272 research outputs found
A search for the presence of magnetic fields in the two Supergiant Fast X-ray Transients IGR J08408-4503 and IGR J11215-5952
A significant fraction of high-mass X-ray binaries are supergiant fast X-ray
transients (SFXTs). The prime model for the physics governing their X-ray
behaviour suggests that the winds of donor OB supergiants are magnetized. To
investigate if magnetic fields are indeed present in the optical counterparts
of such systems, we acquired low-resolution spectropolarimetric observations of
the two optically brightest SFXTs, IGR J08408-4503 and IGR J11215-5952 with the
ESO FORS2 instrument during two different observing runs. No field detection at
a significance level of 3sigma was achieved for IGR J08408-4503. For IGR
J11215-5952, we obtain 3.2sigma and 3.8sigma detections (_hydr =
-978+-308G and _hydr = 416+-110G) on two different nights in 2016. These
results indicate that the model involving the interaction of a magnetized
stellar wind with the neutron star magnetosphere can indeed be considered to
characterize the behaviour of SFXTs. We detected long-term spectral variability
in IGR J11215-5952, while for IGR J08408-4503 we find an indication of the
presence of short-term variability on a time scale of minutes.Comment: 5 pages, 1 table, 7 figures, accepted for publication in MNRA
A multiphase-field approach to small strain crystal plasticity accounting for balance equations on singular surfaces
Contribution of Matrix Metalloproteinase-9 to Cerebral Edema and Functional Outcome following Experimental Subarachnoid Hemorrhage
Background: Cerebral edema is an important risk factor for death and poor outcome following subarachnoid hemorrhage (SAH). However, underlying mechanisms are still poorly understood. Matrix metalloproteinase (MMP)-9 is held responsible for the degradation of microvascular basal lamina proteins leading to blood-brain barrier dysfunction and, thus, formation of vasogenic cerebral edema. The current study was conducted to clarify the role of MMP-9 for the development of cerebral edema and for functional outcome after SAH. Methods: SAH was induced in FVB/N wild-type (WT) or MMP-9 knockout (MMP-9(-/-)) mice by endovascular puncture. Intracranial pressure (ICP), regional cerebral blood flow (rCBF), and mean arterial blood pressure (MABP) were continuously monitored up to 30 min after SAH. Mortality was quantified for 7 days after SAH. In an additional series neurological function and body weight were assessed for 3 days after SAH. Subsequently, ICP and brain water content were quantified. Results: Acute ICP, rCBF, and MABP did not differ between WT and MMP-9(-/-) mice, while 7 days' mortality was lower in MMP-9(-/-) mice (p = 0.03; 20 vs. 60%). MMP-9(-/-) mice also exhibited better neurological recovery, less brain edema formation, and lower chronic ICP. Conclusions: The results of the current study suggest that MMP-9 contributes to the development of early brain damage after SAH by promoting cerebral edema formation. Hence, MMP-9 may represent a novel molecular target for the treatment of SAH. Copyright (C) 2011 S. Karger AG, Base
Psychotherapy Is Chaotic— (Not Only) in a Computational World
Objective: The aim of this article is to outline the role of chaotic dynamics in psychotherapy. Besides some empirical findings of chaos at different time scales, the focus is on theoretical modeling of change processes explaining and simulating chaotic dynamics. It will be illustrated how some common factors of psychotherapeutic change and psychological hypotheses on motivation, emotion regulation, and information processing of the client’s functioning can be integrated into a comprehensive nonlinear model of human change processes.
Methods: The model combines 5 variables (intensity of emotions, problem intensity, motivation to change, insight and new perspectives, therapeutic success) and 4 parameters into a set of 5 coupled nonlinear difference equations. The results of these simulations are presented as time series, as phase space embedding of these time series (i.e., attractors), and as bifurcation diagrams.
Results: The model creates chaotic dynamics, phase transition-like phenomena, bi- or multi-stability, and sensibility of the dynamic patterns on parameter drift. These features are predicted by chaos theory and by Synergetics and correspond to empirical findings. The spectrum of these behaviors illustrates the complexity of psychotherapeutic processes.
