640 research outputs found
Disk winds of B[e] supergiants
The class of B[e] supergiants is characterized by a two-component stellar
wind consisting of a normal hot star wind in the polar zone and a slow and
dense disk-like wind in the equatorial region. The properties of the disk wind
are discussed using satellite UV spectra of stars seen edge-on, i.e. through
the equatorial disk. These observations show that the disk winds are extremely
slow, 50-90 km/s, i.e. a factor of about 10 slower than expected from the
spectral types. Optical emission lines provide a further means to study the
disk wind. This is discussed for line profiles of forbidden lines formed in the
disk.Comment: 7 pages, LaTeX, 3 ps figures, uses lamuphys.sty from Springer-Verlag,
to be published in the proceedings of IAU Coll. 169 "Variable and
Non-spherical Stellar Winds in Luminous Hot Stars" held in Heidelberg 199
Resolving the dusty circumstellar environment of the A[e] supergiant HD 62623 with the VLTI/MIDI
B[e] stars are hot stars surrounded by circumstellar gas and dust responsible
for the presence of emission lines and IR-excess in their spectra. How dust can
be formed in this highly illuminated and diluted environment remains an open
issue. HD 62623 is one of the very few A-type supergiants showing the B[e]
phenomenon. We obtained nine calibrated visibility measurements using the
VLTI/MIDI instrument in SCI-PHOT mode and PRISM spectral dispersion mode with
projected baselines ranging from 13 to 71 m and with various position angles.
We used geometrical models and physical modeling with a radiative transfer code
to analyze these data. The dusty circumstellar environment of HD 62623 is
partially resolved by the VLTI/MIDI even with the shortest baselines. The
environment is flattened and can be separated into two components: a compact
one whose extension grows from 17 mas at 8 microns to 30 mas at 9.6 microns and
stays almost constant up to 13 microns, and a more extended one that is
over-resolved even with the shortest baselines. Using the radiative transfer
code MC3D, we managed to model HD 62623's circumstellar environment as a dusty
disk with an inner radius of 3.85+-0.6 AU, an inclination angle of 60+-10 deg,
and a mass of 2x10^-7Mo. It is the first time that the dusty disk inner rim of
a supergiant star exhibiting the B[e] phenomenon is significantly constrained.
The inner gaseous envelope likely contributes up to 20% to the total N band
flux and acts like a reprocessing disk. Finally, the hypothesis of a stellar
wind deceleration by the companion's gravitational effects remains the most
probable case since the bi-stability mechanism does not seem to be efficient
for this star.Comment: 13 pages, 11 figures. A&A accepted pape
Crowded field 3D spectroscopy of LBV candidates in M33
We present integral field spectroscopy of the LBV candidate stars B416 and
v532 in the local group galaxy M33. B416 is surrounded by an elongated
ring-like nebula, which has a projected radius of 20x30 pc. From the datacube
we create ionization and radial velocity maps of the nebula. The excitation of
the gas decreases towards the outer part of the ring, while the inner part of
the nebula is filled with a more excited gas. In the EW direction the ring is
seen to expand with a maximum projected velocity amplitude of about 40 km/s.
The eastern part approaches the observer. We estimate the nebula dynamical
lifetime 8*10E5 years. It could be a residual MS bubble, which indicates a
main-sequence or pre-LBV status of the star. We classify B416 as an "iron star"
or B[e]-supergiant. In v532 an elongated nebula has been marginally detected.
The total projected size of the nebula along the main axis is 30 pc, and the
total radial velocity gradient is 44+/-11 km/s. v532 exhibits both strong
photometric and spectral variability. At the time of our observations it was in
an intermediate brightness state with a rich nitrogen spectrum. We classify
v532 as an LBV, showing LBV Ofpe/WN transitions. We stress the importance
of integral field spectroscopy as the optimal technique for studying nebulae
and the evolution of LBV-like stars in nearby galaxies.Comment: 12 pages, 10 Postscript figures, A&A accepte
Fast ray-tracing algorithm for circumstellar structures (FRACS). II. Disc parameters of the B[e] supergiant CPD-57° 2874 from VLTI/MIDI data
B[e] supergiants are luminous, massive post-main sequence stars exhibiting
non-spherical winds, forbidden lines, and hot dust in a disc-like structure.
