286 research outputs found
Clumpy dust clouds and extended atmosphere of the AGB star W Hya revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER II. Time variations between pre-maximum and minimum light
Our recent visible polarimetric images of the well-studied AGB star W Hya
taken at pre-maximum light (phase 0.92) with VLT/SPHERE-ZIMPOL have revealed
clumpy dust clouds close to the star at ~2 Rstar. We present second-epoch
SPHERE-ZIMPOL observations of W Hya at minimum light (phase 0.54) in the
continuum (645, 748, and 820 nm), in the Halpha line (656.3 nm), and in the TiO
band (717 nm) as well as high-spectral resolution long-baseline interferometric
observations in 2.3 micron CO lines with the AMBER instrument at the Very Large
Telescope Interferometer (VLTI). The high-spatial resolution polarimetric
images have allowed us to detect clear time variations in the clumpy dust
clouds as close as 34--50~mas (1.4--2.0 Rstar) to the star. We detected the
formation of a new dust cloud and the disappearance of one of the dust clouds
detected at the first epoch. The Halpha and TiO emission extends to ~150 mas
(~6 Rstar), and the Halpha images reveal time variations. The degree of linear
polarization is higher at minimum light (13--18%) than that at pre-maximum
light. The power-law-type limb-darkened disk fit to the AMBER data in the
continuum results in a limb-darkened disk diameter of 49.1+/-1.5 mas and a
limb-darkening parameter of 1.16+/-0.49, indicating that the atmosphere is more
extended with weaker limb-darkening compared to pre-maximum light. Our Monte
Carlo radiative transfer modeling suggests the predominance of small (0.1
micron) grains of Al2O3, Mg2SiO4, and MgSiO3 at minimum light, in marked
contrast to the predominance of large (0.5 micron) grains at pre-maximum light.
The variability phase dependence of the grain size implies that small grains
might just have started to form at minimum light in the wake of a shock, while
the pre-maximum light phase might have corresponded to the phase of efficient
grain growth.Comment: 14 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
The role of cGMP and PKG-I in spinal nociceptive processing
First paragraph (this article has no abstract) Persistent stimulation of nociceptors results in sensitization of nociceptive sensory neurons, which is associated with hyperalgesia and allodynia. The release of NO and subsequent synthesis of cGMP in the spinal cord are involved in this process. cGMP-dependent protein kinase I (PKG-I) has been suggested to act as a downstream target of cGMP, but its exact role in nociception hadn't been characterized yet. To further evaluate the NO/cGMP/PKG-I pathway in nociception we assessed the effects of PKG-I inhibiton and activaton in the rat formalin assay and analyzed the nociceptive behavior of PKG-I-/- mice. Open access article
Untersuchungen an Bulkmaterialien für rauscharme, kryogene Interferometer
Von Gravitationswellen verursachte Verzerrungen in der Raumzeit können in einem interferometrischen Detektor mit Spiegeln als Testmassen (TM) durch Intensitätsschwankungen am Ausgang erfasst werden und die erste direkte Detektion im Herbst 2015 verdeutlicht eindrucksvoll deren Potential. Für eine Astronomie wie mit optischen Teleskopen ist die Empfindlichkeit noch zu gering und kann nur durch das Absenken des Gesamtrauschens gesteigert werden. Im empfindlichsten Frequenzbereich der Detektoren um 100 Hz limitiert insbesondere das thermische Rauschen der TM. Es ist eng mit der Temperatur und dem mechanischen Verlust verknüpft. Das Abkühlen der TM stellt eine vielversprechende Möglichkeit zur Rauschreduktion in Aussicht. Sowohl Silizium als auch Saphir stellen eine geeignete Alternative zum bisher verwendeten Fused Silica für den kryogenen Betrieb dar und wurden daher bezüglich ihrer Verwendung in zukünftigen Gravitationswellendetektoren untersucht. Unter Berücksichtigung der Reinheit bzw. einer möglichen Dotierung sowie der Oberflächengüte kann so eine Minimierung des damit einhergehenden thermischen Rauschens erfolgen. Auch die nötigen Pendelaufhängungen der TM tragen zum thermischen Rauschen bei. Kryogene Detektoren erfordern Fasern mit größeren Durchmessern für eine ausreichende Wärmeabfuhr. Es wurden Saphirfasern aus unterschiedlichen Herstellungsverfahren im Hinblick auf ihren mechanischen Verlust sowie die Wärmeleitfähigkeit bei tiefen Temperaturen charakterisiert. Die übliche Verbindung der TM mit den Pendelfasern erfolgt mittels hydroxid-katalytischem Bonden sowie durch Laserschweißen. Während letzteres die bei tiefen Temperaturen für hohe Wärmeleitfähigkeiten erforderliche Kristallinität stört, erlaubt die sehr dünne Bondschicht einen nahezu ungestörten Wärmefluss. Das hydroxid-katalytische Bonden als etabliertes Fügeverfahren sowie eine alternativ dazu entwickelte Verbindung mittels Indium wurden deshalb bezüglich ihrer Tieftemperaturtauglichkeit überprüft
