176 research outputs found
Two-flow magnetohydrodynamical jets around young stellar objects
We present the first-ever simulations of non-ideal magnetohydrodynamical
(MHD) stellar winds coupled with disc-driven jets where the resistive and
viscous accretion disc is self-consistently described. The transmagnetosonic,
collimated MHD outflows are investigated numerically using the VAC code. Our
simulations show that the inner outflow is accelerated from the central object
hot corona thanks to both the thermal pressure and the Lorentz force. In our
framework, the thermal acceleration is sustained by the heating produced by the
dissipated magnetic energy due to the turbulence. Conversely, the outflow
launched from the resistive accretion disc is mainly accelerated by the
magneto-centrifugal force. We also show that when a dense inner stellar wind
occurs, the resulting disc-driven jet have a different structure, namely a
magnetic structure where poloidal magnetic field lines are more inclined
because of the pressure caused by the stellar wind. This modification leads to
both an enhanced mass ejection rate in the disc-driven jet and a larger radial
extension which is in better agreement with the observations besides being more
consistent.Comment: Accepted for publication in Astrophysics & Space Science. Referred
proceeding of the fifth Mont Stromlo Symposium Dec. 1-8 2006, Canberra,
Australia. 5 pages, 3 figures. For high resolution version of the paper,
please click here http://www.apc.univ-paris7.fr/~fcasse/publications.htm
Accretion-powered chromospheres in classical T Tauri stars
(Abridged) Optical spectra of classical T Tauri stars (cTTS) are rich in
emission lines of low-excitation species that are composed of narrow and broad
components, related to two regions with different kinematics, densities, and
temperatures. The photospheric spectrum is often veiled by an excess continuous
emission. This veiling is usually attributed to radiation from a heated region
beneath the accretion shock. The aim of this research is to clarify the nature
of the veiling, and whether the narrow chromospheric lines of Fe I and other
metals represent a standard chromosphere of a late-type star, or are induced by
mass accretion. From high-resolution spectroscopy of DR Tauri we found that the
amount of veiling in this star varies from practically nothing to factors more
than 10 times the stellar continuum intensity, and that the veiling is caused
by both a non-photospheric continuum and chromospheric line emission filling in
the photospheric absorption lines. This effect can be shown to exist in several
other T Tauri stars. We conclude that enhanced chromospheric emission in cTTS
is linked not only to solar-like magnetic activity, but is powered to a greater
extent by the accreting gas. We suggest that the area of enhanced chromospheric
emission is induced by mass accretion, which modifies the local structure of
stellar atmosphere in an area that is more extended than the hot accretion
spot. The narrow emission lines from this extended area are responsible for the
extra component in the veiling through line-filling of photospheric absorption
lines.Comment: 11 pages, 13 figure
Enhancement of the FGFR1 signaling in the FGFR1-5-HT1A heteroreceptor complex in midbrain raphe 5-HT neuron systems. Relevance for neuroplasticity and depression
New findings show existence of FGFR1-5-HT1A heteroreceptor complexes in 5-HT nerve cells of the dorsal and median raphe nuclei of the rat midbrain and hippocampus. Synergistic receptor-receptor interactions in these receptor complexes indicated their enhancing role in hippocampal plasticity. The existence of FGFR1-5-HT1A heteroreceptor complexes also in midbrain raphe 5-HT nerve cells open up the possibility that antidepressant drugs by increasing extracellular 5-HT levels can cause an activation of the FGF-2/FGFR1 mechanism in these nerve cells as well. Therefore, the agonist modulation of the FGFR1-5-HT1A heteroreceptor complexes and their specific role is now determined in rat medullary raphe RN33B cells and in the caudal midline raphe area of the midbrain rich in 5-HT nerve cells. The combined i.c.v. treatment with FGF-2 and the 5-HT1A agonist 8-OHDPAT synergistically increased FGFR1 and ERK1/2 phosphorylation in the raphe midline area of the midbrain and in the RN33B cells. Cotreatment with FGF2 and the 5-HT1A agonist induced RN33B cell differentiation as seen from development of an increased number and length of extensions per cell and their increased 5-HT immunoreactivity. These signaling and differentiation events were dependent on the receptor interface since they were blocked by incubation with TMV but not by TMII of the 5-HT1A receptor. Taken together, the 5-HT1A autoreceptors by being part of a FGFR1-5-HT1A heteroreceptor complex in the midbrain raphe 5-HT nerve cells appears to have also a trophic role in the central 5-HT neuron systems besides playing a key role in reducing the firing of these neurons
