361 research outputs found
Direct Imaging of Multiple Planets Orbiting the Star HR 8799
Direct imaging of exoplanetary systems is a powerful technique that can
reveal Jupiter-like planets in wide orbits, can enable detailed
characterization of planetary atmospheres, and is a key step towards imaging
Earth-like planets. Imaging detections are challenging due to the combined
effect of small angular separation and large luminosity contrast between a
planet and its host star. High-contrast observations with the Keck and Gemini
telescopes have revealed three planets orbiting the star HR 8799, with
projected separations of 24, 38, and 68 astronomical units. Multi-epoch data
show counter-clockwise orbital motion for all three imaged planets. The low
luminosity of the companions and the estimated age of the system imply
planetary masses between 5 and 13 times that of Jupiter. This system resembles
a scaled-up version of the outer portion of our Solar System.Comment: 30 pages, 5 figures, Research Article published online in Science
Express Nov 13th, 200
Photometric characterization of exoplanets using angular and spectral differential imaging
The direct detection of exoplanets has been the subject of intensive research
in the recent years. Data obtained with future high-contrast imaging
instruments optimized for giant planets direct detection are strongly limited
by the speckle noise. Specific observing strategies and data analysis methods,
such as angular and spectral differential imaging, are required to attenuate
the noise level and possibly detect the faint planet flux. Even though these
methods are very efficient at suppressing the speckles, the photometry of the
faint planets is dominated by the speckle residuals. The determination of the
effective temperature and surface gravity of the detected planets from
photometric measurements in different bands is then limited by the photometric
error on the planet flux. In this work we investigate this photometric error
and the consequences on the determination of the physical parameters of the
detected planets. We perform detailed end-to-end simulation with the CAOS-based
Software Package for SPHERE to obtain realistic data representing typical
observing sequences in Y, J, H and Ks bands with a high contrast imager. The
simulated data are used to measure the photometric accuracy as a function of
contrast for planets detected with angular and spectral+angular differential
methods. We apply this empirical accuracy to study the characterization
capabilities of a high-contrast differential imager. We show that the expected
photometric performances will allow the detection and characterization of
exoplanets down to the Jupiter mass at angular separations of 1.0" and 0.2"
respectively around high mass and low mass stars with 2 observations in
different filter pairs. We also show that the determination of the planets
physical parameters from photometric measurements in different filter pairs is
essentialy limited by the error on the determination of the surface gravity.Comment: 13 pages, 7 figures, 4 tables. Accepted for publication in MNRA
Discovery of a 66 mas Ultracool Binary with Laser Guide Star Adaptive Optics
We present the discovery of 2MASS J21321145+1341584AB as a closely separated
(0.066") very low-mass field dwarf binary resolved in the near-infrared by the
Keck II Telescope using laser guide star adaptive optics. Physical association
is deduced from the angular proximity of the components and constraints on
their common proper motion. We have obtained a near-infrared spectrum of the
binary and find that it is best described by an L5+/-0.5 primary and an
L7.5+/-0.5 secondary. Model-dependent masses predict that the two components
straddle the hydrogen burning limit threshold with the primary likely stellar
and the secondary likely substellar. The properties of this sytem - close
projected separation (1.8+/-0.3 AU) and near unity mass ratio - are consistent
with previous results for very low-mass field binaries. The relatively short
estimated orbital period of this system (~7-12 yr) makes it a good target for
dynamical mass measurements. Interestingly, the system's angular separation is
the tightest yet for any very low-mass binary published from a ground-based
telescope and is the tightest binary discovered with laser guide star adaptive
optics to date.Comment: 10 pages, 3 figures; accepted for publication to A
The VAST Survey - IV. A wide brown dwarf companion to the A3V star Delphini
We report the discovery of a wide co-moving substellar companion to the
nearby ( pc) A3V star Delphini based on imaging and
follow-up spectroscopic observations obtained during the course of our
Volume-limited A-Star (VAST) multiplicity survey. Del was observed over
a five-year baseline with adaptive optics, revealing the presence of a
previously-unresolved companion with a proper motion consistent with that of
the A-type primary. The age of the Del system was estimated as
Myr based on the position of the primary on the colour-magnitude
and temperature-luminosity diagrams. Using intermediate-resolution
near-infrared spectroscopy, the spectrum of Del B is shown to be
consistent with a mid-L dwarf (L), at a temperature of K.
