Modeling non-thermal emission from stellar bow shocks

Runaway O- and early B-type stars passing throughout the interstellar medium at supersonic velocities and characterized by strong stellar winds may produce bow shocks that can serve as particle acceleration sites. Previous theoretical models predict the production of high energy photons by non-thermal radiative processes, but their efficiency is still debated. We aim to test and explain the possibility of emission from the bow shocks formed by runaway stars traveling through the interstellar medium by using previous theoretical models. We apply our model to AE Aurigae, the first reported star with an X-ray detected bow shock, to BD+43 3654, in which the observations failed in detecting high energy emission, and to the transition phase of a supergiant star in the late stages of its life.From our analysis, we confirm that the X-ray emission from the bow shock produced by AE Aurigae can be explained by inverse Compton processes involving the infrared photons of the heated dust. We also predict low high energy flux emission from the bow shock produced by BD+43 3654, and the possibility of high energy emission from the bow shock formed by a supergiant star during the transition phase from blue to red supergiant.Bow shock formed by different type of runaway stars are revealed as a new possible source of high energy photons in our neighbourhood

Radiative two-pion decay of the tau lepton

We consider the bremsstrahlung and model-dependent contributions to the radiative decay $\tau^- \to \pi^-\pi^0\nu_{\tau}\gamma$ in the context of a meson dominance model. We focus on several observables related to this decay, including the branching ratio and the photon and di-pion spectra. Particular attention is paid to the sensitivity of different observables upon the effects of model-dependent contributions and of the magnetic dipole moment of the $\rho^-(770)$ vector meson. Important numerical differences are found with respect to results obtained in the framework of chiral perturbation theory.Comment: 14 pages, 8 figures, submitted for publicatio

Gauge invariance and finite width effects in radiative two-pion tau lepton decay

The contribution of the rho^{\pm} vector meson to the tau -> pi pi nu gamma decay is considered as a potential source for the determination of the magnetic dipole moment of this light vector meson. In order to keep gauge-invariance of the whole decay amplitude, a procedure similar to the fermion loop-scheme for charged gauge bosons is implemented to incorporate the finite width effects of the rho^{\pm} vector meson. The absorptive pieces of the one-loop corrections to the propagators and electromagnetic vertices of the rho^{\pm} meson and W^{\pm} gauge boson have identical forms in the limit of massless particles in the loops, suggesting this to be a universal feature of spin-one unstable particles. Model-dependent contributions to the tau -> pi pi nu gamma decay are suppressed by fixing the two-pion invariant mass distribution at the rho meson mass value. The resulting photon energy and angular distribution is relatively sensitive to the effects of the rho magnetic dipole moment.Comment: 22 pages, 4 postscript figures, references and comments on relevance of perturbative treatment of rho electromagnetic vertex are added, accepted for pub. in Phys. Rev.

Formation of X-ray emitting stationary shocks in magnetized protostellar jets

X-ray observations of protostellar jets show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary. They are interpreted as shock diamonds. We aim at investigating the physics that guides the formation of X-ray emitting stationary shocks in protostellar jets, the role of the magnetic field in determining the location, stability, and detectability in X-rays of these shocks, and the physical properties of the shocked plasma. We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations modelling supersonic jets ramming into a magnetized medium and explored different configurations of the magnetic field. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. We compared the model results with observations, via the emission measure and the X-ray luminosity synthesized from the simulations. Our model explains the formation of X-ray emitting stationary shocks in a natural way. The magnetic field collimates the plasma at the base of the jet and forms there a magnetic nozzle. After an initial transient, the nozzle leads to the formation of a shock diamond at its exit which is stationary over the time covered by the simulations (~ 40 - 60 yr; comparable with time scales of the observations). The shock generates a point-like X-ray source located close to the base of the jet with luminosity comparable with that inferred from X-ray observations of protostellar jets. For the range of parameters explored, the evolution of the post-shock plasma is dominated by the radiative cooling, whereas the thermal conduction slightly affects the structure of the shock.Comment: Accepted for publication in Astronomy and Astrophysic

Behaviour of the Absorptive Part of the W Electromagnetic Vertex

The absorptive part of the $WW\gamma$ vertex induced by massive fermion loops is considered for different kinematical configurations. We show that the axial part of this vertex is different from zero not only when massive fermions are involved but also for massless fermion loops, if one of the W bosons is space-like and the other is time-like. We also discuss in what sense Low's soft photon theorem is satisfied.Comment: 17 pages, 1 figure, LaTe

Quistes de Tarlov sintomáticos: diagnóstico y tratamiento

Los quistes de Tarlov se forman a expensas de la duramadre y de la aracnoides alrededor de las raíces sacras o coccígeas. Habitualmente asintomáticos, en ocasiones pueden ocasionar clínica álgica de irritación radicular. El desarrollo de técnicas de imagen, principalmente la resonancia magnética nuclear (RMN), permiten diagnosticarlos con más frecuencia, aunque determinar si son responsables de los síntomas de los pacientes continúa siendo difícil. El tratamiento inicial es conservador mediante analgésicos convencionales y fisioterapia. En caso de quistes sintomáticos de gran tamaño, sin respuesta al tratamiento inicial, puede ser necesario el tratamiento quirúrgico mediante drenaje percutáneo guiado bajo control de la tomografía axial computerizada (TAC), o bien mediante una técnica abierta que permita la eliminación del quiste y la descompresión del nervio. Describimos dos casos clínicos en pacientes con clínica de neuralgia por atrapamiento de las raíces nerviosas lumbosacras, un paciente tratado con infiltración periradicular y otro que requirió un drenaje percutáneo con buen resultado final.Tarlov cysts are formed of the dura mater and the arachnoid around the sacral or coccygeal roots. Usually asymptomatic, they can occasionally cause clinical radicular irritation. Magnetic resonance imaging (MRI) permit to diagnose them more often, but whether they are responsible for the symptoms remains difficult. The initial treatment is conservative with conventional analgesics and physiotherapy. In case of large symptomatic cysts, with no response to initial treatment may require surgical therapy: a guided percutaneous drainage under computerized tomography (CT) control, or by an open technique that allows removal of the cyst and nerve decompression. We describe two cases in patients with symptomatic neuralgia due to entrapment of lumbosacral nerve roots. One patient treated with periradicular infiltration and another that required percutaneous drainage with good final outcome

Vector-meson magnetic dipole moment effects in radiative tau decays

We study the possibility that the magnetic dipole moment of light charged vector mesons could be measured from their effects in \tau^- --> V^-\nu_{\tau}\gamma decays. We conclude that the energy spectrum and angular distribution of photons emitted at small angles with respect to vector mesons is sensitive the effects of the magnetic dipole moment. Model-dependent contributions and photon radiation off other electromagnetic multipoles are small in this region. We also compute the effects of the magnetic dipole moment on the integrated rates and photon energy spectrum of these $\tau$ lepton decays.Comment: Latex, 12 pages, 4 figures, submitted to PR

The age-mass relation for chromospherically active binaries - III. Lithium depletion in giant components

We present a study of the lithium abundances of a sample of evolved components of Chromospherically Active Binary Systems. We show that a significant part of them have lithium excesses, independently of their mass and evolutionary stage. Therefore, it can be concluded that Li abundance does not depend on age for giant components of CABS. These overabundances appear to be closely related to the stellar rotation, and we interpret them as a consequence of the transfer of angular momentum from the orbit to the rotation as the stars evolve: in and off the Main Sequence, in a similar way as it happens in the dwarf components of the same systems and in the Tidally Locked Binaries belonging to the Hyades and M67