Accretion dynamics in the classical T Tauri star V2129 Oph
We analyze the photometric and spectroscopic variability of the classical T
Tauri star V2129 Oph over several rotational cycles to test the dynamical
predictions of magnetospheric accretion models. The photometric variability and
the radial velocity variations in the photospheric lines can be explained by
rotational modulation due to cold spots, while the radial velocity variations
of the He I (5876 \AA) line and the veiling variability are due to hot spot
rotational modulation. The hot and cold spots are located at high latitudes and
about the same phase, but the hot spot is expected to sit at the chromospheric
level, while the cold spot is at the photospheric level. Using the
dipole+octupole magnetic-field configuration previously proposed in the
literature for the system, we compute 3D MHD magnetospheric simulations of the
star-disk system. We use the simulation's density, velocity and scaled
temperature structures as input to a radiative transfer code, from which we
calculate theoretical line profiles at all rotational phases. The theoretical
profiles tend to be narrower than the observed ones, but the qualitative
behavior and the observed rotational modulation of the H\alpha and H\beta
emission lines are well reproduced by the theoretical profiles. The
spectroscopic and photometric variability observed in V2129 Oph support the
general predictions of complex magnetospheric accretion models with
non-axisymmetric, multipolar fields.Comment: Accepted by Astronomy and Astrophysic
Global 3D Simulations of Disc Accretion onto the classical T Tauri Star V2129 Oph
The magnetic field of the classical T Tauri star V2129 Oph can be modeled
approximately by superposing slightly tilted dipole and octupole moments, with
polar magnetic field strengths of 0.35kG and 1.2kG respectively (Donati et al.
2007). Here we construct a numerical model of V2129 Oph incorporating this
result and simulate accretion onto the star. Simulations show that the disk is
truncated by the dipole component and matter flows towards the star in two
funnel streams. Closer to the star, the flow is redirected by the octupolar
component, with some of the matter flowing towards the high-latitude poles, and
the rest into the octupolar belts. The shape and position of the spots differ
from those in a pure dipole case, where crescent-shaped spots are observed at
the intermediate latitudes. Simulations show that if the disk is truncated at
the distance of 6.2 R_* which is comparable with the co-rotation radius, 6.8
R_*, then the high-latitude polar spots dominate, but the accretion rate
obtained from the simulations is about an order of magnitude lower than the
observed one. The accretion rate matches the observed one if the disk is
disrupted much closer to the star, at 3.4 R_*. However, the octupolar belt
spots strongly dominate. Better match has been obtained in experiments with a
dipole field twice as strong. The torque on the star from the
disk-magnetosphere interaction is small, and the time-scale of spin evolution,
2 x10^7-10^9 years is longer than the 2x10^6 years age of V2129 Oph. The
external magnetic flux of the star is strongly influenced by the disk: the
field lines connecting the disk and the star inflate and form magnetic towers
above and below the disk. The potential (vacuum) approximation is still valid
inside the Alfv\'en (magnetospheric) surface where the magnetic stress
dominates over the matter stress.Comment: 15 pages, 15 figures, after major revision, added 3 figures, 2
tables. Accepted to MNRA
Tracing the origins of permitted emission lines in RU Lupi down to AU scales
Most of the observed emission lines and continuum excess from young accreting
low mass stars (Classical T Tauri stars -- CTTSs) take place in the star-disk
or inner disk region. These regions have a complex emission topology still
largely unknown. In this paper the magnetospheric accretion and inner wind
contributions to the observed permitted He and H near infrared (NIR) lines of
