518 research outputs found
Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73
We aim to improve our knowledge on the structure and dynamics of the
circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution
optical and near-IR spectroscopic data were obtained over a period of 16 and 7
years, respectively. The spectra cover the diagnostic emission lines from
[CaII] and [OI], as well as the CO bands. These features trace the disk at
different distances from the star. We analyzed the kinematics of the individual
emission regions by modeling their emission profiles. A low-resolution
mid-infrared spectrum was obtained as well, which provides information on the
composition of the dusty disk. All diagnostic emission features display
double-peaked line profiles, which we interpret as due to Keplerian rotation.
We find that LHA 120-S 73 is surrounded by at least four individual rings of
material with alternating densities (or by a disk with strongly non-monotonic
radial density distribution). Moreover, we find that the molecular ring must
have gaps or at least strong density inhomogeneities, or in other words, a
clumpy structure. The mid-infrared spectrum displays features of oxygen- and
carbon-rich grain species, which indicates a long-lived, stable dusty disk. We
cannot confirm the previously reported high value for the stellar rotation
velocity. The line profile of HeI 5876 A is strongly variable in both width and
shape and resembles of those seen in non-radially pulsating stars. A proper
determination of the real underlying stellar rotation velocity is hence not
possible. The existence of multiple stable and clumpy rings of alternating
density recalls ring structures around planets. Although there is currently
insufficient observational evidence, it is tempting to propose a scenario with
one (or more) minor bodies or planets revolving around LHA 120-S 73 and
stabilizing the ring system, in analogy to the shepherd moons in planetary
systems.Comment: 14 pages, 13 figure, accepted for pulication in A&
Interplay between pulsations and mass loss in the blue supergiant 55 Cygnus = HD 198478
Blue supergiant stars are known to display photometric and spectroscopic
variability that is suggested to be linked to stellar pulsations. Pulsational
activity in massive stars strongly depends on the star's evolutionary stage and
is assumed to be connected with mass-loss episodes, the appearance of
macroturbulent line broadening, and the formation of clumps in the wind. To
investigate a possible interplay between pulsations and mass-loss, we carried
out an observational campaign of the supergiant 55 Cyg over a period of five
years to search for photospheric activity and cyclic mass-loss variability in
the stellar wind. We modeled the H, He I, Si II and Si III lines using the
nonlocal thermal equilibrium atmosphere code FASTWIND and derived the
photospheric and wind parameters. In addition, we searched for variability in
the intensity and radial velocity of photospheric lines and performed a moment
analysis of the line profiles to derive frequencies and amplitudes of the
variations. The Halpha line varies with time in both intensity and shape,
displaying various types of profiles: P Cygni, pure emission, almost complete
absence, and double or multiple peaked. The star undergoes episodes of variable
mass-loss rates that change by a factor of 1.7-2 on different timescales. We
also observe changes in the ionization rate of Si II and determine a
multiperiodic oscillation in the He I absorption lines, with periods ranging
from a few hours to 22.5 days. We interpret the photospheric line variations in
terms of oscillations in p-, g-, and strange modes. We suggest that these
pulsations can lead to phases of enhanced mass loss. Furthermore, they can
mislead the determination of the stellar rotation. We classify the star as a
post-red supergiant, belonging to the group of alpha Cyg variables.Comment: 20 pages, 18 figures, 3 tables, accepted to Astronomy & Astrophysic
Disease burden and economic impact of diagnosed non-alcoholic steatohepatitis (NASH) in the United Kingdom (UK) in 2018