Conclusion: The model contributes to the development of an integrative conceptualization of psychotherapy. It is consistent with the state of scientific knowledge of common factors, as well as other psychological topics, such as: motivation, emotion regulation, and cognitive processing. The role of chaos theory is underpinned, not only in the world of computer simulations, but also in practice. In practice, chaos demands technologies capable of real-time monitoring and reporting on the nonlinear features of the ongoing process (e.g., its stability or instability). Based on this monitoring, a client-centered, continuous, and cooperative process of feedback and control becomes possible. By contrast, restricted predictability and spontaneous changes challenge the usefulness of prescriptive treatment manuals or other predefined programs of psychotherapy
First measurement of the magnetic field on FK Com and its relation to the contemporaneous star-spot locations
In this study, we present simultaneous low-resolution longitudinal magnetic field measurements and high-resolution spectroscopic observations of the cool single giant FK Com. The variation of the magnetic field over the rotational period of 2.4 d is compared with the star-spot location obtained using Doppler imaging techniques, V-band photometry and V−I colours. The chromospheric activity is studied simultaneously with the photospheric activity using high-resolution observations of the Hα, Hβ and Hγ line profiles. Both the maximum (272 ± 24 G) and minimum (60 ± 17 G) in the mean longitudinal magnetic field, 〈Bz〉, are detected close to the phases where cool spots appear on the stellar surface. A possible explanation for such a behaviour is that the active regions at the two longitudes separated by 0.2 in phase have opposite polaritie
B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD-57{\deg} 3509
We report the detection of a magnetic field in the helium-strong star CPD-57
3509 (B2 IV), a member of the Galactic open cluster NGC3293, and characterise
the star's atmospheric and fundamental parameters. Spectropolarimetric
observations with FORS2 and HARPSpol are analysed using two independent
approaches to quantify the magnetic field strength. A high-S/N FLAMES/GIRAFFE
spectrum is analysed using a hybrid non-LTE model atmosphere technique.
Comparison with stellar evolution models constrains the fundamental parameters
of the star. We obtain a firm detection of a surface averaged longitudinal
magnetic field with a maximum amplitude of about 1 kG. Assuming a dipolar
configuration of the magnetic field, this implies a dipolar field strength
larger than 3.3 kG. Moreover, the large amplitude and fast variation (within
about 1 day) of the longitudinal magnetic field implies that CPD-57 3509 is
spinning very fast despite its apparently slow projected rotational velocity.
The star should be able to support a centrifugal magnetosphere, yet the
spectrum shows no sign of magnetically confined material; in particular,
emission in H{\alpha} is not observed. Apparently, the wind is either not
strong enough for enough material to accumulate in the magnetosphere to become
observable or, alternatively, some leakage process leads to loss of material
from the magnetosphere. The quantitative spectroscopic analysis of the star
yields an effective temperature and a logarithmic surface gravity of 23750+-250
K and 4.05+-0.10, respectively, and a surface helium fraction of 0.28+-0.02 by
number. The surface abundances of C, N, O, Ne, S, and Ar are compatible with
the cosmic abundance standard, whereas Mg, Al, Si, and Fe are depleted by about
a factor of 2. This abundance pattern can be understood as the consequence of a
fractionated stellar wind. CPD-57 3509 is one of the most evolved He-strong
stars known.Comment: 15 pages, 11 figures. Accepted for publication in A&
Observations of Mira stars with the IOTA/FLUOR interferometer and comparison with Mira star models
We present K'-band observations of five Mira stars with the IOTA
interferometer. The interferograms were obtained with the FLUOR fiber optics
beam combiner, which provides high-accuracy visibility measurements in spite of
time-variable atmospheric conditions. For the M-type Miras X Oph, R Aql, RU
Her, R Ser, and the C-type Mira V CrB we derived the uniform-disk diameters
11.7mas, 10.9mas, 8.4mas, 8.1mas, and 7.9mas (+/- 0.3mas), respectively.
Simultaneous photometric observations yielded the bolometric fluxes. The
derived angular Rosseland radii and the bolometric fluxes allowed the
determination of effective temperatures. For instance, the effective
temperature of R Aql was determined to be 2970 +/- 110 K. A linear Rosseland
radius for R Aql of (250 +100/-60) Rsun was derived from the angular Rosseland
radius of 5.5mas +/- 0.2mas and the HIPPARCOS parallax of 4.73mas +/- 1.19mas.