Combining the measured near-infrared magnitude of Del B with the
estimated temperature leads to a model-dependent mass estimate of
M, corresponding to a mass ratio of . At a
projected separation of au, Del B is among the most
widely-separated and extreme-mass ratio substellar companions to a
main-sequence star resolved to-date, providing a rare empirical constraint of
the formation of low-mass ratio companions at extremely wide separations.Comment: 12 pages, 11 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Society, 2014 September 25. Revised to incorporate
typographical errors noted during the proofing proces
The International Deep Planet Survey I. The frequency of wide-orbit massive planets around A-stars
Breakthrough direct detections of planetary companions orbiting A-type stars
confirm the existence of massive planets at relatively large separations, but
dedicated surveys are required to estimate the frequency of similar planetary
systems. To measure the first estimation of the giant exoplanetary systems
frequency at large orbital separation around A-stars, we have conducted a
deep-imaging survey of young (8-400 Myr), nearby (19-84 pc) A- and F-stars to
search for substellar companions in the 10-300 AU range. The sample of 42 stars
combines all A-stars observed in previous AO planet search surveys reported in
the literature with new AO observations from VLT/NaCo and Gemini/NIRI. It
represents an initial subset of the International Deep Planet Survey (IDPS)
sample of stars covering M- to B-stars. The data were obtained with
diffraction-limited observations in H- and Ks-band combined with angular
differential imaging to suppress the speckle noise of the central stars,
resulting in typical 5-sigma detection limits in magnitude difference of 12 mag
at 1", 14 mag at 2" and 16 mag at 5" which is sufficient to detect massive
planets. A detailed statistical analysis of the survey results is performed
using Monte Carlo simulations. Considering the planet detections, we estimate
the fraction of A-stars having at least one massive planet (3-14 MJup) in the
range 5-320 AU to be inside 5.9-18.8% at 68% confidence, assuming a flat
distribution for the mass of the planets. By comparison, the brown dwarf (15-75
MJup) frequency for the sample is 2.0-8.9% at 68% confidence in the range 5-320
AU. Assuming power law distributions for the mass and semimajor axis of the
planet population, the AO data are consistent with a declining number of
massive planets with increasing orbital radius which is distinct from the
rising slope inferred from radial velocity (RV) surveys around evolved A-stars.Comment: 20 pages, 10 figures, 7 tables. Accepted for publication in A&
The VAST Survey - III. The multiplicity of A-type stars within 75 pc
With a combination of adaptive optics imaging and a multi-epoch common proper
motion search, we have conducted a large volume-limited (D 75 pc)
multiplicity survey of A-type stars, sensitive to companions beyond 30 au. The
sample for the Volume-limited A-STar (VAST) survey consists of 435 A-type
stars: 363 stars were observed with adaptive optics, 228 stars were searched
for wide common proper motion companions and 156 stars were measured with both
techniques. The projected separation coverage of the VAST survey extends from
30 to 45,000 au. A total of 137 stellar companions were resolved, including 64
new detections from the VAST survey, and the companion star fraction, projected
separation distribution and mass ratio distribution were measured. The
separation distribution forms a log-normal distribution similar to the
solar-type binary distribution, but with a peak shifted to a significantly
wider value of 387 (+132,-98) au. Integrating the fit to the distribution over
the 30 to 10,000 au observed range, the companion star fraction for A-type
stars is estimated as 33.8%+-2.6%. The mass ratio distribution of closer (<125
au) binaries is distinct from that of wider systems, with a flat distribution
for close systems and a distribution that tends towards smaller mass ratios for
wider binaries. Combining this result with previous spectroscopic surveys of
A-type stars gives an estimate of the total companion star fraction of
