arXiv subjects

P. Ciecielag

Publications and source records attributed to P. Ciecielag.

7 recordsLinked to original sources

arXiv2021

Calibration of Advanced Virgo and reconstruction of detector strain h(t) during the Observing Run O3

The three Advanced Virgo and LIGO gravitational wave detectors participated to the third observing run (O3) between 1 April 2019 15:00 UTC and 27 March 2020 17:00 UTC,leading to several gravitational wave detections per month. This paper describes the Advanced Virgo detector calibration and the reconstruction of the detector strain $h(t)$ during O3, as well as the estimation of the associated uncertainties. For the first time, the photon calibration technique as been used as reference for Virgo calibration, which allowed to cross-calibrate the strain amplitude of the Virgo and LIGO detectors. The previous reference, so-called free swinging Michelson technique, has still been used but as an independent cross-check. $h(t)$ reconstruction and noise subtraction were processed online, with good enough quality to prevent the need for offline reprocessing, except for the two last weeks of September 2019. The uncertainties for the reconstructed $h(t)$ strain, estimated in this paper in a 20-2000~Hz frequency band, are frequency independent: 5% in amplitude, 35 mrad in phase and 10 $μ$s in timing, with the exception of larger uncertainties around 50 Hz.

gr-qc↗

arXiv2009

Algorithmic comparisons of decaying, isothermal, supersonic turbulence

Contradicting results have been reported in the literature with respect to the performance of the numerical techniques employed for the study of supersonic turbulence. We aim at characterising the performance of different particle-based and grid-based techniques on the modelling of decaying supersonic turbulence. Four different grid codes (ENZO, FLASH, TVD, ZEUS) and three different SPH codes (GADGET, PHANTOM, VINE) are compared. We additionally analysed two calculations denoted as PHANTOM A and PHANTOM B using two different implementations of artificial viscosity. Our analysis indicates that grid codes tend to be less dissipative than SPH codes, though details of the techniques used can make large differences in both cases. For example, the Morris & Monaghan viscosity implementation for SPH results in less dissipation (PHANTOM B and VINE versus GADGET and PHANTOM A). For grid codes, using a smaller diffusion parameter leads to less dissipation, but results in a larger bottleneck effect (our ENZO versus FLASH runs). As a general result, we find that by using a similar number of resolution elements N for each spatial direction means that all codes (both grid-based and particle-based) show encouraging similarity of all statistical quantities for isotropic supersonic turbulence on spatial scales k<N/32 (all scales resolved by more than 32 grid cells), while scales smaller than that are significantly affected by the specific implementation of the algorithm for solving the equations of hydrodynamics. At comparable numerical resolution, the SPH runs were on average about ten times more computationally intensive than the grid runs, although with variations of up to a factor of ten between the different SPH runs and between the different grid runs. (abridged)

astro-ph↗

arXiv2007

On gas drag in a circular binary system

We investigate both analytically and numerically the motion of massless particles orbiting primary star in a close circular binary system with particular focus on the gas drag effects. These are the first calculations with particles ranging in size from 1m to 10km, which account for the presence of a tidally perturbed gaseous disk. We have found numerically that the radial mass transport by the tidal waves plays a crucial role in the orbital evolution of particles. Numerical results are confirmed analytical calculations that do not assume anything about origin of the radial flow in the disk. We demonstrate that the migration rate of a particle in a disk out of radial equilibrium is enhanced due to the enhanced mass flux of gas colliding with the particle and the migration is always directed inward regardless of the sign of the radial gas velocity. Within the framework of the perturbation theory we derive general, formulae for short-term variations of the particle semi-major axis, eccentricity and inclination in such disk. The formulae account for departures from axial symmetry by introducing effective components of the gas velocity. They agree with numerical results within several percent. We have also found in numerical simulations that the tidal waves introduce coherence in periastron longitude and eccentricity for particles on neighbouring orbits. The degree of the coherence depends on the particle size and on the distance from the primary star, being most prominent for particles with 10m radius. The results are important mainly in the context of planetesimal formation and, to a lesser degree, during the early planetesimal accretion stage.

