347 research outputs found
The evolved circumbinary disk of AC Her: a radiative transfer, interferometric and mineralogical study
We aim to constrain the structure of the circumstellar material around the
post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial
distribution of the amorphous as well as of the crystalline dust. We present
very high-quality mid-IR interferometric data that were obtained with
MIDI/VLTI. We analyse the MIDI data and the full SED, using the MCMax radiative
transfer code, to find a good structure model of AC Her's circumbinary disk. We
include a grain size distribution and midplane settling of dust
self-consistently. The spatial distribution of crystalline forsterite in the
disk is investigated with the mid-IR features, the 69~m band and the
11.3~m signatures in the interferometric data. All the data are well
fitted. The inclination and position angle of the disk are well determined at
i=50+-8 and PA=305+-10. We firmly establish that the inner disk radius is about
an order of magnitude larger than the dust sublimation radius. Significant
grain growth has occurred, with mm-sized grains being settled to the midplane
of the disk. A large dust mass is needed to fit the sub-mm fluxes. By assuming
{\alpha}=0.01, a good fit is obtained with a small grain size power law index
of 3.25, combined with a small gas/dust ratio <10. The resulting gas mass is
compatible with recent estimates employing direct gas diagnostics. The spatial
distribution of the forsterite is different from the amorphous dust, as more
warm forsterite is needed in the surface layers of the inner disk. The disk in
AC Her is very evolved, with its small gas/dust ratio and large inner hole.
Mid-IR interferometry offers unique constraints, complementary to mid-IR
features, for studying the mineralogy in disks. A better uv coverage is needed
to constrain in detail the distribution of the crystalline forsterite in AC
Her, but we find strong similarities with the protoplanetary disk HD100546.Comment: update with final version published in A&
An interferometric study of the post-AGB binary 89 Herculis. II Radiative transfer models of the circumbinary disk
The presence of disks and outflows is widespread among post-AGB binaries. In
the first paper of this series, a surprisingly large fraction of optical light
was found to be resolved in the 89 Her post-AGB system. The data showed this
flux to arise from close to the central binary. Scattering off the inner rim of
the circumbinary disk, or in a dusty outflow were suggested as two possible
origins. With detailed dust radiative transfer models of the disk we aim to
discriminate between these two configurations. By including Herschel/SPIRE
photometry, we extend the SED such that it now fully covers UV to sub-mm
wavelengths. The MCMax radiative transfer code is used to create a large grid
of disk models. Our models include a self-consistent treatment of dust settling
as well as of scattering. A Si-rich composition with two additional opacity
sources, metallic Fe or amorphous C, are tested. The SED is fit together with
mid-IR (MIDI) visibilities as well as the optical and near-IR visibilities of
Paper I, to constrain the structure of the disk and in particular of its inner
rim. The near-IR visibility data require a smooth inner rim, here obtained with
a two-power-law parameterization of the radial surface density distribution. A
model can be found that fits all the IR photometric and interferometric data
well, with either of the two continuum opacity sources. Our best-fit passive
models are characterized by a significant amount of mm-sized grains, which are
settled to the midplane of the disk. Not a single disk model fits our data at
optical wavelengths though, the reason being the opposing constraints imposed
by the optical and near-IR interferometric data. A geometry in which a passive,
dusty, and puffed-up circumbinary disk is present, can reproduce all the IR but
not the optical observations of 89 Her. Another dusty, outflow or halo,
component therefore needs to be added to the system.Comment: 15 pages, in pres
A mid-IR interferometric survey with MIDI/VLTI: resolving the second-generation protoplanetary disks around post-AGB binaries
We present a mid-IR interferometric survey of the circumstellar environment
of a specific class of post-Asymptotic Giant Branch (post-AGB) binaries. For
this class the presence of a compact dusty disk has been postulated on the
basis of various spatially unresolved measurements. Our interferometric survey
was performed with the MIDI instrument on the VLTI. In total 19 different
systems were observed using variable baseline configurations. Combining all the
visibilities at a single wavelength at 10.7 micron, we fitted two parametric
models to the data: a uniform disk (UD) and a ring model mimicking a
temperature gradient. We compared our observables of the whole sample, with
synthetic data computed from a grid of radiative transfer models of passively
irradiated disks in hydrostatic equilibrium. These models are computed with a
Monte Carlo code that has been widely applied to describe the structure of
protoplanetary disks around young stellar objects (YSO). The spatially resolved
observations show that the majority of our targets cluster closely together in
the distance-independent size-colour diagram, and have extremely compact N-band
emission regions. The typical uniform disk diameter of the N-band emission
region is about 40 mass which corresponds to a typical brightness temperature
of 400-600~K. The resolved objects display very similar characteristics in the
interferometric observables and in the spectral energy distributions.
