1,129 research outputs found
Intracellular Ca2+ release through ryanodine receptors contributes to AMPA receptor-mediated mitochondrial dysfunction and ER stress in oligodendrocytes
Overactivation of ionotropic glutamate receptors in oligodendrocytes induces cytosolic Ca2+ overload and excitotoxic death, a process that contributes to demyelination and multiple sclerosis. Excitotoxic insults cause well-characterized mitochondrial alterations and endoplasmic reticulum (ER) dysfunction, which is not fully understood. In this study, we analyzed the contribution of ER-Ca2+ release through ryanodine receptors (RyRs) and inositol triphosphate receptors (IP3Rs) to excitotoxicity in oligodendrocytes in vitro. First, we observed that oligodendrocytes express all previously characterized RyRs and IP3Rs. Blockade of Ca2+-induced Ca2+ release by TMB-8 following α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) receptor-mediated insults attenuated both oligodendrocyte death and cytosolic Ca2+ overload. In turn, RyR inhibition by ryanodine reduced as well the Ca2+ overload whereas IP3R inhibition was ineffective. Furthermore, AMPA-triggered mitochondrial membrane depolarization, oxidative stress and activation of caspase-3, which in all instances was diminished by RyR inhibition. In addition, we observed that AMPA induced an ER stress response as revealed by α subunit of the eukaryotic initiation factor 2α phosphorylation, overexpression of GRP chaperones and RyR-dependent cleavage of caspase-12. Finally, attenuating ER stress with salubrinal protected oligodendrocytes from AMPA excitotoxicity. Together, these results show that Ca2+ release through RyRs contributes to cytosolic Ca2+ overload, mitochondrial dysfunction, ER stress and cell death following AMPA receptor-mediated excitotoxicity in oligodendrocytes
Properties of bow-shock sources at the Galactic center
There are an enigmatic population of massive stars around the Galactic Center
(GC) that were formed some Ma ago. A fraction of these stars has been found to
orbit the supermassive black hole, SgrA*, in a projected clockwise disk, which
suggests that they were formed in a formerly existing dense disk around SgrA*.
We focus on the extended, near-infrared (NIR) sources IRS1W, IRS5, IRS10W, and
IRS21 that have been suggested to be young, massive stars that form bow-shocks
through their interaction with the ISM. Their nature has impeded accurate
determination of their orbital parameters. We aim at establishing their nature
and kinematics to test whether they form part of the clockwise disk. We
performed NIR multi-wavelength imaging using adaptive optics (AO) and sparse
aperture masking (SAM). We introduce a new method for self-calibration of the
SAM PSF in dense stellar fields. The emission mechanism, morphology and
kinematics of the targets were examined via 3D bow-shock models. We confirm
previous findings that IRS21, IRS1W, and IRS5 are bow-shocks created by the
interaction between mass-losing stars and the interstellar gas. The nature of
IRS10W remains unclear. Our modeling shows that the bow-shock-emission is
caused by thermal emission while the scattering of stellar light does not play
any significant role. IRS 1W appears to be a bow-shock produced by an
anisotropic stellar wind or by locally inhomogeneous ISM density. Our best-fit
models provide an estimate of the local proper motion of the ISM in the NA in
agreement with the published models. Assuming that all of the sources are tied
to SgrA*, their orbital planes were obtained via a Monte-Carlo simulation. Our
orbital analysis suggests that they are not part of any of the clockwise disk.
We thus add more evidence to recent findings that a large part of the massive
stars show apparently random orbital orientations.Comment: accepted for publication by A&A, 17 pages, 11 figures, 1 appendi
Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A with sparse aperture masking and spectroastrometry
Contemporary theory holds that massive stars gather mass during their initial
phases via accreting disk-like structures. However, conclusive evidence for
disks has remained elusive for the most massive young objects. This is mainly
due to significant observational challenges. Incisive studies, even targeting
individual objects, are therefore relevant to the progression of the field. NGC
3603 IRS 9A* is a young massive stellar object still surrounded by an envelope
of molecular gas. Previous mid-infrared observations with long-baseline
interferometry provided evidence for a disk of 50 mas diameter at its core.