The physical properties of their rich and complex circumstellar environment
(CSE) are not well understood, partly because these CSE cannot be easily
resolved at the large distances found for B[e] supergiants (typically \ga
1~kpc). From mid-IR spectro-interferometric observations obtained with
VLTI/MIDI we seek to resolve and study the CSE of the Galactic B[e] supergiant
CPD-57\degr\,2874. For a physical interpretation of the observables
(visibilities and spectrum) we use our ray-tracing radiative transfer code
(FRACS), which is optimised for thermal spectro-interferometric observations.
Thanks to the short computing time required by FRACS (~s per monochromatic
model), best-fit parameters and uncertainties for several physical quantities
of CPD-57\degr\,2874 were obtained, such as inner dust radius, relative flux
contribution of the central source and of the dusty CSE, dust temperature
profile, and disc inclination. The analysis of VLTI/MIDI data with FRACS
allowed one of the first direct determinations of physical parameters of the
dusty CSE of a B[e] supergiant based on interferometric data and using a full
model-fitting approach. In a larger context, the study of B[e] supergiants is
important for a deeper understanding of the complex structure and evolution of
hot, massive stars
Recommendations in Second Opinion Reports of Neurologic Head and Neck Imaging:Frequency, Referring Clinicians? Compliance, and Diagnostic Yield
BACKGROUND AND PURPOSE: Second opinion reports of neurologic head and neck imaging are requested with increased regularity, and they may contain a recommendation to the clinician. Our aim was to investigate the frequency and determinants of the presence of a recommendation and the adherence by the referring physician to the recommendation in a second opinion neurology head and neck imaging report and the diagnostic yield of these recommendations. MATERIALS AND METHODS: This retrospective study included 994 consecutive second opinion reports of neurology head and neck imaging examinations performed at a tertiary care center. RESULTS: Of the 994 second opinion reports, 12.2% (121/994) contained a recommendation. An oncologic imaging indication was significantly (P = .030) associated with a lower chance of a recommendation in the second opinion report (OR = .67; 95% CI, 0.46?0.96). Clinicians followed 65.7% (88/134) of the recommendations. None of the investigated variables (patient age, sex, hospitalization status, indication for the second opinion report, experience of the radiologist who signed the second opinion report, strength of the recommendation, and whether the recommendation was made due to apparent quality issues of the original examination) were significantly associated with the compliance of the referring physician to this recommendation. The 134 individual recommendations eventually led to the establishment of 52 (38.2%) benign diagnoses and 28 (20.6%) malignant diagnoses, while no definitive diagnosis could be established in 56 (41.2%) cases. CONCLUSIONS: Recommendations are relatively common in second opinion reports of neurology head and neck imaging examinations, though less for oncologic indications. They are mostly followed by requesting physicians, thus affecting patient management. In most cases, they also lead to the establishment of a diagnosis, hence adding value to patient care
The Carbon footprint of B[e] supergiants
We report on the first detection of C enhancement in two B[e]
supergiants in the Large Magellanic Cloud. Stellar evolution models predict the
surface abundance in C to strongly increase during main-sequence and
post-main sequence evolution of massive stars. However, direct identification
of chemically processed material on the surface of B[e] supergiants is hampered
by their dense, disk-forming winds, hiding the stars. Recent theoretical
computations predict the detectability of enhanced C via the molecular
emission in CO arising in the circumstellar disks of B[e] supergiants.