astro-ph↗

arXiv2006

A comparative study of disc-planet interaction

We perform numerical simulations of a disc-planet system using various grid-based and smoothed particle hydrodynamics (SPH) codes. The tests are run for a simple setup where Jupiter and Neptune mass planets on a circular orbit open a gap in a protoplanetary disc during a few hundred orbital periods. We compare the surface density contours, potential vorticity and smoothed radial profiles at several times. The disc mass and gravitational torque time evolution are analyzed with high temporal resolution. There is overall consistency between the codes. The density profiles agree within about 5% for the Eulerian simulations while the SPH results predict the correct shape of the gap although have less resolution in the low density regions and weaker planetary wakes. The disc masses after 200 orbital periods agree within 10%. The spread is larger in the tidal torques acting on the planet which agree within a factor 2 at the end of the simulation. In the Neptune case the dispersion in the torques is greater than for Jupiter, possibly owing to the contribution from the not completely cleared region close to the planet.

astro-ph↗

arXiv2004

Likelihood analysis of the Local Group acceleration revisited

We reexamine likelihood analyzes of the Local Group (LG) acceleration, paying particular attention to nonlinear effects. Under the approximation that the joint distribution of the LG acceleration and velocity is Gaussian, two quantities describing nonlinear effects enter these analyzes. The first one is the coherence function, i.e. the cross-correlation coefficient of the Fourier modes of gravity and velocity fields. The second one is the ratio of velocity power spectrum to gravity power spectrum. To date, in all analyzes of the LG acceleration the second quantity was not accounted for. Extending our previous work, we study both the coherence function and the ratio of the power spectra. With the aid of numerical simulations we obtain expressions for the two as functions of wavevector and σ_8. Adopting WMAP's best determination of σ_8, we estimate the most likely value of the parameter βand its errors. As the observed values of the LG velocity and gravity, we adopt respectively a CMB-based estimate of the LG velocity, and Schmoldt et al.'s (1999) estimate of the LG acceleration from the PSCz catalog. We obtain β= 0.66^{+0.21}_{-0.07}; thus our errorbars are significantly smaller than those of Schmoldt et al. This is not surprising, because the coherence function they used greatly overestimates actual decoherence between nonlinear gravity and velocity.

astro-ph↗

arXiv2001

Local Group Velocity Versus Gravity: Nonlinear Effects

We use numerical simulations to study the relation between the velocity of the Local Group and its gravitational acceleration. This relation serves as a test for the kinematic origin of the CMB dipole and as a method for estimating beta. We calculate the misalignment angle between the two vectors and compare it to the observed value for the PSCz survey. The latter value is near the upper limit of the 95% confidence interval for the angle; therefore, the nonlinear effects are unlikely to be responsible for the whole observed misalignment. We also study the relation between the amplitudes of the LG velocity and gravity vectors. In an Omega=1 Universe, the smoothed gravity of the LG turns out to be a biased low estimator of the LG (unsmoothed) velocity. In an Omega=0.3 Universe, the estimator is biased high. The discussed biases are, however, only a few per cent, thus the linear theory works to good accuracy. The gravity-based estimator of the LG velocity has also a scatter that limits the precision of the estimate of beta in the LG velocity-gravity comparisons. The random error of beta due to nonlinear effects amounts to several per cent.

astro-ph↗

arXiv2000

High-resolution simulations and visualization of protoplanetary disks

A problem of mass flow in the immediate vicinity of a planet embedded in a protoplanetary disk is studied numerically in two dimensions. Large differences in temporal and spatial scales involved suggest that a specialized discretization method for solution of hydrodynamical equations may offer great savings in computational resources, and can make extensive parameter studies feasible. Preliminary results obtained with help of Adaptive Mesh Refinement technique and high-order explicit Eulerian solver are presented. This combination of numerical techniques appears to be an excellent tool which allows for direct simulations of mass flow in vicinity of the accretor at moderate computational cost. In particular, it is possible to resolve the surface of the planet and to model the process of planet growth with minimal set of assumptions. Some issues related to visualization of the results and future prospects are discussed briefly.

astro-ph↗