453 research outputs found
Direct imaging constraints on planet populations detected by microlensing
Results from gravitational microlensing suggested the existence of a large
population of free-floating planetary mass objects. The main conclusion from
this work was partly based on constraints from a direct imaging survey. This
survey determined upper limits for the frequency of stars that harbor giant
exoplanets at large orbital separations. Aims. We want to verify to what extent
upper limits from direct imaging do indeed constrain the microlensing results.
We examine the current derivation of the upper limits used in the microlensing
study and re-analyze the data from the corresponding imaging survey. We focus
on the mass and semi-major axis ranges that are most relevant in context of the
microlensing results. We also consider new results from a recent M-dwarf
imaging survey as these objects are typically the host stars for planets
detected by microlensing. We find that the upper limits currently applied in
context of the microlensing results are probably underestimated. This means
that a larger fraction of stars than assumed may harbor gas giant planets at
larger orbital separations. Also, the way the upper limit is currently used to
estimate the fraction of free-floating objects is not strictly correct. If the
planetary surface density of giant planets around M-dwarfs is described as
df_Planet ~ a^beta da, we find that beta ~ 0.5 - 0.6 is consistent with results
from different observational studies probing semi-major axes between ~0.03 - 30
AU. Having a higher upper limit on the fraction of stars that may have gas
giant planets at orbital separations probed by the microlensing data implies
that more of the planets detected in the microlensing study are potentially
bound to stars rather than free-floating. The current observational data are
consistent with a rising planetary surface density for giant exoplanets around
M-dwarfs out to ~30 AU.Comment: Accepted for publication in A&A as Research Note, 3 page
Comparaison de deux méthodes de dissémination de résultats de recherche dans le domaine de la santé : les arts et le café scientifique
Un nombre croissant de chercheurs du domaine de la santé se tournent vers des formes novatrices de recherche alliant les méthodologies des sciences sociales et des arts performatifs, littéraires et visuels. Cet article compare et analyse deux méthodes de dissémination de résultats de recherche dans le domaine de la santé : le café scientifique et la performance artistique (arts visuels, chant, poésie, théâtre). L’analyse de questionnaires remplis par 78 répondants et d’entrevues menées auprès de ces personnes indique que la performance artistique est plus efficace dans la communication de résultats de recherche selon trois des quatre critères d’évaluation utilisés : elle suscite davantage d’émotions chez les membres de l’auditoire, suscite plus de questions sur le sujet couvert et influence un plus grand nombre de personnes à modifier leur point de vue et leurs pratiques. Tant le café scientifique que la performance artistique aident les participants à comprendre la problématique exposée. Les arts permettent cependant une compréhension différente.A growing numbers of researchers in the health sector are opting for innovative research approaches that combine methodologies from the social sciences and the performing, literary and visual arts. This article compares and contrasts two methods for disseminating research findings related to health : science cafés and artistic performance (visual arts, song, poetry, theatre). An analysis of questionnaires and interviews completed by 78 respondents shows that artistic performance is more effective in communicating research results based on three of the four evaluation criteria used : it triggers more emotions among audience members, generates more questions on the topic concerned, and influences a greater number of people to alter their viewpoints and change their practices. Science cafés and artistic performance both help participants to better understand the issues examined. The arts, however, shine a different light on these issues.Un creciente número de investigadores del área de la salud se dirige hacia formas de investigación innovadoras, utilizando metodologÃas de las ciencias sociales y de las artes interpretativas, literarias y visuales. Ese artÃculo compara y contrasta dos métodos de diseminación de los resultados de investigación en el área de la salud : el café cientÃfico y la interpretación artÃstica (artes visuales, canto, poesÃa, teatro). El análisis de los cuestionarios y de las entrevistas realizadas por 78 individuos indica que la interpretación artÃstica es más eficaz en la comunicación de resultados de investigación según tres de los cuatro criterios de evaluación utilizados : aquella suscita más emociones en los miembros del auditorio, genera más cuestionamientos acerca del tema tratado e influye a un mayor número de personas en cuanto a la modificación de su punto de vista y sus prácticas. Tanto el café cientÃfico como la interpretación artÃstica ayudan a los participantes a comprender la problemática expuesta. Sin embargo, las artes permiten una comprensión diferente
VLT/NACO astrometry of the HR8799 planetary system. L'-band observations of the three outer planets
HR8799 is so far the only directly imaged multiple exoplanet system. The
orbital configuration would, if better known, provide valuable insight into the
formation and dynamical evolution of wide-orbit planetary systems. We present
L'-band observations of the HR8799 system obtained with NACO at VLT, adding to
the astrometric monitoring of the planets HR8799b, c and d. We investigate how
well the two simple cases of (i) a circular orbit and (ii) a face-on orbit fit
the astrometric data for HR8799d over a total time baseline of ~2 years. The
results indicate that the orbit of HR8799d is inclined with respect to our line
of sight, and suggest that the orbit is slightly eccentric or non-coplanar with
the outer planets and debris disk.Comment: 5 pages, 4 figures, 1 table, accepted for publication in A\&A.