Entwicklung eines Managementkonzeptes für Biosphärenreservate zur Förderung nachhaltiger Innovationen am Beispiel des Biosphärenreservates Rhön
In dieser Arbeit soll im Rahmen der Entwicklung eines Managementkonzeptes für Biosphärenreservate zur Förderung nachhaltiger Innovationen im Wesentlichen analysiert werden, wie die vielfältigen Erfahrungen aus dem betrieblichen Innovationsmanagement zur Verbesserung der regional vorhandenen Innovationspotenziale in einem Biosphärenreservate (im folgenden meist BR abgekürzt) beitragen können. Dabei fußt die Arbeit zum einen auf der Recherche der einschlägigen Fachliteratur und veröffentlichten Erfahrungsberichten zum Thema Netzwerkarbeit sowie auf Ergebnissen eigener Untersuchungen. Hierzu zählen eine Umfrage bei allen BR-Verwaltungen im deutschsprachigen Raum mittels eines Fragebogens (siehe Anhang 14.1) sowie Interviews und Fachgespräche mit den Ansprechpartnern der Verwaltungen des Biosphärenreservats Rhön (Interviewleitfaden siehe Anhang 14.3)
Gas dynamics in the inner few AU around the Herbig B[e] star MWC297: Indications of a disk wind from kinematic modeling and velocity-resolved interferometric imaging
We present near-infrared AMBER (R = 12, 000) and CRIRES (R = 100, 000)
observations of the Herbig B[e] star MWC297 in the hydrogen Br-gamma-line.
Using the VLTI unit telescopes, we obtained a uv-coverage suitable for aperture
synthesis imaging. We interpret our velocity-resolved images as well as the
derived two-dimensional photocenter displacement vectors, and fit kinematic
models to our visibility and phase data in order to constrain the gas velocity
field on sub-AU scales. The measured continuum visibilities constrain the
orientation of the near-infrared-emitting dust disk, where we determine that
the disk major axis is oriented along a position angle of 99.6 +/- 4.8 degrees.
The near-infrared continuum emission is 3.6 times more compact than the
expected dust-sublimation radius, possibly indicating the presence of highly
refractory dust grains or optically thick gas emission in the inner disk. Our
velocity-resolved channel maps and moment maps reveal the motion of the
Br-gamma-emitting gas in six velocity channels, marking the first time that
kinematic effects in the sub-AU inner regions of a protoplanetary disk could be
directly imaged. We find a rotation-dominated velocity field, where the blue-
and red-shifted emissions are displaced along a position angle of 24 +/- 3
degrees and the approaching part of the disk is offset west of the star. The
visibility drop in the line as well as the strong non-zero phase signals can be
modeled reasonably well assuming a Keplerian velocity field, although this
model is not able to explain the 3 sigma difference that we measure between the
position angle of the line photocenters and the position angle of the dust
disk. We find that the fit can be improved by adding an outflowing component to
the velocity field, as inspired by a magneto-centrifugal disk-wind scenario.Comment: 15 pages, 13 Figure
On the nature of the Herbig B[e] star binary system V921 Scorpii: Geometry and kinematics of the circumprimary disk on sub-AU scales
V921 Scorpii is a close binary system (separation 0.025") showing the
B[e]-phenomenon. The system is surrounded by an enigmatic bipolar nebula, which
might have been shaped by episodic mass-loss events, possibly triggered by
dynamical interactions between the companion and the circumprimary disk (Kraus
et al. 2012a). In this paper, we investigate the spatial structure and
kinematics of the circumprimary disk, with the aim to obtain new insights into
the still strongly debated evolutionary stage. For this purpose, we combine,
for the first time, infrared spectro-interferometry (VLTI/AMBER, R=12,000) and
spectro-astrometry (VLT/CRIRES, R=100,000), which allows us to study the
AU-scale distribution of circumstellar gas and dust with an unprecedented
velocity resolution of 3 km*s^-1. Using a model-independent photocenter
analysis technique, we find that the Br-gamma-line emission rotates in the same
plane as the dust disk. We can reproduce the wavelength-differential
visibilities and phases and the double-peaked line profile using a
Keplerian-rotating disk model. The derived mass of the central star is
5.4+/-0.4 M_sun*(d/1150 pc), which is considerably lower than expected from the
