57 research outputs found
The kinematic Sunyaev Zeldovich effect and transverse cluster velocities
The polarization of the CMBR scattered by galaxy clusters in the kinematic
Sunyaev Zeldovich effect depends on the transverse velocity of the cluster.
This polarizing effect is proportional to the transverse velocity squared, and
so weaker that the change in intensity due to the radial motion in the
kinematic effect. The value given by Sunyaev and Zeldovich, and which is
frequently cited, underestimates the polarizing effect by a factor of ten. We
show furthermore that the polarization has a strong frequency dependence. This
means that the polarization should be detectable with the new generation of
CMBR probes, at least for some clusters. Thus this effect offers, almost
uniquely, a method of obtaining the vectorial velocity of clusters.Comment: Submitted to MNRAS letter. 5 pages using mnras file style. email:
[email protected]
The use of light polarization for weak-lensing inversions
The measurement of the integrated optical polarization of weakly
gravitationally lensed galaxies can provide considerable constraints on lens
models. The method outlined depends on fact that the orientation of the
direction of optical polarization is not affected by weak gravitational
lensing. The angle between the semi-major axis of the imaged galaxy and the
direction of integrated optical polarization thus informs one of the distortion
produced by the gravitational lensing. Although the method depends on the
polarimetric measurement of faint galaxies, large telescopes and improved
techniques should make such measurements possible in the near future.Comment: 13 pages, 11 figures, uses mnras style file. Accepted for publication
in MNRA
Radiative, magnetic and numerical feedbacks on small-scale fragmentation
Radiative feedback and magnetic field are understood to have a strong impact
on the protostellar collapse. We present high resolution numerical calculations
of the collapse of a 1 solar mass dense core in solid body rotation, including
both radiative transfer and magnetic field. Using typical parameters for
low-mass cores, we study thoroughly the effect of radiative transfer and
magnetic field on the first core formation and fragmentation. We show that
including the two aforementioned physical processes does not correspond to the
simple picture of adding them separately. The interplay between the two is
extremely strong, via the magnetic braking and the radiation from the accretion
shock.Comment: 4 pages, 2 figures ; to appear in "IAU Symposium 270: Computational
Star formation", Eds. J. Alves, B. Elmegreen, J. Girart, V. Trimbl
A Godunov-Type Solver for the Numerical Approximation of Gravitational Flows
International audienceWe present a new numerical method to approximate the solutions of an Euler-Poisson model, which is inherent to astrophysical flows where gravity plays an important role. We propose a discretization of gravity which ensures adequate coupling of the Poisson and Euler equations, paying particular attention to the gravity source term involved in the latter equations. In order to approximate this source term, its discretization is introduced into the approximate Riemann solver used for the Euler equations. A relaxation scheme is involved and its robustness is established. The method has been implemented in the software HERACLES and several numerical experiments involving gravitational flows for astrophysics highlight the scheme
Radiative, magnetic and numerical feedbacks on small-scale fragmentation
Radiative feedback and magnetic field are understood to have a strong impact on the protostellar collapse. We present high resolution numerical calculations of the collapse of a 1 M⊙ dense core in solid body rotation, including both radiative transfer and magnetic field. Using typical parameters for low-mass cores, we study thoroughly the effect of radiative transfer and magnetic field on the first core formation and fragmentation. We show that including the two aforementioned physical processes does not correspond to the simple picture of adding them separately. The interplay between the two is extremely strong, via the magnetic braking and the radiation from the accretion shoc
Measure of precursor electron density profiles of laser launched radiative shocks
We have studied the dynamics of strong radiative shocks generated with the
high-energy subnanosecond iodine laser at Prague Asterix Laser System facilityComment: with small correction in Fig.1
Experimental study of radiative shocks at PALS facility
We report on the investigation of strong radiative shocks generated with the
high energy, sub-nanosecond iodine laser at PALS. These shock waves are
characterized by a developed radiative precursor and their dynamics is analyzed
over long time scales (~50 ns), approaching a quasi-stationary limit. We
present the first preliminary results on the rear side XUV spectroscopy. These
studies are relevant to the understanding of the spectroscopic signatures of
accretion shocks in Classical T Tauri Stars.Comment: 21 pages, 1 table, 7 figure
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