Updated version includes minor changes made in the proof
Two Wide Planetary-Mass Companions to Solar-Type Stars in Upper Scorpius
At wide separations, planetary-mass and brown dwarf companions to solar type
stars occupy a curious region of parameters space not obviously linked to
binary star formation or solar-system scale planet formation. These companions
provide insight into the extreme case of companion formation (either binary or
planetary), and due to their relative ease of observation when compared to
close companions, they offer a useful template for our expectations of more
typical planets. We present the results from an adaptive optics imaging survey
for wide (50-500 AU) companions to solar type stars in Upper Scorpius. We
report one new discovery of a ~14 M_J companion around GSC 06214-00210, and
confirm that the candidate planetary mass companion 1RXS J160929.1-210524
detected by Lafreniere et al (2008) is in fact co-moving with its primary star.
In our survey, these two detections correspond to ~4% of solar type stars
having companions in the 6-20 M_J mass and 200-500 AU separation range. This
figure is higher than would be expected if brown dwarfs and planetary mass
companions were drawn from an extrapolation of the binary mass function.
Finally, we discuss implications for the formation of these objects.Comment: 11 Pages, 7 Figures, Accepted for Ap
On the origin of planets at very wide orbits from the re-capture of free floating planets
In recent years several planets have been discovered at wide orbits (>100 AU)
around their host stars. Theoretical studies encounter difficulties in
explaining their formation and origin. Here we propose a novel scenario for the
production of planetary systems at such orbits, through the dynamical recapture
of free floating planets (FFPs) in dispersing stellar clusters. This process is
a natural extension of the recently suggested scenario for the formation of
wide stellar binaries. We use N-body simulations of dispersing clusters with
10-1000 stars and comparable numbers of FFPs to study this process. We find
that planets are captured into wide orbits in the typical range ~100-10^6 AU,
and have a wide range of eccentricities (thermal distribution). Typically, 3-6
x (f_FFP/1) % of all stars capture a planetary companion with such properties
(where f_FFP is the number of FFP per star). The planetary capture efficiency
is comparable to that of capture-formed stellar-binaries, and shows a similar
dependence on the cluster size and structure. It is almost independent of the
specific planetary mass; planets as well as sub-stellar companions of any mass
can be captured. The capture efficiency decreases with increasing cluster size,
and for a given cluster size the it increases with the host/primary mass. More
than one planet can be captured around the same host and planets can be
captured into binary systems. Planets can also be captured into pre-existing
planetary and into orbits around black holes and massive white dwarfs, if these
formed early enough before the cluster dispersal. In particular, stellar black
holes have a high capture efficiency (>50 % and 5-10 x (f_FFP/1) % for capture
of stars and planetary companions, respectively) due to their large mass.
Finally, although rare, two FFPs or brown dwarfs can become bound and form a
FFP-binary system with no stellar host.Comment: ApJ, in press. Added two figure
Discovery of the brightest T dwarf in the northern hemisphere
We report the discovery of a bright (H=12.77) brown dwarf designated SIMP
J013656.5+093347. The discovery was made as part of a near-infrared proper
motion survey, SIMP (Sondage Infrarouge de Mouvement Propre), which uses proper
motion and near-infrared/optical photometry to identify brown dwarf candidates.
A low resolution (lambda/dlambda~40) spectrum of this brown dwarf covering the
0.88-2.35 microns wavelength interval is presented. Analysis of the spectrum
indicates a spectral type of T2.5+/-0.5. A photometric distance of 6.4+/-0.3 pc
is estimated assuming it is a single object. Current observations rule out a
binary of mass ratio ~1 and separation >5 AU. SIMP 0136 is the brightest T
dwarf in the northern hemisphere and is surpassed only by Eps Indi Bab over the
whole sky. It is thus an excellent candidate for detailed studies and should
become a benchmark object for the early-T spectral class.Comment: 4 pages, 3 figures, To be published in November 1, 2006 issue of
ApJL. Following IAU recommendation, the survey acronym (IBIS) was changed to
SIM
MESS (Multi-purpose Exoplanet Simulation System): A Monte Carlo tool for the statistical analysis and prediction of exoplanets search results
The high number of planet discoveries made in the last years provides a good
sample for statistical analysis, leading to some clues on the distributions of
planet parameters, like masses and periods, at least in close proximity to the
host star. We likely need to wait for the extremely large telescopes (ELTs) to
have an overall view of the extrasolar planetary systems. In this context it
would be useful to have a tool that can be used for the interpretation of the
present results,and also to predict what the outcomes would be of the future
instruments. For this reason we built MESS: a Monte Carlo simulation code which
uses either the results of the statistical analysis of the properties of
discovered planets, or the results of the planet formation theories, to build
synthetic planet populations fully described in terms of frequency, orbital
elements and physical properties. They can then be used to either test the
consistency of their properties with the observed population of planets given
different detection techniques or to actually predict the expected number of
planets for future surveys. In addition to the code description, we present
here some of its applications to actually probe the physical and orbital
properties of a putative companion within the circumstellar disk of a given
star and to test constrain the orbital distribution properties of a potential
planet population around the members of the TW Hydrae association. Finally,
using in its predictive mode, the synergy of future space and ground-based
telescopes instrumentation has been investigated to identify the mass-period
parameter space that will be probed in future surveys for giant and rocky
planetsComment: 14 pages, 16 figure
Clouds and Chemistry in the Atmosphere of Extrasolar Planet HR8799b
Using the integral field spectrograph OSIRIS, on the Keck II telescope, broad
near-infrared H and K-band spectra of the young exoplanet HR8799b have been
obtained. In addition, six new narrow-band photometric measurements have been
taken across the H and K bands. These data are combined with previously
published photometry for an analysis of the planet's atmospheric properties.