This work aims at a comprehensive study of the physics and morphology of IRS 9A
at near-infrared wavelengths. New sparse aperture masking interferometry data
taken with NACO/VLT at Ks and Lp filters were obtained and analysed together
with archival CRIRES spectra of the H2 and BrG lines. The calibrated
visibilities recorded at Ks and Lp bands suggest the presence of a partially
resolved compact object of 30 mas at the core of IRS 9A, together with the
presence of over-resolved flux. The spectroastrometric signal of the H2 line
shows that this spectral feature proceeds from the large scale extended
emission (300 mas) of IRS 9A, while the BrG line appears to be formed at the
core of the object (20 mas). This scenario is consistent with the brightness
distribution of the source for near- and mid-infrared wavelengths at various
spatial scales. However, our model suffers from remaining inconsistencies
between SED modelling and the interferometric data. Moreover, the BrG
spectroastrometric signal indicates that the core of IRS 9A exhibits some form
of complexity such as asymmetries in the disk. Future high-resolution
observations are required to confirm the disk/envelope model and to flesh out
the details of the physical form of the inner regions of IRS 9A.Comment: Accepted to be published in Astronomy & Astrophysics, 13 pages, 14
figure
Direct Detection of the Tertiary Component in the Massive Multiple HD 150 136 with VLTI
Massive stars are of fundamental importance for almost all aspects of
astrophysics, but there still exist large gaps in our understanding of their
properties and formation because they are rare and therefore distant. It has
been found that most O-stars are multiples. HD 150 136 is the nearest system to
Earth with >100 M_sol, and provides a unique opportunity to study an extremely
massive system. Recently, evidence for the existence of a third component in HD
150 136, in addition to the tight spectroscopic binary that forms the main
component, was found in spectroscopic observations. Our aim was to image and
obtain astrometric and photometric measurements of this component using long
baseline optical interferometry to further constrain the nature of this
component. We observed HD150136 with the near-infrared instrument AMBER
attached to the ESO VLT Interferometer. The recovered closure phases are robust
to systematic errors and provide unique information on the source asymmetry.
Therefore, they are of crucial relevance for both image reconstruction and
model fitting of the source structure. The third component in HD 150 136 is
clearly detected in the high-quality data from AMBER. It is located at a
projected angular distance of 7.3 mas, or about 13 AU at the line-of-sight
distance of HD 150 136, at a position angle of 209 degrees East of North, and
has a flux ratio of 0.25 with respect to the inner binary. We resolved the
third component of HD 150 136 in J, H and K filters. The luminosity and color
of the tertiary agrees with the predictions and shows that it is also an O
main-sequence star. The small measured angular separation indicates that the
tertiary may be approaching the periastron of its orbit. These results, only
achievable with long baseline near infrared interferometry, constitute the
first step towards the understanding of the massive star formation mechanisms
Colour Evolution of Rosé Wines after Bottling
This research reports on the colour evolution of six rosĂ© wines during sixteen months of storage in the bottle.Colour changes were determined in terms of CIELAB colour parameters and in terms of the common colourcategories used in visual assessment. The colour measurement method reproduces the visual assessmentconditions during wine tasting with respect to wine sampler, illuminating source, observing background andsample-observer geometry. CIELAB L*, a*, b*, C* and hab colour coordinates were determined at seven differenttimes (t = 0, 20, 80, 153, 217, 300 and 473 days). The time evolution of colour coordinate values was studied usingmodels related to linear, quadratic and exponential rise to a maximum. Adjusted R2, average standard error andCIELAB ÎE* colour difference were used to compare models and evaluate their performance. For each colourcoordinate, the accuracy of model predictions was similar to the standard deviation associated with a singlemeasurement. An average ÎE* = 0.92 with a 90 percentile value ÎE*90% = 1.50 was obtained between measuredand predicted colour. These values are smaller than human colour discrimination thresholds. The classificationinto colour categories at different times depends on the wine sample. It was found that all wines take three tofour months to change from raspberry to strawberry colour and seven to eight months to reach the redcurrantcategory. Only two wines had developed salmon colour by the end of the experiment
Sub-milliarcsecond Imaging of Quasars and AGN
We have used the VLBA at 15 GHz to image the structure of 132 strong compact
AGN and quasars with a resolution better than one milliarcsecond and a dynamic
range typically exceeding 1000 to 1. These observations were made as part of a
program to investigate the sub-parsec structure of quasars and AGN and to study
