysis which ensures robustness of the CL, but also
imposes a substantial limitation on corresponding achievable detection limits
(thus contrast) at small angles. This unavoidable fundamental statistical
effect has a significant impact on current coronagraphic and future high
contrast imagers. Finally, the paper concludes with practical recommendations
to account for small number statistics when computing the sensitivity to
companions at small angles and when exploiting the results of direct imaging
planet surveys.Comment: 12 pages, 10 figures, accepted to Ap
Design study and first performance simulation of the ELT/MICADO focal plane coronagraphs
In this paper, we present the design and the expected performance of the
classical Lyot coronagraph for the high contrast imaging modes of the
wide-field imager MICADO. MICADO is a near-IR camera for the Extremely Large
Telescope (ELT, previously E-ELT), with wide-field, spectroscopic and
coronagraphic capabilities. MICADO is one of the first-light instruments
selected by the ESO. Optimized to work with a multi-conjugate adaptive optics
corrections provided by the MOARY module, it will also come with a SCAO
correction with a high-level, on-axis correction, making use of the M4 adaptive
mirror of the telescope.
After presenting the context of the high contrast imaging modes in MICADO, we
describe the selection process for the focal plane masks and Lyot stop. We will
also show results obtained in realistic conditions, taking into account AO
residuals, atmospheric refraction, noise sources and simulating observations in
angular differential imaging (ADI) mode. Based on SPHERE on-sky results, we
will discuss the achievable gain in contrast and angular separation provided by
MICADO over the current instruments on 10-m class telescopes, in particular for
imaging young giant planets at very short separations around nearby stars as
well as planets on wider orbits around more distant stars in young stellar
associations.Comment: 10 pages, 5 figures, AO4ELT 5 conference proceedin
SPOTS: The Search for Planets Orbiting Two Stars. I. Survey description and first observations
Direct imaging surveys for exoplanets commonly exclude binary stars from
their target lists, leaving a large part of the overall planet demography
unexplored. To address this gap in our understanding of planet formation and
evolution, we have launched the first direct imaging survey dedicated to
circumbinary planets: SPOTS, the Search for Planets Orbiting Two Stars. In this
paper, we discuss the theoretical context, scientific merit, and technical
feasibility of such observations, describe the target sample and observational
strategy of our survey, and report on the first results from our pilot survey
of 26 targets with the VLT NaCo facility. While we have not found any confirmed
substellar companions to date, a number of promising candidate companions
remain to be tested for common proper motion in upcoming follow-up
observations. We also report on the astrometry of the three resolved binaries
in our target sample. This pilot survey constitutes a successful proof of
concept for our survey strategy and paves the way for a second stage of
exploratory observations with VLT SPHERE.Comment: 12 pages, 4 figures, 3 tables. Accepted for publication in A&
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