Therefore, the physical properties of the disks around our targets must be
similar. The grid of protoplanetary disk models covers very well the observed
objects. Much like for young stars, the spatially resolved N-band emission
region is determined by the hot inner rim of the disk. Continued comparisons
between post-AGB and protoplanetary disks will help to understand grain growth
and disk evolution processes,Comment: 30 pages, 21 figures, in press in Astronomy and Astrophysic
ER stress activates the NLRP3 inflammasome via an UPR-independent pathway
Uncontrolled endoplasmic reticulum (ER) stress responses are proposed to contribute to the pathology of chronic inflammatory diseases such as type 2 diabetes or atherosclerosis. However, the connection between ER stress and inflammation remains largely unexplored. Here, we show that ER stress causes activation of the NLRP3 inflammasome, with subsequent release of the pro-inflammatory cytokine interleukin-1β. This ER-triggered proinflammatory signal shares the same requirement for reactive oxygen species production and potassium efflux compared with other known NLRP3 inflammasome activators, but is independent of the classical unfolded protein response (UPR). We thus propose that the NLRP3 inflammasome senses and responds to ER stress downstream of a previously uncharacterized ER stress response signaling pathway distinct from the UPR, thus providing mechanistic insight to the link between ER stress and chronic inflammatory diseases
The orbits of subdwarf B + main-sequence binaries. I: The sdB+G0 system PG 1104+243
The predicted orbital period histogram of an sdB population is bimodal with a
peak at short ( 250 days) periods. Observationally, there
are many short-period sdB systems known, but only very few long-period sdB
binaries are identified. As these predictions are based on poorly understood
binary interaction processes, it is of prime importance to confront the
predictions to observational data. In this contribution we aim to determine the
absolute dimensions of the long-period sdB+MS binary system PG1104+243.
High-resolution spectroscopy time-series were obtained with HERMES at the
Mercator telescope at La Palma, and analyzed to obtain radial velocities of
both components. Photometry from the literature was used to construct the
spectral energy distribution (SED) of the binary. Atmosphere models were used
to fit this SED and determine the surface gravity and temperature of both
components. The gravitational redshift provided an independent confirmation of
the surface gravity of the sdB component. An orbital period of 753 +- 3 d and a
mass ratio of q = 0.637 +- 0.015 were found from the RV-curves. The sdB
component has an effective temperature of Teff = 33500 +- 1200 K and a surface
gravity of logg = 5.84 +- 0.08 dex, while the cool companion is found to be a
G-type star with Teff = 5930 +- 160 K and logg = 4.29 +- 0.05 dex. Assuming a
canonical mass of Msdb = 0.47 Msun, the MS component has a mass of 0.74 +- 0.07
Msun, and its Teff corresponds to what is expected for a terminal age
main-sequence star with sub-solar metalicity. PG1104+243 is the first
long-period sdB binary in which accurate physical parameters of both components
could be determined, and the first sdB binary in which the gravitational
redshift is measured. Furthermore, PG1104+243 is the first sdB+MS system that
shows consistent evidence for being formed through stable Roche-lobe overflow.Comment: Accepted by A&A on 05-10-201
Antitumour and antiangiogenic effects of Aplidin® in the 5TMM syngeneic models of multiple myeloma
Aplidin® is an antitumour drug, currently undergoing phase II evaluation in different haematological and solid tumours. In this study, we analysed the antimyeloma effects of Aplidin in the syngeneic 5T33MM model, which is representable for the human disease. In vitro, Aplidin inhibited 5T33MMvv DNA synthesis with an IC50 of 3.87 nM. On cell-cycle progression, the drug induced an arrest in transition from G0/G1 to S phase, while Western blot showed a decreased cyclin D1 and CDK4 expression. Furthermore, Aplidin induced apoptosis by lowering the mitochondrial membrane potential, by inducing cytochrome c release and by activating caspase-9 and caspase-3. For the in vivo experiment, 5T33MM-injected C57Bl/KaLwRij mice were intraperitoneally treated with vehicle or Aplidin (90 μg kg−1 daily). Chronic treatment with Aplidin was well tolerated and reduced serum paraprotein concentration by 42% (P<0.001), while BM invasion with myeloma cells was decreased by 35% (P<0.001). Aplidin also reduced the myeloma-associated angiogenesis to basal values. This antiangiogenic effect was confirmed in vitro and explained by inhibition of endothelial cell proliferation and vessel formation. These data indicate that Aplidin is well tolerated in vivo and its antitumour and antiangiogenic effects support the use of the drug in multiple myeloma
On the structure of high performance anticorrosive PMMA–siloxane–silica hybrid coatings