BACKGROUNDS AND AIMS: Non-alcoholic steatohepatitis (NASH) â a progressive subset of non-alcoholic fatty liver disease (NAFLD) â is a chronic liver disease that can progress to advanced fibrosis, cirrhosis, and end-stage liver disease (ESLD) if left untreated. Early-stage NASH is usually asymptomatic, meaning a large proportion of the prevalent population are undiagnosed. Receiving a NASH diagnosis increases the probability that a patient will receive interventions for the purpose of managing their condition. The purpose of this study was to estimate the disease burden and economic impact of diagnosed NASH in the United Kingdom (UK) adult population in 2018. METHODS: The socioeconomic burden of diagnosed NASH from a societal perspective was estimated using cost-of-illness methodology applying a prevalence approach. This involved estimating the number of adults with diagnosed NASH in the UK in a base period (2018) and the economic and wellbeing costs attributable to diagnosed NASH in that period. The analysis was based on a targeted review of the scientific literature, existing databases and consultation with clinical experts, health economists and patient groups. RESULTS: Of the prevalent NASH population in the UK in 2018, an estimated 79.8% were not diagnosed. In particular, of the prevalent population in disease stages F0 to F2, only 2.0% (F0), 2.0% (F1) and 16.5% (F2), respectively, were diagnosed. Total economic costs of diagnosed NASH in the UK ranged from ÂŁ2.3 billion (lower prevalence scenario, base probability of diagnosis scenario) to ÂŁ4.2 billion (higher prevalence scenario, base probability of diagnosis scenario). In 2018, people with NASH in the UK were estimated to experience 94,094 to 174,564 disability-adjusted life years (DALYs) overall. Total wellbeing costs associated with NASH in 2018 were estimated to range between ÂŁ5.6 to ÂŁ10.5 billion. CONCLUSIONS: The prevention and appropriate management of adult NASH patients could result in reduced economic costs and improvements in wellbeing
Lack of behavioural responses of humpback whales (Megaptera novaeangliae) indicate limited effectiveness of sonar mitigation
publishedVersio
Wind modelling of very massive stars up to 300 solar masses
Some studies have claimed a universal stellar upper-mass limit of 150 Msun. A
factor that is often overlooked is that there might be a difference between the
current and initial masses of the most massive stars, as a result of mass loss.
We present Monte Carlo mass-loss predictions for very massive stars in the
range 40-300 Msun, with large luminosities and Eddington factors Gamma. Using
our new dynamical approach, we find an upturn in the mass-loss vs. Gamma
dependence, at the point where the winds become optically thick. This coincides
with the location where wind efficiency numbers surpass the single-scattering
limit of Eta = 1, reaching values up to Eta = 2.5. Our modelling suggests a
transition from common O-type winds to Wolf-Rayet characteristics at the point
where the winds become optically thick. This transitional behaviour is also
revealed with respect to the wind acceleration parameter beta, which starts at
values below 1 for the optically thin O-stars, and naturally reaches values as
high as 1.5-2 for the optically thick Wolf-Rayet models. An additional finding
concerns the transition in spectral morphology of the Of and WN characteristic
He II line at 4686 Angstrom. When we express our mass-loss predictions as a
function of the electron scattering Gamma_e (=L/M) only, we obtain a mass-loss
Gamma dependence that is consistent with a previously reported power-law Mdot
propto Gamma^5 (Vink 2006) that was based on our semi-empirical modelling
approach. When we express Mdot in terms of both Gamma and stellar mass, we find
Mdot propto M^0.8 Gamma^4.8 for our high Gamma models. Finally, we confirm that
the Gamma-effect on the mass-loss predictions is much stronger than that of an
increased helium abundance, calling for a fundamental revision in the way mass
loss is incorporated in evolutionary models of the most massive stars.Comment: minor language changes (Astronomy & Astrophysics in press - 11 pages,
10 figures
Discovery of Small-Scale Spiral Structures in the Disk of SAO 206462 (HD 135344B): Implications for the Physical State of the Disk from Spiral Density Wave Theory
We present high-resolution, H-band, imaging observations, collected with
Subaru/HiCIAO, of the scattered light from the transitional disk around SAO
206462 (HD 135344B). Although previous sub-mm imagery suggested the existence
of the dust-depleted cavity at r~46AU, our observations reveal the presence of
scattered light components as close as 0.2" (~28AU) from the star. Moreover, we
have discovered two small-scale spiral structures lying within 0.5" (~70AU). We
present models for the spiral structures using the spiral density wave theory,
and derive a disk aspect ratio of h~0.1, which is consistent with previous
sub-mm observations. This model can potentially give estimates of the
temperature and rotation profiles of the disk based on dynamical processes,
independently from sub-mm observations. It also predicts the evolution of the
spiral structures, which can be observable on timescales of 10-20 years,
providing conclusive tests of the model. While we cannot uniquely identify the
origin of these spirals, planets embedded in the disk may be capable of
exciting the observed morphology. Assuming that this is the case, we can make
predictions on the locations and, possibly, the masses of the unseen planets.
