1,142 research outputs found
CO ro-vibrational lines in HD100546: A search for disc asymmetries and the role of fluorescence
We have studied the emission of CO ro-vibrational lines in the disc around
the Herbig Be star HD100546 with the final goal of using these lines as a
diagnostic to understand inner disc structure in the context of planet
formation. High-resolution IR spectra of CO ro-vibrational emission at eight
different position angles were taken with CRIRES at the VLT. From these spectra
flux tables, CO ro-vibrational line profiles, and population diagrams were
produced. We have investigated variations in the line profile shapes and line
strengths as a function of slit position angle. We used the thermochemical disc
modelling code ProDiMo based on the chemistry, radiation field, and temperature
structure of a previously published model for HD100546. Comparing observations
and the model, we investigated the possibility of disc asymmetries, the
excitation mechanism (UV fluorescence), the geometry, and physical conditions
of the inner disc. The observed CO ro-vibrational lines are largely emitted
from the inner rim of the outer disc at 10-13 AU. The line shapes are similar
for all v levels and line fluxes from all vibrational levels vary only within
one order of magnitude. All line profile asymmetries and variations can be
explained with a symmetric disc model to which a slit correction and pointing
offset is applied. Because the angular size of the CO emitting region (10-13
AU) and the slit width are comparable the line profiles are very sensitive to
the placing of the slit. The model reproduces the line shapes and the fluxes of
the v=1-0 lines as well as the spatial extent of the CO ro-vibrational
emission. It does not reproduce the observed band ratios of 0.5-0.2 with higher
vibrational bands. We find that lower gas volume densities at the surface of
the inner rim of the outer disc can make the fluorescence pumping more effcient
and reproduce the observed band ratios.Comment: 20 pages, 21 figure
Secondary and Tertiary Hyperparathyroidism:A Narrative Review
End-stage renal disease is often complicated by the occurrence of secondary and eventually tertiary hyperparathyroidism, characterized by increased parathormone, calcium, and phosphate concentrations. Related symptoms include pruritus and osteodynia, concentration difficulties, and feelings of depression may be present. In the long-term, end-stage renal disease patients with hyperparathyroidism have an increased risk of all-cause and cardiovascular mortality. Among treatment options are vitamin D supplements, phosphate binders, calcimimetics, and surgical parathyroidectomy. Determining the optimal treatment for the individual patient is challenging for nephrologists and endocrine surgeons. This review resumes the pathogenesis of hyperparathyroidism, clinical presentation, required diagnostic work-up, and discusses indications for the available treatment options for patients with secondary and tertiary hyperparathyroidism
The structure of the protoplanetary disk surrounding three young intermediate mass stars. II. Spatially resolved dust and gas distribution
[Abridged] We present the first direct comparison of the distribution of the
gas, as traced by the [OI] 6300 AA emission, and the dust, as traced by the 10
micron emission, in the protoplanetary disk around three intermediate-mass
stars: HD 101412, HD 135344 B and HD 179218. N-band visibilities were obtained
with VLTI/MIDI. Simple geometrical models are used to compare the dust emission
to high-resolution optical spectra in the 6300 AA [OI] line of the same
targets. The disks around HD 101412 and HD 135344 B appear strongly flared in
the gas, but self-shadowed in the dust beyond ~ 2 AU. In both systems, the 10
micron emission is rather compact (< 2 AU) while the [OI] brightness profile
shows a double peaked structure. The inner peak is strongest and is consistent
with the location of the dust, the outer peak is fainter and is located at 5-10
AU. Spatially extended PAH emission is found in both disks. The disk around HD
179218 is flared in the dust. The 10 micron emission emerges from a double
ring-like structure with the first ring peaking at ~ 1 AU and the second at ~
20 AU. No dust emission is detected between ~ 3 -- 15 AU. The oxygen emission
seems also to come from a flared structure, however, the bulk of this emission
is produced between ~ 1 -- 10 AU. This could indicate a lack of gas in the
outer disk or could be due to chemical effects which reduce the abundance of OH
-- the parent molecule of the observed [OI] emission -- further away from the
star. The three systems, HD 179218, HD 135344 B and HD 101412, may form an
evolutionary sequence: the disk initially flared becomes flat under the
combined action of gas-dust decoupling, grain growth and dust settling.Comment: Accepted for publication in A&
Community assembly in Lake Tanganyika cichlid fish:Quantifying the contributions of both niche-based and neutral processes