spectral classification, suggesting that V921 Sco might be more distant (d
approx 2kpc) than commonly assumed. Using the geometric information provided by
our Br-gamma spectro-interferometric data and Paschen, Brackett, and Pfund line
decrement measurements in 61 hydrogen recombination line transitions, we derive
the density of the line-emitting gas (N_e=2...6*10^19 m^-3). Given that our
measurements can be reproduced with a Keplerian velocity field without
outflowing velocity component and the non-detection of age-indicating
spectroscopic diagnostics, our study provides new evidence for the
pre-main-sequence nature of V921 Sco.Comment: 17 pages, 11 figures, 3 tables, accepted by Ap
Wolf-Rayet stars probed by AMBER/VLTI
Massive stars deeply influence their surroundings by their luminosity and the
injection of kinetic energy. So far, they have mostly been studied with
spatially unresolved observations, although evidence of geometrical complexity
of their wind are numerous. Interferometry can provide spatially resolved
observations of massive stars and their immediate vicinity. Specific geometries
(disks, jets, latitude-dependent winds) can be probed by this technique. The
first observation of a Wolf-Rayet (WR) star (\gamma^2 Vel) with the AMBER/VLTI
instrument yielded to a re-evaluation of its distance and an improved
characterization of the stellar components, from a very limited data-set. This
motivated our team to increase the number of WR targets observed with AMBER. We
present here new preliminary results that encompass several spectral types,
ranging from early WN to evolved dusty WC. We present unpublished data on
WR79a, a massive star probably at the boundary between the O and Wolf- Rayet
type, evidencing some Wolf-Rayet broad emission lines from an optically thin
wind. We also present new data obtained on \gamma^2 Vel that can be compared to
the up-to-date interferometry-based orbital parameters from North et al.
(2007). We discuss the presence of a wind-wind collision zone in the system and
provide preliminary analysis suggesting the presence of such a structure in the
data. Then, we present data obtained on 2 dusty Wolf-Rayet stars: WR48a-b and
WR118, the latter exhibiting some clues of a pinwheel-like structure from the
visibility variations.Comment: This paper will be published in the proceeding of SPIE ``astronomical
Telescopes and Instrumentation: Optical and Infrared Interferometry'
High spectral resolution imaging of the dynamical atmosphere of the red supergiant Antares in the CO first overtone lines with VLTI/AMBER
We present high spectral resolution aperture-synthesis imaging of the red
supergiant Antares (alpha Sco) in individual CO first overtone lines with
VLTI/AMBER. The reconstructed images reveal that the star appears differently
in the blue wing, line center, and red wing and shows an asymmetrically
extended component. The appearance of the star within the CO lines changes
drastically within one year, implying a significant change in the velocity
field in the atmosphere. Our modeling suggests an outer atmosphere (MOLsphere)
extending to 1.2--1.4 stellar radii with CO column densities of
(0.5--1)x10^{20} cm^{-2} and a temperature of ~2000 K. While the velocity field
in 2009 is characterized by strong upwelling motions at 20--30 km/s, it changed
to strong downdrafts in 2010. On the other hand, the AMBER data in the
continuum show only a slight deviation from limb-darkened disks and only
marginal time variations. We derive a limb-darkened disk diameter of
37.38+/-0.06 mas and a power-law-type limb-darkening parameter of
(8.7+/-1.6)x10^{-2} (2009) and 37.31+/-0.09 mas and (1.5+/-0.2)x10^{-1} (2010).
We also obtain Teff = 3660+/-120 K and log L/Lsun = 4.88+/-0.23, which suggests
a mass of 15+/-5 Msun with an age of 11-15 Myr. This age is consistent with the
recently estimated age for the Upper Scorpius OB association. The properties of
the outer atmosphere of Antares are similar to those of another well-studied
red supergiant, Betelgeuse. The density of the extended outer atmosphere of
Antares and Betelgeuse is higher than predicted by the current 3-D convection
simulations by at least six orders of magnitude, implying that convection alone
cannot explain the formation of the extended outer atmosphere.Comment: 18 pages, 16 figures, accepted for publication in Astronomy and
Astrophysics, short discussion on the age of Antares and the Upper Scorpius
OB association added, movies of the reconstructed images available at
http://www.mpifr-bonn.mpg.de/staff/kohnaka
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