92 research outputs found
Proplyds and Massive Disks in the Orion Nebula Cluster Imaged with CARMA and SMA
[Abridged] We imaged a 2' x 2' region of the Orion Nebula cluster in 1.3 mm
wavelength continuum emission with the recently commissioned Combined Array for
Research in Millimeter Astronomy (CARMA) and with the Submillimeter Array
(SMA). Our mosaics include >250 known near-IR cluster members, of which 36 are
so-called "proplyds" that have been imaged previously with the Hubble Space
Telescope. We detected 40 sources in 1 mm continuum emission, and several of
them are spatially resolved with our observations. Dust masses inferred for
detected sources range from 0.01 to 0.5 Msun, and the average disk mass for
undetected sources is estimated to be ~0.001 Msun, approximately an order of
magnitude smaller than the minimum mass solar nebula. Most stars in the ONC
thus do not appear to currently possess sufficient mass in small dust grains to
form Jupiter-mass (or larger) planets. Comparison with previous results for
younger and older regions indicates that massive disks evolve significantly on
~Myr timescales. We also show that the percentage of stars in Orion surrounded
by disks more massive than ~0.01 Msun is substantially lower than in Taurus,
indicating that environment has an impact on the disk mass distribution.
Finally, we explore potential correlations of disk mass with stellar mass and
location within the cluster.Comment: 45 pages, 11 figures. Accepted for publication in Ap
Ultrasound-responsive gene-activated matrices (GAMs) for osteogenic gene therapy using matrix-assisted sonoporation (MAS)
Detection of Strong Millimeter Emission from the Circumstellar Dust Disk Around V1094 Sco: Cold and Massive Disk around a T Tauri Star in a Quiescent Accretion Phase?
We present the discovery of a cold massive dust disk around the T Tauri star
V1094 Sco in the Lupus molecular cloud from the 1.1 millimeter continuum
observations with AzTEC on ASTE. A compact (320 AU) continuum
emission coincides with the stellar position having a flux density of 272 mJy
which is largest among T Tauri stars in Lupus. We also present the detection of
molecular gas associated with the star in the five-point observations in
CO J=3--2 and CO J=3--2. Since our CO and CO
observations did not show any signature of a large-scale outflow or a massive
envelope, the compact dust emission is likely to come from a disk around the
star. The observed SED of V1094 Sco shows no distinct turnover from near
infrared to millimeter wavelengths, which can be well described by a flattened
disk for the dust component, and no clear dip feature around 10 \micron
suggestive of absence of an inner hole in the disk. We fit a simple power-law
disk model to the observed SED. The estimated disk mass ranges from 0.03 to
0.12 M_\sun, which is one or two orders of magnitude larger than the
median disk mass of T Tauri stars in Taurus.Comment: 18 pages, 4 figures, accepted for publication in Ap
Direct imaging of extra-solar planets in star forming regions: Lessons learned from a false positive around IM Lup
Most exoplanet imagers consist of ground-based adaptive optics coronagraphic
cameras which are currently limited in contrast, sensitivity and astrometric
precision, but advantageously observe in the near-IR (1- 5{\mu}m). Because of
these practical limitations, our current observational aim at detecting and
characterizing planets puts heavy constraints on target selection, observing
strategies, data reduction, and follow-up. Most surveys so far have thus
targeted young systems (1-100Myr) to catch the putative remnant thermal
radiation of giant planets, which peaks in the near-IR. They also favor systems
in the solar neighborhood (d<80pc), which eases angular resolution requirements
but also ensures a good knowledge of the distance and proper motion, which are
critical to secure the planet status, and enable subsequent characterization.