To test this potential method and to unambiguously identify a post-main
sequence B[e]SG by its CO emission, we have obtained high-quality
-band spectra of two known B[e] supergiants in the Large Magellanic Cloud,
using the Very Large Telescope's Spectrograph for INtegral Field Observation in
the Near-Infrared (VLT/SINFONI). Both stars clearly show the CO band
emission, whose strength implies a strong enhancement of C, in agreement
with theoretical predictions. This first ever direct confirmation of the
evolved nature of B[e] supergiants thus paves the way to the first
identification of a Galactic B[e] supergiant.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Discovery and quantitative spectral analysis of an Ofpe/WN9 (WN11) star in the Sculptor spiral galaxy NGC 300
We have discovered an Ofpe/WN9 (WN11 following Smith et al.) star in the
Sculptor spiral galaxy NGC 300, the first object of this class found outside
the Local Group, during a recent spectroscopic survey of blue supergiant stars
obtained at the ESO VLT. The light curve over a five-month period in late 1999
displays a variability at the 0.1 mag level. The intermediate resolution
spectra (3800-7200 A) show a very close resemblance to the Galactic LBV AG Car
during minimum. We have performed a detailed non-LTE analysis of the stellar
spectrum, and have derived a chemical abundance pattern which includes H, He,
C, N, O, Al, Si and Fe, in addition to the stellar and wind parameters. The
derived stellar properties and the He and N surface enrichments are consistent
with those of other Local Group WN11 stars in the literature, suggesting a
similar quiescent or post-LBV evolutionary status.Comment: 9 pages, 4 figures, 2 tables. Accepted for publication in the
Astrophysical Journal Letter
On the Effect of Magnetic Spots on Stellar Winds and Angular Momentum Loss
We simulate the effect of latitudinal variations in the location of star
spots, as well as their magnetic field strength, on stellar angular momentum
loss to the stellar wind. We use the Michigan solar corona global
MagnetoHydroDynamic model, which incorporates realistic relation between the
magnetic field topology and the wind distribution. We find that the spots
location significantly affects the stellar wind structure, and as a result, the
total mass loss rate and angular momentum loss rate. In particular, we find
that the angular momentum loss rate is controlled by the mass flux when spots
are located at low latitudes but is controlled by an increased plasma density
between the stellar surface and the Alfven surface when spots are located at
high latitudes. Our results suggest that there might be a feedback mechanism
between the magnetic field distribution, wind distribution, angular momentum
loss through the wind, and the motions at the convection zone that generate the
magnetic field. This feedback might explain the role of coronal magnetic fields
in stellar dynamos
Skeletal muscle mass and sarcopenia can be determined with 1.5-T and 3-T neck MRI scans, in the event that no neck CT scan is performed
Objectives: Cross-sectional area (CSA) measurements of the neck musculature at the level of third cervical vertebra (C3) on CT scans are used to diagnose radiological sarcopenia, which is related to multiple adverse outcomes in head and neck cancer (HNC) patients. Alternatively, these assessments are performed with neck MRI, which has not been validated so far. For that, the objective was to evaluate whether skeletal muscle mass and sarcopenia can be assessed on neck MRI scans. Methods: HNC patients were included between November 2014 and November 2018 from a prospective data-biobank. CSAs of the neck musculature at the C3 level were measured on CT (n = 125) and MRI neck scans (n = 92 on 1.5-T, n = 33 on 3-T). Measurements were converted into skeletal muscle index (SMI), and sarcopenia was defined (SMI < 43.2 cm 2/m 2). Pearson correlation coefficients, Bland–Altman plots, McNemar test, Cohen’s kappa coefficients, and interclass correlation coefficients (ICCs) were estimated. Results: CT and MRI correlated highly on CSA and SMI (r = 0.958–0.998, p < 0.001). The Bland–Altman plots showed a nihil mean ΔSMI (− 0.13–0.44 cm 2/m 2). There was no significant difference between CT and MRI in diagnosing sarcopenia (McNemar, p = 0.5–1.0). Agreement on sarcopenia diagnosis was good with κ = 0.956–0.978 and κ = 0.870–0.933, for 1.5-T and 3-T respectively. Observer ICCs in MRI were excellent. In general, T2-weighted images had the best correlation and agreement with CT. Conclusions: Skeletal muscle mass and sarcopenia can interchangeably be assessed on CT and 1.5-T and 3-T MRI neck scans. This allows future clinical outcome assessment during treatment irrespective of used modality. Key Points: • Screening for low amount of skeletal muscle mass is usually measured on neck CT scans and is highly clinical relevant as it is related to multiple adverse outcomes in head and neck cancer patients. • We found that skeletal muscle mass and sarcopenia determined on CT and 1.5-T and 3-T MRI neck scans at the C3 level can be used interchangeably. • When CT imaging of the neck is missing for skeletal muscle mass analysis, patients can be assessed with 1.5-T or 3-T neck MRIs
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