The cichlid family features some of the most spectacular examples of adaptive radiation. Evolutionary studies have highlighted the importance of both trophic adaptation and sexual selection in cichlid speciation. However, it is poorly understood what processes drive the composition and diversity of local cichlid species assemblages on relatively short, ecological timescales. Here, we investigate the relative importance of niche-based and neutral processes in determining the composition and diversity of cichlid communities inhabiting various environmental conditions in the littoral zone of Lake Tanganyika, Zambia. We collected data on cichlid abundance, morphometrics, and local environments. We analyzed relationships between mean trait values, community composition, and environmental variation, and used a recently developed modeling technique (STEPCAM) to estimate the contributions of niche-based and neutral processes to community assembly. Contrary to our expectations, our results show that stochastic processes, and not niche-based processes, were responsible for the majority of cichlid community assembly. We also found that the relative importance of niche-based and neutral processes was constant across environments. However, we found significant relationships between environmental variation, community trait means, and community composition. These relationships were caused by niche-based processes, as they disappeared in simulated, purely neutrally assembled communities. Importantly, these results can potentially reconcile seemingly contrasting findings in the literature about the importance of either niche-based or neutral-based processes in community assembly, as we show that significant trait relationships can already be found in nearly (but not completely) neutrally assembled communities; that is, even a small deviation from neutrality can have major effects on community patterns
Cell-surface insulin receptor cycling and its implication in the glycogenic response in cultured foetal hepatocytes
A survey for near-infrared H2 emission in Herbig Ae/Be stars: emission from the outer disks of HD 97048 and HD 100546
A survey for near-infrared H2 emission in Herbig Ae/Be stars: emission from the outer disks of HD 97048 and HD 100546
We report on a sensitive search for H2 1-0 S(1), 1-0 S(0) and 2-1 S(1)
ro-vibrational emission at 2.12, 2.22 and 2.25 micron in a sample of 15 Herbig
Ae/Be stars employing CRIRES, the ESO-VLT near-infrared high-resolution
spectrograph, at R~90,000. We detect the H2 1-0 S(1) line toward HD 100546 and
HD 97048. In the other 13 targets, the line is not detected. The H2 1-0 S(0)
and 2-1 S(1) lines are undetected in all sources. This is the first detection
of near-IR H2 emission in HD 100546. The H2 1-0 S(1) lines observed in HD
100546 and HD 97048 are observed at a velocity consistent with the rest
velocity of both stars, suggesting that they are produced in the circumstellar
disk. In HD 97048, the emission is spatially resolved and it is observed to
extend at least up to 200 AU. We report an increase of one order of magnitude
in the H2 1-0 S(1) line flux with respect to previous measurements taken in
2003 for this star, which suggests line variability. In HD 100546 the emission
is tentatively spatially resolved and may extend at least up to 50 AU. Modeling
of the H2 1-0 S(1) line profiles and their spatial extent with flat keplerian
disks shows that most of the emission is produced at a radius >5 AU. Upper
limits to the H2 1-0 S(0)/ 1-0 S(1) and H2 2-1 S(1)/1-0 S(1) line ratios in HD
97048 are consistent with H2 gas at T>2000 K and suggest that the emission
observed may be produced by X-ray excitation. The upper limits for the line
ratios for HD 100546 are inconclusive. Because the H2 emission is located at
large radii, for both sources a thermal emission scenario (i.e., gas heated by
collisions with dust) is implausible. We argue that the observation of H2
emission at large radii may be indicative of an extended disk atmosphere at
radii >5 AU. This may be explained by a hydrostatic disk in which gas and dust
are thermally decoupled or by a disk wind caused by photoevaporation.Comment: Accepted by A&A. 16 pages, 7 figure
Probing the Early Evolution of Young High-Mass Stars
Near-infrared imaging surveys of high-mass star-forming regions reveal an
amazingly complex interplay between star formation and the environment
(Churchwell et al. 2006; Alvarez et al. 2004). By means of near-IR spectroscopy
the embedded massive young stars can be characterized and placed in the context
of their birth site. However, so far spectroscopic surveys have been hopelessly
incomplete, hampering any systematic study of these very young massive stars.
New integral field instrumentation available at ESO has opened the possibility
to take a huge step forward by obtaining a full spectral inventory of the
youngest massive stellar populations in star-forming regions currently
accessible. Simultaneously, the analysis of the extended emission allows the
characterization of the environmental conditions. The Formation and Early
Evolution of Massive Stars (FEMS) collaboration aims at setting up a large
observing campaign to obtain a full census of the stellar content, ionized
material, outflows and PDR's over a sample of regions that covers a large
parameter space. Complementary radio, mm and infrared observations will be used
for the characterization of the deeply embedded population. For the first eight
regions we have obtained 40 hours of SINFONI observations. In this
contribution, we present the first results on three regions that illustrate the
potential of this strategy.Comment: To appear in ASP Conf. Proceedings of "Massive Star Formation:
Observations confront Theory", H. Beuther et al. (eds.), held in Heidelberg,
September 200
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