Because of their youth, it is very tempting to target the nearby star forming
regions, which are typically twice as far as the bulk of objects usually combed
for planets by direct imaging. Probing these interesting reservoirs sets
additional constraints that we review in this paper by presenting the planet
search that we initiated in 2008 around the disk-bearing T Tauri star IM Lup
(Lupus star forming region, 140-190pc). We show and discuss why age
determination, the choice of evolutionary model for the central star and the
planet, precise knowledge of the host star proper motion, relative or absolute
astrometric accuracy, and patience are the key ingredients for exoplanet
searches around more distant young stars. Unfortunately, most of the time,
precision and perseverance are not paying off: we discovered a candidate
companion around IM Lup in 2008, which we report here to be an unbound
background object. We nevertheless review in details the lessons learned from
our endeavor, and additionally present the best detection limits ever
calculated for IM Lup.Comment: 8 pages, 3 figures, 3 tables, accepted to A&
Probing dust grain evolution in IM Lupi's circumstellar disc. Multi-wavelength observations and modelling of the dust disc
We present a panchromatic study, involving a multiple technique approach, of
the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). We have
undertaken a comprehensive observational study of IM Lupi using photometry,
spectroscopy, millimetre interferometry and multi-wavelength imaging. For the
first time, the disc is resolved from optical and near-infrared wavelengths in
scattered light, to the millimetre regime in thermal emission. Our data-set, in
conjunction with existing photometric data, provides an extensive coverage of
the spectral energy distribution, including a detailed spectrum of the silicate
emission bands. We have performed a simultaneous modelling of the various
observations, using the radiative transfer code MCFOST, and analysed a grid of
models over a large fraction of the parameter space via Bayesian inference. We
have constructed a model that can reproduce all of the observations of the
disc. Our analysis illustrates the importance of combining a wide range of
observations in order to fully constrain the disc model, with each observation
providing a strong constraint only on some aspects of the disc structure and
dust content. Quantitative evidence of dust evolution in the disc is obtained:
grain growth up to millimetre-sized particles, vertical stratification of dust
grains with micrometric grains close to the disc surface and larger grains
which have settled towards the disc midplane, and possibly the formation of
fluffy aggregates and/or ice mantles around grains.Comment: 20 pages, 13 figures. Accepted for publication in A&
Spatial and Spectral Coherent Control with Frequency Combs
Quantum coherent control (1-3) is a powerful tool for steering the outcome of
quantum processes towards a desired final state, by accurate manipulation of
quantum interference between multiple pathways. Although coherent control
techniques have found applications in many fields of science (4-9), the
possibilities for spatial and high-resolution frequency control have remained
limited. Here, we show that the use of counter-propagating broadband pulses
enables the generation of fully controlled spatial excitation patterns. This
spatial control approach also provides decoherence reduction, which allows the
use of the high frequency resolution of an optical frequency comb (10,11). We
exploit the counter-propagating geometry to perform spatially selective
excitation of individual species in a multi-component gas mixture, as well as
frequency determination of hyperfine constants of atomic rubidium with
unprecedented accuracy. The combination of spectral and spatial coherent
control adds a new dimension to coherent control with applications in e.g
nonlinear spectroscopy, microscopy and high-precision frequency metrology.Comment: 12 page
Optical and infrared flares from a transient Galactic soft gamma-ray repeater
Soft gamma-ray repeaters (SGRs) are a rare type of gamma-ray transient
sources that are ocasionally detected as bursts in the high-energy sky. They
are thought to be produced by magnetars, young neutron stars with very strong
magnetic fields of the order of 10^(14-15) G. Only three such objects are known
in our Galaxy, and a fourth one is associated with the supernova remnant N49 in
the Large Magellanic Cloud. In none of these cases has an optical counterpart
to either the gamma-ray flares or the quiescent source been identified. Here we
present multi-wavelength observations of a puzzling source, SWIFT
J195509+261406, for which we detected more than 40 flaring episodes in the
optical band over a time span of 3 days, plus a faint infrared flare 11 days
later, after which it returned to quiescence. We propose that SWIFT
J195509+261406 is a member of a subgroup of SGRs for which the long-term X-ray
emission is transient in nature. Furthermore, it is the first SGR for which
bursts have been detected in the optical and near-infrared bands and maybe the
link between the "persistent" SGRs and the dim isolated neutron stars.Comment: Version submitted to Nature on 31 Jan 2008. A substantially revised
version of this work has been published in Nature, vol. 455 issue 7212 pp
506-509 under the title "Flares from a Galactic magnetar suggest a missing
link to dim isolated neutron stars
Tissue engineering of functional articular cartilage: the current status
Osteoarthritis is a degenerative joint disease characterized by pain and disability. It involves all ages and 70% of people aged >65 have some degree of osteoarthritis. Natural cartilage repair is limited because chondrocyte density and metabolism are low and cartilage has no blood supply. The results of joint-preserving treatment protocols such as debridement, mosaicplasty, perichondrium transplantation and autologous chondrocyte implantation vary largely and the average long-term result is unsatisfactory. One reason for limited clinical success is that most treatments require new cartilage to be formed at the site of a defect. However, the mechanical conditions at such sites are unfavorable for repair of the original damaged cartilage. Therefore, it is unlikely that healthy cartilage would form at these locations. The most promising method to circumvent this problem is to engineer mechanically stable cartilage ex vivo and to implant that into the damaged tissue area. This review outlines the issues related to the composition and functionality of tissue-engineered cartilage. In particular, the focus will be on the parameters cell source, signaling molecules, scaffolds and mechanical stimulation. In addition, the current status of tissue engineering of cartilage will be discussed, with the focus on extracellular matrix content, structure and its functionality
Exploring higher-lying electronic states of a molecular switch by coherent triggered-exchange 2D electronic spectroscopy
We use pump-repump-probe transient absorption spectroscopy to investigate the role of higher-lying electronic states in the photochemistry of a molecular switch. Moreover, replacing the pump pulse by a pulse-shaper-generated phase-stable double pulse, triggered-exchange two-dimensional (TE2D) electronic spectroscopy is established in the visible regime
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