1,814 research outputs found
Interferometric observations of eta Carinae with VINCI/VLTI
Context: The bright star eta Carinae is the most massive and luminous star in
our region of the Milky Way. Though it has been extensively studied using many
different techniques, its physical nature and the mechanism that led to the
creation of the Homunculus nebula are still debated. Aims: We aimed at
resolving the central engine of the eta Carinae complex in the near-infrared on
angular scales of a few milliarcseconds. Methods: We used the VINCI instrument
of the VLTI to recombine coherently the light from two telescopes in the K
band. Results: We report a total of 142 visibility measurements of eta Car,
part of which were analyzed by Van Boekel et al. (2003). These observations
were carried out on projected baselines ranging from 8 to 112 meters in length,
using either two 0.35 m siderostats or two 8-meter Unit Telescopes. These
observations cover the November 2001 - January 2004 period. Conclusions: The
reported visibility data are in satisfactory agreement with the recent results
obtained with AMBER/VLTI by Weigelt et al. (2006), asuming that the flux of eta
Car encircled within 70 mas reaches 56% of the total flux within 1400 mas, in
the K band. We also confirm that the squared visibility curve of eta Car as a
function of spatial frequency follows closely an exponential model.Comment: Accepted for publication in A&A as a Research not
Embedded AGN and star formation in the central 80 pc of IC 3639
[Abridged] Methods: We use interferometric observations in the -band with
VLTI/MIDI to resolve the mid-IR nucleus of IC 3639. The origin of the nuclear
infrared emission is determined from: 1) the comparison of the correlated
fluxes from VLTI/MIDI with the fluxes measured at subarcsec resolution
(VLT/VISIR, VLT/ISAAC); 2) diagnostics based on IR fine-structure line ratios,
the IR continuum emission, IR bands produced by polycyclic aromatic
hydrocarbons (PAH) and silicates; and 3) the high-angular resolution spectral
energy distribution. Results: The unresolved flux of IC 3639 is at , measured with three different baselines in
VLTI (UT1-UT2, UT3-UT4, and UT2-UT3; -), making this the
faintest measurement so far achieved with mid-IR interferometry. The correlated
flux is a factor of - times fainter than the VLT/VISIR total flux
measurement. The observations suggest that most of the mid-IR emission has its
origin on spatial scales between and (-). A composite scenario where the star formation component dominates
over the AGN is favoured by the diagnostics based on ratios of IR
fine-structure emission lines, the shape of the IR continuum, and the PAH and
silicate bands. Conclusions: A composite AGN-starburst scenario is able to
explain both the mid-IR brightness distribution and the IR spectral properties
observed in the nucleus of IC 3639. The nuclear starburst would dominate the
mid-IR emission and the ionisation of low-excitation lines (e.g. [NeII]) with a net contribution of . The AGN accounts for the
remaining of the mid-IR flux, ascribed to the unresolved component
in the MIDI observations, and the ionisation of high-excitation lines (e.g.
[NeV] and [OIV]).Comment: Accepted for publication in A&
Spectral line profiles changed by dust scattering in heavily obscured young stellar objects
It is known that scattering of radiation by circumstellar dust can strongly
change the line profiles in stellar spectra. This hampers the analysis of
spectral lines originating in the emitting regions of heavily obscured young
stars. To calculate the line profile of the scattered radiation, we suggest to
use the approximation of remote scattering particles. This approximation
assumes that the scattering dust grains are at a distance from the star that is
much larger than the characteristic size of the emitting region. Using this
method, we calculated the line profiles of several simple models. They show the
H alpha line profiles of Herbig AeBe stars in the presence and absence of
motionless or moving dust
Role of Protected Block Curriculum in Surgical Education
A protected block curriculum for surgical resident training began at the Medical College of Wisconsin in 2005. The curriculum has evolved with time as educational emphasis has changed. However, the concept of having resident learners relieved of clinical duty to focus on learning has not changed. Separate protected block curriculums are held for PGY1 and PGY 2 during which residents have no clinical responsibilities. These periods are defined at the beginning of each academic year and are distributed to all faculties. The systematic design, implementation, and evaluation of the protected block curriculum (PBC) Model provides an educationally grounded model for training surgical residents consistent with accreditation council for graduate medical education (ACGME) competency mandates. Resident evaluations consistently support the use of our PBC as a method to attain and practice skill sets in a nonthreatening environment. Faculty benefits are able to evaluate residents’ knowledge, skills, and attitudes in a nonclinical setting and engage residents as individuals. The format extended into the PGY3–5 years of training as it evolved. Over more than a decade of using PBC, we have performed a number of analyses on the program and even determined a cost for the program. The program continues to be adjusted to new technology and curriculum initiatives
Nematode communities, plant nutrient economy and life-cycle characteristics jointly determine plant monoculture performance over 12 years
Visual/infrared interferometry of Orion Trapezium stars: Preliminary dynamical orbit and aperture synthesis imaging of the Theta 1 Orionis C system
Located in the Orion Trapezium cluster, Theta 1 Orionis C is one of the
youngest and nearest high-mass stars (O5-O7) and also known to be a close
binary system. Using new multi-epoch visual and near-infrared bispectrum
speckle interferometric observations obtained at the BTA 6 m telescope, and
IOTA near-infrared long-baseline interferometry, we trace the orbital motion of
the Theta 1 Ori C components over the interval 1997.8 to 2005.9, covering a
significant arc of the orbit. Besides fitting the relative position and the
flux ratio, we apply aperture synthesis techniques to our IOTA data to
reconstruct a model-independent image of the Theta 1 Ori C binary system.
The orbital solutions suggest a high eccentricity (e approx. 0.91) and
short-period (P approx. 10.9 yrs) orbit. As the current astrometric data only
allows rather weak constraints on the total dynamical mass, we present the two
best-fit orbits. From these orbital solutions one can be favoured, implying a
system mass of 48 M_sun and a distance to the Trapezium cluster of 434 pc. When
also taking the measured flux ratio and the derived location in the HR-diagram
into account, we find good agreement for all observables, assuming a spectral
type of O5.5 for Theta 1 Ori C1 (M=34.0 M_sun) and O9.5 for C2 (M=15.5 M_sun).
We find indications that the companion C2 is massive itself, which makes it
likely that its contribution to the intense UV radiation field of the Trapezium
cluster is non-negligible. Furthermore, the high eccentricity of the
preliminary orbit solution predicts a very small physical separation during
periastron passage (approx. 1.5 AU, next passage around 2007.5), suggesting
strong wind-wind interaction between the two O stars.Comment: 13 pages, 9 figures, Accepted for publication in Astronomy &
Astrophysic
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