Such planets may be detected by future multi-wavelengths observations.Comment: 8 pages, 5 figures, ApJL in press, typo correcte
High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A
We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on
the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk
object, with a gap structure separating its inner and outer disks. Our imagery
taken with the 0.15 (21 AU) radius coronagraphic mask has revealed a strongly
polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a
spatial resolution of 0.1 (14 AU). It is inclined by 46 \pm 2 degree as the
west side is nearest. Although SED modeling and sub-millimeter imagery
suggested the presence of a gap in the disk, with the inner edge of the outer
disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at
the limit of our inner working angle (23 AU) at the near-infrared wavelength.
We attribute the observed strong polarization (up to 66 %) to light scattering
by dust grains in the disk. However, neither polarization models of the
circumstellar disk based on Rayleigh scattering nor Mie scattering
approximations were consistent with the observed azimuthal profile of the
polarization degrees of the disk. Instead, a geometric optics model of the disk
with nonspherical grains with the radii of 30 micron meter is consistent with
the observed profile. We suggest that the dust grains have experienced frequent
collisional coagulations and have grown in the circumstellar disk of UX Tau A.Comment: 20 pages, 8 figures, and 1 table. accepted to PAS
X-ray emission from the Sombrero galaxy: discrete sources
We present a study of discrete X-ray sources in and around the
bulge-dominated, massive Sa galaxy, Sombrero (M104), based on new and archival
Chandra observations with a total exposure of ~200 ks. With a detection limit
of L_X = 1E37 erg/s and a field of view covering a galactocentric radius of ~30
kpc (11.5 arcminute), 383 sources are detected. Cross-correlation with Spitler
et al.'s catalogue of Sombrero globular clusters (GCs) identified from HST/ACS
observations reveals 41 X-rays sources in GCs, presumably low-mass X-ray
binaries (LMXBs). We quantify the differential luminosity functions (LFs) for
both the detected GC and field LMXBs, whose power-low indices (~1.1 for the
GC-LF and ~1.6 for field-LF) are consistent with previous studies for
elliptical galaxies. With precise sky positions of the GCs without a detected
X-ray source, we further quantify, through a fluctuation analysis, the GC LF at
fainter luminosities down to 1E35 erg/s. The derived index rules out a
faint-end slope flatter than 1.1 at a 2 sigma significance, contrary to recent
findings in several elliptical galaxies and the bulge of M31. On the other
hand, the 2-6 keV unresolved emission places a tight constraint on the field
LF, implying a flattened index of ~1.0 below 1E37 erg/s. We also detect 101
sources in the halo of Sombrero. The presence of these sources cannot be
interpreted as galactic LMXBs whose spatial distribution empirically follows
the starlight. Their number is also higher than the expected number of cosmic
AGNs (52+/-11 [1 sigma]) whose surface density is constrained by deep X-ray
surveys. We suggest that either the cosmic X-ray background is unusually high
in the direction of Sombrero, or a distinct population of X-ray sources is
present in the halo of Sombrero.Comment: 11 figures, 5 tables, ApJ in pres
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