the bright southern CTTS RU Lupi are investigated for the first time. Previous
optical observations of RU Lupi showed a large H-alpha profile, due to the
emission from a wind in the line wings, and a micro-jet detected in forbidden
lines. We extend this analysis to NIR lines through seeing-limited high
spectral resolution spectra taken with VLT/ISAAC, and adaptive optics (AO)
aided narrow-band imaging and low spectral resolution spectroscopy with
VLT/NACO. Using spectro-astrometric analysis we investigate the presence of
extended emission down to very low spatial scales (a few AU). The HeI 10830
line presents a P Cygni profile whose absorption feature indicates the presence
of an inner stellar wind. Moreover the spectro-astrometric analysis evidences
the presence of an extended emission superimposed to the absorption feature and
likely coming from the micro-jet detected in the optical. On the contrary, the
origin of the Hydrogen Paschen and Brackett lines is difficult to address. We
tried tentatively to explain the observed line profiles and flux ratios with
both accretion and wind models showing the limits of both approaches. The lack
of spectro-astrometric signal indicates that the HI emission is either compact
or symmetric. Our analysis confirms the sensitivity of the HeI line to the
presence of faint extended emission regions in the close proximity of the star.Comment: 11 pages, 4 figures, accepted for publication on A&
Sraštenost prstiju uz istodobnu višestruku nerazvijenost mekuši na sve četiri noge sa sekundarnom kontrakturom duboke fleksorne tetive u šteneta.
A 2-month-old, 7 kg, male Belgian shepherd Malinois was presented for evaluation of simple and complete syndactyly a nd metacarpal/tarsal pad agenesis in all four limbs, as well as deep digital flexor tendon contracture in the left thoracic and right pelvic limbs. A deep digital flexor tenotomy (digits 2 to 5) was initially performed at the level of the proximal and middle phalanges in the left thoracic limb. Pelvic limb surgery was not performed because the puppy showed less severe signology in this limb and to evaluate the consequences of the thoracic limb surgery. The patient responded partially, and was then treated with a subsequent bilateral tenotomy made more proximal to the previously described, at the level of the lateral lumbrical muscles in the left thoracic and right pelvic limbs. At 7-month post-operative examination, the patient had minimal lameness, especially regarding concurrent syndactyly and pad agenesis of all extremities that was not treated.U radu je iznesen opis i procjena stanja u dvomjesečnog, 7 kg teškog šteneta, belgijskog Malinois ovčara, s jednostavnom i potpunom sraštenošću prstiju, nerazvijenim metakarpalnim/metatarzalnim mekušina na sve 4 noge te s kontrakturama duboke digitalne fleksorne tetive na lijevoj prednjoj i desnoj stražnjoj nozi. U slučaju prve lijeve noge obavljeno je presjecanje duboke digitalne fleksorne tetive (2. do 5. prsta) na razini gornje i srednje falange. Operacija stražnje noge nije obavljena jer je štene na tom ekstremitetu pokazivalo manje izražene simptome, a željelo se prvo i procjeniti učinke zahvata na prednjoj nozi. Stanje pacijenta djelomično se poboljšalo, stoga je naknadno provedeno bilateralno presijecanje tetiva na mjestu iznad prethodne operacije, na razini lateralnih lumbrikalnih mišića prednje lijeve i stražnje desne noge. Postoperativnom kontrolom nakon 7 mjeseci, kod pacijenta je utvrđena minimalna šepavost, posebice vezana za neliječenu popratnu sraštenost prstiju i nerazvijenost mekuši na svim ekstremitetima
Two-component magnetohydrodynamical outflows around young stellar objects Interplay between stellar magnetospheric winds and disc-driven jets
We present the first-ever simulations of non-ideal magnetohydrodynamical
(MHD) stellar magnetospheric winds coupled with disc-driven jets where the
resistive and viscous accretion disc is self-consistently described. These
innovative MHD simulations are devoted to the study of the interplay between a
stellar wind (having different ejection mass rates) and an MHD disc-driven jet
embedding the stellar wind. The transmagnetosonic, collimated MHD outflows are
investigated numerically using the VAC code. We first investigate the various
angular momentum transports occurring in the magneto-viscous accretion disc. We
then analyze the modifications induced by the interaction between the two
components of the outflow. Our simulations show that the inner outflow is
accelerated from the central object's hot corona thanks to both the thermal
