562 research outputs found
Orbital Stability of Planets in Binary Systems: A New Look at Old Results
About half of all known stellar systems with Sun-like stars consist of two or
more stars, significantly affecting the orbital stability of any planet in
these systems. This observational evidence has prompted a large array of
theoretical research, including the derivation of mathematically stringent
criteria for the orbital stability of planets in stellar binary systems, valid
for the "coplanar circular restricted three-body problem". In the following, we
use these criteria to explore the validity of results from previous theoretical
studies.Comment: 3 pages, 1 figure; submitted to: Exoplanets: Detection, Formation and
Dynamics, IAU Symposium 249, eds. Y.-S. Sun, S. Ferraz-Mello, and J.-L. Zhou
(Cambridge: Cambridge University Press
A survey of young, nearby, and dusty stars to understand the formation of wide-orbit giant planets
Direct imaging has confirmed the existence of substellar companions on wide
orbits. To understand the formation and evolution mechanisms of these
companions, the full population properties must be characterized. We aim at
detecting giant planet and/or brown dwarf companions around young, nearby, and
dusty stars. Our goal is also to provide statistics on the population of giant
planets at wide-orbits and discuss planet formation models. We report a deep
survey of 59 stars, members of young stellar associations. The observations
were conducted with VLT/NaCo at L'-band (3.8 micron). We used angular
differential imaging to reach optimal detection performance. A statistical
analysis of about 60 % of the young and southern A-F stars closer than 65 pc
allows us to derive the fraction of giant planets on wide orbits. We use
gravitational instability models and planet population synthesis models
following the core-accretion scenario to discuss the occurrence of these
companions. We resolve and characterize new visual binaries and do not detect
any new substellar companion. The survey's median detection performance reaches
contrasts of 10 mag at 0.5as and 11.5 mag at 1as. We find the occurrence of
planets to be between 10.8-24.8 % at 68 % confidence level assuming a uniform
distribution of planets in the interval 1-13 Mj and 1-1000 AU. Considering the
predictions of formation models, we set important constraints on the occurrence
of massive planets and brown dwarf companions that would have formed by GI. We
show that this mechanism favors the formation of rather massive clump (Mclump >
30 Mj) at wide (a > 40 AU) orbits which might evolve dynamically and/or
fragment. For the population of close-in giant planets that would have formed
by CA, our survey marginally explore physical separations (<20 AU) and cannot
constrain this population
High-resolution physical map for chromosome 16q12.1-q13, the Blau syndrome locus
BACKGROUND: The Blau syndrome (MIM 186580), an autosomal dominant granulomatous disease, was previously mapped to chromosome 16p12-q21. However, inconsistent physical maps of the region and consequently an unknown order of microsatellite markers, hampered us from further refining the genetic locus for the Blau syndrome. To address this problem, we constructed our own high-resolution physical map for the Blau susceptibility region. RESULTS: We generated a high-resolution physical map that provides more than 90% coverage of a refined Blau susceptibility region. The map consists of four contigs of sequence tagged site-based bacterial artificial chromosomes with a total of 124 bacterial artificial chromosomes, and spans approximately 7.5 Mbp; however, three gaps still exist in this map with sizes of 425, 530 and 375 kbp, respectively, estimated from radiation hybrid mapping. CONCLUSIONS: Our high-resolution map will assist genetic studies of loci in the interval from D16S3080, near D16S409, and D16S408 (16q12.1 to 16q13)
Deep imaging survey of young, nearby austral stars: VLT/NACO near-infrared Lyot-coronographic observations
Context. High contrast and high angular resolution imaging is the optimal search technique for substellar companions to nearby stars at physical separations larger than typically 10 AU. Two distinct populations of substellar companions, brown dwarfs and planets, can be probed and characterized. As a result, fossile traces of processes of formation and evolution can be revealed by physical and orbital properties, both for individual systems and as an ensemble.
Aims. Since November 2002, we have conducted a large, deep imaging, survey of young, nearby associations of the southern hemisphere. Our goal is detection and characterization of substellar companions with projected separations in the range 10–500 AU. We have observed a sample of 88 stars, primarily G to M dwarfs, younger than 100 Myr, and within 100 pc of Earth.
Methods. The VLT/NACO adaptive optics instrument of the ESO Paranal Observatory was used to explore the faint circumstellar environment between typically 0.1 and 10". Diffraction-limited observations in H and K_s-band combined with Lyot-coronagraphy enabled us to reach primary star-companion brightness ratios as small as 10^(-6). The existence of planetary mass companions could therefore be probed. We used a standardized observing sequence to precisely measure the position and flux of all detected sources relative to their visual primary star. Repeated observations at several epochs enabled us to discriminate comoving companions from background objects.
