31 research outputs found
Disruption of a Proto-Planetary Disk by the Black Hole at the Milky Way Centre
Recently, an ionized cloud of gas was discovered plunging toward the
supermassive black hole, SgrA*, at the centre of the Milky Way. The cloud is
being tidally disrupted along its path to closest approach at ~3100
Schwarzschild radii from the black hole. Here, we show that the observed
properties of this cloud of gas can naturally be produced by a proto-planetary
disk surrounding a low-mass star, which was scattered from the observed ring of
young stars orbiting SgrA*. As the young star approaches the black hole, its
disk experiences both photo-evaporation and tidal disruption, producing a
cloud. Our model implies that planets form in the Galactic centre, and that
tidal debris from proto-planetary disks can flag low mass stars which are
otherwise too faint to be detected.Comment: Accepted to Nature Communications; new Figure 4b provides predicted
Br-gamma emission as a function of tim
An extrasolar planetary system with three Neptune-mass planets
Over the past two years, the search for low-mass extrasolar planets has led
to the detection of seven so-called 'hot Neptunes' or 'super-Earths' around
Sun-like stars. These planets have masses 5-20 times larger than the Earth and
are mainly found on close-in orbits with periods of 2-15 days. Here we report a
system of three Neptune-mass planets with periods of 8.67, 31.6 and 197 days,
orbiting the nearby star HD 69830. This star was already known to show an
infrared excess possibly caused by an asteroid belt within 1 AU (the Sun-Earth
distance). Simulations show that the system is in a dynamically stable
configuration. Theoretical calculations favour a mainly rocky composition for
both inner planets, while the outer planet probably has a significant gaseous
envelope surrounding its rocky/icy core; the outer planet orbits within the
habitable zone of this star.Comment: 17 pages, 3 figures, preprint of the paper published in Nature on May
18, 200
Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets
Nature, 435, pp. 466-469, http://dx.doi.org./10.1038/nature03676International audienc
Rapid in situ imaging and whole genome sequencing of biofilm in neonatal feeding tubes: a clinical proof of concept
The bacterial flora of nasogastric feeding tubes and faecal samples were analysed for a low-birth weight (725g) neonate EGA 25 weeks in intensive care. Samples were collected at age 6 and 8 weeks of life. Optical coherence tomography (OCT) was used to visualise bacterial biofilms inside the nasogastric feeding tubes. The biofilm was heterogeneously distributed along the tube lumen wall, and had a depth of up to 500µm. The bacterial biofilm and faecal samples included Enterococcus faecalis and Enterobacter hormaechei. Representative strains, recovered from both feeding tubes and faecal samples, were whole genome sequenced using Illumina, Mi-Seq, which revealed indistinguishable strains, each with less than 28 SNP differences, of E. faecalis and E. hormaechei. The E. faecalis strains were from two sequence types (ST191 and ST211) and encoded for a number of traits related to biofilm formation (BopD), adherence (Epb pili), virulence (cps loci, gelatinase, SprE) and antibiotic resistances (IsaA, tetM). The E. hormaechei were all ST106, and encoded for blaACT-15 β–lactamase and fosfomycin resistance (fosA). This proof of concept study demonstrates that bacterial flora within the neonatal feeding tubes may influence the bacterial colonisation of the intestinal tract and can be visualised nondestructively using OCT
Do All Stars in the Solar Neighbourhood Form in Clusters?
We present a global study of low mass, young stellar object (YSO) surface
densities (Sigma) in nearby (< 500 pc) star forming regions based on a
comprehensive collection of Spitzer Space Telescope surveys. We show that the
distribution of YSO surface densities is a smooth distribution, being
adequately described by a lognormal function from a few to 10^3 YSOs per pc^2,
with a peak at ~22 stars pc^-2. The observed lognormal Sigma is consistent with
predictions of hierarchically structured star-formation at scales below 10 pc,
arising from the molecular cloud structures. We do not find evidence for
multiple discrete modes of star-formation (e.g. clustered and distributed).