68.9%+-7.0%. The most complete assessment of higher order multiples was
estimated from the 156-star subset of the VAST sample with both adaptive optics
and common proper motion measurements, combined with a literature search for
companions, yielding a lower limit on the frequency of single, binary, triple,
quadruple and quintuple A-type star systems of 56.4 (-4.0,+3.8), 32.1
(-3.5,+3.9), 9.0 (-1.8,+2.8), 1.9 (-0.6,+1.8) and 0.6 (-0.2,+1.4) per cent,
respectively.Comment: 46 pages, 24 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Society, 7th October 201
GQ Lup B Visible & Near-Infrared Photometric Analysis
We have re-analyzed archival HST and Subaru data of the recently discovered
planetary mass companion (PMC) GQ Lup B. With these we produce the first R and
I band photometry of the companion and fit a radius and effective temperature
using detailed model atmospheres. We find an effective temperature of 2335 +/-
100K, and a radius of 0.38 +/- 0.05 Rsol and luminosity of log(L/Lsol) = -2.42
+/- 0.07 (at 140pc). Since we fit wavelengths that span most of the emitted
radiation from GQ Lup this luminosity estimate is robust, with uncertainty
dominated by the distance uncertainty (+/- 50 pc). The radius obtained for
140pc (0.38Rsol) is significantly larger than the one originally derived and
larger than model predictions. The mass of the object is much more
model-dependent than the radiative properties, but for the GAIA dusty models we
find a mass between 10-20 MJup, in the range of the brown dwarf and PMC
deuterium burning boundary. Assuming a distance of 140pc, observations fit to
1sigma the Baraffe evolution model for a ~15 MJup brown dwarf. Additionally,
the F606W photometric band is significantly overluminous compared to model
predictions and other brown dwarfs. Such overluminosity could be explained by a
bright Halpha emission from chromospheric activity, interaction with another
undetected companion, or accretion. Assuming that GQ Lup B has a bright Halpha
emission line, its Halpha emission strength is 10^(-1.71 +/- 0.10) Lbol,
significantly larger than field late-type dwarfs. GQ Lup B might be strongly
accreting and still be in its formation phase.Comment: 14 pages, 3 figures, ApJL final accepted versio
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
Local habitat filtering shapes microbial community structure in four closely spaced lakes in the High Arctic
Arctic lakes are experiencing increasingly shorter periods of ice cover due to accelerated warming at northern high latitudes. Given the control of ice cover thickness and duration over many limnological processes, these changes will have pervasive effects. However, due to their remote and extreme locations even first-order data on lake ecology is lacking for many ecosystems. The aim of this study was to characterize and compare the microbial communities of four closely spaced lakes in Stuckberry Valley (northern Ellesmere Island, Canadian Arctic Archipelago), in the coastal margin zone of the Last Ice Area, that differed in their physicochemical, morphological and catchment characteristics. We performed high-throughput amplicon sequencing of the V4 16S rRNA gene to provide inter- and intra-lake comparisons. Two deep (>25 m) and mostly oxygenated lakes showed highly similar community assemblages that were distinct from those of two shallower lakes (<10 m) with anoxic bottom waters. Proteobacteria, Verrucomicrobia, and Planctomycetes were the major phyla present in the four water bodies. One deep lake contained elevated proportions of Cyanobacteria and Thaumarchaeota that distinguished it from the others, while the shallow lakes had abundant communities of predatory bacteria, as well as microbes in their bottom waters that contribute to sulfur and methane cycles. Despite their proximity, our data suggest that local habitat filtering is the primary determinant of microbial diversity in these systems. This study provides the first detailed examination of the microbial assemblages of the Stuckberry lakes system, resulting in new insights into the microbial ecology of the High Arctic
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