The observations were compared with theoretical Mira star models of Bessel et
al. (1996) and Hofmann et al. (1998). The effective temperatures of the M-type
Miras and the linear radius of R Aql indicate fundamental mode pulsation.Comment: 12 pages, 4 postscript figure
The magnetic field and the evolution of element spots on the surface of the HgMn eclipsing binary AR Aur
The system AR Aur is a young late B-type double-lined eclipsing binary with a primary star of HgMn peculiarity. We applied the Doppler imaging method to reconstruct the distribution of Fe and Y over the surface of the primary using spectroscopic time series obtained in 2005 and from 2008 October to 2009 February. The results show a remarkable evolution of the element distribution and overabundances. Measurements of the magnetic field with the moment technique using several elements reveal the presence of a longitudinal magnetic field of the order of a few hundred gauss in both stellar components and a quadratic field of the order of 8 kG on the surface of the primary star.Fil: Hubrig, S.. Astrophysikalisches Institut Potsdam; AlemaniaFil: Savanov, I.. Russian Academy of Sciences. Institute of Astronomy; RusiaFil: Ilyin, I.. Astrophysikalisches Institut Potsdam; AlemaniaFil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico San Juan. Instituto de Ciencias Astronomicas de la Tierra y del Espacio; ArgentinaFil: Korhonen, H.. European Southern Observatory; AlemaniaFil: Lehmann, H.. Thuringer Landessternwarte; AlemaniaFil: Schöller, M.. European Southern Observatory; AlemaniaFil: Granzer, T.. Astrophysikalisches Institut Potsdam; AlemaniaFil: Weber, M.. Astrophysikalisches Institut Potsdam; AlemaniaFil: Strassmeier, K. G.. Astrophysikalisches Institut Potsdam; AlemaniaFil: Hackman, T.. Thuringer Landessternwarte; AlemaniaFil: Tkachenko, A.. Thuringer Landessternwarte; Argentin
Close binary companions of the HAeBe stars LkHa 198, Elias 1, HK Ori and V380 Ori
We present diffraction-limited bispectrum speckle interferometry observations
of four well-known Herbig Ae/Be (HAeBe) stars, LkHa 198, Elias 1, HK Ori and
V380 Ori. For two of these, LkHa 198 and Elias 1, we present the first
unambiguous detection of close companions. The plane of the orbit of the new
LkHa 198 companion appears to be significantly inclined to the plane of the
circumprimary disk, as inferred from the orientation of the outflow. We show
that the Elias 1 companion may be a convective star, and suggest that it could
therefore be the true origin of the X-ray emission from this object. In the
cases of HK Ori and V380 Ori, we present new measurements of the relative
positions of already-known companions, indicating orbital motion. For HK Ori,
photometric measurements of the brightness of the individual components in four
bands allowed us to decompose the system spectral energy distribution (SED)
into the two separate component SEDs. The primary exhibits a strong infrared
excess which suggests the presence of circumstellar material, whereas the
companion can be modelled as a naked photosphere. The infrared excess of HK Ori
A was found to contribute around two thirds of the total emission from this
component, suggesting that accretion power contributes significantly to the
flux. Submillimetre constraints mean that the circumstellar disk cannot be
particularly massive, whilst the near-infrared data indicates a high accretion
rate. Either the disk lifetime is very short, or the disk must be seen in an
outburst phase.Comment: 14 pages, 10 figures, 22 separate figure file
Tracing the young massive high-eccentricity binary system Theta 1 Orionis C through periastron passage
The nearby high-mass star binary system Theta 1 Orionis C is the brightest
and most massive of the Trapezium OB stars at the core of the Orion Nebula
Cluster, and it represents a perfect laboratory to determine the fundamental
parameters of young hot stars and to constrain the distance of the Orion
Trapezium Cluster. Between January 2007 and March 2008, we observed T1OriC with
VLTI/AMBER near-infrared (H- and K-band) long-baseline interferometry, as well
as with bispectrum speckle interferometry with the ESO 3.6m and the BTA 6m
telescopes (B'- and V'-band). Combining AMBER data taken with three different
3-telescope array configurations, we reconstructed the first VLTI/AMBER
closure-phase aperture synthesis image, showing the T1OriC system with a
resolution of approx. 2 mas. To extract the astrometric data from our
spectrally dispersed AMBER data, we employed a new algorithm, which fits the
wavelength-differential visibility and closure phase modulations along the H-
and K-band and is insensitive to calibration errors induced, for instance, by
changing atmospheric conditions. Our new astrometric measurements show that the
companion has nearly completed one orbital revolution since its discovery in
1997. The derived orbital elements imply a short-period (P=11.3 yrs) and
high-eccentricity orbit (e=0.6) with periastron passage around 2002.6. The new
orbit is consistent with recently published radial velocity measurements, from
which we can also derive the first direct constraints on the mass ratio of the
binary components. We employ various methods to derive the system mass
(M_system=44+/-7 M_sun) and the dynamical distance (d=410+/-20 pc), which is in
remarkably good agreement with recently published trigonometric parallax
measurements obtained with radio interferometry.Comment: 15 pages, 15 figures, accepted by A&
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