pressure and the Lorentz force. In our framework, the thermal acceleration is
sustained by the heating produced by the dissipated magnetic energy due to the
turbulence. Conversely, the outflow launched from the resistive accretion disc
is mainly accelerated by the magneto-centrifugal force.}{The simulations show
that the MHD disc-driven outflow extracts angular momentum more efficiently
than do viscous effects in near-equipartition, thin-magnetized discs where
turbulence is fully developed. We also show that, when a dense inner stellar
wind occurs, the resulting disc-driven jet has a different structure, namely a
magnetic structure where poloidal magnetic field lines are more inclined
because of the pressure caused by the stellar wind. This modification leads to
both an enhanced mass-ejection rate in the disc-driven jet and a larger radial
extension that is in better agreement with the observations, besides being more
consistent.Comment: 16 pages, Accepted in A&A 04/08/200
Treatment of a submerged anaerobic membrane bioreactor (SAnMBR) effluent by an activated sludge system: the role of sulphide and thiosulphate in the process
This work studies the use of a well-known and spread activated sludge system (UCT configuration) to treat the effluent of a submerged anaerobic membrane bioreactor (SAnMBR) treating domestic waste-water. Ammonia, phosphate, dissolved methane and sulphide concentrations in the SAnMBR effluent were around 55 mg NH4-N L-1, 7 mg PO4-P L-1, 30 mg non-methane biodegradable COD L-1, and 105 mg S2- L-1 respectively. The results showed a nitrification inhibition caused by the presence of sulphur compounds at any of the solids retention time (SRT) studied (15,20 and 25 days). This inhibition could be overcome increasing the hydraulic retention time (HRT) from 13 to 26 h. Among the sulphur compounds, sulphide was identified as the substance which caused the nitrification inhibition. When the nitrification was well established, removal rates of nitrogen and phosphorus of 56% and 45% were reached respectively. The sulphide present in the influent was completely oxidised to sulphate, contributing this oxidation to the denitrification process. Moreover, the presence of methanotrophic bacteria, detected by FISH technique, could also contribute to the denitrification. (C) 2014 Elsevier Ltd. All rights reserved.This research project has been supported by Ministry of Science and Innovation (project CTM2011-28595-C02-01/02) and University of Valencia (precompetitive project UV-INV-AE11-40539) which is gratefully acknowledged.Sánchez RamĂrez, JE.; Seco Torrecillas, A.; Ferrer, J.; Bouzas Blanco, A.; GarcĂa Usach, MF. (2015). Treatment of a submerged anaerobic membrane bioreactor (SAnMBR) effluent by an activated sludge system: the role of sulphide and thiosulphate in the process. Journal of Environmental Management. 147:213-218. https://doi.org/10.1016/j.jenvman.2014.04.043S21321814
The non-dipolar magnetic fields of accreting T Tauri stars
Models of magnetospheric accretion on to classical T Tauri stars often assume
that stellar magnetic fields are simple dipoles. Recently published surface
magnetograms of BP Tau and V2129 Oph have shown, however, that their fields are
more complex. The magnetic field of V2129 Oph was found to be predominantly
octupolar. For BP Tau the magnetic energy was shared mainly between the dipole
and octupole field components, with the dipole component being almost four
times as strong as that of V2129 Oph. From the published surface maps of the
photospheric magnetic fields we extrapolate the coronal fields of both stars,
and compare the resulting field structures with that of a dipole. We consider
different models where the disc is truncated at, or well-within, the Keplerian
corotation radius. We find that although the structure of the surface magnetic
field is particularly complex for both stars, the geometry of the larger scale
field, along which accretion is occurring, is somewhat simpler. However, the
larger scale field is distorted close to the star by the stronger field
regions, with the net effect being that the fractional open flux through the
stellar surface is less than would be expected with a dipole magnetic field
model. Finally, we estimate the disc truncation radius, assuming that this
occurs where the magnetic torque from the stellar magnetosphere is comparable
to the viscous torque in the disc.Comment: 14 pages, 8 figures. Figures are reduced resolutio
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