Results. We report the discovery of 17 new close (0.1–5.0") multiple systems. HIP 108195 AB and C (F1 III-M6), HIP 84642 AB (a~14 AU, K0-M5) and TWA22 AB (a~1.8 AU; M6-M6) are confirmed comoving systems. TWA22 AB is likely to be a rare astrometric calibrator that can be used to test evolutionary model predictions. Among our complete sample, a total of 65 targets were observed with deep coronagraphic imaging. About 240 faint companion candidates were detected around 36 stars. Follow-up observations with VLT or HST for 83% of these stars enabled us to identify a large fraction of background contaminants. Our latest results that pertain to the substellar companions to GSC 08047-00232, AB Pic and 2M1207 (confirmed during this survey and published earlier), are reviewed. Finally, a statistical analysis of our complete set of coronagraphic detection limits enables us to place constraints on the physical and orbital properties of giant planets between typically 20 and 150 AU
Report on the excavation of a Punic tomb
On 19th November 2001, while two of us (DB, NJC)
were preparing a drawn record of the Punic tomb
that is situated on Bajda Ridge, Xemxija, a small
ceramic bowl (100211) was uncovered from below
a few centimetres of soil that covered the inner part
of the threshold to the rock-cut chamber (Fig. 1).
An official from the Museums Department was
informed of the discovery on the same day and a
site inspection was carried out. It was realised that
more artefacts could lie undisturbed within the
chamber and a decision was taken to excavate the
deposit. Authorisation for the Department of
Classics and Archaeology, University of Malta, to
undertake the excavation was received from the
Director, Museums Department, and the excavation
was completed on the 22nd November.
The tomb is located on the ridge, near a path that
diverges eastwards from the track that links Pwales
valley to the Mistra valley. It is cut in the Upper
Coralline limestone that outcrops in the area on a
North-South axis and consists of a sub-rectangular
chamber that is reached through a low entrance at
the bottom of a rectangular shaft (Fig. 1).
The tomb appears in an inventory for the first time
in 1996 when it was listed in the survey of
archaeological sites prepared by Malta University
Services for the Planning Authority by Anthony
Bonanno in connection with the preparation of the
North-West local plan for Malta. The tomb had been
examined and photographed by one of us (NCV) in
1992. At the time, it was littered with debris and it
was only with difficulty that a view of the chamber
could be achieved through the entrance that was
partly concealed by an irregular blocking stone. Late
in 2000, members of the St Paul's Bay Heritage
Group lifted the debris from the trench and cleared
the area around the site.peer-reviewe
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
Discovery of a probable 4-5 Jupiter-mass exoplanet to HD 95086 by direct-imaging
Direct imaging has just started the inventory of the population of gas giant
planets on wide-orbits around young stars in the solar neighborhood. Following
this approach, we carried out a deep imaging survey in the near-infrared using
VLT/NaCo to search for substellar companions. We report here the discovery in
L' (3.8 microns) images of a probable companion orbiting at 56 AU the young
(10-17 Myr), dusty, and early-type (A8) star HD 95086. This discovery is based
on observations with more than a year-time-lapse. Our first epoch clearly
revealed the source at 10 sigma while our second epoch lacked good observing
conditions hence yielding a 3 sigma detection. Various tests were thus made to
rule out possible artifacts. This recovery is consistent with the signal at the
first epoch but requires cleaner confirmation. Nevertheless, our astrometric
precision suggests the companion to be comoving with the star, with a 3 sigma
confidence level. The planetary nature of the source is reinforced by a
non-detection in Ks-band (2.18 microns) images according to its possible
extremely red Ks - L' color. Conversely, background contamination is rejected
with good confidence level. The luminosity yields a predicted mass of about
4-5MJup (at 10-17 Myr) using "hot-start" evolutionary models, making HD 95086 b
the exoplanet with the lowest mass ever imaged around a star.Comment: accepted for publication to APJ
Incidence of traumatic spinal cord injury in Italy during 2013–2014: a population-based study
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Spectral estimates for saddle point matrices arising in weak constraint four-dimensional variational data assimilation
We consider the large-sparse symmetric linear systems of equations that arise in the solution of weak constraint four-dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a block structure but block eliminations can be performed to reduce them to saddle point systems with a block structure, or further to symmetric positive definite systems. In this paper, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds
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