Thick photospheric dust cloud opacity is invoked to explain the planet's red
near-IR colors and relatively smooth near-IR spectrum. Strong water absorption
is detected, indicating a Hydrogen-rich atmosphere. Only weak CH4 absorption is
detected at K band, indicating efficient vertical mixing and a disequilibrium
CO/CH4 ratio at photospheric depths. The H-band spectrum has a distinct
triangular shape consistent with low surface gravity. New giant planet
atmosphere models are compared to these data with best fitting bulk parameters,
Teff = 1100K +- 100 and log(g) = 3.5 +-0.5 (for solar composition). Given the
observed luminosity, log(Lobs/Lsun) ~ -5.1, these values correspond to a radius
of 0.75 Rjup (+0.17, -0.12) and mass ~ 0.72 Mjup (+2.6,-0.6) -- strikingly
inconsistent with interior/evolution models. Enhanced metallicity (up to ~ 10
times that of the Sun) along with thick clouds and non-equilibrium chemistry
are likely required to reproduce the complete ensemble of spectroscopic and
photometric data and the low effective temperatures (< 1000K) required by the
evolution models.Comment: 17 pages, accepted for publication in The Astrophysical Journa
Discovery of the Coldest Imaged Companion of a Sun-Like Star
We present the discovery of a brown dwarf or possible planet at a projected
separation of 1.9" = 29 AU around the star GJ 758, placing it between the
separations at which substellar companions are expected to form by core
accretion (~5 AU) or direct gravitational collapse (typically >100 AU). The
object was detected by direct imaging of its thermal glow with Subaru/HiCIAO.
At 10-40 times the mass of Jupiter and a temperature of 550-640 K, GJ 758 B
constitutes one of the few known T-type companions, and the coldest ever to be
imaged in thermal light around a Sun-like star. Its orbit is likely eccentric
and of a size comparable to Pluto's orbit, possibly as a result of
gravitational scattering or outward migration. A candidate second companion is
detected at 1.2" at one epoch.Comment: 5 pages, 3 figures, 2 tables. Accepted for publication in ApJ Letter
Spitzer 3.6 micron and 4.5 micron full-orbit lightcurves of WASP-18
We present new lightcurves of the massive hot Jupiter system WASP-18 obtained
with the Spitzer spacecraft covering the entire orbit at 3.6 micron and 4.5
micron. These lightcurves are used to measure the amplitude, shape and phase of
the thermal phase effect for WASP-18b. We find that our results for the thermal
phase effect are limited to an accuracy of about 0.01% by systematic noise
sources of unknown origin. At this level of accuracy we find that the thermal
phase effect has a peak-to-peak amplitude approximately equal to the secondary
eclipse depth, has a sinusoidal shape and that the maximum brightness occurs at
the same phase as mid-occultation to within about 5 degrees at 3.6 micron and
to within about 10 degrees at 4.5 micron. The shape and amplitude of the
thermal phase curve imply very low levels of heat redistribution within the
atmosphere of the planet. We also perform a separate analysis to determine the
system geometry by fitting a lightcurve model to the data covering the
occultation and the transit. The secondary eclipse depths we measure at 3.6
micron and 4.5 micron are in good agreement with previous measurements and
imply a very low albedo for WASP-18b. The parameters of the system (masses,
radii, etc.) derived from our analysis are in also good agreement with those
from previous studies, but with improved precision. We use new high-resolution
imaging and published limits on the rate of change of the mean radial velocity
to check for the presence of any faint companion stars that may affect our
results. We find that there is unlikely to be any significant contribution to
the flux at Spitzer wavelengths from a stellar companion to WASP-18. We find
that there is no evidence for variations in the times of eclipse from a linear
ephemeris greater than about 100 seconds over 3 years.Comment: 17 pages, 10 figures. Accpeted for publication in MNRA
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