the changes in their structure with time. Many of the sources included in our
study, particularly those located south of +35 degrees, have not been
previously imaged with milliarcsecond resolution. Each of the sources has been
observed at multiple epochs. In this paper we show images of each of the 132
sources which we have observed. For each source we present data at the epoch
which had the best quality data. The milliarcsecond jets generally appear
one-sided but two-sided structure is often found in lower luminosity radio
galaxies and in high luminosity quasars with gigahertz peaked spectra. Usually
the structure is unresolved along the direction perpendicular to the jet, but a
few sources have broad plumes. In some low luminosity radio galaxies, the
structure appears more symmetric at 2 cm than at long wavelengths. The apparent
long wavelength symmetry in these sources is probably due to absorption by
intervening material. A few sources contain only a single component with any
secondary feature at least a thousand times weaker. We find no obvious
correlation of radio morphology and the detection of gamma-ray emission by
EGRET.Comment: 19 pages, 3 tables, 3 figures. Figure 2 (132 contour diagrams) is
long and is omitted here. Figure 2 may be viewed at
http://www.cv.nrao.edu/2cmsurvey/ In press, Astronomical Journal, April 199
Serendipitous discovery of the long-sought AGN in Arp 299-A
Context: The dusty nuclear regions of luminous infra-red galaxies (LIRGs) are
heated by either an intense burst of massive star formation, an active galactic
nucleus (AGN), or a combination of both. Disentangling the contribution of each
of those putative dust-heating agents is a challenging task, and direct imaging
of the innermost few pc can only be accomplished at radio wavelengths, using
very high-angular resolution observations. Aims: We observed the nucleus A of
the interacting starburst galaxy Arp 299, using very long baseline
interferometry (VLBI) radio observations at 1.7 and 5.0 GHz. Our aim was to
characterize the compact sources in the innermost few pc region of Arp 299-A,
as well as to detect recently exploded core-collapse supernovae. Methods: We
used the European VLBI Network (EVN) to image the 1.7 and 5.0 GHz compact radio
emission of the parsec-scale structure in the nucleus of Arp 299-A with
milliarcsecond resolution. Results: Our EVN observations show that one of the
compact VLBI sources, A1, previously detected at 5.0 GHz, has a flat spectrum
between 1.7 and 5.0 GHz and is the brightest source at both frequencies. Our
1.7 GHz EVN image shows also diffuse, low-surface brightness emission extending
westwards from A1 and displays a prominent core-jet structure. Conclusions: The
morphology, radio luminosity, spectral index and ratio of radio-to-X-ray
emission of the A1-A5 region is consistent with a low-luminosity AGN (LLAGN),
and rules out the possibility that it is a chain of young radio supernovae
(RSNe) and supernova remnants (SNRs). We therefore conclude that A1-A5 is the
long-sought AGN in Arp 299-A. This finding may suggest that both starburst and
AGN are frequently associated phenomena in mergers.Comment: Accepted for publication in Letters to Astronomy and Astrophysics on
12 August 2010. 4 pages, 1 figur
The population of SNe/SNRs in the starburst galaxy Arp 220. A self-consistent analysis of 20 years of VLBI monitoring
The nearby ultra-luminous infrared galaxy (ULIRG) Arp 220 is an excellent
laboratory for studies of extreme astrophysical environments. For 20 years,
Very Long Baseline Interferometry (VLBI) has been used to monitor a population
of compact sources thought to be supernovae (SNe), supernova remnants (SNRs)
and possibly active galactic nuclei (AGNs). Using new and archival VLBI data
spanning 20 years, we obtain 23 high-resolution radio images of Arp 220 at
wavelengths from 18 cm to 2 cm. From model-fitting to the images we obtain
estimates of flux densities and sizes of all detected sources. We detect radio
continuum emission from 97 compact sources and present flux densities and sizes
for all analysed observation epochs. We find evidence for a LD-relation within
Arp 220, with larger sources being less luminous. We find a compact source LF
with , similar to SNRs in normal
galaxies. Based on simulations we argue that there are many relatively large
and weak sources below our detection threshold. The observations can be
explained by a mixed population of SNe and SNRs, where the former expand in a
dense circumstellar medium (CSM) and the latter interact with the surrounding
interstellar medium (ISM). Nine sources are likely luminous, type IIn SNe. This
number of luminous SNe correspond to few percent of the total number of SNe in
Arp 220 which is consistent with a total SN-rate of 4 yr as inferred
from the total radio emission given a normal stellar initial mass function
(IMF). Based on the fitted luminosity function, we argue that emission from all
compact sources, also below our detection threshold, make up at most 20\% of
the total radio emission at GHz frequencies.Comment: Accepted for publication in Astronomy and Astrophysic
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