Comparing the observed Sigma distribution to previous Sigma threshold
definitions of clusters show that they are arbitrary. We find that only a low
fraction (< 26$) of stars are formed in dense environments where their
formation/evolution (along with their circumstellar disks and/or planets) may
be affected by the close proximity of their low-mass neighbours.Comment: 7 Pages, 2 Figures, JENAM conference (Lisbon
Planetary population synthesis
In stellar astrophysics, the technique of population synthesis has been
successfully used for several decades. For planets, it is in contrast still a
young method which only became important in recent years because of the rapid
increase of the number of known extrasolar planets, and the associated growth
of statistical observational constraints. With planetary population synthesis,
the theory of planet formation and evolution can be put to the test against
these constraints. In this review of planetary population synthesis, we first
briefly list key observational constraints. Then, the work flow in the method
and its two main components are presented, namely global end-to-end models that
predict planetary system properties directly from protoplanetary disk
properties and probability distributions for these initial conditions. An
overview of various population synthesis models in the literature is given. The
sub-models for the physical processes considered in global models are
described: the evolution of the protoplanetary disk, the planets' accretion of
solids and gas, orbital migration, and N-body interactions among concurrently
growing protoplanets. Next, typical population synthesis results are
illustrated in the form of new syntheses obtained with the latest generation of
the Bern model. Planetary formation tracks, the distribution of planets in the
mass-distance and radius-distance plane, the planetary mass function, and the
distributions of planetary radii, semimajor axes, and luminosities are shown,
linked to underlying physical processes, and compared with their observational
counterparts. We finish by highlighting the most important predictions made by
population synthesis models and discuss the lessons learned from these
predictions - both those later observationally confirmed and those rejected.Comment: 47 pages, 12 figures. Invited review accepted for publication in the
'Handbook of Exoplanets', planet formation section, section editor: Ralph
Pudritz, Springer reference works, Juan Antonio Belmonte and Hans Deeg, Ed
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
The same frequency of planets inside and outside open clusters of stars
Most stars and their planets form in open clusters. Over 95 per cent of such
clusters have stellar densities too low (less than a hundred stars per cubic
parsec) to withstand internal and external dynamical stresses and fall apart
within a few hundred million years. Older open clusters have survived by virtue
of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when
they formed. Such clusters represent a stellar environment very different from
the birthplace of the Sun and other planet-hosting field stars. So far more
than 800 planets have been found around Sun-like stars in the field. The field
planets are usually the size of Neptune or smaller. In contrast, only four
planets have been found orbiting stars in open clusters, all with masses
similar to or greater than that of Jupiter. Here we report observations of the
transits of two Sun-like stars by planets smaller than Neptune in the
billion-year-old open cluster NGC6811. This demonstrates that small planets can
form and survive in a dense cluster environment, and implies that the frequency
and properties of planets in open clusters are consistent with those of planets
around field stars in the Galaxy.Comment: 18 pages, 6 figures, 1 table (main text + supplementary information
Quantum dot loaded immunomicelles for tumor imaging
<p>Abstract</p> <p>Background</p> <p>Optical imaging is a promising method for the detection of tumors in animals, with speed and minimal invasiveness. We have previously developed a lipid coated quantum dot system that doubles the fluorescence of PEG-grafted quantum dots at half the dose. Here, we describe a tumor-targeted near infrared imaging agent composed of cancer-specific monoclonal anti-nucleosome antibody 2C5, coupled to quantum dot (QD)-containing polymeric micelles, prepared from a polyethylene glycol/phosphatidylethanolamine (PEG-PE) conjugate. Its production is simple and involves no special equipment. Its imaging potential is great since the fluorescence intensity in the tumor is twofold that of non-targeted QD-loaded PEG-PE micelles at one hour after injection.</p> <p>Methods</p> <p>Para-nitrophenol-containing (5%) PEG-PE quantum dot micelles were produced by the thin layer method. Following hydration, 2C5 antibody was attached to the PEG-PE micelles and the QD-micelles were purified using dialysis. 4T1 breast tumors were inoculated subcutaneously in the flank of the animals. A lung pseudometastatic B16F10 melanoma model was developed using tail vein injection. The contrast agents were injected via the tail vein and mice were depilated, anesthetized and imaged on a Kodak Image Station. Images were taken at one, two, and four hours and analyzed using a methodology that produces normalized signal-to-noise data. This allowed for the comparison between different subjects and time points. For the pseudometastatic model, lungs were removed and imaged <it>ex vivo </it>at one and twenty four hours.</p> <p>Results</p> <p>The contrast agent signal intensity at the tumor was double that of the passively targeted QD-micelles with equally fast and sharply contrasted images. With the side views of the animals only tumor is visible, while in the dorsal view internal organs including liver and kidney are visible. <it>Ex vivo </it>results demonstrated that the agent detects melanoma nodes in a lung pseudometastatic model after a 24 hours wash-out period, while at one hour, only a uniform signal is detected.</p> <p>Conclusions</p> <p>The targeted agent produces ultrabright tumor images and double the fluorescence intensity, as rapidly and at the same low dose as the passively targeted agents. It represents a development that may potentially serve to enhance early detection for metastases.</p
Connecting Planetary Composition with Formation
The rapid advances in observations of the different populations of
exoplanets, the characterization of their host stars and the links to the
properties of their planetary systems, the detailed studies of protoplanetary
disks, and the experimental study of the interiors and composition of the
massive planets in our solar system provide a firm basis for the next big
question in planet formation theory. How do the elemental and chemical
compositions of planets connect with their formation? The answer to this
requires that the various pieces of planet formation theory be linked together
in an end-to-end picture that is capable of addressing these large data sets.
In this review, we discuss the critical elements of such a picture and how they
affect the chemical and elemental make up of forming planets. Important issues
here include the initial state of forming and evolving disks, chemical and dust
processes within them, the migration of planets and the importance of planet
traps, the nature of angular momentum transport processes involving turbulence
and/or MHD disk winds, planet formation theory, and advanced treatments of disk
astrochemistry. All of these issues affect, and are affected by the chemistry
of disks which is driven by X-ray ionization of the host stars. We discuss how
these processes lead to a coherent end-to-end model and how this may address
the basic question.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018). 46 pages, 10
figure