Environmentally compliant organic–inorganic hybrid coatings for efficient corrosion protection of metallic surfaces are potential alternatives to the current method based on chromate passivation. In this context PMMA–siloxane–silica (PMMA–SS) hybrid films were prepared using the sol–gel process from the radical copolymerization of methyl methacrylate and 3-(trimethoxysilyl)propyl methacrylate followed by acidic hydrolysis and polycondensation of tetraethoxysilane (TEOS), under variation of the ethanol to H2O ratio (0.0–1.0). The structural properties of about 2 μm thick coatings, deposited by dip-coating onto carbon steel, were related with their corrosion protection efficiency. The correlation of data obtained by X-ray photoelectron spectroscopy, nuclear magnetic resonance and small angle X-ray scattering has shown for intermediate ethanol to H2O ratios the highest connectivity (∼83%) of the inorganic phase, bonded covalently to organic moieties, yielding a dense and homogeneous nanocomposite structure with high thermal stability, very good adhesion to the metallic substrate and excellent barrier properties. The electrochemical impedance spectroscopy measurements have shown for coatings prepared at intermediate EtOH/H2O ratios a high corrosion resistance of almost 10 GΩ cm2, which remained unchanged for more than 6 months in contact with 3.5% NaCl solution and more than 3 months exposed to an acidic NaCl environment
A Tale of Two Stars: Interferometric Studies of Post-AGB Binaries
Binaries with circumbinary disks are commonly found among optically bright
post-AGB stars. Although clearly linked to binary interaction processes, the
formation, evolution and fate of these disks are still badly understood. Due to
their compactness, interferometric techniques are required to resolve them.
Here, we discuss our high-quality multiwavelength interferometric data of two
prototypical yet very different post-AGB binaries, AC and 89 Herculis, as well
as the modeling thereof with radiative transfer models. A detailed account of
the data and models of both objects is published in three separate papers
elsewhere; here we focus on comparing the modeling results for the two objects.
In particular we discuss the successes and limitations of the models which were
developed for protoplanetary disks around young stars. We conclude that
multiwavelength high-angular-resolution observations and radiative transfer
disk models are indispensible to understand these complex interacting objects
and their place in the grand scheme of the (binary) evolution of low and
intermediate mass stars.Comment: 5 pages, 1 figure, Conference proceedings for contributed talk at
"Why Galaxies care about AGB stars III
Discovery of a TiO emission band in the infrared spectrum of the S star NP Aurigae
We report on the discovery of an infrared emission band in the Spitzer
spectrum of the S-type AGB star NP Aurigae that is caused by TiO molecules in
the circumstellar environment. We modelled the observed emission to derive the
temperature of the TiO molecules (\approx 600 K), an upper limit on the column
density (\approx 10^17.25 cm^{-2}) and a lower limit on the spatial extent of
the layer that contains these molecules. (\approx 4.6 stellar radii). This is
the first time that this TiO emission band is observed. A search for similar
emission features in the sample of S-type stars yielded two additional
candidates. However, owing to the additional dust emission, the identification
is less stringent. By comparing the stellar characteristics of NP Aur to those
of the other stars in our sample, we find that all stars with TiO emission show
large-amplitude pulsations, s-process enrichment, and a low C/O ratio. These
characteristics might be necessary requirements for a star to show TiO in
emission, but they are not sufficient.Comment: 4 pages, 4 figures, letter to the edito
On the structure of the transition disk around TW Hya
For over a decade, the structure of the inner cavity in the transition disk
of TW Hydrae has been a subject of debate. Modeling the disk with data obtained
at different wavelengths has led to a variety of proposed disk structures.
Rather than being inconsistent, the individual models might point to the
different faces of physical processes going on in disks, such as dust growth
and planet formation. Our aim is to investigate the structure of the transition
disk again and to find to what extent we can reconcile apparent model
differences. A large set of high-angular-resolution data was collected from
near-infrared to centimeter wavelengths. We investigated the existing disk
models and established a new self-consistent radiative-transfer model. A
genetic fitting algorithm was used to automatize the parameter fitting. Simple
disk models with a vertical inner rim and a radially homogeneous dust
composition from small to large grains cannot reproduce the combined data set.
Two modifications are applied to this simple disk model: (1) the inner rim is
smoothed by exponentially decreasing the surface density in the inner ~3 AU,
and (2) the largest grains (>100 um) are concentrated towards the inner disk
region. Both properties can be linked to fundamental processes that determine
the evolution of protoplanetary disks: the shaping by a possible companion and
the different regimes of dust-grain growth, respectively. The full
interferometric data set from near-infrared to centimeter wavelengths requires
a revision of existing models for the TW Hya disk. We present a new model that
incorporates the characteristic structures of previous models but deviates in
two key aspects: it does not have a sharp edge at 4 AU, and the surface density
of large grains differs from that of smaller grains. This is the first
successful radiative-transfer-based model for a full set of interferometric
data.Comment: 22 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
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